Study On Preparation Of Functionalized Graphene Oxide Modified Ultrafiltration Membrane And Its Anti-Fouling Performance

Ultrafiltration membranes can effectively intercept organics and microorganisms in seawater,and can be used in the pretreatment unit of reverse osmosis desalination process to slow down the organic pollution and biological pollution of reverse osmosis membranes.However,when filtering seawater,the surface of the ultrafiltration membrane also has problems such as Ca²⁺and Mg²⁺fouling,organic pollution and bacterial adhesion,which causes the flux of the ultrafiltration membrane to decrease,the membrane needs to be cleaned frequently,and the service life is reduced.Therefore,the development of ultrafiltration membranes that resist Ca²⁺and Mg²⁺scaling,organic pollution and bacterial adhesion is of great significance for improving the effectiveness of ultrafiltration membranes in seawater desalination pretreatment.This article intends to prepare different functionalized graphene oxide materials and modify the ultrafiltration membrane to explore the anti-pollution performance and mechanism of the modified membrane.In this paper,firstly,graphene oxide（GO）is prepared by the improved Hummers method,GO is carboxylated to obtain carboxylated graphene oxide（CGO）,and antibacterial quaternary ammonium salt groups are grafted on the surface of GO to obtain quaternary ammonium salt graphene oxide（QGO）.The chemical composition and microstructure of the three materials were characterized by infrared spectroscopy,scanning electron microscopy and other characterization methods.The results show that GO,CGO and QGO all contain a large amount of hydrophilic oxygen-containing functional groups,maintain a good nanosheet structure,and can be used as membrane material modifiers.In this paper,polyvinylidene fluoride（PVDF）is used as the matrix material for the preparation of ultrafiltration membranes,and GO,CGO and QGO are respectively used as modifiers of the membrane materials.Prepared the GO modified PVDF ultrafiltration membrane（GO-M）,CGO modified PVDF ultrafiltration membrane（CGO-M）and QGO modified PVDF ultrafiltration membrane（QGO-M）by the phase separation method,simultaneously preparing PVDF ultrafiltration membrane（Blank-M）as a control sample without adding modifier,A series of characterization and performance tests were carried out on various membrane materials prepared.Related test results show that the introduction of carbon nanomaterials such as GO,CGO and QGO can effectively improve the hydrophilicity and permeability of the membrane surface.In the range of p H=4～10,the membrane surface potential has always maintained the trend of QGO-M>Blank-M>GO-M>CGO-M.The relatively high potential on the surface of QGO-M is due to the introduction of Positively charged quaternary ammonium salt group.Taking the flux recovery rate as an indicator,membranes were treated on aqueous solutions containing Ca²⁺and Mg²⁺,aqueous solutions containing humic acid（HA）,aqueous solutions containing a mixture of Ca²⁺,Mg²⁺and humic acids,and simulated seawater with humic acid added.In the filtration experiment to test the anti-pollution performance of the membrane.QGO-M maintains a flux recovery rate of 92.3%～95.65%for the above four solutions,which is better than other membrane materials.This is because there are positively charged quaternary ammonium salt groups on the surface of QGO-M,which can effectively resist the scaling of Ca²⁺and Mg²⁺,at the same time,divalent cations are complexed with negatively charged HA,which reduces the surface electronegativity of HA,inhibits the electrostatic attraction between HA and QGO-M,and reduces organic pollution,therefore,QGO-M shows good resistance to Ca²⁺and Mg²⁺,organic matter and other pollution in seawater.In addition,the culture experiments of membrane materials and bacteria show that compared with Blank-M,the antibacterial properties of the modified membrane have been improved to a certain extent.Among them,the antibacterial rate of QGO-M can reach more than 95.7%.The mechanism analysis suggests that after the modification of this kind of membrane material,the improvement of surface hydrophilicity and the special structure of the blended QGO will help improve its antibacterial ability.In particular,the grafted quaternary ammonium salt group is a broad-spectrum antibacterial group,which can inactivate the bacteria in contact with it and achieve the antibacterial effect.Therefore,the antibacterial ability of Q-GM is more prominent.