Photocatalytic degradation pathways and adsorption modes of H-acid in TiO2 suspensions

Effect of adsorption mode on photodegradation of H-acid in TiO₂ suspension was studied using DFT calculation, UV-Vis spectroscopy, FTIR, and ionic chromatography. At pH 2.5, H-acid was adsorbed on TiO₂ surfaces by one dissociated sulfonic group. The adsorbed sulfonic group was attacked by surface ·OH, resulting in the production of SO₄ ²⁻ and the cleavage of the naphthalene ring. At pH 5.0, H-acid was adsorbed on TiO₂ surfaces by two sulfonic groups. The two adsorbed sulfonic groups were simultaneously attacked by surface ·OH, leading to a faster initial production of SO₄ ²⁻ and initial degradation rate of H-acid than those under pH 2.5. Microscopic adsorption structures may be more important than adsorption amount in controlling the photodegradation pathways of organic pollutants.