Dr. Cezar COMANESCU
Scientific Researcher III
Laboratory of Magnetism and Superconductivity
cezar[DOT]comanescu[AT]infim[DOT]roProjects
1. Nanoconfinement for Energy Storage in Metal Organic Frameworks
Project Type: TE, Start Date: 2022-05-15 End Date: 2024-05-14
Publications
1. Paving the Way to the Fuel of the Future-Nanostructured Complex Hydrides
Authors:
Comanescu, C
Published: JAN 2023, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 24, 143, DOI: 10.3390/ijms24010143
Hydrides have emerged as strong candidates for energy storage applications and their study has attracted wide interest in both the academic and industry sectors. With clear advantages due to the solid-state storage of hydrogen, hydrides and in particular complex hydrides have the ability to tackle environmental pollution by offering the alternative of a clean energy source: hydrogen. However, several drawbacks have detracted this material from going mainstream, and some of these shortcomings have been addressed by nanostructuring/nanoconfinement strategies. With the enhancement of thermodynamic and/or kinetic behavior, nanosized complex hydrides (borohydrides and alanates) have recently conquered new estate in the hydrogen storage field. The current review aims to present the most recent results, many of which illustrate the feasibility of using complex hydrides for the generation of molecular hydrogen in conditions suitable for vehicular and stationary applications. Nanostructuring strategies, either in the pristine or nanoconfined state, coupled with a proper catalyst and the choice of host material can potentially yield a robust nanocomposite to reliably produce H-2 in a reversible manner. The key element to tackle for current and future research efforts remains the reproducible means to store H-2, which will build up towards a viable hydrogen economy goal. The most recent trends and future prospects will be presented herein.
2. New superdielectric materials: (1-x) SrFe12O19 - x BNT-BT nanocomposites
Authors:
Greculeasa, SG; Comanescu, C; Iacob, N; Kuncser, A; Smaranda, I; Amarande, L; Cioangher, M; Burdusel, M; Teodorescu, V
Published: OCT 1 2022, PHYSICA B-CONDENSED MATTER, 642, 414139, DOI: 10.1016/j.physb.2022.414139
Novel (1-x) SrFe12O19 - x BNT-BT0.08 (x = 0; 0.5; 0.8; 1) nanocomposites were explored in this study. The samples were produced by sol-gel method and compacted by conventional sintering. The composition, morphology, local structure, dielectric and magnetic properties were investigated by X-ray diffraction, Transmission Electron Microscopy, Impedance Analysis, Mossbauer spectroscopy, and SQUID magnetometry. The desired composition and the presence of the magnetoplumbite SrFe12O19 and perovskite BNT-BT structures were verified by X-ray diffraction. Irregular morphology and large size distributions are evidenced in the electron microscopy micrographs. The reported room temperature dielectric constants in this study are the highest values obtained in multiferroic composites at room temperature: giant dielectric constants (similar to 1.3 x 10(6)) were obtained, relative to 0.13 x 10(4) in BNT-BT. The hyperfine parameters allowed the identification of the Wyckoff positions of the Fe ions corresponding closely to the theoretical case. The hard magnetic character of the SrFe12O19 phase is evidenced from the magnetic measurements. For the first time in multifermic composites, superdielectric characteristics are evidenced at room temperature.
3. EXCHANGE COUPLED NANOCOMPOSITES: MAGNETOPLUMBITE Sr FERRITE AND MAGNETITE
Authors:
Greculeasa, SG; Comanescu, C; Iacob, N; Kuncser, A
Exchange coupling in a SrFe12O19 - Fe3O4 nanocomposite magnet was explored in this study. The composition, microstructure, local structure and magnetic properties were investigated by XRD, SEM, Mossbauer spectroscopy, and SQUID magnetometry. The magnetoplumbite SrFe12O19 and spinel Fe3O4 structures were verified by X-ray diffraction. The morphology of the composite reveals the characteristics of the two components. The hyperfine parameters allowed the identification of the Wyckoff positions of the iron ions corresponding to the involved phases. The magnetic measurements of the composite, showing a single-phase-like magnetic hysteresis loop, confirmed the exchange coupling between the hard and soft magnetic phases.
4. DIELECTRIC AND ELECTRIC PROPERTIES OF NOVEL CORE-SHELL NANOCOMPOSITE: SrFe12O19 - BNT-BT
Authors:
Greculeasa, SG; Comanescu, C; Cioangher, M
The dielectric and electric properties of a core-shell SrFe12O19 - BNT-BT nanocomposite were explored in this study. The desired composition and the existence of the magnetoplumbite SrFe12O19 and perovskite BNT-BT structures were verified by X-ray diffraction. The dielectric constant values approached the case of BNT-BT due to the small amount of hexaferrite content. The electric properties were also derived.
5. Complex Metal Borohydrides: From Laboratory Oddities to Prime Candidates in Energy Storage Applications
Authors:
Comanescu, C
Published: MAR 2022, MATERIALS, 15, 2286, DOI: 10.3390/ma15062286
Despite being the lightest element in the periodic table, hydrogen poses many risks regarding its production, storage, and transport, but it is also the one element promising pollution-free energy for the planet, energy reliability, and sustainability. Development of such novel materials conveying a hydrogen source face stringent scrutiny from both a scientific and a safety point of view: they are required to have a high hydrogen wt.% storage capacity, must store hydrogen in a safe manner (i.e., by chemically binding it), and should exhibit controlled, and preferably rapid, absorption-desorption kinetics. Even the most advanced composites today face the difficult task of overcoming the harsh re-hydrogenation conditions (elevated temperature, high hydrogen pressure). Traditionally, the most utilized materials have been RMH (reactive metal hydrides) and complex metal borohydrides M(BH4)(x) (M: main group or transition metal; x: valence of M), often along with metal amides or various additives serving as catalysts (Pd2+, Ti4+ etc.). Through destabilization (kinetic or thermodynamic), M(BH4)(x) can effectively lower their dehydrogenation enthalpy, providing for a faster reaction occurring at a lower temperature onset. The present review summarizes the recent scientific results on various metal borohydrides, aiming to present the current state-of-the-art on such hydrogen storage materials, while trying to analyze the pros and cons of each material regarding its thermodynamic and kinetic behavior in hydrogenation studies.
6. Recent Development in Nanoconfined Hydrides for Energy Storage
Authors:
Comanescu, C
Published: JUL 2022, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 23, 7111, DOI: 10.3390/ijms23137111
Hydrogen is the ultimate vector for a carbon-free, sustainable green-energy. While being the most promising candidate to serve this purpose, hydrogen inherits a series of characteristics making it particularly difficult to handle, store, transport and use in a safe manner. The researchers' attention has thus shifted to storing hydrogen in its more manageable forms: the light metal hydrides and related derivatives (ammonia-borane, tetrahydridoborates/borohydrides, tetrahydridoaluminates/alanates or reactive hydride composites). Even then, the thermodynamic and kinetic behavior faces either too high energy barriers or sluggish kinetics (or both), and an efficient tool to overcome these issues is through nanoconfinement. Nanoconfined energy storage materials are the current state-of-the-art approach regarding hydrogen storage field, and the current review aims to summarize the most recent progress in this intriguing field. The latest reviews concerning H-2 production and storage are discussed, and the shift from bulk to nanomaterials is described in the context of physical and chemical aspects of nanoconfinement effects in the obtained nanocomposites. The types of hosts used for hydrogen materials are divided in classes of substances, the mean of hydride inclusion in said hosts and the classes of hydrogen storage materials are presented with their most recent trends and future prospects.
7. Magnetic Nanoparticles: Current Advances in Nanomedicine, Drug Delivery and MRI
Authors:
Comanescu, C
Published: SEP 2022, CHEMISTRY-SWITZERLAND, 4, DOI: 10.3390/chemistry4030063
Magnetic nanoparticles (MNPs) have evolved tremendously during recent years, in part due to the rapid expansion of nanotechnology and to their active magnetic core with a high surface-to-volume ratio, while their surface functionalization opened the door to a plethora of drug, gene and bioactive molecule immobilization. Taming the high reactivity of the magnetic core was achieved by various functionalization techniques, producing MNPs tailored for the diagnosis and treatment of cardiovascular or neurological disease, tumors and cancer. Superparamagnetic iron oxide nanoparticles (SPIONs) are established at the core of drug-delivery systems and could act as efficient agents for MFH (magnetic fluid hyperthermia). Depending on the functionalization molecule and intrinsic morphological features, MNPs now cover a broad scope which the current review aims to overview. Considering the exponential expansion of the field, the current review will be limited to roughly the past three years.
8. Optimization of magnetic fluid hyperthermia with respect to nanoparticle shape-related parameters: case of magnetite ellipsoidal nanoparticles
Authors:
Iacob, N; Kuncser, A; Comanescu, C; Palade, P; Kuncser, V
Published: MAY 22 2020, JOURNAL OF NANOPARTICLE RESEARCH, 22, DOI: 10.1007/s11051-020-04842-6
Issues related to the optimization of heat transfer mechanisms dominated by superparamagnetic relaxation are considered in the case of AC (alternating current) magnetic field hyperthermia procedures. The key role in the conversion of electromagnetic energy to the thermal one via the superparamagnetic relaxation mechanism is played by the magnetic anisotropy of nanoparticles, easily to be controlled via the shape anisotropy component. The optimization process has been discussed in the case of magnetite (Fe3O4) ellipsoidal nanoparticles with dominant shape anisotropy dispersed in different media. Nanoparticles of different sizes and aspect ratios have been considered in correlation with those specific parameters of the actuating AC magnetic field which respect an established biological safely criterion. It has been proven that the dissipated power can be maximized for a given set of biological compatible RF (radiofrequency) field parameters (frequency and field amplitude at the sample space) only for specific pairs of particle sizes and aspect ratios. For instance, it has been shown that ellipsoidal magnetite nanoparticles with 10 nm equatorial size and aspect ratio of 2 are optimal for a maximum transferred power under radiofrequency excitations of 250 kHz and field amplitude of 20 kA/m, if high viscosity dispersion media are used. The methodology for deriving the optimal shape (geometrical) parameters of a specific type of nanoparticles in conditions of using available radiofrequency excitations, or vice versa, for deriving the optimal radiofrequency working parameters in the case of ferrofluids with specific nanoparticles (type and geometry) is described and discussed in detail.
9. Mesoporous Cobalt Ferrite Nanosystems Obtained by Surfactant-Assisted Hydrothermal Method: Tuning Morpho-structural and Magnetic Properties via pH-Variation
Authors:
Palade, P; Comanescu, C; Kuncser, A; Berger, D; Matei, C; Iacob, N; Kuncser, V
Published: MAR 2020, NANOMATERIALS, 10, DOI: 10.3390/nano10030476
A facile and cheap surfactant-assisted hydrothermal method was used to prepare mesoporous cobalt ferrite nanosystems with BET surface area up to 151 m(2)/g. These mesostructures with high BET surface areas and pore sizes are made from assemblies of nanoparticles (NPs) with average sizes between 7.8 and 9.6 nm depending on the initial pH conditions. The pH proved to be the key factor for controlling not only NP size, but also the phase purity and the porosity properties of the mesostructures. At pH values lower than 7, a parasite hematite phase begins to form. The sample obtained at pH = 7.3 has magnetization at saturation M-s = 38 emu/g at 300 K (54.3 emu/g at 10 K) and BET surface area S-BET = 151 m(2)/g, whereas the one obtained at pH = 8.3 has M-s = 68 emu/g at 300 K (83.6 emu/g at 10 K) and S-BET = 101 m(2)/g. The magnetic coercive field values at 10 K are high at up to 12,780 Oe, with a maximum coercive field reached for the sample obtained at pH = 8.3. Decreased magnetic performances are obtained at pH values higher than 9. The iron occupancies of the tetrahedral and octahedral sites belonging to the cobalt ferrite spinel structure were extracted through decomposition of the Mossbauer patterns in spectral components. The magnetic anisotropy constants of the investigated NPs were estimated from the temperature dependence of the hyperfine magnetic field. Taking into consideration the high values of BET surface area and the magnetic anisotropy constants as well as the significant magnetizations for saturation at ambient temperature, and the fact that all parameters can be adjusted through the initial pH conditions, these materials are very promising as recyclable anti-polluting agents, magnetically separable catalysts, and targeted drug delivery vehicles.
10. Rhodium-Catalyzed Annulation of ortho-Alkenyl Anilides with Alkynes: Formation of Unexpected Naphthalene Adducts
Authors:
Seoane, A; Comanescu, C; Casanova, N; Garcia-Fandino, R; Diz, X; Mascarenas, JL; Gulias, M
Published: FEB 4 2019, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 58, 1704, DOI: 10.1002/anie.201811747
o-Alkenyl N-triflylanilides underwent rhodium(III)-catalyzed oxidative annulations with alkynes to produce different types of naphthylamides in a process which involves the cleavage of two C-H bonds. Remarkably, besides formal dehydrogenative (4C+2C) cycloadducts, the reaction also produces variable amounts of isomeric naphthylamides, whose formation requires a formal migration of the alkenyl moiety from the ortho to the meta position of the anilide. The annulation reaction can be efficiently carried out in the absence of external oxidants, such as Cu(OAc)(2).
11. Structural, Magnetic, and Mossbauer Investigation of Ordered Iron Nitride with Martensitic Structure Obtained from Amorphous Hematite Synthesized via the Microwave Route
Authors:
Palade, P; Plapcianu, C; Mercioniu, I; Comanescu, C; Schinteie, G; Leca, A; Vidu, R
Published: MAR 22 2017, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 56, 2966, DOI: 10.1021/acs.iecr.6b04574
Amorphous hematite synthesized by a simple and fast microwave route was used to obtain Fe16N2 fine particles by reducing in 5% H-2/Ar gas flow, followed by long time nitridation in ammonia gas flow at temperatures below 200 degrees C. Depending on nitridation temperature, various amounts of metallic iron were present along with the alpha" -Fe16N2 main phase. A small amount of iron oxide was observed by Mossbauer spectroscopy, but it was undetected by X-ray diffraction due to its high degree of amorphization. Increased amounts of Fe3N and Fe4N phases were observed at a nitridation temperature above 150 degrees C, which had a detrimental effect on the magnetic properties. Structural information and phase composition were extracted from Rietveld refinement of the XRD data. Values of the magnetization at saturation measured at 40 kOe and 25 degrees C of 222 emu/g for alpha"-Fe16N2 and 192 emu/g for metallic iron were obtained via magnetic measurements, Rietveld, and Mossbauer analysis.
12. MOSSBAUER AND MAGNETIC INVESTIGATION OF IRON NITRIDE WITH MARTENSITE STRUCTURE SYNTHESISED FROM OXY-HYDROXIDE TYPE PRECURSOR
Authors:
Palade, P; Plapcianu, C; Mercioniu, I; Comanescu, CC; Schinteie, G
Published: JAN-MAR 2016, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 11, 63, DOI:
Fe16N2 fine particles were prepared by reduction in 5% H-2/Ar gas mixture flow, starting from goethite or hematite precursors, followed by nitridation in ammonia gas flow. Small amounts of metallic iron and iron oxide are present besides the main phase which is an ordered iron nitride having martensite structure (alpha''-Fe16N2) as revealed by Mossbauer spectroscopy measurements. However, X-ray diffraction data do not show any traces of oxides due to their high degree of amorphization. When nitridation is performed at about 150 C-0, Fe4N phase begins to form and its presence deteriorates the magnetic properties. The samples prepared by nitridation of goethite present better magnetic properties compared to those obtained by nitridation of hematite. Magnetic and Mossbauer measurements performed at ambient temperature were corroborated in order to extract the magnetization at saturation value for each phase which occurs in the obtained samples. The corresponding values are 226 emu/g for Fe16N2 and 198 emu/g for metallic iron contained in the prepared powders.
13. Synthesis and characterization of novel mesocomposites Co3O4 and CuO@OMS (ordered mesoporous silica) as active catalysts for hydrocarbon oxidation
Authors:
Comanescu, C
Published: FEB 22 2014, JOURNAL OF NANOPARTICLE RESEARCH, 16, DOI: 10.1007/s11051-014-2323-4
Novel metal nanoporous transition metal oxides M (x) O (y) (Co3O4, CuO) have been synthesized by thermal decomposition of inorganic salts precursors (acetates, nitrates) impregnated into hexagonal mesoporous silica (OMS, ordered mesoporous silica) of SBA-15 type (prepared in-house) at different precursor loadings, the mesocomposites thus obtained being monitored after each impregnation-calcination step by small and wide angle powder XRD. The pore size for the ordered silica host range from 5.08 to 7.06 nm. Retention of the hexagonal silica framework has been observed in spite of the temperatures up to 500 A degrees C. Mesoporous Co3O4 has been obtained by leaching the silica through overnight HF dissolution, which partially preserved the small-range ordering found in the parent Co3O4@OMS composite prior to leaching. Both Co3O4 (meso) and Co3O4@SBA-15 have been tested in methane oxidation and were found to be superior to the bulk Co3O4 performance, with mesoporous Co3O4 being able to fully oxidize methane to CO2 and H2O at 350 A degrees C, while Co3O4@OMS exhibits a lower activity with 20 % conversion at 350 A degrees C. CuO@OMS shows the lowest activity, with only similar to 13 % conversion at 500 A degrees C.
14. Effects of ZnO Nanoparticles on the Wet Scrub Resistance and Photocatalytic Properties of Acrylic Coatings
Authors:
Vaja, F; Comanescu, C; Oprea, O; Ficai, D; Guran, C
In this work zinc oxide, ZnO, nanopowders were synthesized by co-precipitation method from a zinc acetate, Zn(CH3COO)(2), solution. The obtained nanoparticles were morphologically and structurally characterized by XRD diffraction, SEM, IR and UV-Vis spectroscopy. The new obtained material was investigated as an additive in coatings for improving wet scrub resistance, self-cleaning properties etc. The XRD pattern of the ZnO nanoparticles highlights the wurtzite hexagonal structure and also proves its purity. The correlations made based on their crystallization planes identified ZnO as the sole product. ZnO nanoparticles obtained by co-precipitation method have been introduced by strong shaking in the coating system; this has positively influenced the surface properties of the films.
15. Nanoconfinement in activated mesoporous carbon of calcium borohydride for improved reversible hydrogen storage
Authors:
Comanescu, C; Capurso, G; Maddalena, A
Published: SEP 28 2012, NANOTECHNOLOGY, 23, DOI: 10.1088/0957-4484/23/38/385401
Mesoporous carbon frameworks were synthesized using the soft-template method. Ca(BH4)(2) was incorporated into activated mesoporous carbon by the incipient wetness method. The activation of mesoporous carbon was necessary to optimize the surface area and pore size. Thermal programmed absorption measurements showed that the confinement of this borohydride into carbon nanoscaffolds improved its reversible capacity (relative to the reactive portion) and performance of hydrogen storage compared to unsupported borohydride. Hydrogen release from the supported hydride started at a temperature as low as 100 degrees C and the dehydrogenation rate was fast compared to the bulk borohydride. In addition, the hydrogen pressure necessary to regenerate the borohydride from the dehydrogenation products was reduced.
16. IMPROVEMENTS OF HYDROGEN DESORPTION OF LITHIUM BOROHYDRIDE BY IMPREGNATION ONTO MSU-H CARBON REPLICA
Authors:
Palade, P; Comanescu, C; Mercioniu, I
Published: NOV-DEC 2012, JOURNAL OF OVONIC RESEARCH, 8, 160, DOI:
The hydrogen storage material lithium borohydride was infiltrated from solvent solution into the pores of the carbon replica of MSU-H mesoporous silica by the incipient wetness method. Different amounts of lithium borohydride up to 40 % from the weight of the high surface area carbonic material were used. By this method was achieved a good dispersion of the hydride into the carbonaceous support. The hydrogen desorption starts at temperatures as low as 150 degrees C for the sample with 8 wt% LiBH4 dispersed onto the MSU-H carbon replica while pure LiBH4 does not release hydrogen below 300 degrees C. After rehydrogenation, a lower amount of hydrogen is desorbed due to the fact that increasing temperature up to 400 degrees C a part of hydride segregates outside the pores of the carbonaceous support.
17. Improvements of kinetic properties of LiBH4 by supporting on MSU-H type mesoporous silica
Authors:
Comanescu, C; Guran, C; Palade, P
Published: MAY 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 708, DOI:
Lithium borohydride (LiBH4) is a promising material for hydrogen storage, featuring a high gravimetric storage density (above 13 wt. % in the first decomposition step). However, studies of re-hydrogenation of the decomposition products have proven less successful, leading us to the requirement of modified-LiBH4 materials with better absorption-desorption behavior. A Mo-doped mesoporous material was obtained starting from commercial MSU-H and ammonium molybdate. This mesoporous material (MSU-H-type functionalized with molybdenum salt) was used as support in order to impregnate LiBH4. Even though the thermodynamics of LiBH4 hydrogen absorption-desorption is not modified, the desorption kinetics of supported LiBH4 is improved compared to that of pure LiBH4. Moreover, after re-hydrogenation at 450 degrees C only 3.2 wt. % H-2 of storage capacity is recovered for LiBH4, while for supported LiBH4 we achieved almost 5.2 wt. % H-2.
18. EXCHANGE COUPLED NANOCOMPOSITES: MAGNETOPLUMBITE Sr FERRITE AND MAGNETITE
Authors:
Greculeasa, SG; Comanescu, C; Iacob, N; Kuncser, A
Published: , ROMANIAN JOURNAL OF PHYSICS, 2022, DOI: 606
Exchange coupling in a SrFe12O19 - Fe3O4 nanocomposite magnet was explored in this study. The composition, microstructure, local structure and magnetic properties were investigated by XRD, SEM, Mossbauer spectroscopy, and SQUID magnetometry. The magnetoplumbite SrFe12O19 and spinel Fe3O4 structures were verified by X-ray diffraction. The morphology of the composite reveals the characteristics of the two components. The hyperfine parameters allowed the identification of the Wyckoff positions of the iron ions corresponding to the involved phases. The magnetic measurements of the composite, showing a single-phase-like magnetic hysteresis loop, confirmed the exchange coupling between the hard and soft magnetic phases.
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