Mechanisms Of Photocatalyst Biochar For Tetracycline Polluted Water Redmediation And Its Effect On Sediment Bacterial Community

Tetracycline(TC)is commonly applied as anti-infectionmedicine and growth promoter.As TC has a relatively low bioavailable rate in nature,the accumulation of TC has caused water pollution,posing a huge threat to ecological environment and human health.Therefore,developing a simply and efficiently remediate technology for TC contaminated enviroments has become a hot spot in environmental ecology.Photocatalytic biochar(PBC)has broad application potential to remediate TC polluted water.However,due to the short history of PBC development,the improvement is largely needed to expand their resource as well as to understand their photodegradation mechanism and ecological security.To understand the potential and remediation mechanisim of PBC and its influence on ecology security,new methods were developed to prepare and produce two PBC products,PbMoO4@BC and g-C3N4@BC,by using poplar residue as raw material.The photodegradation ability and mechanism of PbMoO4@BC and g-C3N4@BC for removing TC in polluted water were investigated.The influence of g-C3N4 and g-C3N4@BC on the sediment bacterial community structure was examined.The potential ecotoxicity of g-C3N4@BC application in environment was evaluated.The main results were as follows:(1)A novel PBC,PbMoO4@BC,was successfully synthesized in situ via combining coprecipitation with pyrolysis treatment of poplar sawdusts for the degradation of TC.Three PbMoO4@BC composites(PbMoO4@BC-1,-2,-3 with the mass ratio of PbMoO4:PS=1:20;1:5;and 1:1.25,respectively)displayed higher activity compared to pure PbMoO4.The PbMoO4@BC-lexhibited the highest photocatalytic capacity among the three PbMoO4@BC products.The catalysts were analyzed by XRD,SEM,EDS,XPS,PL and UV-vis DRS.The characterization demonstrated that the presence of biochar improved the light adsorption,narrowed the band gap,and enhanced the charge separation,thus increase the photodegradation capacity of PbMoO4.When the dosage of catalyst was 300 mg,the initial concentration of TC was 150 mg·L-1,and the reaction volume was 100 mL,the removal rate t of TC by PbMoO4@BC-1 was 61%in 120 min,which was 2.1 times that of pure PbMoO4(28%).PbMoO4@BC-1 had an ability to remove TC from TC contaiminated water,and exhibited the high removal capacity in low TC solutions.The TC removal was the synergistic effect of photodegradation and adsorption.Moreover,PbMoO4@BC-1 had a good stability and its removal rate of TC decreased less than 8.9%after 5 cycles.The reactions in the presence of radical quenchers indicated that h+ and ·O2-were the dominant active species for the photodegradation.(2)Using polar sawdustes as raw material to prepare biochar by pyrolysis at 600?,and then mixing the biochar with melamine undre pyrolyzed treatment at 520?,the new PBC product of g-C3N4@BC was synthesized.The g-C3N4@BC obtained by 6%biochar,namely 6%-g-C3N4@BC,had the best efficiency for TC removal.The catalysts were analyzed by XRD,SEM,EDS,XPS,PL and UV-vis DRS,demonstrating that the presence of biochar widen the bandgap,enhanced the redox ability as well as facilitated charge separation.When the dosage of catalyst was 50 mg,the initial concentration of TC was 50 mg·L-1,and the reaction volume was 100 mL,the degradation rate t of TC by 6%-g-C3N4@BC was 86.4%in 120 min,which was nearly 10%higher than that of pure g-C3N4(76.8%).For 50 mg·L-1 TC in different water matrices,the degradation rate of TC all exceeded 80%by 6%-g-C3N4@BC.The TC removal was attributed to photodegradation.In addition,6%-g-C3N4@BC illustrated a good stability and the rate of TC degradation only decreased abOTU 6%after 5 cycles.The reactions in the presence of radical quenchers indicated that h+ and ·O2-were the dominant active species for the photodegradation.Compated with PbMoO4@BC,6%-g-C3N4@BC had the advantages of higher removal efficiency,more stability and lower cost.(3)Graphitic carbon nitrin with different concentrations was used to analyze the change of bacterial community in river sediment and to investigate the potential ecological toxicity of g-C3N4 in enviroments.The high-throughput sequencing analysis showed that g-C3N4 changed the microbial community structure,and each microflora had different response to g-C3N4.The Chaol and Shannon indexes of the samples were improved by g-C3N4.?-diversity analysis showed that low concentrations of-g-C3N4 caused the greatest variability.The phylums of Actinobacteria,Firmicutes,and Cyanobacteria had relatively significant change.g-C3N4 reduced the abundance of Firmicutes and Actinobacteria,in which medium concentration of g-C3N4 showed the greatest inhibition.The low concentration of g-C3N4 had an inhibitory effect on Cyanobacteria,but the abundance of Cyanobacteria increased in the sample with high concentration of g-C3N4.However,the change in diversity index and abundance of bacteria was small,implying that g-C3N4 had slight effect on the community structure and diversity of sediment bacteria,and could maintain the stability of bacterial community structure.The results indicated that g-C3N4 had minor impact on the ecological environment.(4)The bacterial community structure in river sediment under various g-C3N4@BC concentrations were examined to evaluate its ecological toxicity.The analysis illustrated that g-C3N4@BC changed the microbial community structure,and the response of each microflora to g-C3N4@BC was different.The diversity could remain stable effectively with high or low g-C3N4@BC concentration.Actinobacteria,Firmicutes and Cyanobacteria exhibited a ralatively significant change.g-C3N4@BC increased the abundance of Firmicutes,however,the increase was hindered by high g-C3N4@BC concentration.g-C3N4@BC with all concentration prevented the growth of Cyanobacteria in samples.In addition,high concentration of g-C3N4@BC improved the abundance of Actinobacteriota.Howerer,the change in the abundance of bacteria was little.The results suggested that g-C3N4@BC with different concentrations had mild effect on the community structureand and diversity of bacteria in river sediments,and the composition of the bacterial colony was basically maintained stable.g-C3N4@BC had minor ecological impact on the river sediment,and possessed good ecological security.In conclusion,two PBC products,PbMoO4@BC and g-C3N4@BC,were successfully synthesized.The results showed that PbMoO4@BC and g-C3N4@BC had higher efficiency for TC removal than PbMoO4 or g-C3N4,respectiely.The biochar enhanced the charge separation of the two PBC products,by improving the light adsorption of PbMoO4@BC but narrow the light adsorption of g-C3N4@BC.The two PBC had good stability and effectively photodegrated TC by ·O2-and h+ in different water matrices.g-C3N4@BC was more suitable to remediate TC in TC polluted water effectively than PbMoO4@BC.Both g-C3N4 and g-C3N4@BC had minor effect on community structure and diversity of sediment bacteria,suggesting g-C3N4@BC is safe for ecological enviroment.This study provided scientific references and practical guidances for further research and development of PBC and the photocatalytic remediation of organic pollution in enviroments.