National Institute Of Materials Physics - Romania

Nanoscale Condensed Matter Laboratory

Publications

Year:

183 articles found

1. 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 , DOI: 10.1007/s10854-021-07615-6

Abstract: 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.

2. Nitrogen and Bromide Co-Doped Hydroxyapatite Thin Films with Antimicrobial Properties

Authors: Iconaru, SL; Ciobanu, CS; Predoi, D; Motelica-Heino, M; Negrila, CC; Badea, ML; Predoi, MV; Chifiriuc, CM; Popa, M

Published: DEC 2021, DOI: 10.3390/coatings11121505

Abstract: Hydroxyapatite (Ca-10(PO4)(6)(OH)(2), HAp), due to its high biocompatibility, is widely used as biomaterial. Doping with various ions of hydroxyapatite is performed to acquire properties as close as possible to the biological apatite present in bones and teeth. In this research the results of a study performed on thin films of hydroxyapatite co-doped with nitrogen and bromine (NBrHAp) are presented for the first time. The NBrHAp suspension was obtained by performing the adapted co-precipitation method using cetyltrimethylammonium bromide (CTAB). The thin layers of NBrHAp were obtained by spin-coating. The stability of the NBrHAp suspension was examined by ultrasound measurements. The thin layers obtained by the spin-coating method were examined by scanning electron microscopy (SEM), optical microscopy (OM), and metallographic microscopy (MM). The presence of nitrogen and bromine were highlighted by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) studies. Fourier transform infrared spectroscopy (FTIR) was used to highlight the chemical status of nitrogen and bromine. In addition, the powder obtained from the NBrHAp suspension was analyzed by XRD. Moreover, the in vitro antimicrobial activity of the NBrHAp suspensions and coatings was investigated using the reference microbial strains Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Candida albicans ATCC 10231. The results highlighted the successful obtainment of N and Br co-doped hydroxyapatite suspension for the first time by an adapted co-precipitation method. The obtained suspension was used to produce pure NBrHAp composite thin films with superior morphological properties. The NBrHAp suspensions and coatings exhibited in vitro antimicrobial activity against bacterial and fungal strains and revealed their good antimicrobial activity.

3. Nanocrystalline rhenium-doped TiO2: an efficient catalyst in the one-pot conversion of carbohydrates into levulinic acid. The synergistic effect between Bronsted and Lewis acid sites

Authors: Avramescu, S; Ene, CD; Ciobanu, M; Schnee, J; Devred, F; Bucur, C; Vasile, E; Colaciello, L; Richards, R; Gaigneaux, EM; Verziu, MN

Published: JAN 4 2022, DOI: 10.1039/d1cy01450a

Abstract: Catalytic activity of TiO2, 2%Re-TiO2 and 10%Re-TiO2 in the conversion of carbohydrates into levulinic acid under autoclave conditions was evaluated. These materials were prepared by aerogel method, for the first time to the best of our knowledge, and characterized by XPS, SEM-EDX, DRIFTS, DR UV-vis, Raman, N-2 adsorption/desorption isotherms, TGA and XRD. Further, the surface acidity was probed by NH3-TPD and pyridine-FT-IR where it was observed that increasing the amount of rhenium doped into TiO2 led to an increase in the total number of acid sites (Lewis + Bronsted) but with an overall lower strength. The presence of both Bronsted and Lewis acid sites led to the hypothesis that these materials may be well suited for conversion of carbohydrates into levulinic acid. Indeed a levulinic acid yield of 57% was reached over 10%Re-TiO2 for a low mass ratio catalyst to glucose (1 : 5). Moreover, the 10%Re-TiO2 catalyst was reused in the conversion of glucose for four catalytic cycles without a significant loss of the catalytic activity.

4. Catalytic transformation of the marine polysaccharide ulvan into rare sugars, tartaric and succinic acids

Authors: Podolean, I; Coman, SM; Bucur, C; Teodorescu, C; Kikionis, S; Ioannou, E; Roussis, V; Primo, A; Garcia, H; Parvulescu, VI

Published: JAN 1 2022, DOI: 10.1016/j.cattod.2020.06.086

Abstract: The green macroalga Ulva rigida represents a promising feedstock for biorefinary due to its fast growth and cosmopolitan distribution. The main component of the cell walls of U. rigida is a sulfated glucuronorhamnan polysaccharide known as ulvan. Herein it was found that due to the high (hydrogen)sulfate group content of ulvan, hydrothermal autohydrolysis at 130 degrees C renders a high percentage of rhamnose (78-79 % recovery from the initial content in the raw material), a rare sugar of high added value. In addition, acid catalysis by a triflate-based graphene oxide under oxygen-free conditions at 180 degrees C affords moderate amounts of tartaric acid (24-26 %). The same triflate-based graphene oxide catalyst under oxygen pressure yields remarkably high percentages of succinic acid (65 %). The catalyst preserves its activity for at least five consecutive reuses.

5. THERMAL BEHAVIOR OF Cu-DOPED TiO2 GELS SYNTHESIZED BY THE SOL-GEL METHOD

Authors: Pandele-Cusu, J; Atkinson, I; Rusu, A; Apostol, N; Teodorescu, V; Predoana, L; Szilagyi, IM; Pokol, G; Zaharescu, M

Published: MAR 2021, DOI: 10.33224/rrch.2021.66.3.01

Abstract: The thermal behavior of Cu-doped TiO2 gels obtained by the sol-gel method was investigated by thermogravimetric and differential thermal analysis (TG/DTG/DTA) and differential scanning calorimetry (DSC) measurements. The comparative investigation of the structure and morphology of the as-prepared gels and of the nanopowders obtained by annealing them was realized by transmission electron microscopy (TEM), Fourier transmission infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Significant differences were noticed depending on the amount of dopant (0.5 or 2.0 mol % CuO). A higher dopant concentration resulted in a more complex decomposition of the sample. This behavior was associated with the formation of various molecular species in the sol-gel solutions before gelation, determined by the different amount of the dopant used.

6. 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, DOI: 10.1016/j.jssc.2021.122310

Abstract: 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.

7. Effect of Vanadium Oxide on the Structure and Li-Ion Conductivity of Lithium Silicate Glasses

Authors: Gaddam, A; Allu, AR; Ganisetti, S; Fernandes, HR; Stan, GE; Negrila, CC; Jamale, AP; Mear, F; Montagne, L; Ferreira, JMF

Published: AUG 5 2021, DOI: 10.1021/acs.jpcc.1c05059

Abstract: The commercially ubiquitous liquid electrolytes for lithium-ion batteries have several shortcomings in terms of safety. Therefore, development of solid electrolytes, especially those that are glass-based, has been gaining increasing interest in recent times. However, the fundamental understanding of the changes in the glass structure and the corresponding changes in the properties due to the addition of dopants is necessary for the development of glasses. Therefore, here, we report a study on the role of vanadium on the glass structure, ionic conduction, crystallization behavior, and other properties of lithium silicate-based glasses (23Li(2)O-2.64K(2)O-2.64Al(2)O(3)-71.72SiO(2)) as a solid electrolyte for high-temperature Li-ion battery applications. Furthermore, we proposed a mathematical model to describe/quantify the ion-conducting channels' connectivity in glasses. The experimental glass structures were assessed using Si-29, V-51, Al-27 nuclear magnetic resonance, Fourier transform infrared, and ultraviolet-visible spectroscopy techniques. The ionic conductivity was measured by impedance spectroscopy, and the crystallization behavior was studied by optical microscopy and X-ray diffraction. Furthermore, molecular dynamics simulations were also used to gain structural insights of the glasses. In the designed compositions, the addition of vanadium decreased the overall concentration of Li+ ions. However, the results revealed that the ionic conductivity improved with the addition of vanadium in spite of a decrease in the number of charge carriers. This suggests that vanadium makes the pathways easier for the conducting ions. Thus, we conclude that vanadium modifies the conduction channels to promote better hoping of the ions from one site to another.

8. Thermoelectric Efficiency of Epitaxial GeSn Alloys for Integrated Si-Based Applications: Assessing the Lattice Thermal Conductivity by Raman Thermometry

Authors: Spirito, D; Driesch, NV; Manganelli, CL; Zoellner, MH; Corley-Wiciak, AA; Ikonic, Z; Stoica, T; Grutzmacher, D; Buca, D; Capellini, G

Published: JUL 26 2021, DOI: 10.1021/acsaem.1c01576

Abstract: Energy harvesting for Internet of Things applications, comprising sensing, life sciences, wearables, and communications, requires efficient thermoelectric (TE) materials, ideally semiconductors compatible with Si technology. In this work, we investigate the potential of GeSn/Ge layers, a group IV material system, as TE material for low-grade heat conversion. We extract the lattice thermal conductivity, by developing an analytical model based on Raman thermometry and heat transport model, and use it to predict thermoelectric performances. The lattice thermal conductivity decreases from 56 W/(m.K) for Ge to 4 W/(m.K) by increasing the Sn atomic composition to 14%. The bulk cubic Ge0.86Sn0.14 alloy features a TE figure of merit of ZT similar to 0.4 at 300 K and an impressive 1.04 at 600 K. These values are extremely promising in view of the use of GeSn/Ge layers operating in the typical on-chip temperature range.

9. 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, DOI: 10.1039/d1ta03644k

Abstract: 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.

10. NiO/Sr doped Ce(0.85)Pr0.10 Er0.05O(2-delta) mesoarchitectured catalyst for partial oxidation of CH4 and anode fueled by H-2

Authors: Navarrete, L; Florea, M; Osiceanu, P; Calderon-Moreno, JM; Trandafir, MM; Somacescu, S; Serra, JM

Published: AUG 2021, DOI: 10.1016/j.micromeso.2021.111171

Abstract: Our study focuses on an advanced exploratory research based on the development of the new IT-SOFCs anode compositions in conjunction with surfactants as template to obtain mesoarchitectured catalysts. We designed NiO/Sr doped Ce0.85Pr0.10 Er0.05O2-o (2.5 and 5 mol.% Sr) mesoarchitectures with robust crystalline framework following a hydrothermal synthesis route. NiO was deposited by wet impregnation and calcined in air at 900.C, in order to assure a good interaction between Ni and mesoporous matrix. The obtained materials exhibit a cubic CeO2 fluorite phase with Pr2O3 and SrCeO3 as secondary phase traces and these were assessed as catalyst for the partial oxidation of CH4 over time and IT-SOFCs anode under reducing atmosphere. The electrochemical behavior as anode fed by wet H2 (2.5% vol. H2O) was investigated in the NiO/CPS/YSZ/GDC/Pt electrochemical cells. The compositional effect on the structural properties, surface chemistry, catalytic and electrochemical performance were highlighted. Sr incorporated in the lattice, proved by X-ray Photoelectron Spectroscopy, guarantees an excellent stability of the catalysts over time for 20h, during partial oxidation of CH4 with high CH4 conversion and CO selectivity (90% in the range 700-800.C) as well as a better performance as IT-SOFCs anode.