Preparation Of Multifunctional Nanofiltration Membrane Based On Interfacial Regulation And Its Application In Water Treatment

Organic micropollutants(OMPs),including pharmaceuticals and polycyclic aromatic hydrocarbons,etc.,have been widely detected in natural waters.Molecular weight of OMPs is generally lower than 500 Da,and most of them have high toxicity and bioaccumulation,resulting in potential threat to human health and ecological system.Nanofiltration(NF)is considered as an advanced technology for OMPs removal.However,most commercially available NF membranes have strong affinity with OMPs,which leads to serious membrane fouling during filtration process,causing reduced water permeability and lower retention ability.Therefore,it is important to regulate interfacial interactions during membrane filtration for improving OMPs removal.In this work,firstly,the effect of the properties of membranes and OMPs on their NF performance is evaluated through investigating filtration behaviors of NF membranes when treating the OMPs-containing wastewater,and the corresponding membrane fouling mechanisms are analyzed.Then,based on the surface modification and grafting strategies,the multifunctional NF membrane is prepared through loading biocatalysts or chemical catalysts on the membrane surface,respectively.The resultant multifunctional NF membranes show high removal of various OMPs due to the synergistic effect of membrane separation and catalysis degradation.The detailed results are as follows:(1)Five commercially available polyamide(PA)NF membranes are used to treat three OMPs which widely exist in natural waters.The effect of OMPs adsorption in membrane on the NF performance is evaluated in terms of water permeability and retention ability for three OMPs and several neutral hydrophilic molecules.The results indicate that size exclusion and adsorption are main mechanisms of the OMPs removal by PA NF membrane.The effect of size exclusion is more important for OMPs with weaker polarity and higher molecular weights.OMPs mainly adsorb in the membrane pores resulting in the reduction in porosity and permeability,and the adsorption-diffusion-desorption behavior of OMPs also leads to their lower retention by the PA NF membranes.The NF membrane with small pore size and narrow pore size distribution is preferred for OMPs removal due to its lower permeability loss and indiscriminate pore blocking effect.(2)The surface functionalization strategy is used to prepare a regenerable biocatalytic membrane for the OMPs removal.Polydopamine(PDA)and polyethyleneimine(PEI)are successively used to modify the NF membrane surface.PDA/PEI coating not only can enhance antifouling ability of NF membrane,but also can immobilize laccase on the membrane surface through electrostatic and hydrophobic interactions with PEI molecules.With the addition of mediator,the biocatalytic membrane shows near 100%removal for bisphenol A(BPA,endocrine disruptor)due to the synergistic effect of membrane rejection and adsorption as well as laccase catalysis.The BPA removal by the biocatalytic membrane keeps higher than 97%during 7 reuse cycles.(3)A graphene oxide(GO)NF membrane is prepared by the targeted surface modification strategy for the OMPs removal,which has the narrow pore size distribution and strong antifouling ability.Firstly,ferric ions(Fe3+)mediated GO nanosheets are used to prepare a stable GO membrane.The existence of Fe3+ can amplify the signals of GO membrane defects to facilitate the deposition of the coating of tannic acid and 3-(aminopropyl)triethoxysilane,thus narrowing the membrane defects.This targeted modification strategy can simultaneously enhance antifouling ability and regulate transport channels of the GO membrane.The resulted GO membrane shows high and steady rejections for various OMPs,even in the long-term operation,cross-flow filtration or under high-pressure.(4)A photo-Fenton self-cleaning NF membrane is prepared for the OMPs removal based on biomimetic mineralization strategy.A ?-FeOOH layer is loaded on the above GO NF membrane surface via in-situ mineralization method.In the presence of visible light and H2O2 the ?-FeOOH layer shows high photocatalytic activity for tetracycline hydrochloride(TCH)degradation through photo-Fenton reaction,endowing the NF membrane with strong self-cleaning ability.When such membrane fouled by TCH molecules,its membrane permeability can be completely recovered through photo-Fenton reaction in 5 min,without any damage on membrane retention ability.