| The shortage of water resources and water pollution are the prominent bottlenecks restricting the construction of ecological civilization in China.Therefore,it is urgent to highlight the research of reclaimed water purification technology in order to realize the resource utilization of sewage.M embrane separation technology is widely used in the field of drinking water purification and water reuse due to its easy operation and maintenance without secondary pollution.At present,traditional membranes are liable to be polluted in practical application,and it is difficult to remove small molecular weight micro-pollutants.Moreover,they are subject to the trade-off effect between permeability and selectivity,resulting in high energy consumption cost and low separation efficiency,which limits the application of membrane technology.Therefore,it is necessary to develop high-performance membranes to meet specific separation requirements.Guided by the functional engineering of membrane surface,a series of membrane preparation and surface modificati on methods were proposed by adopting the polyphenol-based surface engineering strategy.The antifouling performance and separation efficiency of the membrane were improved by regulating the important properties of membrane surface,such as hydrophilicity,surface charge and reactivity.Based on the abundant moieties on polyphenol medium layer,the cyclodextrin molecules with high hydrophilic outside were grafted on membrane surface by secondary modification.A hydration layer formed due to the abundant hydroxyl structure of modified membrane surface.Both static BSA adsorption and dynamic organic fouling showed a significant reduction,indicating that modified membrane has a “fouling resistance” effect towards organic pollutants.At the same time,the functional molecules with bactericidal effect were introduced by host-guest assembly with cyclodextrin.Antibacterial experiments showed that membrane surface with both anti-adhesion and bacterial inactivation(“fouling attack”)properties were obtained.Dynamic fouling test showed that the flux reduction of the modified membrane was 31% lower than that of the original membrane,and the contents of total organic carbon and ATP accumulated on the membrane were significantly reduced,which indicates successful inhibition of biofilm formation.The antibacterial mechanism based on inhibiting bacterial reproduction rather than damaging cell membrane was proposed,which provided a better choice for membrane fouling control.A bioinspired dualfunctionalization strategy of membrane surface was provided,enabling both“defensive”(adhesion resistance)and “offensive”(bacterial inactivation)efficacies,which provided theoretical guidance for membrane fouling control in the treatment of actual complex wastewater.In order to achieve the energy-saving separation of macromolecules,a dually charged low-pressure nanofiltration membrane was constructed based on polyphenol-engineered membrane surface modification strategy.On the basis of traditional dopamine deposition strategy,rapid polyphenol deposition and polyethyleneimine induced co-deposition technology were developed.On one hand,the stability and uniformity of deposition coating were effectively improved.On the other hand,functional layers with different charges were constructed on membrane surface,so as to prepare composite separation layer with “sandwich”structure and alternating charges.By adjusting the composition and deposition time of the polyphenol deposition system,the surface charge structure on the membrane surface can be well-tuned,thus optimizing the membrane separation efficiency for organic molecules with different charges.An efficient separation mechanism based on the synergistic effect of Donnan repulsion and micro-electric field was proposed.In addition,the rapid deposition process introduced a large number of carboxyl and amino groups,resulting a loose surface structure with high charge and high hydrophilicity.The developed dually charged composite membrane can obtain high water flux under low driving pressure.Compared with the traditional NF membrane,this dual-charged loose nanofiltration membrane exhibited a removal rate of more than 90% for dye molecules with different charges at low pressure(1.5 bar),which achieve efficient separation of charged molecules at low energy consumption,and has a c ertain application potential for wastewater treatment in restricted areas.Finally,in view of the low removal efficiency of toxic micropollutants by traditional membranes,a novel biocatalytic membrane was prepared based on polyphenol-induced in situ biomimetic mineralization method.The biocatalytic composite membrane was based on the ultrafiltration membrane,and the media layer was constructed on the membrane surface by the co-deposition technology of polyphenol amine and polyethyleneimine.Uniform and continuous MOF-enzyme catalytic functional layer was formed on the membrane surface by the in-situ biomineralization method under mild conditions.Based on the synergistic mechanism of adsorption,catalytic oxidation and membrane rejection,the removal rate of bisphenol A by biocatalytic membrane in continuous mode reached 98 %.The nanoporous structure of MOFs is conducive to the adsorption and enrichment of BPA molecules near the active center,providing a limited microenvironment for enzymatic reactions,thereby improving the catalytic efficiency of biocatalytic membranes.At the same time,the metal-organic framework provides a rigid and continuous protective shell for e fficient biological enzymes,which still maintains the original activity 92% after five cycles,effectively solving the problem of enzyme reusability and stability.This study breaks through the bottleneck of poor removal efficiency of micro-pollutants by traditional separation membrane,solves the problem of poor stability of traditional biocatalytic membrane,and provides a new way to realize efficient removal of micro-pollutants under low pressure. |
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