Construction,Structural Control And Separation Characteristics Of Self Cleaning Membranes

Water pollution is one of the major global challenges due to rapid population growth and industrialisation.In addition,natural water supplies are decreasing due to climate change and over-exploitation in developing countries.Wastewater treating system like ozonation is distressed by cost limitations.In addition,some classes of contaminants are resistant to aerobic degradation,and anaerobic process does not treat the water to desired limits.In contrast,due to the double advantage of cost and performance,membrane separation,especially for ultrafiltration and nanofiltration,is getting more and more attention.Low cost and ease of use make the process an attractive solution for water remediation,while facing with the inevitable membrane fouling problem.At the same time,advanced oxidation processes（AOP）that generate highly reactive species（e.g.H₂O₂ and·OH）for degradation of contaminants,has received growing interests for treatment of waste effluents.Photocatalysis is one of the AOP techniques and is known for its ability of degrading organic contaminants under visible and UV light.However,difficulty in filtration,particle agglomeration and inconvenient recovery of nanoparticles from slurry are some of the biggest practical challenges to its commercial viability.Carbon nanotube（CNT）based adsorbents have attracted extensive research interest for aqueous pollutants removal.However,such adsorbents face the problems of limited adsorption capacities and costly regeneration.Here,we report a highly adsorptive photo-regenerable CNT based multifunctional membrane with excellent self-cleaning properties via the facile vacuum filtration method,followed by FeOOH in-situ anchoring and silver-amino reaction.Various dyes（Rhodamine B,methylene blue,eosin Y and acid orange 7）and emerging contaminants（bisphenol A,amoxicillin and p-nitrophenol）were tested with the CNT based membrane.Our membrane exhibited superior adsorption performance to dyes among CNT based adsorbents reported in literature.In particular,the CNT based composite membrane displayed even better adsorption performance to cationic dyes.The adsorption capacities of the membrane for Rhodamine B and methylene blue were up to 181 and 247 mg/g,respectively.The membrane also had excellent self-cleaning and photo-regenerable properties after severe organic fouling.Our multifunctional CNT based membrane combined the features of adsorption,membrane separation,and catalytic degradation into one system,showing great promise for dye polluted wastewater purification.This study also offers a new strategy to engineer robust adsorptive,self-cleaning and regenerable membranes for wastewater treatment.Herein,a dense rutile nano-titanium dioxide（TiO₂）coating was constructed on the nonwoven fabric（NWF）membrane surfaces via the bio-inspired TiO₂ sol-gel method.The mineralization of nano-TiO₂ was large-scale and uniform on the non-woven fabrics（NWF）surface,reducing membrane surface roughness and pore sizes;nevertheless,largely improving the dynamic water super-wetting,water penetration,and underwater oil repellency due to the excellent water affinity.Nuclear magnetic resonance（NMR）revealed the hydration layer of the NWF was reinforced by the surface-mineralized nano-TiO₂,thus preventing the bovine serum albumin（BSA）and emulsified oil droplets from fouling.Even after the 180 min of continuous emulsion separation,the mineralized NWF（TiO₂-PDA/PEI-NWF-M）only suffered from the mild decline of permeation fluxes from～55 L/m²·h to～43 L/m²·h and oil rejection from～94%to～83%,respectively.After illuminated under UV light,it was recovered successfully because of the in-situ generation of reactive species（e.g.·OH,·O₂^-and ¹O₂）on TiO₂ weakened the interaction of foulants on the membrane surface.The photoactive self-cleaning provided the TiO₂-PDA/PEI-NWF-M with better efficiency of oil-fouling reduction,permeation fluxes recovery,and oil removal than those of simple water and harsh NaClO washing.Most importantly,the TiO₂-PDA/PEI-NWF-M maintained its surface physical and chemical characteristics after vigorous cross-flow shearing for 48 h.It provided the practical potential in developing the high-efficient and free-chemical self-cleaning with the high and stable flux recovery for the tricky crude oil/water emulsion remediation.