Intimate Coupling Of Photocatalysis And Biodegradation System Based On B-doped G-C₃N₄/BiVO₄ Catalyst For Bromophenol Removal

Due to the teratogenicity,carcinogenicity,mutagenicity and genotoxicity characters of halogenated phenols compounds in chemical processing,conventional biological treatment technology could not effectively degrade toxic contaminants.It is of great significance to develop novel,efficient and green treatment methods for practical application.In this study,4-Bromophenol（4-BP）,which is typical halogenated phenol,is the main target pollutant.The p-n heterojunction composite semiconductor catalyst with g-C₃N₄ and BiVO₄ as the main materials was prepared.Then the photocatalyst was loaded on different carriers to construct intimately coupled photocatalysis and biodegradation（ICPB）system.The research results are as follows:The B doped g-C₃N₄/BiVO₄ have been fabricated by depositing n-type BiVO₄ on the surface of p-type B-doped g-C₃N₄.The results revealed that the photocatalytic activity of p-n heterojunction was greatly enhanced compared with n-type BiVO₄ and p-type B-doped g-C₃N₄.B doped g-C₃N₄/BiVO₄ heterostructure showed the best photocatalytic degradation activity,which was 2.3-fold higher than that of BiVO₄.The scanning electron microscope（SEM）,X-ray diffraction analysis and X-ray photoelectron spectroscopy（XPS）data confirmed the formation of monoclinic and tetragonal mixed phase BiVO₄.The formation of mixed phase BiVO₄ was attributed to the high temperature calcination as well as surface energy of B doped g-C₃N₄.B doped g-C₃N₄/BiVO₄ formed a heterojunction between g-C₃N₄ and BiVO₄to suppress the recombination of photogenerated charge carriers.Ultraviolet diffuse reflection and photocatalytic degradation experiments showed that BVCN composite photocatalyst had enhanced light absorption capacity and excellent photocatalytic effect.The BVCN composite photocatalyst was loaded on three different carriers of carbon paper,graphite felt,and polyurethane,and a intimately coupled photocatalysis and biodegradation system was constructed to enhance the treatment of 4-BP simulated wastewater,exploring the influence of different carriers on the ICPB system.The results showed that when polyurethane was used as the carrier,there was a dense biofilm inside the carrier.Under the synergistic effect of photocatalysis and biology,the removal rate of 4-BP reached 100%,which was compared with that of photocatalysis alone,the degradation rate of 4-BP increased by 50%.And compared with carbon paper and graphite felt,the mineralization efficiency of polyurethane system was51.11%after 24 hours of reaction,while the mineralization efficiency of carbon paper and graphite felt were 13.8%and 31.51%,respectively.Compared the Excitation-Emission-Matrix Spectra of the inlet water and the outlet water of the three systems,it could been seen that the polyurethane carrier system degrads 4-BP most thoroughly.In the system with polyurethane as the carrier,the bromophenol-degrading bacteria（Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium and Pseudomonas）and the bioflocculation bacteria Terrimonas were significantly enriched.Finally,the possible degradation mechanism of 4-BP with B-doped g-C₃N₄/BiVO₄coupled biodegradation system was proposed.Compared with single photodegradation and biological treatment,the ICPB system based on B-doped g-C₃N₄/BiVO₄ exhibites excellent adsorption,degradation and mineralization effects on 4-BP,and has excellent performance in the removal of refractory halogenated phenols compounds.