Improving removal of 4-chlorophenol using a TiO₂ photocatalytic system with microwave and ultraviolet radiation

A conventional photocatalytic system is a viable tool to purify wastewaters, whereas poor degradation performance due to diverse pollutants under various conditions still leaves it behind commercial markets. This study aimed to determine the degradation efficiency and mechanism of 4-chlorophenol in a hybrid system integrating a series of unit processes such as a conventional TiO₂ photocatalytic reactor as well as microwave and ultraviolet (UV) radiation. The decomposition (rate) of 4-chlorophenol was assessed with respect to the microwave intensity, pH, circulating fluid velocity, hydrogen peroxide level, and oxygen gas injection, along with a mix of individual processes. Results showed that there were favorable conditions for improving the degradation performance within certain limits. However, a significant synergy effect was also observed in the combined processes, which was substantially larger than any single process. Out of them, the best degradation performance was achieved using microwave irradiation and hydrogen peroxide in the photocatalytic reactor. The four intermediates (i.e., benzoquinone, hydroquinone, 4-chlorocatechol, and hydroxyhydroquinone) appeared to be generated through hydroxyl radicals-mediated hydroxylation and dechlorination in the proposed photocatalytic pathway. The present research is expected to provide new insights into designing the high performance photocatalytic system with affordable cost.