Interface-Confined Channels Facilitating Water Transport through an IL-Enriched Nanocomposite Membrane.

Improving the permeance of the polyamide (PA) membrane while maintaining the rejection is crucial for promoting the development of membrane separation technology in the practical water-treatment industry. Herein, a novel metal-ionic liquid (Zn-IL) coordination compound was synthesized by in situ growth to improve the water permeance of PA nanofiltration membranes, using an amine-functionalized IL (1-aminopropyl-3-methylimidazolium chloride, [AEMIm][Cl]) as a ligand to react with Zn(NO3)2·6H2O. Piperazine (PIP) and trimesoyl chloride (TMC) were adopted to prepare the PA layer covering the Zn-IL complex. Due to the unique property of the Zn-IL complex, the Zn-IL/PIP-TMC absorbing force to water was increased, enabling the fast transport of water molecules through the membrane pore channels in the form of free water. The resulting Zn-IL/PIP-TMC nanocomposite membrane exhibited a high permeance of up to 26.5 L m-2 h-1 bar-1, which is 3 times that of the PIP-TMC membrane (8.8 L m-2 h-1 bar-1), combined with rejection above 99% for dyes such as methyl blue.

Microphase Diffusion-Controlled Interfacial Polymerization for an Ultrahigh Permeability Nanofiltration Membrane.

The key to improving nanofiltration membrane permeance is reducing its thickness while maintaining high rejection. Herein, a 25 nm thick ultrathin polyamide layer was prepared by a microphase diffusion-controlled interfacial polymerization (MDC-IP) of poly(ethyleneimine) and trimesoyl chloride, which is much thinner than the conventional interfacial polymerization (CIP) polyamide layer. A new formation mechanism for such an ultrathin layer is presented, which included a microphase interfacial reaction and eliminated loose layers due to the confinement of microphase diffusion and the termination of stepwise diffusion. Moreover, the polyamide layer was post-cross-linked to form a stable dual-cross-linked interwoven structure. Such a membrane showed an ultrahigh permeance of 1246 kg/(m2 h MPa), which was 23 times that of CIP membranes. MDC-IP could efficiently control the microinterface between two immiscible phases, which provided a facile way to regulate the membrane at nanoscale.

One-Step Assembly of Molecular Separation Membranes by Direct Atomizing Oligomers.

Polymeric membranes are important materials for efficient sieving of targeted components at the molecular level and have made significant advancement in many industrial applications such as biofuel production, water purification, fuel combustion, and carbon dioxide capture. Although their separation efficiencies have been widely investigated, lack of more efficient, greener, and lower-cost membrane fabrication mechanisms is still a major hurdle for mass production, because the conventional membrane-making process is always time-consuming, highly inefficient, and consumes a large amount of organic solvents. Herein we report a one-step assembly concept capable of directly processing low-viscosity oligomers into polymer-based molecular separation membranes in an ultrafast and green manner. This process was implemented by alternate atomizing-depositing of low-viscosity oligomers and reaction auxiliary agents onto a rotating support and followed by an ultrafast interfacial reaction under solvent-free conditions. Without the need for dissolution processing of polymer, solvent evaporation, and any post-treatments, the whole technological process could be accomplished within a few seconds/minutes, which is 2-3 orders of magnitude faster than conventional solution-coating technologies. The universality of this facile approach has also been demonstrated by successfully producing various defect-free polymeric membranes and homodispersed nanohybrid membranes with excellent and stable performance for bioalcohol production and recovery of different trace organics from dilute solutions.

Natural organic matter fouling behaviors on superwetting nanofiltration membranes.

Nanofiltration has been widely recognized as a promising technology for the removal of micro-molecular organic components from natural water. Natural organic matter (NOM), a very important precursor of disinfection by-products, is currently considered as the major cause of membrane fouling. It is necessary to develop a membrane with both high NOM rejection and anti-NOM fouling properties. In this study, both superhydrophilic and superhydrophobic nanofiltration membranes for NOM removal have been fabricated. The fouling behavior of NOM on superwetting nanofiltration membranes has been extensively investigated by using humic acid (HA) as the model foulant. The extended Derjaguin-Landau-Verwey-Overbeek approach and nanoindentor scratch tests suggested that the superhydrophilic membrane had the strongest repulsion force to HA due to the highest positive total interaction energy (ΔG(TOT)) value and the lowest critical load. Excitation emission matrix analyses of natural water also indicated that the superhydrophilic membrane showed resistance to fouling by hydrophobic substances and therefore high removal thereof. Conversely, the superhydrophobic membrane showed resistance to fouling by hydrophilic substances and therefore high removal capacity. Long-term operation suggested that the superhydrophilic membrane had high stability due to its anti-NOM fouling capacity. Based on the different anti-fouling properties of the studied superwetting membranes, a combination of superhydrophilic and superhydrophobic membranes was examined to further improve the removal of both hydrophobic and hydrophilic pollutants. With a combination of superhydrophilic and superhydrophobic membranes, the NOM rejection (RUV254) and DOC removal rates (RDOC) could be increased to 83.6% and 73.3%, respectively.