Fabrication of self-organized TiO2 nanotube arrays for photocatalytic reduction of CO2

Abstract

The photocatalytic conversion of CO2 and H2O to alcohols was achieved using self-organized TiO2 nanotube arrays (TNAs), which were prepared by electrochemical anodization of Ti foils in 1 M (NH4)2SO4 electrolyte containing 0.5 wt% NH4F. Experimental results revealed that the morphology and structure of self-organized TNAs could be strongly influenced by the applied voltage and anodization temperature, and the optimized TNAs were prepared by electrochemical anodization of Ti foils under optimal conditions (i.e., at 20 V for 2 h at 30 °C). The as-prepared TNAs were amorphous and could be transformed to anatase phase during the thermal treatment at 450 °C in air for 3 h. By using the annealed TNAs as a photocatalyst, the photocatalytic reduction of CO2 to alcohol, predominately methanol and ethanol, was demonstrated under Xenon lamp illumination. Based on the photocatalytic measurements, the production rates of methanol and ethanol were calculated to be ∼10 and ∼9 nmol cm−2 h−1, respectively. In addition, the formation mechanism of methanol and ethanol was also tentatively proposed.