Visible Light Photocatalysis of TiO<sub>2</sub> Complexed with Albumin via a Ligand-to-Metal Charge Transfer (LMCT) Pathway
Min Sun Kim, Han Yi Yoo, Ga Eun Choi, Sihyeon Jo, Hyeyoung Shin, Jonghun Lim
Abstract
A variety of adsorbates have been combined with TiO 2 to form surface complexes that enable the absorption of visible light through a ligand-to-metal charge transfer (LMCT) process. However, proteins have not been investigated as a complex ligand for the LMCT sensitization of TiO 2 . In this study, we employed albumin as a model protein and investigated an albumin/TiO 2 LMCT complex for visible light photocatalysis. We confirmed the surface adsorption of albumin on TiO 2 using various analytical methods such as Fourier transform infrared (FTIR) spectroscopy, zeta-potential analysis, X-ray photoelectron spectroscopy (XPS), and electron energy-loss spectroscopy (EELS). The LMCT process occurs between the highest occupied molecular orbital (HOMO) level of albumin to the conduction band of TiO 2 . The surface complex of albumin and TiO 2 induced significant reductive conversion of Cr(VI) to Cr(III) and production of H 2 O 2 from O 2 reduction under visible light irradiation (λ > 420 nm). In contrast, surface fluorination of TiO 2 (F-TiO 2 ) hindered the complex formation with albumin, which markedly decreased the visible light reactivity. We also confirmed that reaction parameters such as the mass ratio of albumin to TiO 2, irradiation wavelengths, initial pH, and temperature considerably influenced the activity of the albumin/TiO 2 complex.