Enhanced photocatalytic reduction of CO2 into CH4 over N, Eu co-doped TiO2: Insight into the synergistic effect of N and Eu

Abstract

The synthesis of photocatalysts with good activity and strong product selectivity is of strategic importance for photocatalytic reduction of carbon dioxide (CO2). In this study, an improved sol-gel method was employed for the synthesis of N-doped TiO2, Eu-doped TiO2, and N, Eu co-doped TiO2 photocatalysts. The phase structures, optical and electrical properties of the catalysts were thoroughly investigated by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller Surface area analysis, Ultraviolet-visible diffuse reflectance spectroscopy, Photoluminescence spectroscopy, and electrochemical measurements. The experimental results of photocatalytic CO2 reduction indicated that both N and Eu doping could effectively improve the photoresponse of TiO2, but the synergistic effect of N and Eu made the N, Eu co-doped TiO2 exhibit superior photocatalytic activity and product selectivity, the formation rate of methane (CH4) by photocatalytic reduction of CO2 using N-Eu/TiO2 as the catalyst could reach 13.48 μmol·gcat−1·h−1, which was about 12 times higher than that of pure TiO2, and the selectivity reached nearly 100%. Finally, this synergistic effect was explained using DFT calculation and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and the possible mechanism of photocatalytic CO2 reduction over N-Eu/TiO2 was elucidated.