Preparation Of MOF/GO Composite Nanofiltration Membrane For Dye Wastewater Treatment

With the socio-economic development and the deterioration of the water environment,the separation of organic dye wastewater has become an important part of water environmental protection that cannot be ignored.Organic dyes have high chromaticity,poor biodegradability,and high toxicity,which are potential threats to the environment and human health.It is essential to strengthen the research on dye wastewater treatment methods.Compared with other technologies,nanofiltration membrane separation technology exhibits outstanding treatment efficiency and no secondary pollution.In order to break through the trade-off upper limit of water flux and rejection rate,this paper selects the hydrophilic two-dimensional material graphene oxide（GO）as the reject layer of membrane.The hydrophic groups of rich carboxyl,hydroxyl and epoxy in GO can provide a large number of modification sites.Due to the strong interaction between adjacent nanosheets,GO membranes are easy to stack,resulting in a narrow interlayer spacing,which would limit water molecular transportion.The interlayer spacing between GO layers is adjusted by ZIF-8 with porous channel structure and hydrophilic tannic acid（TA）,which provides a solution for enlarging the transport channel of water molecules and avoiding pollutions accumulation.Combining experiment and computational fluid dynamics（CFD）simulation technology to provide guidance for the design of nanofiltration membranes in practical applications.In this study,ZIF-8/GO composite nanofiltration membrane（ZG-NF）was prepared by blending method and layer-by-layer self-assembly method respectively.Based on polyethersulfone（PES）membrane,ZIF-8 was used to adjust the GO layer spacing.The composite membrane material was characterized and tested,and the effects of the two preparation methods on the microstructure and dye filtration performance of the modified nanofiltration membrane material under different operating conditions were compared.The results show that the Zn²⁺ of ZIF-8 and the carboxyl group of GO are successfully combined through strong interaction,and the thickness and interlayer distance of the modified GO composite membrane are significantly increased.The water flux of methyl blue（MB）solution of ZIF-8/GO nanofiltration membrane（B-ZG-NF）prepared by blending method is up to 40.58 L/m²/h/bar,compared to unmodified GO sodium The membrane flux is increased by 1.46 times.The MB solution water flux of ZIF-8/GO nanofiltration membrane（L-ZG-NF）prepared by layer-by-layer self-assembly method is compared with that of unmodified GO nanofiltration membrane.Increased by 1.43 times,MB rejection rate of both methods reached more than 90%.TA is used to further modify the ZIF-8/GO composite nanofiltration membrane,and TA is deposited on the ZIF-8/GO composite membrane substrate to prepare TA-ZGNF.The composite membrane material is characterized and tested to explore the concentration of TA And the effect of deposition time on the microstructure of modified nanofiltration membrane materials and the filtration performance of dyes.The results showed that TA was successfully adsorbed onto GO through π-π interaction.At the same time,TA was also incorporated with ZIF-8 nanoparticles,which played a precise role in regulating the GO layer spacing.Compared with the ZIF-8/GO nanofiltration membrane prepared by layer-by-layer self-assembly method,the flux of TA-ZG-NF methyl blue increased by 15.04%.Based on the experimental results of dye wastewater treatment with modified nanofiltration membranes,CFD software Fluent was used to simulate the dye wastewater treatment to realize the visualization of the nanofiltration process and explore the effect of hydraulic operating conditions on the polarization polarization of the dye wastewater.The results show that when the flow is laminar,the concentration polarization causes the flux in most areas of the nanofiltration membrane to remain low.When the flow rate is increased and the flow becomes turbulent,the effect of concentration polarization is reduced.