Cuiyan Li

Topotactic synthesis and photocatalytic performance of one-dimensional ZnNb2O6 nanostructures and one-dimensional ZnNb2O6/KNbO3 hetero-nanostructures

This paper introduces one-dimensional ZnNb2O6/KNbO3 hetero-nanostructures and one-dimensional ZnNb2O6 nanostructures. These nanostructures are synthesized via in situ topotactic structural transformation reaction using the tunnel structure K2Nb2O6 filiform crystal as precursor. Firstly, Zn2+ ions intercalate into K2Nb2O6 crystal by exchanging K+ ions from the K2Nb2O6 crystal with Zn2+ from Zn(NO3)2 or Zn(CH3COO)2 aqueous solution, to form two different Zn2+-exchanged samples, and then these Zn2+-exchanged samples topotacticly transform into one-dimensional ZnNb2O6/KNbO3 hetero-nanostructures and ZnNb2O6 nanostructures during heat-treatment. The formation reaction and structure of these samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and energy-dispersive spectroscopy (EDS). Photocatalytic experiments showed that one-dimensional ZnNb2O6/KNbO3 hetero-nanostructures and ZnNb2O6 nanostructures have excellent photocatalytic performance for the degradation of methylene blue (MB), rhodamine B (RhB), and methyl orange (MO).

Ti-O-O coordination bond caused visible light photocatalytic property of layered titanium oxide.

The layered titanium oxide is a useful and unique precursor for the facile and rapid preparation of the peroxide layered titanium oxide H1.07Ti1.73O4·nH2O (HTO) crystal with enhanced visible light photoactivity. The H2O2 molecules as peroxide chemicals rapidly enter into the interlayers of HTO crystal, and coordinate with Ti within TiO6 octahedron to form a mass of Ti-O-O coordination bond in the interlayers. The introduction of these Ti-O-O coordination bonds result in lowering the band gap of HTO, and promoting the separation efficiency of the photo induced electron–hole pairs. Meanwhile, the photocatalytic investigation indicates that such peroxide HTO crystal has the enhanced photocatalytic performance for RhB degradation and water splitting to generate oxygen under visible light irradiating.

Influence of hydrothermal treatment on the microstructure and oxidation resistance of a Zn4B2O7·H2O (4ZnO·B2O3·H2O) coating for C/C composites

Antioxidant modification for C/C composites by in situ hydrothermal synthesise at 140 °C of a 4ZnO·B2O3·H2O crystallite coating has been successfully achieved. The influence of hydrothermal time on the phase composition, microstructure of the as-prepared Zn4B2O7·H2O (4ZnO·B2O3·H2O), and its antioxidant modification for C/C composites were investigated. Samples were characterised by XRD, SEM, isothermal oxidation test and TG-DSC. Results show that, 4ZnO·B2O3·H2O crystalline coating is achieved on the surface of C/C composites after the hydrothermal treatment at 140 °C for time in the range of 2–12 h. A smooth and crack-free 4ZnO·B2O3·H2O layer can be obtained when the hydrothermal time reaches 8 h. Isothermal oxidation test demonstrates that the oxidation resistance of C/C composites is improved. The as-modified composites exhibit only 1.52 g·cm−2 weight loss after oxidation at 600 °C for 15 h, while the non-modified one shows a 6.57 g·cm−2 weight loss after only 10 h oxidation. For the uncoated C/C composite the oxidation rate is approximately linear with time (non-protective oxidation), thus at 15 h exposure one can estimate the mass loss to be 6.57 g·cm−2 after 10 h for direct comparison with the coated samples.

Cf/C–SiC–MoSi2 composites with good ablation performance prepared via a two-step hydrothermal method

Cf/C–SiC–MoSi2 composites were prepared via a simple hydrothermal method. The kinetics of the hydrothermal penetration process, the mechanical properties, and ablation behaviors of the composites were investigated. Results showed that the penetration activation energy was only 51.3 kJ mol−1. The flexural strength of the composites was 111.7 MPa. The Cf/C–SiC–MoSi2 composites exhibited good ablation properties after being exposed to plasma flame at 2300 °C. During the ablation, molten SiO2 could prevent carbon from oxidation. Moreover, the transformation from MoO2 to gaseous MoO3 consumed considerable amounts of oxygen and absorbed a large amount of heat, which prevented the composites from further ablation.