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

Abstract

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 °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 μmol g_cat⁻¹, respectively, under UVA (8 W, 63 μW 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.