| Sea water reverse osmosis(SWRO)is an economical and efficient process for the preparation of drinking water from seawater.In order to inhibit the proliferation of microorganisms in seawater,pretreatment of seawater is an essential process.However,the disinfection by-products(DBPs)produced by the reaction between disinfectants and organic compounds have carcinogenicity and teratogenicity.At present,the seawater desalination reverse osmosis membrane is mostly made of polyamide.Due to its physical and chemical characteristics,the rejection rate of small molecule DBPs is low(less than 70%).These problems can be solved by further modification to improve DBPs removal performance of polyamide reverse osmosis membrane.Thesis,based on the high specific surface area and the efficient separation of water and sodium hydrate,three kinds of ZIF-8 particles(50,150 and 400 nm)were synthesized by adjusting reaction conditions.ZIF-8/polyamide composite membranes(labeled TFN-50,TFN-150 and TFN-400)were prepared by adding them into organic phase during interfacial polymerization process.The membrane flux,antifouling performance and DBPs removal performance of the composite membranes were investigated.Results showed that the performance of TFN-50membrane prepared by 0.3 wt%50 nm ZIF-8 was the best,the water flux was 1.85L/m2·h·bar,and the rejection rate of sodium chloride was 99%.However,the performance of TFN-400 membrane prepared with the same amount of addition was much lower than that of TFN-50 membrane.The effect of particle size on the physicochemical properties of ZIF-8/polyamide membrane was studied by means of field emission scanning electron microscopy,atomic force microscopy and X-ray photoelectron spectroscopy.It demonstrated that the dispersion of ZIF-8 in polyamide layer caused by particle size was the main factor for the performance difference of the synthesized membranes.The highest concentration of Zn2+in TFN-50 was 51.30?g/cm2,while that in TFN-400 was only 5.14?g/cm2.Results showed that the rejection rate of TFN-50 for small molecule TCM and NDMA was more than 75%,which proved that the addition of ZIF-8 particles with adsorption effect on DBPs could improve the DBPs removal performance of membrane.In order to further improve the adsorption performance of ZIF-8 for DBPs,two preparation methods of modified ZIF-8 particles were proposed to enhance the removal performance of polyamide reverse osmosis membrane for DBPs:(1)carbon quantum dots(CQDS)were prepared by in-situ pyrolysis of glucose adsorbed into ZIF-8 pore structure to form CQDs@ZIF-8;(2)hydrophilic polyvinylpyrrolidone(PVP)and zwitterionic polymers(DMAPS)were introduced in the preparation of ZIF-8 to fabricate PZ@ZIF-8.During the interface polymerization,CQDs@ZIF-8and PZ@ZIF-8 were added to the organic phase to synthesize CQDs@ZIF-8/polyamide composite membrane(labeled as CQDs@ZIF-8 TFN)and PZ@ZIF-8/polyamide composite membrane(labeled as PZ@ZIF-8 TFN).FE-SEM and AFM were used to investigate the effect of modified ZIF-8 particles on the surface microstructure of the membrane.The basic properties of the modified ZIF-8/polyamide reverse osmosis membrane,such as water flux,chlorine resistance and fouling resistance,were investigated to optimize the preparation process.Results showed that the water flux of CQDs@ZIF-8 TFN membrane was 1.9 L/m2·h·bar,and the rejection rate of sodium chloride was 98.2%.After soaking in sodium hypochlorite solution,the rejection rate of CQDs@ZIF-8 TFN membrane for sodium chloride was only reduced by 11%.The water flux of PZ@ZIF-8 TFN membrane was 2.68 L/m2·h·bar,and the rejection rate of sodium chloride was 98%.The chlorine resistance and fouling resistance of PZ@ZIF-8 TFN membrane were enhanced simultaneously by adding PZ@ZIF-8 particles.The performance of modified ZIF-8/polyamide reverse osmosis membrane for19 kinds of DBPs was determined.The removal rate of small molecular DBPs was more than 80%,and the removal rate of macromolecular DBPs was more than 90%.By means of Fourier transform infrared spectroscopy(FT-IR),XPS and dissolution-diffusion model,the mechanism of DBPs removal by modified ZIF-8 TFN membranes were illustrated.The results show that CQDs released from partial decomposition of CQDs@ZIF-8 resulted in the formation of hydroxyl and carboxyl groups on the surface of the membrane.The formation of HCl partially degraded the acid sensitive PZ@ZIF-8,releasing DMAPS and PVP in the process of interfacial polymerization.The released substance could improve the adsorption energy of the membrane surface,and inhibit DBPs diffusion into the polyamide layer through hydrogen bonding interaction with DBPs.When the DBPs penetrated into the polyamide layer,the modified ZIF-8 particles could adsorb DBPs molecules and reduce the diffusion coefficient of DBPs in the membrane.Under the synergistic effect of size exclusion effect and adsorption effect,the modified ZIF-8 particles reduce the permeability coefficient of DBPs and improve the DBPs removal performance of polyamide reverse osmosis membrane.This paper provides a new method for the preparation of metal organic framework/polyamide reverse osmosis membrane with high water flux and high DBPs removal performance,which has important environmental,technical and economic significance. |
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