Electrospun carbon nanofibers with manganese dioxide nanoparticles for nonenzymatic hydrogen peroxide sensing

Carbon nanofibers (CNFs) decorated by manganese dioxide nanoparticles (MnO₂NPs) are prepared by an electrospinning technique, followed by thermal treatments in different environments. The obtained MnO₂NPs–CNFs composite was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). SEM images showed that the surface of the CNFs was decorated with homogeneously dispersed nanoparticles with narrow size distribution. XRD and XPS characterizations confirmed the main composition of the nanoparticles was MnO₂. Furthermore, for the strong catalytic oxidation ability of MnO₂ toward hydrogen peroxide, the composite material was used as the matrix for nonenzymatic sensor construction. Cyclic voltammetry and amperometric response were applied to investigate the performance of the sensor. Under the optimum conditions, a wide linear range from 10 μM to 15 mM (R = 0.9994, R represents the correlation coefficient) with a low detection limit of 1.1 μM was obtained. The proposed sensor also displayed short response time, high sensitivity, good reproducibility and stability. These superior performances could be attributed to the large surface area and excellent electrocatalytic activity of the MnO₂NPs–CNFs.     

Synthesis of manganese dioxide/reduced graphene oxide composites with excellent electrocatalytic activity toward reduction of oxygen

MnO₂/reduced graphene oxide(RGO) composites were synthesized by a facile and effective polymer-assisted chemical reduction method. The synthetic MnO₂/RGO composites have a uniform surface distribution and large coverage of MnO₂ nanoparticles onto graphene, which were characterized with scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction and cyclic voltammetry. The synthetic MnO₂/RGO composites were studied with respect to its electrocatalytic activity toward the reduction of oxygen in alkaline media and were found to possess a good electrocatalytic activity toward the four-electron reduction of oxygen.     

Structural,electrical, and rheological properties of palladium/silver bimetallic nanoparticles prepared by conventional and ultrasonic-assisted reduction methods

Polyvinylpyrrolidone stabilized Pd/Ag bimetallic nanoparticles (NPs) with average particle sizes of 9 and 6 nm were synthesized by simultaneous reduction in the presence and absence of ultrasound waves, respectively. The prepared NPs were characterized by six methods including X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution-TEM (HRTEM), UV–vis spectroscopy, scanning tunneling microscopy (STM), and energy dispersive X-ray (EDX) analysis. The rheological properties of Pd/Ag NPs in ethylene glycol as a base fluid with various mass fractions of NPs from 2% to 5% at different temperatures were studied experimentally and theoretically. The experimental results showed that viscosity of Pd/Ag NPs in ethylene glycol increases with increasing particle mass fraction and decreases with increasing temperature. A maximum of 31.58% increase in viscosity of ethylene glycol at 20 °C was observed when 5% Pd/Ag NPs was added. Measurement of the electrical conductivity of nanofluids of Pd/Ag bimetallic NPs in distilled water at different mass fractions and temperatures was performed. A 3841% increase in electrical conductivity of distilled water at 25 °C was observed when 1% Pd/Ag NPs was added. Both the rheological and electrical properties of Pd/Ag bimetallic NPs were measured in ethylene glycol and distilled water, respectively for the first time.     

Palladium was supported on superparamagnetic nanoparticles: A magnetically recoverable catalyst for Heck reaction

A novel and high-performance palladium-based catalyst for Heck reaction was prepared easily by the co-precipitation method. The catalyst was characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), vibrating sample magnetometry (VSM), X-ray photoelectron spectroscopy (XPS) and atomic absorption spectrophotometry (AAS). The catalyst afforded a fast conversion of the 4-bromonitrobenzene to 4-nitrostilbene at a catalyst loading of 5 mol%, and the efficiency of the catalyst remains unaltered even after 6 repeated cycles. The excellent catalytic performance of the Pd/Fe₃O₄ catalyst might be attributed to the enhanced synergistic effect between Pd nanoparticles and magnetite.     

Metal nanoparticle templating and electrocatalytic modification using functionalized graphene sheets

Metal and metal-oxide nanoparticles (Ni, Ru, Pt, Fe@Fe₂O₃ NPs) supported on commercial Functionalized Graphene Sheets (FGS) were synthesized using a simple one-pot method in the absence of traditional surfactants or reducing agents from their respective precursor solutions. The supported NPs were characterized by transmission electron microscopy and powder X-ray diffraction techniques and found to be relatively monodisperse in size and metallic in nature. Using X-ray photoelectron spectroscopy, the FGSs were found to contain slight impurities that appear to have their origin in the manufacturing process and are not completely removed through solvent (water or acetone) washing. Electrochemical analysis (rotating disk electrochemistry and CO stripping) of the FGS-Pt NPs was used to compare the metal-support interactions by monitoring the catalytic activity for CO-tolerant H₂ electro-oxidation. The results are compared to related materials in the literature and suggest that the metal-support interactions can be varied to dramatically alter the catalytic activity of the catalyst system.     

Mechanistic aspects of formation of MgO nanoparticles under microwave irradiation and its catalytic application

This work reports a preparation of Mg(OH)₂ and MgO nanoparticles (NPs) using magnesium acetate in benzylamine and mechanistic study of its formation. The benzylamine acts as a solvent, base, promoter and capping agent in this reaction. The structure and morphology of particles were analyzed by X-ray diffraction pattern (XRD), transmission electron microscopy (TEM), high resolution TEM (HRTEM), selected area energy dispersion (SAED), energy-dispersive X-ray spectroscopy (EDAX), thermogravimetric analysis (TGA), FT-IR, CO₂–temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) surface area analysis techniques. The application of as prepared MgO NPs was used in catalysis as a catalyst for the formylation of amines with recyclability studies of nanocatalyst.     

The effect of molybdenum on optical properties of ZnO nanoparticles in Ultraviolet–Visible region

Zn_1?xMo_xO (x = 0.0, 0.01, 0.03, and 0.05) nanoparticles (NPs) are synthesized by using gelatin, via the sol-gel method. A calcination temperature of 600 °C is maintained for 2 h. The influence of molybdenum concentration on the structural and optical properties of these NPs is demonstrated. Synthesized NPs are characterized using X-ray diffraction (XRD), UV–vis spectroscopy, and transmission electron microscopy (TEM). XRD patterns reveal the crystallite nature of samples that exist in the hexagonal wurtzite phase. TEM images manifest the existence of nearly spherically-shaped NPs. The UV–vis spectroscopy results showed that the absorption edge of ZnO nanoparticles is red-shifted by adding molybdenum. Finally, the optical parameters of the refractive index and permittivity of the synthesized samples were calculated using Kramers-Kronig relations using the UV–vis spectra.     

直接热分解法制备单相Pd-Fe合金催化剂及电催化氧还原活性

以醋酸钯和醋酸亚铁为前驱体, 采用直接热分解法制备了碳载Pd₃-Fe₁(Pd₃-Fe₁/C)催化剂。用X射线衍射(XRD)、透射电镜(TEM)和X射线光电子能谱(XPS)等技术对催化剂进行了表征, 用循环伏安法和线性扫描伏安法研究了催化剂对氧的电催化还原性能。结果表明, 制备的Pd₃-Fe₁/C复合催化剂具有单相均一的合金结构, Fe进入Pd晶格改变了Pd电子结构和结构常数。电化学数据表明, Pd₃-Fe₁/C对氧还原比Pd/C催化剂有更高的电催化性能。     

Magnetically recoverable nano Pd/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/ZnO catalyst: preparation,characterization, and application for the synthesis of 2-oxazolines and benzoxazoles

A novel palladium-based catalysts supported on Fe₃O₄/ZnO nanoparticles have been prepared by a simple method. The catalyst was characterized by transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, atomic absorption spectrophotometry, FT-IR, and BET analysis. The catalyst afforded efficient synthesis of 2-oxazolines and benzoxazoles from aromatic nitriles under solvent-free conditions. The significant features of this method are short reaction times, good to high yields of the products, simple operation, solvent-free condition, non-toxicity, reusability of the catalyst without significant loss of catalytic activity, and using ultra small amount of Pd (0.004 g of catalyst contains 9.16 × 10^?3 mmol Pd which was determined by ICP).     

Synthesis of a carbon-coated NiO/MgO core/shell nanocomposite as a Pd electro-catalyst support for ethanol oxidation

Carbon coated on NiO/MgO in a core/shell nanostructure was synthesized by the single-step RAPET (reaction under autogenic pressure at elevated temperatures) technique, and the obtained formation mechanism of the core/shell nanocomposite was presented. The carbon-coated NiO/MgO and its supported Pd catalyst, Pd/(NiO/MgO@C), were characterized by SEM, HR-TEM, XRD and cyclic voltammetry. The X-ray diffraction patterns confirmed the face-centered cubic crystal structure of NiO/MgO. Raman spectroscopy measurements provided structural evidence for the formation of a NiO/MgO composite and the nature of the coated carbon shell. The high-resolution transmission electron microscopy images showed the core and shell morphologies individually. The electrocatalytic properties of the Pd/(NiO/MgO@C) catalyst for ethanol oxidation were investigated in an alkaline solution. The results indicated that the prepared Pd–NiO/MgO@C catalyst has excellent electrocatalytic activity and stability.     

Tailor of ZnO morphology by heterogeneous nucleation in the aqueous solution

The umbrella-like ZnO nanostructures have been prepared by the morphological tailoring in the aqueous solution at 95 °C in the addition of heterogeneous seeds such as MnO₂ and CdS nanoparticles. The morphology and structure of as-synthesized umbrella-like ZnO nanostructures have been characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscope (HRTEM), electron energy loss spectroscopy (EELS), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The heterogeneous seeds play the critical role for the formation of umbrella-like ZnO nanostructures. Furthermore, the formation mechanism of the umbrella-like nanostructures has been phenomenally presented.     

Annealing effect on the structural and optical properties of embedded Au nanoparticles in silicon suboxide films

Au/SiO_x nanocomposite films have been fabricated by co-sputtering Au wires and SiO₂ target using an RF magnetron co-sputtering system before the thermal annealing process at different temperatures. The structural and optical properties of the samples were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), optical transmission, and reflection spectroscopy. XPS analysis confirms that the as-prepared SiO_x films are silicon-rich suboxide films. FESEM images reveal that with an increase in annealing temperature, the embedded Au NPs tend to diffuse toward the surface of the SiO_x films. In IR spectra, the intensity of the Si-O-Si absorption band increases with the annealing temperature. Optical spectra reveal that the position and intensity of the surface plasmon resonance (SPR) peak are dominated by the effect of the inter-particle distance and size of the Au NPs embedded in the SiO_x films, respectively. The SPR absorption peak shows the blue-shift from 672 to 600 nm with an increase in annealing temperature. The growth of silica nanowires (SiO_x NWs) is observed in the film prepared on a c-Si substrate instead of a quartz substrate and annealed at temperatures of 1000 °C.     

Effect of Mn precursors on the morphology and electrocatalytic activity toward water oxidation of micro-nanostructured MnO<Subscript>x</Subscript> films prepared by voltammetric deposition

MnO_x is a promising nonprecious metal-based water oxidation catalyst that is low in cost, abundant, and has low toxicity. The electrocatalytic properties of micro/nanostructured materials depend partially on the material’s morphology type. Here, we describe the morphology-dependent electrocatalytic activities toward water electrooxidation, i.e., the oxygen evolution reaction, of micro-nanostructured MnO_x films prepared by voltammetric deposition. Films were prepared under fixed deposition conditions using one of three water soluble Mn salt precursors: manganese nitrate (Mn(NO₃)), manganese acetate (Mn(CH₃COO)₂), and manganese chloride (MnCl₂). Each of the as-prepared MnO_x films was heated at 400 °C to tune the morphology, oxidation state of Mn and water electrooxidation efficiency. The as-prepared films lost significant amounts of their activity over several voltammetric water oxidation cycles. Heat treatment of the as-prepared films significantly improved the signal and stability of the water electrooxidation reaction. The water oxidation signal at 1.5 V, obtained using 400 °C-heated micro-nanostructured MnO_x films prepared from each of the three precursors, followed the order Mn(NO₃)₂?>?Mn(CH₃COO)₂?>?MnCl₂. The reason of these different activities was due to their different morphologies as the same phase, ɑ-Mn₂O₃, was found in the entire 400 °C-treated MnO_x films. The nanostructured MnO_x film prepared from Mn(NO₃)₂ was heated at different temperatures, and a temperature of 300 °C was found to be optimal for water electrooxidation efficiency. The high resolution transmission electron microscopic image and X-ray photoelectron spectra revealed that the optimal MnO_x was α-Mn₃O₄ phase, which might be a factor along with its special morphology for improving water oxidation reaction.     

Synthesis and shape evolution of novel cuniform-like MnO2 in aqueous solution

In this paper, the cuniform-like MnO₂ particles were first successfully synthesized with dodecylbenzenesulfonic acid (DBSA) as surfactant in aqueous solution. The samples were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and infrared spectroscopy (IR). The possible mechanisms of the shape evolution for the formation of MnO₂ samples were discussed.     

Efficient and green oxidative degradation of methylene blue using Mn-doped ZnO nanoparticles (Zn1−xMnxO)

Mn-doped ZnO nanoparticles, Zn_1?xMn_xO, were synthesised by a polyethylene glycol (PEG) sol–gel method and the physicochemical properties of compounds were characterised by atomic absorption spectroscopy (AAS), energy-dispersive X-ray analysis, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The catalytic degradation of an organic dye, methylene blue (MB), in the presence of Zn_1?xMn_xO as the catalyst and hydrogen peroxide (H₂O₂) as the oxidant at room temperature in water has been studied. Effects of oxidant, catalyst amount, catalyst composition, pH value of the solution and an OH-radical scavenging agent on the degree of the decomposition of MB dye were also studied.     

Palladium nanoparticle-graphene hybrids as active catalysts for the Suzuki reaction

Graphene has been successfully modified with palladium nanoparticles in a facile manner by reducing palladium acetate [Pd(OAc)₂] in the present of sodium dodecyl sulfate (SDS), which is used as both surfactant and the reducing agent. The palladium nanoparticle-graphene hybrids (Pd-graphene hybrids) are characterized by high-resolution transmission electron microscopy, atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and energy dispersive X-ray spectroscopy. We demonstrate that the Pd-graphene hybrids can act as an efficient catalyst for the Suzuki reaction under aqueous and aerobic conditions, with the reaction reaching completion in as little as 5 min. The influence of the preparation conditions on the catalytic activities of the hybrids is also investigated.     

Collagen fiber with surface-grafted polyphenol as a novel support for Pd(0) nanoparticles: Synthesis,characterization and catalytic application

The aim of this study is to use collagen fiber (CF) as a natural polymeric support to synthesize a novel palladium (Pd) nanoparticle catalyst. To achieve a stable immobilization of Pd on CF support, epigallocatechin-3-gallate (EGCG), a typical plant polyphenol, was grafted onto CF surface, acting both as dispersing and stabilizing agent for Pd nanoparticles. Scanning electron microscopy showed that this catalyst was in ordered fibrous state with high flexibility. The presence of EGCG grafted on CF and the interaction mechanism of Pd ions with support was investigated by X-ray photoelectron spectroscopy. X-ray diffraction and transmission electron microscopy offered evidence that the well-dispersed Pd nanoparticles were generated on the outer surface of CF. By using the hydrogenation of allyl alcohol as a model reaction, the synthesized catalyst presented remarkably improved activity, selectivity and reusability as compared with the Pd catalyst supported by CF without grafting of EGCG.     

Templated synthesis of polyaniline nanotubes with Pd nanoparticles attached onto their inner walls and its catalytic activity on the reduction of p-nitroanilinum

In this paper, polyaniline (PANI) nanotubes with palladium nanoparticles (NPs) attached onto their inner walls were synthesized via a templating method which contains three steps. First, electrospun polystyrene (PS) nanofibers were coated with nearly monodispersed Pd NPs (d = 3.411 nm, σ = 0.687 nm, d is the average diameter of Pd NPs and σ is the standard deviation of their diameters) through in situ reduction of Pd²⁺ ions on the surface of sulfonated PS nanofibers. Then we used a self-assembly method to coat the composite with a PANI layer. The final product was obtained after the removal of PS nanofibers by diluting them in tetrahydrofuran. The morphology of samples was analyzed by scanning electron microscopy and transmission electron microscopy and the structure was characterized by Fourier transform infrared, ultraviolet–visible spectra, X-ray diffraction patterns and X-ray photoelectron spectroscopic patterns. Inductively coupled plasma atomic spectra were used to show the weight percentage of Pd nanoparticles. Its catalytic activity on the reduction of p-nitroanilinum was also investigated and compared to Pd/C catalyst and Pd/MWNTs.     

Microwave-assisted green synthesis of MnO2 nanoplates with environmental catalytic activity

In this paper, MnO₂ nanoplates were synthesized in aqueous solution under the microwave irradiation, without using any templates, catalysts, and organic reagents. The as-prepared MnO₂ nanoplates were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC) and thermo-gravimetric (TG) analysis, and nitrogen sorption measurements. Microwave irradiation could produce MnO₂ with uniform size and well-defined shape as well as high crystallinity. On the basis of experimental results, a possible formation mechanism of MnO₂ nanoplates was proposed. Furthermore, the resulting MnO₂ nanoplates were found to exhibit remarkable environmental catalytic performance in degradation of Rhodamine B (RhB) in aqueous solution, indicating these MnO₂ nanoplates is very promising for wastewater treatment.     

Effects of Nd concentration on structural and magnetic properties of ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Zinc ferrite nanomaterials have been received significant attention in recent years on account of their potential applications in the fields of electronics, optoelectronics and magnetics. To enhance the magnetic properties of zinc ferrites, Nd-doped zinc ferrites (ZnFe_2?xNd_xO₄, x?=?0, 0.01, 0.02, 0.03) nanoparticles (NPs) have been prepared by the sol–gel method. The effects of Nd doping concentration on the structural and magnetic properties of zinc ferrites were studied. The results of X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy indicated that the Nd ions were incorporated into the crystal lattice of ZnFe₂O₄ and substituted for the Fe³⁺ sites. Unlike pure zinc ferrites with paramagnetism, Nd doped ZnFe₂O₄ NPs were superparamagnetic at room temperature. Vibrating sample magnetometry results showed, with the increase of Nd content, the saturation magnetization of Nd doped ZnFe₂O₄ NPs increased.