Chengyan Ge

Engineering the TiO2 -graphene interface to enhance photocatalytic H2 production.

In this work, TiO2 -graphene nanocomposites are synthesized with tunable TiO2 crystal facets ({100}, {101}, and {001} facets) through an anion-assisted method. These three TiO2 -graphene nanocomposites have similar particle sizes and surface areas; the only difference between them is the crystal facet exposed in TiO2 nanocrystals. UV/Vis spectra show that band structures of TiO2 nanocrystals and TiO2 -graphene nanocomposites are dependent on the crystal facets. Time-resolved photoluminescence spectra suggest that the charge-transfer rate between {100} facets and graphene is approximately 1.4 times of that between {001} facets and graphene. Photoelectrochemical measurements also confirm that the charge-separation efficiency between TiO2 and graphene is greatly dependent on the crystal facets. X-ray photoelectron spectroscopy reveals that Ti-C bonds are formed between {100} facets and graphene, while {101} facets and {001} facets are connected with graphene mainly through Ti-O-C bonds. With Ti-C bonds between TiO2 and graphene, TiO2 -100-G shows the fastest charge-transfer rate, leading to higher activity in photocatalytic H2 production from methanol solution. TiO2 -101-G with more reductive electrons and medium interfacial charge-transfer rate also shows good H2 evolution rate. As a result of its disadvantageous electronic structure and interfacial connections, TiO2 -001-G shows the lowest H2 evolution rate. These results suggest that engineering the structures of the TiO2 -graphene interface can be an effective strategy to achieve excellent photocatalytic performances.

Comparative study on the catalytic CO oxidation properties of CuO/CeO2 catalysts prepared by solid state and wet impregnation

A series of CuO/CeO2 catalysts were prepared by solid state impregnation (SSI) and wet impregnation (WI) methods and characterized by X-ray diffraction, H2 temperature-programmed reduction (H2-TPR), laser Raman spectroscopy (LRS), in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), and X-ray photoelectron spectroscopy (XPS). XPS and H2-TPR results showed that SSI increased the dispersion of the copper species on the catalyst surface, which benefited the reduction of CuO species. LRS results indicated that a higher concentration of oxygen vacancies was obtained by the SSI method unlike the WI method. CO oxidation results showed that at a given CuO loading, the activity of the catalysts prepared by SSI was higher than that of their counterparts prepared by WI. Based on the combined characterization results, it was suggested that the enhanced activity was closely related to the higher concentrations of oxygen vacancies and Cu+-CO species on the catalysts. Last, a possible synergetic mechanism was proposed for CO oxidation over the CuO/CeO2 catalysts.

Engineering the NiO/CeO2 interface to enhance the catalytic performance for CO oxidation

In this work, NiO/CeO2 catalysts were synthesized with tunable CeO2 crystal facets ({110}, {111} and {100} facets) to study the crystal-plane effects on the catalytic properties. Kinetic studies of CO oxidation showed that NiO/CeO2 {110} had the lowest activation energy. Furthermore, the obtained samples were characterized by means of TEM, XRD, Raman, N2-physisorption, UV-Vis DRS, XPS, H2-TPR and in situ DRIFTS technologies. The results demonstrated that the geometric and electronic structures of the nickel species were dependent on the NiO/CeO2 interfaces, which had an influence on the synergetic interaction of absorbed CO and active oxygen species, and then the generation of the formate intermediate played an important role in the catalytic performance. The possible interface structures of nickel species on the CeO2 {110}, {111} and {100} surface were proposed through the incorporation model, suggesting that the advantageous NiO/CeO2 {110} interface facilitated CO adsorption/activation and active oxygen species formation, leading to the best catalytic performance.

Treatment induced remarkable enhancement of low-temperature activity and selectivity of copper-based catalysts for NO reduction

The poor low-temperature (200–300 °C) activity and N2 selectivity of Cu-based catalysts for NO reduction by CO has driven us to further advance this process. The present work offers a simple but very promising strategy to achieve this goal by CO pre-treatment of the binary CuM/γ-Al2O3 (M = V, Mn, Fe, Co, Ni, Zn) catalysts to tailor the surface active sites. The results demonstrate that CO pre-treatment significantly enhanced the low temperature NO conversion and N2 selectivity of CuM/γ-Al2O3, depending on the type of metal oxides. Among these catalysts, CO pre-treated CuNi/γ-Al2O3 exhibited the highest activity/selectivity (i.e., about 90% at 200 °C) and excellent stability. The activity improvement resulted from the following: 1) the obtainment of oxygen vacancies and more Cu+ species with the suitable ratio of dispersed Cu2+/Cu+, 2) the decrease of apparent activation energy for NO conversion and 3) the more favourable activation and dissociation of NO on the reduced surface, as evidenced by X-ray photoelectron spectroscopy (XPS) and in situ Fourier transform infrared (FTIR) spectroscopy results.

Retracted article: Synthesis of Pt@TiO2@MnOx hollow spheres with high spatial charge separation efficiency for photocatalytic overall water splitting

We, the named authors, hereby wholly retract this Journal of Materials Chemistry A article due to the subsequent realisation that the O2 evolution rates reported and summarised in Fig. 5 cannot be repeated in the Valencia labs. However, the H2 evolution rates can still be reproduced. Because the oxidation products are mainly radicals or H2O2, we do not observe much O2 evolved. In addition, we also find that the O2 evolution rates seem to be related to the activity test equipment (the Hg lamp we used and the additives in H2O). Signed: Lichen Liu, Weixin Zou, Xianrui Gu, Chengyan Ge, Yu Deng, Changjin Tang, Fei Gao, Lin Dong and Avelino Corma, February 2014. Retraction endorsed by Liz Dunn, Managing Editor, Journal of Materials Chemistry A. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.