Synergistic degradation of chlorobenzene using intimate coupling of visible-light responsive TiO2/oxygenous groups decorated g-C3N4 composites and Ralstonia sp. XZW-1

The effective and economic treatment of chlorobenzenes has become one of the most intractable issues in the field of air pollution control. Herein, a visible-light photocatalysis coupled with biodegradation (VPCB) system was developed by integrating an innovative visible-light responsive TiO2/oxygenous groups decorated g-C3N4 (TiO2/OCN) with polyurethane carriers immobilized with Ralstonia sp. XZW-1 for chlorobenzene removal. Performance tests showed that light intensity, preparation of the MICs, catalyst dosage and composition of the TiO2/OCN cast significant influence on chlorobenzene removal efficiency, with the degradation efficiency, mineralization and dechlorination ratios of VPCB achieving 100%, 35.5%, and 99.4% under the optimal conditions, respectively, outcompeting the sum of visible-light photocatalytic system and biodegradation protocols. Cycling tests further demonstrated the excellent stability of VPCB. Mechanism analysis found that increased reactive sites, improved visible-light harvesting, accelerated charge transfer and separation, and the resulting abundant active species jointly contributed to the enhanced photocatalytic activity of TiO2/OCN. Photogenerated holes were most significant active species for chlorobenzene removal, followed by OH and O2− radicals. The carriers could effectively protect microorganisms from light illumination and strong oxidizing species, allowing the further microbial metabolism of chlorobenzene photocatalytic oxidation intermediates with good biodegradability, not only greatly promoting the microbial growth and activity, but further enhancing chlorobenzene photocatalytic degradation. Plausible synergistic mechanism for chlorobenzene degradation between photocatalysis and biodegradation was also revealed. Furthermore, the VPCB system constructed presented wide applicability towards various pollutants, and its performance was found closely related with the hydrophobicity of pollutants. This work provided insight into the design and application of the VPCB system for the efficient and economic treatment of refractory pollutants.