Preparation Of PDI-based Catalysts And Their Efficacy And Mechanism For Visible Light Catalysis/activation Of Persulfate System For Degradation Of Typical Organic Pollutants

The pollution status of organic pollutants in water is becoming increasingly serious.As most of the organic pollutants have strong carcinogenic,teratogenic and mutagenic effects,they cause great harm to the ecological environment and human health.Therefore,the treatment of organic pollutants in water environment is urgent.Studies have shown that advanced oxidation processes are effective in removing low concentrations of organic pollutants from water.Considering the economic efficiency and energy consumption,photocatalysis is a commonly used technology in the current research of organic pollutant degradation.However,the reaction efficiency was limited due to the high recombination rate of photo-generated electron-hole pairs in the photocatalyst.The development of highly active photocatalysts or their coupling with other technologies is the core of current technologies for the treatment of organic pollutants in water.Perylene diimide(PDI)is a narrow band gap(?1.69 e V)n-type organic semiconductor with high visible light absorption capacity,low cost,and easily tunable chemical structure,which is a potentially efficient organic photocatalyst.Therefore,the bismuth oxychloride(BiOCl),metal-organic framework(MOF)and biochar(BC)were combined with PDI to construct different photocatalysts.The persulfate(PS)system activated under visible light was constructed.The active species of the reaction system were controlled by internal construction of heterojunction and external PS addition,and used for the degradation of organic pollutants(dyes,phenols,iodine X-ray contrast agents,etc.)in water.The internal and external means could hinder the recombination of electron-hole in PDI.The effects of different times and degrees of self-assembly of PDI on the photocatalytic activity were studied,and the synergistic effect and mechanism of PDI and its composites in the photocatalysis coupled persulfate system were studied.The specific research contents are as follows:(1)The band adjustment was realized through secondary self-assembly,and the n-n heterojunction photocatalyst was prepared.BiOCl/PDI supramolecular heterojunctions with different self-assembly times were successfully prepared by the water bath heating method,which had excellent photocatalytic activity under visible light irradiation.Secondary self-assembly(BiOCl/PDI-2)showed a better adsorption capacity for Rh B than primary self-assembly(BiOCl/PDI-1)because of the larger absolute value of electronegativity.The removal rates of 5 mg/L phenol(non-ionic type),methyl orange(MO,anionic type),rhodamine B(Rh B,cationic type)and 10 mg/L Rh B by secondary self-assembly BiOCl/PDI-2 were 8.0%,3.4%,27.8%and 78.9%,which were higher than BiOCl/PDI-1 under visible light,because of its different exposed surface,narrower planar spacing,stronger visible light absorption performance and better transmittance.BiOCl/PDI-2 showed good recycling performance,and the contribution rate of the produced active species·O₂^-and ¹O₂was higher than that of BiOCl/PDI-1.The n-n heterojunction was optimized by secondary self-assembly,which made the?-?stack tighter and enhanced charge transport.(2)The degree of self-assembly to optimize supramolecule was modulated and the photocatalysis coupled persulfate system(PDI/PS/Vis)was constructed.The degree of supramolecular self-assembly was regulated by different acid addition amounts.Different degrees of self-assembly can affect the interlayer spacing,oxygen content,dispersibility,electronegativity,bandgap width,electron and hole separation efficiency of PDI,leading to the alteration of the photocatalytic activity.When the catalyst dosage was 0.5 g/L and the PS concentration was 1.5 m M,the constructed PDI/PS/Vis system showed a removal rate of 100%for 5 mg/L bisphenol A(BPA,50 m L)solution in 15 min and about 71.1%of the BPA was mineralized after 1 h degradation.The contribution of the reactive species in the PDI/PS/Vis system was ranked as h⁺?·O₂^->·OH?SO₄·^-.Based on the analysis of density functional theory(DFT)and ecological structure activity relationship(ECOSAR)program,BPA will eventually be converted into non-toxic ring-opening products.The PDI/PS/Vis system also showed efficient performance in eliminating organic pollutants such as phenol and 2,4 dichlorophenol.Furthermore,the SA-PDI photocatalyst had relatively high stability and recyclability.The chain reaction and mutual conversion reaction of free radicals occurred in the system.(3)The PDI/metal-organic framework/PS/Vis(PM/PS/Vis)system was constructed.The yield of active species was increased and the synergistic effect of photocatalytic coupling with persulfate was realized.A novel visible light photocatalysis coupling persulfate system was constructed to eliminate IOH micropollutant.The high stability MIL-101(Cr)MOF material was chosen.A one-pot method was employed to synthesize PDI/MOF heterojunction,which can achieve PDI self-assembly,Cr reduction,and formation of heterojunction simultaneously.Different mass ratios of PDI and MOF were investigated and PM-7(PDI:MOF=9:7,w/w)exhibited better e^-/h⁺separation efficiency and visible light absorption capacity.When the catalyst dosage was 0.5 g/L and the PS concentration was 3.0 m M,the PM-7/PS/Vis system can completely degrade 5 mg/L IOH solution(50 m L)within 35 min and about 67.4%of the IOH was mineralized after 1 h reaction.Active species h⁺and·OH played dominant roles.Free radical chain reactions and interconversions occurred in the PM-7/PS/Vis system.Moreover,the PM-7photocatalyst had relatively excellent stability and recyclability.Furthermore,the PM-7heterojunction displayed excellent efficiency in activating persulfate under actual sunlight.(4)The PDI loaded biochar/PS/Vis system(PB/PS/Vis)was constructed.Low-cost addition of reactive active sites for efficient production of active species was realized.SA-PDI was successfully loaded on BC by one-pot method.PDI/BC can generate free electrons for PS activation to produce active species,which can eliminate IOH efficiently.The prepared PB-9(PDI:BC=1:9,w/w)displayed excellent photocatalytic activity towards IOH micropollutants under visible light irradiation with the removal rate of 100%within 2h(The catalyst dosage was 0.5 g/L,and the PS concentration was 1.5 m M).A-BC(acidified biochar)could activate PS to generate more free radicals than BC.The PDI band gap can be controlled by the amount of BC doped to construct an electron transport channel,while PS was added as an electron acceptor to hinder photo-generated e^-/h⁺recombination.Active species h⁺and·OH played dominant roles in the PB-9/PS/Vis system.Based on liquid chromatography-mass spectrometry and DFT calculations,the amide hydrolysis,amine oxidation,hydrogen extraction,deiodination reaction,addition of·OH and oxidation of C-OH occurred during the process of IOH degradation.The toxicity prediction of the ECOSAR program indicated that the intermediates of IOH performed high chronic toxicity to aquatic organisms.In this study,the e^-/h⁺separation efficiency of was improved by internal construction heterojunction and external addition of persulfate to regulate the active species of the reaction system.The PDI was introduced into the photocatalysis coupled persulfate system.This thesis enhances the understanding of the relationship between the number of self-assembly of PDI,the degree of self-assembly and the photocatalytic oxidation activity.It provides a reference for the construction and design of a new type of photocatalysis coupled persulfate system.It provides design ideas for increasing the production pathway of active species and improving the oxidation activity of the photocatalysis coupled persulfate system.It provides a design strategy for low-cost,controllable change of the PDI band gap to improve the oxidation activity of the photocatalysis coupled persulfate system.