Preparation Of SnO₂-AgBr Composite Photocatalyst And Study On Degradation Of Typical Pollutants In Dye Wastewate

As a method of using solar energy to solve the problem of environmental pollution,photocatalytic technology has attracted extensive attention because of its low cost and environmental protection.Tin dioxide（SnO₂）is a typical semiconductor material with excellent photoelectric properties and low cost.However,due to its wide band gap（3.6e V）,it hardly responds to visible light,which greatly limits its application as a photocatalytic material.Therefore,it needs to be modified by certain technology to broaden the response range of SnO₂to light.In this paper,SnO₂-AgBr composite photocatalyst in response to visible light was prepared by using narrow band gap semiconductor silver bromide（AgBr）composite SnO₂.Compared with other photocatalysts,the catalyst has rich raw materials,simple preparation and good repeatability.Under the condition of low dosage（1.0g/L）,it still has a good treatment effect on dye pollutants with high concentration（30mg/L）,and has a certain application prospect.The specific research results are as follows.（1）Firstly,the optimum preparation conditions of SnO₂were discussed.Pure SnO₂was prepared by hydrothermal method under four conditions with SnCl₄·5H₂O as tin source.Through characterization and adsorption experiments,it was determined that SnO₂prepared under hydrothermal conditions of 180℃for 10h had good crystallinity,minimum particle size and most uniform particle size.Subsequently,SnO₂-AgBr composite photocatalysts with three doping ratios were prepared with Ag NO₃and KBr as raw materials.Various characterization showed that when the mole ratio of SnO₂to AgBr in the composite was 1:1,the two semiconductors were combined evenly,the optical properties were the best.（2）Methyl orange（MO）and malachite green（MG）were selected as the target pollutants.The photocatalytic activities of the three mole ratio materials were discussed through photocatalytic experiments.Combined with the kinetic model analysis,it was found that the material with mole ratio of 1:1 had the highest activity,which was consistent with the characterization results.Under the conditions of room temperature,solution neutrality,pollutant concentration of 30mg/L and catalyst dosage of 1g/L,the degradation efficiencies of MO and MG after 30min dark adsorption and 120min light reaction were 96.71%and 93.36%respectively.In addition,the effects of catalyst dosage,initial pollutant concentration,humic acid concentration and initial p H of solution on the degradation were discussed.The reuse experiment showed that the prepared catalyst had good stability in the previous cycles,but the activity became worse and worse with the increase of the number of cycles.After four cycles,the degradation effect of MO and MG decreased to 66.42%and70.86%respectively.The XRD characterization before and after the reaction showed that a small part of Ag⁺in the catalyst was reduced to Ag.（3）The reaction mechanism of catalyst degradation of target pollutants was discussed through free radical capture experiment.The degradation products and degradation paths of pollutants were speculated by using UV-vis wavelength full scanning and high performance liquid chromatography-mass spectrometry.The capture experiment showed that·O₂^-,·OH and h⁺were all active substances in the degradation process of SnO₂-AgBr,but·O₂^-contributed the most,and the order of intensity was·O₂^->·OH>h⁺.Combined with the results of full wavelength scanning and HPLC-MS,a possible degradation path was proposed:under the action of active substances·O₂^-,·OH,MO was degraded mainly through substitution reaction,C-N bond breaking,dehydroxylation,demethylation and other reactions;MG is degraded by demethylation,carboxylation,C-C bond breaking,debenzylation and other reactions.With the progress of degradation reaction,they are finally transformed into CO₂,H₂O and other inorganic small molecular compounds.