Spontaneous oxidation of arsenite on platinized TiO2 through activating molecular oxygen under ambient aqueous condition

Abstract

The pre-oxidation of As(III) is essential for effective removal of arsenic in contaminated water. Although diverse arsenic oxidation methods have been developed, most require the input of chemical oxidants and external energy (e.g., electricity, photon energy). This study investigated the spontaneous catalytic oxidation of As(III) over Pt nanoparticles loaded on TiO2 under ambient aqueous conditions (i.e., air-saturated and room temperature). The proposed catalytic process requires dissolved O2 only as an oxidant, instead of chemical oxidants and energy input, where electrons spontaneously transfer from As(III) to O2 on the Pt–TiO2 catalyst. The oxidation rate of As(III) was highly dependent on (i) the content of Pt, (ii) the oxidation state of Pt, (iii) the presence of an electron acceptor (e.g., O2 and Fe(III)), (iv) the Pt support (e.g., TiO2, Al2O3, SiO2, etc.), and (v) the hetero-junction between Pt and TiO2. In this catalytic system, zero-valent Pt was confirmed as an active species for As(III) oxidation, and TiO2 acted as not only a support for the dispersion of Pt nanoparticles but also as an activator of in situ-generated H2O2 that is utilized in As(III) oxidation. Although Pt is expensive, the operation of Pt–TiO2 at room temperature without needing additional energy and chemical inputs, along with its high durability, can compensate for the high material cost. Therefore, the method presented here represents a viable treatment option for the pre-treatment of As(III)-contaminated water.