| The global industrialization proeess has intensified,and organic wastewater is increasingly produced by industry and have become one of the most serious global environmental problems.In response to China's strategic to maintain the construction of ecological civilization,the management of organic wastewater is imminent.Heterogeneous photocatalysis,as one of advanced oxidation technology,has been proven to efficiently degrade various organic pollutants.MOFs(or COFs)have attracted extensive attention in heterogeneous photocatalytic degradation of organic pollution due to its simple synthesis,adjustable structure,high specific surface area and crystallinity.This thesis is devoted to solving the problem of low photocatalytic activity of single photocatalysts.A series of multifunctional nanocomposites based on MOFs or COFs are designed,synthesized and characterized for the removal of organic pollutants.(1)TiO2 anchored onto NH2-MIL-88B(Fe)composites were prepared by solvothermal method for adsorption and photocatalytic degradation of methylene blue(MB).During the preparation process,the TiO2 and the MOF are simultaneously formed,and it is not necessary to separately prepare the TiO2.In addition,the TiO2 Particles are uniformly distributed on the MOF surface and have significant interfacial contact.The adsorption capacity TiO2@NH2-MIL-88B(Fe)towards MB reached 172 mg/g.Photocatalytic experiments show that the removal rate of TiO2@NH2-MIL-88B(Fe)towards methylene blue is close to 100%under visible LED light,which is better than TiO2(10%)and NH2-MIL-88B(Fe)(30%).In addition,the catalyst still maintains good catalytic activity after 5 times of photocatalytic cycling,and has great practical application potential.(2)The g-C3N4/PDI@MOF(CPM)heterojunction photocatalyst were prepared.In the presence of H2O2 and visible LED light,CPM is capable of removing 90%of tetracycline,78%of carbamazepine,100%of bisphenol A and 100%of p-nitrophenol.The catalyst also rapidly catalyzes the degradation of low concentrations of phenolic organic contaminants(2 ppm)into small molecules(by HPLC analysis)in 10 minutes.In addition,the photocatalytic performance of CPM is better than that of g-C3N4@NH2-MIL-53(Fe),indicating the NH2-MIL-53(Fe)and g-C3N4/PDI electronic band structures may be better matched than g-C3N4.(3)The effect of interfacial contact on the photocatalytic performance of composites was investigated.g-C3N4/MIL-68(In)-NH2(CM)composite was prepared by solvothermal method.Interestingly,MIL-68(In)-NH2 was uniformly grown in situ on the g-C3N4 nanosheet(CNNS)surface.CM exhibit high photocatalytic performance and can photodegradation 70%of TC,which is better than the original CNNS(30%)and MIL-68(In)-NH2(58%),indicating that close interfacial contact between CNNS and MIL-68(In)-NH2 is required for improving photocatalytic performance.(4)For the unstable problem of photocatalysts and improve photocatalysis performance,a free-metal CNNS/COF heterojunction photocatalyst is designed and synthesized.The photodegradation rate constant of rhodamine B over CNNS/TPA-COF is(0.121 min-1),which is about 50 times(0.024 min-1)of CNNS and 57 times(0.021 min-1)of TPA-COF.The increase in photocatalytic performance may be due to the fact that the introduction of TPA-COF not only improves visible light absorption but also promotes separation of electrons and holes.The studies above show that composite materials based on MOFs or COFs have good activity in photocatalytic degradation of organic pollutants.The adsorption performance and separation efficiency of the photogenerated electrons and holes of MOFs/TiO2 or g-C3N4 composites are improved.In particular,free-metal CNNS/COF heterojunctions not only have strong visible light absorption and effective photo-generated carrier separation,but also maintain good stability in harsh condition.Thus,this thesis will provide a new method for designing photocatalysts for organic wastewater treatment. |
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