Zhangxian Chen

Synthesis of Ti3+ self-doped TiO2 nanocrystals based on Le Chatelier's principle and their application in solar light photocatalysis

Self-doping by Ti3+ and introducing oxygen vacancies in TiO2 is an important and effective strategy to extend its optical absorption from the UV into the visible region. In this paper, we report the synthesis of a series of Ti3+ self-doped TiO2 nanocrystals via a hydrothermal method using TiCl3 and (NH4)2TiF6 as the source of Ti3+ and Ti4+, respectively. The oxidation of Ti3+ can be inhibited by (NH4)2TiF6 based on Le Chateliers principle. The samples are characterized by X-ray diffraction, UV-Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance, field-emission scanning electron microscopy and transmission electron microcopy, respectively. The results indicate that Ti3+ is localized in the bulk of the as-prepared TiO2 nanocrystals, rather than on the surface. In comparison with pristine TiO2, the Ti3+ self-doped TiO2 nanocrystals exhibit an enhanced photocatalytic activity of 86.3% towards the photodegradation of methylene blue solution under simulated solar light irradiation and 99% under natural solar irradiation. It is found that the molar ratio of Ti4+/Ti3+ used during the synthesis has significant effects on the photocatalytic activity of Ti3+ self-doped TiO2 photocatalysts, since the electronic structures of the resulting Ti3+ self-doped TiO2 nanocrystals can be finely tuned by changing the ratios. The significantly enhanced photocatalytic activity should be due to the self-doping of Ti3+ in TiO2 nanocrystals, which not only increases the optical absorption in the visible light region, but also helps to spatially separate the photogenerated charge carriers.

pH-controlled assembly of three-dimensional tungsten oxide hierarchical nanostructures for catalytic oxidation of cyclohexene to adipic acid

Tungsten oxide has a wide range of applications in chromic devices and catalysis. Effective control over the morphology of tungsten oxide remains a major challenge. Here, we present a facile pH-controlled strategy for synthesizing three-dimensional tungsten oxide architectures with different morphologies without using any templates or surfactants. These hierarchical architectures with rod-like, disk-like and sphere-like morphologies are assembled from one-dimensional tungsten oxide nanowires/nanorods. The influence of the single parameter of the pH value on the morphologies and crystal structures of tungsten oxide is systematically studied. The results indicate that different polytungstate anions obtained at various pH values give rise to different crystal nuclei by a dehydration process. These crystal nuclei grow into similar phases (crystal structures) but distinct morphologies via hydrothermal treatment. Here, the similarity of the crystal structures of h-WO3 and o-WO3·0.33H2O plays a key role in the structural transformation. Further experiments show that these three-dimensional tungsten oxide architectures display promising applications as catalysts in green chemistry for the oxidation of cyclohexene to adipic acid using an environmentally friendly oxidant (hydrogen peroxide).

A galvanic replacement reaction to synthesise metal/ZnO heterostructured films on zinc substrates for enhanced photocatalytic performance

The construction of non-precious transition metal/ZnO heterostructured films is being considered as an effective way to promote photocatalytic efficiency for their practical applications. Herein, a general and facile approach is reported for the first time to synthesize a series of M/ZnO (M = Cu, Cd, Co) heterostructured films on Zn substrate based on a simple one-step galvanic replacement reaction between Zn substrate and metal salt solution under hydrothermal condition without the use of any other reactants or additives. Zn substrate functions as not only the reducing agent, but also the source of ZnO to simplify the recipes and facilitate the synthetic procedures. Among M/ZnO heterostructured films, due to their matching degree of phase and cell parameters, two kinds can be prepared, including Cu/ZnO and Co/ZnO heterostructures with metal nanoparticles (e.g. Cu and Co) anchored on ZnO nanorods and Cd/ZnO heterostructures assembled by Cd nanorod core and ZnO nanorod branches. A pine tree-like Cu/ZnO heterostructured film is chosen as a representative to demonstrate the facility and effectiveness of the strategy, which exhibits higher photocatalytic efficiency towards visible light irradiation than bare ZnO nanospindles. The enhanced photocatalytic activities may be mainly attributed to the surface plasmon absorption of Cu nanoparticles in the visible region, which increases the optical absorption of the Cu/ZnO heterostructures and promotes the transfer of photo-induced electrons from Cu nanoparticles into ZnO nanorods. This general method can be further explored to guide the design of metal/metal oxide heterostructured films on other substrates, such as Cu, Ni and Ti foils.

Sequential precipitation induced interdiffusion: A general strategy to synthesize microtubular materials for high performance lithium-ion battery electrodes

1D hollow structures are of great interest for wide applications, owing much to their kinetic transport advantages, but their facile synthesis through rational design remains a key challenge. In this work, we report for the first time a sequential precipitation induced interdiffusion strategy to synthesize a series of tubular electrode materials by the lithium impregnation and annealing of tube-like oxalate precursors. Different from conventional Ostwald ripening-induced mass migration within a single component, here the sequential precipitation is designed to promote non-equilibrium interdiffusion between different components, thus hollowing out the core. We show the wide scope of this strategy by rationally designing hollow electrode materials of multi-metal oxides. In particular, the syntheses of the most promising high energy cathode materials, Ni-rich LiNi0.8Co0.1Mn0.1O2 and Li-rich Li1.2Ni0.13Co0.13Mn0.54O2 microtubes, have been demonstrated, which deliver excellent electrochemical performance in terms of the initial coulombic efficiency, reversible capacity, rate capability and cycling stability.

ZnMn2O4 nanorods: an effective Fenton-like heterogeneous catalyst with t2g3eg1 electronic configuration

Fenton-like catalysis is promising in the treatment of organic-containing wastewater owing to easy separation of solid catalysts, wide working pH range, and high efficiency. Although α-Mn2O3 with Mn3+ in t2g3eg1 electronic configuration displays high activity in photocatalytic oxidation of water, it is not preferred as a Fenton-like catalyst due to its low phase-transition temperature. Herein, we developed a Fenton-like catalyst with both high activity and stability. Two catalysts, namely, spinel ZnMn2O4 and ZnMnO3 nanorods were synthesized by a facile co-precipitation method. Experimental results indicate that the two Mn-containing catalysts have similar rod-like morphology, but with different crystallographic structures and oxidation states of Mn. DFT calculations suggest t2g3eg1 electron configuration of Mn in ZnMn2O4 with strong Jahn–Teller distortion of MnO6 units. ZnMn2O4 nanorod Fenton-like catalyst displays high activity in the degradation of methyl violet with a degradation ratio of 100% at 120 min and a TOC removal rate near 90% after 240 min. ˙OH and ˙OOH/˙O2− reactive radicals generated in the catalytic system were studied by EPR spectroscopy. The ZnMn2O4 nanorods exhibited much better catalytic performance than ZnMnO3 nanorods. The t2g3eg1 configuration of Mn in spinel ZnMn2O4, facilitating the dissociation of various oxygen-containing radicals through strong JT distortion, is responsible for its higher catalytic activity.