Dr. Neatu Florentina
Scientific Researcher I
Laboratory of Catalytic Materials and Catalysis
florentina[DOT]neatu[AT]infim[DOT]roEducation
2003 – 2009: PhD in Chemistry, Faculty of Chemistry, University of Bucharest.
2003 – 2005: Master in Catalysis and Catalytic Processes, Faculty of Chemistry, University of Bucharest.
1999 – 2003: Graduate in Chemistry, Faculty of Chemistry, University of Bucharest.
Positions
April 2020 - onwards: Scientific researcher I degree, National Institute of Material Physiscs, Magurele, Romania
March 2018 - April 2020: Scientific researcher II degree, National Institute of Material Physiscs, Magurele, Romania
January 2017 - March 2018: Scientific researcher III degree, National Institute of Material Physiscs, Magurele, Romania
October 2008 - December 2016: University assistant, Faculty of Chemistry, University of Bucharest, Romania
October 2007 - December 2016: Research assistant, Catalysis and Catalytic Processes Research Center, Faculty of Chemistry, University of Bucharest, Romania
Awards
3
Expertize
Dr. Florentina Neațu, scientific researcher 1st degree at the National Research and Development Institute for Materials Physics earned her Ph.D. in Chemistry from the University of Bucharest's Faculty of Chemistry in 2009. Research interests in the area of heterogeneous catalysis, and more specifically green and sustainable chemistry, include the discovery of acidic heterogeneous catalysts for PET depolymerization and the development of alternative methods for the synthesis of important monomers in the polymer industry that make use of renewable resources. Dr. Florentina Neațu is an expert in a wide range of fields, including the development of novel catalytic methods for performing hydrogenation and selective oxidation reactions, and the fabrication of solid catalysts using a number of different approaches.
H index: 21
Citation number: >1300
ISI Articles: 65
Scholarships: 7
Prizes: 3
Book Chapter: 1
Projects: 7
Books
1
Patents
3
Projects
1. Chemical recycling of PET – a new heterogeneous catalytic route
Project Type: TE, Start Date: 2020-09-01 End Date: 2022-10-31
2. Tunable acid-base mesoporous hollow spheres advanced materials for rubber intermediates
Project Type: TE, Start Date: 2018-05-02 End Date: 2020-10-31
Publications
1. Catalytic behaviour of CuOx and VOx on Ti3SiC2 support for direct oxidation of methane
Authors:
Iacoban, AC; Haldar, T; Neatu, F; Chirica, IM; Mirea, AG; Neatu, S; Barsoum, MW; Florea, M
Published: JAN 1 2025, CATALYSIS TODAY, 443, 114959, DOI: 10.1016/j.cattod.2024.114959
Herein we show that the Ti3SiC2 MAX phase can be used as a support for deposition of different amounts of metal oxides (MOx, M = Cu or V) (5, 10 and 20 wt%) for the direct oxidation of methane to formaldehyde using molecular oxygen, at relatively low temperatures and atmospheric pressure. The oxides were deposited using a hydrothermal method at 180 degrees C without affecting the bulk MAX phase structure. However, during the hydrothermal treatment (HT) a thin oxide layer - found to play an important role in the reaction's selectivity- was evidenced by X-ray photoelectron spectroscopy. We thus conclude that the MOx species are responsible for the CH4 activation, while the Ti3SiC2 surface is responsible for the high selectivity to formaldehyde indicating that, Ti3SiC2 has great potential for designing innovative catalysts for direct oxidation of methane using molecular oxygen and at atmospheric pressure.
2. Influence of molybdenum incorporation on the structural, chemical, and catalytic properties of iron cobaltite and cobalt ferrite catalysts
Authors:
Mitran, G; Pavel, OD; Urda, A; Mirea, AG; Neatu, F; Neatu, S; Florea, M
Published: JUN 2 2024, APPLIED CATALYSIS A-GENERAL, 679, 119739, DOI: 10.1016/j.apcata.2024.119739
In this study, molybdenum doped iron cobaltite and cobalt ferrite catalysts were prepared by coprecipitation, and their structural, morphological, and optical, properties were evaluated by XRD, BET, SEM, FTIR, Raman, XPS and UV-VIS techniques. Their catalytic behavior evaluated in the malic acid oxidative decarboxylation reaction underlined the importance of the incorporation of Mo into the structure of iron cobaltite and cobalt ferrite catalysts. The catalysts with the highest molybdenum content forming cobaltite and iron molybdate phases showed better activity, with cobaltite-based catalysts being more active than ferrite-based ones.
3. Honey-Derived Hydrochar Containing 2,2,6,6-tetramethylpiperidine-1-oxyl Free Radical for Degradation of Aqueous Organic Pollutants
Authors:
Patrinoiu, G; Musuc, AM; Calderon-Moreno, JM; Florea, M; Neatu, F; Ionita, P
Published: DEC 2024, ENVIRONMENTAL PROCESSES-AN INTERNATIONAL JOURNAL, 11, 60, DOI: 10.1007/s40710-024-00731-5
The increasing demand for greener technologies in environmental remediation makes carbon materials from biomass and its derivatives some of the most attractive resources for a sustainable future. However, integrating these materials with stable free radicals remains challenging. This study presents a straightforward one-pot hydrothermal route using raw honey as the carbon source and 4-amino 2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) as the free radical. The addition of TEMPO derivative initiates Maillard reactions between its amino group and the carbonyl groups of the carbohydrates in honey, resulting in the formation of a functionalized hydrochar with a spherical morphology (similar to 8 mu m). The presence of free radicals within the carbonaceous matrix was confirmed by electron spin resonance spectroscopy, supported by infrared spectroscopy, elemental analysis, thermal analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy. The free radical content was estimated at 0.4 mmol center dot g(-1). The material effectively removed methylene blue, fluorescein, and doxorubicin from water in the presence of green oxidants like hydrogen peroxide and sodium hypochlorite. After 24 h, removal efficiencies reached 92% for doxorubicin, 73% for methylene blue, and 23% for fluorescein. Moreover, the hydrochar demonstrated good regeneration capability, maintaining its dye removal efficiency over several cycles.
4. Acid-Modified, Ti3C2-Based MXene as Catalysts for Upcycling Polyethylene Terephthalate
Authors:
Chirica, IM; Mirea, AG; Suteu, T; Kuncser, A; Neatu, S; Florea, M; Barsoum, MW; Neatu, F
Published: JUN 14 2024, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, 12, DOI: 10.1021/acssuschemeng.4c01920
Plastics are indispensable materials for packaging and many products from our daily life, and their recycling is essential to ensure a circular economy. In this study, -SO3H-modified, Ti3C2-MXene was used as a recoverable solid acid catalyst for upcycling of polyethylene terephthalate (PET) to terephthalic acid (TPA) and ethylene glycol by hydrolysis. For the grafting of -SO3H groups to the Ti3C2Tx surface (where T-x represents the surface moieties, such as -OH or -O), sulfonation with an aryl diazonium salt obtained from sulfanilic acid was employed. X-ray photoelectron and Fourier transform infrared spectroscopy analyses provided a direct indication that sulfonation of the Ti3C2Tx was successfully performed, while X-ray diffraction and transmission electron microscopy analyses evidence the presence of -SO3H groups between the Ti3C2Tx layers due to the increases of the interlayer spacing through the intercalation of functional groups. The higher the concentration of acid groups, the higher the interlayer spacing. The depolymerization of PET in water occurred with a very good isolated yield in TPA (99%) for the MXene with the highest amount of sulfonic acid groups. We conclude that the acidity is mandatory to perform the hydrolysis reaction, in agreement with the acidity measurements, which show that the MXenes modified with the highest amount of derived sulfonic acids are the most active. Nevertheless, the accessibility to the acidic sites is a key factor that promotes the 2D acid-modified MXene materials as important catalysts for PET upcycling to TPA.
5. Acid-Modified, Ti3C2-Based MXene as Catalysts for Upcycling Polyethylene Terephthalate
Authors:
Chirica, IM; Mirea, AG; Suteu, T; Kuncser, A; Neatu, S; Florea, M; Barsoum, MW; Neatu, F
Published: 2024 JUN 14 2024, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, DOI: 10.1021/acssuschemeng.4c01920
Plastics are indispensable materials for packaging and many products from our daily life, and their recycling is essential to ensure a circular economy. In this study, -SO3H-modified, Ti3C2-MXene was used as a recoverable solid acid catalyst for upcycling of polyethylene terephthalate (PET) to terephthalic acid (TPA) and ethylene glycol by hydrolysis. For the grafting of -SO3H groups to the Ti3C2Tx surface (where T-x represents the surface moieties, such as -OH or -O), sulfonation with an aryl diazonium salt obtained from sulfanilic acid was employed. X-ray photoelectron and Fourier transform infrared spectroscopy analyses provided a direct indication that sulfonation of the Ti3C2Tx was successfully performed, while X-ray diffraction and transmission electron microscopy analyses evidence the presence of -SO3H groups between the Ti3C2Tx layers due to the increases of the interlayer spacing through the intercalation of functional groups. The higher the concentration of acid groups, the higher the interlayer spacing. The depolymerization of PET in water occurred with a very good isolated yield in TPA (99%) for the MXene with the highest amount of sulfonic acid groups. We conclude that the acidity is mandatory to perform the hydrolysis reaction, in agreement with the acidity measurements, which show that the MXenes modified with the highest amount of derived sulfonic acids are the most active. Nevertheless, the accessibility to the acidic sites is a key factor that promotes the 2D acid-modified MXene materials as important catalysts for PET upcycling to TPA.
6. A comparative overview of MXenes and metal oxides as cocatalysts in clean energy production through photocatalysis
Authors:
Nair, MM; Iacoban, AC; Neatu, F; Florea, M; Neatu, S
Published: JUN 20 2023, JOURNAL OF MATERIALS CHEMISTRY A, 11, DOI: 10.1039/d2ta08983a
Photocatalytic conversion of H2O, CO2 and N-2 represents one promising approach to harvest and store solar energy, for which efficient visible light responsive semiconductors are inevitable. Often, the presence of a small amount of an additional component called a "cocatalyst", is required to synergistically enhance the performance of the photocatalyst. Tremendous efforts were made in the past to identify inexpensive materials to be used as cocatalysts, for which metal oxides (MOs) are one of the traditional choices. Among alternative categories of materials investigated, the recently discovered MXenes display enormous potential owing to their unique 2D layered structure, tuneable composition, abundant surface functionalities and superior electronic conductivity. Specifically, MOs and MXenes encompass a variety of distinct as well as analogous characteristics that allows them to be tailored to different extents. Unfortunately, a comprehensive overview covering the synthetic, structural and photocatalytic aspects of MOs and MXenes is not available as of now. Herein, we intend to summarize the progress achieved so far in these two families of materials to be used as cocatalysts for the photoconversion of H2O, CO2 and N-2. Followed by a general introduction, we briefly outline the fundamental principles and the role of cocatalysts in photocatalytic reactions. A discussion regarding the use of MOs and MXenes as cocatalysts for the conversion of H2O, CO2 and N-2 is then provided in separate sections. Critical assessment regarding structure and morphology control, surface properties and stability concerns can not only help to recognize the challenges that limit further advancement, but can also highlight the future research directions of these materials for the effective transformation of H2O, CO2 and N-2.
7. Understanding the Photocatalytic Activity of Sodium Hexatitanate Nanoparticles for Pollutants Degradation: A Spectroscopic Insight
Authors:
Teixeira, ARFA; de Oliveira, ALM; Neatu, F; Kuncser, AC; Galca, AC; Rostas, AM; dos Santos, IMG
Published: MAR 2023, ACS APPLIED NANO MATERIALS, DOI: 10.1021/acsanm.2c05577
Sodium hexatitanate (Na2Ti6O13) nanoparticles have been synthesized by the hydrothermal method with microwave and conven-tional heating, after which their photocatalytic properties toward an azo dye pollutant degradation have been investigated. Insights into the dynamics and reactivity of the species involved in the photocatalytic mechanism of the (Na2Ti6O13) samples were precisely investigated, for the first time, by X-band electron paramagnetic resonance (EPR) spectroscopy under different experimental conditions. X-ray diffraction structural analysis revealed that all samples crystallized in a monoclinic C2/m structure, with different short-range structural order according to the employed heating, as indicated by Raman. Field-emission scanning electron microscopy and transmission electron microscopy results revealed the formation of rod-and fiber-like nanoparticles with different diameters and lengths. EPR measurements indicated the presence of different Ti3+ point defects and F centers in the samples. X-ray photoelectron spectroscopy analysis proved the presence of oxygen-related defects, but no Ti3+ was detected on the surface. Spin trapping experiments monitored the generation of hydroxyl (OH center dot) radicals over UV-irradiation time. Various parameters contribute to the photocatalytic activity of the samples; however, the type of defect and particle morphology appeared as key factors for enhanced efficiency. Our study provides significant information about paramagnetic defects in Na2Ti6O13 materials and their role in photocatalysis to design other Ti-based photocatalysts.
8. Iron-doped Co3O4 catalysts prepared by a surfactant-assisted method as effective catalysts for malic acid oxidative decarboxylation
Authors:
Mitran, G; Neatu, S; Pavel, OD; Urda, A; Mirea, AG; Florea, M; Neatu, F
Published: JUL 31 2023, CATALYSIS SCIENCE & TECHNOLOGY, 13, DOI: 10.1039/d3cy00121k
Iron-doped Co3O4 oxides prepared by a surfactant-assisted method exhibited good catalytic activity in malic acid conversion, and the oxygen defects associated with the presence of Co2+ played a key role in catalyst activation for pyruvic acid production. The most active catalyst, for which the malic acid conversion was 70% and the pyruvic acid yield was 24%, has an inverse spinel type structure (Fe3+ replaces Co2+ from tetrahedral sites, while Fe2+ replaces Co3+ from octahedral sites) as well as a small energy difference between the highest occupied orbital and the lowest unoccupied orbital (low band-gap, E-g). The catalyst with the highest Co2+ loading showed the highest yield of pyruvic acid.
9. Understanding the Photocatalytic Activity of Sodium Hexatitanate Nanoparticles for Pollutants Degradation: A Spectroscopic Insight
Authors:
Teixeira, ARFA; de Oliveira, ALM; Neatu, F; Kuncser, AC; Galca, AC; Rostas, AM; dos Santos, IMG
Published: MAR 24 2023, ACS APPLIED NANO MATERIALS, 6, DOI: 10.1021/acsanm.2c05577
Sodium hexatitanate (Na2Ti6O13) nanoparticles have been synthesized by the hydrothermal method with microwave and conven-tional heating, after which their photocatalytic properties toward an azo dye pollutant degradation have been investigated. Insights into the dynamics and reactivity of the species involved in the photocatalytic mechanism of the (Na2Ti6O13) samples were precisely investigated, for the first time, by X-band electron paramagnetic resonance (EPR) spectroscopy under different experimental conditions. X-ray diffraction structural analysis revealed that all samples crystallized in a monoclinic C2/m structure, with different short-range structural order according to the employed heating, as indicated by Raman. Field-emission scanning electron microscopy and transmission electron microscopy results revealed the formation of rod-and fiber-like nanoparticles with different diameters and lengths. EPR measurements indicated the presence of different Ti3+ point defects and F centers in the samples. X-ray photoelectron spectroscopy analysis proved the presence of oxygen-related defects, but no Ti3+ was detected on the surface. Spin trapping experiments monitored the generation of hydroxyl (OH center dot) radicals over UV-irradiation time. Various parameters contribute to the photocatalytic activity of the samples; however, the type of defect and particle morphology appeared as key factors for enhanced efficiency. Our study provides significant information about paramagnetic defects in Na2Ti6O13 materials and their role in photocatalysis to design other Ti-based photocatalysts.
10. A comparative overview of MXenes and metal oxides as cocatalysts in clean energy production through photocatalysis
Authors:
Nair, MM; Iacoban, AC; Neatu, F; Florea, M; Neatu, S
Published: JAN 2023, JOURNAL OF MATERIALS CHEMISTRY A, DOI: 10.1039/d2ta08983a
Photocatalytic conversion of H2O, CO2 and N-2 represents one promising approach to harvest and store solar energy, for which efficient visible light responsive semiconductors are inevitable. Often, the presence of a small amount of an additional component called a "cocatalyst", is required to synergistically enhance the performance of the photocatalyst. Tremendous efforts were made in the past to identify inexpensive materials to be used as cocatalysts, for which metal oxides (MOs) are one of the traditional choices. Among alternative categories of materials investigated, the recently discovered MXenes display enormous potential owing to their unique 2D layered structure, tuneable composition, abundant surface functionalities and superior electronic conductivity. Specifically, MOs and MXenes encompass a variety of distinct as well as analogous characteristics that allows them to be tailored to different extents. Unfortunately, a comprehensive overview covering the synthetic, structural and photocatalytic aspects of MOs and MXenes is not available as of now. Herein, we intend to summarize the progress achieved so far in these two families of materials to be used as cocatalysts for the photoconversion of H2O, CO2 and N-2. Followed by a general introduction, we briefly outline the fundamental principles and the role of cocatalysts in photocatalytic reactions. A discussion regarding the use of MOs and MXenes as cocatalysts for the conversion of H2O, CO2 and N-2 is then provided in separate sections. Critical assessment regarding structure and morphology control, surface properties and stability concerns can not only help to recognize the challenges that limit further advancement, but can also highlight the future research directions of these materials for the effective transformation of H2O, CO2 and N-2.
11. Design of electrocatalysts with reduced Pt content supported on mesoporous NiWO4 and NiWO4-graphene nanoplatelets composite for oxygen reduction and hydrogen oxidation in acidic medium
Authors:
Somacescu, S; Osiceanu, P; Moreno, JMC; Culita, DC; Neatu, F; Trandafir, MM; Neatu, S; Kuncser, A; Szijjártó, GP; Tálas, E; Tompos, A; Borbáth, I; Florea, M
Published: FEB 22 2023, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 48, DOI: 10.1016/j.ijhydene.2022.04.270
Herein, a new direct synthesis route leading to a mesoporous NiWO4 with crystalline framework and NiWO4 -graphene nanoplatelets (GNP) composite is reported. Ni and W assembled into a mesoporous tungstate type of symmetry by co-precipitation synthesis route and its composite with GNP were used as supports for electrocatalysts, with reduced Pt content (8 wt.%), in oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) in acidic medium. A comprehensive assessment of the modifications related to the crystalline and porous structures, morphological aspects as well as the surface chemistry aiming to explain the electrochemical properties was performed. It was found that the presence of GNP during the synthesis process leads, mainly, to the enhanced growth of NiWO4 nanocrystallites, as well as induces changes in the surface chemistry. The elec-trochemical results show that the introduction of GNPs into the NiWO4 composite support leads to a significant improvement in the activity of the Pt electrocatalyst in ORR and HOR compared to both initial NiWO4 and Pt/NiWO4 samples, as well as mechanical mixtures of these catalysts with carbon. Mass activity for hydrogen oxidation, determined in a mixed kinetic-diffusion controlled region, obtained on the 8 wt.% Pt/NiWO4-GNP catalyst was significantly higher compared to the commercial 20 wt.% Pt/C Quintech catalyst. Our comprehensive structural and surface chemistry assessments indicate this composite material as a viable electrocatalyst for PEMFCs using a broader type of fuels.& COPY; 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
12. Photo-stable, 1D-nanofilaments TiO2-based lepidocrocite for photocatalytic hydrogen production in water-methanol mixtures
Authors:
Badr, HO; Natu, V; Neatu, S; Neatu, F; Kuncser, A; Rostas, AM; Racey, M; Barsoum, MW; Florea, M
Published: SEP 6 2023, MATTER, 6, DOI: 10.1016/j.matt.2023.05.026
Water and sunlight are the cleanest, most renewable, and abundant resources on Earth. Developing inexpensive, scalable photocatalysts that are highly stable for hydrogen (H-2) production has long been a cherished dream of humanity. Herein, we report on one-dimensional lepidocrocite-based sub-nanofilaments (NFs), approximate to 5 x 7 & Aring;(2) in cross-section, that generate H-2 from 80:20 v/v water/methanol mixtures when illuminated by simulated sunlight. The NFs were stable in the mixtures for times >4,300 h, 300 h of which were under irradiation. Apparent quantum yields as high as 11.7% were obtained. Based on deuterated water results, we conclude that water is the H-2 source. Further, no carbon dioxide (CO2) due to photocatalytic degradation of methanol was detected. Therefore, the NFs have strong green credentials and lucrative economic prospects for large scale up. We expect these NFs will lead to new lines for developing cheap and ultra-stable materials to produce H-2 photochemically for a long time.
13. Deciphering the role of water and a zinc-doping process in a polyol-based approach for obtaining Zn/Co/Al-based spinels: toward "green" mesoporous inorganic pigments
Authors:
Alexandru, MG; Ianculescu, AC; Carp, O; Culita, DC; Preda, S; Ene, CD; Vasile, BS; Surdu, VA; Nicoara, AI; Neatu, F; Pintilie, I; Visinescu, D
Published: AUG 1 2023, DALTON TRANSACTIONS, 52, DOI: 10.1039/d3dt00972f
Two new families of zinc/cobalt/aluminum-based pigments, with a unique composition, were obtained through the polyol method. The hydrolysis process of a mixture of Co(CH3COO)(2), Zn(acac)(2) and Al(acac)(3) (acac(-) = acetylacetonate ion) in 1,4-butanediol afforded dark blue gels (wPZn(x)Co(1-x)Al), in the presence of a supplementary amount of water, and light green powders (PZnxCo1-xAl), respectively, for the water-free procedure (x = 0, 0.2, 0.4). The calcination of the precursors yielded dark green (wZn(x)Co(1-x)Al) and blue (ZnxCo1-xAl) products. XRD measurements and Rietveld refinement indicate the co-existence of three spinel phases, in different proportions: ZnxCo1-xAl2O4, Co3O4 and the defect spinel, ?-Al2.67O4. The Raman scattering and XPS spectra are in agreement with the compositions of the samples. The morphology of wZn(x)Co(1-x)Al consists of large and irregular spherical particle aggregates (ca. 5-100 mm). Smaller agglomerates (ca. 1-5 mm) with a unique silkworm cocoon-like hierarchical morphology composed of cobalt aluminate cores covered with flake-like alumina shells are formed for ZnxCo1-xAl. TEM and HR-TEM analyses revealed the formation of crystalline, polyhedral particles of 7-43 nm sizes for wZn(x)Co(1-x)Al, while for ZnxCo1-xAl, a duplex-type morphology, with small (7-13 nm) and larger (30-40 nm) particles, was found. BET assessment showed that both series of oxides are mesoporous materials, with different pore structures, with the water-free samples exhibiting the largest surface areas due, most likely, to the high percent of aluminum oxide. A chemical mechanism is proposed to highlight the role of the water amount and the nature of the starting compounds in the hydrolysis reaction products and, further, in the morpho-structural features and composition of the resulting spinel oxides. The CIE L*a*b* and C* colorimetric parameters indicate that the pigments are bright, with a moderate degree of luminosity, presenting an outstanding high blueness.
14. Green synthesis of aminated hyaluronic acid-based silver nanoparticles on modified titanium dioxide surface: Influence of size and chemical composition on their biological properties
Authors:
Stoian, M; Kuncser, A; Neatu, F; Florea, M; Popa, M; Voicu, SN; Chifiriuc, MC; Hanganu, A; Anghel, ME; Tudose, M
Published: DEC 31 2023, INTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES, 253, 127445, DOI: 10.1016/j.ijbiomac.2023.127445
This is the first report on an efficient, "environmentally friendly" chemical reduction method for the synthesis of aminated hyaluronic acid-based silver nanoparticles on the modified surface of titanium dioxide nanoparticles aimed for biological applications. Silver nanoparticles exhibit well-known physical-chemical and optical prop-erties appropriate for different biological applications. Modifying the nanoparticles leads to a change in their expected bioactivity. This represents an important topic for the current research. We have developed a novel aminated hyaluronic acid (HA-EDA)-based protocol to obtain silver nanoparticles, in which HA-EDA was used for the first time as a reducing and stabilizing agent. The effect of the size of silver nanoparticles on the titanium dioxide surface and the chemical composition of the obtained materials were investigated by TEM, XRD, XPS, ATR-FTIR, Raman spectroscopy, NMR and H2-TPR analyses. The antioxidant, in vitro biocompatibility, and antimicrobial activity of the fabricated composites have been evaluated. The results prove that the prepared materials exhibit antimicrobial, antioxidant, and anti-inflammatory activity, thus providing protection against infection and supporting tissue regeneration, these two key effects being of paramount importance for promoting wound healing.
15. A comparative overview of MXenes and metal oxides as cocatalysts in clean energy production through photocatalysis
Authors:
Nair, MM; Iacoban, AC; Neatu, F; Florea, M; Neatu, S
Published: 2023 JAN 16 2023, JOURNAL OF MATERIALS CHEMISTRY A, DOI: 10.1039/d2ta08983a
Photocatalytic conversion of H2O, CO2 and N-2 represents one promising approach to harvest and store solar energy, for which efficient visible light responsive semiconductors are inevitable. Often, the presence of a small amount of an additional component called a "cocatalyst", is required to synergistically enhance the performance of the photocatalyst. Tremendous efforts were made in the past to identify inexpensive materials to be used as cocatalysts, for which metal oxides (MOs) are one of the traditional choices. Among alternative categories of materials investigated, the recently discovered MXenes display enormous potential owing to their unique 2D layered structure, tuneable composition, abundant surface functionalities and superior electronic conductivity. Specifically, MOs and MXenes encompass a variety of distinct as well as analogous characteristics that allows them to be tailored to different extents. Unfortunately, a comprehensive overview covering the synthetic, structural and photocatalytic aspects of MOs and MXenes is not available as of now. Herein, we intend to summarize the progress achieved so far in these two families of materials to be used as cocatalysts for the photoconversion of H2O, CO2 and N-2. Followed by a general introduction, we briefly outline the fundamental principles and the role of cocatalysts in photocatalytic reactions. A discussion regarding the use of MOs and MXenes as cocatalysts for the conversion of H2O, CO2 and N-2 is then provided in separate sections. Critical assessment regarding structure and morphology control, surface properties and stability concerns can not only help to recognize the challenges that limit further advancement, but can also highlight the future research directions of these materials for the effective transformation of H2O, CO2 and N-2.
16. Aminocoumarin derivatives grafted on graphene oxide - new antimicrobial agents to combat the resistance of Mycobacterium tuberculosis and ESKAPE pathogens
Authors:
Müuk, GR; Popa, M; Chifiriuc, MC; Voicu, SN; Florea, M; Neatu, F; Mihalache, I; Stoian, M; Anghel, EM; Culita, DC; Mitran, RA; Petrescu, S; Tudose, M
Published: DEC 1 2023, APPLIED SURFACE SCIENCE, 639, 158224, DOI: 10.1016/j.apsusc.2023.158224
Two hybrid materials, based on 7-amino-4-(trifluoromethyl)coumarin and 7-amino-4-methyl-coumarin that attach covalently to graphene oxide (GO) have been synthesized in two steps: i) increasing the number of carboxyl groups required for functionalization with aminocoumarin derivatives by derivatization of the hydroxyls groups with chloroacetic acid, transforming GO into GO-COOH material; ii) activation of carboxylic groups using the carbodiimide-promoted reaction. The obtained composites were characterized by numerous methods that highlighted their successful obtaining. The antimicrobial activity was evaluated on resistant Mycobacterium tuberculosis strains, as well as on ESKAPE pathogens ((Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) in planktonic and biofilm growth states. The biocompatibility of the materials has been assayed using 3-(4, 5-dimethylthiazol-2-yl)2, 5-diphenyltetrazolium bromide assay as well as by measuring the level of nitric oxide/total reactive oxygen species and superoxide release in treated cells. The results have shown that materials exhibited improved inhibitory activity against resistant M. tuberculosis strains in comparison with GO, but also against planktonic and adherent strains. Also, the tested composites have been proved to be biocompatible on the MRC-5 fibroblast cells, demonstrating their promising potential to develop novel agents effective against multidrug resistant pathogens, including M. tuberculosis, as well as by the activation of a pro-inflammatory and of an oxidative response in the mammalian cells.
17. Structural properties and near-infrared light from Ce3+/Nd3+-co-doped LaPO4 nanophosphors for solar cell applications
Authors:
AitMellal, O; Oufni, L; Messous, MY; Tahri, M; Neatu, S; Florea, M; Neatu, F; Secu, M
Published: JAN 2022, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, DOI: 10.1007/s10854-021-07615-6
To enhance the spectral response of solar cells, an experimental study on LaPO4:0.01Ce(3+)/xNd(3+) (x = 0, 2, 4 mol%) was carried out, where structural and morphological properties of the prepared samples were well characterized by the means of X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electronic microscope. Additionally, the photoluminescence behavior of phosphors in ultraviolet-visible (UV-VIS) and Near-infrared (NIR) regions were investigated to confirm the energy transfer (ET) from Ce3+ to Nd3+. Moreover, the quantum efficiency of Ce3+/Nd3+-co-doped samples was estimated as high as similar to 172% and the possible ET process was described. Accordingly, the LaPO4:Ce3+/Nd3+ phosphors can convert the UV light (275 nm) into NIR photons (approx. 1059 nm) through the possible two-pathway energy transfer processes from Ce3+ sensitizer ions to Nd3+ activators. Obtained NIR down-conversion emissions are suitable for improving the conversion efficiency of c-Si solar cells.
18. Tuning the acidity by addition of transition metal to Mn modified hollow silica spheres and their catalytic activity in ethanol dehydration to ethylene
Authors:
Florea, M; Bocirnea, A; Neatu, S; Kuncser, AM; Trandafir, MM; Neatu, F
Published: SEP 25 2022, APPLIED CATALYSIS A-GENERAL, 646, 118860, DOI: 10.1016/j.apcata.2022.118860
Due to the currently worldwide petrochemical feedstock shortage, the ethylene synthesis from renewable non-oil sources becomes of high interest. The catalysts were prepared in two steps: (i) formation of spheres containing the carbon-coated Mn core by hydrothermal method, (ii) formation of the Si-Zr oxide shell by sol-gel method. The prepared catalysts were characterized by N2 physisorption, SEM-EDX, XRD, XPS, and NH3-TPD. The catalytic results have shown that Fe, Zn or Ni modified Mn core exhibited superior activity compared to the catalysts containing only Mn in the core. With 75% yield and 98% ethanol conversion at 350 degrees C and WHSV of 1.4 h-1, MnNi@SiZr was the best catalyst. These results are due to an increased number of acid sites compared to the other materials and an optimal ratio of weak/medium acid sites. Our findings suggest new lines for developing active and stable catalysts for ethylene synthesis from ethanol.
19. A green way for pyruvic acid synthesis from biomass-derived L-malic acid on tetrahedral versus octahedral cobalt sites/hematite
Authors:
Mitran, G; Urda, A; Pavel, OD; Neatu, S; Florea, M; Neatu, F
Published: MAR 2022, BIOMASS CONVERSION AND BIOREFINERY, DOI: 10.1007/s13399-022-02513-1
A series of cobalt-iron mixed oxides, CoxFe3-xO4 (x = 0; 0.05; 0.1; 0.15), were synthesized by coprecipitation and tested for oxidative decarboxylation of malic acid to pyruvic or malonic acid. The characterization of catalysts was performed by different techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT) and Ultraviolet-visible spectroscopy (UV-Vis). Among studied catalysts, Co0.15Fe2.85O4 sample (denoted Co3Fe) showed the highest malic acid conversion in oxidative decarboxylation reaction as well as the highest pyruvic acid yield. This behavior can be due to the fact that this sample has the highest content of tetrahedral Co2+ that replaces Fe3+ from octahedral position that determine an increased number of defects that play a crucial role for the malic acid conversion.
20. Structural properties and near-infrared light from Ce3+/Nd3+-co-doped LaPO4 nanophosphors for solar cell applications
Authors:
AitMellal, O; Oufni, L; Messous, MY; Tahri, M; Neatu, S; Florea, M; Neatu, F; Secu, M
Published: MAR 2022, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 33, DOI: 10.1007/s10854-021-07615-6
To enhance the spectral response of solar cells, an experimental study on LaPO4:0.01Ce(3+)/xNd(3+) (x = 0, 2, 4 mol%) was carried out, where structural and morphological properties of the prepared samples were well characterized by the means of X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electronic microscope. Additionally, the photoluminescence behavior of phosphors in ultraviolet-visible (UV-VIS) and Near-infrared (NIR) regions were investigated to confirm the energy transfer (ET) from Ce3+ to Nd3+. Moreover, the quantum efficiency of Ce3+/Nd3+-co-doped samples was estimated as high as similar to 172% and the possible ET process was described. Accordingly, the LaPO4:Ce3+/Nd3+ phosphors can convert the UV light (275 nm) into NIR photons (approx. 1059 nm) through the possible two-pathway energy transfer processes from Ce3+ sensitizer ions to Nd3+ activators. Obtained NIR down-conversion emissions are suitable for improving the conversion efficiency of c-Si solar cells.
21. Enhancing stability of hybrid perovskite solar cells by imidazolium incorporation
Authors:
Tomulescu, AG; Leonat, LN; Neatu, F; Stancu, V; Toma, V; Derbali, S; Neatu, S; Rostas, AM; Besleaga, C; Patru, R; Pintilie, I; Florea, M
Published: AUG 1 2021, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 227, DOI: 10.1016/j.solmat.2021.111096
Hybrid perovskites based solar cells have demonstrated high conversion efficiency but poor long-term stability. This study reports on the results obtained after doping the CH3NH3PbI2.6Cl0.4 mixed halide perovskite with imidazolium (C3N2H5+, denoted IM) on the "A site" position of a perovskite, to improve photovoltaic performances and stability of hybrid perovskite solar cells. The perovskite films were investigated exhaustively by different characterization techniques: X-ray diffraction, Atomic Force Microscopy, Scanning Electron Microscopy, UV-Vis, X-ray Photoelectron Electron Paramagnetic Resonance spectroscopies, Impedance Spectroscopy and Incident Photon-to-Electron Conversion Efficiency. The photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. The amount of IM inserted in the perovskite play a key role on the film properties. The calculated new tolerance factors according to the "globularity factor" are experimentally proved and thus at doping concentrations greater than 20% for CH3NH3PbI2.6Cl0.4 perovskite the 3D structure is no longer obtained. However, below this value, the IM substituted perovskite film possesses an improved film quality and crystallinity as compared to the pristine film. Substituting MA+ with IM+ provides a favorable way to reduce recombination processes and shows great potential to achieve high stability, and an improved charge generation, resulting in increased PCE values. We find that the optimal percentage of imidazolium incorporation to achieve better stability of solar cells is 6%.
22. Comparative investigation of structural, EPR, optical and photoluminescence properties of nanostructured LaPO4:Ce/RE/Me and LaPO4:Yb/Er phosphors prepared by co-precipitation method
Authors:
AitMellal, O; Oufni, L; Messous, MY; Trandafir, MM; Chirica, IM; Florea, M; Neatu, S; Rostas, AM; Secu, M; Neatu, F
Published: SEP 2021, JOURNAL OF SOLID STATE CHEMISTRY, 301, DOI: 10.1016/j.jssc.2021.122310
In this work, the structural, thermal, vibrational, morphological, magnetic and optical properties of LaPO4:Ce/RE/Me (RE=Nd3+, Tb3+; Me-Cr3+, Mn2+) and LaPO4:Yb3+/Er3+ phosphors prepared by the co-precipitation method are presented. The obtained materials crystallized in monoclinic structure with the P2(1)/n space group and the particles were of nanorod shape with about 200 nm in length and the diameter approximately 19 nm. The presence of dopant ions was confirmed by both electron paramagnetic resonance (EPR) and UV-visible spectroscopies. In addition, the down-conversion (DC) and up-conversion (UC) of the LaPO4 nanophosphors via the 275 and 980 nm excitations, respectively, were considered, and a wide range of electronic transitions was observed. Based on the photoluminescence (PL) spectra, there is an efficient energy transfer (ET) process from Ce3+ donors to Nd3+ and Tb3+ acceptors, and the computed ET efficiency was 70% and 88%, respectively. The Ce3+/Cr3+ and Ce3+/Mn2+ doped LaPO4 showed weak far-red and green luminescence with much smaller ET efficiency of about 3.7 and 0.4%, respectively. LaPO4:Yb3+/Er3+ showed UC luminescence under the 980 nm laser radiation, and the resulted red and green light was attributed to the Er3+ transitions.
23. Structural Details of BaTiO3 Nano-Powders Deduced from the Anisotropic XRD Peak Broadening
Authors:
Pasuk, I; Neatu, F; Neatu, S; Florea, M; Istrate, CM; Pintilie, I; Pintilie, L
Published: MAY 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11051121
In this study, nano-BaTiO3 (BTO) powders were obtained via the solvothermal method at different reaction times and were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The results were compared with those obtained for a larger crystallite size BTO powder (BTO-m). The sizes of the cuboid crystallites (as determined by XRD and TEM) ranged from about 18 to 24 nm, depending on the reaction time. The evolution with temperature of the structure parameters of nano-BTO was monitored by means of X-ray diffraction and Raman spectroscopy and no signs of phase transition were found up to 170 degrees C. Careful monitoring of the dependence of the XRD peak widths on the hkl indices showed that the effect of the cubic crystallite shape upon the XRD peak widths was buried by the effect of hidden tetragonal line splits and by anisotropic microstrain. The good correlation of the line widths with the tetragonal split amplitudes, observed especially for BTO-m above the transition temperature, indicates tetragonal deformations, as also revealed by Raman spectroscopy. The large anisotropic microstrain shown by the nano-powders, which had a maximum value in the directions, was considered evidence of the phenomenon of surface relaxation of cubic crystallites edged by {100} faces. The observed behavior of the nano-BTO structures with increasing temperature may suggest a correlation between the surface relaxation and tetragonal deformation in the nano-cubes. The experimental results for both nano-BTO and mezoscale-BTO are in agreement with the core-shell model.
24. Recent progress in electrocatalysts and electrodes for portable fuel cells
Authors:
Neatu, S; Neatu, F; Chirica, IM; Borbath, I; Talas, E; Tompos, A; Somacescu, S; Osiceanu, P; Folgado, MA; Chaparro, AM; Florea, M
Published: AUG 28 2021, JOURNAL OF MATERIALS CHEMISTRY A, 9, 17128, DOI: 10.1039/d1ta03644k
Fuel cells are devices that transform efficiently the chemical energy of hydrogen or another fuel into clean electricity. The fuel cell technology is attractive for its high-energy efficiency and expanded fuel flexibility and it became very relevant in the last decade. Moreover, the utilization of fuel cells for portable electronic devices has seen remarkable increase in the last few years. Performances of fuel cells, among others, strongly depend on the types of electrocatalysts and membrane, anion exchange or cation exchange, used in the system. Therefore, a status report about the latest advances in electrocatalysts and electrodes for portable fuel cells is the objective of this review paper. Herein, the recent progress in designing electrocatalysts for producing high performance fuel cells with truly potential applicability to be used in portable devices is highlighted.
25. Structural and Optical Investigations of Ce3+/Mn2+-Doped LaPO4 Phosphors
Authors:
Aitmellal, O; Oufni, L; Messous, MY; Neatu, F; Florea, M; Neatu, S; Rostas, AM; Secu, M
Published: APR 2021, JOURNAL OF ELECTRONIC MATERIALS, 50, 2147, DOI: 10.1007/s11664-020-08678-7
Lanthanum orthophosphate (LaPO4) and La0.95-xCe0.05MnxPO4 (x = 0.00, 0.03, 0.10) phosphors were synthesized by a simple and cost-efficient co-precipitation method and the formation of LaPO4 nanorods with a monoclinic P21/n crystal structure was observed. X-ray diffraction pattern analysis indicated a slight distortion of the LaPO4 crystalline structure and an increase of the lattice strain as a consequence of the Mn2+ and Ce3+ dopants incorporation in the host matrix. Scanning electron microscopy revealed that the microstructure of all powders consists of agglomerations of nanorods, which are around 17 +/- 3 nm in diameter and length ranging from 100 nm to 300 nm. Electron paramagnetic resonance measurements have indicated the presence of Mn2+ in isolated species, but also as agglomerates. Ce3+ and Mn2+ doping of LaPO4 resulted also in a decrease of the band gap up to 4.70 eV compared to the un-doped sample. Because of an energy transfer effect from Ce3+ to Mn2+ ions, green emission of Mn2+ ions at around 550 nm was observed upon 275 nm excitation.
26. Carbon-Coated SiO2 Composites as Promising Anode Material for Li-Ion Batteries
Authors:
Buga, MR; Spinu-Zaulet, AA; Ungureanu, CG; Mitran, RA; Vasile, E; Florea, M; Neatu, F
Published: AUG 2021, MOLECULES, 26, DOI: 10.3390/molecules26154531
Porous silica-based materials are a promising alternative to graphite anodes for Li-ion batteries due to their high theoretical capacity, low discharge potential similar to pure silicon, superior cycling stability compared to silicon, abundance, and environmental friendliness. However, several challenges prevent the practical application of silica anodes, such as low coulombic efficiency and irreversible capacity losses during cycling. The main strategy to tackle the challenges of silica as an anode material has been developed to prepare carbon-coated SiO2 composites by carbonization in argon atmosphere. A facile and eco-friendly method of preparing carbon-coated SiO2 composites using sucrose is reported herein. The carbon-coated SiO2 composites were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetry, transmission and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, cyclic voltammetry, and charge-discharge cycling. A C/SiO2-0.085 M calendered electrode displays the best cycling stability, capacity of 714.3 mAh center dot g(-1), and coulombic efficiency as well as the lowest charge transfer resistance over 200 cycles without electrode degradation. The electrochemical performance improvement could be attributed to the positive effect of the carbon thin layer that can effectively diminish interfacial impedance.
27. Applications of MAX phases and MXenes as catalysts
Authors:
Chirica, IM; Mirea, AG; Neatu, S; Florea, M; Barsoum, MW; Neatu, F
Published: SEP 21 2021, JOURNAL OF MATERIALS CHEMISTRY A, 9, 19612, DOI: 10.1039/d1ta04097a
MAX phases and MXenes are important materials that have recently gained great popularity due to their special properties, which render them particularly useful in many applications, including catalytic ones. This can be seen in the large number of publications that appear annually on these materials and their applications. This review aims to evaluate MAX phases and MXenes as materials for heterogeneous, non-electrocatalytic, catalytic applications. The review begins with a brief introduction to the MAX phase and MXene properties that recommend them as potential materials for heterogeneous catalytic applications, followed by four sections grouped according to the processes in which they have already proven effective. These include supports to activate the C-H or C-O bonds in applications such as dehydrogenation of light or aromatic alkanes, methanol formation from CH4, dry reforming, and CO oxidation or the water gas shift reaction (Section 2), and their use in fine chemical reactions (Section 3) and in chemical degradation (Section 4). The last section deals with photocatalytic applications (Section 5). The review ends by highlighting the huge potential of these materials for a wide range of heterogeneous catalytic applications as well as the challenges ahead.
28. Degenerated TiO(2)Semiconductor Modified with Ni and Zn as Efficient Photocatalysts for the Water Splitting Reaction
Authors:
Neatu, F; Abramiuc, LE; Trandafir, MM; Negrea, RF; Florea, M; Teodorescu, CM; Neatu, S
Published: SEP 17 2020, CHEMCATCHEM, 12, DOI: 10.1002/cctc.202000691
The development of robust, safe, cost-effective and efficient photocatalytic systems for water splitting should take into account the presence of a proper and powerful photon absorber and an efficient, low-cost and earth-abundant electrocatalyst to perform the reaction at high conversions. In this study, Ni-Zn/TiO(2)ternary composites with high photocatalytic activity for water splitting under UV irradiation were successfully prepared via a simple and low-cost deposition-precipitation route. Thus, different Ni : Zn molar ratios (1 : 0, 1 : 1, 3 : 1, 6 : 1, 9 : 1, and 0 : 1) were deposited on TiO(2)in order to reach a total metal loading of 50 wt. %. The obtained composites were characterized using several techniques, such as: X-ray diffraction, UV-Vis spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The most active synthesized composite, namely Ni-Zn/TiO2(9 : 1), exhibits H(2)generation rate above 17 mmols g(-1) h(-1), which is nearly one thousand times higher than that obtained with TiO(2)Evonik P25. Our study demonstrates that TiO(2)becomes a degenerated semiconductor in the presence of Ni and ZnO, with remarkable photocatalytic properties. Thus, the obtained results can open new opportunities in the preparation of very active materials for hydrogen production based on the optimization of three-component structures.
29. Degenerated TiO2 Semiconductor Modified with Ni and Zn as Efficient Photocatalysts for the Water Splitting Reaction
Authors:
Neatu, F; Abramiuc, LE; Trandafir, MM; Negrea, RF; Florea, M; Teodorescu, CM; Neatu, S
Published: SEP 17 2020, CHEMCATCHEM, 12, 4651, DOI: 10.1002/cctc.202000691
The development of robust, safe, cost-effective and efficient photocatalytic systems for water splitting should take into account the presence of a proper and powerful photon absorber and an efficient, low-cost and earth-abundant electrocatalyst to perform the reaction at high conversions. In this study, Ni-Zn/TiO(2)ternary composites with high photocatalytic activity for water splitting under UV irradiation were successfully prepared via a simple and low-cost deposition-precipitation route. Thus, different Ni : Zn molar ratios (1 : 0, 1 : 1, 3 : 1, 6 : 1, 9 : 1, and 0 : 1) were deposited on TiO(2)in order to reach a total metal loading of 50 wt. %. The obtained composites were characterized using several techniques, such as: X-ray diffraction, UV-Vis spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The most active synthesized composite, namely Ni-Zn/TiO2(9 : 1), exhibits H(2)generation rate above 17 mmols g(-1) h(-1), which is nearly one thousand times higher than that obtained with TiO(2)Evonik P25. Our study demonstrates that TiO(2)becomes a degenerated semiconductor in the presence of Ni and ZnO, with remarkable photocatalytic properties. Thus, the obtained results can open new opportunities in the preparation of very active materials for hydrogen production based on the optimization of three-component structures.
30. Influence of doping the inorganic cation with Eu or Sb on the properties of perovskite films
Authors:
Stancu, V; Leonat, LN; Tomulescu, AG; Derbali, S; Pintilie, L; Besleaga, C; Galca, AC; Neatu, F; Neatu, T; Florea, M; Pintilie, I
Published: JUL 2020, PHYSICA SCRIPTA, 95, DOI: 10.1088/1402-4896/ab90be
This study reports on the results obtained after doping the [CH3NH3](0.94)[C3N2H5](0.06)PbI2.6Cl0.4 mixt halide perovskite with europium or antimony (Eu3+/Sb3+) at the 'B site'. This way two new complex compounds were obtained, [CH3NH3](0.94)[C3N2H5](0.06)Pb1-yByI2.6Cl0.4 (B = Eu or Sb and y = 0-0.05) as perovskite precursor solutions and deposited as thin films. The properties of the perovskite films were investigated by various characterization techniques: x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), UV-vis spectroscopy while the photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. We find that doping the mixt halide perovskite with very small quantities of Sb improves the quality of the perovskite films and further improves the stability of perovskite solar cells.
31. CeO2:Mn3O4 Catalytic Micro-Converters Tuned for CH4 Detection Based on Catalytic Combustion under Real Operating Conditions
Authors:
Simion, CE; Florea, OG; Florea, M; Neatu, F; Neatu, S; Trandafir, MM; Stanoiu, A
Published: MAY 2020, MATERIALS, 13, DOI: 10.3390/ma13092196
Mesoporous CeO2:Mn3O4 materials (3:7 and 7:3 molar ratio) were prepared by co-precipitation and deposited as porous thick films over alumina (Al2O3) planar substrate provided with Pt meander. The aim was oriented towards detecting low levels methane (CH4) at moderate operating temperatures. Herein we demonstrated that the sensitivity of catalytic micro-converters (CMCs) towards a given peak of CH4 concentration corresponds to specific gas-surface interaction phenomena. More precisely, a transition from thermal conductivity to combustion rate is likely to occur when CMCs are operated under real atmospheric conditions (normal pressure, presence of relative humidity, and constant operating temperature). The response to CH4 was analyzed over different gas flows and different gas concentrations under the same operating regime. The materials were fully characterized by adsorption-desorption isotherms, H-2-Temperature Programmed Reduction (H-2-TPR), X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), and Raman spectroscopies. Thus, the applicative aspect of using CeO2:Mn3O4 as moderate temperature CMC for CH4 detection is brought to the fore.
32. Crown-ether functionalized graphene oxide for metal ions sequestration
Authors:
Petrescu, S; Avramescu, S; Musuc, AM; Neatu, F; Florea, M; Ionita, P
Published: FEB 2020, MATERIALS RESEARCH BULLETIN, 122, DOI: 10.1016/j.materresbull.2019.110643
Graphene oxide has been synthesized, additionally derivatized with chloroacetic acid for increase the number of available carboxylic groups and further functionalized with crown-ether moieties. The thus obtained material was characterized by IR, thermal analysis, SEM, Raman, and XPS. Tests on adsorption of several metal cations showed that cooper and iron are more retained than potassium.
33. Undoped SnO2 as a Support for Ni Species to Boost Oxygen Generation through Alkaline Water Electrolysis
Authors:
Neatu, S; Neatu, F; Diculescu, VC; Trandafir, MM; Petrea, N; Somacescu, S; Krumeich, F; Wennmacher, JTC; Knorpp, AJ; van Bokhoven, JA; Florea, M
Published: APR 22 2020, ACS APPLIED MATERIALS & INTERFACES, 12, 18420, DOI: 10.1021/acsami.9b19541
In this study, the synergistic behavior of Ni species and bimodal mesoporous undoped SnO2 is investigated in oxygen evolution reactions (OERs) under alkaline conditions without any other modification of the compositional phases or using noble metals. An efficient and environmentally friendly hydrothermal method to prepare bimodal mesoporous undoped SnO2 with a very high surface area (>130 m(2) g(-1)) and a general deposition-precipitation method for the synthesis of well-dispersed Ni species on undoped SnO2 are reported. The powders were characterized by adsorption-desorption isotherms, TG-DTA, XRD, SEM, TEM, Raman, TPRH2, and XPS. The best NiSn composite generates, under certain experimental conditions, a very high TOF value of 1.14 s(-1) and a mass activity higher than 370 A g(-1), which are remarkable results considering the low amount of Ni deposited on the electrode (3.78 ng). Moreover, in 1 M NaOH electrolyte, this material produces more than 24 mA cm(-2) at an overpotential value of approximately +0.33 V, with only 5 wt % Ni species. This performance stems from the dual role of undoped SnO2, on the one hand, as a support for active and well-dispersed Ni species and on the other hand as an active player through the oxygen vacancies generated upon Ni deposition.
34. Exploring the effect of aliovalent substitution of Pb2+ by Eu3+ on structural, morphological and optical properties of CH3NH3PbI3 perovskite films
Authors:
Derbali, S; Nouneh, K; Florea, M; Neatu, F; Neatu, S; Leonat, LN; Secu, M; Tomulescu, AG; Stancu, V; Pintilie, L; Touhami, ME; Galca, AC
Published: APR 2020, PHYSICA SCRIPTA, 95, DOI: 10.1088/1402-4896/ab5baa
In this work, the effect of aliovalent substitution of Pb2+ by Eu3+ on structural, morphological and optical properties of CH3NH3PbI3 (MAPbI(3)) was studied, aiming to improve the properties of perovskite films used in solar cells application. The surface morphology, the microstructure and the optical properties of the obtained films containing different Europium (Eu) concentrations were characterized by atomic force microscopy, x-ray photoelectron spectroscopy, x-ray diffraction, UV-vis spectroscopy and photoluminescence spectroscopy.
35. Highly Efficient Ultralow Pd Loading Supported on MAX Phases for Chemoselective Hydrogenation
Authors:
Trandafir, MM; Neatu, F; Chirica, IM; Neatu, S; Kuncser, AC; Cucolea, EI; Natu, V; Barsoum, MW; Florea, M
Published: MAY 15 2020, ACS CATALYSIS, 10, 5908, DOI: 10.1021/acscatal.0c00082
Palladium is one of the most efficient metals for the hydrogenation of organic compounds. However, when molecules, such as nitroaromatics, with several reducible functionalities, are hydrogenated, Pd, like any other very active metal, such as nickel or platinum, often behaves unselectively. One strategy to render Pd more selective is to choose the proper support. Herein, we show that MAX phase powders of Ti3SiC2, Ti2AlC, or Ti3AlC2 can chemoselectively hydrogenate 4-nitrostyrene to 4-aminostyrene, with 100% selectivity, at around 3-4% conversion. To boost the latter, we loaded Ti3SiC2 with 0.0005 wt % Pd and increased the conversion to 100% while maintaining the 4-AS selectivity at >90%. By optimizing the Pd loading, we were also able to increase the turnover frequency 100-fold relative to previous literature results. The identification of this highly efficient and chemoselective system has broad implications for the design of cost-effective, earth-abundant, nontoxic, metal catalysts, with ultralow noble metal loadings.
36. Methane Combustion Using Pd Deposited on CeOx-MnOx/La-Al2O3 Pellistors
Authors:
Florea, OG; Stanoiu, A; Gheorghe, M; Cobianu, C; Neatu, F; Trandafir, MM; Neatu, S; Florea, M; Simion, CE
Published: NOV 2020, MATERIALS, 13, DOI: 10.3390/ma13214888
Pd deposited on CeOx-MnOx/La-Al2O3 has been prepared as a sensitive material for methane (CH4) detection. The effect of different amounts (1.25%, 2.5% and 5%) of Pd loading has been investigated. The as prepared materials were deposited on Pt microcoils using a drop-coating method, as a way of developing pellistors operated using a Wheatstone bridge configuration. By spanning the operating temperature range between 300 degrees C and 550 degrees C, we established the linearity region as well as the maximum sensitivity towards 4900 ppm of CH4. By making use of the sigmoid dependence of the output voltage signal from the Wheatstone bridge, the gas surface reaction and diffusion phenomena have been decoupled. The pellistor with 5% Pd deposited on CeOx-MnOx/La-Al2O3 exhibited the highest selective-sensitivity in the benefit of CH4 detection against threshold limits of carbon monoxide (CO), sulfur dioxide (SO2) and hydrogen sulfide (H2S). Accordingly, adjusting the percent of Pd makes the preparation strategies of pellistors good candidates towards CH4 detection.
37. VAlPOs as Efficient Catalysts for Glycerol Conversion to Methanol
Authors:
Mitran, G; Neatu, F; Neatu, S; Trandafir, MM; Florea, M
Published: JUL 2020, CATALYSTS, 10, DOI: 10.3390/catal10070728
The catalytic activity of a series of vanadium aluminophosphates catalysts prepared by sol-gel method followed by combustion of the obtained gel was evaluated in glycerol conversion towards methanol. The materials were characterized by several techniques such as X-ray diffraction (XRD), UV-vis, Fourier-transform infrared (FTIR), Raman and X-ray photoelectron (XPS) spectroscopies. The amount of vanadium incorporated in aluminophosphates framework played an important role in the catalytic activity, while in the products distribution the key role is played by the vanadium oxidation state on the surface. The sample that contains a large amount of V(4+)has the highest selectivity towards methanol. On the sample with the lowest vanadium loading the oxidation path to dihydroxyacetone is predominant. The catalyst with higher content of tetrahedral isolated vanadium species, such V5APO, is less active in breaking the C-C bonds in the glycerol molecule than the one containing polymeric species.
38. Bulk Versus Surface Modification of Alumina with Mn and Ce Based Oxides for CH4 Catalytic Combustion
Authors:
Neatu, S; Trandafir, MM; Stanoiu, A; Florea, OG; Simion, CE; Leonat, LN; Cobianu, C; Gheorghe, M; Florea, M; Neatu, F
Published: JUN 1 2019, MATERIALS, 12, DOI: 10.3390/ma12111771
This study presents the synthesis and characterization of lanthanum-modified alumina supported cerium-manganese mixed oxides, which were prepared by three different methods (coprecipitation, impregnation and citrate-based sol-gel method) followed by calcination at 500 degrees C. The physicochemical properties of the synthesized materials were investigated by various characterization techniques, namely: nitrogen adsorption-desorption isotherms, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and H-2-temperature programmed reduction (TPR). This experimental study demonstrated that the role of the catalytic surface is much more important than the bulk one. Indeed, the incipient impregnation of CeO2-MnOx catalyst, supported on an optimized amount of 4 wt.% La2O3-Al2O3, provided the best results of the catalytic combustion of methane on our catalytic micro-convertors. This is mainly due to: (i) the highest pore size dimensions according to the Brunauer-Emmett-Teller (BET) investigations, (ii) the highest amount of Mn4+ or/and Ce4+ on the surface as revealed by XPS, (iii) the presence of a mixed phase (Ce2MnO6) as shown by X-ray diffraction; and (iv) a higher reducibility of Mn4+ or/and Ce4+ species as displayed by H-2-TPR and therefore more reactive oxygen species.
39. Next frontiers in cleaner synthesis: 3D printed graphene-supported CeZrLa mixed -oxide nanocatalyst for CO2 utilisation and direct propylene carbonate production
Authors:
Middelkoop, V; Slater, T; Florea, M; Neatu, F; Danaci, S; Onyenkeadi, V; Boonen, K; Saha, B; Baragau, LA; Kellici, S
Published: MAR 20 2019, JOURNAL OF CLEANER PRODUCTION, 214, 614, DOI: 10.1016/j.jclepro.2018.12.274
A rapidly-growing 3D printing technology is innovatively employed for the manufacture of a new class of heterogenous catalysts for the conversion of CO2 into industrially relevant chemicals such as cyclic carbonates. For the first time, directly printed graphene-based 3D structured nanocatalysts have been developed combining the exceptional properties of graphene and active CeZrLa mixed-oxide nano particles. It constitutes a significant advance on previous attempts at 3D printing graphene inks in that it does not merely explore the printability itself, but enhances the efficiency of industrially relevant reactions, such as CO2 utilisation for direct propylene carbonate (PC) production in the absence of organic solvents. In comparison to the starting powder, 3D printed GO-supported CeZeLa catalysts showed improved activity with higher conversion and no noticeable change in selectivity. This can be attributed to the spatially uniform distribution of nanoparticles over the 2D and 3D surfaces, and the larger surface area and pore volume of the printed structures. 3D printed GO-supported CeZeLa catalysts compared to unsupported 3D printed samples exhibited higher selectivity and yield owing to the great number of new weak acid sites appearing in the supported sample, as observed by NH3-TPD analysis. In addition, the catalyst's facile separation from the product has the capacity to massively reduce materials and operating costs resulting in increased sustainability. It convincingly shows the potential of these printing technologies in revolutionising the way catalysts and catalytic reactors are designed in the general quest for clean technologies and greener chemistry. 2019 Elsevier Ltd. All rights reserved.
40. Bimodal mesoporous NiO/CeO2-delta-YSZ with enhanced carbon tolerance in catalytic partial oxidation of methane-Potential IT-SOFCs anode
Authors:
Somacescu, S; Cioatera, N; Osiceanu, P; Calderon-Moreno, JM; Ghica, C; Neatu, F; Florea, M
Published: FEB 2019, APPLIED CATALYSIS B-ENVIRONMENTAL, 241, 406, DOI: 10.1016/j.apcatb.2018.09.065
In the present study we report on the activity, selectivity and stability of the bimodal mesoporous NiO/CeO2-delta-YSZ anodes for IT-SOFCs applications. These materials present high concentration of C3+ ions stably retained in the lattice, which proved to be efficient for the catalytic partial oxidation of CH4 to syngas in the temperature range 600-800 degrees C. The excellent carbon tolerance was proved by a comprehensive XPS analysis, which monitored the amount of carbon before and after catalytic partial oxidation of methane (CPOM) tests. The mesoporous anodes templated by hexadecyltrimethylammonium bromide (CTAB) and tripropylamine (TPA) were obtained using a hydrothermal synthesis route. The effect of Ni and Ce incorporation on the yttria stabilized zirconia (YSZ) structure, texture, morphology and surface chemistry was discussed and correlated with catalytic and electrochemical behavior. The exhaustive characterization of the bulk and surface properties of the catalysts have been accomplished by means of complementary methods: XRD, SEM / EDX / HR TEM, TGA / TPR, XPS. The electrochemical and catalytic performance were improved when the surface contains more reduced ceria and NiO was formed as secondary phase. These features lead to a large number of vacancies and consequently a better oxygen migration, which facilitate the carbon removal.
41. Behavior of Molybdenum-Vanadium Mixed Oxides in Selective Oxidation and Disproportionation of Toluene
Authors:
Mitran, G; Neatu, F; Pavel, OD; Trandafir, MM; Florea, M
Published: MAR 1 2019, MATERIALS, 12, DOI: 10.3390/ma12050748
This study deals with the behavior of molybdenum-vanadium (Mo/V) mixed oxides catalysts in both disproportionation and selective oxidation of toluene. Samples containing different Mo/V ratios were prepared by a modified method using tetradecyltrimethylammonium bromide and acetic acid. The catalysts were characterized using several techniques: nitrogen adsorption-desorption isotherms, X-Ray diffraction (XRD), ammonia temperature-programmed desorption (TPD-NH3), temperature-programmed reduction by hydrogen (H-2-TPR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Fourier-transform infrared-spectroscopy (FTIR) and ultraviolet-visible spectroscopies (UV-VIS). The XRD results evidenced the presence of orthorhombic -MoO3 and V2O5 phases, as well as monoclinic -MoO3 and V2MoO8 phases, their abundance depending on the Mo to V ratio, while the TPD-NH3 emphasized that, the total amount of the acid sites diminished with the increase of the Mo loading. The TPR investigations indicated that the samples with higher Mo/V ratio possess a higher reducibility. The main findings of this study led to the conclusion that the presence of strong acid sites afforded a high conversion in toluene disproportionation (Mo/V = 1), while a higher reducibility is a prerequisite to accomplishing high conversion in toluene oxidation (Mo/V = 2). The catalyst with Mo/V = 1 acquires the best yield to xylenes from the toluene disproportionation reaction, while the catalyst with Mo/V = 0.33 presents the highest yield to benzaldehyde.
42. La0.75Sr0.25XO3 (X = Fe, Mn or Cr) with coking tolerance for CH4/H2O reaction: effect of H2S on catalytic performance
Authors:
Florea, M; Somacescu, S; Postole, G; Urda, A; Neatu, F; Neatu, S; Massin, L; Gelin, P
Published: MAY 7 2019, CATALYSIS SCIENCE & TECHNOLOGY, 9, 2366, DOI: 10.1039/c9cy00065h
The influence of the B type cation from the ABO(3) perovskite formulation La0.75Sr0.25XO3 (LSX, where X is Fe, Mn or Cr) on the C and H2S tolerance and its catalytic activity for the methane/water reaction has been studied. The samples were prepared by a simple and cost-efficient citrate method. The exhaustive characterization of the bulk and surface properties of the catalysts has been accomplished by means of complementary methods: nitrogen adsorption-desorption isotherm measurements, XRD, TPR and XPS. Their catalytic properties in CH4/H2O reactions (CH4/H2O molar ratios of 10 and 1) were studied in the presence and absence of H2S in order to evaluate their potential use as anode materials in solid oxide fuel cells operated on natural gas. Before addition and upon suppression of H2S, the activity varied in the following order: LSF > LSM >> LSC. This correlates with the oxygen mobility determined by TPR. A strong promoting effect of H2S on the catalytic activity is observed for LSC, which makes this sample the most active of the series, while H2S has a weak influence on the other perovskites. The oxygen vacancies and the presence of S2- were identified as being responsible for the enhanced catalytic activity upon H2S addition.
43. Selective catalytic oxidation reaction of p-xylene on manganese-iron mixed oxide materials
Authors:
Nicolae, S; Neatu, F; Florea, M
Published: MAR-APR 2018, COMPTES RENDUS CHIMIE, 21, 361, DOI: 10.1016/j.crci.2017.06.005
Mixed manganese iron oxides (Mn/Fe/O) as heterogeneous catalysts were prepared by hydrothermal treatment and citrate methods to be tested in the oxidation of p-xylene (PX) using as oxidation agent molecular oxygen, hydrogen peroxide, and tert-butyl hydroperoxide. Preparation of mixed Mn-Fe oxide by the citrate method releases materials with smaller particle size and lower degree of crystallinity as compared with the hydrothermal one, which further leads to a higher activity toward the oxidation of PX. A conversion of PX of 98% and a yield in p-toluic acid of 93% were obtained in the presence of Mn/Fe/O prepared by the citrate method using tert-butyl hydroperoxide as an oxidizing agent. (C) 2017 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
44. Doped ceria prepared by precipitation route for steam reforming of methane
Authors:
Florea, M; Matei-Rutkovska, F; Postole, G; Urda, A; Neatu, F; Parvulescu, VI; Gelin, P
Published: MAY 15 2018, , DOI: 10.1016/j.cattod.2016.12.006
45. Synthesis and Mechanical Properties of Polyurea-Based Hybrid Composites for Ballistic Individual Protection
Authors:
Petre, R; Zecheru, T; Petrea, N; Ginghina, R; Sandu, S; Muresan, M; Matache, LC; Sava, AC; Neatu, F
During conflict situations, the combat staff is exposed to a wide variety of aggressions, such as temperature and pressure variations and dynamic impacts (from ammunition or fragments). Textiles used in the manufacture of the military uniforms and devices have always played an important role in defending the military against these hazards, and an adequate level of individual protection equipment is required. In this respect, novel fibre-reinforced polymer composite materials for military application, such as reducing blunt trauma for ballistic protection equipment, have been studied in terms of thermal and mechanical properties and ballistic protection, obtaining very good results.
46. The Cu- and Zn-complex-catalyzed methanolysis of the chemical warfare nerve agents soman, sarin, and VX
Authors:
Petrea, N; Petre, R; Pretorian, A; Toader, C; Somoghi, V; Neatu, F; Florea, M; Neatu, S
Published: MAR-APR 2018, COMPTES RENDUS CHIMIE, 21, 345, DOI: 10.1016/j.crci.2017.08.006
The catalytic methanolysis of the chemical warfare nerve agents soman, sarin, and VX was investigated by using Cu or Zn complexes. Although VX withstood decontamination, the decomposition yield being around 96%, the soman and sarin deposited on different surfaces were almost fully destroyed under ambient conditions. The catalytic tests performed on a wide range of contaminated surfaces confirm the activity of the investigated catalytic systems, these complexes being suitable, from an economical point of view, for use in the formulation of a possible decomposition kit with military or civilian applicability. (C) 2017 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
47. Influence of Gd and Pr doping on the properties of ceria: texture, structure, redox behaviour and reactivity in CH4/H2O reactions in the presence of H2S
Authors:
Florea, M; Postole, G; Matei-Rutkovska, F; Urda, A; Neatu, F; Massin, L; Gelin, P
Published: MAR 7 2018, CATALYSIS SCIENCE & TECHNOLOGY, 8, 1348, DOI: 10.1039/c7cy02192e
Ceria materials doped by Gd and/or Pr were prepared by a precipitation route and calcined in air at 500 and 900 degrees C. The effects of doping and thermal treatment on the materials' surfaces were studied by X-ray photoelectron and Raman spectroscopies. The redox properties were investigated using temperature-programmed reduction experiments in H-2 and CH4 followed by temperature-programmed oxidation in O-2. The catalytic properties of these materials in CH4/H2O reaction in the absence/presence of H2S were evaluated at 750 degrees C in a large excess of CH4 with respect to H2O. The materials were classified by order of reactivity as follows: CPO > CGPO > CeO2 > CGO, which can be primarily related to the surface area variation. Comparing the activity per m(2) of various samples indicates that the catalytic activity is correlated with the Ce3+ concentration at the surface as measured by XPS. Gd-doped and undoped samples exhibit the highest surface Ce3+ concentration as well as the highest activity in SMR per m(2), while Pr-doped samples are the least active (activity per m(2)) with the lowest surface Ce3+ concentrations. H2S has a sharp promoting effect on the catalytic behavior of ceria-based materials, improving the production of H-2 by almost one order of magnitude.
48. Potential application of Ni and Co stabilized zirconia as oxygen reduction reaction catalyst
Authors:
Neatu, F; Trandafir, MM; Marcu, M; Preda, L; Calderon-Moreno, JM; Neatu, S; Somacescu, S; Florea, M
Published: APR 2017, CATALYSIS COMMUNICATIONS, 93, 42, DOI: 10.1016/j.catcom.2016.12.026
A new facile template method for the preparation of Ni, Co doped ZrO2 self-assembled electrocatalysts for oxygen reduction reaction was employed. The effect of the Ni and Co incorporation into ZrO2 lattice on the structural, texturaL surface chemistry and its activity on ORR was emphasized. As X-ray diffraction reveals, the pseudo-cubic lattice of the tetragonal ZrO2 polymorph (t-ZrO2) is stabilized when Ni and Co are co-doping ZrO2. The results indicate that the synergetic effects arisen from the intimate electronic interaction of the mixed oxides present in the lattice of the zirconia phase, i.e. Nil-xCoxO (or NiO and CoO) in NCZ enhance the electrocatalytic activity of the catalyst. (C) 2017 Elsevier B.V. All rights reserved.
49. An adamantane-based COF: stability, adsorption capability, and behaviour as a catalyst and support for Pd and Au for the hydrogenation of nitrostyrene (vol 6, pg 8344, 2016)
Authors:
Trandafir, MM; Pop, L; Hadade, ND; Florea, M; Neatu, F; Teodorescu, CM; Duraki, B; van Bokhoven, JA; Grosu, I; Parvulescu, VI; Garcia, H
Published: 2016, CATALYSIS SCIENCE & TECHNOLOGY, 6, 8573, DOI: 10.1039/c6cy90113a
50. An adamantane-based COF: stability, adsorption capability, and behaviour as a catalyst and support for Pd and Au for the hydrogenation of nitrostyrene
Authors:
Trandafir, MM; Pop, L; Hadade, ND; Florea, M; Neatu, F; Teodorescu, CM; Duraki, B; van Bokhoven, JA; Grosu, I; Parvulescu, VI; Garcia, H
Published: 2016, Catalysis Science & Technology, 6, 8354, DOI: 10.1039/c6cy01631f
A bimodal (micro/mesoporous) COF was synthesized by coupling tetrakis-1,3,5,7-(4'-iodophenyl) adamantane with 4,4'-diethynylbiphenyl following a Sonogashira protocol. The COF preparation strategy led, however, to the incomplete recovery of the palladium catalyst and ICP-OES analysis indicated that around 0.1 wt% palladium remained inside the pores. Noteworthily, the remnant palladium catalyst is still accessible and can be valorised in additional catalytic reactions like the hydrogenation of nitrostyrene. Further deposition of 0.5 wt% active metals (like palladium or gold) enhanced the catalytic activity and tuned the catalyst selectivity with respect to analogous metal catalysts prepared using active carbon as a support. The resulting COF-supported metal NPs are stable and recyclable catalysts. Under normal conditions, this COF is also able to adsorb large amounts of weak electrophilic gases like carbon dioxide.
51. Oxidation of 5-hydroxymethyl furfural to 2,5-diformylfuran in aqueous media over heterogeneous manganese based catalysts
Authors:
Neatu, F; Petrea, N; Petre, R; Somoghi, V; Florea, M; Parvulescu, VI
Published: DEC 1 2016, , DOI: 10.1016/j.cattod.2016.03.031
52. Synthesis of Terephthalic Acid by p-Cymene Oxidation using Oxygen: Toward a More Sustainable Production of Bio-Polyethylene Terephthalate
Authors:
Neatu, F; Culica, G; Florea, M; Parvulescu, VI; Cavani, F
Published: NOV 9 2016, , DOI: 10.1002/cssc.201600718
53. Graphene from Alginate Pyrolysis as a Metal-Free Catalyst for Hydrogenation of Nitro Compounds
Authors:
Trandafir, MM; Florea, M; Neatu, F; Primo, A; Parvulescu, VI; Garcia, H
Published: JUL 7 2016, , DOI: 10.1002/cssc.201600197
54. Heterogeneous Gold Catalyst: Synthesis, Characterization, and Application in 1,4-Addition of Boronic Acids to Enones
Authors:
Moragues, A; Neatu, F; Parvulescu, VI; Marcos, MD; Amoros, P; Michelet, V
Published: SEP 2015, ACS CATALYSIS, 5, 5067, DOI: 10.1021/acscatal.5b01207
The new 1 wt % Au/TiO2-UVM-7 catalyst was prepared and fully characterized. This heterogeneous catalyst proved to be active, selective and recyclable for the unprecedented gold-catalyzed 1,4-addition of various functionalized arylboronic acids to 2-cyclohexen-1-one and other selected enones using toluene as a solvent. The gold-based catalyst was recycled two times and played an active role in this reaction, and the nature of the solvent determined a remarkable change in the products' selectivities.
55. Dielectric Properties of LDH-Type Layered Materials Containing Zn or Mg Ions : On the Non Monotonous Temperature Dependence of Relaxation Times
Authors:
Frunza, L; Frunza, S; Ganea, CP; Zgura, I; Neatu, F; Parvulescu, VI
Published: 2015, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 18, 328, DOI:
The electrical behavior of layered double hydroxides containing Al or Ga as the trivalent ions and Mg or Zn as bivalent ions was evaluated using broadband dielectric spectroscopy in a wide temperature range. Besides conduction effects a relaxation peak is observable at high frequencies which is assigned to the reorientational fluctuations of water molecules adsorbed on the oxide surface or in the interlayer voids. The Maxwell-Wagner-Sillars peak, superimposed to the conductivity phenomenon is observable at low frequencies. A non-monotonous temperature dependence of the relaxation rates of the relaxation process has been found. A quantitative description of this dependence was possible based on a model assuming two competing processes: rotational fluctuation of water molecules and formation of additional defects. Reasonable values for the characteristic parameters were obtained. Thus the water behavior in the studied layered oxides is similar to that observed for water in other porous materials. However, the activation energy of the rotational fluctuation, the pre exponential factor and the number of defects are higher whereas the value of the energy of defect formation is lower in the layered oxide materials than for water confined to nanoporous molecular sieves, porous glasses or in bulk ice.
56. Arylation of alkynes over hydrotalcite docked Rh-m-TPPTC complex
Authors:
Neatu, F; Ciobanu, M; Stoflea, LE; Frunza, L; Parvulescu, VI; Michelet, V
Published: JUN 1 2015, CATALYSIS TODAY, 247, 162, DOI: 10.1016/j.cattod.2014.07.004
Rh-m-TPPTC complex was successful immobilized onto a hydrotalcite Zn-Al to convert selectively in aqueous media both the symmetric and nonsymmetric alkynes into functionalized alkenes, with boronic acids. The complex preserved its activity after the ionic exchange, leading to excellent results (similar to 87%) for the symmetric alkynes and also for the non-symmetrical alkynes (up to 99%). (C) 2014 Elsevier B.V. All rights reserved.
57. Layered materials of LDH-type containing Zn ions: dielectric measurements show rotational fluctuations of water molecules
Authors:
Frunza, L; Ganea, P; Zgura, I; Frunza, S; Neatu, F; Parvulescu, VI
Published: 2015, 2015 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 70, DOI:
Layered double hydroxide (LDH) materials containing Zn ions were studied by broadband dielectric spectroscopy to follow up rotational molecular dynamics of confined water. One main relaxation process was observed in the experimental window; it was assigned to fluctuations of water molecules forming a strongly adsorbed thin layer upon the oxide surface. The temperature dependence of the relaxation rates has an unusual shape characterized by the presence of a maximum. Despite the characteristic parameters, this non-monotonous dependence is shown to be a rather general feature for water confined to LDHs.
58. Mesostructured vanadia-alumina catalysts for the synthesis of vitamin K-3
Authors:
Florea, M; Marin, RS; Palasanu, FM; Neatu, F; Parvulescu, VI
Published: OCT 1 2015, , DOI: 10.1016/j.cattod.2014.12.026
59. Graphenes in the absence of metals as carbocatalysts for selective acetylene hydrogenation and alkene hydrogenation
Authors:
Primo, A; Neatu, F; Florea, M; Parvulescu, V; Garcia, H
Published: OCT 2014, , DOI: 10.1038/ncomms6291
60. Spectroscopic Analysis of the Interstitial Anions in Some Layered Double Hydroxide Materials
Authors:
Frunza, L; Gheorghe, N; Iova, F; Ganea, P; Neatu, F; Parvulescu, VI
Layered double hydroxide materials with Zn2+ and Mg2+ as bivalent cations and Al3+ and Ga3+ as trivalent cations were studied. The anions to balance the positive charge of the network were carbonate and/or nitrate. The samples were prepared in laboratory and routinely characterized. Here the investigations by Fourier transform infrared spectra and thermogravimetric measurements are detailed. On the basis of calibration curves for carbonate and nitrate ions obtained from IR spectra of the corresponding salts, the sample analysis of the interlayer anions was performed quantitatively.
61. Novel Pd heterogeneous catalysts for cycloisomerisation of acetylenic carboxylic acids
Authors:
Neatu, F; Protesescu, L; Florea, M; Parvulescu, VI; Teodorescu, CM; Apostol, N; Toullec, PY; Michelet, V
Published: DEC 2010, GREEN CHEMISTRY, 12, 2149, DOI: 10.1039/c0gc00258e
The Pd-TPPTS complex (TPPTS - trisodium salt of 3,3',3 ''-phosphanetriyl benzenesulfonic acid) and PdCl42- salt heterogenised onto Zn2AlNO3 layered double hydroxide (LDH) using an ion-exchange procedure, have been shown to be efficient green catalysts in the cycloisomerisation reaction of acetylenic carboxylic acids to the corresponding 5-membered heterocycles.
62. Iron oxide colloids and their heterogenization by silica sol-gel entrapment: Catalytic and magnetic properties
Authors:
Neatu, F; Kraynov, A; D'Souza, L; Parvulescu, VI; Kranjc, K; Kocevar, M; Kuncser, V; Richards, R
Published: AUG 31 2008, APPLIED CATALYSIS A-GENERAL, 346, 35, DOI: 10.1016/j.apcata.2008.04.024
Fe3O4 colloids modified by the chiral ligand cinchonidine were prepared with the goal of obtaining a magnetic and catalytic nano-material and were subsequently embedded in silica to form a heterogeneous catalyst. The systems were characterized by TEM and XRD measurements, while the Mossbauer technique was applied for measuring the magnetic properties of the Fe3O4 colloids. The hyperfine magnetic field distribution was consistent with one type of Fe oxide, namely, the magnetite (Fe304). These colloids, both as 'quasi-homogenous catalysts' (or soluble heterogeneous catalysts) and embedded in silica (heterogeneous catalysts) were employed in the selective hydrogenolysis of complex bicyclo[2.2.2]oct-7-enes (bicyclo[2.2.2]oct-2-enes when unsubstituted). (C) 2008 Published by Elsevier B.V.
63. Structural and Optical Investigations of Ce3+/Mn2+-Doped LaPO4 Phosphors
Authors:
Aitmellal, O; Oufni, L; Messous, MY; Neatu, F; Florea, M; Neatu, S; Rostas, AM; Secu, M
Published: , JOURNAL OF ELECTRONIC MATERIALS, DOI: 10.1007/s11664-020-08678-7
Lanthanum orthophosphate (LaPO4) and La0.95-xCe0.05MnxPO4 (x = 0.00, 0.03, 0.10) phosphors were synthesized by a simple and cost-efficient co-precipitation method and the formation of LaPO4 nanorods with a monoclinic P21/n crystal structure was observed. X-ray diffraction pattern analysis indicated a slight distortion of the LaPO4 crystalline structure and an increase of the lattice strain as a consequence of the Mn2+ and Ce3+ dopants incorporation in the host matrix. Scanning electron microscopy revealed that the microstructure of all powders consists of agglomerations of nanorods, which are around 17 +/- 3 nm in diameter and length ranging from 100 nm to 300 nm. Electron paramagnetic resonance measurements have indicated the presence of Mn2+ in isolated species, but also as agglomerates. Ce3+ and Mn2+ doping of LaPO4 resulted also in a decrease of the band gap up to 4.70 eV compared to the un-doped sample. Because of an energy transfer effect from Ce3+ to Mn2+ ions, green emission of Mn2+ ions at around 550 nm was observed upon 275 nm excitation.
65. A green way for pyruvic acid synthesis from biomass-derived L-malic acid on tetrahedral versus octahedral cobalt sites/hematite
Authors:
Mitran, G; Urda, A; Pavel, OD; Neatu, S; Florea, M; Neatu, F
A series of cobalt-iron mixed oxides, CoxFe3-xO4 (x = 0; 0.05; 0.1; 0.15), were synthesized by coprecipitation and tested for oxidative decarboxylation of malic acid to pyruvic or malonic acid. The characterization of catalysts was performed by different techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT) and Ultraviolet-visible spectroscopy (UV-Vis). Among studied catalysts, Co0.15Fe2.85O4 sample (denoted Co3Fe) showed the highest malic acid conversion in oxidative decarboxylation reaction as well as the highest pyruvic acid yield. This behavior can be due to the fact that this sample has the highest content of tetrahedral Co2+ that replaces Fe3+ from octahedral position that determine an increased number of defects that play a crucial role for the malic acid conversion.
66. Applications of MAX phases and MXenes as catalysts
Authors:
Chirica, IM; Mirea, AG; Neatu, S; Florea, M; Barsoum, MW; Neatu, F
Published: , JOURNAL OF MATERIALS CHEMISTRY A, DOI: 10.1039/d1ta04097a
67. Structural properties and near-infrared light from Ce3+/Nd3+-co-doped LaPO4 nanophosphors for solar cell applications
Authors:
AitMellal, O; Oufni, L; Messous, MY; Tahri, M; Neatu, S; Florea, M; Neatu, F; Secu, M
Published: , JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, DOI:
To enhance the spectral response of solar cells, an experimental study on LaPO4:0.01Ce(3+)/xNd(3+) (x = 0, 2, 4 mol%) was carried out, where structural and morphological properties of the prepared samples were well characterized by the means of X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electronic microscope. Additionally, the photoluminescence behavior of phosphors in ultraviolet-visible (UV-VIS) and Near-infrared (NIR) regions were investigated to confirm the energy transfer (ET) from Ce3+ to Nd3+. Moreover, the quantum efficiency of Ce3+/Nd3+-co-doped samples was estimated as high as similar to 172% and the possible ET process was described. Accordingly, the LaPO4:Ce3+/Nd3+ phosphors can convert the UV light (275 nm) into NIR photons (approx. 1059 nm) through the possible two-pathway energy transfer processes from Ce3+ sensitizer ions to Nd3+ activators. Obtained NIR down-conversion emissions are suitable for improving the conversion efficiency of c-Si solar cells.
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