Thin-film composite (TFC) membranes prepared via interfacial polymerization (IP) have long suffered from a trade-off between selectivity and permeability, primarily due to the uncontrolled IP reaction that leads to a thick polyamide (PA) layer and high mass transfer resistance. Herein, we propose a dual-confinement strategy based on tannic acid (TA)-based organic nanoreactors with a unique morphology. The phenolic hydroxyl groups on the nanoreactors surface specifically interact with piperazine (PIP) molecules, restricting monomer migration to the organic phase and thus confining the reaction zone to exert spatial confinement. In addition, the unique surface mesoporous structure anchors PIP via strong hydrogen bonding within the nanoreactors, modulating the local chemical microenvironment and providing structural confinement. Benefiting from this dual confinement, the resulting nanofiltration membrane forms an ultrathin polyamide selective layer featuring Turing structures, high carboxyl density and a pore size comparable to that of the control. The membrane exhibits significantly enhanced overall performance, achieving a water permeance of 23.4 L m−2 h−1·bar−1 and a Na2SO4 rejection of 97.6%, along with good anti-fouling properties and operational stability. This strategy also shows regulatory effects in reverse osmosis membrane fabrication and holds potential for scale-up, highlighting its application prospects. The study establishes a facile approach to regulating IP that effectively mitigates the selectivity–permeability trade-off, offering a promising strategy for the preparation of high-performance TFC membranes.
In this work, a mechanically robust and highly conductive porous ion-solvating membrane (ISM) based on hydroxyapatite (HAp)-reinforced polysulfone (PSU)/polyvinylpyrrolidone (PVP) was developed for alkaline water electrolysis (AWE). HAp nanoparticles were synthesized via co-precipitation followed by hydrothermal treatment and incorporated into the polymer matrix using the non-solvent-induced phase separation (NIPS) method. The effect of HAp loading (1-10 wt%) on membrane structure and properties was systematically investigated. HAp incorporation enhanced membrane hydrophilicity, promoted the formation of continuous ion-conduction pathways, and improved mechanical properties. The optimized membrane containing 5 wt% HAp exhibited high water uptake (223%), electrolyte uptake (131%), higher hydroxide conductivity of 49.4 mS cm−1 at room temperature, and lower area resistance (0.16 Ω cm2). Mechanical strength was significantly improved, with a Young's modulus of 1850 MPa and elongation at break of 44%. The membrane showed excellent chemical and thermal stability, retaining >97% mass after immersion in 3 M KOH at 60 °C for one week. Long-term immersion in 3 M KOH further confirmed its outstanding chemical and structural stability, with no detectable morphological or chemical changes after approximately 4300 h of static immersion. In preliminary single-cell AWE tests using bare nickel foam electrodes in 4.5 M KOH at 80 °C, the membrane achieved a cell voltage of 2.7 V at 500 mA cm−2, demonstrating its strong potential for AWE applications.
Carbon capture is an important strategy for mitigating climate change, and membrane-based CO2 separation offers advantages such as low energy consumption, operational simplicity, and continuous operation. Incorporating metal-organic frameworks (MOF), improving the interface between MOF and polymers, and introducing sites with CO2 affinity are effective approaches for enhancing mixed matrix membranes (MMMs) performance. In this study, poly(ionic liquid) (PIL)-modified MOF-808 fillers were synthesized through in situ polymerization and incorporated into Pebax membranes. The PIL modification adjusted the pore environment of MOF-808, introduced imidazolium and -COOH groups, and strengthened interactions between the filler and Pebax, thereby restricting Pebax chain mobility. The optimized MMM exhibited a CO2 permeability of 124.57 Barrer at 0.1 MPa and 35 °C, with CO2/N2 selectivity surpassing the 2008 Robeson upper bound and CO2/CH4 selectivity also substantially improved. Positron annihilation lifetime spectroscopy (PALS) revealed a reduction in fractional free volume compared with pristine Pebax, while time-lag analysis showed a corresponding decrease in gas diffusivity. In contrast, the CO2 solubility coefficient increased markedly because of the CO2 affinity introduced by PIL. The increase in CO2 solubility was larger than the loss in diffusivity, leading to enhanced CO2 permeability and selectivity despite reduced free volume. By combining PALS with time-lag analysis, nanoscale free volume evolution was connected with diffusion and solubility contributions. These results show that PIL-modified MOF-808 changes the balance between diffusivity and solubility in MOF/Pebax MMMs and clarify why CO2 transport can be improved even when free volume and diffusivity decrease.
Positively charged nanofiltration membranes (PC-NFMs) with dense immobilized cationic sites have wide-ranging separation applications, yet conventional fabrication strategies are plagued by inherent drawbacks including severe permeability-selectivity trade-off, insufficient surface charge density and poor structural durability. To address these bottlenecks, this work proposed a facile reactive crosslink-packing methodology to construct hierarchically porous PC-NFM using two types of hyperbranched polymeric nanoparticles (NPs), rigid quaternized poly(vinyl benzyl chloride) NPs (MHP, intrinsic intra-pore size: 3.48 nm) and flexible hyperbranched poly(amido-amine) (HBP) NPs. Homogeneous, integral positively charged selective layer (MHP-HBP) is uniformly deposited onto ultrafiltration substrates via pre-crosslinking followed by thermal curing. The dual-NP covalent network inherits abundant intrinsic voids from both hyperbranched building blocks, generating interconnected continuous water transport nanochannels within the separation layer. Strikingly, the as-fabricated MHP-HBP PC-NFM exhibits unique pressure-tunable hydrated pore architectures. The pore size cut-off dynamically varies from 1.07 nm to 2.05 nm under operating pressures spanning 1∼30 bar, enabling adaptive separation performance for diverse desalination scenarios. At an optimal pressure of 4.0 bar, the membrane delivers a pure water permeance of 10.48 L/m2·h·bar alongside a MgCl2 rejection rate of 90.58%. Benefiting from the robust covalently crosslinked dual-hyperbranched network, the MHP-HBP PC-NFM demonstrates outstanding mechanical, acidic and alkaline stability. This work establishes a universal dual-NP crosslink-packing platform for constructing high-performance PC-NFMs and offers a novel paradigm for designing pressure-responsive separation materials.
