Journal of Membrane Science最新文献

Membrane fouling has been a major factor hindering the development of ultrafiltration membranes. Herein, a novel in situ oxidation system was constructed via introducing MnFe₂O₄/MWCNTs into polyvinylidene fluoride (PVDF) membranes, utilizing sunlight to synergistically activate persulfate (PMS) to mitigate ultrafiltration membrane fouling. The mechanism of mitigating membrane fouling in MnFe₂O₄/MWCNTs-PVDF ultrafiltration membranes was systematically explored under four system (single filtration, single sunlight irradiation, single PMS oxidation and sunlight co-activated PMS). The MnFe₂O₄/MWCNTs-PVDF membranes exhibited different fouling characteristics under the four systems, with the sunlight and MnFe₂O₄/MWCNTs membrane co-activated PMS filtration system showing the highest humic acid (HA) removal efficiency of 90.2 %, as well as the lowest Rr (0.2108 × 10¹²m⁻¹) and Rir (0.4525 × 10¹²m⁻¹). To further evaluate the practicality and effectiveness of the sunlight-MnFe₂O₄/MWCNTs-PMS system, the secondary effluent was selected to verify the treatment effect on natural organic matter (NOM) of actual water. By observing the microscopic morphology of the fouled membrane surface, it was evident that, compared with the other three filtration systems, the filter cake layer on the MnFe₂O₄/MWCNTs membrane surface of the sunlight co-activated PMS system was obviously reduced, and the structure of the cake layer was more loose. It can be concluded that the principle behind the synergistically activated system to alleviate the membrane fouling was to accelerate the mineralization rate of HA molecules, oxidize the HA into a smaller particle size that can pass through the membrane pores. The main reactive oxygen species and HA degradation mechanism in the synergistic activation system were further elucidated by electron paramagnetic resonance (EPR) analysis and density functional theory calculations (DFT). The results indicated that the degradation of HA by the synergistically activated PMS system involved a combination of free radicals (·O₂⁻、SO₄^·− and ·OH) and non-free radicals (¹O₂). Overall, the in-situ oxidation system provided an alternative way to alleviate ultrafiltration membrane fouling.

Low flux and membrane fouling are major challenges in membrane distillation (MD) for treating concentrated wastewater. This study compared the performance of GO composite membranes with different interlayer distances, by covalently bonding the terminal amine groups of ethylenediamine (EDA) and 1,12-diaminododecane (DADD) with the carboxyl groups present on the GO sheets. The results indicated that the GO-DADD/PTFE membrane, with longer carbon chain cross-linking, achieved the highest flux and antifouling properties. At 70 °C, the pure water flux reached 68.5 kg/m²·h, and the fluxes for treating NaCl, HA containing NaCl, and BSA containing NaCl were 29.8 %, 37.1 %, and 38.5 % higher than the uncrosslinked GO/PTFE, and 95.7 %, 121.2 %, and 146.9 % higher than the PTFE membrane, respectively. Through mathematical models for mass and heat transfer, the study identified the key to this enhancement as the increased d-spacing within the GO layer due to cross-linking, which weakened the Kelvin effect and enhanced the vapor partial pressure on the hot side. The unique surface structure and electrostatic interactions induced by long-chain cross-linking further boosted the antifouling effect. These modifications not only overcome the typical trade-off between retention rates and flux but also offer a scalable and efficient solution for advanced membrane distillation applications.

In this study, we explore the role of the polysulfone (PSU) support membrane skin-layer and whole-body pore morphology on the physical-chemical properties and separation performance of hand-cast polyamide-PSU (PA-PSU) composite seawater reverse osmosis (SWRO) membranes. We tailor the support membrane pore morphology by varying the PSU concentration and the coagulation bath temperature. In order to isolate the impacts of the PSU support, all of the porous supports are coated using identical m-phenylene diamine (MPD) and trimesoyl chloride (TMC) solution compositions, reaction conditions, and post-treatments. As PSU concentration increases, PSU support membrane pore size, surface and body porosity, water permeability, MPD mass uptake (by the PSU support), and PA-PSU composite membrane water permeability decrease, while MPD and TMC conversion, PA film mass and thickness, crosslinking degree (XD), and PA-PSU composite membrane NaCl rejection increase. As PSU support membrane coagulation bath temperature increases, support membrane pore size, surface and body porosity, MPD uptake, PA film mass, thickness and XD, MPD and TMC conversion, and NaCl rejection increase, while composite PA-PSU membrane water and NaCl permeability decrease. Composite membrane permeabilities were 70–90 percent of the (theoretical) unsupported PA film permeabilities due to the high XD and low PA coating film thickness. Composite PA-PSU membrane water/salt permeabilities both correlate most strongly with PA coating film mass/thickness and XD, which in turn correlate most strongly with TMC conversion. The key to increasing water permeability is lower PA film mass/thickness and XD with higher support membrane surface pore size and porosity. In contrast, the key to increasing NaCl rejection is higher PA film mass/thickness and XD with lower support membrane surface pore size and porosity.

Ultrafiltration membranes have significant potential for application in wastewater treatment. However, membrane fouling seriously affects the separation efficiency and service life of the membrane. The preparation of conductive membranes offers a novel idea for removing membrane fouling. In this work, polyethersulfone (PES) mixed matrix membranes containing epigallocatechin gallate-modified multi-walled carbon nanotubes and silanized MXene were simply prepared by nonsolvent-induced phase inversion. Due to the introduction of a three-dimensional network structure electrostatically assembled with the two nanomaterials, the membranes have a great potential for balancing permeability, separating ability, and electrical conductivity. In addition, due to the presence of two kinds of fillers, the modified membrane also showed excellent electrical conductivity and antimicrobial performance, with a conductivity of up to 6.4 mS/cm, while exhibiting an ultra-high bacterial inhibition rate of close to 100 %. More importantly, through electrochemically assisted cleaning, the membrane fouling was efficaciously removed by nanobubbles and electrostatic force, and the flux recoveries after membrane filtration of CR and BSA reached 93.1 % and 91.7 %, respectively. In summary, the composite membrane has lots of promise for use in the purification of wastewater due to its considerable pollution removal effect and long-term operational performance.

The wet oxidation process is a promising method for simultaneously removing SO₂, NO, and Hg⁰ from coal-fired flue gas. However, the resource utilization of the resulting wastewater, which is enriched with complex ions such as Hg²⁺, NH₄⁺, NO₃⁻, and SO₄²⁻, remains a significant challenge. To achieve the simultaneous goals of concentrating NH₄⁺/NO₃⁻/SO₄²⁻ ions, adsorbing and separating Hg²⁺ ions, and reusing wastewater, a bifunctional MXene composite nanofiltration membrane with large interlayer spacing and excellent electrostatic repulsion was developed. The membrane was prepared by co-depositing MXene nanosheets, carboxylated multi-walled carbon nanotubes (MWCNTs), and sodium dodecyl sulfate (SDS) onto an NF-90 membrane. The resulting MXene-MWCNTs-SDS (MMS-COOH) composite membrane demonstrated exceptional salt rejection of 84.4 % for NO₃⁻, 89.0 % for NH₄⁺, 99.8 % for SO₄²⁻, and 99.7 % for Hg²⁺. After 30 cycles, the membrane structure remained stable, maintaining good reusability, with NH₄⁺ and SO₄²⁻ rejection still reaching 90.0 %. Moreover, the maximum adsorption capacity for Hg²⁺ was 2869.6 mg g⁻¹, while the capacities for Cr⁶⁺ and Pb²⁺ were 577.6 and 316.8 mg g⁻¹, respectively. The MMS-COOH composite membrane introduces an innovative method for the benign treatment of wet oxidation flue gas purification wastewater and facilitates the recovery of (NH₄)₂SO₄ and NH₄NO₃ as fertilizers, holding a promising application prospect.

When introducing acid groups in the diamine monomer for the fabrication of polyamide (PA) membranes through interfacial polymerization (IP), the acid groups not only reduce the diffusion flux of diamine monomer for the polymerization to prepare ultrathin membrane but also provide the negative charges on the membrane surface. However, the introduction of acid groups often weakens the reactivity of diamine monomers, resulting in the formation of thick and loose PA membranes with low rejection of ions. This study proposes a strategy of modulating the IP process of piperazine-2-carboxylic acid (CPIP) by employing an acid acceptor (NaOH) to prepare thin nanofiltration membranes. The acid acceptor can neutralize the HCl to prevent CPIP from being protonated during the IP process, thereby facilitating the cross-linking reaction rate. The thickness of the resulting membrane decreases from 180 nm to 30 nm, accompanied by the fortification of the negative charge, an increase in cross-linking density, and a reduction in pore size. The resulting PA-AA/CPIP_1.0 membrane exhibits a water permeance of 44.6 L m⁻² h⁻¹ bar⁻¹, with a significantly increased Na₂SO₄ rejection of 98.4 % compared with 50.4 % of the PA-AA/CPIP_0 membrane fabricated without acid acceptor. This work may open a new avenue to fabricating high-performance PA membranes for nanofiltration.

The escalating global demand for clean water has driven a growing interest in developing thin-film composite (TFC) membranes with high permeability and selectivity for wastewater treatment and desalination processes. Engineering polymer materials with precisely tunable properties for selective molecular separation remains a challenging step toward achieving this goal. Herein, we have fabricated a highly permselective asymmetric polyamide nanofilm with a dual-layer structure in which the bottom layer is a porous hyperbranched aromatic polyamide (HBPA) interlayer, and the top layer is a dense polyamide layer with a nanostrip structure. The HBPA porous layer was covalently assembled in situ via oxidative coupling reaction with ammonium persulfate on a polysulfone (PSF) substrate. The hydrophilic porous HBPA interlayer forms nanosized cavities that may enhance the storage and confine amine monomer diffusion, leading to the construction of a striped pattern PA nanofilm. The resulting asymmetric PA membrane exhibits excellent water permeability of 18.39 ± 1 L m⁻² h⁻¹ bar⁻¹ (3.98 times that of control membranes) and improved divalent salt (Na₂SO₄) rejection (≥98 %), surpassing most of the commercial and reported nanofiltration membranes. The HBPA-regulated interfacial polymerization provides a groundbreaking framework for developing high-performance membranes for precisely controlled nanofiltration.