Photocatalytic Degradation Of Oxytetracycline From Wastewater By ZIF-8/PSF/TPU Membrane

Oxytetracycline（OTC）is a broad-spectrum antibacterial drug with a wide range of uses.However,due to its good chemical stability,low biodegradation rate and high toxicity,it may cause serious environmental pollution problems.Therefore,OTC pollution problem needs to be solved.Zeolite imidazole frameworks（ZIFs）are a subclass of metal-organic frameworks,which play an important role in adsorption,separation and catalysis.ZIF-8 is a widely studied and applied ZIFs,which has the advantages of large specific surface area,adjustable pore size,good hydrothermal stability.Meanwhile,ZIF-8 has potential application value as heterogeneous catalyst.In this thesis,ZIF-8 was prepared by simple agitation method,the adsorption performance of ZIF-8 on OTC was investigated,the degradation effect of ZIF-8/VL system on OTC was studied,and the possible degradation mechanism of OTC was preliminatively analyzed.ZIF-8/PSF/TPU membrane was prepared by electrospinning,and its characterization and OTC photocatalytic degradation were studied.The main results and conclusions are as follows:（1）ZIF-8 was prepared by simple agitation method and applied to adsorb OTC in simulated wastewater.The experimental results showed that under the optimal reaction conditions,the removal rate of OTC with an initial concentration of 80 mg L^-1 reached 93.19%in 240 min.By adsorption isotherm fitting,the adsorption of OTC by ZIF-8 conforms to Freundlich isotherm model,indicating that the adsorption behavior of OTC by ZIF-8 is multi-molecular layer adsorption,and the adsorption reaction is easy to carry out.According to the adsorption kinetics study,the adsorption behavior of ZIF-8 on OTC could be described by pseudo second-order kinetics model.The fitting results showed that the adsorption behavior of ZIF-8 on OTC was based on chemical mechanism,and it was further confirmed that ZIF-8 had a good removal effect on OTC less than 80 mg L^-1.XRD,SEM,FTIR and XPS characterization showed that OTC was adsorbed on the surface of the material,and theπ-πinteraction between OTC and ZIF-8 promoted the adsorption behavior.（2）ZIF-8 was used as a catalyst to degrade OTC in simulated wastewater in ZIF-8/VL system.The experimental results showed that under the optimal reaction conditions,the basic removal of 20 mg L^-1 OTC in ZIF-8/VL system was achieved within 45 min.When the initial OTC concentration is increased to 80 mg L^-1,the OTC removal rate reaches 90%in105 min,indicating that the system has the advantage of high reaction efficiency.Moreover,ZIF-8 still maintained a good OTC removal rate after four cycles of experiment,indicating that ZIF-8 has good stability and recycling.The degradation mechanism of ZIF-8/VL system was confirmed by XRD,SEM,FTIR and XPS characterization.In the ZIF-8/VL system,OTC was adsorbed to the surface by ZIF-8,and activated free radicals were stimulated by VL irradiation,followed by electron transfer and/or dehydrogenation reaction to degrade and remove pollutants.The OTC degradation products were analyzed by high performance liquid chromatography-mass spectrometry,and the identification of six representative intermediates revealed that the OTC degradation process includes demethylation,decarbonylation,and hydroxylation.（3）PSF/TPU membrane was prepared by electrostatic spinning method,and the optimal substrate was determined by CA test and SEM characterization.The optimal ratio of spinning solution of the film was TPU:PSF=40:60,and the optimal electrospinning conditions were as follows:The spinning voltage was 25 k V,the distance between the spinneret and the receiving plate was fixed at 15cm,and the spinning fluid flow was adjusted to 1.0 m L h^-1 with a micro-injection pump,and the spinning time was 12 h.ZIF-8/PSF/TPU membrane were prepared by in-situ growth method,and the MOF films were characterized by SEM,ATR-IR,XPS and AFM.The best membrane ZPT-3 could remove 40%of 10 mg L^-1 OTC within 1h.SEM,ATR-IR,XPS and AFM were used to characterize the ZIF-8membrane after reaction.The results showed that the z IF-8 on the surface of ZPT-3membrane after reaction was lost,but the internal structure remained stable.