TiO2/Saponite composite catalyst for ultraviolet photocatalytic ozonation of coal chemical wastewater

Abstract

In ultraviolet photocatalytic ozonation (UV-PCO 3 ) systems, the limited ozone adsorption capability of conventional catalysts restricts the synergistic coupling between catalytic ozonation and photocatalysis. In this study, a TiO 2 /saponite (TiO 2 /Sap) composite catalyst was synthesized and applied to the UV-PCO 3 treatment of coal chemical wastewater (CCW). The TiO 2 /Sap catalyst achieved 82.34% COD removal within 20 min in the UV-PCO 3 system, which was higher than the sum of the COD removal efficiencies of UV photocatalysis (3.68%) and catalytic ozonation (67.98%), demonstrating a synergistic effect between the two processes. The preparation parameters were optimized through single-factor experiments and response surface methodology (RSM), and the experimentally verified optimal conditions were determined as a calcination temperature of 520 °C, a calcination time of 3 h, and a tetrabutyl titanate content of 40%. Under these conditions, the COD removal efficiency reached 83.59%. Furthermore, the TiO 2 /Sap catalyst exhibited favorable stability, maintaining a COD removal efficiency of 79.83% after five consecutive cycles. Radical quenching experiments and EPR revealed that ·OH was the dominant reactive species, accompanied by the generation of 1 O 2 and ·O 2 − . DFT calculations demonstrated that Si sites on the Sap (001) surface provided strong ozone adsorption sites with an adsorption energy of −2.76 eV, whereas TiO 2 functioned as the active component facilitating ozone activation. Overall, Sap promoted ozone enrichment and TiO 2 acted as the active component for ozone activation and photocatalytic oxidation. This study provides an effective strategy for constructing highly efficient photocatalytic ozonation catalysts by integrating ozone enrichment and catalytic activation functions.