Preparation Of BiOBr-Based Composite Photocatalytic Materials And Their Degradation Of Dyeing Wastewater

Advanced treatment technology of printing and dyeing wastewater and its application is one of the key technologies urgently needed to break through in the 13th five-year national science and technology innovation plan.Accelerate the development of advanced treatment technology of printing and dyeing wastewater represented by photocatalysis is very significant to improve the recycling rate of printing and dyeing wastewater and protect the ecological environment.In this study,in order to solve the two main bottlenecks which are low quantum efficiency and difficult recycling of powder photocatalysts in photocatalytic degradation of printing and dyeing wastewater,layered semiconductor BiOBr was selected as the research object.Meanwhile,the separation efficiency of photo-generated carriers and recycling performance of BiOBr were gradually improved in respects of morphology optimization,photocatalytic modification and fiber immobilization.Moreover,the effects of raw materials,reactant concentration,solvent and chelating agent on morphology of BiOBr were investigated.The photocatalytic enhancement mechanism of BiOBr-based composite photocatalysts with Ag deposition modification by using various illuminates and semiconductor coupling modification based on Z-Scheme,p-n junction and ferroelectrics/semiconductor model were discussed.The effect of internal electric fields of ferroelectric materials on charge carrier dynamics of BiOBr was elaborated.In addition,the BiOBr composite photocatalytic materials were prepared.We also evaluated the effect of fiber carriers on recycling performance of BiOBr.In conclusion,this study presents an important theoretical guiding significance for improving the quantum efficiency of BiOBr and accelerates the pratical application of photocatalytic technology in the advanced treatment of printing and dyeing wastewater.The main contents and conclusions are as follows:（1）BiOBr photocatalysts with different morphologies and sizes were successfully synthesized and the effects of synthesis conditions on the morphologies were also studied.BiOBr nanoparticles（<50 nm）were synthesized by solvothermal method using 1,2-dibromobenzene as raw materials.Hollow BiOBr fibers with regular morphology were prepared using polyester as a template.Size-controlled BiOBr sheets（100-1000 nm）were successfully synthesized by adjusting the concentration of precursor reactants.The hierarchical BiOBr microspheres were synthesized by solvothermal method.The pore size of BiOBr microspheres decreased with the decreasing of solvent polarity.2D BiOBr nanoplates aligned tightly to form 3D BiOBr thick plates whilst citric acid（CA）was employed as a chelating agent.By comparing the photocatalytic properties of BiOBr with different morphologies and sizes,it was found that the BiOBr nanosheets with controllable size showed a superior photocatalytic performance,which is suitable as a matrix material.Hierarchical BiOBr microsphere synthesized by ethylene glycol（EG）and BiOBr thick plates showed excellent adsorption property and photocatalytic activity,respectively,which can be used to prepare BiOBr/fiber composites photocatalysts.（2）A variety of BiOBr composite photocatalysts were prepared by noble metal deposition modification and semiconductor coupling modification.The structure-function relationship between microstructure and photocatalytic performance was studied revealing the photocatalytic enhancement mechanisms of different modification methods.The metallic Ag particles on the surface of 0.03Ag-0.97BiOBr played roles of electron trap and surface plasma resonance effect in reducing charge-carrier recombination under two different wavelengths light irradiation（390 ± 20 nm and 570 ± 40 nm）.The enhanced photocatalytic activity can be attributed to the above two effects under full the wavelength light irradiation.The degradation rate of 0.03Ag-0.97BiOBr for RhB dye was 97.50%under the full wavelength light irradiation for 30 min.Z-Scheme BiOBr/g-C₃N₄ can reduce the recombination of photon-generated carrier.Adding CNT between BiOBr and g-C₃N₄ can accelerate the transformation of photo-generated electrons from BiOBr conduction band to g-C₃N₄ valence band.Photo-generated holes（h⁺）and superoxide radical（O₂^-）were two main active species in BiOBr/CNT/g-C₃N₄ for photocatalytic degrading weak acid dyes.The enhanced photocatalytic activity of the hybrid photocatalyst involving Bi₄Ti₃O₁₂ and BiOBr with a similar band structure can be attributed to the p-n junction.The photo-generated electrons of BiOBr migrated to the conduction band of Bi₄Ti₃O₁₂,which effectively reduced the recombination of photo-generated carriers.The photodegradation rate of 0.2BiOBr/0.8Bi₄Ti₃O₁₂ to weak acid dye was 1.3 times higher than that of Bi₄Ti₃O₁₂ or BiOBr.The internal electric field of ferroelectric phase Ba_1-xSr_xTiO₃ could significantly promote the separation of photo-generated carriers of BiOBr.The photodegradation rate of ferroelectric 0.8BiOBr/0.2Ba_0.8Sr_0.2TiO₃ for direct lake Blue 5B dye was 1.2 times and 1.3 times higher than that of Ba_0.8Sr_0.2TiO₃ and BiOBr at 35℃.This work provided a theoretical basis for the regulation of photo-generated carriers separation by internal electric field in ferroelectric materials.（3）Fiber-supported BiOBr composite photocatalysts can effectively reduce the agglomeration and improve the recycling performance of BiOBr.For EG-B/CF and CA-B/AF,hierarchical BiOBr microspheres and BiOBr thick plates were evenly distributed on the surface of carbon fibers（CF）and aramid fibers（AF）.Porous polylactic acid（PLA）fibers with rich porous structure and uniform fineness can be prepared by using CH₂Cl₂ as solvent when the spinning solution concentration was 7 wt%.The Ag-BiOBr exposed on the surface of PLA fibers with pore-formation by volatility of solvents.The photocatalytic performance of Ag-BiOBr/PLA was significantly superior to that of EG-B/CF and CA-B/AF.The degradation rates of Ag-BiOBr/PLA for direct dyes,acid dyes and reactive dyes were above 99%under xenon lamp light for 60 minutes.The photodegradation rate of 10th Ag-BiOBr/PLA were still higher than 93%.Generally,Ag-BiOBr/PLA shows non-selective photodegradation performances of dyes and stable recycling performances.（4）According to GB 4287-2012,the third-party test results showed that all the indexes of the post-degradation wastewater were accord with the direct discharge limit of pollutants stipulated in the discharge standard of water pollutant for dyeing and finishing of textile industry.BiOBr-based composite photocatalytic materials display practical applications in deep treatment of printing and dyeing wastewater.