Synthesis of sulfur-doped carbon nanotubes from sulfur powder using chemical vapor deposition

Sulfur-doped carbon nanotubes (SCNT) with high sulfur contents have been prepared using chemical vapor deposition (CVD) from sulfur powder, acetylene gas and Fe/CaCO₃ (as catalyst). In this regard, various growth's temperatures were examined to investigate its effects on the structure and the sulfur content of prepared SCNT. The best condition was obtained at 700°C and using 4 g of sulfur powder. The product was characterized using FE-SEM and EDS, which showed rode-like SCNT with about 40 nm diameter and 10.75% sulfur content. Moreover, TEM, Raman and XPS analyses were employed to obtain more details related to the product. The XPS results confirmed the presence of sulfur atoms, which covalently incorporated in the carbon framework. Finally, the catalytic ability of the product in oxygen evolution reaction was examined and the results showed high stability and low oxygen production rate for this product.     

Processing of heat-treated silicon carbide-reinforced aluminum alloy composites

The present study investigates the processing of heat-treated silicon carbide (SiC) particle-reinforced 6061 aluminum alloy (AA) composites. As-received SiC powders were heat treated at 1300ºC, 1400ºC, and 1500ºC in nitrogen atmosphere for 2 h, and the 6061 AA–SiC composites were developed by spark plasma sintering at 560ºC and 60 MPa for 5 min in argon atmosphere. The amorphous silicon nitride is found to form in SiC particles as a result of heating at 1400ºC. The microstructure of the composites exhibited uniform distribution of SiC or SiC/Si₃N₄ particles in 6061 AA matrix. Further, the heat-treated SiC-reinforced 6061AA composites exhibited improved mechanical properties. A typical combination of UTS of 240 MPa and elongation of 21% is obtained for the 6061 AA composites prepared using SiC powders heated at 1400ºC.     

Enhanced hydrothermal stability of ZSM-5 formed from nanocrystalline seeds for naphtha catalytic cracking

We successfully synthesized hydrothermally stable ZSM-5 with crystalline nano seeds. We employed a template-free method using ZSM-5 crystalline nano seeds and sodium silicate as a silica source. The prepared ZSM-5 exhibited uniform crystal size and relative crystallinity greater than 100 %. The size of the crystalline nano seed in the scale of 100 nm was found to be the optimum size for obtaining uniform, highly crystalline ZSM-5 with structural stability. After P-modification, the synthesized ZSM-5 with the optimally sized seed showed high hydrothermal stability and improved catalytic naphtha cracking activity compared to a commercial ZSM-5 catalyst. In order to find the elements for the increased hydrothermal stability, the samples were evaluated by studying crystallinity, aluminum spectrum, and acidity using XRD, solid-state NMR, and NH₃-TPD, respectively after steaming at 800 °C for 24 h. It is speculated that the increased hydrothermal stability of the ZSM-5 resulted mainly from the increased aluminum structural stability.     

Grafted NiO on natural olivine for dry reforming of methane

Natural olivine is used for gasification of biomass in a fluidised bed. Characterisations by X-raydiffraction and electron microscopies (SEM and TEM) have proved the presence of a (Mg,Fe)₂SiO₄ structure (Mg/Fe ratio: 9/1) with a rather broad distribution in elemental composition. Temperature programmed reduction has revealed equally the presence of iron oxides outside of this structure. The nature of free iron oxides can be both modified by increasing the temperature of calcination and confirmed by measurements of magnetism.

The introduction of nickel oxide upon natural olivine is obtained by impregnation with a nitrate salt. The type of interaction of nickel oxide with olivine is different depending upon the preparationmethod and the calcination temperature. For calcination at 1100 ºC, the effects of the amount ofNiO and the number of impregnation have been studied. At a high temperature of calcination (1400 ºC), NiO is integrated into the olivine structure and the amount of free iron increases. Integrated NiO on olivine is non-reducible, resulting in an inactive catalyst. At lower calcination temperatures grafted NiO is formed, a species which is reduced under catalytic test conditions without aggregation of particles. A single impregnation of nickel (5.5 wt% of NiO) gives a stable catalyst activated directly under reaction conditions (CH₄ + CO₂) yielding 96% CO and 76% H₂. Catalysts with lower amounts of NiO or a double impregnation of nickel salt lead to a less stable system.

Analysis reveals that no change in olivine structure nor size of nickel deposit occurs under test conditions. Equally there are no carbon deposits formed on these catalysts. A model of the evolution of each catalytic system arising from the different preparation methods is proposed. The observed deactivation of such catalysts is attributed to the increase in the amount of free iron, which favours the oxidative properties of the catalytic system.     

Preparation of 6N high-purity indium by method of physical-chemical purification and electrorefining

The increasing demands for indium in recent years require high purity indium as raw materials. Physical-chemical purification and electrorefining have been performed to obtain 6N high purity indium. Indium is smelted by using NaOH, NaCl and NaNO₃ for 20 min at 400°C, the removing rate of Sn, Zn, Al reaches 40, 60 and 37% respectively. The removing rate of Cd is 90–95% and that of Tl reaches 40–60% when indium is smelted for 10 min by 20% glycerin solution of KI and I₂ at 180°C. When indium metal is vacuum refined in two stages: 800–900°C for 2 h and 950–1050°C for 2 h, the major impurity elements, Pb, Zn, and Bi, are effectively removed. When indium is electrolytic refined in In₂(SO₄)₃-H₂SO₄ system, in which indium content is 60–80 g/L, pH 2.0–3.0, current density 50–80 A/m², the content of impurities can be dropped and the product of indium reaches 99.9999%.     

Effect of solvents on the structural, optical and morphological properties of Zn0.96Cu0.04O nanoparticles

Zn_0.96Cu_0.04O nanoparticles were synthesized by co-precipitation method using different solvents like ethanol, water and mixer of ethanol and water in 50:50 ratios. Crystalline phases and optical studies of the nanoparticles were studied by X-ray diffraction (XRD) and UV–visible photo-spectrometer. The XRD showed that the prepared nanoparticles have different microstructure without changing a hexagonal wurtzite structure. The calculated average crystalline size was high for ethanol (27.3 nm) due to the presence of more defects and low for water (26 nm) due to the reduction of defects and vacancies. The energy dispersive X-ray analyses confirmed the presence of Cu in ZnO system and the weight percentage is nearly equal to their nominal stoichiometry within the experimental error. The presence of lower Zn and Cu percentage in the sample prepared using ethanol than other solvents was due low reaction rate which was confirmed by XRD spectra. Water solvent has relatively stronger transmittance in the visible region which leads to the industrial applications especially in opto-electronic devices. The average crystalline size is slowly decreased from 27.3 nm (ethanol) to 26 nm (water) whereas energy gap is steadily increased from 3.56 eV (ethanol) to 3.655 eV (water) when water concentration is increased from 0 to 100 % in ethanol. Existence of functional groups and bonding were analyzed by FTIR spectra. The observed blue shift of UV emission from ethanol (349 nm) to water (340 nm) solution and the high I_UV/I_G ratio in water solution in photoluminescence spectra was due to the decrease of crystalline size and defects/secondary phases. The intensity of blue–green band emission was gradually decreased due to the reduction of defects and vacancies when water concentration is increased from 0 to 100 % in ethanol solution, which was consistent with the XRD observation.     

Preparation and characterization of carbon nano-onions by nanodiamond annealing and functionalization by radio-frequency Ar/O2 plasma

Carbon nanomaterials can be prepared by several methods having in common that need a carbon source and often require high energies. In this study, we report the synthesis and characterization of carbon nano-onions by annealing of commercially available nanodiamonds and explore for the first time their functionalization with a radio frequency Ar/O₂ plasma. Heat treatment of nanodiamonds at 1200°C for 6 hours under argon atmosphere afforded small spherical carbon nano-onion particles of 3–4 nm diameter and 5–6 graphitic shells. The prepared CNOs were visualized by HRTEM and showed the characteristic XRD and Raman features. The results have been compared with a sample prepared by annealing at 1600°C. Plasma functionalization in Ar/O₂ atmosphere was used to introduce oxygen moieties into the surface of synthesized CNOs. X-ray photoemission spectroscopy showed that oxygen-containing groups like C─O, C═O and O─C═O were introduced on the surface of CNOs, a process that is accompanied by a surface reorganization as evidenced by the change of I_D/I_G ratios in the Raman spectra, indicating a conversion of sp² to sp³ as a result of functionalization in the surface of CNO.     

High oxygen ion conduction in some Bi2O3-Y2O3 (Er2O3) solid solutions

Highly densified bodies (~ 98 % theoretical density) of the Bi₂O₃-Y₂O₃(Er₂O₃) systems containing 30 moles % Y₂O₃ and 20 moles % Er₂O₃ respectively were prepared from both mixed oxides and coprecipitated oxalates. DC ionic conductivity and impedance complex plane analysis on sintered samples were performed. Under oxygen partial pressure ranging from 1 to 10 Pa was found that, samples containing 30 moles % yttria showed a pure ionic conductivity up to an oxygen partial pressure of 10⁻²⁰ Pa. Samples containing 20 moles % erbia, extended its ionic conductivity up to an oxygen partial pressure of 10⁻²² Pa. The impedance analysis shows the presence of only one semicircle at low tempertures and it is attributed to bulk conductivity contribution. The conductivity was higher for the Bi₂O₃-Er₂O₃ sintered solid electrolytes, in such a case, a conductivity as high as 1.38 ohm cm at 700ºC was obtained. The activation enthalpy for the conduction process was calculated in the temperature range from 200º to 700ºC in all the cases. Microstructural development in the sintered sample was also studied.     

Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods with secondary plate-like nanostructures; preparation,characterization and application as high performance electrode material in supercapacitors

Mn₃O₄ nanorods with secondary plate-like structures were prepared through precipitation from a 0.005 M manganese chloride bath, under the applying direct current mode (i = 2 mA cm^?2). The structural analysis through XRD and FTIR confirmed that the deposited nanopowder has pure monoclinic phase of Mn₃O₄. Further morphological assessment through SEM proved the product to have the Mn₃O₄ nanorods in large quantity, which constructed the secondary plate-like building blocks. Cyclic voltammetric and charge–discharge experiments on the product indicated the prepared Mn₃O₄ to possess high specific capacitance (SC) values of 298 F g^?1, as well as an outstandingly durable cycling stability (95.1 % of initial capacity after discharging 1000 cycles).     

A facile fabrication of nanoflower-like Co<Subscript>3</Subscript>O<Subscript>4</Subscript> catalysts derived from ZIF-67 and their catalytic performance for CO oxidation

Herein, we reported a facile method for fabricating nanoflower-like Co₃O₄ catalysts via calcination treatment based on ZIF-67. The catalytic performances of the obtained Co₃O₄ catalysts were evaluated for the model reaction of CO oxidation. The results demonstrated that calcination temperature had a strong effect on the structure and catalytic reaction activity of Co₃O₄ catalyst. Co₃O₄ catalyst prepared at 400 °C (Co₃O₄-400) exhibited the optimum catalytic activity with a complete CO conversion temperature of 105 °C. This phenomenon was ascribed to the higher specific surface areas, smaller particle size, unique structure, good low-temperature reduction and higher abundances of surface Co²⁺ and adsorbed oxygen species. The addition of 1.0% water vapor had a negative effect on CO oxidation and the prepared Co₃O₄-400 catalyst presented long-term stability.     

Copper oxide coated polyester fabrics with enhanced catalytic properties towards the reduction of 4-nitrophenol

A novel functional polyester fabric (PF) was successfully prepared by a facile method. PF were coated by copper oxide (CuO) followed by chemical grafting of 3-chloropropyltriethoxysilane (ClPTES) and diethanolamine (DEA). The morphology and structure of the resulting material PF@CuO–Si–N(OH)₂ was characterized by X-ray diffraction, scanning electron and optical microscopy, thermogravimetry and Fourier-transformed infrared spectroscopy. The results revealed that the CuO particles were densely surrounded PF, and the covalent surface-grafting of ClPTES and DEA within PF was confirmed. It was also demonstrated that CuO/ClPTES/DEA addition generated new functional sites at the PF surface, improving the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The prepared PF@CuO–Si–N(OH)₂ exhibited high catalytic activity with appreciable cycling stability for the reduction of 4-NP to 4-AP, even after six successive cycles with nearly 90% conversion. Hence, it may be conclude that the catalytic activity and stability of this catalyst allows envisaging great prospect for large scale reduction of 4-NP.     

High mobility polymer gated organic field effect transistor using zinc phthalocyanine

Organic thin film transistors were fabricated using evaporated zinc phthalocyanine as the active layer. Parylene film prepared by chemical vapour deposition was used as the organic gate insulator. The annealing of the samples was performed at 120 °C for 3 h. At room temperature, these transistors exhibit p-type conductivity with field-effect mobilities ranging from 0·025–0·037 cm²/Vs and a (I _on/I _off) ratio of ～10³. The effect of annealing on transistor characteristics is discussed.     

Properties of (Bi2Sb5Se3Te6I3)1 ? xMx (M = Ce, Pr) solid solutions

The effect of doping with Ce and Pr on the physicochemical properties of Bi₂Sb₅Se₃Te₆I₃ has been studied using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements. The results demonstrate that n-type Bi₂Sb₅Se₃Te₆I₃ dissolves 3.5 at % Ce. The Bi₂Sb₅Se₃Te₆I₃-Ce system has a eutectic at 10 mol % Ce, which melts at 360°C. The Pr solubility in Bi₂Sb₅Se₃Te₆I₃ is 4 at %. This system has a peritectic point at 10 at % Pr, with a peritectic temperature of 550°C.     

Enhanced performance of 4,4′-bipyridine-doped PVDF/KI/I<Subscript>2</Subscript> based solid state polymer electrolyte for dye-sensitized solar cell applications

Pure (PVDF/KI/I₂) and 4,4′-bipyridine-doped PVDF/KI/I₂ solid state polymer electrolytes were prepared by solution casting method using N,N-dimethylformamide (DMF) as solvent. The solid state polymer electrolytes were characterized by the powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR), AC-impedance, dielectric measurements and scanning electron microscopy (SEM) analysis. The crystallinity of the solid state polymer electrolytes was analyzed by PXRD measurement. The functional groups of the solid state polymer electrolytes were confirmed by FTIR analysis. The AC-impedance analysis was carried out to calculate the ionic conductivity of the solid state polymer electrolytes. The ionic conductivity value of pure (PVDF/KI/I₂) and 4,4′-bipyridine-doped PVDF/KI/I₂ solid state polymer electrolytes are 2.00?×?10^?6 S cm^?1 and 4.60?×?10^?5 S cm^?1, respectively. The dielectric properties of solid state polymer electrolytes were calculated by using the dielectric measurements. From the SEM analysis, the surface morphology of the solid state polymer electrolytes was analyzed. The power conversion efficiencies of pure (PVDF/KI/I₂) and 4,4′-bipyridine-doped PVDF/KI/I₂ solid state polymer electrolytes are 1.8% and 4.4%, respectively. 4,4′-bipyridine-doped PVDF/KI/I₂ solid state polymer electrolyte has higher power conversion efficiency due to its increased amorphous nature and ionic mobility.     

Preparation and characterization of molybdenum disulphide catalysts

Molybdenum disulphide has been prepared by atmospheric-pressure hydrogen reduction of molybdenum trisulphide in the temperature range 400–750 °C for 4 h and characterized. Chemical analysis of the product confirmed the S to Mo ratio 2.00 as desired for MoS₂, consistent with its thermogravimetric analysis data in an air atmosphere. MoS₂ prepared under these reducing conditions possessed a hexagonal structure with n-type diamagnetic semiconducting behaviour and a lower surface area. The catalytic activity of the MoS₂ was studied for liquid-phase hydrogenation of nitrobenzene. X-ray studies on MoS₃ when reduced at 750 °C for 48 h indicated that MoS₂ so formed is unstable, resulting in the formation of its over-reduced products Mo₂S₃ and Mo.     

The Effect of Precipitants on MnOx-Ni/TiO2 SCR Catalysts Prepared by Titanium Slag as Raw Material

Mn-Ni/TiO₂ catalysts were prepared using a joint precipitation method with acid-dissolved titanium slag as raw material for selective catalytic reduction of nitrogen oxide. The joint precipitation method was accomplished with different precipitants, such as sodium hydroxide, carbamide, ammonia, or hydrogen peroxide. The deNOx activities of the catalysts prepared by different precipitants were investigated with SCR activity reactor within temperatures of 90–350°C. It is evident that the Mn-Ni/TiO₂ catalyst with carbamide-ammonia-hydrogen peroxide as precipitant has superior catalytic activity, which the NO conversion can reach 90% at 120°C, with a wider temperature window (120–300°C) for the NH₃-SCR reaction. H₂-TPR results showed that the reduction potential of MnOx species on Mn-Ni/TiO₂ catalysts is increased compared to that of Mn/TiO₂ catalysts. Oxygen mobility is enhanced by interaction between Ni and Mn atoms due to use of carbamide-ammonia peroxide as precipitant. XPS results suggest that the presence of MnO₂ is the major phase in nickel-doped Mn/TiO₂ catalysts. Our NH₃-TPD results illustrated that the catalysts have a lot of acid-active sites, which lead to attracting more ammonia to participate in the catalytic reaction.     

Electrodeposition of platinum nanoparticles on polypyrrole-functionalized graphene

In this study, the new electrocatalyst of platinum support on polypyrrole-functionalized graphene (GNS–PPy/PtNPs) is reported. The polypyrrole-functionalized graphene (GNS–PPy) is constructed first with graphene nanosheets (GNS) and polypyrrole (PPy) particles by constant potential deposition. And then PtNPs are deposited on the surface of GNS–PPy by cyclic voltammetry. The as-prepared GNS–PPy/PtNPs is characterized by scanning electron microscopy, energy-dispersive spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The prepared GNS–PPy/PtNPs catalyst is employed for methanol oxidation reactions. Compared with GNS/PtNPs and PPy/PtNPs, the GNS–PPy/PtNPs has higher catalytic activity (508 mA/mg), better stability, and stronger poisoning-tolerance (I _f/I _b = 4.18) due to high dispersion of PtNPs on large surface of GNS–PPy as well as synergic effect among the GNS, PPy particles, and PtNPs. The experimental results indicate that GNS–PPy/PtNPs may be an ideal candidate catalyst for direct methanol fuel cell.     

Highly efficient metal–organic-framework catalysts for electrochemical synthesis of ammonia from N<Subscript>2</Subscript> (air) and water at low temperature and ambient pressure

Metal–organic-frameworks (MOFs) (i.e., MOF(Fe), MOF(Co) and MOF(Cu)) were synthesized by a hydrothermal process. The prepared MOFs were characterized using X-ray diffraction, Fourier transform infrared spectroscopy and N₂ adsorption–desorption. The catalytic activities of the MOFs for the electrochemical synthesis of ammonia were evaluated when using N₂ (air) and water as raw materials at low temperature and ambient pressure. The results indicated that the prepared MOFs have fine crystalline structures, abundant micropores, and large specific surface areas. The prepared MOFs showed excellent catalytic activity for the electrochemical synthesis of ammonia at low temperature and ambient pressure. Among these MOFs, the MOF(Fe) displayed the best catalytic activity, and the highest ammonia formation rate and the highest current efficiency reached 2.12 × 10^?9 mol s^?1 cm^?2 and 1.43%, respectively, at 1.2 V and 90 °C, when using pure N₂ and water as raw materials. The prepared MOFs in this work showed remarkable catalytic activities for the electrochemical synthesis of ammonia at low temperature and ambient pressure among the non-noble metal catalysts. It was the first exploration to apply MOFs as the electrocatalysts for the electrochemical synthesis of ammonia at low temperature and ambient pressure.     

Investigation on the structural and optical properties of sonochemically synthesized BiVO<Subscript>4</Subscript> for photocatalytic degradation of methylene blue

BiVO₄ has been successfully synthesised using facile sonication method by varying the ultrasonic output power. The crystal structure, morphology and catalytic efficiency of the samples prepared using sonication technique with different power output has been compared with the sample prepared by normal magnetic stirring. An ideal output power which yields better catalytic efficiency is figured out. The crystal structure and phases of the samples were analyzed using X-ray diffraction which confirmed that all samples had monoclinic scheelite structure. The morphology has been investigated using scanning electron microscopy. The band gap determined using DRS revealed that sample sonicated with 120 W output power had lower bandgap and an increased surface area of 2.24 times greater than that of the as prepared sample. The photocatalytic activities of the samples were evaluated by decolorization of methyl blue under visible light and sample sonicated with 120 W power output possessed higher photocatalytic activity than other samples.     

添加Al对燃料电池阴极催化剂(Pt-Fe)/Pt合金微观组织及氧还原催化性能的影响

为提高燃料电池阴极催化剂(Pt-Fe)/Pt合金的氧还原催化活性和稳定性,在Pt-Fe合金体系中引入元素Al,熔炼得到中间合金(Pt-Fe)Al,再经过NaOH溶液定向腐蚀得到(Pt1-xFex)₃Al/Pt合金,用其作为燃料电池氧还原反应的催化剂,并对其结构、催化活性和稳定性进行了研究。结果表明,所制备的催化剂材料(Pt1-xFex)₃Al/Pt合金具有由几个原子层厚的纯Pt外壳和成分为(Pt1-xFex)₃Al的内核构成的双模孔隙且内部互通的包覆式结构。相比于传统燃料电池的氧还原反应催化剂Pt/C材料以及由Pt-Fe体系制备的Pt₄₆Fe₅₄/Pt合金,(Pt1-xFex)₃Al/Pt合金的比活性分别是Pt₄₆Fe₅₄/Pt合金、Pt/C比活性的 1.21倍和2.69倍,其质量活性分别是Pt₄₆Fe₅₄/Pt和Pt/C的1.17倍和5.3倍。在催化稳定性方面,(Pt1-xFex)₃Al/Pt的电化学活性面积在10 000圈伏安循环后衰减到89%,然后趋于稳定,且循环40 000圈后其仍保留80%的电化学活性面积。由此可见,所制备的催化剂材料(Pt1-xFex)₃Al/Pt合金具有较高的催化活性及催化稳定性。