Single-layered GO/LDH hybrid nanoporous membranes with improved stability for salt and organic molecules rejection

Few-layer MoS2 co-assembly with GO to optimize defect channels and stability of GO membranes for high-performance organic-inorganic separation

The selective separation of organic compounds and inorganic salts is essential for wastewater recycling in fine chemical industries such as pharmaceuticals and pesticides. Membrane separation technology offers a promising solution. However, conventional organic membranes often face challenges related to precise separation and solvent resistance. While graphene oxide (GO) membranes exhibit excellent solvent resistance, their separation performance and structural stability require further improvement. In this study, we developed a GO/few-layer molybdenum disulfide (FLMoS2) membrane via co-assembly. The optimized GO/FLMoS2 membrane demonstrated a water permeability of 28.4 LMH/bar, approximately four times higher than conventional GO membranes, and achieved a separation factor exceeding 900 for organic/inorganic mixtures-among the highest reported for two-dimensional (2D) membranes. Comprehensive characterization, including low-field nuclear magnetic resonance (LF-NMR), revealed that this superior performance was attributed to controlled defect channels, enhanced interlayer cross-linking, and the intrinsic rigidity of FLMoS2, which provided high structural stability and minimal swelling. Moreover, mechanical strength assessments, including critical destructive load force and nanoindentation tests, confirmed significant improvement in structural robustness. As a result, the GO/FLMoS2 membrane maintained stable water permeability and separation efficiency over 100 hours of continuous operation and six chemical cleaning cycles, demonstrating its potential for sustainable wastewater treatment and resource recovery.

Recent Advances in Layered-Double-Hydroxide-Based Separation Membranes

The use of two-dimensional materials shows great promise for the development of next-generation membrane materials, thanks to their atomic thinness and the ease with which precise nanochannels can be constructed. Among these materials, layered double hydroxides (LDHs) stand out as an important class, possessing many features that make them ideal for constructing high-performance membranes. LDHs offer many advantages, such as their abundant and tunable interlayer anions, which enable the preparation of membranes with adjustable sub-nanometer pore sizes. Additionally, their hydrophilicity and positive charge characteristics afford them unique benefits. LDHs have been found to be effective in gas separation, ion sieving, and nanofiltration. This review provides a summary of the latest progress in using LDHs for membrane separation. It begins by introducing the basic properties of LDHs, followed by the assembly strategy for LDH membranes. Furthermore, the review presents the research status of LDHs membranes in various fields in a systematic manner. Lastly, the paper highlights some challenges and future prospects for preparing and applying LDHs membranes.

Dopamine modified layered double hydroxide membranes based on nanofibril architectures: Toward superior tellurium separation properties for water treatment

Two-dimensional (2D) membrane materials are widely employed for the accurate sieving of ionic contaminants and are of great importance for water reuse. However, 2D membrane materials often suffer from uneven thickness and surface defects, which severely limit their application prospects. Herein, a continuous 2D membrane (LCUM/D) was prepared using cellulose nanofibrils (CNFs) as the support backbone for the assembled layered double hydroxides (LDHs) and dopamine (DA) as the adhesive. The results demonstrated that LDHs could be uniformly distributed in the network structure of CNFs, and the defects on the membrane surface could be effectively compensated by DA. Simultaneously, the continuous LCUM/D showed excellent rejection (97.18%) and selectivity of ionic contaminants tellurium. Dopamine not only compensated for the surface defects of the 2D membrane and enhanced the rejection of tellurium, but also caused no significant loss of water permeance. Moreover, the LCUM/D exhibited stability, which facilitated its long-term application. In addition, the improved hydrophilicity allowed LCUM/D satisfactory anti-fouling properties. This study provides new dimensional insights into the fabrication of continuous 2D membranes for the removal of ionic contaminant and enhances their application prospects in wastewater treatment.

Emulsion Assembly of Graphene Oxide/Polymer Composite Membranes

Graphene oxide/polymer composite water filtration membranes were developed via coalescence of graphene oxide (GO) stabilized Pickering emulsions around a porosity-generating polymer. Triptycene poly(ether ether sulfone)-CH₂NH₂:HCl polymer interacts with the GO at the water-oil interface, resulting in stable Pickering emulsions. When they are deposited and dried on polytetrafluoroethylene substrate, the emulsions fuse to form a continuous GO/polymer composite membrane. X-ray diffraction and scanning electron microscopy demonstrate that the intersheet spacing and thickness of the membranes increased with increasing polymer concentration, confirming the polymer as the spacer between the GO sheets. The water filtration capability of the composite membranes was tested by removing Rose Bengal from water, mimicking separations of weak black liquor waste. The composite membrane achieved 65% rejection and 2500 g m^-2 h^-1 bar^-1. With high polymer and GO loading, composite membranes give superior rejection and permeance performance when compared with a GO membrane. This methodology for fabrication membranes via GO/polymer Pickering emulsions produces membranes with a homogeneous morphology and robust chemical separation strength.

Selective Ion Transport in Two-Dimensional Lamellar Nanochannel Membranes

Precise and ultrafast ion sieving is highly desirable for many applications in environment-, energy-, and resource-related fields. The development of a permselective lamellar membrane constructed from parallel stacked two-dimensional (2D) nanosheets opened a new avenue for the development of next-generation separation technology because of the unprecedented diversity of the designable interior nanochannels. In this Review, we first discuss the construction of homo- and heterolaminar nanoarchitectures from the starting materials to the emerging preparation strategies. We then explore the property-performance relationships, with a particular emphasis on the effects of physical structural features, chemical properties, and external environment stimuli on ion transport behavior under nanoconfinement. We also present existing and potential applications of 2D membranes in desalination, ion recovery, and energy conversion. Finally, we discuss the challenges and outline research directions in this promising field.

CNTs Intercalated LDH Composite Membrane for Water Purification with High Permeance

The pursuit of improved water purification technology has motivated extensive research on novel membrane materials to be carried out. In this paper, one-dimensional carboxylated carbon nanotubes (CNTs) were intercalated into the interlayer space of layered double hydroxide (LDH) to form a composite membrane for water purification. The CNTs/LDH laminates were deposited on the surface of the hydrolyzed polyacrylonitrile (PAN) ultrafiltration membrane through a vacuum-assisted assembly strategy. Based on the characterization of the morphology and structure of the CNTs/LDH composite membrane, it was found that the intercalation of CNT created more mass transfer channels for water molecules. Moreover, the permeance of the CNTs/LDH membrane was improved by more than 50% due to the low friction and rapid flow of water molecules in the CNT tubes. Additionally, the influence of preparation conditions on the separation performance was investigated using Evans blue (EB). Optimized fabrication conditions were given (the concentration of CoAl-LDH was 0.1 g/L and the weight ratio of CNTs was 2 wt.%). Next, the separation performances of the prepared CNTs/LDH composite membrane were evaluated using both single and mixed dye solutions. The results showed that the composite membrane obtained possessed a retention of 98% with a permeance of 2600 kg/(m²·h·MPa) for EB, which was improved by 36% compared with the pristine LDH composite membrane. Moreover, the stability of the CNTs/LDH composite membrane was investigated in 100 h with no obvious permeance drop (less than 13%), which exhibited its great potential in water purification.

Durable and chemical resistant ultra-permeable nanofiltration membrane for the separation of textile wastewater

It is highly challenging to prepare durable and chemical resistant ultra-permeable membranes that can quickly separate small organic molecules like dye or inorganic salt in the complex textile wastewater industry. Here, side-chain sulfonated poly(ether ether ketone) (SPEEK) was synthesized and prepared the poly(ether ether ketone) (PEEK) - SPEEK nanofiltration (NF) membrane by a simple dipping coating and heat treatment. Single component filtration tests of the optimized membrane showed ultrahigh pure water flux (126 Lm^-2 h^-1 bar^-1) and relatively low NaCl rejection (6.7%). Moreover, the negatively charged membrane exhibited excellent rejection of 98.8% toward Congo red (CR). The pure water flux was about 9 folds than that of commercial NF270 with comparable solutes rejection. The separation tests of CR and NaCl mixed solution at optimized conditions exhibited ultra-high permeation flux (34 Lm^-2 h^-1 bar^-1), satisfactory dye (98.8%)/salt (< 10%) rejection and the separation performance remained stable after 10 cycles. Finally, the contaminated membrane was washed with ethanol, the permeation flux and the CR rejection remained constant after several cycles, while the commercial NF1 membrane exhibited serious swelling only within one cycle. The prepared membrane exhibited good organic solvents resistance and antifouling properties. Thus, this work confirmed the PEEK-SPEEK NF membrane showed great potential in the sustainable treatment of textile wastewater.