| One of the most serious challenges in modern society is to secure adequate water resources with specific quality for various designated applications.Highly efficient and economical membrane separation technology is playing an increasingly crucial role in versatile fields including drinking water treatment,brackish and seawater desalination and wastewater treatment.Generally,there is imperative need to remove salts from mixtures that contain low molecular weight organic compounds in many fields(textile industry,food industry,agriculture,pharmaceutical industry and mining industry,etc.)because of the growing demand for internal recycling and the conservation of chemicals.Especially for high salinity textile wastewater,the fractionation of dye/salt mixture will not only allow to recycle valuable organic products,but also alleviate the issues ascribed to high salinity,which in return can be used as a renewable resource with the appearance of forward osmosis(FO),pressure retarded osmosis(PRO),reverse electrodialysis(RED)and bipolar membrane electrodialysis(BMED).Pressure driven membrane processes such as nanofiltration(NF)and reverse osmosis(RO)or electrodriven membrane processes such as electrodialysis(ED)may be applied for fractionation of organic compounds with low molecular weight and salts(Mg2+SO42-,Cl-,Na+,etc.).Obviously,these processes inevitably result in a loss of valuable salts.Therefore,in the treatment of textile wastewater,advanced membranes should have the following virtues:high water permeability,dyes rejection and salts permeation in view of sustainability and resource recovery(both salts and dyes).The main contents are as follows:(1)Charged mosaic membranes containing equivalent cationic and anionic exchange capacities are capable of decreasing the Donnan effect and thus accelerating salts permeation,while maintaining a high rejection of low molecular weight organics.In this study,charged nanosheets zwitterion-hydrotalcite(ZHT)was synthesized by grafting sulfobetaine methacrylate(SBMA)on the surface of positively charged Mg/Al hydrotalcite via surface initiated reverse atom transfer radical polymerization(RATRP).Subsequently,charged mosaic membranes were prepared by embedding different amounts of zwitterion-hydrotalcite into polyethersulfone(PES)casting solution via non-solvent induced phase separation(NIPS).Fourier transforms infrared spectra(FT-IR)and transmission electron microscopy(TEM)indicates that the zwitterion-hydrotalcite was successfully synthesized and well exfoliated.X-ray photoelectron spectroscopy(XPS),scanning electron microscopy(SEM),ionic exchange capacity(IEC),surface zeta potential measurement and water contact angle were employed to investigate the effect of ZHT content on overall performance of prepared membranes.It was found that charged mosaic membranes manifested an enhanced ionic exchange capacity,surface hydrophilicity and hydraulic permeability compared to original membrane.Importantly,the charged mosaic membranes presented excellent dyes retention(86.7%for Reactive Red 49),superior salt permeation,and high water flux(80.2 L m-2 h-1)under 0.4 MPa.Furthermore,the retention of MgCl2,Na2SO4 and NaCl was as low as 9.3%,7.6%and 0.53%,respectively.It is worth noting that ultra-high salt permeation as a bright spot of charged mosaic membranes could be achieved,which was ascribed to the introduction of zwitterion-hydrotalcite.A mechanism of salt transport through charged mosaic membranes is proposed in this study.Overall,these promising results demonstrate the potential of charged mosaic membranes and suggest their comfortable use in dyes separation.(2)Developing separation membranes with antibacterial activity is imperative for water purification and has always been the hotspot topic researchers concern.In this paper,a ubiquitous and cheap enzyme with antibacterial activity named lysozyme was used to prepared antibacterial membranes for dyes removal.Instead of piperazine(PIP)and m-phenylenediamine(MPD),lysozyme was deployed as aqueous monomer to react with TMC to construct separation membranes by interfacial polymerization.The formation of an ultrathin lysozyme-polymer active layer was verified by ATR-FTIR and FESEM.Surface imaging by FESEM showed a rugged structure with a uniform distribution of large bumps.The degree of crosslinking,controlled by the concentration of lysozyme and TMC,appeared to have a significant influence on the physicochemical properties of the resultant membrane,as well as its separation performance.The filtration results demonstrate that the ultrathin lysozyme membranes have high water flux(58.04 L m-2 h-1)and allow for the simultaneous retention of low molecular weight reactive dyes(98.9%)and selective permeation of salts(96.6%).Furthermore,the antibacterial activity of the lysozyme membranes was assessed against gram-negative E.coli bacteria;the membranes with higher lysozyme concentration exhibited a sufficient antibacterial activity(81.9%).This facile strategy of enzyme immobilization not only allows for an in-situ preparation of enzyme-polymer membranes,but also maintain the native enzyme activity despite the high degree of covalent bonding between proteins.The resultant lysozyme membranes prove their potential in dyes removal,while also corroborating the value of interfacial polymerization in the field of enzyme immobilization and protein-polymer film construction.(3)A rational manipulation of the surface structures and properties of thin-film composite membranes is important to optimize their separation performance and service durability.In this study,facile strategy is reported for fabricating electroneutral loose nanofiltration membranes based on the rapid co-deposition of biomimetic adhesive polydopamine and poly(ethylene imine)(PEI)by using CUSO4/H2O2 as a trigger.Through this strategy,the surface properties and the filtration performance of the membranes can be easily tailored by the addition of PEI and CuSO4/H2O2,as well as tuning the deposition time.UV,XPS,SEM,AFM,zeta potential,water contact angle and nanofiltration measurements were used to investigate the membrane performance.Surface characterization revealed that overall enhanced surface properties including low roughness,favourable hydrophilicity,and relatively neutral charge can be achieved after the addition of PEI.The optimum membranes,with 1 h co-deposition of PDA and PEI,show an ultrahigh water permeability(26.2 Lm-2 h-1 bar-1),distinguished rejection for both negatively and positively charged dyes and a high permeation of divalent salts(>90%).Furthermore,the optimum membranes also show an excellent operational stability in long-term nanofiltration operation in alkaline solution.This study provides an efficient and facile approach to tailoring the membrane properties and structure for loose nanofiltration membranes.(4)Nowadays,a growing number of sewage treatment plants are equipped with nanofiltration(NF)process for wastewater bleaching and desalination.The surface characteristic of the NF selective layer could greatly impact the filtration and separation performance.In this study,a mussel-inspired facile method is employed for NF membrane fabrication.The hydroxyl radical activation generated by CuSO4/H2O2 is used for a rapid PDA deposition.To obtain an electroneutral,anti-fouling and anti-bacterial surface,the zwitterionic polymer(SBMA)is introduced for PDA/SBMA codeposition and polymerization.The XPS,FTIR,SEM,AFM and water contact angle analysis were employed to investigate the selective layer characterization.The RD-1S membrane was considered as the most optimized NF membrane.In addition,the filtration and separation performance of multivalent salts(monovalent and divalent ion)and dyes(negatively and positively charged)is investigated in detail and the separation performance of dyes and salts are diverse.The anti-fouling performance of RD-1S membrane is excellent,especially from the view of irreversible fouling resistance.At last,the co-exist of chelated copper and SBMA provides a reliable anti-bacterial performance. |
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