The Membrane Fouling Control And Cleaning Performance Of Ultrafiltration Membranes Enhanced By MoS₂ Functional Layer On The Membrane Surface

Membrane separation technology plays an important role in the water treatment and purification process,while membrane fouling hinders its development and practical application.The mitigation of membrane fouling and the development of efficient membrane cleaning strategies have been one of the hot topics in the field of membrane water treatment and resource recovery.Therefore,in this study,MoS₂ nanomaterials with excellent physical and chemical properties were selected to modulate the surface of ultrafiltration membranes（PES membranes）for the purpose of reducing membrane fouling and achieving efficient green membrane cleaning.Firstly,MoS₂ nanomaterials were prepared by hydrothermal synthesis,and MoS₂ functional layer was constructed on the surface of the PES-based membrane by pressure-assisted filtration,namely the MoS₂/PES membrane.Then,the mitigation process and membrane fouling mechanism of organic fouling and biofouling on the membrane surface enhanced by MoS₂functional layer were investigated,respectively.Finally,considering the peroxidase-like properties of MoS₂ nanomaterials,H₂O₂ was used as a membrane cleaning agent.the MoS₂/PES membrane cleaning parameters were investigated to achieve efficient and green membrane cleaning.The membrane cleaning mechanism was illustrated in detail.The conclusions of the study are as follows:（1）MoS₂ nanomaterials were prepared by a hydrothermal synthesis method.The results of characterization and analysis show that the prepared MoS₂ nanomaterials possess a 1T/2H mixed-phase structure with a large specific surface area,and abundant surface defects of which could provide more catalytic active sites.It has been experimentally demonstrated that MoS₂ has peroxidase-like properties and could catalyze the production of large amounts of ROS and oxygen.And then,MoS₂/PES membranes were prepared by pressure-assisted filtration,and the structure and properties of which were characterized.The MoS₂ functional layer was approximately36μm thick,and which showed a stacked honeycomb pore structure for providing nano-channels to transfer ROS during the catalytic process.（2）Humic acid（HA）as a representative organic foulant was used to investigate organic membrane fouling control and the membrane cleaning mechanism of MoS₂/PES membrane.During filtration of HA,the filtration efficiency of the MoS₂/PES membrane（91%）was increased by 6%compared to the original PES membrane.After cleaning with H₂O₂（1%,p H=4.0）solution,the flux recovery rate（75%）of the MoS₂/PES membrane was approximately 5 times higher than that of the original PES membrane.And the removal efficiency of irreversible foulants for the MoS₂/PES membrane reached 80.15%,which was much higher than that for the PES membrane（19.46%）.Results of 7 cycles of consecutive membrane fouling and cleaning demonstrated MoS₂ functional layers not only relieved membrane fouling but also exhibited higher water flux.The cleaning mechanism of organic foulants for MoS₂/PES membranes was as follows:MoS₂ nanosheets catalyzed H₂O₂ to produce·OH and ¹O₂radicals to degrade organic foulants on the membrane surface directly,and the reaction system was accompanied by oxygen generation,which not only accelerated the mass transfer of ROS,but also the turbulence of oxygen facilitated the separation of irreversible foulants from the membrane surface.（3）Escherichia coli（E.coli）was used as a typical biological foulants.The antimicrobial properties and membrane cleaning performance of the MoS₂/PES membranes were investigated.Furthermore,the cleaning mechanism was illustrated.The prepared MoS₂ nanomaterials exhibited high bactericidal properties（97%）with a concentration dependence.The MoS₂/PES membranes showed in situ antibacterial properties with high bactericidal efficiency.During the filtration of E.coli bacterial suspensions,the permeate flux of the MoS₂/PES membrane was reduced by 30.93%and the permeate flux of which was twice as high as that of the PES membrane,demonstrating excellent antifouling properties.After washing in H₂O₂ solution for 5min,the flux recovery of the MoS₂/PES membrane was 61.56%,which was much higher than that of the PES membrane（24.27%）.The antibacterial mechanism of MoS₂/PES membrane was as follows:the MoS₂ functional layer induces oxidative stress in bacteria to produce ROS.On the other hand,cell membrane was disrupted in direct contact with the sharp edges of MoS₂ nanosheets.The biofouling cleaning mechanism of MoS₂/PES membrane was as follows:MoS₂ nanosheets catalyzed H₂O₂to generate a large amount of ROS for inducing oxidative stress and a certain amount of oxygen turbulence for facilitating the detachment of the biofilm.Therefore,biofilm fouling control and effective membrane cleaning were both achieved.（4）As for the filtration of the secondary effluent form wastewater treatment plant,the larger suspended foulants formed a loose cake layer on the surface of the MoS₂/PES membrane,which could be removed by physical flushing.The flux recovery rate of MoS₂/PES membrane was only 25%,which was possibly due to the complexity of the secondary effluent water quality.However,the cleaning performance of MoS₂/PES membrane was still higher than that of PES membrane.