Fabrication And Properties Of Prussian Blue Derivative Nanofiltration Membranes

As a classic MOFs materials,Ni-Fe PBA（Prussian blue analogue）was rarely applied to the preparation of nanofiltration membranes.Therefore,this thesis explored emphatically how to apply this MOFs material to prepare a high-performing nanofiltration composite membrane and improve the flexibility of composite film modified by rigid Ni-Fe PBA crystal layer.Following on that,we designed and fabricated a“funnel-shaped”water channel on the membrane by combing ZIF-8 with Ni-Fe PBA with different porous structures.The microstructure and nanofiltration performance were also studied in detail.The work here could make positive exploration for the application of MOFs materials in the nanofiltration field.In the thesis,the L-dopa was firstly chosen as an intermediate layer to modify the PSF ultrafiltration membrane,while the dense Ni-Fe PBA crystals were constructed on the L-PDA/PSF composite membrane surface by in-situ growth method to form Ni-Fe PBA/L-//PSF nanofiltration membrane.The as-fabricated membrane was characterized by WCA,ATR-FTIR,SEM,XRD,XPS and AFM.As suggested,the Ni-Fe PBA can be uniformly assembled on the membrane.Nevertheless,the crystal layer still faces challenges of layer cracking,which has a tremendous negative impact on the nanofiltration performance.In order to solve the crystal layer cracking problem,the TA-Fe³⁺was introduced as the intermediate connecting layer and polyethylene-imine molecules to prepare PEI@Ni-Fe PBA/TA-Fe³⁺/PSF nanofiltration membrane.ATR-FTIR and XPS were applied to investigate the chemical composition of membrane surface.XRD results showed that Ni-Fe PBA has high crystallinity.SEM and AFM were used to reveal the surface morphology of membrane.It indicated that the membrane cracking could be well resolved by our design.The prepared nanofiltration membrane showed good hydrophilicity by giving a low WCA.The nanofiltration performance of the membrane was systematically tested,giving dye rejection rates of>99%,76.78%and 60.42%for large molecular（>342 Da）,methyl orange and isatin,respectively.Such membrane also showed excellent water purification efficiency as～65L·m^-2·h^-1·bar^-1,good long-term stability and anti-fouling performance.In addition,the long-term stability and fouling resistance test also showed that the prepared PEI@Ni-Fe PBA/TA-Fe³⁺/PSF nanofiltration membrane has a very stable nanofiltration performance during the continuous operation of 32 h,as well as excellent anti-pollution ability（flux recovery rate（FRR）:96.5%）.To further improve the nanofiltration performance for small molecular dye,we designed and fabricated the Ni-Fe PBA/ZIF-8/PDA/PSF nanofiltration membrane with funnel-shaped water channels by combing ZIF-8（pore sizes:3.4（?））and Ni-Fe PBA（pore size:5.1（?））.ATR-FTIR and XPS results confirmed that the ZIF-8 and Ni-Fe PBA could be well composited.The prepared membranes showed excellent rejection rates of 98.86%and 95.47%for methyl orange and isatin,respectively(corresponding water flux of～35.9 L·m^-2·h^-1·bar^-1),which were much better than the ZIF-8 nanofiltration membrane（methyl orange:93.5%,isatin:92.7%）.Besides,the water stability of Ni-Fe PBA/ZIF-8/PDA/PSF nanofiltration membrane was also better than that of the control membrane.