Mechanistic insights into complete oxidation of chlorobenzene to CO2 via wet scrubber coupled with UV/PDS

Chlorobenzene is a typical chlorinated volatile organic compound (CVOC), and the degradation of chlorobenzene frequently produces high-toxic byproducts such as dioxins in the treatment process. To prevent this, complete oxidation of chlorobenzene into harmless CO2 is highly desirable. Wet scrubber coupled with advanced oxidation processes (AOPs) for gaseous VOCs treatment has been widely reported, but their mineralization capacity and mechanism are still poorly understood. Herein, this study developed an efficient technology for chlorobenzene oxidation via wet scrubbing process coupled with UV/peroxydisulfate (PDS), with UV/H2O2 as comparison. The mineralization efficiency of chlorobenzene was much higher in UV/PDS (75.4%) than that in UV/H2O2 (42.0%), although the removal efficiencies in both AOPs were similar at 90-97%. Sulfate radical (SO4 center dot-) was predominant for the initial oxidation of chlorobenzene, forming the intermediates that were favorable for the mineralization process. Then, O-2 and HO center dot played important roles on the formation of CO2 in the complete oxidation of chlorobenzene in UV/PDS. The role of O-2 was further comfirmed by the result that high toxic dimeric products, rather than CO2, were generated in UV/PDS in the absence of O-2. The possible pathway on chlorobenzene oxidation was proposed based on the evolution of intermediates and Density Functional Theory (DFT) calculation. Carbon cation radical was formed from the initial oxidation of chlorobenzene by SO4 center dot-, followed by the ring-opening and more CO2 yields via the synergetic effect of SO4 center dot-, O-2 and HO center dot. This study not only provides an environment-friendly method to improve the VOC removal efficiency, but also gets a deep understanding of the different functions of SO4 center dot-, HO center dot and O-2 on the mineralization process.