The photo-electrochemical studies of Eu doped yttrium orthovanadate–zinc oxide–reduced graphene oxide nanohybrid

A new class of nanostructured photo-electrocatalyst Eu³⁺ doped yttrium orthovanadate–zinc oxide–reduced graphene oxide (YVO₄:Eu³⁺–ZnO–RGO) nanohybrid was developed by a simple electrostatic self-assembly at room temperature, using ZnO, YVO₄:Eu³⁺ and RGO as building blocks. Interaction among YVO₄:Eu³⁺, ZnO and RGO is indicated by variation in hydrodynamic diameter (H_D) and zeta potentials of the products as compared to their individual components, thus suggesting that YVO₄:Eu³⁺–ZnO–RGO is a nanohybrid and not a physical mixture. Electrochemical response of this nanohybrid towards the redox couple of Fe(CN)₆^3−/4− was investigated before and after UV irradiation. Apart from quenching of the green emission of ZnO in photoluminescence spectrum, which serves as a probe to monitor the interfacial electron transfer from excited ZnO to RGO, degradation in electrochemical redox process provides an additional path to monitor interfacial electron transfer.     

Magnesia supported Au and Ag catalysts for the preparation of few-layer graphene–metal nanocomposites: relationship between catalyst structure and the properties of graphene composites

Magnesia supported Au, Ag, and Au–Ag nanostructured catalysts were prepared, characterized, and used to synthesize few-layer graphene–metal nanoparticle (Gr–MeNP) composites. The catalysts have a mezoporous structure and a mixture of MgO and MgO·H₂O as support. The gold nanoparticles (AuNPs) are uniformly dispersed on the surface of the Au/MgO catalysts, and have a uniform round shape with a medium size of ~8 nm. On the other hand, the silver nanoparticles (AgNPs) present on the Ag/MgO catalyst have an irregular shape, larger diameters, and less uniform dispersion. The Au–Ag/MgO catalyst contains large Au–Ag bimetallic particles of ~20–30 nm surrounded by small (5 nm) AuNPs. Following the RF-CCVD process and the dissolution of the magnesia support, relative large, few-layer, wrinkled graphene sheets decorated with metal nanoparticles (MeNPs) are observed. Graphene–gold (Gr–Au) and graphene–silver (Gr–Ag) composites had 4–7 graphitic layers with a relatively large area and similar crystallinity for samples prepared in similar experimental conditions. Graphene–gold–silver composites (Gr–Au–Ag) presented graphitic rectangles with round, bent edges, higher crystallinity, and a higher number of layers (8–14). The MeNPs are encased in the graphitic layers of all the different samples. Their size, shape, and distribution depend on the nature of the catalyst. The AuNPs were uniformly distributed, had a size of about 15 nm, and a round shape similar to those from Au/MgO catalyst. In Gr–Ag, the AgNPs have a round shape, very different from that of the Ag/MgO catalyst, large size distribution and are not uniformly distributed on the surface. Agglomerations of AgNPs together with large areas of pristine few-layer graphene were observed. In Gr–Au–Ag composites, almost exclusively large bimetallic particles of about 25–30 nm, situated at the edge of graphene rectangles have been found.     

Study on preparation of Co–Pt–W alloy films by electrodeposition

Abstract

Co–Pt–W alloy films were prepared by the electroplating method to replace costly sputtering on a copper substrate. Effects of different pH values and current densities on composition, microstructure and magnetic properties of films were investigated. With the rise in pH values, the amounts of tungsten and cobalt decrease simultaneously as a result of less tungstate oxides in higher OH– concentration solution. Almost all the deposited films were crystalline and formed fcc CoPt(111) and hcp CoPt(002). Co–Pt–W alloy films intend to change from fcc to hcp structure when the current density was >20 mA cm^?2. It was found that hcp structures of Co–Pt–W alloy films possess high coercivity performance. Moreover, higher pH values induced lower saturation magnetisation while higher current densities could result in larger saturation magnetisation. Dissimilar surface morphology could be detected under different current densities. With increasing the current density, grains of films tend to agglomerate and grow perpendicularly to substrate. Bigger agglomerated particles and ‘hill-like’ structure could be observed when the current density was up to 30 mA cm^?2.     

Combination of supported bimetallic rhodium–molybdenum catalyst and cerium oxide for hydrogenation of amide

Hydrogenation of cyclohexanecarboxamide to aminomethylcyclohexane was conducted with silica-supported bimetallic catalysts composed of noble metal and group 6–7 elements. The combination of rhodium and molybdenum with molar ratio of 1:1 showed the highest activity. The effect of addition of various metal oxides was investigated on the catalysis of Rh–MoO_x/SiO₂, and the addition of CeO₂ much increased the activity and selectivity. Higher hydrogen pressure and higher reaction temperature in the tested range of 2–8 MPa and 393–433 K, respectively, were favorable in view of both activity and selectivity. The highest yield of aminomethylcyclohexane obtained over Rh–MoO_x/SiO₂ + CeO₂ was 63%. The effect of CeO₂ addition was highest when CeO₂ was not calcined, and CeO₂ calcined at >773 K showed a smaller effect. The use of CeO₂ as a support rather decreased the activity in comparison with Rh–MoO_x/SiO₂. The weakly-basic nature of CeO₂ additive can affect the surface structure of Rh–MoO_x/SiO₂, i.e. reducing the ratio of Mo–OH/Mo–O⁻ sites.     

Reduced graphene oxide supported palladium–silver bimetallic nanoparticles for ethanol electro-oxidation in alkaline media

Palladium–silver bimetallic nanoparticles loaded on reduced graphene oxide (Pd–Ag/RGO) were prepared by co-reduction of mixed metal salts and graphene oxide (GO) with urea-assisted ethylene glycol (EG). The as-obtained Pd–Ag/RGO nanocomposites were characterized by X-ray diffraction, transmission electronic microscopy, and UV–Vis absorption spectroscopy. The results show that the nanoparticles with an average particle size of 5 nm are dispersed on the surface of RGO highly uniformly, besides the Pd–Ag bimetallic nanoparticles are more helpful to promote the reduction of GO than monometal ones. The electrochemical activities of the as-prepared nanocomposites for ethanol oxidation were investigated by using cyclic voltammetry and chronoamperometry in alkaline solution. Compared to the Pd–Ag/E-tek carbon (Pd–Ag/C) and Pd–Ag/multi-walled carbon nanotubes (Pd–Ag/MWCNTs) which were fabricated by the same method, the Pd–Ag/RGO exhibit much higher electrocatalytic activity, stronger tolerance to CO and better stability during the ethanol electro-oxidation reaction in alkaline media. The electrocatalytic performances of Pd–Ag/RGO with different mass ratios of Pd–Ag toward ethanol oxidation in alkaline media were also studied. The results indicate that the electrocatalytic activity of Pd–Ag/RGO with 1:1 mass ratio of Pd–Ag is the best.     

Exploration of photoreduction ability of reduced graphene oxide–cadmium sulphide hetero-nanostructures and their intensified activities against harmful microbes

Journal of Materials Science - Fabrication of effective photocatalyst using semiconductors and graphene or reduced graphene oxide has been regarded as one of the most promising task to attenuate...     

Facile synthesis of FeCo@NC core–shell nanospheres supported on graphene as an efficient bifunctional oxygen electrocatalyst

Electrocatalytic conversion of oxygen holds great potential for clean energy technologies,including water electrolysis,regenerative fuel cells,and rechargeable metal-air batteries.The development of highly efficient and inexpensive oxygen electrocatalysts as replacements for precious metal-based catalysts is vitally important for large-scale practical application in the future.A bifunctional oxygen electrocatalyst based on FeCo nanoparticles/N-doped carbon core-shell spheres supported on N-doped graphene sheets was prepared via one-step pyrolysis of graphitic carbon nitride and acetylacetonates.The optimized product exhibited an oxygen electrode activity of 0.87 V and excellent durability.The remarkable performance is mainly attributed to the synergetic effect arising from the FeCo nanoparticles and N-doped carbon shell.This study introduces an inexpensive and simple way to develop highly active bifunctional oxygen electrocatalysts.     

Synthesis and electrical properties of graphene–manganese oxide hybrid nanostructures

Journal of Materials Science: Materials in Electronics - In the present contribution, grapheme–manganese oxide hybrid nanostructures (G/MnO2) were synthesized via rapid and facile microwave...     

Conducting polymer and reduced graphene oxide Langmuir–Blodgett films: a hybrid nanostructure for high performance electrode applications

In this work, we prepared a reduced graphene oxide (RGO)/poly(3,4-ethylenedioxythiophene) (PEDOT) hybrid composite with well defined nanostructure. The graphene oxide (GO) was first deposited on substrate through the Langmuir–Blodgett (LB) deposition, which provided a tunable and ordered GO arrangement on substrate. Then the GO LB films were reduced to RGO by following thermal treatment, and a ultrathin conducting polymer (CP) PEDOT was directly coated on RGO through a vapor phase polymerization process. The RGO/PEDOT nanocomposite exhibits excellent electrical conductivity about 377.2 S/cm. Electrochemical activity investigation revealed that this nanocomposite exhibits 213 F/g high specific capacitance at a 0.5 A/g current density and shows better capacitance retention rate than pure PEDOT. The detailed study also confirmed that the arrangement of RGO shows distinct influence on the electrical and electrochemical properties of obtained nanocomposite. Large area RGO/PEDOT nanocomposite with high conductivity and electrochemical activity can be deposited on different substrates. Such high conductivity and electrochemical activity RGO/CP nanocomposite shows promising application future in organic and flexible electrode materials for sustainable energy storage.     

One-step synthesis of mesoporous silica–graphene composites by simultaneous hydrothermal coupling and reduction of graphene oxide

Silica–graphene oxide composites were synthesized by hydrothermal method with simultaneous functionalization and reduction of graphene oxide (GO) in the presence of mesoporous silica. Two types of silica were used in the study, mesoporous synthetic silica (MSU-F) synthesized by sol-gel method and mesoporous mineral silica (meso-celite) from pseudomorphic synthesis. The infrared spectra of the composites showed the disappearance of the carboxyl peak at 1735 cm^-1 which could be due to the reduction of the –COOH group. The enhancement of the band at 1385 cm^–1 is attributed to the vibration of the Si–O–C=O moiety formed by reaction of the –COOH group of GO and the silanol (Si–OH) of silica. The Raman spectra of the composites show a diminished intensity ratio of D to G band indicating that GO was reduced to graphene sheets. The TEM images demonstrate the coupling of silica to GO surface revealing dense loading of silica on GO in planar structure.     

Li2O–ZnO–Co3O4–TiO2 composite thin-film electrocatalyst for efficient water oxidation catalysis

Thin films of different Li₂O–ZnO–Co₃O₄–TiO₂ (LZCT) compositions were prepared and employed as electrocatalysts (i.e., anodes) to perform water oxidation reaction (WOR). The electrocatalytic activities of these thin films were compared with those exhibited by the sodium salt of cobalt phosphate (Na₂CoP₂O₇) (CP) thin-film electrocatalyst, which is a well-known water oxidation catalyst (WOC). These results suggest that the 10Li₂O–10ZnO–40Co₃O₄–40TiO₂ composition exhibits a better catalytic activity in terms of higher faradaic efficiency (>98%), lower over potentials (<400?mV), higher reaction stability (up to 30 continuous cyclic voltammetry (CV) cycles), and the rate of O₂ and H₂ gas evolution in terms of current density (about 1?mA/cm²) in comparison with those exhibited by CP thin-film electrocatalyst. Furthermore, these LZCT thin films exhibited very high specific surface area values and due to the unique microstructure of ZnCo₂O₄ phase evolved out of these LZCT compositions at a calcination temperature of 550°C for 30?min it has been found to be responsible for the higher specific surface area values measured for these thin-film compositions.     

Mesoporous titanium dioxide@ zinc oxide–graphene oxide nanocarriers for colon-specific drug delivery

In this project, TiO₂@ZnO nanoparticles core–shell nanostructured and titanium dioxide@ mesoporous zinc oxide–graphene oxide (TiO₂@ZnO–GO) hybrid nanocomposites as controlled targeted drug delivery systems were synthesized by a facile sono-chemical method. We prepared a novel mesoporous and core–shell structure as a drug nanocarrier (NCs) for the loading and pH-responsive characteristics of the chemotherapeutic curcumin. The structure, surface charge, and surface morphology of NCs were studied using with X-ray diffraction, Fourier transform infrared spectroscopy, dynamic light scattering, brunauer–emmett–teller, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The SEM and TEM images of NCs show the uniform hexagonal mesoporous morphology with average grain size of about ～ 190 nm. The drug loading was very high about 16 and 19 for TiO₂@ZnO and TiO₂@ZnO–GO, respectively. The NCs showed pH-dependent drug release behavior. Drug release from TiO₂@ZnO–GO in neutral pH were higher than in acidic medium, due to anionic charge of GO nanosheet. MTT assay results showed that the curcumin-loaded NCs showed significant toxicity due to which cell viability reduced to below 50% at 140 μg/mL concentration, thereby confirming its anticancer effects. The goal of this study is the application of water-dispersed TiO₂@ZnO–GO with pH-dependent release properties for design a new drug delivery carrier.     

Correction to: Exploration of photoreduction ability of reduced graphene oxide–cadmium sulphide heteronanostructures and their intensified activities against harmful microbes

Journal of Materials Science -     

Synthesis and characterization of Co–Fe nanoparticles supported on mesoporous silicas

Co–Fe bimetallic samples containing 25 wt% total of metal content were prepared by incipient wetness impregnation of cobalt nitrate and iron nitrate salts over hexagonal mesoporous silica (HMS) and SBA-15 supports. Changes in the textural properties and reduction behavior were compared with monometallic cobalt/iron-based samples. The samples were characterized by N₂ physisorption, X-ray diffraction (XRD), H₂-temperature programmed reduction (TPR), transmission electron microscopy (TEM) and H₂ chemisorption. The amount of incorporated metal was estimated by atomic absorption spectroscopy (AAS). Morphological properties revealed that after introduction of the metal to the SBA-15 support, the specific area, pore volume and pore diameter decreased to a lesser extent for bimetallic samples. XRD measurements detected the formation of Co₃O₄ and CoFe₂O₄ phases for both bimetallic samples. TPR profiles indicated similar behavior for both the bimetallic and monometallic samples. Higher temperatures were observed for the reducibility of Co–Fe/HMS as compared to Co–Fe/SBA-15. Dispersion values of the bimetallic samples were higher than Fe monometallic samples and lower than Co monometallic samples according to hydrogen chemisorption. The particle size distribution of the bimetallic samples estimated by TEM microphotographs showed a smaller fraction of larger size particles for Co–Fe/SBA-15.     

Synthesis,characterization and comparison of polythiophene–carbon nanocomposite materials as Pt electrocatalyst supports for fuel cell applications

A novel polymer–carbon (PTh–C) nanocomposites containing different percentages of polythiophene (10, 20 and 50% (w/w)) and carbon (Vulcan XC-72) was prepared by a facile solution dispersion method and used to support platinum nanoparticles. The effect of using different percentages of polythiophene in nanocomposites and subsequently prepared electrocatalysts was investigated. The resultant electrocatalysts were extensively characterized by physical (X-ray diffraction (XRD) and transmission electron microscopy (TEM)) and electrochemical (cyclic voltammetry (CV)) techniques. The TEM results showed that the fine Pt nanoparticles prepared by ethylene glycol (EG) method were distributed on the surface of the 50% PTh–C nanocomposites successfully. From the XRD patterns, the average size of dispersed Pt nanoparticles with the face-centered cubic (fcc) structure on 50% PTh–C, 20% PTh–C, 10% PTh–C and carbon were about 4.9, 5.2, 5.4 and 6.1 nm, respectively. The conductivity of PTh–C with different percentages of pure PTh was compared with the conductivity of the corresponding support of pure PTh. It is observed that the conductivity of 50% PTh–C nanocomposites is about 600 times higher than that of pure PTh. Finally, CV measurements of hydrogen and methanol oxidations indicated that Pt/50% PTh–C had a higher electrochemical surface area and higher catalytic activity for methanol oxidation reaction compared to other electrocatalysts. These measurements showed that the Pt/50% PTh–C electrocatalyst by the value of 3.85 had higher \(I_{\mathrm{f}}/I_{\mathrm{b}}\) ratio with respect to Pt/10% PTh–C and Pt/20% PTh–C by the values of 2.66 and 2.0, respectively.     

Composition-tuned oxidation levels of Pt–Re bimetallic nanoparticles for the etherification of allylic alcohols

The catalytic performance of metal nanoparticles is often affected by surface oxidation levels. Instead of post-synthesis oxidation/reduction, we propose an efficient method to modulate the oxidation levels by tuning the composition of bimetallic nanoparticles. Here we report a series of Pt–Re bimetallic nanoparticles synthesized via a facile thermal co-reduction process, with a uniform size of approximately 3 nm. The investigation of the growth of the Pt–Re nanoparticles suggests that the Re atoms were enriched on the surface, as confirmed by X-ray photoelectron spectroscopy. Furthermore, X-ray absorption spectroscopy showed that metallic Re was decreased and high-valency ReO_x species were increased in particles with higher Re/Pt ratios. In the etherification of allylic alcohols catalyzed by Pt–Re nanoparticles of different compositions under ambient conditions, particles with higher Re/Pt ratios exhibited significantly better performances. The highest mass activity of Pt–Re bimetallic nanoparticles (127 μmol·g^?1·s^?1) was more than forty times that of the industrial catalyst CH₃ReO₃ (3 μmol·g^?1·s^?1). The catalytically active sites were associated with ReO_x and could be tuned by adjusting the Pt ratio.

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