Jiuyang Lin

Surface zwitterionic functionalized graphene oxide for a novel loose nanofiltration membrane

Surface zwitterionization of graphene oxide (GO) was firstly conducted by grafting poly(sulfobetaine methacrylate) (PSBMA) onto the GO surface via reverse atom transfer radical polymerization (RATRP). Then, a novel type of GO-PSBMA/polyethersulfone (PES) loose nanofiltration membrane (NFM) was constructed by mixing with modified GO composites via phase inversion. FTIR, XRD, TEM, XPS and TGA were applied to analyze the chemical composition and morphology, confirming a favorable synthesis of GO-PSBMA composites. Besides, the effect of the embedded GO-PSBMA nanoplates on the morphology and overall performance of the hybrid membranes was systematically investigated based on the SEM images, water contact angle, zeta potential, and fouling parameters. It was found that the water flux of the hybrid membrane was greatly enhanced from 6.44 L m−2 h−1 bar−1 to 11.98 L m−2 h−1 bar−1 when the GO-PSBMA content increased from 0 to 0.22 wt%. The antifouling tests revealed that the GO-PSBMA embedded membranes had an excellent antifouling performance: a high flux recovery ratio (ca. 94.4%) and a low total flux decline ratio (ca. 0.18). Additionally, the hybrid membranes exhibited a distinct advance in the mechanical strength due to the addition of highly rigid GO. Notably, compared with unmodified membranes, the hybrid membranes had a higher retention of Reactive Black 5 (99.2%) and Reactive Red 49 (97.2%), and a lower rejection of bivalent salts (10% for Na2SO4) at an operational pressure of 0.4 MPa, rendering the membranes promising for dye/salt fractionation.

Elevated Performance of Thin Film Nanocomposite Membranes Enabled by Modified Hydrophilic MOFs for Nanofiltration

Metal-organic frameworks (MOFs) are studied for the design of advanced nanocomposite membranes, primarily due to their ultrahigh surface area, regular and highly tunable pore structures, and favorable polymer affinity. However, the development of engineered MOF-based membranes for water treatment lags behind. Here, thin-film nanocomposite (TFN) membranes containing poly(sodium 4-styrenesulfonate) (PSS) modified ZIF-8 (mZIF) in a polyamide (PA) layer were constructed via a facile interfacial polymerization (IP) method. The modified hydrophilic mZIF nanoparticles were evenly dispersed into an aqueous solution comprising piperazine (PIP) monomers, followed by polymerizing with trimesoyl chloride (TMC) to form a composite PA film. FT-IR spectroscopy and XPS analyses confirm the presence of mZIF nanoparticles on the top layer of the membranes. SEM and AFM images evince a retiform morphology of the TFN-mZIF membrane surface, which is intimately linked to the hydrophilicity and adsorption capacity of mZIF nanoparticles. Furthermore, the effect of different ZIF-8 loadings on the overall membrane performance was studied. Introducing the hydrophilizing mZIF nanoparticles not only furnishes the PA layer with a better surface hydrophilicity and more negative charge but also more than doubles the original water permeability, while maintaining a high retention of Na2SO4. The ultrahigh retentions of reactive dyes (e.g., reactive black 5 and reactive blue 2, >99.0%) for mZIF-functionalized PA membranes ensure their superior nanofiltration performance. This facile, cost-effective strategy will provide a useful guideline to integrate with other modified hydrophilic MOFs to design nanofiltration for water treatment.

The use of BMED for glyphosate recovery from glyphosate neutralization liquor in view of zero discharge.

Alkaline glyphosate neutralization liquors containing a high salinity pose a severe environmental pollution problem by the pesticide industry. However, there is a high potential for glyphosate recovery due to the high concentration of glyphosate in the neutralization liquors. In the study, a three-compartment bipolar membrane electrodialysis (BMED) process was applied on pilot scale for the recovery of glyphosate and the production of base/acid with high concentration in view of zero discharge of wastewater. The experimental results demonstrate that BMED can remove 99.0% of NaCl from the feed solution and transform this fraction into HCl and NaOH with high concentration and purity. This is recycled for the hydrolysis reaction of the intermediate product generated by the means of the Mannich reaction of paraformaldehyde, glycine and dimethylphosphite catalyzed by triethylamine in the presence of HCl and reclamation of the triethylamine catalyst during the production process of glyphosate. The recovery of glyphosate in the feed solution was over 96%, which is acceptable for industrial production. The current efficiency for producing NaOH with a concentration of 2.0 mol L(-1) is above 67% and the corresponding energy consumption is 2.97 kWh kg(-1) at a current density of 60 mA cm(-2). The current efficiency increases and energy consumption decreases as the current density decreases, to 87.13% and 2.37 kWh kg(-1), respectively, at a current density of 30 mA cm(-2). Thus, BMED has a high potential for desalination of glyphosate neutralization liquor and glyphosate recovery, aiming at zero discharge and resource recycling in industrial application.

Nano-WS2 embedded PES membrane with improved fouling and permselectivity

The application of nanoparticles as additives in membrane synthesis for improving the resistance of membranes against fouling has triggered recent interest in new membrane types. However, most nanoparticle-enhanced membranes suffer from the tradeoff between permeability and selectivity. In this paper, nano-WS2 was explored as the additive in membrane synthesis by non-solvent induced phase separation (NIPS). Blended PES-WS2 flat-sheet membranes with the incorporation of ultra-low concentrations of nanoparticles (from 0.025% to 0.25%, WS2/PES ratio) were manufactured and investigated in terms of permeability, fouling resistance and solute rejection. Remarkably, a significant enhancement in the permeability was observed as a result of the incorporation of ultra-low fractions of nano-WS2 to the membrane structure. The optimum permeability values were obtained for modified membranes with 0.075-0.10% nanoparticle/polymer concentration ratios. In general, fouling resistance and solute rejection were significantly enhanced by the incorporation of nanoparticles into the membrane structure. Specifically, fouling resistance increased by around 50%.

Mussel-Inspired Architecture of High-Flux Loose Nanofiltration Membrane Functionalized with Antibacterial Reduced Graphene Oxide–Copper Nanocomposites

Graphene-based nanocomposites have a vast potential for wide-ranging antibacterial applications due to the inherently strong biocidal activity and versatile compatibility of such nanocomposites. Therefore, graphene-based functional nanomaterials can introduce enhanced antibiofouling and antimicrobial properties to polymeric membrane surfaces. In this study, reduced graphene oxide-copper (rGOC) nanocomposites were synthesized as newly robust biocides via in situ reduction. Inspired by the emerging method of bridging ultrafiltration membrane surface cavities, loose nanofiltration (NF) membranes were designed using a rapid (2 h) bioinspired strategy in which rGOC nanocomposites were firmly codeposited with polydopamine (PDA) onto an ultrafiltration support. A series of analyses (SEM, EDS, XRD, XPS, TEM, and AFM) confirmed the successful synthesis of the rGO-Cu nanocomposites. The secure loading of rGOC composites onto the membrane surfaces was also confirmed by SEM and AFM images. Water contact angle results display a high surface hydrophilicity of the modified membranes. The PDA-rGOC functionalization layer facilitated a high water permeability (22.8 L m-2 h-1 bar-1). The PDA-rGOC modification additionally furnished the membrane with superior separation properties advantageous for various NF applications such as dye purification or desalination, as ultrahigh (99.4% for 0.5 g L-1 reactive blue 2) dye retention and high salt permeation (7.4% for 1.0 g L-1 Na2SO4, 2.5% for 1.0 g L-1 NaCl) was achieved by the PDA-rGOC-modified membranes. Furthermore, after 3 h of contact with Escherichia coli (E. coli) bacteria, the rGOC-functionalized membranes exhibited a strong antibacterial performance with a 97.9% reduction in the number of live E. coli. This study highlights the use of rGOC composites for devising loose NF membranes with strong antibacterial and separation performance.