Abstract

Arsenic water pollution is a serious global environmental issue because of the high toxicity of this chemical element. Hence, the development of versatile materials that can efficiently remove different arsenic species from water is a global challenge. In this study, the bi-functionality of anatase TiO2 nanostructures (nanoparticles (TNP) and nanotubes (TNT)) for the simultaneous photo-oxidation of As(III) to As(V) and adsorption of the generated As(V) was evaluated, and the effect of morphology on the photo-oxidation and adsorption behaviors of the nanomaterials at different pH conditions was determined. In the dark, both the photocatalysts exhibited a remarkably high As(III) adsorption capacity in alkaline conditions because of the high hydroxylation of the nanomaterial surfaces at a basic pH. Upon irradiation, the As(III) ions completely oxidized into As(V) ions in a short time by the TNT and TNP samples at different initial pHs. However, compared with TNP, TNT exhibited a remarkably enhanced photoactivity because of their one-dimensional nanotubular morphology that facilitates the transfer of the photogenerated electron-hole to the surface, improving the hydroxyl radicals photogeneration. Moreover, post-reaction XPS analysis revealed that the As(III) ions adsorbed on TNP under dark conditions completely oxidized into As(V) upon irradiation. As evidenced by the experimental results, TNP exhibited excellent bi-functionality for arsenic removal since the As(V) ions generated by As(III) oxidation both on the material surface and in the aqueous medium were simultaneously adsorbed on the nanoparticle surface. Thus, a better understanding of the morphological effect on the photocatalytic system for oxidizing As(III) and adsorbing As(V) at different pHs was presented and mechanisms are proposed. The study provides guidance for the development of bi-functional nanoparticles through morphological design and surface engineering.