Mitigating the hydraulic compression of nanofiltration hollow fiber membranes through a single-step direct spinning technique

A PEI/TMC membrane modified with an ionic liquid with enhanced permeability and antibacterial properties for the removal of heavy metal ions

Heavy metal ions in drinking water severely threaten public health in various places worldwide. Nanofiltration (NF) membrane technology is an attractive option for heavy metal ions removal; however, improving NF membrane filtration performance is required to make their industrial application viable. In this study, a positively charged THPC/PEI-TMC NF membrane was designed via simple one-step incorporation of Tetrakis (hydroxymethyl) phosphonium chloride (THPC) biocide on the surface of PEI-TMC membranes, significantly optimizing surface morphology, roughness, hydrophilicity, and zeta potential of PEI-TMC membranes. It was found that the pure water permeability (11.6 Lm^-2h^-1bar^-1) of the THPC modified membrane was three times larger than that of the original PEI-TMC membrane (3.4 Lm^-2h^-1bar^-1) while maintaining a high level of ion rejections (around 95% for Zn²⁺, Cd²⁺, Ni²⁺, Cu²⁺ and about 90% for Pb²⁺). Additionally, the incorporation of the THPC on the original PEI-TMC membrane surface also conferred good antibacterial properties, which protect the organic membrane from bacterial growth and prolong the lifespan of the membrane.

Polybenzimidazole Membrane Crosslinked with Epoxy-Containing Inorganic Networks for Organic Solvent Nanofiltration and Aqueous Nanofiltration under Extreme Basic Conditions

In this study, a novel polybenzimidazole (PBI)-based organic solvent nanofiltration (OSN) membrane possessing excellent stability under high pH condition was developed. To improve the chemical stability, the pristine PBI membrane was crosslinked with a silane precursor containing an epoxy end group. In detail, hydrolysis and condensation reaction of methoxysilane in the 3-glycidyloxypropyl trimethoxysilane (GPTMS) yields organic–inorganic networks within the PBI membrane structure. At the same time, the epoxy end groups on the organosiloxane network (Si–O–Si) reacted with amine groups of PBI to complete the crosslinking. The resulting crosslinked PBI membrane exhibited a good stability upon exposure to organic solvents and was not decomposed even in basic solution (pH 13). Our membrane showed an ethanol permeance of 27.74 LMHbar⁻¹ together with a high eosin Y rejection of >90% under 10 bar operation pressure at room temperature. Furthermore, our PBI membrane was found to be operational even under an extremely basic condition, although the effective pore size was slightly enlarged due to the pore swelling effect. The results suggest that our membrane is a promising candidate for OSN application under basic conditions.

Graphene Oxide Nanofiltration Membranes Containing Silver Nanoparticles: Tuning Separation Efficiency via Nanoparticle Size

Three types of graphene oxide/silver nanoparticles (GO/AgNPs) composite membranes were prepared to investigate size-effect of AgNPs on nanofiltration ability. The size of AgNPs was 8, 20, and 33 nm, which was characterized by UV-visible spectroscopy and transmission electron microscopy. The morphology and structure of GO and GO/AgNPs composite membranes were characterized by atomic force microscopy, scanning electron microscopy, and X-ray diffraction. The filtration performance of membranes were evaluated on a dead-end filtration device. When the size of AgNPs is 20 nm, the GO/AgNPs composite membrane has the highest water flux (106.1 L m⁻² h⁻¹ bar⁻¹) and rejection of Rhodamine B (RhB) (97.73%) among three types of composite membranes. The effect of feed concentration of dye solution and the flux of common solvent was also investigated. The mechanism was discussed, which demonstrated that both interlaying spacing and defect size influence the filtration ability of membrane, which is instructive to future study.

Graphene oxide/nanometal composite membranes for nanofiltration: synthesis, mass transport mechanism, and applications

We reviewed the recent developments in graphene-based composite membranes and discussed their challenges in this paper.

Nanometric Graphene Oxide Framework Membranes with Enhanced Heavy Metal Removal via Nanofiltration

A novel dual-modification strategy, including (1) the cross-linking and construction of a GO framework by ethylenediamine (EDA) and (2) the amine-enrichment modification by hyperbranched polyethylenimine (HPEI), has been proposed to design stable and highly charged GO framework membranes with the GO selective layer thickness of 70 nm for effective heave metal removal via nanofiltration (NF). Results from sonication experiments and positron annihilation spectroscopy confirmed that EDA cross-linking not only enhanced structural stability but also enlarged the nanochannels among the laminated GO nanosheets for higher water permeability. HPEI 60K was found to be the most effective post-treatment agent that resulted in GO framework membranes with a higher surface charge and lower transport resistance. The newly developed membrane exhibited a high pure water permeability of 5.01 L m(-2) h(-1) bar(-1) and comparably high rejections toward Mg(2+), Pb(2+), Ni(2+), Cd(2+), and Zn(2+). These results have demonstrated the great potential of GO framework materials in wastewater treatment and may provide insights for the design and fabrication of the next generation two-dimensional (2D)-based NF membranes.