High Efficiency Photocatalytic System Construct and Its Photocatalytic Mechanism for β-Lactam Antibiotics Degradation

Author:Zhao Yan Yan

Supervisor:fan jun

Database:Doctor

Degree Year:2019

Download:202

Pages:164

Size:19469K

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The studies of environmental science and epidemiological indicated that approximate7090%of human diseases are related to the environmental pollution.With the improvement of national medical level and the pharmaceutical market booming,the species of antibiotics continues to increase in recent years,andβ-lactam antibiotics have been excessive consumption due to the broad-spectrum antimicrobial activity,superior antibacterial effects,as well as the long half-life,which results in the release of residues into wastewater,thereby threatening biota,and disrupting indigenous microbial populations,lead to a series of probable damages to ecological environment and human health.Modern chemistry aims to synthesize the photocatalyst with outstanding photocatalytic activity for antibiotic degradation.In this paper,the novel photocatalyst with excellent photocatalytic performance were synthesized to degrade the typicalβ-lactam antibiotics such as 7-ACA,6-APA,ceftriaxone sodium,cefixime,benzylpenicillin sodium salt and amoxicillin in aquatic environment.The main research contents are as follows:(1)Bi2WO6 photocatalyst with nano-flower,nanoplates,knot shape,rodlike and irregular morphologies have been successfully synthesized through a highly facile hydrothermal process by simply adjusting pH values,reactive solvents and temperature.Photocatalytic activity of the as-prepared samples were evaluated by degradation of ceftriaxone sodium under visible light irradiation(λ>420 nm),the results indicated that all the as-prepared Bi2WO6 samples exhibit morphology-associated photocatalytic activity,and the 3D flowerlike-structure of Bi2WO6 composed of well-ordered nanoplates displayed the outstanding photocatalytic activity,about 70.18%of ceftriaxone sodium has been degraded at 240 min under visible light irradiation.Through getting insight into the mechanism,h+and·O2-play major roles compared with·OH in photocatalytic degradation process.The possible pathway of ceftriaxone sodium were proposed based on the LC-MS and HPLC experiments,and ceftriaxone sodium could be degrade to intermediates firstly,then degrade to CO2 and H2O.(2)Efficient photocatalytic system composed of Bi2WO6 nanoflowers and g-C3N4nanosheets were successfully synthesized by hydrothermal method.The Bi2WO6/g-C3N4were presented for ceftriaxone sodium degradation in the aquatic environment at lowconcentrations under visible light irradiation.The 40%-Bi2WO6/g-C3N4 showed the excellent photocatalytic activity,about 94.50%of ceftriaxone sodium could be degraded under visible light irradiation for 120 min.The adsorption test showed the excellent adsorbability,the UV-vis results indicated the expanded light-harvesting scope,and the PL and transient photocurrent response results illustrated the efficient separation of photogenerated electron-hole pairs of 40%-Bi2WO6/g-C3N4 composite.From the active species capture experiments we can kown that h+and·O2-played major roles compared with·OH during photocatalytic process.(3)A novel composite with excellent photocatalytic activity was firstly synthesized by loading small size of ZnSe Quantum dots(QDs)and nano-Ag onto the surface of the CN.The novel composite(ZnSe-Ag/CN)was used to degrade ceftriaxone sodium in the aquatic environment at low concentrations under visible light irradiation,and the 7%-ZnSe-Ag/CN composite displayed superior photocatalytic activity,approximately 89.24%of Ceftriaxone sodium has been degraded under visible light irradiation for 90 min,which was approximately 10.14,2.72,2.09 and 1.39-folds higher than pure ZnSe QDs,CN,7%-Ag/CN and 5%-ZnSe/CN sample,respectively.Based on the adsorption test,the UV-vis diffuse reflectance spectra(DRS),the N2 adsorption-desorption isotherm,the photoluminescence spectra,the transient photocurrent response and the electrochemical impedance spectroscopy(EIS)measurements,the enhanced photocatalytic activity of the ZnSe-Ag/CN composite could be attributed to the excellent adsorbability,expansion of the light-harvesting scope,as well as the efficient separation of photogenerated electron-hole pairs.Meanwhile,the ZnSe-Ag/CN composite could produce a large amount of the hydroxyl radicals(·OH)during the photocatalytic degradation process.(4)A visible-light-induced antibiotics degradation system based on a nano-Ag,CsPbBr3 QDs and bulk g-C3N4 ternary assembly(Ag-CsPbBr3/CN)has been firstly constructed under an organic phase environment.The new ternary assembly of Ag-CsPbBr3/CN composite was used to degrade 7-ACA in the aquatic environment under visible light irradiation at low concentrations,and the 7%-Ag-CsPbBr3/CN composite displayed the superior photocatalytic activity,approximately 92.79%of 7-ACA has been degraded to CO2,H2O and other small molecules at 140 min,which was approximately1.49,1.56,3.01 and 11.43-folds higher than 9%-CsPbBr3/CN,7%-Ag/CN,pure CN and pure CsPbBr3,respectively.Furthermore,a possible 7-ACA degradation pathway was investigated based on the Liquid Chromatography-Mass spectroscopy(LC-MS)experiment to better understand the degradation process.The 7%-Ag-CsPbBr3/CN also could degrade cefixime and ceftriaxone sodium under visible light irradiation,and the degradation rates were about 94.23%and 93.41%at 140 min.A possible mechanism for7-ACA degradation over Ag-CsPbBr3/CN composite were proposed according to detailed measurements of adsorption test,Brunauer-Emmett-Teller(BET)measurement,UV-vis diffuse reflectance spectra(DRS),photoluminescence spectra(PL),transient photocurrent response and electrochemical impedance spectroscopy(EIS)measurement,and the enhanced photocatalytic activity of Ag-CsPbBr3/CN composite could be attributed to the excellent adsorbability,the enhanced light-harvesting and reduced charge recombination,as well as the synergistic effects of nano-Ag and CsPbBr3 co-loaded with CN.In addition,h+and·OH played major roles,e-and·O2-played minor roles based on the reactive-species-trappingexperiments,theNBTtransformationandthe7-hydroxycoumarin fluorescent experiments.(5)A novel CsPbCl3/CN composite was firstly synthesized by loading small size of CsPbCl3 onto the surface of CN,and the 7%-CsPbCl3/CN showed excellent photocatalytic activity to degrade 6-APA in the aquatic environment under visible light irradiation,about78.82%could be degraded at 120 min,the photocatalytic activity was higher that 3%,5%and 9%-CsPbCl3/CN.The CsPbCl3/CN system also could degrade benzylpenicillin sodium salt and amoxicillin under visible light irradiation,and the degradation rates were about81.54 and 84.89%at 120 min.In addition,e-,h+and·OH play major roles compared with·O2-in photocatalytic degradation process.The possible pathway of 6-APA were proposed based on the LC-MS experiment,and 6-APA could be degrade to intermediates firstly,then degrade to CO2 and H2O.