Electrospinning Preparation of GaN:ZnO Solid Solution Nanorods with Visible-Light-Driven Photocatalytic Activity toward H2 Production

The development of a facile method for the synthesis of GaN:ZnO solid solution, an attractive material with a wurtzite-type structure, is vital to enhance its photocatalytic activity toward H2 evolution. Herein, GaN:ZnO solid solution nanorods with diameters of around 180 nm were fabricated by combining the electro-spun method with a sequentially calcinating process. Photocatalytic water-splitting activities of the as-obtained samples loaded with Rh2−yCryO3 co-catalyst were estimated by H2 evolution under visible-light irradiation. The as-prepared GaN:ZnO nanorods at a nitridation temperature of 850 °C showed the optimal performance. Careful characterization of the GaN:ZnO solid solution nanorods indicated that the nitridation temperature is an important parameter affecting the photocatalytic performance, which is related to the specific surface area and the absorbable visible-light wavelength range. Finally, the mechanism of the GaN:ZnO solid solution nanorods was also investigated. The proposed synthesis strategy paves a new way to realize excellent activity and recyclability of GaN:ZnO solid solution nanorod photocatalysts for hydrogen generation.

Recycling of the Diamond-wire Saw Powder by Ni-catalyzed Nitridation to Prepare Si3N4

In this paper, the acceleration of nickel (Ni) in the direct nitridation process of the diamond-wire saw powder (DWSP) was investigated. The DWSP doped with Ni additives were nitrided at different temperatures. To study the mechanism of accelerated nitridation, the thermodynamics of Si-O-N-Ni was analyzed by FactSage 7.2 and single-crystal silicon blocks were also nitrided instead of the DWSP. The results revealed that Ni decreased the nitridation temperature at which the DWSP began to gain significant weight and exhibited an excellent accelerating effect on the nitridation of the DWSP. At 1300℃, the DWSP containing 2.0 wt.% Ni additives had been completely nitrided within 2 h, whereas the DWSP without Ni additives had not been nitrided yet. Based on the equivalent substitution experiment, it could be conducted that the presence of Ni additives accelerated the nitridation and promoted the formation of the α-Si3N4 nanorods through facilitating the generation of the SiO(g) and destructing the silica film on the surface of silicon at lower temperature. Meanwhile, Ni additives also played an important part in the growth of α-Si3N4 nanorods by forming liquid Ni-Si alloy in the product.

ZrN Phase Formation, Hardening and Nitrogen Diffusion Kinetics in Plasma Nitrided Zircaloy-4

Plasma nitridation was conducted to modify the surfaces of Zircaloy-4. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman analysis were used to characterize microstructures and phases. Surface indentation and cross-sectional indentation were performed to evaluate mechanical property changes. Nitridation forms a thin layer of ZrN phase, followed by a much deeper layer affected by nitrogen diffusion. The ZrN phase is confirmed by both TEM and Raman characterization. The Raman peaks of ZrN phase show a temperature dependence. The intensity increases with increasing nitridation temperatures, reaches a maximum at 700 °C, and then decreases at higher temperatures. The ZrN layer appears as continuous small columnar grains. The surface polycrystalline ZrN phase is harder than the bulk by a factor of ~8, and the nitrogen diffusion layer is harder by a factor of ~2–5. The activation energy of nitrogen diffusion was measured to be 2.88 eV. The thickness of the nitrogen-hardened layer is controllable by changing the nitridation temperature and duration.

Synthesis of Hollow Mesoporous TiN Nanostructures as an Efficient Catalyst Support for Methanol Electro-Oxidation

The development of efficient catalyst materials that can drive high catalytic performance is challenging. Here, we report a well-defined hollow mesoporous TiN nanostructure for use as Pt catalyst support material for methanol electro-oxidation. The hollow TiN nanostructure was synthesized by the ammonia nitridation of pre-synthesized mother hollow anatase TiO2, which was prepared by SiO2 template-assisted sol–gel synthesis followed by chemical etching, acid treatment, and sequential calcination. The variation in the ammonia nitridation temperature allowed the crystalline properties of the samples to be finely tuned. As the ammonia nitrification temperature increased, the crystallinity of the resulting hollow TiN continuously increased, and the corresponding Pt catalysts showed enhanced activity toward methanol electro-oxidation. The hollow TiN-800 sample (H-TiN-800), with a well-developed pure TiN phase, exhibited the highest electrical conductivity and the lowest resistance. The corresponding Pt/H-TiN-800 catalyst exhibited significantly enhanced catalytic activity. In this study, we systemically analyzed the physicochemical characteristics and electrochemical performance of hollow TiN samples and their corresponding Pt catalysts.

Growth of Semi-Polar (101¯3) AlN Film on M-Plane Sapphire with High-Temperature Nitridation by HVPE

Aluminum nitride (AlN) films were grown on the m-plane sapphire by high-temperature hydride vapor phase epitaxy (HVPE). The effect of high-temperature nitridation on the quality of AlN film was studied. The high-temperature nitridation is favorable for the formation of semi-polar single (101¯3) orientation AlN film, the quality of which shows strong dependence on the nitridation temperature. The full width at half maximum of X-ray diffraction for (101¯3) AlN film was only 0.343° at the optimum nitridation temperature of 1300 °C. It is found that the nano-holes were formed on the surface of substrates by the decomposition of sapphire in the process of high-temperature nitridation, which is closely related to the quality improvement of AlN. At the critical nitridation temperature of 1300 °C, the average size of the nano-holes is about 70 nm, which is in favor of promoting the rapid coalescence of AlN micro-grains in the early stages. However, the size of nano-holes will be enlarged with the further increase of nitridation temperature, which begins to play a negative role in the coalescence of AlN grains. As a result, the grain size will be increased and extended to the epilayer, leading to the deterioration of the AlN film.

Nitridation Temperature Effect on Carbon Vanadium Oxynitrides for a Symmetric Supercapacitor

In this work, porous carbon-vanadium oxynitride (C-V2NO) nanostructures were obtained at different nitridation temperature of 700, 800 and 900 °C using a thermal decomposition process. The X-ray diffraction (XRD) pattern of all the nanomaterials showed a C-V2NO single-phase cubic structure. The C-V2NO obtained at 700 °C had a low surface area (91.6 m2 g−1), a moderate degree of graphitization, and a broader pore size distribution. The C-V2NO obtained at 800 °C displayed an interconnected network with higher surface area (121.6 m2 g−1) and a narrower pore size distribution. In contrast, at 900 °C, the C-V2NO displayed a disintegrated network and a decrease in the surface area (113 m2 g−1). All the synthesized C-V2NO yielded mesoporous oxynitride nanostructures which were evaluated in three-electrode configuration using 6 M KOH aqueous electrolyte as a function of temperature. The C-V2NO@800 °C electrode gave the highest electrochemical performance as compared to its counterparts due to its superior properties. These results indicate that the nitridation temperature not only influences the morphology, structure and surface area of the C-V2NO but also their electrochemical performance. Additionally, a symmetric device fabricated from the C-V2NO@800 °C displayed specific energy and power of 38 W h kg−1 and 764 W kg−1, respectively, at 1 A g−1 in a wide operating voltage of 1.8 V. In terms of stability, it achieved 84.7% as capacity retention up to 10,000 cycles which was confirmed through the floating/aging measurement for up to 100 h at 10 A g−1. This symmetric capacitor is promising for practical applications due to the rapid and easy preparation of the carbon-vanadium oxynitride materials.