Modification Of Bi-rich Bismuth Oxyiodide For Photocatalytic Degradation Of Rhodamine B

Dye wastewater was widely concerned due to its large discharge,deep chroma,and poor biodegradability.Photocatalytic technology is considered to be one of the most effective methods for treating dye wastewater because it directly uses solar energy to eliminate harmful pollutants without causing secondary pollution.As a new type of photocatalytic material developed in recent years,bismuth-based semiconductors have been widely used in water purification.In this paper,three composite photocatalytic materials,Bi₄O₅I₂/Ag₃PO₄,Bi₅O₇I/Ag₃PO₄ and Bi₄O₅I₂/Bi₅O₇I,were synthesized,and the crystal structure,micro-morphology,elemental composition,functional groups and absorption spectra were characterized by XRD,SEM,EDS,FTIR and UV-vis DRS,respectively.The photocatalytic performance of the as-prepared catalyst was evaluated by the degradation rate of the Rh B solution under light and the effects of catalyst ratio,reaction temperature,and initial p H of the solution on the photocatalytic activity were investigated.The main active species in the reaction were identified through capture experiments.The mechanism of photocatalysis was initially discussed and a possible charge transfer mechanism was proposed.The main conclusions are summarized as follows:1.Bi₄O₅I₂/Ag₃PO₄ composite photocatalysts were prepared by calcining the Bi OI precursor and co-precipitation method in aerobic atmosphere.The catalyst showed microscopic morphology in which Ag₃PO₄ particles were uniformly embedded on the flower-like surface of Bi₄O₅I₂.When the molar ratio of Bi₄O₅I₂ and Ag₃PO₄ was 1:3,the samples obtained showed the most satisfactory photocatalytic activity.2.Bi₅O₇I/Ag₃PO₄ composite photocatalysts were prepared by alkaline hydro-thermal method and co-precipitation method.Ag₃PO₄ particles in the composite were uniformly adhered to the rod-shaped smooth surface of Bi₅O₇I.When the content of Ag₃PO₄ is 25%,the ability of photocatalytic degradation of Rh B was the strongest.3.The Bi₄O₅I₂/Bi₅O₇I composite photocatalysts were prepared by controlling the calcination temperature of the Bi OI precursor in an aerobic atmosphere.As the calcination temperature increased,the light absorption edge of the samples shifted from503 nm to 392 nm,and the band gap energy increased from 2.22 e V to 2.97 e V.The samples obtained at the calcination temperature was 450°C had the strongest photocatalytic ability.4.The optimum reaction temperature and initial p H of the three composite catalysts for photocatalytic degradation of Rh B were T=308K and p H=9.Under these conditions,when the degradation rate of the composite catalyst Bi₄O₅I₂/Ag₃PO₄（1:3）,Bi₅O₇I/Ag₃PO₄-25%and Bi₄O₅I₂/Bi₅O₇I-450 for Rh B solution（250 m L,10 mg/L）reached 99%,the corresponding TOC removal rates were 98%,59.89%and 75.54%,respectively.5.Trapping experiments confirmed that the main active species in the photo-catalytic degradation of Rh B by Bi₄O₅I₂/Ag₃PO₄（1:3）,Bi₅O₇I/Ag₃PO₄-25%and Bi₄O₅I₂/Bi₅O₇I-450 were photo-generated holes（h⁺）.The enhanced photocatalytic performance was mainly due to the improvement of built-in electric field and the effective separation of photogenerated electron-hole pairs.In summary,all three composite photocatalysts exhibit excellent degradation performance and mineralization ability for Rh B,and have broad application prospects in the field of photocatalytic treatment of dye wastewater.