Preparation Of 2D Bi-based Photocatalysts For Promoting Pollution Degradation

With the continuous acceleration of social industrialization,more and more carcinogens hexavalent chromium（Cr（VI））and tetracycline antibiotics（TC）have been detected in industrial wastewater,which seriously endangers ecological safety.Fortunately,semiconductor photocatalysis technology based on advanced oxidation processes has demonstrated potential in the removal of water pollutants and the core of which is photocatalyst.Among the numerous nano photocatalytic materials,bismuth oxybromide（Bi OBr）and bismuth tungstate（Bi₂WO₆）in the bismuth-based semiconductor materials have gained immense research interest among researchers due to their unique layered structures,suitable band gaps,and stable physicochemical properties.However,the low utilization of visible light and low separation rate of photogenerated charges of Bi OBr and Bi₂WO₆ plague the practical applications.To maximize the extraction of charge carriers of the above materials while suppressing their recombination,the above photocatalysts were optimized by bulk modification and surface modification,and four kinds of visible-light-driven Bi OBr（Bi₂WO₆）photocatalysts were successfully prepared.The ion doping and noble metal loading methods enhance the visible light responsiveness of bismuth-based materials.The formation of two-dimensional structure and S-scheme heterojunctions significantly improves the effective charge concentration and photogenerated electron-hole separation efficiency in bismuth-based photocatalysts,and the efficient degradation of tetracycline and chromium-containing wastewater is realized.The specific research contents are as follows:（1）A certain amount of copper was doped into Bi OBr（Cu/Bi OBr）with a 2D structure through a simple hydrothermal method to improve its capability to degrade tetracycline hydrochloride（TC）.The morphologies and photoelectrochemical characteristics of the prepared samples were characterized by SEM,TEM,XRD,XPS,FT-IR,Uv-vis DRS and other methods.By adjusting the Cu Cl₂·2H₂O amounts in the mixture,the 1 wt%Cu/BOB（Cu/Bi OBr-1）displayed a TC degradation efficiency of 86.2%within 50 min,which was 1.34times higher than that of pure Bi OBr.The DFT calculation results indicated that the Cu 3d and Cu 4s orbitals constituted the doped energy level,which modified the band structure of pure Bi OBr and effectively improved the visible light response capability.Moreover,the doped copper ions optimized the chemical adsorption capacity of TC by regulating the microenvironment around the active sites on the Bi OBr and accelerated the separation of photogenerated charge carriers.This work could provide an insight into the 2D Bi OBr photocatalysts for photocatalytic antibiotic degradation.（2）A series of Cu₂O/BiOBr S-scheme composite photocatalysts were successfully prepared by a hydrothermal and subsequent precipitation method to purify the water body where Cr（Ⅵ）and TC coexist.The optimal Cu₂O/Bi OBr with 15 wt%Cu₂O（CB-15）provided the best photocatalytic activity.CB-15 exhibited a Cr（Ⅵ）reduction efficiency21.75 times higher than Bi OBr.The TC degradation efficiency of CB-15 was 1.21 times higher than Cu₂O.It was interesting that the synergistic photocatalytic activity of CB-15 in the mixed system was improved.The reduction ability of Cr（Ⅵ）and the degradation ability of TC were increased by 1.67 times and 1.18 times,respectively.The enhanced activity of CB-15 was ascribed to the S-scheme heterojunction and 3D/2D structure.The S-scheme transfer mechanism in CB-15 could suppress the recombination of photogenerated carriers and thus prolong the fluorescence lifetime of carriers.While the 3D/2D heterostructure with a large number of contact areas and active sites could further promote the efficiency of the photocatalytic reaction.Notably,the photocatalyst still maintained an excellent degradation ability after four recycles.In general,this paper provided new insights into the design of3D/2D S-scheme heterojunction photocatalysts and the degradation of mixed wastewater.（3）The CuBi₂O₄/BiOBr S-scheme photocatalysts,combining 1D CuBi₂O₄ nanorods and2D BiOBr nanosheets were successfully synthesized by a hydrothermal method to activate peroxymonosulfate（PMS）towards efficient tetracycline（TC）degradation.Benefiting from the construction of S-scheme heterojunction,the Cu²⁺/Cu⁺cycle of Cu Bi₂O₄/Bi OBr-50（CBB-50）had been greatly boosted and further promoted the activation of PMS for TC degradation.Compared with bare Cu Bi₂O₄ and Bi OBr,CBB-50 could degrade 90.3%of TC within 35 minutes,and the degradation kinetic rate was notably increased by 8.4 and 3.3 times,respectively.The results of the cycling degradation experiment indicated that the as-prepared CBB-50 retained 91.7%of the degradation ability,implying its excellent stability.Interestingly,compared with the harsh p H requirements of traditional Fenton reactions,CBB-50 could perform photocatalytic reactions in the p H range of 2.5-10.5 and maintain excellent TC degradation performance.The XPS analysis,band structure and trapping results further verified that the transfer of photogenerated carriers conformed to the S-scheme mechanism.Considering its excellent performance,stability and applicability,CBB-50 would become a reliable candidate for the large-scale practical application of PMS activation in the degradation of antibiotics.（4）In this work,tetracycline hydrochloride（TC）was efficiently photocatalytic degraded over 2D/2D S-scheme Agx-g-C₃N₄-Bi₂WO₆（Ax C/B）photocatalysts,which were prepared using a simple hydrothermal method.The TC degradation efficiency of photocatalyst（A3C/B）with Ag loading of 3 wt%was reached 81.4%in 60 min,which was 2.85 times and 1.52 times as those of pure CN and pure BWO,respectively.The enhanced degradation performance of TC by A3C/B was mainly due to the synergistic effect of the abundant active sites and efficient photo-generated carrier separation rate in the 2D/2D S-scheme system.In addition,Ag nanoparticles acted as cocatalysts,which would promote electron migration from the conduction band of CN by forming a Schottky barrier between CN and Ag.The main reactive species,superoxide radical（·O₂^-）,hydroxyl radical（·OH）and hole（h⁺）were all involved in the reaction,which was proved by trapping experiment.In summary,this research showed that A3C/B was significant for TC degradation under visible-light illumination and provided a novel strategy for TC degradation of various 2D/2D S-scheme photocatalysts.