Highly dispersed Cu2O clusters loaded on TiO2 nanosheets with dominant exposed {001} facets are prepared by a hydrothermal treatment followed by photodeposition. The physicochemical properties of the as-prepared samples are characterized carefully. The deposition position and chemical state of the Cu2O clusters are characterized by X-ray diffraction, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, EPR spectroscopy, and in situ CO-adsorbed FTIR spectroscopy, respectively. The results show that in situ Cu deposition leads to in situ formation of abundant oxygen vacancies (Vo) on the surface of the TiO2 nanosheets. Interestingly, the co-existence of Vo and Cu2O clusters could promote the photoactivity of CO2 reduction efficiently. The surface Vo play a significant role in the reduction of CO2. Meanwhile, the deposited Cu(I) species serve also as active sites for the formation of CH4, and then protect CH4 from degradation by generated oxidation species. For the photoreduction of CO2 to CH4, it is found that the content level of Cu2O has a significant influence on the activity. Cu-TiO2-1.0 shows the highest photocatalytic activity, which is over 30 times higher than that of the parent TiO2. This great enhancement of photocatalytic activity may be contributed by high CO2 adsorption capacity, high electron mobility, and high concentration of Vo. However, the effect of the surface area of the samples on the activity is negligible. All of this evidence is obtained by CO2-sorption, electrochemistry, in situ FTIR spectroscopy, in situ ERP techniques, etc. The reaction intermediates are detected by in situ FTIR spectroscopy. Finally, a probable mechanism is proposed based on the experimental results. It is hoped that our work could render one of the most effective strategies to achieve advanced properties over photofunctional materials for solar energy conversion of CO2.

This paper mainly focuses on the synergistic effect of Sn and N dopants to enhance the photocatalytic performance of anatase TiO2 under visible light or simulated solar light irradiation. The Sn and N co-doped TiO2 (SNT-x) photocatalysts were successfully prepared by the facile sol-gel method and the post-nitridation route in the temperature range of 400-550 °C. All the as-prepared samples were characterized in detail by X-ray diffraction, UV-vis diffuse reflectance spectroscopy, transmission electron microscopy, X-ray photoelectron and electron spin resonance spectroscopy and photoelectrochemical measurements. The characterization results reveal that the co-incorporation of Sn and N atoms remarkably modifies the electronic structure of TiO2, which gives rise to a prominent separation of photogenerated charge carriers and more efficient interfacial charge-transfer reactions in a photocatalytic process. The enhanced photocatalytic activity is attributed to the intensified active oxygen species including hydroxyl radicals (˙OH) and superoxide anion radicals (O2˙(-)) for degradation of organic pollutants. And the result of photocatalytic hydrogen production further confirms the existence of the synergistic effect in the SNT-x samples, because they exhibit higher photocatalytic activity than the sum of N/TiO2 and Sn/TiO2. This work provides a paradigm to consolidate the understanding of the synergistic effect of metal and non-metal co-doped TiO2 in domains of photocatalysis and photoelectrochemistry.

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The C-doped CdO photocatalysts were simply prepared by high-temperature solid-state process. The as-prepared photocatalysts were characterized by X-ray powder diffraction (XRD), diffuse reflectance spectroscopy (UV-Vis DRS), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the carbon was doped into CdO, resulting in the red-shift of the optical absorption of CdO. The photocatalytic behavior of CdO and C-doped CdO was evaluated under the visible light irradiation by using the photocatalytic hydrogen evolution as a model reaction. The C-doped CdO photocatalysts had higher photocatalytic activity over parent CdO under visible light irradiation. The results indicated that the H2production was due to the existence of CdS and the enhancement of visible light photocatalytic activity of H2production was originated from the doping of carbon into the CdO lattice. The probably reaction mechanism was also discussed and proposed.