| Antibiotics are widely used as antibacterial agents and growth promoters in the fields of disease treatment and livestock breeding.However,only a small amount of antibiotics can be absorbed and transformed by humans and animal organisms.30-90%of antibiotics are exereted in the form of prototypes and metabolites with feces and urine,which poses potential harm to ecological environment and human health.The semiconductor photocatalytic degradation technology has the advantages of greenness,high efficiency,thorough degradation,especially the treatment of antibiotic pollutants in wastewater.Therefore,it is very important to develop and fabricate semiconductor catalysts with high photoresponse efficiency.In this paper,a simple synthetic method was used to prepare AgBr/Ag3PO4@Fe2O3 composite semiconductor visible light catalysts.The structure,composition,morphology and photochemical properties of the catalysts were characterized by XRD and TEM,etc.The photocatalytic properties of the catalysts were studied.Taking the mixed antibiotic solution as the research object,the photocatalytic degradation of antibiotics under visible light was studied.The factors that influence the degradation of antibiotics,the mechanism of photocatalytic degradation and the degradation pathway of antibiotics were studied.1.Synthesis and Characterization of AgBr/Ag3PO4@Fe2O3Four different silver-containing composite semiconductor photocatalysts AgBr/Ag3PO4@Fe2O3 were synthesized by solution titration.The XRD diffraction peaks of the four different photocatalysts with different silver content were in good agreement with JCPDS standard cards of AgBr,Ag3PO4 and Fe2O3.The higher the silver content,the weaker the characteristic peak intensity of Fe2O3.The SEM and TEM characterization charts showed that the AgBr/Ag3PO4 crystals uniformly distributed on the surface of Fe2O3.The XPS scanning pattern of the composite catalyst indicated that the catalyst contains Br,P,Ag,O and Fe elements.XPS scan of single element showed that the valence of Br,P,Ag,0 and Fe in the catalyst was-1,+5,+1,-2,+3 respectively,and the valence characteristics of each element were consistent with AgBr/Ag3PO4@Fe2O3.BET characterization results showed that the specific surface areas of the four photocatalytic materials with the mole ratio of silver to Fe2O3 of 0.5,1.0,1.5,and 2.0 were 7.6,7.8,9.2,and 7.4 m2/g,respectively.UV-vis DRS characterization results showed that Fe2O3 and four kinds of photocatalysts with different amounts of silver exhibited strong absorption of visible light.When the ratio of silver to Fe2O3 was 1.5,the bandgap energy was the lowest,which was 1.44 eV.2.Antibiotic degradation characteristicsTaking methylene blue as the target pollutant,the photocatalytic performance of AgBr/Ag3PO4@Fe2O3 catalyst with different silver content was studied.The experimental results showed that when the mole ratio of silver to Fe2O3 was 1.5,abbreviated as Ag1.5BrPFe,the degradation rate of methylene blue was fastest and methylene blue was completely degraded within 30 min.After 4 cycles of recycling,the removal rate of methylene blue reached 84.0%within 30 min,and the catalytic performance was stable.Using Agl.SBrPFe as catalyst,the photocatalytic degradation of 1.0 mg/L sulfadiazine,norfloxacin,ciprofloxacin and tetracycline was studied.The factors influencing their degradation were studied.The experimental results are as follows:? At room temperature with the pH value was 7.0,when the dosage of catalyst was 0.17 g/L,the mixed antibiotic wastewater had the fastest degradation rate and the four antibiotics were basically completely degraded at 30 min;?At room temperature,the lower the initial pH value of the solution,the more conducive to the reaction,and the high pH would inhibit the degradation of antibiotics;?The presence of chloride(Cl-)in the reaction system would inhibit the degradation of antibioties.The presence of sulfate ions(SO42-)promoted the degradation of antibiotics.The presence of other organic substances in the solution would inhibit the degradation of antibiotics.The mechanism of AgBr/Ag3PO4@Fe2O3 degrading organics was studied.The results showed that in the photocatalytic process,superoxide radical(·O2-),hydroxyl radical(·OH)and hole(h+)existed at the same time,and ·O2-played a major role.3.Antibiotic degradation pathwayThe possible degradation pathways of the four antibiotics during the reaction were studied respectively.The results are as follows:CDThe degradation pathway of sulfadiazine under photocatalysis was divided into two types:the first was the sulfapyridine de-SO2 reaction,generating the substance of m/z=187;the other was a H on the pyrimidine ring replaced by hydroxyl,resulting in two isomers of m/z?267,and then the pyrimidine ring opening reaction or the pyrimidine ring directly opened,resulting in the substance of m/z=215;? Norfloxacin under photocatalytic effects generated five degradation intermediate products,mass and charge ratio of which were 251,279,294,322,350,and these products were generated from the piperazine ring gradually oxidized.?The degradation process of ciprofloxacin was similar to that of norfloxacin.During the degradation process,the oxidized sites occurred in the piperazine ring.Three degradation intermediates were found with mass and charge ratio of 362,334,and 263,respectively;?Sites where tetracyclines were oxidized in the photocatalytic process occurred on the branches,and a total of four intermediates were found with mass-to-charge ratios of 475,459,431,and 396,respectively. |
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