Ultrasound-Assisted Synthesis of Nonmetal-Doped Titanium Dioxide Photocatalysts for Simultaneous H2 Production and Chemical Oxygen Demand Removal from Industrial Wastewater.

Abstract

A series of nonmetal-doped titanium dioxide (Nmx/TiO2, where x is the weight fraction of nonmetal elements) photocatalysts was prepared via ultrasonic-assisted impregnation for simultaneous hydrogen (H2) production and chemical oxygen demand (COD) removal from industrial wastewater. Three types of Nm elements, carbon (C), silicon (Si), and phosphorus (P), were explored. The P1/TiO2 exhibited a higher photocatalytic activity for H2 production and COD removal than the C1/TiO2 and Si1/TiO2 photocatalysts. Approximately 6.43 mmol/g photocatalyst of H2 was produced, and around 26% COD removal was achieved at a P1/TiO2 loading of 4.0 g/L, a light intensity of 5.93 mW/cm2, and a radiation time of 4 h. This is because the P1/TiO2 photocatalyst exhibited lower point of zero charge values and a more appropriate band position compared with other Nmx/TiO2 photocatalysts to produce H+, which can consequently form H2, and reactive oxygen species (HO· and O2·–), which serve as oxidizing agents to degrade the organic pollutants. Increasing the content of the P element doped into the TiO2-based material up to 7.0% by weight enhanced the H2 production and COD removal up to 8.34 mmol/g photocatalyst and 50.6%, respectively. This is attributed to the combined effect of the point of zero charge value and the SBET of the prepared photocatalysts. The photocatalytic activity of the P7/TiO2 photocatalyst was still higher than the TiO2-based material after the fourth use.