Water-soluble polymers stabilize defects in a new peroxo-titania: visible light-active y-TiO2 for photocatalytic pollutant degradation and hydrogen production

Abstract

The introduction of defects into photocatalyst materials has attracted current research attention because of the critical role that defects play in enhancing light absorption, charge transfer and interfacial reactions. However, the harsh synthesis conditions and the instability of surface defects in air leads to the loss of the reactive interface sites. Therefore, the sustainable development of stable, defect-rich photocatalysts remains a significant challenge. In this work, we discovered that water-soluble polymeric dispersants stabilize defects in a new peroxo-TiO2 exhibiting four different titanium valence states; Ti4+, Ti3+, Ti2+ and Ti0, which has not yet been reported. The multiple oxidation states of Ti is due to the generation of titanium vacancies in the y-TiO2, resulting in a low band gap of 2.04 eV, high surface area and photocatalytic activity for hydrogen production and pollutant degradation. The calcined y-TiO2 with 1% deposited Pt achieved a remarkably high production (1.65 mmol g-1 h-1) which is nearly 20 times as high as that of the pristine, as-prepared yellow TiO2 (0.082 mmol g-1 h-1) under solar-simulated irradiation. This value far exceeds the hydrogen production of similar defect-rich catalyst materials reported so far when sunlight is used as irradiation source. The y-TiO2 catalyst particles were immobilized onto a plate and into alginate films and beads, which readily adsorbed and degraded methylene blue dye. The plates, films and beads were regenerated multiple times under solar simulation. Thus, this strategy of using water-soluble polymers to synthesize stable defects in photocatalysts offers new insights into solving the issue of defect instability in catalytic materials.