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 (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 mu mol center dot g(cat)(-1)center dot 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.