Chunhe Li

Study of the enhanced visible-light-sensitive photocatalytic activity of Cr2O3-loaded titanate nanosheets for Cr(VI) degradation and H2 generation

Visible-light-sensitive titanate nanosheets (TNSs) were synthesized with Cr2O3 successfully loaded and well dispersed on Cr(III)-TNSs by a one-step hydrothermal method for enhanced photocatalytic activity. As in our previous reports, the as-prepared samples clearly exhibited a porous flake-like structure with a large specific surface area (300–400 m2 g−1). Accompanied with the hydrothermal growth of the TNSs, the loaded Cr2O3 not only influenced the layered structure of the TNSs, but also brought about a remarkable enhancement of the visible-light response and the separation of photogenerated carriers. The XPS fitting results indicated that the Cr ions mainly existed in the trivalent form and caused a change in the binding states towards Ti and O. Based on the evaluation of the photocatalytic activity, it was found that the Cr(III)-TNSs obtained a significant improvement for RhB and K2Cr2O7 (Cr(VI)) degradation under visible-light irradiation, which was attributed to retarding the charge recombination and the effective electron transfer from Cr2O3 to TNSs. The better photocatalytic activity was obtained with an optimal content (0.5 at%) of Cr3+, and the degradation rate (Kapp) was 2.9-fold and 4.1-fold, respectively, as compared to TNSs. The samples were also evaluated in photocatalytic H2 generation with the photodeposition of Pt nanoparticles as cocatalysts. The results showed that the visible-light H2 production rate of Pt0.25/Cr(III)-TNSs (0.25 wt% of Pt) was observably enhanced under the efficient sacrificial agent/water system, giving a relatively high H2 generation rate of 473 μmol h−1 g−1 at 0.5 at% of Cr3+ content. The cyclic tests demonstrated the good stability and recycling performance of the samples. Alternative mechanisms for the visible-light-sensitive photocatalytic activity were also proposed.

A surfactant-free solvothermal synthesis of Cu2O microcrystals and their photocatalytic activity

The Cu2O octahedral microcrystals have been successfully fabricated by a surfactant-free solvothermal approach. The morphology and structure of the as-prepared sample were characterized by scanning electron microscopy, X-ray powder diffraction and UV-Vis spectroscopy. It was found that the structure and morphology of Cu2O microcrystals were strongly affected by synthesis time and temperature. Based on the time-dependent experiment, the possible formation mechanism of Cu2O octahedral microcrystals was proposed. The photocatalytic activities of as-prepared Cu2O samples were also evaluated for degradation of methyl orange under visible-light irradiation. The results showed that the Cu2O synthesized at 180 °C for 4 h had a better photocatalytic performance due to its high percentage of exposed (111) crystal facet and the lowest band gap energy.

Enhanced photoelectrochemical and photocatalytic activities of CdS nanowires by surface modification with MoS 2 nanosheets

Nanocomposites composed of one-dimensional (1D) CdS nanowires (NWs) and 1T-MoS2 nanosheets have been fabricated through a two-step solvothermal process. 5 mol% of MoS2 loading results in the best optical properties, photoelectrochemical (PEC) as well as photocatalytic activities for hydrogen evolution reaction (HER). Compared with pure CdS NWs, the optimized nanocomposite shows 5.5 times enhancement in photocurrent and 86.3 times increase for HER in the presence of glucose and lactic acid as hole scavengers. The enhanced PEC and HER activities are attributed to the intimate contact between MoS2 and CdS that efficiently enhances charge carrier separation. In addition, ultrafast transient absorption (TA) measurements have been used to probe the charge carrier dynamics and gain deeper insight into the mechanism behind the enhanced PEC and photocatalytic performance.摘要本论文通过两步水热法合成了MoS2纳米片/CdS纳米线复合光催化剂. 采用扫描电子显微镜、透射电子显微镜、X射线粉末衍射仪、拉曼光谱仪、X射线光电子能谱仪、比表面积分析仪、紫外可见漫反射光谱仪、荧光光谱方法和光电化学测试对复合光催化剂进行了表征. 研究表明复合光催化剂的性能和MoS2负载量的多少密切相关. 当MoS2的负载量为5 mol%时复合光催化剂具有最优的光学、光电化学和光催化产氢活性. 与纯的CdS纳米线相比, 优化后的复合光催化剂以葡萄糖和乳酸为空穴牺牲剂, 光电流提高了5.5倍, 光催化产氢活性提高了74倍, 这主要归因于MoS2纳米片和CdS纳米线之间的紧密接触有利于提高电荷的分离效率. 为了进一步理解光电化学和光催化活性提高的机理, 采用瞬态吸收光谱仪深入探究了电荷分离和转移的动力学过程. 该工作不仅涉及了具有优良光电化学和光催化活性的复合光催化剂的制备方法, 而且展示了葡萄糖在光解水产氢中的应用.

Controllable preparation and catalytic performance of Pt/metal oxide nanocomposites for glycerol hydrogenation

Abstract A surfactant-free and facile one-pot synthetic route in the alkaline glycol system has been developed for the fabrication of Pt/metal oxide nanocomposites. The structure and chemical composition of the as-prepared products were characterised by X-ray diffraction (XRD), transmission electron microscopy (TEM) and inductively coupled plasma-mass spectrometry (ICP-MS). It is found that the corresponding precursors have been completely converted into the Pt/metal oxide nanocomposites. As for Pt/ZnO nanocomposites, the Pt loading amount can be controlled by the different molar ratios of Pt and Zinc precursor, while Pt nanoparticle sizes can be adjusted through the different mass of NaHCO3 added. In addition, the catalytic activities of Pt/metal oxide nanocomposites for glycerol hydrogenation were also studied. When the amount of platinum metal was kept constant, different metal oxide supporters demonstrated different levels of catalytic activation. The diverse reason of the catalytic activation for the different Pt/metal oxide nanocomposites was also speculated.