Solution Reduction Process Research Articles

Control of Ir oxidation states to overcome the trade-off between activity and stability for the oxygen evolution reaction

To improve the efficiency of polymer electrolyte membrane water electrolyzers (PEMWEs), catalysts with high activity and stability in the oxygen evolution reaction (OER) have been extensively investigated. In this study, using a novel solution-reduction process, self-assembled Ir/IrOx OER catalysts are prepared, with a controlled Ir oxidation-state ratios. Spectroscopic and electron microscopic analyses confirm that these catalysts have a gradient oxidation state, which gradually decreases from the shell to the core. In half-cell tests, before and after the accelerated stress test (AST) at 10 mA cm−2, the optimized Ir/IrOx catalyst exhibits an overpotential change of approximately 21 mVRHE, which is 3.3 times lesser than that of the state-of-the-art IrO2 (approximately 69 mVRHE). Further, quantification of the dissolved Ir content during the AST shows that the Ir/IrOx catalyst has a strong corrosion resistance under acidic OER conditions. Single-cell testing of the as-prepared OER catalyst demonstrates a remarkable cell performance of 1.73 V at 1.0 A cm−2. After 48-h durability testing, the increase in the membrane electrode assembly cell voltage with the as-prepared OER catalyst is approximately 5.3 times lesser than that of the reference at 250 mA cm−2. The proposed novel catalyst with high activity and stability can aid the development of cost-effective PEMWE systems.

Au nanoparticle-functionalized 3D SnO2 microstructures for high performance gas sensor

Three-dimensional (3D) nanostructures of metal oxides have been widely used for gas sensor devices. In this work, 3D porous SnO2 microstructures constructed by two-dimensional (2D) nanosheets were prepared via a simple hydrothermal process combined with subsequent annealing. Gold (Au) nanoparticles were successfully immobilized onto the surface of SnO2 nanosheets to serve as a sensitizer by a facile solution reduction process. This novel 3D Au/SnO2 microstructure has been investigated for gas senor and exhibits remarkably enhanced sensing performances to ethanol, e.g. high response, fast recovery time and good stability. The possible sensing mechanism is also discussed in terms of the special effect of Au functionalization.

One-step construction of N/Ti3+ codoped TiO2 nanotubes photoelectrode with high photoelectrochemical and photoelectrocatalytic performance

In this study, we reported a facile strategy to fabricate N, Ti3+ codoped TiO2 nanotubes (N-Ti3+/TiO2 NTs) photoelectrode through one-step solution reduction process. The hydrazine hydrate treatment induced the simultaneous formation of Ti3+ species and N-doping in the lattice of TiO2 NTs. In addition, the N-Ti3+/TiO2 NTs photoelectrode exhibited intense visible light absorption ranging from 400 to 800nm, high transient photoinduced current of 0.213mAcm−2, charge carriers concentration of 0.92×1019cm−3, generation of hydroxyl radicals and PEC efficiency of 100% for the degradation of diclofenac solution within 4h visible light irradiation. The enhanced-visible-light PEC performance was mainly attributed to the enhancement of visible light absorbance, narrow band gap energy and high separation efficiency of photoinduced charge carriers. This study provides a facile strategy to construct intense visible light active catalyst, which could be applied in the fields of wastewater/air purification, solar energy conversion and water splitting.

High-performance gas sensor based on ZnO nanowires functionalized by Au nanoparticles

One-dimensional (1D) semiconductor nanostructure has been widely used for gas sensor devices. In this work, a high performance gas sensor based on Au-functionalized ZnO nanorods was fabricated. Au nanoparticles were successfully immobilized onto the surface of ZnO nanorods to serve as a sensitizer by a facile solution reduction process. The hybrid Au/ZnO nanorods have been systematically characterized by XRD, SEM, EDS, TEM and optical absorption spectrum. Gas sensing tests reveal that the Au/ZnO sensor has remarkably enhanced performance compared to pure ZnO. It could detect ethanol gas in a wide concentration range with very high response, fast response–recovery time, good selectivity and stable repeatability. The possible sensing mechanism is discussed. The superior sensing features indicate the present Au/ZnO nanorods are promising for gas sensors.

One-Pot Green Synthesis of Ni Nanoparticles and Study of Its Catalytic Activity in the Hydrothermal Reduction of p-Nitrophenol

One-pot synthesis of Ni nanoparticles was carried by solution reduction process successfully in aqueous media by using hydrazine hydrate as a reducing agent. Greener stabilizing agent starch is used as a stabilizer, which also acts as a particle protector toward oxidation. The morphologies of the synthesized Ni nanoparticles were characterized by TEM and XRD. The prepared Ni nanoparticles were used as a catalyst in the reduction of p-nitrophenol to p-aminophenol under hydrothermal condition in the presence of sodium borohydrate as a source of hydrogen. The conversion was excellent (97%), as confirmed by LCMS. This also confirmed by the UV-visible spectrum study of the reaction mixture. The Ni nanoparticles were recycled at least five times without much loss in the catalytic activity.

Spectral, thermal and morphological studies of chromium nanoparticles

Cr(0) nanoparticles were synthesized by solution reduction process successfully. The influence of parameters on the size of Cr(0) nanoparticles was studied and the referential process parameters were obtained. The morphology and structure of the synthesized Cr(0) nanoparticles were characterized by Transmission Electron Microscopy (TEM), Powder X-ray Diffraction (XRD), Thermal Gravimetric Analysis (TGA), QELS Data and Infrared Spectroscopy (IR). The results show that Cr(0) nanoparticles are of high purity. XRD analysis revealed all relevant Bragg’s reflection for crystal structure of Cr metal. XRD spectrum also indicates that there is no oxidation of Cr(0) nanoparticles to chromium oxide. TEM showed nearly uniform distribution of particles in methanol which was confirmed by QELS. Cr(0) nanoparticles can be synthesized easily by reducing agent and are quite stable too.

Synthesis of Al nanoparticles: Transmission electron microscopy, thermal and spectral studies

Nanoparticles of Al(0) were synthesized by solution reduction process successfully. The influence of parameters on the size of Al(0) nanoparticles were studied and the referential process parameters were obtained. The morphology and structure of the synthesized Al(0) nanoparticles were characterized by Transmission Electron Microscopy (TEM), Powder X-ray Diffraction (XRD), Thermal Gravimetric Analysis (TGA), QELS Data and Infrared Spectroscopy (IR). The results show that nanoparticles of Al(0) are of high purity. XRD analysis revealed all relevant Bragg's reflection for crystal structure of Al metal. XRD spectrum also indicates there is no oxidation of Al(0) nanoparticles to aluminum oxide. TEM showed nearly uniform distribution of the particles in methanol and it was confirmed by QELS. Al(0) nanoparticles can be synthesized easily by reducing agent and are quite stable too.

Controllable synthesis of monodisperse polyhedral nickelnanocrystals

Monodisperse polyhedral nickel nanoparticles composed of small nanocrystals have been successfully synthesized by a facile poly(N-vinyl-2-pyrrolidone) (PVP) mediated solution reduction process with hydrazine hydrate as the reducing agent. The phase structure, morphology and magnetic properties of the as-prepared products were extensively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). XRD pattern indicated that the as-synthesized products were nickel with well-crystallized face-centered cubic structure. SEM and TEM observations showed that the polyhedral nanoparticles consist of nanocrystals with size around 2 nm. The formation of these polyhedral nanoparticles is attributed to the oriented aggregation of nickel nanocrystals around a polymer-Ni2+ complex framework structure. The magnetic property investigation shows that the polyhedral nickel nanoparticles exhibit a ferromagnetic behavior and possess a higher coercive field value than that of the bulk nickel.

Synthesis of Ni nanoparticles and their characterizations

Ni nanoparticles were synthesized by solution reduction process successfully. The influence of parameters on the size of Ni nanoparticles was studied and the referential process parameters were obtained. The morphology and structure of the synthesized Ni nanoparticles were characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), QELS data and infrared spectroscopy (IR). The result shows that Ni nanoparticles are of high purity and the average size of Ni nanoparticles was found to be 13±2nm.

Comparative study on nanostructured MnO 2/carbon composites synthesized by spontaneous reduction for supercapacitor application

MnO 2 has been deposited onto two types of carbon (C) substrates, including a non-porous multi-wall carbon nano-tube (CNT) and a porous carbon black (CB) powder, by a solution reduction process where MnO 4 − was reduced at 80 °C by the C substrate so as to give nano-crystalline MnO 2 directly at the C surface. The nature of the C substrate has profound effects on polymorphicity, microstructure and electrochemical properties, in terms of supercapacitor application, of the resulting oxide. Deposition on CNT produces meso/macro-porous layer containing predominantly spinel MnO 2 strongly bonded to the CNTs and having a larger surface area, while that on CB results in birnessite granules with a lower surface area. In addition to having a higher specific capacitance (309 F g −1), the MnO 2/CNT electrode exhibits superior power performance (221 F g −1 at 500 mV s −1 or ca. 20 Wh kg −1at 88 kW kg −1) to MnO 2/CB due to reduced electronic and ion-diffusion resistances. Furthermore, the MnO 2/CNT electrode also exhibits slower self-discharging rate and greater cycling stability. The results indicate that the MnO 2 spinel/CNT holds promise for supercapacitor applications.

Synthesis and characterization of copper nanoparticles by reducing agent

Cu nanoparticles were synthesized by solution reduction process successfully. The influence of parameters on the size of Cu nanoparticles was studied and the referential process parameters were obtained. The morphology and structure of the synthesized Cu nanoparticles were characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), QELS data, infrared spectroscopy (IR) and solid state UV. The average size of nanoparticles was found between 15 ± 2 nm.

Nanoscale synthesis and optical features of metallic nickel nanoparticles by wet chemical approaches

Nickel nanoparticles (Ni-NPs) were successfully synthesized and attached on indium tin oxide (ITO) substrate by two different methods: from solution reduction process by using sodium borohydride (NaBH 4) as reducing agent in the presence of poly( N-vinilpyrrolidone) (PVP) as protective and stabilizing agents and by polyol process under ethylene glycol EG as a solvent. The results indicated that the samples prepared in aqueous solution show the occurrence of face-centered cubic metallic nickel nanoparticles with a medium diameter of ∼31 nm and good size dispersion compared to the preparation in EG that revealed large size ∼150 nm. The dynamics of the nanoparticle's growth in the solvents and comparison with optical absorption is presented.

Magnetophoresis behaviour at low gradient magnetic field and size control of nickel single core nanobeads

Magnetic separation of organic compounds, proteins, nucleic acids and other biomolecules, and cells from complex reaction mixtures is becoming the most suitable solution for large production in bioindustrial purification and extraction processes. Optimal magnetic properties can be achieved by the use of metals. However, they are extremely sensitive to oxidation and degradation under atmospheric conditions. In this work Ni nanoparticles are synthesised by conventional solution reduction process with the addition of a non-ionic surfactant as a surface agent. The nanoparticles were surfacted in citric acid and then coated with silica to form single core Ni nanobeads. A magnetophoresis study at different magnetic field gradients and at the different steps of synthesis route was performed using Horizontal Low Gradient Magnetic Field (HLGMF) systems. The reversible aggregation times are reduced to a few seconds, allowing a very fast separation process.

Facile synthesis and characterization of Co nanoplatelets with tunable dimensions via solution reduction process

Plate-like Co nanoparticles with different sizes were synthesized by solution reduction process. The size of Co nanoplatelets can be tuned by varying the concentration of CoCl2·6H2O and the dosage of N2H4·2H2O. The Co nanoplatelets with the different size all exist in both fcc and hcp crystal structures. The normal direction of the nanoplatelets is perpendicular to the (002) planes of hcp phase or to the (111) planes of fcc phase. The saturation magnetizations of the samples are lower than the corresponding bulk value. The coercivities of the samples vary with the phase content and the particle size. The shape control mechanism was discussed.

Large scale synthesis and characterization of Ni nanoparticles by solution reduction method

Ni nanoparticles were mass synthesized by solution reduction process successfully. The influence of the parameters on the particle size of Ni nanoparticles were studied and the referential process parameters were obtained. The morphology and structure of the synthesized Ni nanoparticles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis and infrared spectroscopy (IR). The results show that Ni nanoparticles are of high purity and are covered by hydroxyethyl carboxymethyl cellulose (HECMC) layer and the mean size being about 31 nm. The magnetic measurement revealed that Ni nanoparticles are ferromagnetic.

Size-controlled synthesis, microstructure and magnetic properties of Ni nanoparticles

Ni nanoparticles with different mean diameters of 15–83 nm were synthesized by solution reduction process. The size of Ni nanoparticles can be controlled by varying the concentration of NiCl 2·6H 2O and synthesis temperature. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). Results show that the synthesized particles are single-phased Ni with a face-centered cubic crystal structure. Magnetic measurements indicate that Ni nanoparticles are ferromagnetic. The lattice constants and coercivities of the samples are size-dependent.

Preparation of ZnSe films through chemical solution reduction process

In a novel wet process, zinc selenide films were prepared on Teflon and polycrystalline α-Al 2O 3 substrates using zinc chloride, selenium, and aluminum foil as source materials. This method is simple and can be fulfilled easily. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectrum (XPS).