Photochemical pollutant degradation on facet junction-engineered TiO2 promoted by organic arsenical: Governing roles of arsenic-terminated surface chemistry and bulk-free radical speciation

Photochemical oxidation based on semiconducting metal oxides is an efficient strategy to remove environmental pollutants in water, air and soil. The fine manipulation of photo-carriers separation, surface chemistry and radical speciation is of considerable interest for environmental remediation. In this work, the morphology- and structure-tailored TiO2 single crystals with epitaxial {101}/{001} facet junction were designed, prepared and tested for photochemical pollutant oxidation in the presence of organic arsenicals, the main component in swine wastewater from livestock industry, although they have been forbidden for several years. The facet junction-tailored TiO2 deserved an efficient photo-carriers separation with high quantum efficiency. The photochemical oxidation of 4-chlorophenol (4-CP), phenol and bisphenol A (BPA) was substantially improved by roxarsone (ROX). ROX-enhanced photochemical activity of TiO2 was mainly attributed to the in-situ arsenic-terminated surface chemistry by Ti-(OAsO3)-O-V/-(OAsO2)-O-III. This surface played governing roles in water/TiO2 interactions, and changed water adsorption from dissociative to molecular configuration. Furthermore, center dot OH was finely regulated from low-activity surface-bound to high-activity bulk-free speciation between as-generated photoholes with free water molecules. Our findings provided a new chance to refine the TiO2-based photochemical oxidation, and a modifying technology to treat swine wastewater from livestock industry with much reduced secondary pollution.