Enhancing the photocatalytic activity of defective titania for carbon dioxide photoreduction via surface functionalization

Abstract

The hydrophilic surface of defective titanium dioxide lowers its adsorption capacity towards CO₂ molecules. To get rid of this drawback, we conducted surface functionalization of defective titania with ammonium fluoride in order to acquire hydrophobicity and increase the adsorption capacity for CO₂ molecules. Besides, the surface Ti–F bonds and substitution of excess bulk oxygen vacancies with F ions formed upon the fluorination treatment of defective TiO₂ jointly function to promote the separation of photoinduced carriers, and the Ti³⁺–F species formed upon surface functionalization from the surface fluoride and bulk Ti³⁺ can form a self-built electric field to allow the Ti³⁺ impurity energy level to move upward and improve the reduction ability of photogenerated electrons. Compared with unmodified defective TiO₂, the generation rates of CH₄ and CO of the optimized F-TiO₂-SBO-3 increased more than 6 and 2 times, respectively. Moreover, corresponding DFT calculations give evidence of the improvement in the photocatalytic activity of fluorinated defective TiO₂ photocatalysts; and relevant in situ DRIFTS data provide insights into the increased selectivity of the fluorinated defective titania for CH₄ production upon CO₂ photoreduction. This approach could be helpful for better understanding the mechanism of the CO₂ photocatalytic reaction and for establishing a feasible pathway to acquire highly efficient photocatalysts for CO₂ photoreduction.