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

The synthesis of photocatalysts with good activity and strong product selectivity is of strategic importance for photocatalytic reduction of carbon dioxide (CO 2 ). In this study, an improved sol-gel method was employed for the synthesis of N-doped TiO 2 , Eu-doped TiO 2 , and N, Eu co-doped TiO 2 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 CO 2 reduction indicated that both N and Eu doping could effectively improve the photoresponse of TiO 2 , but the synergistic effect of N and Eu made the N, Eu co-doped TiO 2 exhibit superior photocatalytic activity and product selectivity, the formation rate of methane (CH 4 ) by photocatalytic reduction of CO 2 using N-Eu/TiO 2 as the catalyst could reach 13.48 μmol·g cat −1 ·h −1 , which was about 12 times higher than that of pure TiO 2 , 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 CO 2 reduction over N-Eu/TiO 2 was elucidated.