Construction Of The Selective Layer Of Anti-Biofouling Thin-film Composite Membrane For Nanofiltration Applications

With the development of global industrialization,water shortage and pollution problems have become increasingly prominent.Under the circumstances,the membrane separation technology with high separation efficiency and low energy consumption emerges,providing environmentally friendly and sustainable solutions for water treatment.Nanofiltration(NF),capable of removing multivalent ions and small neutral organics with molecular weight above 200 Da,has been wildly applied to seawater/brackish water desalination,wastewater treatment,food processing and chemical industries.However,membrane separation always faces with inevitable fouling(expecially the bio-fouling)problem that restricts its long-term applications and therefore further development.Despite that extensive efforts have been paid to alter the structure and physical-chemical properties of the membrane to address this issue,antifouling modified NF memrbanes still face unsatisfying antifouling effect,as well as the complicated modification procedures and compromised separation efficiency.Herein,a dual strategy to enhance anti-adhesive and antibacterial properties simetaneously of thin film composite(TFC)NF membrane is first proposed.Next,the modification procedures for anti-biofouling TFC membrane are simplified and the anti-biofouling duration is prolonged by introducing antibacterial agents into TFC membranes in situ with the assistant of catechols.Further,newly emerged twodimensional Mexene nanosheets with remarkable antibacterial effect is employed to construct the selective layer with well-regulated pore structure,developing an antibacterial and high flux TFC membrane.The four following parts are mainly included in this thesis.(1)Two different zwitterions(SO3--based and COO--based)are employed to modify polyamide(PA)TFC membranes,which are applied as Ag+anchors for subsquent in-situ formation of silver nanoparticles(AgNPs)and deposition of silver chloride(AgCl)particles on the TFC membranes.It is found that the presence of zwitterions is key to enhancing Ag content,resulting in significantly improved anti-microbial and anti-fouling properties without compromising the nanofiltration separation performance.In addition,COO--based zwitterions are more favourable towards Ag metallization and mineralization compared to SO3--based zwitterions,thus maximizing the anti-adhesive and antibacterial properties of the membrane.(2)A catechol-rich NF TFC membrane is developed via facile interfacial polymerization,with tannic acid and trimesoyl chloride as reaction monomers.During the Ag+retention,the abundant catechol groups of dense skin layer endow the membrane the strong affinity toward Ag+and facilitate the in-situ formation of Ag in the membrane surface and pores.This modification method not only achieves the purification of Ag-containing wastewater(Ag+rentention of 95.4%),but also simplifies the procedures to constructe antibacterial TFC memrbanes.It also endows the membrane with satisfactory Ag loading(15.6 μg/cm2),stable Ag+release and an prolonged antibacterial duration.(3)Ti3C2Tx MXene nanosheets with antibacterial effect is selected to fabricate MXenebased anti-biofouling TFC membranes.To achieve ultrahigh water flux,organic phosphate acids(OPA)are applied to enlarge the inner space of MXene laminates.OPA molecules fixed on the MXene nanosheets regulate stacking behavior of MXene nanosheets,altering the nanochannels’parameter of MXene laminates.The intercalation of OPA in the MXene layer enhaces the stability of the MXene TFC membrane while bringing little effect on the antibacterial properties.In addition,the resultant membranes show five-fold increase in water permeances(as high as 510 LMH/bar)when compared with the pure MXene membrane,and the rejection to Congo red is also improved to 99.7%(4)Antibacterial poly(ionic liquid)s(PILs)are employed as tailor-made surface modifier to assemble MXene laminates via electrostatic interactions to fabricate antibacterial MXene/PILs active layer with no defects.The introduction of PILs not only improves the antibacterial properties of MXene TFC membranes significantly,but also endows the membrane pores wall with adjustable hydrophilicity via anion exchange.A judicious choice of counter anions endows the membrane with more hydrophobic nanochannels for better water transport while also maintaining the desirable parameters of the nanogalleries for precise sieving.