Study On Bismuth-based Catalyst Supported On Diatomite And Photocatalytic Degradation Of Organic Pollutants By Cuprous Oxide

At present,industrial and agricultural processes produce a large number of water pollutants.The overuse of some antibiotics,herbicides and insecticides has led to their detection in wastewater,which has a great impact on the environment,human and biological.How to effectively remove the pollution in wastewater has become a hot research topic.There are many kinds of wastewater treatment methods,such as physical adsorption,ultrasonic and photocatalytic technology.Among them,photocatalysis is characterized by high efficiency,strong oxidation capacity,less secondary pollution and low cost,which plays an important role in the degradation of organic pollutants.In this thesis,porous diatomite is used as the base,which has the advantages of green,non-toxic,large specific surface area and good corrosion resistance.It can not only show strong adsorption performance,but also show high chemical stability.However,diatomite itself has little ability to photocatalyze the degradation of organic pollutants.The composite of other photocatalytic semiconductor materials on the surface of diatomite can effectively improve its photocatalytic degradation ability,such as Ag/Bi OCl,Ag₃VO₄/Bi₂MoO₆,Ag₂O/BiVO₄,etc.At the same time,diatomite can be used as substrate support for these materials to avoid the caking of composite catalyst.The specific research is as follows:（1）In this study,Ag/Bi OCl/diatomite composite material was prepared by simple hydrothermal method on the basis of diatomite,which has the dual effect of degrading tetracycline and inactivation of microorganisms（E.coli）.The photocatalytic degradation results showed that Ag（7.5%）/Bi OCl/diatomite composites had a tetracycline degradation rate of 97.8%and a bacteriosuppressive effect of 99.9%against Escherichia coli within 60 minutes under visible light irradiation.After three repeated experiments,the prepared composite samples still have good catalytic performance,which shows the stability of the catalyst.Finally,a possible photocatalytic degradation mechanism was proposed.Oxygen vacancies（OVs）,superoxide radicals（·O₂^-）,holes（h⁺）and hydroxyl radicals（·OH）are signifcance active substances,which play an important role in the photodegradation of TC.In this experiment,Ag/Bi OCl/diatomite composite material was prepared to degrade tetracycline in water with high antimicrobial activity,which provides a simple method and has a certain application prospect.（2）In this study,with diatomite as the carrier,Ag₃VO₄/Bi₂MoO₆/diatomite ternary composite was synthesized by hydrothermal method and used to activate persulfate（PS）to degrade atrazine（ATZ）under visible light irradiation.The prepared catalysts were characterized by a series of different test methods,such as XRD,FT-IR,SEM,XPS,BET,photocurrent response and so on.Meanwhile,the effects of diatomite dosage,Ag₃VO₄ dosage,PS concentration and initial p H value on ATZ removal were studied.The structural stability and reusability of Ag₃VO₄/Bi₂MoO₆/diatomite composites can be verifed by cyclic experiments.Besides,the intermediate products degraded by ATZ were detected by liquid chromatography and mass spectrometry（LC-MS）,and the possible transformation pathway was proposed.At the same time,the quenching experiment and EPR test showed that superoxide radical（·O₂^-）hydroxyl radical（·OH）sulfate radical(SO₄^·-)and h⁺both promoted the degradation of ATZ.Finally,on the basis of comprehensive analysis,the reasonable reaction mechanism of removing ATZ by Ag₃VO₄/Bi₂MoO₆/diatomite+PS system was proposed.The results of this study promoted the application of Ag₃VO₄/Bi₂MoO₆/diatomite composites as organic degradation catalysts,reflecting the potential of composite materials in the removal of pesticide residues in environmental remediation.（3）In this study,Ag₂O/BiVO₄/diatomite composite with p-n heterojunction structure was synthesized by simple hydrothermal method with diatomite as carrier.It was found that under the action of hydrogen peroxide（H₂O₂）,the imidacloprid（IMD）could be effectively degraded by the composite.Systemic evaluations was conducted on effects of p H value,catalyst dosage,H₂O₂ concentration,initial IMD concentration,and anion on how effeciently this new photocatalytic composite can degrade IMD.The results show that the p-n heterojunction formed between the two contact surfaces of Ag₂O nanoparticle and BiVO₄ promotes the charge transfer between the interfaces,inhibits recombination of electrons and holes,and thus significantly improves the catalytic performance.The stability and reusability of Ag₂O/BiVO₄/diatomite composites were tested with ICP experiment and cyclic experiment.Active substance capture experiment and ESR reveal the photocatalytic reaction mechanism and confirm that superoxide radical（·O₂^-）,hydroxyl radical（·OH）,and h⁺can promote the degradation of IMD.The degradation products and the intermediates of IMD were identified through LC-MS,on a basis of which the possible transformation pathway was proposed.In situ synthesis of p-type Ag₂O and n-type BiVO₄ heterojunction composites has opened a new direction for photocatalytic degradation of organic pollutants.（4）In this study,Cu₂O/g-C₃N₄ composite with photocatalytic activity was successfully prepared by chemical precipitation method.The catalytic degradation of ciprofloxacin（CIP）by Cu₂O and Cu₂O/g-C₃N₄ composites with different morphologies was investigated.The effective structure and properties of Cu₂O/g-C₃N₄composites were tested by a series of characterization methods.The photocatalytic test results show that the Cu₂O/g-C₃N₄ composite photocatalyst has good stability and good photocatalytic performance,which is attributed to the effective hetero-junction structure formed by the combination of Cu₂O and g-C₃N₄,which promotes the interfacial charge separation.The addition of g-C₃N₄ can reduce the crystal size of Cu₂O,improve the crystal morphology,and increase its light utilization.Among the synthesized catalysts,the Cu₂O-3（20%）/g-C₃N₄ composite has the highest catalytic activity,and the photocatalytic oxidation efficiency of CIP is 96%.By free radical capture and ESR analysis,it was verified that·OH,h⁺and·O₂^-radicals may be the main active substances involved in CIP photodegradation.Finally,various degradation products and intermediates of CIP were identified by LC-MS,and the possible conversion pathways were proposed.