Xinmei Hou

Bare and boron-doped cubic silicon carbide nanowires for electrochemical detection of nitrite sensitively.

Fabrication of eletrochemical sensors based on wide bandgap compound semiconductors has attracted increasing interest in recent years. Here we report for the first time electrochemical nitrite sensors based on cubic silicon carbide (SiC) nanowires (NWs) with smooth surface and boron-doped cubic SiC NWs with fin-like structure. Multiple techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) were used to characterize SiC and boron-doped SiC NWs. As for the electrochemical behavior of both SiC NWs electrode, the cyclic voltammetric results show that both SiC electrodes exhibit wide potential window and excellent electrocatalytic activity toward nitrite oxidation. Differential pulse voltammetry (DPV) determination reveals that there exists a good linear relationship between the oxidation peak current and the concentration in the range of 50–15000 μmoL L−1 (cubic SiC NWs) and 5–8000 μmoL L−1 (B-doped cubic SiC NWs) with the detection limitation of 5 and 0.5 μmoL L−1 respectively. Compared with previously reported results, both as-prepared nitrite sensors exhibit wider linear response range with comparable high sensitivity, high stability and reproducibility.

Superior Photodetectors Based on All-Inorganic Perovskite CsPbI3 Nanorods with Ultrafast Response and High Stability

Currently, one-dimensional all-inorganic CsPbX3 (X = Br, Cl, and I) perovskites have attracted great attention, owning to their promising and exciting applications in optoelectronic devices. Herein, we reported the exploration of superior photodetectors (PDs) based on a single CsPbI3 nanorod. The as-constructed PDs had a totally excellent performance with a responsivity of 2.92 × 103 A·W-1 and an ultrafast response time of 0.05 ms, respectively, which were both comparable to the best ones ever reported for all-inorganic perovskite PDs. Furthermore, the detectivity of the PDs approached up to 5.17 × 1013 Jones, which was more than 5 times the best one ever reported. More importantly, the as-constructed PDs showed a high stability when maintained under ambient conditions.

Improved microwave absorption performance of modified SiC in the 2–18 GHz frequency range

Aiming to improve the microwave absorption performance of SiC, various methods including doping and changing the shape were adopted. In view of doping, B-doped silicon carbide (B–SiC) with a B content of 3 mass% was prepared via a simple carbothermal reduction method. By using different raw materials, SiC both in nanowire and powder forms was obtained. The microwave absorption performance was investigated. The results show that B–SiC nanowires exhibit a far more improved microwave absorption ability in the frequency range of 2–18 GHz compared with SiC nanowires. The effective absorption bandwidth of the reflection loss below −10 dB is 3.52 GHz, and the maximum reflection loss of −37.94 dB at 14 GHz with a thickness of 1.5 mm indicates that B–SiC nanowires could be used as an effective microwave absorbing material. The combination of the enhanced electrical conductivity caused by B doping and the network formed from nanowires contributes to the enhanced microwave absorption.

SiC Nanowires with Tunable Hydrophobicity/Hydrophilicity and Their Application as Nanofluids

In this paper, several methods including HF, NaOH, TEOS, and PVP treatment were adopted to modify the wettability of silicon carbide (SiC) nanowires switching from hydrophobic to hydrophilic. The phase and microstructure investigated by XRD, FT-IR, XPS, TGA, SEM, and TEM demonstrated SiC nanowires switching from hydrophobic to hydrophilic due to the surface-tethered hydrophilic layer as well as increasing interspace between nanowires. Besides this, SiC nanowires with hydrophilicity may effectively improve the thermal conductivity of a fluid. The thermal conductivity of aqueous SiC nanowires after TEOS treatment with just 0.3 vol % was remarkably improved up to ca. 13.0%.

Kinetics of reduction of titano-magnetite powder by H 2

Abstract Reduction of titano-magnetite powder containing 56.9 mass% of iron and 9.01 mass% of TiO2 with H2-Ar gas mixtures was investigated in isothermal experiments using thermo-gravimetric analyzer (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The reduction of titano-magnetite was proved to proceed via a dual reactions mechanism. The first reaction is reduction of titano-magnetite to wüstite and ilmenite and the second one is reduction of wüstite and ilmenite to iron and titanium-containing phase. It was found that the dual reactions occurred simultaneously during the reduction. The reduction kinetics of titano-magnetite was analyzed according to a dual reactions kinetic model and the results indicated that the gaseous species diffusion in product layer was the rate controlling step for the first reaction, and interfacial chemical reaction was that for the second reaction. The apparent activation energies were extracted to be 98 kJ/mol and 115 kJ/mol for the first and second reaction, respectively.

Single crystalline β-SiAlON nanowhiskers: preparation and enhanced properties at high temperature

Single crystalline β-SiAlON (z = 1.0) nanowhiskers with uniform morphology were prepared using a reaction sintering method at 1773 K for 6 h under flowing nitrogen atmosphere. The as-synthesized whiskers were well-crystallized with about 100-200 nm in diameter and a few hundred microns in length. According to the thermodynamic calculation, Al(g) and SiO(g) are important intermediate reactants to synthesize β-SiAlON whiskers. In the experiment, the two phases was controlled by changing the flow rate of nitrogen to make β-SiAlON whiskers grow in a stable way. The formation of β-SiAlON whiskers occurred through a vapor-solid (VS) mechanism. SiAlON was found to grow as a single crystal whisker from the (10 ̅10) plane of the granule. Furthermore, an enhanced oxidation resistance for β-SiAlON whiskers at high temperature was also observed using the thermogravimetry method (TG), demonstrating that β-SiAlON whiskers with uniform morphology is a promising candidate as a reinforcing agent in composite.

Dissolution and diffusion of TiO2 in the CaO-Al2O3-SiO2 slag

The dissolution of TiO2 in the CaO-Al2O3-SiO2 slag under static conditions was studied in the temperature range from 1643 K to 1703 K. After TiO2 dissolved, the microstructure of the interface between TiO2 and the slag was observed by scanning electron microscopy, and the concentration profiles of Ti4+ and other ions across the TiO2/slag interfaces were analyzed by energy-dispersive X-ray spectroscopy. On the basis of these results, the dissolution behavior of TiO2 was evaluated, and the diffusivity of Ti4+ in the bulk slag was estimated. According to the Stokes-Einstein relation, the viscosity calculated by a previously reported model gave a diffusivity of Ti4+ ions greater than that estimated by the concentration profiles of Ti4+ ions. The mechanism of TiO2 dissolution in the CaO-Al2O3-SiO2 slag is discussed in detail.

General Strategy for Rapid Production of Low-Dimensional All-Inorganic CsPbBr3 Perovskite Nanocrystals with Controlled Dimensionalities and Sizes

Currently, all-inorganic CsPbX3 (X = Br, I, Cl) perovskite nanocrystals (NCs) are shining stars with exciting potential applications in optoelectronic devices such as solar cells, light-emitting diodes, lasers, and photodetectors, due to their superior performance in comparison to their organic-inorganic hybrid counterparts. In the present work, we report a general strategy based on a microwave technique for the rapid production of low-dimensional all-inorganic CsPbBr3 perovskite NCs with tunable morphologies within minutes. The effect of the key parameters such as the introduced ligands, solvents, and PbBr2 precursors and microwave powers as well as the irradiation times on the production of perovskite NCs was systematically investigated, which allowed their growth with tunable dimensionalities and sizes. As a proof of concept, the ratio of OA to OAm as well as the concentration of PbBr2 precursor played important roles in triggering the anisotropic growth of the perovskite NCs, favoring their growth into 1D/2D single-crystalline nanostructures. Meanwhile, their sizes could be tailored by controlling the microwave powers and irradiation times. The mechanism for the tunable growth of perovskite NCs is discussed.

Fabrication of Ordered Mullite Nanowhisker Array with Surface Enhanced Raman Scattering Effect

Mullite nanowhiskers are prepared by a facile technique at low temperature using mica and AlF3 as raw material. Mica acts as reactant as well as substrate. By controlling the reaction temperature and holding time, the mullite nanowhisker array with uniform morphology is obtained. The nanowhisker array possesses Al-rich single crystalline with an average of 80 nm in diameter and 20 μm in length. After decorated with Au nanoparticles, the array exhibits high surface enhanced Raman scattering (SERS) activity with an SERS enhancement factor (EF) of 1.35 × 109. It also remains good SERS signal detection with a relative standard deviation of 7.33% under corrosion condition.

Preparation of hexagonal BN whiskers synthesized at low temperature and their application in fabricating an electrochemical nitrite sensor

Hexagonal boron nitride (h-BN) whiskers were synthesized via the polymeric precursor method using boric acid (H3BO3) and melamine (C3H6N6) as raw materials at 1073–1273 K in flowing nitrogen/hydrogen (5% hydrogen). The phase and morphology of the obtained products were characterized using XRD, FTIR, SEM, TEM and BET techniques. The results show that h-BN wishers can be successfully fabricated at 1073–1273 K with 0.5–3 μm diameters and 50–200 μm lengths. They possess micropores and mesopores. Moreover, the as-prepared BN whiskers can be used as a sensing electrode for detection of nitrite (NO2−). Compared with other electrodes for nitrite detection, the h-BN wishers electrode shows a much higher sensitivity in the wider range from 10 to 1000 μM, with a detection limit of 0.089 μM (10–400 μM) and 0.412 μM (400–6300 μM) (S/N = 3), respectively. The oxidation process of NO2− on the h-BN whiskers electrode is controlled by a diffusion process.