Enhanced photocatalytic decomposition of 4-nonylphenol by surface-organografted TiO2: a combination of molecular selective adsorption and photocatalysis

n-Octyl-grafted TiO₂ (C8-TiO₂) was prepared as a model of a photocatalyst with high molecular adsorption selectivity, and its photocatalytic activity for the decomposition of dilute 4-nonylphenol (an endocrine disrupter, ca. 2 ppm) in water was investigated. The catalyst was highly active in the presence of concentrated phenol (1000 ppm), and the 4-nonylphenol was decomposed in 180 min, while pristine TiO₂ (P-25) under the same conditions showed much lower activity. The high C8-TiO₂ activity was ascribed to the molecular selective adsorption of the organic molecules on the alkyl-grafted hydrophobic surface. Infrared spectra showed that the grafted alkyl groups were gradually decomposed under photoirradiation. The model catalyst demonstrated that molecular selective adsorption is important for removal of low-concentration contaminants in the presence of other, more concentrated compounds.