A kind of novel electro-neutral nanofiltration (NF) membrane at neutral pH was fabricated by interfacial polymerization from a novel zwitterionic amine monomer PEI-g-SBMA. The zwitterionic amine endowed the resultant NF membrane with an electro-neutral separation layer under neutral condition and enhanced antifouling property via regulation of surface charge balance. The electro-neutral zwitterionic NF membranes (PEI-g-SBMA/TMC) showed a high water flux of 132 L/ (m 2 h MPa), i.e. over 2 times higher than that of the PEI/TMC membranes without grafted SBMA. The PEI-g-SBMA/TMC membrane exhibited a high dye rejection (90.6% for Orange GII) but a low salt rejection (7.1% for NaCl and 50.4% for Na 2 SO 4 ). Meanwhile, the antifouling property against bovine serum albumin (BSA), sodium alginate (SA) and humic acid (HA) was significantly improved compared with the PEI/TMC membranes. The as-fabricated electro-neutral PEI-g-SBMA/TMC membranes with high organics rejection and low salt rejection as well as good antifouling property may find promising application potential in food, pharmaceutical, chemical industry and membrane bioreactor (MBR) processes.
Electroneutral nanofiltration (NF) membranes are crucial to the treatment of textile wastewaters with high salinity, but it is challenging to generate electroneutral thin-film composite (TFC) membranes in a broad pH range. In this paper, we demonstrate the fabrication of an electroneutral NF composite membrane with the selective layer comprising of a zinc cation-integrated cross-linked polyvinyl alcohol (PVA)-polyethyleneimine (PEI) polymer network, which was deposited on an interlayer membrane of polydopamine-wrapped carbon nanotubes. The highly ionizable coordinative bonds formed between the Zn(II) ionic species and the amino groups in PEI facilitated ionization to generate hydrophilic and nearly electroneutral membranes with tenable electroneutrality over a broad pH range of 5.0–8.6. Subsequently, the membrane afforded excellent rejection (>99.7%) of bromothymol blue, congo red and direct yellow dye molecules while the low salt retentions of 3.35% (NaCl) and 11.57% (Na 2 SO 4 ) were realized with moderately high water flux of up to 84 L m −2 h −1 at 5 bar. Further prolonged filtration of a salt/dye mixed feed system demonstrated that the salt presence did not affect the dye separation efficiency leading to the attainment of an unprecedented high NaCl/Congo red selectivity of 932. This highlighted the potentiality of the presented approach for designing membranes with tunable surface charges for the purification of saline textile wastewaters.
In the present work, the bulk and homogeneous composite hydrogels were successfully constructed from positively charged chitosan (CS) and negatively charged carrageenan (CG) in alkali/urea aqueous solution via a simple one-step approach for the first time. An electroneutral CS solution was achieved in alkali/urea, leading to a homogeneous solution blended by CS and CG, which could not be realized in acidic medium because of the agglomeration caused by polycation and polyanion. Subsequently, the CS/CG composite hydrogels with multiple cross-linked networks were prepared from blend solution by using epichlorohydrin (ECH) as the cross-linking agent. The composite hydrogels exhibited hierarchically porous architecture, excellent mechanical properties as well as pH- and salt-responsiveness. Importantly, the composite hydrogels were successfully applied for spreading ATDC5 cells, showing high attachment and proliferation of cells. The results of fluorescent micrographs and scanning electronic microscope images revealed that the CS/CG composite hydrogels enhanced the adhesion and viability of ATDC5 cells. The alcian blue staining, glycosaminoglycan quantification, and real-time PCR analysis proved that the CS/CG composite hydrogels could induce chondrogenic differentiation of ATDC5 cells in vitro, exhibiting great potential for application in cartilage repair. This work provides a facile and fast fabrication pathway for the construction of ampholytic hydrogel from polycation and polyanion in an electroneutrality system.
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