Quanling Xie,Shishen Zhang,Zhuan Hong,Hanjun Ma,Birong Zeng,Xiao Gong,Wenyao Shao,Qiuquan Wang
A novel double-modified strategy by introducing sulfonated graphene (SG) and maleic anhydride modified graphene oxide (MAH-GO) nanofillers into the supporting layer and selective layer, respectively, was adopted to develop high-performance thin-film nanocomposite (TFN) nanofiltration (NF) membrane. First, the supporting layer was successively modified by investigating the impacts of sulfonated PSU and SG on the morphologies, properties and performance of the supporting membranes and the resultant thin-film composite (TFC) NF membranes. The results indicated that the structures and properties of supporting layers had significant influences on the resultant polypiperazine-amide (PPA) TFC NF membranes. The pristine PSU support exhibited a large surface pore size, medium porosity and strong hydrophobicity, which generated a low-flux PPA-TFC NF membrane. After modification with SPSU and SG, the optimal PSU-SPSU-SG blend support showed a small surface pore size, high porosity and improved hydrophilicity, which resulted in favor of the formation of a defect-free TFC NF membrane with a relatively high flux. Using the optimal PSU-SPSU-SG blend support, the further incorporation of MAH-GO nanofillers into the selective layer led to a thinner, smoother and more strongly hydrophilic TFN NF membrane with enhanced negative charge. The double-modified TFN NF membrane showed the superior permeaselectivity, anti-fouling ability and chlorine resistance over the conventional PPA-TFC NF membrane. Notably, without sacrificing the high salt rejection, the maximum water flux significantly reached 85.8 L m −2 h −1 equal to 264.8% of PPA-TFC membrane. This novel double-modified strategy shows a great potential in developing high-performance TFN NF membranes.
A thin-film composite (TFC) membrane with hydrophilic double-skinned support layer was developed to improve anti-fouling performance. The double-skinned separate casting technology was applied to obtain the double-skinned support layer and the polyacrylonitrile (PAN) concentration in the bottom casting solution was adjusted. Then, the support layer was carboxylated by immersing in a 1.5 M NaOH solution for 2 h. Finally, TFC membrane with hydrophilic double-skinned support layer was obtained by the interfacial polymerization. When the PAN concentration in the bottom casting solution was 10 wt%. TFC membrane with hydrophilic double-skinned support layer (TFC-10 %) showed the best performance. The water flux of TFC-10 % reached 17.6 LMH and the reverse salt flux was 5.6 gMH. Under the double interception effect of the double-skinned structure and the steric hindrance of the hydration layer on the support layer, good anti-fouling property of TFC-10 % was observed under bovine serum albumin (BSA) foulant. Compared to the traditional TFC membrane, the normalized flux of TFC-10 % increased by 80 %. The anti-fouling performance was also analyzed by microaction mechanisms using AFM and QCM-D. It was found that the adhesion force between TFC-10 % and BSA was small, therefore fewer pollutants were adsorbed on TFC-10 %, and its adsorption layer was loose and easy-cleaning.
This work focused on the construction of an acid-resistant composite nanofiltration membrane with the selective layer of bulk cross-linked hydroxyethyl cellulose (HEC)-silica and a support of porous polypropylene . Membranes were fabricated through in-situ sol-gel reaction and slot-die coating method employing tetraethyl orthosilicate (TEOS) as the silica precursor and cross-linking agent of HEC. Membrane structure and performance were tuned by controlling the hydrolysis time of TEOS and differentiating TEOS and HEC contents, and systematically characterized in terms of physico-chemical property, permeation attribution and acid stability. It was found that membrane performance was strongly correlated with the relative contents of C–O–Si and Si–O–Si bonds of the formed HEC-silica selective layer. High content of C–O–Si bond formed via condensation reaction of HEC and TEOS endowed the selective layer with denser network structure and good rejection ability. Both insufficient and excessive hydrolysis led to a poor rejection ability of formed membrane. The optimized HEC-silica membrane possessed an average pore size of about 1.43 nm within the scope of nanofiltration membrane, a high pure water permeability coefficient of around 10.5 LMH/bar, and a medium rejection of 85.2% to 500 mg/l Na 2 SO 4 aqueous solution at 5.0 bar. No changes in both chemical structure and separation performance occurred with the HEC-silica composite membrane after being soaked in aqueous H 2 SO 4 solution of 4.9 wt% for 7 days, while evident structure destruction and serious performance degradation occurred with the compared polyamide-based commercial membrane NF270. Long-term soaking test using 15.0 wt% H 2 SO 4 aqueous solution for 30 days also demonstrated that the acid resistance HEC silica membrane was comparable with those reported acid stable nanofiltration membranes. Furthermore, the HEC-silica membrane also maintained its water permeation and solute rejection abilities during a 30-day continuous filtration of aqueous solution of 4.9 wt% H 2 SO 4 and 50 mg/l polyethylene glycol fraction (PEG2000). The good acid resistance of the HEC-silica composite membrane was attributed to its bulk cross-linked network structure composed of C–O–Si, Si–O–Si and C–C bonds.
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