Construction Of Porphyrin Metal Organic Framework And Study Of Its Photocatalytic Removal Of Organic Pollutants In Water

With the rapid development of modern industry,water pollution has become an inevitable problem in the world.Antibiotic pollutants,endocrine pollutants and other organic compounds emitted during production in medical,paper,chemical,machinery manufacturing and food processing industries have become an urgent social problem to be solved.Visible light photocatalysis is a green technology that effectively uses solar energy to generate reactive oxygen species(ROS)to achieve efficient removal of pollutants with high mineralization rates,and is widely used in wastewater treatment.However,in the actual photocatalytic process,ROS are easily quenched to form weak radicals by salt ions and natural organic matter(NOM),leading to a significant reduction in catalytic efficiency.Therefore,how to improve the ability of photocatalysis to resist the interference of complex water is the key to realize its practical application.Porphyrin metal-organic frameworks(MOFs)materials are prepared by metal clusters and porphyrin ligands,which exhibits attractive photosensitive properties and good stability.In addition,the rich micro-and mesoporous structures of porphyrin MOFs not only facilitate rapid adsorption of contaminants,but also isolate them from the complex aqueous environment.In this work,a series of porphyrin MOFs catalytic materials were designed and synthesized for the adsorption and photocatalytic degradation of organic pollutants in the complex aqueous environment.The main research contents and findings of this paper are as follows.(1)Zr-porphyrin MOF visible photocatalytic material was synthesized by hydrothermal method and applied to the photocatalytic system for the removal of bisphenol F(BPF)in saline water.In the Zr-porphyrin-MOF/visible-light system,O2·-and 1O2 dominated the degradation of BPF,and the unique structure of Zr-porphyrin MOF can generate more hydroxyl radicals in the presence of salt ions,which had a good resistant to NOM(2-10 mg/L),coexisting anions,etc.,thus greatly improving its performance in removing BPF in complex environments.Zrporphyrin MOF exhibited good adsorption capacity(49.59 mg/g)and stable photocatalytic degradation performance for BPF;the rich pore of Zr-porphyrin-MOF could well adsorb pollutants and reduce the contact distance between pollutants and ROS.The degradation pathway analysis and toxicity prediction showed that most of the BPF molecules were degraded to low toxic organic molecules in the Zr-porphyrin-MOF/visible-light system in salt water.(2)These four Zr6O8-porphyrin MOFs were prepared by adding different ratios of monocarboxylic acids and ligands to investigate the differences in photocatalytic performance of porphyrin MOFs with different configurations.BPA degradation experiments showed that the higher the percentage of monocarboxylic acids,the greater the degree of defects in the catalysts,resulting in better adsorption performance and more obvious advantages in photocatalytic performance.MOF-525 was selected for the anion influence experiments,and the results displayed that the coexisting anions could significantly promote the adsorption and photocatalytic degradation of BPA.And the EPR and quenching experiments showed that the content of O2·-,1O2,·OH was significantly increased in the MOF-525/visible-light system after the addition of Cl-.The DFT calculation also illustrated that the presence of Cl-not only promoted the charge transfer from MOF-525 to BPA molecules,but also promoted the separation of electrons and holes with a significant supercharge transfer in the photocatalytic process.In addition,the MOF-525/visible-light system can maintain good BPA removal efficiency with a wide pH range,high coexisting ion,and actual aqueous matrices,and performed well in cycling experiments.(3)Hf-porphyrin MOFs with different defect densities(Hf-TCPP-X)were constructed by introducing monocarboxylic acid linkers with different acids and used for adsorption and visible photocatalytic degradation of norfloxacin(NFX).The results showed that Hf-TCPP-FA with the highest defect density could remove more NFX molecules,and the removal efficiency increased from 8.5%to 93.6%.In the effect of anions experiments,anions(Cl-SO42-,NO3-,HCO3-)could promote the adsorption and photocatalytic degradation of NFX molecules by HfTCPP-FA.The quenching experiments and EPR analysis revealed that the addition of Cl-could significantly enhance the contents of O2·-,1O2 and ·OH.DFT calculations demonstrated that the adsorption energy of Hf-TCPP-FA on NFX decreased from-12.128 eV to-19.1 57 eV after the addition of Cl-.Cl-participated in the electronic rearrangement within the catalyst and promoted the electron transfer in the material,and the electron delocalization of Hf in the Hf-TCPP-FA/Clsystem increased with an enhanced electron transfer.In the photocatalytic process,the coexisting anions could play the role of additional electron donors to transfer their own electrons into the Hf(Ⅳ)metal cluster to form more low-valent Hf(Ⅲ),and subsequently,Hf(Ⅲ)could react with dissolved oxygen to produce more superoxide radicals to promote the degradation of NFX.(4)Hf-porphyrin MOFs with different defect densities(TCPP@UiO-66(Hf))were synthesized by doping different contents of TCPP in situ synthesis due to the good stability of UiO-66.A large number of oxyfluorofloxacin(OFL)degradation experiments showed that the removal of OFL by the catalyst increased from 13.4%to more than 96%after doping TCPP.In the effect of anion experiments,anion improved the adsorption rate and degradation rate of OFL in TCPP-UiO-66/visible-light system.The quenching experiments and EPR analysis proved that it was dominated by O2·-,1O2 and OH,and the content of these three active species increased significantly in high salt water,and SO4·-was produced in the system after the addition of SO42-.In the photocatalytic process,the coexisting anions can play the role of additional electron donors to transfer their own electrons into the Hf-O metal cluster to form more low-valent Hf(Ⅲ)and SO4·-,while Hf(Ⅲ)can react with dissolved oxygen to produce more superoxide radicals.In addition,for the degradation of different pollutant molecules,the TCPP-UiO-66 catalyst preferentially degraded pollutant molecules containing functional groups such as-COOH and-OH.