Effects of annealing on phase evolution,microstructure and magnetic properties of mechanically synthesized nickel-ferrite

The influence of milling and subsequent annealing on nickel-ferrite phase formation was investigated by X-ray diffraction (XRD). Microstructure and magnetic properties of NiFe₂O₄ were determined by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and vibration sample magnetometry (VSM). Single phase nanosized nickel-ferrite was obtained by 30 h mechanical alloying (MA) and subsequent annealing at 600 °C for 1 h. Magnetic properties of the milled powder were extensively affected by the annealing temperature. Considerable growth of the particles and necking by sintering resulted from annealing at 1000 °C.     

A simple approach for the synthesis of bi-functional Fe3O4@WO3 − x core–shell nanoparticles with magnetic-microwave to heat responsive properties

A facile direct precipitation method has been developed for the synthesis of multi-functional magnetic, microwave to heat responsive properties with Fe₃O₄ nanoparticles as the core and WO_3 − x as the shell. Transmission electron microscopy (TEM) images revealed that the obtained bi-functional nanoparticles had a core-shell structure and a spherical morphology. The average size was ~ 250 nm, and the thickness of the shell was ~ 15 nm. The X-ray diffraction (XRD) patterns showed that a cubic spinel structure of Fe₃O₄ core and the WO_3 − x shell were obtained. The nanoparticles showed both strong magnetic, and unique microwave to heat responsive properties, which may lead to development of nanoparticles with great potential for applications in drug targeting delivery, controlled release drug, photo- and microwave-thermal combination therapy and water treatment.     

Hierarchical heterostructure of porous NiO nanosheets on flower-like ZnO assembled by hexagonal nanorods for high-performance gas sensor

A novel hierarchical heterostructure consisting of porous NiO nanosheets and flower-like ZnO assembled by hexagonal nanorods was successfully fabricated by a simple two-step hydrothermal approach. Flower-like ZnO was obtained by the first step hydrothermal method. Through the second step hydrothermal method, porous NiO nanosheets grew on the surface of flower-like ZnO to realize integration of ZnO and NiO, so the p-n heterostructure between ZnO and NiO formed. The samples were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX). Gas sensing test results showed that the sensor based on NiO/ZnO composite exhibited superior sensing properties to acetone. The sensor response to 100 ppm acetone was about 205.14 at the optimum working temperature of 240 °C, and the response and recovery times were about 7 and 20 s, respectively. The enhanced response might be attributed to heterojunction and larger specific surface area provided by attached porous NiO nanosheets. The rapid response and recovery characteristics and improved selectivity attributed to the porous structure and good catalytic actions of NiO nanosheets.     

Effect of carbon doping on WO3/TiO2 coupled oxide and its photocatalytic activity on diclofenac degradation

The improved photocatalyst carbon-doped WO₃/TiO₂ mixed oxide was synthesized in this study using the sol–gel method. The catalyst was thoroughly characterized by X-ray diffraction (XRD), diffuse reflectance UV–vis spectroscopy, N₂ adsorption desorption analysis, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic efficiency of the prepared materials was evaluated with respect to the degradation of sodium diclofenac (DCF) in a batch reactor irradiated under simulated solar light. The progress of the degradation process of the drug was evaluated by high-performance liquid chromatography (HPLC), whereas mineralization was monitored by total organic carbon analysis (TOC) and ion chromatography (IC). The results of the photocatalytic evaluation indicated that the modified catalyst with tungsten and carbon (TWC) exhibited higher photocatalytic activity than TiO₂ (T) and WO₃/TiO₂ (TW) in the degradation and mineralization of diclofenac (TWC>TW>T). Complete degradation of diclofenac occurred at 250 kJ m⁻² of accumulated energy, whereas 82.4% mineralization at 400 kJ m⁻² was achieved using the photocatalytic system WO₃/TiO₂-C. The improvement in the photocatalytic activity was attributed to the synergistic effect between carbon and WO₃ incorporated into the TiO₂ structure.     

Thermal annealing induced mazy structure on MoO3 thin films and their high sensing performance to NO gas at room temperature

MoS₂ thin films were prepared by radio frequency (RF) magnetron sputtering and then annealed in air. X-ray diffraction (XRD), field-emission electron scanning microscopy (FESEM) and transmission electron microscopy (TEM) were adopted to characterize the phase structure and surface morphology. Interestingly, upon thermal annealing in air, MoS₂ thin films changed into α-MoO₃ with mazy morphology, and the thin films were covered by MoO₃ nano-sheets with a length of 30–50 nm and a width of 10 nm. α-MoO₃ thin films with mazy morphology showed excellent response to NO gas at room temperature. The response of 5% and 92% was obtained at 5 ppm and 200 ppm, respectively, and the response and recovery times were 30 s and 1500 s. Moreover, the mazy structure of MoO₃ exhibited good selectivity to NO gas with respect to SO₂, NH₃ and H₂ gases. The high surface-to-volume ratio was the dominant factor for high sensing performance.     

Enhanced anode performance of micro/meso-porous reduced graphene oxide prepared from carbide-derived carbon for energy storage devices

Micro/meso-porous reduced graphite oxide (MMRGO) nanosheets were produced using precursor carbide-derived carbon (CDC), which was produced at a high temperature of 1200 °C, through a massive wet chemistry synthetic route involving graphite oxidation and microwave reduction. X-ray diffraction (XRD) and transmission electron microscopy (TEM) show that the MMRGO nanosheets were fabricated with 2–3 layers and ripple-like corrugations. N₂ sorption isotherms confirmed that micro/meso-pores coexisted in the RGO sample from CDC. In the anode application of Li-ion batteries, this RGO sample had an enhanced capacity performance at the 0.1 C rate and 1 C rate, with ∼1200 mAh g⁻¹ at the 100th cycle and ∼1000 mAh g⁻¹ at the 200th cycle, respectively.     

The study of BiCrxFe1−xO3 thin films synthesized by sol–gel technique

Cr-doped bismuth ferrite (BiCr_xFe_1?xO₃, BCFO) thin films were prepared by a sol–gel method with the value of x varying from 0 mol% to 10 mol%. The structures of the BCFO thin films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis was employed to represent the surface and cross-sectional morphologies of the thin films. Dielectric, electrical, ferroelectric and magnetic properties were measured by HP4294A, Keithley 4200, RT6000 and 6700 Magnet Controller at room temperature, respectively. The dielectric behaviour and insulation are improved in 3% Cr-doped BFO thin film which may be due to the reduced concentration of oxygen vacancies by 3% Cr doping.     

Facile synthesis of CdS nanoparticles photocatalyst with high performance

A simple one-step solid-state reaction has been introduced to synthesize CdS nanoparticles. The as-prepared CdS product was characterized by X-ray powder diffraction (XRD), BET surface area measurement, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), particle size distribution (PSD) and UV–vis absorption spectrum. The experiment results reveal that the CdS product was composed of nanoparticles about 60 nm in diameter, of which specific surface area is 78.02 m²/g. The photocatalysis results indicate that the CdS nanoparticles exhibit excellent photocatalytic activity for the degradation of rhodamine B under UV irradiation. Nearly 95% of rhodamine B was degraded after 60 min of irradiation, higher than that of P25, which is due to the large specific surface area and mesoporous structure.     

Synthesis and properties of nanocomposites of WO3 and exfoliated g-C3N4

The nanocomposites of WO₃ nanoparticles and exfoliated graphitized C₃N₄ (g-C₃N₄) particles were prepared and their properties were studied. For this purpose, common methods used for characterization of solid samples were completed with dynamic light scattering (DLS) method and photocatalysis, which are suitable for study of aqueous dispersions.The WO₃ nanoparticles of monoclinic structures were prepared by a hydrothermal method from sodium tungstate and g-C₃N₄ particles were prepared by calcination of melamine forming bulk g-C₃N₄, which was further thermally exfoliated. Its specific surface area (SSA) was 115 m² g⁻¹.The nanocomposites were prepared by mixing of WO₃ nanoparticles and g-C₃N₄ structures in aqueous dispersions acidified by hydrochloric acid at pH = 2 followed by their separation and calcination at 450 °C. The real content of WO₃ was determined at 19 wt%, 52 wt% and 63 wt%. It was found by the DLS analysis that the g-C₃N₄ particles were covered by the WO₃ nanoparticles or their agglomerates creating the nanocomposites that were stable in aqueous dispersions even under intensive ultrasonic field. Using transmission electron microscopy (TEM) the average size of the pure WO₃ nanoparticles and those in the nanocomposites was 73 nm and 72 nm, respectively.The formation of heterojunction between both components was investigated by UV–Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photocatalysis and photocurrent measurements. The photocatalytic decomposition of phenol under the LED source of 416 nm identified the formation of Z-scheme heterojunction, which was confirmed by the photocurrents measurements. The photocatalytic activity of the nanocomposites decreased with the increasing content of WO₃, which was explained by shielding of the g-C₃N₄ surface by bigger WO₃ agglomerates. This study also demonstrates a unique combination of various characterization techniques working in solid and liquid phase.     

Spark plasma assisted carbothermal reduction-nitridation synthesis of (Ti,W, Mo)(C,N)-(Ni,Co) powders

Ultrafine (Ti, W, Mo)(C, N)-(Ni, Co) cermet powders were rapidly synthesized from various metal oxides, mainly anatase-TiO₂, by spark plasma assisted carbothermal reduction-nitridation (SPCRN) at low temperature. The phase evolution of the SPCRN reaction was investigated using X-ray diffraction (XRD) and the microstructure of the product powders was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). NiO, Co₃O₄ and MoO₃ were converted to Ni, Co and Mo₂C by CR reaction at temperatures below 900 °C. WO₃ was successively transformed from W₂C to WC by CR reaction up to 1100 °C. Finally, at up to 1350 °C, (Ti, W, Mo)(C, N) formed into the sequence of TiO₂, Ti₄O₇, Ti₃O₅, Ti(O, N), Ti(C, N), (Ti, W)(C, N) and (Ti, W, Mo)(C, N). The crystal structure of (Ti, W, Mo)(C, N)-(Ni, Co) cermet powders was analyzed by the Rietveld method and transmission electron microscopy (TEM). The findings demonstrated that the pure (Ti, W, Mo)(C, N)-(Ni, Co) cermet powders with grain size of below 0.5 µm were synthesized from metal oxides by SPCRN reaction at 1400 °C for 10 min.     

Solvothermal synthesis of CNTs–WO3 hybrid nanostructures with high photocatalytic activity under visible light

The CNTs–WO₃ hybrid nanostructures were fabricated by solvothermal synthesis. The morphologies, phase structures and optical properties of the nanostructures were investigated by TEM, XRD, UV–vis DRS and XPS respectively. The CNTs–WO₃ hybrid nanostructures exist higher photocatalytic activity than pure WO₃ nanosheets and the mechanical mixture of WO₃ and CNTs for the degradation of methyl blue (MB) under visible light. This is attributed to their large surface area, absorption enhancement in visible light region and effective separation of electrons and holes. The presence of radical scavengers such as KI, Fe^3 + and methanol in photocatalytic experiments demonstrates that photogenerated electrons are responsible for the photocatalytic degradation of MB on CNTs–WO₃.     

Liquid flame spray fabrication of WO3-reduced graphene oxide nanocomposites for enhanced O3-sensing performances

WO₃ is one of the inspiring sensing materials that show high response to O₃; an efficient fabrication of WO₃ film with incorporation of complementary additives is essential for enhanced sensitivity. Here we report film deposition by liquid flame spraying, characterization of nanostructured WO₃-reduced graphene oxide (rGO) composites and their gas-sensing activities to O₃. The starting feedstock was prepared from WC_l6 and rGO for pyrolysis synthesis by flame spraying. Nano-porous WO₃-rGO films were successfully fabricated and characterized by transmission electron microscopy, field emission scanning electron microscopy, Raman spectrometry, thermal analyses and X-ray diffraction. Nanosized WO₃ grains exhibited oriented nucleation on rGO flakes whereas rGO retained intact its nano-structural features after spraying. Constrained grain growth of WO₃ of 60–70 nm in size was realized in the rGO-containing films with as compared to ~220 nm in the pure WO₃ film. The WO₃-rGO film sensors showed quicker response to O₃ and faster recovery than rGO-free WO₃ film sensors. Addition of rGO in 1.0 wt% or 3.0 wt% in the films caused a significantly reduced effective working temperature of the film sensors from ~ 250 °C to ~ 150 °C.     

Investigation on mechanochemical combustion behavior of Mg–V2O5–Co3O4-C reactive system to synthesize VC–Co nanocomposite powder

VC–Co nanocomposite powders were obtained by mechanochemical combustion synthesis from a mixture of V₂O₅, Co₃O₄, C and Mg powders. The synthesized powders were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). VC–Co nanocomposite was directly produced after 10 min milling through a mechanically induced self-sustaining reaction without further heat treatment. TEM analysis showed that a nanostructured powder with a mean particle size of 100 nm was procured in the sample milled for 10 min.     

Dielectric properties of CaCu3Ti4O12 improved by chromium/lanthanum co-doping

The dielectric properties of Cr + La co-doped CaCu₃Ti₄O₁₂ ceramics prepared by a solid-state reaction method were evaluated and compared to Cr-doped, La-doped, and parent CaCu₃Ti₄O₁₂ (CCTO). Their structure and grain size were evaluated by X-ray diffraction and scanning electron microscopy, respectively. No secondary phase was detected based on the XRD analysis. The results show that, the room temperature dielectric loss of the co-doped samples is reduced to 43% compared to CCTO and their dielectric permittivity is higher than the un-doped, Cr-doped, and La-doped samples at frequencies over 325 kHz, 30 kHz, and 12 Hz, respectively. Furthermore, the temperature stability of the co-doped sample is significantly more convenient than that of CCTO, and its dielectric loss is three times lower. The results also indicated that the co-doping method is effective in reducing the dielectric loss, still maintaining the high dielectric permittivity.     

Hydrothermal synthesis of dumbbell-shaped ZnO microstructures

Dumbbell-shaped ZnO microstructures have been successfully synthesized by a facile hydrothermal method using only Zn(NO₃)₂·6H₂O and NH₃·H₂O as raw materials at 150 °C for 10 h. The results from X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) show that the prepared ZnO samples exhibit dumbbell-shaped morphology and hexagonal wurtzite structure. The length of ZnO dumbbells is about 5–20 μm, the diameters of the two ends and the middle part are about 1–5 μm and 0.5–3 μm, respectively. The dumbbell-shaped ZnO microstructures may be formed by self-assembly of ZnO nanorods with 1–5 μm in length and 100–200 nm in diameter. The photoluminescence (PL) spectrum of dumbbell-shaped ZnO microstructures at room temperature shows three emission peaks at about 362, 384 and 485 nm.     

The synthesis of single phase WC nanoparticles/C composite by solid state reaction involving nitrogen-rich carbonized polyaniline

Single phase tungsten carbide nanoparticles (WC-NPs), (mean particle diameter 5.4 nm), distributed over carbonized polyaniline (C-PANI) nanotubes/nanosheets were synthesized by a solid state reaction between WO₃ and nitrogen-rich carbonized polyaniline at 1000 °C in a reducing atmosphere. The resulting composite was characterized by X-ray diffractometry, electron microscopy, thermogravimetry in oxidizing and reduction atmospheres and elemental analysis. We suggested that the synthesis of WC as a single phase was facilitated by reactive C atoms with dangling bonds, formed upon nitrogen removal.     

Microstructural features of nanocomposite of alumina@carbon nanotubes/alumina nanoparticles synthesized by a solvothermal method

The present study focuses on the synthesis of nanocomposite gamma alumina (γ-Al₂O₃), boehmite and multi- walled carbon nanotubes (MWCNTs) via a solvothermal procedure. The method is based on the ex situ filling of opened CNTs by liquid reactants. The microstructure and morphology of the synthesized nanocomposite Al₂O₃@CNTs/Al₂O₃ was characterized by high resolution transmission electron microscopy (HRTEM), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and N₂ adsorption–desorption analysis.Based on the experimental results, it was determined that the volume ratio of γ-Al₂O₃/MWCNTs and the surface tension of the solvent both greatly influence the morphology of the nanocomposite. The resultant MWCNTs were coated and filled by homogeneous and uniform boehmite and γ-Al₂O₃ layers and nanoparticles with thicknesses of 1–3 nm and diameters of 20–40 nm, when the volume ratio of γ-Al₂O₃/MWCNT_S is 1 and the surface tension of the solvent is approximately 26 mN m^?1 at 20 °C, far below the maximum value (100–200 mN m^?1) for MWCNT filling.     

Highly sensitive acetone sensor based on Eu-doped SnO2 electrospun nanofibers

In this study, a series of undoped and Eu-doped SnO₂ nanofibers were synthesized via a simple electrospinning technique and subsequent calcination treatment. Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were carefully used to characterize the morphologies, structures and chemical compositions of these samples. The results reveal that the as-prepared nanofibers are composed of crystallite grains with an average size of about 10 nm and Eu³⁺ ions are successfully doped into the SnO₂ lattice. Compared with pure SnO₂ nanofibers, Eu-doped SnO₂ nanofibers demonstrate significantly enhanced sensing characteristics (e.g., large response value, short response/recovery time and outstanding selectivity) toward acetone vapor, especially, the optimal sensor based on 2 mol% Eu-doped SnO₂ nanofibers shows the highest response (32.2 for 100 ppm), which is two times higher than that of the pure SnO₂ sensor at an operating temperature of 280 °C. In addition, the sensor exhibits a good sensitivity to acetone in sub-ppm concentrations and the detection limit could extend down to 0.3 ppm, making it a potential candidate for the breath diagnosis of diabetes.     

Direct microwave synthesis of graphitic C3N4 with improved visible-light photocatalytic activity

The graphitic carbon nitride (g-C₃N₄) was rapidly synthesized via direct high-energy microwave heating approach. During the preparation process, only low-cost melamine and artificial graphite powders were used, without any metal catalysts or inert protective gas. The microstructure was investigated by using X-ray diffraction (XRD), Flourier transformed infrared (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM). The spectra of XRD and HRTEM indicated that the obtained g-C₃N₄ had a high crystallinity. The optical spectra covering Photoluminescence (PL) and Ultraviolet-visible (UV–vis) were also measured at room temperature. PL peak and UV–vis absorption edge of the g-C₃N₄ were shown at 455 nm and 469 nm, respectively, indicating visible-light photocatalytic property. Finally, the photocatalytic activity of g-C₃N₄ was investigated and evaluated as photocatalyst for the photo-degradation of Rhodamine B (RhB) and Methyl Orange (MO) in aqueous solution under visible-light (λ>420 nm) irradiation, respectively. Results indicated that the g-C₃N₄ sample displayed an excellent performance of removing of RhB and MO due to the improved crystallinity and large surface area of 126 m²/g. After the visible-light photocatalytic reaction for 40 min, the decolorization ratios of RhB and MO reached up to 100% and 94.2%, respectively.     

In2O3 nanosheets array directly grown on Al2O3 ceramic tube and their gas sensing performance

Arrayed In₂O₃ nanosheets were synthesized directly via a two-step solution approach on an Al₂O₃ ceramic tube. Their morphology and structure were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–Vis absorption spectroscopy, and scanning electron microscopy (SEM). The results reveal that the length of each nanosheet is about 1 µm, the width of the bottom of nanosheet is about 200 nm. Importantly, the In₂O₃ nanosheets with large specific surface area possess highly sensing performance for ethanol detection. The response value to 100 ppm ethanol is about 45 at an operating temperature of 280 °C, and the response and recovery time are extremely short. It is expected that the directly grown In₂O₃ nanosheets with large specific surface area and excellent sensing properties will become a promising functional material in monitoring and detecting ethanol.