Insights into the role of MgAl layered double oxides interlayer in Pt/TiO2 toward photocatalytic CO2 reduction

Abstract

The representative TiO2 loaded with cocatalyst (e.g., Pt) have been used extensively for the photocatalytic CO2 reduction in solar-to-chemical energy conversion. However, it still suffers from low efficiency, due to the weak adsorption/activation of CO2. In this work, an MgAl layered double oxides (MgAl-LDO) was successfully introduced into the interface of Pt/TiO2, by in-situ deposition of MgAl layered double hydroxides and subsequent high temperature calcination. The structure, optical property and the photocatalytic activity for CO2 reduction of as-fabricated Pt/MgAl-LDO/TiO2 were experimentally investigated. Especially, the roles of MgAl-LDO during the CO2 reduction process were highlighted. It concluded MgAl-LDO possessed Lewis acidic and Lewis basic bifunctional roles that enhanced the performance of the photocatalytic CO2 reduction. The optimal yields of CO and CH4 of Pt/MgAl-LDO/TiO2 exhibited ca. 2 and 11 times as high as that of Pt/TiO2, respectively. The adsorption states of CO2 and the adsorbed species in the course of photoreduction of CO2 with H2O vapor on Pt/MgAl-LDO/TiO2 were examined by in-situ infrared spectroscopy. Monodentate carbonate (m-CO32−) and monodentate bicarbonate (m-HCO3−) were found to be the main surface species that adsorbed. In the presence of H2O, m-CO32− species could be readily converted to active m-HCO3− intermediate, which was subsequently transformed into surface CO2−. This was attributed to the fact that MgAl-LDO contains much more strong Lewis basic sits for CO2 adsorption to produce m-CO32− and the Lewis acid sites for the dissociation of H2O into H+ and OH groups. Moreover, photoluminescence spectra further indicated that oxygen vacancy existed in the interface of MgAl-LDO/TiO2, which facilitated the photogenerated charges separation and also contributed to the enhanced photocatalytic performance. As a result, the Lewis acidic-basic characteristics of MgAl-LDO, as well as the improved charges separation, should be responsible for the increased photocatalytic activity of Pt/MgAl-LDO/TiO2 toward CO2 reduction.