Characteristics and performance of rutile/anatase/brookite TiO2 and TiO2–Ti2O3(H2O)2(C2O4)·H2O multiphase mixed crystal for the catalytic degradation of emerging contaminants

Abstract

Rutile TiO₂ and binary/ternary/quaternary the TiO₂–Ti₂O₃(H₂O)₂(C₂O₄)·H₂O mixed crystal possessing self-assembled morphology and serving as catalysts for the photocatalytic degradation of organic pollutants or as photoanodes for photoelectrochemical (PEC) water splitting have been prepared by in situ growth via changing the concentration of potassium titanyl oxalate. The rutile/anatase TiO₂ with mesoporous structure has a specific surface area of 27.896 m² g⁻¹ and an average pore size of 3.411 nm. The sample has a relatively more regular self-assembly morphology after heat-treatment at different temperatures; however, its photocatalytic activity is reduced. Excellent catalytic oxidation of methyl orange (MO) and hydroxylbenzoic acid (HBA) is observed on the as-synthesized samples, wherein rutile/anatase TiO₂ and rutile/anatase/brookite TiO₂–Ti₂O₃(H₂O)₂(C₂O₄)·H₂O show excellent photocatalytic activity under UV-light. With the novel TiO₂–Ti₂O₃(H₂O)₂(C₂O₄)·H₂O mixed crystal catalyst, this study illustrates the photocatalysis mechanism of a multiphase mixed crystal for the removal of emerging contaminants in water. Based on the Mott–Schottky, XPS and energy band structure data, we consider that an indirect Z-scheme transmission mode is generated between rutile/anatase TiO₂ or TiO₂–Ti₂O₃(H₂O)₂(C₂O₄)·H₂O mixed crystal, wherein the photo-induced electrons in rutile TiO₂ combined with the holes in anatase TiO₂ or Ti₂O₃(H₂O)₂(C₂O₄)·H₂O, leading to enhanced charge carrier extraction and utilization upon photoexcitation.