The Performance Studies Of Polyethersulfone-based Composite Ultrafiltration Membranes With Functional Cellulose Nanocrystal

Ultrafiltration technology was widely used in wastewater treatment for its efficient separation process,environmental friendliness,and simple operation.However,some problems that cannot be ignored in the practical application of ultrafiltration membranes,such as terrible filtration performance,ease to be pollution,and the"trade off"between water flux and rejection performance,which severely restricts its development.To overcome the above problems,functional nanocellulose was used as the filler to enhance the polyethersulfone（PES）ultrafiltration membrane to broaden its application,and explored its internal structure and ultrafiltration performance in detail in this work.First,highly multi-branches cellulose nanocrystal（Multi CNC）additives with abundant hydroxyl（-OH）and carboxyl（-COOH）groups were prepared by an alternate grafting strategy by taking advantage of the easily modified surface chemistry of cellulose nanocrystals（CNC）.It was successfully introduced into the PES membrane through the blending modification technology.Thanks to the strong hydrogen bond between PES and Multi CNC,the prepared highly hydrophilic composite ultrafiltration membrane possesses excellent performance.Specifically,with the increase of Multi CNC content,the hydrophilic property,charge,water flux and anti-fouling performance of the composite membrane were improved comprehensively.When the content of Multi CNC reached 1 wt%especially,the water flux of the composite membrane was as high as961.65 L/m²·h,and the retention rate of BSA reached the maximum value of 96.4%.As the result shows,the permeability and retention rate of the composite membrane can be effectively improved,indicating that the limitation of"trade off"effect was overcome.In addition,the anti-fouling performance of the composite membrane was explored,and the flux recovery rate of the composite membrane containing 1 wt%Multi CNC was 74.08%,which was 2.1 times higher than that of the original PES membrane（FRR=34.81%）,indicating that Multi CNC can effectively improve the composite membrane anti-fouling.A novel MOF@Multi CNC composite filler was in situ generated by compounding porous Ni-Zn MOF with Multi CNC.Two different structures,lamellar and nanosphere,were prepared by different synthesis methods.MOF@Multi CNC/PES composite ultrafiltration membrane was prepared by blending with PES.The synergistic effect of the super hydrophilic Multi CNC and the porous structure of MOF greatly improved the filtration performance and anti-fouling performance of the composite membrane.In particular,Ni-Zn MOF@Multi CNC_0.05/PES membrane and Ni-Zn MOF@Multi CNC_0.01/PES membrane showed high water fluxes of 1151.00 and 1388.49L/m²·h,respectively,which increased 83%and 120%compared with pure PES membrane.However,the Ni-Zn MOF@Multi CNC_0.05/PES membranes showed a BSA retention rate of more than 99%.Thus,the Ni-Zn MOF@Multi CNC/PES membrane performance was substantially improved across the board.Finally,the effects of differently structured nanofillers on the performance of polyethersulfone ultrafiltration membranes were investigated.Compared with the MOF@Multi CNC composite fillers with nano-spherical structure,the petal-shaped composite fillers have higher specific surface area and richer pore structure,which provides more additional transport channels,thereby improving the screening performance and permeability of the composite membrane.In addition,the MOF@Multi CNC/PES composite membrane was used for milk solution filtration,which exhibited good sieving ability and improved the proportion of milk protein effectively.