EFFECT OF ADSORPTION MODES ON THE PHOTOCATALYTIC DEGRADATION OF ORGANIC MATTERS 2. PHOTOCATALYTIC DEGRADATION PATHWAYSOF H-ACID ON TiO_ 2

H-acid adsorbed onto TiO_ 2 surface by sulphonic groups, which were first attacked by free radicals of OH_ ads followed by the cleavage of the naphthalene rings during the photo-degradation of H-acid on TiO_2 surfaces. At pH 2.5,H-acid adsorbed onto TiO_ 2 surface by one sulphonic group, which lead to a higher adsorption capacity but weaker adsorption bonds.Photo-degradation rates under this condition were therefore slower than at pH 5.0. At pH 5.0, H-acid adsorbed onto TiO_ 2 surface by two sulphonic groups, which had a lower adsorption capacity but stronger adsorption bonds. Photo-degradation rates were therefore faster than at pH 2.5. Different adsorption modes were the fundamental reason why the photocatalytic degradation pathways and degradation rates were different under different pH conditions.