Добірка наукової літератури з теми "Bimetallic NiFe oxide nanoparticles"

The reactivity of nanoscale zero-valent iron is limited by surface passivation and particle agglomeration. Here, Ni/Fe bimetallic nanoparticles embedded into graphitized carbon (NiFe@GC) were prepared from Ni/Fe bimetallic complex through a carbothermal reduction treatment. The Ni/Fe nanoparticles were uniformly distributed in the GC matrix with controllable particle sizes, and NiFe@GC exhibited a larger specific surface area than unsupported nanoscale zero-valent iron/nickel (FeNi NPs). The XRD results revealed that Ni/Fe bimetallic nanoparticles embedded into graphitized carbon were protected from oxidization. The NiFe@GC performed excellently in 2,4,6-trichlorophenol (TCP) removal from an aqueous solution. The removal efficiency of TCP for NiFe@GC-50 was more than twice that of FeNi nanoparticles, and the removal efficiency of TCP increased from 78.5% to 94.1% when the Ni/Fe molar ratio increased from 0 to 50%. The removal efficiency of TCP by NiFe@GC-50 can maintain 76.8% after 10 days of aging, much higher than that of FeNi NPs (29.6%). The higher performance of NiFe@GC should be ascribed to the significant synergistic effect of the combination of NiFe bimetallic nanoparticles and GC. In the presence of Ni, atomic H* generated by zero-valent iron corrosion can accelerate TCP removal. The GC coated on the surface of Ni/Fe bimetallic nanoparticles can protect them from oxidation and deactivation.

The study of NiFe magnetic nanoparticles (MNPs) has a wide range of applications because of the unique composition and its magnetism. In this paper, a brief review is presented on the different methods for the preparation of the bimetallic magnetic nanoparticles, along with our preliminary work on the synthesis of this kind of alloy nanoparticles.

A NiFe alloy nanoparticle/graphene oxide hybrid (NiFe/GO) was prepared for electrochemical glucose sensing. The as-prepared NiFe/GO hybrid was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results indicated that NiFe alloy nanoparticles can be successfully deposited on GO. The electrochemical glucose sensing performance of the as-prepared NiFe/GO hybrid was studied by cyclic voltammetry and amperometric measurement. Results showed that the NiFe/GO-modified glassy carbon electrode had sensitivity of 173 μA mM−1 cm−2 for glucose sensing with a linear range up to 5 mM, which is superior to that of commonly used Ni nanoparticles. Furthermore, high selectivity for glucose detection could be achieved by the NiFe/GO hybrid. All the results demonstrated that the NiFe/GO hybrid has promise for application in electrochemical glucose sensing.

Hexavalent chromium (Cr(vi)) is one of the most toxic heavy metal pollutants in groundwater, and thus the detection of Cr(vi) with high sensitivity, accuracy, and simplicity and low cost is of great importance.

Toluene is extensively used in many industrial products, which needs to be effectively detected by sensitive gas sensors even at low-ppm-level concentrations. Here, NiFe2O4 nano-octahedrons were calcinated from NiFe-bimetallic metal-organic framework (MOFs) octahedrons synthesized by a facile refluxing method. The co-existence of p-Phthalic acid (PTA) and 3,3-diaminobenzidine (DAB) promotes the formation of smooth NiFe-bimetallic MOFs octahedrons. After subsequent thermal treatment, a big weight loss (about 85%) transformed NiFe2O4 nanoparticles (30 nm) into NiFe2O4 porous nano-octahedrons with hollow interiors. The NiFe2O4 nano-octahedron based sensor exhibited excellent gas sensing properties for toluene with a nice stability, fast response, and recovery time (25 s/40 s to 100 ppm toluene), and a lower detection limitation (1 ppm) at 260 °C. The excellent toluene-sensing properties can not only be derived from the hollow interiors combined with porous nano-octahedrons to favor the diffusion of gas molecules, but also from the efficient catalytic activity of NiFe2O4 nanoparticles.

Dans ce travail, différents systèmes catalytiques nanostructurés ont été synthétisés par une approche organométallique pour obtenir des nanoparticules de petite taille et de distribution de taille étroite, et leur activité catalytique dans la réaction d'oxydation de l'eau a été évaluée. Premièrement, des NPs de fer stabilisées par l'acide oléique ont été synthétisées qui présentaient une taille moyenne d'env. 10 nm ± 1,1 nm. Une couche d'oxyde, gamma-Fe_2O_3, d'env. 2,6 nm d'épaisseur a été formée à leur surface pour obtenir des structures cœur-coquille Fe@FeOx d'env. 11,5 ± 2,3 nm de diamètre. Malgré leur hydrophobicité, ces nanoparticules ont montré une bonne activité électrocatalytique en conditions alcalines. La coquille d'oxyde gamma-Fe_2O_3 étant bien adaptée au greffage de groupements phosphoniques, ces NPs Fe@FeOx ont été greffées avec différents acides aminophosphoniques afin de les transférer dans l'eau. Une évaluation préliminaire de leur activité catalytique montre une amélioration lorsque les NPs sont greffées avec l'acide 3-aminopropyl phosphonique, ce qui ouvre des perspectives prometteuses. En outre, un photosensibilisateur, un complexe Ru-phénanthroline avec un groupe phosphonate pendant, a été synthétisé et greffé sur les NPs Fe@FeOx pour former une photoanode hybride et catalyser la photoélectrodécomposition de l'eau. Des processus mono et biphasiques ont été étudiés pour greffer le complexe à la surface des nanoparticules. Le processus monophasique s'est avéré plus efficace car il a fourni une densité de greffage plus élevée (respectivement 56 et 9 Ru par NP pour les processus mono et biphasiques). Des mesures photoélectrochimiques ont montré que le nanocatalyseur hybride comprenant la teneur en Ru la plus élevée était env. 9 fois plus actif qu'un simple mélange entre un photosensibilisateur au ruthénium sans fonction de greffage et les nanoparticules Fe@FeOx, et env. 40 fois plus actif que les NPs Fe@FeOx. L'amélioration des performances pourrait être attribuée à un transfert d'électrons plus efficace entre le photosensibilisateur et le catalyseur Fe@FeOx grâce à la liaison covalente entre ces deux composants. Le greffage covalent s'est avéré améliorer non seulement l'activité photocatalytique mais également la stabilité du système. Enfin, des NPs NiFe amorphes (diamètre env. 4 nm) avec deux compositions différentes (Ni_0,5Fe_0,5 NPs et Ni_0,68Fe_0,32 NPs) ont été synthétisées, oxydées à l'air et fonctionnalisées avec de l'acide 3-aminopropyl phosphonique. L'activité électrocatalytique de ces NP hydrosolubles a été étudiée en milieu alcalin, en comparaison avec des NPs NiOx, FeOx et Ni_0.1Fe_0.9Ox. Les NPs hydrosolubles contenant 32% de Fe (Ni_0,68Fe_0,32Ox) ont montré l'activité la plus élevée et une bonne durabilité en solution alcaline. Ces caractéristiques rendent ces NP amorphes potentiellement applicables dans les cellules photoélectrochimiques pour la photodécomposition de l'eau
In this work, different nanostructured catalytic systems have been synthesized by an organometallic approach to produce nanoparticles (NPs) of small size and narrow size distribution, and their catalytic activity in the water oxidation reaction has been evaluated. First Fe NPs stabilized by oleic acid were synthesized that displayed an average size of ca. 10 nm ± 1.1 nm. A gamma-Fe_2O_3 oxide layer ca. 2.6 nm thick has been formed at their surface to obtain Fe@FeOx core-shell structure of ca. 11.5 ± 2.3 nm in diameter. Despite their hydrophobicity, these nanoparticles showed good electrocatalytic activity in alkaline conditions. As the gamma-Fe_2O_3 oxide shell is well adapted to the grafting of phosphonic groups, these Fe@FeOx NPs were grafted with different aminophosphonic acids in order to transfer them into water. Preliminary assessment of their catalytic activity showed improved activity for the NPs functionalized by 3-aminopropylphosphonic acid which opens promising prospects. Subsequently, a Ru-phenanthroline light-harvester with a pendant phosphonate group was synthesized and grafted onto the Fe@FeOx core/shell NPs to afford a novel hybrid photoanode for solar-driven water splitting. Mono- and biphasic processes were investigated to graft the Ru-complex at the surface of the NPs. The monophasic process was found to be more efficient as it provided a higher grafting density at the surface of the NPs (respectively 56 and 9 Ru per nanoparticles for the mono and biphasic processes). Photoelectrochemical measurements showed that the hybrid nanocatalyst comprising the highest Ru content was ca. 9-fold more catalytically active than a simple mixture between a ruthenium polypyridyl photosensitizer bearing no grafting group and the Fe@FeOx nanoparticles, and 40-fold more active than the pristine Fe@FeOx NPs. The performance enhancement could be attributed to a more efficient electron transfer between the ruthenium polypyridyl photosensitizer and the Fe@FeOx water oxidation catalyst thanks to the covalent bonding between these two components. The covalent grafting was found to improve not only the photocatalytic activity but also the stability of the system. Finally, amorphous NiFe NPs (diameter ca. 4 nm) with two different ratios between Ni and Fe (Ni_0.5Fe_0.5 NPs and Ni_0.68Fe_0.32 NPs) were synthesized, oxidized in air and grafted with 3-aminopropylphosphonic acid in order to obtain hydrophilic systems. The electrocatalytic activity of these water-soluble NPs was studied in alkaline solution, in comparison with that of crude NiOx NPs, FeOx NPs, and Ni_0.1Fe_0.9Ox NPs. The water soluble NPs containing 32 % of Fe (Ni_0.68Fe_0.32Ox) showed the highest activity and a good durability in alkaline solution. These characteristics make these amorphous NPs potentially applicable in photoelectrochemical cells for water splitting

Environmental pollution by polychlorinated chlorinated organic wastes is of great concern. Catalytic hydrodechlorination is considered clean and efficient methodology for safe disposal of chlorinated organic wastes. This work aims at studying the catalytic hydrodechlorination reaction for the removal of environmentally polluting chlorinated organic wastes: 1,2,4-trichlorobenzene (1,2,4-TCB) and Trichloroethylene (TCE). The research has focused on evaluation of the activity, selectivity and stability of newly synthesized Pd based catalysts for hydrodechlorination of 1,2,4-trichlorobenzene and trichloroethylene. The first part, related to the HDC of 1,2,4-TCB, is to obtain active and stable catalyst for the hydrodechlorination of C-Cl bond of aromatic compounds to non chlorinated organic aromatic compound (benzene). While the second part aims at obtaining catalysts that allow high selectivity to ethylene formation during the HDC Trichloroethylene. Pd based hydrotalcite derived mixed oxides with different surface property were explored as catalysts for hydrodechlorination reaction. In addition, bimetallic and monometallic heterogeneous catalytic systems were investigated for selective hydrodechlorination reaction. Detailed characterization of the active centers of the newly synthesized catalysts by different techniques was achieved. This work presents original ideas, which could find a practical application, for the treatment of organo-halogenated pollutants.
La contaminación ambiental mediante compuestos policlorados aromáticos y alifáticos es de gran preocupación. La reacción de hidrodecloración catalítica selectiva (HDC) se presenta como una nueva tecnología eficaz para una eliminación segura de estos tipos de compuestos orgánicos clorados. Es por ello, que este trabajo de investigación se ha enfocado en el estudio de nuevos catalizadores activos, selectivos y estables en diferentes reacciones de hidrodecloración de dos familias de compuestos orgánicos clorados: 1,2,4-triclorobenceno (1,2,4-TCB-compuestos aromáticos clorados) y el tricloroetileno (representativo de un compuesto clorado alifático). La primera parte de la tesis relacionadas con el HDC de 1,2,4-TCB, tiene como objetivo la obtención de catalizadores activos y estables para la hidrogenación del enlace C-Cl en compuestos aromáticos y la obtención final del compuesto aromático orgánico declorado. Mientras que la segunda parte tiene por objeto la obtención de catalizadores que permitan una gran selectividad a etileno y no hacia etano (hidrogenación profunda del tricloroetileno) durante la HDC de tricloroetileno. Por otra parte se ha realizado un estudio profundo en la síntesis de estos nuevos catalizadores, así como en la caracterización de los centros activos de dichos catalizadores, para su correlación con la actividad, selectividad y estabilidad de dichos catalizadores. Presenta ideas originales, lo que podría encontrar una aplicación práctica, para el tratamiento de compuestos órgano-halogenados contaminantes.

Controlling catalyst morphology and composition are required to make meaningful structure-activity/stability relationships for the design of future catalysts. Herein, we have employed strategies of presynthesis and infusion or electroless deposition to achieve exquisite control over catalyst composite morphology. The oxygen reduction (ORR) and the oxygen evolution reactions (OER) were chosen as model systems, as their slow kinetics is a major limiting factor preventing the commercialization of fuel cells and rechargeable metal air batteries. In acid, bimetallic (Pt-Cu, Pd-Pt) and monometallic (Pt) catalysts were presynthesized in the presence of capping ligands. Well alloyed Pt-Cu nanoparticles (3-5 nm) adsorbed on graphitic mesoporous carbon (GMC) displayed an ORR activity >4x that of commercial Pt. For both presynthesized Pt and Pt-Cu nanocrystals on GMC, no activity loss was also observed during degradation cycling due to strong metal-support interactions and the oxidation resistance of graphitic carbon. Similar strong metal-support interactions were achieved on non-graphitic carbon for Pd3Pt2 (<4 nm) nanoparticles due to disorder in the metal surface This led to enhanced mass activity 1.8x versus pure Pt, as well as improved stability. For basic electrolytes, we developed an electroless co-deposition scheme to deposit Ag (3 nm) next to MnOx nanodomains on carbon. We achieved a mass activity for Ag-MnOx/VC, 3x beyond the linear combination of pure component activities due to ensemble effects, where Ag and MnOx domains catalyze different ORR steps, and ligand effects from the unique electronic interaction at the Ag-MnOx interface. Activity synergy was also shown for Ag-Pd alloys (~5 nm), achieving up to 5x activity on a Pd basis, resulting from the unique alloy surface of single Pd atoms surrounded by Ag. Lastly, we combined arrested growth of amorphous nanoparticles with thin film freezing to create a high surface area, pure phase perovskite aggregate of nanoparticles after calcination. Sintering was mitigated during the high temperature calcination required to form the perovskite crystals. The high surface areas and phase purity led to OER mass activities ~2.5x higher than the benchmark IrO2 catalyst.
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In this work we investigate the use of NiCo bimetal/oxide as catalyst for hydrogen production from ethanol, with a focus on the deactivation pattern and the nature of the observed carbon deposition. It is well known that sintering and coke deposition during decomposition reaction significantly reduces the activity of the catalysts at higher temperature, by blocking the active sites of the catalysts. During ethanol decomposition reaction, the cleavage of C-C bond produces adsorbed *CH4 and *CO species that further decompose to form carbonaceous compounds. FTIR in-situ analysis was conducted between 50 to 400°C for all the catalysts to understand the reaction mechanism and product selectivity. Cobalt was found to be selective for aldehyde and acetate, whereas bimetallic Ni-Co was selective for the formation of CO at 400°C along with aldehyde. Complete conversion of ethanol was observed at 350°C and 420°C for NiCo and Cobalt respectively indicating an improvement in the rate of conversion when Ni was added to cobalt. The crystallinity, morphology and particle analysis of the used catalyst after reaction were studied using XRD, SEM and TEM respectively. The XRD shows the complete phase change of porous NiCoO2 to NiCo alloy and SEM indicates the presence of fibrous structure on the surface with 91.7 % of carbon while keeping 1:1 ratio of Ni and Co after the reaction. The detailed analysis of carbon structure using HRTEM-STEM shows the simultaneous growth of carbon nano fibers (CNFs) and multiwalled carbon nanotubes (MWCNTs) that were favored on larger and smaller crystallites respectively. Analysis of carbon formation on individual Co catalyst and bimetallic NiCo catalyst shows a clear difference in the initiation pattern of carbon deposition. Metallic Co nanoparticles were found to be more mobile where Co disperses along the catalysts surface, whereas NiCo nanoparticles were relatively less mobile, and maintained their structure.