Spectroelectrochemical determination of the conduction band level of mesoporous titanium dioxide semiconductor in diverse reaction media

Abstract

The conduction band edge (E_CB) energy levels of a mesoporous TiO₂ film were investigated in aprotic dimethylformamide (DMF) and aqueous media to explore the influence of various proton additives and electron donors. Spectroelectrolysis (SE) technique was employed to measure the E_CB in non-aqueous solvents, revealing a significantly negative E_CB in dry non-aqueous solvents compared to values obtained in aqueous solvents. In non-aqueous DMF, the E_CB of TiO₂ was found to be highly dependent on the proton-donating additive due to the establishment of a proton adsorption–desorption equilibrium, reaching –(1.42–1.94) V versus SCE. The introduction of a well-known electron donor, 1,3-dimethyl-2-phenyl-1,3-dihydrobenzimidazole (BIH) led to a slight positive shift in the TiO₂ E_CB, indicating that the electron donor contributes to the to the CB energetics of the mesoporous TiO₂ films. Under aqueous conditions and in the presence of various electron donors (TEA, TEOA, ascorbic acid, EDTA•2Na, and sodium ascorbate), the proton-donating/accepting capacity of the additive significantly influenced the pH of the aqueous solvent, causing changes in the TiO₂ E_CB across the electrolyte solution. This study emphasizes the crucial role of proton additives and electron donors in influencing the CB energetics of mesoporous TiO₂ electrodes and aims to determine the extent to which the E_CB of TiO₂ can shift as a result of the adsorption and intercalation of protons on its surface. The findings obtained herein contribute to the understanding of the energy efficiency of TiO₂-mediated photocatalytic systems in various solvent environments.