Study On Preparation Of Bismuth Oxybromide-based Photocatalysts And Their Properties For Degradation Of Rhodamine B

Nowadays,with the development of industrialization,a large number of organic wastewater is discharged into the ecological environment,and the problem of water pollution has aroused great concern of the public.Therefore,protecting nature and purifying organic pollutants in industrial wastewater is undoubtedly a“green project”for the benefit of the earth.According to relevant studies,photocatalysis technology has low operation cost and no secondary pollution,so it is a very effective method to treat industrial wastewater.Bismuth oxybromide（BiOBr）has suitable band gap,stable physical and chemical properties,and has a potential application prospect in the field of photocatalysis.In this paper,three photocatalysts were prepared based on BiOBr and the degradation experiment of Rhodamine B（RhB）in wastewater was carried out.Its main contents are as follows:1.The AgI/BiOBr composite photocatalysts were prepared by two strategies:regulating the hydrothermal pH of the precursor solution and constructing heterojunctions.Firstly,three pure BiOBr catalysts with different hydrothermal pH values,BOB-4（pH=4）,BOB-7（pH=7）and BOB-10（pH=10）,were synthesized,and after finding the best sample BOB-4 by photocatalytic experiments,AgI/BiOBr Z-type heterojunction composite photocatalysts were then prepared by co-precipitation method.Under the synergistic effect of the two strategies,BAI-5（AgI loading of 13 wt%）exhibited the best photocatalytic activity,and the removal rate of RhB was 86.06%under visible light irradiation for 120 min,with significantly improved catalytic performance.Finally,the possible mechanism of its photocatalysis was illustrated and explained.2.g-C₃N₄/WO₃/BiOBr ternary“double Z-type”heterojunction photocatalysts were prepared by one-pot solvent heat method.WO₃ and g-C₃N₄ were simultaneously grown in situ on the BiOBr surface in the presence of ethylene glycol.The charge capture effect of WO₃ was used to enhance the absorption of visible light and promote the charge separation at the catalyst interface.While g-C₃N₄ usually exhibits a stable layered stacked structure of extensiveπ-conjugated electron system with light-induced electron-hole pairs migrating randomly in the interlayer collisions,the introduction of g-C₃N₄ is an effective strategy to enhance charge separation and extend the spectral response range.Here,combined with the excellent photoelectric properties of the above two materials,we designed a g-C₃N₄/WO₃/BiOBr ternary heterojunction photocatalyst supported by g-C₃N₄ nanolayered structure.Due to the formation of internal electric field in the interface,it follows“double Z-type”charge transfer path,and its photocatalytic activity is improved compared with binary heterojunction.The removal rate of RhB was 91.67%under visible light irradiation for 120 min.3.Since the enhancement of catalyst performance by constructing heterojunctions was relatively limited,BiOBr was modified by energy band modulation and surface modification.CQDs/BiOCl_xBr_1-x solid solutions were synthesized by a one-step co-precipitation method at room temperature.The relative proportion of halogens in the anion layer was adjusted to change the crystal plane spacing,induce lattice strain,and thus regulate the band gap structure.The comparison test showed that the degradation rates of RhB on BiOBr,BiOCl and BiOCl_0.5Br_0.5were 55.66%,24.03%and 94.91%with 36 min of light,respectively.BiOCl_xBr_1-xsolid solutions showed higher photocatalytic activity than BiOCl or BiOBr alone.Subsequently,BiOCl_xBr_1-xsolid solutions were modified with carbon quantum dots（CQDs）to increase the overall specific surface area and reduce the recombination efficiency of photogenerated electrons and holes.After photocatalytic degradation for 18 min,the degradation rate of RhB on3CQDs/BiOCl_0.5Br_0.5（CQDs loading of 0.42 wt%）was close to 100%.Through the synergistic effect of band gap adjustment and CQDs modification,the photocatalytic performance of BiOBr is significantly improved.