Membrane technology underpins modern water treatment, yet its manufacture remains dependent on toxic dipolar aprotic solvents that are now restricted under REACH and Environmental Protection Agency (EPA) rulings, and that generate an estimated 50 billion liters of contaminated effluent annually. Existing reviews on green membrane fabrication treat aqueous phase separation (APS) as one entry within broad solvent-substitution inventories, and reviews of polyelectrolyte complexation address materials science rather than membrane formation; consequently, no critical synthesis has yet connected APS demixing mechanisms to membrane structure, transport, and separation performance. This review addresses that gap. We show that APS is not a single technique but a family of mechanisms, unified by aqueous processing and stimulus-triggered demixing rather than by any one chemistry, comprising stimuli-responsive demixing of single polymers and polyelectrolyte complexation (PEC) induced by pH or salinity shifts. Mapping these mechanisms onto classical phase-inversion theory shows that the composition-path, binodal-crossing, and instantaneous-versus-delayed-demixing concepts developed for nonsolvent-induced phase separation transfer directly to APS, with electrostatic screening replacing solvent quality as the controlling variable. From this framework, three quantitative conclusions emerge. First, APS membranes span the full microfiltration-to-nanofiltration range, with pH-shift systems reaching divalent-salt rejections of 94–98% at 1.7–4.5 L·m−2·h−1·bar−1, comparable to commercial softening-grade nanofiltration membranes, whereas salt-shift systems achieve similar rejection at permeabilities one to two orders of magnitude lower. Second, monovalent rejection plateaus at 40–70% across every system reported to date, a ceiling imposed by the Donnan-exclusion mechanism itself; APS membranes are therefore credible as solvent-free desalination pretreatment, but not as stand-alone seawater desalination membranes. Third, mechanical performance, not selectivity, is the binding constraint on scale-up: hollow-fiber APS membranes remain limited to below 1 bar, and long-term oxidant stability is largely unquantified. Priorities are consequently identified as raising crosslink density to break the monovalent-rejection ceiling, quantifying chemical durability under realistic cleaning protocols, and demonstrating continuous production beyond flat-sheet laboratory casting.
To promote the practical application of membrane separation technology in actual degreasing wastewaters (DGWs), the crux of performance degradation attributable to oil-fouling must be addressed. Photocatalytic technology was considered a promising technology for membrane self-cleaning and water resource acquisition due to simplicity, greenness and environmental friendliness. Here, a super hydrophilic black zinc oxide/copper oxide (Black@ZnO/CuO) heterojunction was grown on carbon fibers (CF) via electroless plating followed by chemical oxidation. Underwater superoleophobicity (159.0°) along with outstanding antifouling were imparted to the membrane by rough micro-nano structure generated by the rice-like Black@ZnO covering the CuO clusters. For high viscosity #1 DGW, the separation efficiency and flux reached 98.2% and 6087.0 L·m−2·h−1; for emulsified #2 DGW, they were 79.3% and 4523.6 L·m−2·h−1. Coupling of self-cleaning and evaporation processes yielded recovery rates of 95.9% for separation efficiency (SERR) and 92.8% for flux (FRR). A permeate evaporation rate of 2.31 kg·m−2·h−1 was achieved, while measured rejection rates of ions and TOC remained above 98.8%. For the enlarged Black@ZnO/CuO-CF membrane with an area of 86.5 cm2, it showed high separation efficiency (91.2% and 70.1%) and flux (7650.0 L·m−2·h−1 and 6420.7 L·m−2·h−1) for DGWs. After self-cleaning and evaporation experiments, the SERR and FEE also reach 97.0% and 96.7%. An evaporation rate of 1.82 kg·m−2·h−1 was attained, while maintaining a 98.2% rejection rate. Then, this strategy of combining super hydrophilic heterojunction and membrane separation technology provides a new strategy for the technology of separation and self-cleaning-photothermal evaporation to achieve water resource acquisition.
The global lithium demand surge necessitates energy-efficient extraction technologies for hard-rock resources, yet conventional spodumene processing is bottlenecked by energy-intensive calcination (>1000 °C) and hazardous waste generation. Here, we report a microwave-assisted mechanical activation (MAMA) strategy that enables direct alkaline lithium extraction from α-spodumene at sub-350 °C under atmospheric pressure, eliminating the high-temperature phase transformation entirely. The synergistic coupling of mechanical defect engineering and selective microwave dielectric heating reduces the apparent activation energy to 89 kJ mol−1, achieving a 97.3% lithium extraction efficiency at 310 °C. The recovered Li2CO3 product exceeds 99.5% purity, meeting battery-grade specifications, while the analcime byproduct exhibits a CO2 capture capacity of 3.22 mmol g−1 with 94% cyclic stability. Life cycle assessment reveals an 83% reduction in global warming potential and a 68% reduction in cumulative energy demand compared to conventional acid routes. This work establishes a low-carbon, zero-hazardous-waste paradigm for sustainable lithium production.
In this study, CaAl-layered double hydroxide (CA) composites modified with Spirogyra sp. biomass and hydrochar were synthesized for the selective adsorption of anionic dyes from aqueous solutions. Structural characterization confirmed the preservation of the characteristic CaAl-LDH framework after composite formation, accompanied by changes in surface functionality and structural characteristics following biomass-to-hydrochar transformation. Selective adsorption experiments using mixed anionic dyes revealed preferential adsorption toward Remazol Red (RR). Among the synthesized materials, the hydrochar-based composite (CAHS) exhibited the highest maximum adsorption capacity of 138.889 mg/g, with optimum adsorption observed at pH 2 and equilibrium reached within approximately 70 min. Adsorption kinetics were better described by the pseudo-second-order model, while the equilibrium data were best fitted by the Freundlich isotherm, and thermodynamic analysis indicated a spontaneous and endothermic adsorption process. More importantly, FTIR, zeta potential, and XPS analyses revealed that biomass-to-hydrochar transformation altered the adsorption mechanism of the CaAl-LDH composites. RR adsorption on biomass-based composite (CAS) was predominantly governed by electrostatic attraction and nitrate-sulfonate interlayer ion exchange, whereas CAHS exhibited a more synergistic adsorption mechanism involving interactions with hydrochar carbon domains, π–π interactions, hydrogen bonding, and partial electrostatic attraction. Regeneration experiments showed a progressive decline in adsorption performance over repeated cycles, while ICP-MS analysis revealed measurable Ca and Al leaching under strongly acidic adsorption conditions. These findings demonstrate that biomass-to-hydrochar transformation not only affects adsorption performance but also alters the dominant interactions governing RR adsorption, providing mechanistic insights into the design of biomass-derived LDH composites for selective dye removal.
Uranium extraction from seawater could significantly alleviate the shortage of uranium resources. Herein, an in-situ growth strategy was employed to uniformly anchor the crown ether-functionalized metal-organic framework (MOF-18Cr6) onto the surface of copper nanowires (Cu NWs), thereby constructing a structurally robust Cu NWs@MOF-18Cr6. Coupled with the selective trapping capability of crown ether cavities and the high reductive activity of Cu NWs, the composites achieved efficient U(VI) enrichment and subsequent reductive stabilization. Static adsorption results showed that the uranium adsorption capacity of the material was up to 225.7 mg/g, with a value of 6.21 mg/g in actual seawater environments. Furthermore, Cu NWs@MOF-18Cr6 exhibited excellent selectivity and superior antibacterial activity. Finally, mechanistic analysis revealed that crown ether selectively captured U(VI) through size matching and chelation, whereas Cu NWs enabled in-situ reduction of U(VI) to U(IV), thereby realizing efficient uranium extraction. Thus, Cu NWs@MOF-18Cr6 may be a promising adsorbent for uranium recovery from natural seawater via synergistic adsorption-reduction.
