Photocatalytic reduction of CO2 using molybdenum-doped titanate nanotubes in a MEA solution

In this study, the photocatalytic reduction of CO2 in a monoethanolamine solution to form valuable energy sources was investigated using Mo-doped TNTs photocatalysts for the first time. The results revealed that the structure of Mo-doped TNTs changed with the increase of calcination temperature. For Mo-doped TNTs calcined at 500 degrees C, the partial corruption of titanate nanotubes into anatase particles caused the reduction of Mo species from Mo6+ to Mo5+ and produced oxygen vacancies, which resulted in the highest CO2 reduction ability. The yield rates of CH4, CO and total combustible organic compounds were 0.52, 10.41 and 13.53 mu mol g(cat)(-1), respectively, under UVA (8 W, 63 mu W cm(-2)) irradiation. The photoreduction quantum efficiencies of CH4 and CO were achieved at 0.036% and 0.180%, respectively. It was found that the molybdenum structure and oxygen vacancies could be the key factors controlling the photocatalytic reduction efficiency of CO2. A possible structure transformation of Mo-doped TNTs at different calcination temperatures was inferred and the reaction mechanism for photocatalytic CO2 reduction with oxygen vacancy sites of Mo-doped TNTs was proposed.