Construction Of Hybrid Ultrafiltration Membrane With In Situ Formed Functional Nanoparticles For Antifouling Performance And Mechanism Investigation

By integrating the distinct physicochemical properties of nanoparticle and simple preparation process and good flexibility of polymeric membrane,nanoparticles-enhanced membrane has extensive application prospects in water treatment,which possessed a series of advantages,such as enhanced pure water permeability and improved hydrophilicity.However,with the introduction of nanoparticles into composite membrane with traditional adding strategy,the aggregation and leaching of nanoparticles are two challenges for its fabrication and application processes.In this thesis,in situ preparative techniques were proposed to introduce functional nanoparticles into polymeric casting solution system,which constructed innovative nanoparticles-based membrane.The antifouling performances and mechanisms were also profoundly investigated.By controlling the chemical reduction or sol-gel process of nanoparticle precursors in casting solution or membrane formation process,the well dispersion or directional distribution for nanoparticles can be realized in membrane matrix or around membrane pores,which effectively restrained the aggreagation phenomenon.The results about performance evaluation indicated that the addition of in situ formed nanoparticles significantly improved the hydrophilicity,ultrafiltration properties and antifouling performances.Moreover,based on the adhesion force measurement with AFM,the fouling behavior and antifouling mechanism were also revealed.The detailed research contents are presented as follow:(1).The preparation of hybrid membrane with in situ formed metal nanoparticles and its antifouling performances.Ag nanoparticle was selected as the representation for metal nanoparticle.With the in situ chemical reduction,well dispersed Ag nanoparticles could be synthesized in PVDF casting solution with the size of 5 to 10 nm.The in situ formation of Ag nanoparticles accelerated the demixing rate of casting solution and tailored the micro structure of hybrid membrane,which significantly enhanced the hydrophilicity and ultrafiltration performance.More importantly,the Ag-decorated membrane restrained the formation and growth of biofilm on the membrane surface,presenting the obviously anti-biofouling property.(2).The fabrication of hybrid membranes with in situ formed metal oxide nanoparticles and their antifouling performances.ZnO and TiO2 nanoparticles were selected as the representation for metal oxide nanoparticles.With the in situ sol-gel process,the in situ formation for ZnO nanoparticles in PES casting solution and the self-assembly of TiO2 nanoparticles around the PES membrane pores could be realized.Especially for the preparation of PES hybrid membrane with TiO2 nanoparticles,the in situ preparative strategy induced the simultaneous formation of TiO2 nanoparticles and PES membrane matrix by controlling the hydrolysis and condensation rates of precursors.With the'traction' function of Pluronic F127,the self-assembled structure for TiO2 nanaoparticles around the membrane pores could be obtained.The in situ sol-gel process significantly ameliorated the hydrophilicity and pure water flux of hybrid membrane,which endowed membrane with functional application.Also,the self-assembled membrane showed antifouling performance,which presented in the higher flux recovery and lower fouling flux reduction,compared with pure PES membrane.More importantly,the introduction of F127 enhanced the stability of in situ formed TiO2 nanoparticles,which is benefit to the long term antifouling performance.(3).The investigation of fouling behavior and antifouling mechanism for PES hybrid membrane with in situ formed nanoparticles.Base on the preparation of hybrid ultrafiltraiton membrane with in situ formed metal oxide nanoparticles,sodium alginate(SA),bovine serum albumin(BSA)and humic acid(HA)were selected as the models of organic foulants to investigate the fouling process.With the application of adhesion force measurement technique of AFM,the interactions between organic foulant molecules and membrane surface at different fouling stages were revealed under micro perspective.Furthermore,the main antifouling mechanisms for hybrid membrane with in situ formed nanoparticles were also investigated by applying the classical fouling process modeling.The results indicated that the characteristics of organic foulant molecules in salt solution and the distribution of nanoparticles in membrane matrix have a significant effect on the antifouling mechanism for nano-based membrane.Compared with the hybrid membrane containing embedded nanoparticles,the self-assembled structure of nanoparticles around membrane pores fully presented the advantages of hydrophilic nanoparticles in improving the antifouling performance,which effectively restrained the adsorption of organic foulant molecules on the membrane surface or in membrane pores.