Regulating the thickness of nanofiltration membranes for efficient water purification

Fabrication of an organic polymer nanofiltration membrane with both high water permeability and high salt rejection is still a big challenge. Herein, phytic acid (PhA)-modified graphene oxide (GO) was used as the membrane thickness modifier, which was introduced into the thin-film nanoparticle composite (TFN) membrane via in situ interfacial polymerization (IP) on a porous substrate. The water flux of the optimally tuned TFN-GP-0.2 composite membrane is 48.9 L m-2 h-1, which is 1.3 times that of the pristine thin-film composite (TFC) nanofiltration membrane (37.9 L m-2 h-1) (GP represents the PhA modified GO composite). The rejection rate of 2000 ppm MgSO4 for TFN-GP-0.2 membranes was maintained at 97.5%. The increased water flux of the TFN-GP composite membrane compared to that of the TFN nanofiltration membrane was mainly attributed to enhanced hydrophilicity and reduced thickness of the polyamide (PA) layer. Molecular dynamics (MD) simulations confirm that the diffusion rate of amine monomers is reduced by the presence of a GP complex in the IP process, which facilitates the formation of PA layer with thinner thickness. In addition, the TFN-GP-0.2 composite membrane also showed good long-term stability; after 12 h of continuous operation, the water flux only decreased by 0.1%. This study sheds new light on the development of GO-based nanofiltration for potential implementation, as well as a unique concept for manufacturing high-performance nanofiltration membranes.

A stable and easily regenerable solid amine adsorbent derived from a polyethylenimine-impregnated dialdehyde-cellulose/graphene-oxide composite

A DAC-GO composite adsorbent with high CO2 adsorption capacity and low regeneration energy consumption was prepared through oxidation-gelation and crosslinking-amination.

Thin film nanocomposite membrane with triple-layer structure for enhanced water flux and antibacterial capacity

Triple-layered thin film composite (TFC) forward osmosis (FO) membranes prepared on interlayer-based supports have overcome the limitations of conventional porous substrates due to the formation of ultrathin and highly selective polyamide (PA) layers. However, mitigating the internal concentration polarization (ICP) and biofouling of TFC membranes remain a great challenge. Herein, we designed a novel triple-layered thin film nanocomposite (TFN) FO membrane with incorporation of silver (Ag) decorated graphene oxide quantum dots (GOQD) into PA layer via interfacial polymerization on a carbon nanotube (CNT) interlayer-based polyether sulfone substrate. By contrast with the TFC membranes, the newly developed GOQD/Ag incorporated triple-layered TFN membrane (TFN-GOQD/Ag) exhibited a great alleviation for ICP accompanied with a prominently enhanced water flux of 65.8 L·m^-2·h^-1 and decreased specific reverse salt flux of 1.4 g·m^-2·h^-1 by employing 1 M NaCl solution as draw solution. Moreover, the TFN-GOQD/Ag membrane possessed prominent antibacterial activity against both E. coli (99.8%) and S. aureus (97.3%). Noteworthy, the obtained TFN membrane demonstrated a controlled release of Ag⁺ along with long-term antibacterial potential and outstanding fouling resistance during the FO process. This work provides a new avenue to fabricate newly FO membranes with superior performance for water cleaning treatment.

Progress of Interfacial Polymerization Techniques for Polyamide Thin Film (Nano)Composite Membrane Fabrication: A Comprehensive Review

In this paper, we review various novel/modified interfacial polymerization (IP) techniques for the fabrication of polyamide (PA) thin film composite (TFC)/thin film nanocomposite (TFN) membranes in both pressure-driven and osmotically driven separation processes. Although conventional IP technique is the dominant technology for the fabrication of commercial nanofiltration (NF) and reverse osmosis (RO) membranes, it is plagued with issues of low membrane permeability, relatively thick PA layer and susceptibility to fouling, which limit the performance. Over the past decade, we have seen a significant growth in scientific publications related to the novel/modified IP techniques used in fabricating advanced PA-TFC/TFN membranes for various water applications. Novel/modified IP lab-scale studies have consistently, so far, yielded promising results compared to membranes made by conventional IP technique, in terms of better filtration efficiency (increased permeability without compensating solute rejection), improved chemical properties (crosslinking degree), reduced surface roughness and the perfect embedment of nanomaterials within selective layers. Furthermore, several new IP techniques can precisely control the thickness of the PA layer at sub-10 nm and significantly reduce the usage of chemicals. Despite the substantial improvements, these novel IP approaches have downsides that hinder their extensive implementation both at the lab-scale and in manufacturing environments. Herein, this review offers valuable insights into the development of effective IP techniques in the fabrication of TFC/TFN membrane for enhanced water separation.

Constructing Positively Charged Thin-Film Nanocomposite Nanofiltration Membranes with Enhanced Performance

Using polyethylenimine (PEI) as the aqueous reactive monomers, a positively charged thin-film nanocomposite (TFN) nanofiltration (NF) membrane with enhanced performance was developed by successfully incorporating graphene oxide (GO) into the active layer. The effects of GO concentrations on the surface roughness, water contact angle, water flux, salt rejection, heavy metal removals, antifouling property, and chlorine resistance of the TFN membranes were evaluated in depth. The addition of 20 ppm GO facilitated the formation of thin, smooth, and hydrophilic nanocomposite active layers. Thus, the TFN-PEI-GO-20 membrane showed the optimal water flux of 70.3 L·m-2·h-1 without a loss of salt rejection, which was 36.8% higher than the thin-film composite (TFC) blank membrane. More importantly, owing to the positively charged surfaces, both the TFC-PEI-blank and TFN-PEI-GO membranes exhibited excellent rejections toward various heavy metal ions including Zn2+, Cd2+, Cu2+, Ni2+, and Pb2+. Additionally, compared with the negatively charged polypiperazine amide NF membrane, both the TFC-PEI-blank and TFN-PEI-GO-20 membranes demonstrated superior antifouling performance toward the cationic surfactants and basic protein due to their hydrophilic, smooth, and positively charged surface. Moreover, the TFN-PEI-GO membranes presented the improved chlorine resistances with the increasing GO concentration.

Cerium oxide doped nanocomposite membranes for reverse osmosis desalination

Cerium oxide (CeO₂) nanoparticles (NPs) have indicated great potentials as nanofiller owing to its high surface area, antioxidant properties and low cost. In this paper, thin film nanocomposite (TFN) RO membranes were proposed to be prepared through incorporation of hydrophilic CeO₂ NPs in polyamide (PA) selective layers via interfacial polymerization (IP). EDX, XPS, SEM, AFM, contact angle and zeta potential were used to examine the property and morphology of the prepared membranes. CeO₂ NPs were successfully embedded in the PA network, which endowed the TFN membranes with rougher surfaces and thinner PA layers. The TFN membranes were fabricated with different CeO₂ NPs contents (0, 50, 100, 150, 200, 400 mg/L). With increasing CeO₂ NPs loading amount, the hydrophilicity improved from 85.4° to 65.7° and the surface charge declined from -19.4 to -34.2 mV. These characteristics contributed to a 50% enhancement in water flux of TFN-CeO₂100 membrane (containing 100 mg/L of CeO₂ NPs) without compromise the NaCl rejection (98%). Moreover, CeO₂ embedded membrane exhibited an enhanced fouling resistance property through preventing the adhesion of hydrophobic foultants. This study demonstrated the desirable applicability of CeO₂ NPs in synthesizing novel TFN membranes for desalination application.

Development of Copper-Aluminum Layered Double Hydroxide in Thin Film Nanocomposite Nanofiltration Membrane for Water Purification Process

This study aims to fabricate a thin film composite (TFC) membrane, modified with copper-aluminium layered double hydroxide (LDH) nanofillers via interfacial polymerization technique for nanofiltration (NF) processes. It was found that Cu-Al LDH nanofillers possessed layered structured materials with typical hexagonal plate-like shape and positive surface charge. The study revealed that TFN membrane exhibits a relatively smooth surface and a less nodular structure compared to pristine TFC membrane. The contact angle of TFN progressively decreased from 54.1° to 37.25°, indicating enhancement in surface hydrophilicity. Moreover, the incorporation of LDH nanofillers resulted in a less negative membrane as compared to the pristine TFC membrane. The best NF performance was achieved by TFN2 membrane with 0.1° of Cu-Al LDH loading and a water flux of 7.01 Lm-2h-1.bar. The addition of Cu-Al LDH resulted in excellent single salt rejections of Na2SO4 (96.8%), MgCl2 (95.6%), MgSO4 (95.4%), and NaCl (60.8%). The improvement in anti-fouling properties of resultant TFN membranes can be observed from the increments of pure water flux recovery and normalized water flux by 14% and 25% respectively. The findings indicated that Cu-Al LDH is a promising material in tailoring membrane surface properties and fouling resistance. The modification of the LDH-filled TFN membrane shows another alternative to fabricating a high-performance composite membrane, especially for water softening and partial desalination process.

Design of ultrathin hybrid membranes with improved retention efficiency of molecular dyes

Nanocellulose–graphene oxide ultrathin coatings for water purification membranes with excellent swelling resistance, permeability and dyes retention are presented.

A thin film nanocomposite membrane with pre-immobilized UiO-66-NH2 toward enhanced nanofiltration performance

A facile controlled interfacial polymerization strategy was proposed for the synthesis of novel thin film nanocomposite (TFN) membranes for enhanced nanofiltration performance. UiO-66 nanoparticles were aminated and pre-immobilized onto a polymer substrate via polydopamine (PDA) coating to achieve a continuous and defect-free polyamide dense layer. The mediation of the PDA coating could not only enhance the structural stability of TFN nanofiltration membranes, but also improve the dispersion and anchorage of UiO-66-NH₂, thus closely fixing the position of UiO-66-NH₂ nanoparticles on the polymer substrate. Moreover, since the amino group (–NH₂) further reacted with PDA via Michael addition or Schiff base reaction, the in situ mutual reaction reduced the nanoparticle losses significantly during the draining off of the monomer solution in the fabrication process, which effectively cut down the actual dosage. The results showed that the PDA interlayer could induce the tight attachment of the PA layer to the support, enhancing the structural stability of TFN membranes. Furthermore, the dosage of UiO-66-NH₂ in the as-prepared TFN membranes could also be decreased to as low as 0.01 w/v%, which was nearly a 10–20-fold reduction in the required amount of UiO-66-NH₂ for the synthesis. The fabricated TFN/UiO-66-NH₂ membranes exhibited very high water permeance and competitive salt rejections in cross-flow nanofiltration, which shows the huge potential for the application of novel TFN membranes with controlled nanoparticle incorporation in industrial separation.

A facile controlled interfacial polymerization strategy was proposed for the synthesis of novel thin film nanocomposite (TFN) membranes for enhanced nanofiltration performance.

A Novel Thin-Film Nanocomposite Nanofiltration Membrane by Incorporating 3D Hyperbranched Polymer Functionalized 2D Graphene Oxide

In order to develop a high-performance thin-film nanocomposite (TFN) nanofiltration (NF) membrane, the functionalized graphene-based nanomaterial (GO-HBE-COOH) was synthesized by combining two-dimensional graphene oxide (GO) with a three-dimensional hyperbranched polymer, which was used as the novel nanofiller and successfully embedded into the polypiperazine-amide (PPA) active layers on polysulfone (PSU) substrates via interfacial polymerization (IP) process. The resultant NF membranes were characterized using ATR-FTIR, SEM, and AFM, while their performance was evaluated in terms of water flux, salt rejection, antifouling ability, and chlorine resistance. The influence of GO-HBE-COOH concentration on the morphologies, properties, and performance of TFN NF membranes was investigated. With the addition of 60 ppm GO-HBE-COOH, the TFN-GHC-60 NF membrane exhibited the optimal water flux without a sacrifice of the salt rejection. It was found that the introduction of GO-HBE-COOH nanosheets favored the formation of a thinner and smoother nanocomposite active layer with an enhanced hydrophilicity and negative charge. As a result, TFN NF membranes demonstrated a superior permeaselectivity, antifouling ability, and chlorine resistance over the conventional PPA thin-film composite (TFC) membranes.

Bifunctional Solid Catalyst for Organic Reactions in Water: Simultaneous Anchoring of Acetylacetone Ligands and Amphiphilic Ionic Liquid "Tags" by Using a Dihydropyran Linker

The use of solid catalysts to promote organic reactions in water faces the inherent difficulty of the poor mass-transfer efficiency of organic substances in water, which is often responsible for insufficient reaction and low yields. To solve this problem, the solid surface can be manipulated to become amphiphilic. However, the introduction of surfactant-like moieties onto the surface of silica-based materials is not easy. By using an accessible dihydropyran derivative as a grafting linker, a surfactant-combined bifunctional silica-based solid catalyst that possessed an ionic liquid tail and a metal acetylacetonate moiety was prepared through a mild Lewis-acid-catalyzed ring-opening reaction with a thiol-functionalized silica. The surfactant-combined silica-supported metal acetylacetone catalysts displayed excellent catalytic activity in water for a range of reactions. The solid catalyst was also shown to be recyclable, and was reused several times without significant loss in activity.