Photocatalytic reduction of CO2 with H2O to CH4 on Cu(I) supported TiO2 nanosheets with defective {001} facets

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 (V-o) on the surface of the TiO2 nanosheets. Interestingly, the co-existence of V-o and Cu2O clusters could promote the photoactivity of CO2 reduction efficiently. The surface V-o 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 V-o. 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.