In situ formation of porous organic polymer-based thin polyester membranes for loose nanofiltration

Micelles regulated thin film nanocomposite membrane with enhanced nanofiltration performance

The desalination performance of thin film nanocomposite (TFN) membranes is significantly influenced by the nature of nanofillers and the structure of the polyamide (PA) layer. Herein, a micelles regulated interfacial polymerization (MRIP) strategy is reported for the preparation of TFN membranes with enhanced nanofiltration (NF) performance. Specially, stable and ultrafine micelles, synthesized from the poly(ethylene oxide)-b-poly(4-vinyl pyridine)-b-polystyrene (PEO-PVP-PS) triblock copolymers, were utilized as regulators in the aqueous phase during the interfacial polymerization (IP) process. TFN membranes were fabricated with varying concentrations of micelles to improve their properties and performances. The structure of the PA layer was further regulated by modulating the content of trimesoyl chloride (TMC), which significantly enhances the performance of the TFN membrane with micelles. Attributable to the homogeneously dispersed micelles and the modified PA layer, the optimized membrane denoted as TFN-2-0.3 exhibits an improved separation performance of 20.7 L m-2h-1 bar-1 and 99.3 % Na2SO4 rejection, demonstrating nearly twice the permeance and 2.7 % higher rejection than that of the original control membrane, respectively. The mechanism of this MRIP strategy was investigated through the diffusion experiments of piperazine (PIP) and interfacial tension tests. The incorporated micelles effectively lower the interfacial tension, promote the diffusion of PIP and accelerate the IP reaction, resulting in a denser and thinner PA layer. Collectively, these findings demonstrate that TFN membranes with micelles exhibit increased roughness, enhanced hydrophilicity, superior rejection to divalent salts, and better acid-base resistance, highlighting their potential applications in the design of TFN membranes.

Fabrication of crown ether-containing copolymer porous membrane and their enhanced adsorption performance for cationic dyes: Experimental and DFT investigations

Adsorptive separation membranes are widely utilized for the removal of toxic dyeing pollutants from dyeing wastewater. However, developing novel adsorption membranes with large adsorption capacities and enhanced adsorption performance for dyes in actual wastewater poses a significant challenge. This study focuses on the fabrication of crown ether-containing copolymer porous membrane (CRPM) and investigation of the adsorption performance of dyes from aqueous solutions. The morphology structure and pore size distribution revealed that the membrane was endowed with rich micropores and hierarchical porous structures. Three typical cationic dyes (MB, RhB, CV) and an anionic dye (MO) were selected to evaluate the adsorption behavior. The results of adsorption isotherms and kinetics demonstrated that the adsorption data could be well-fitted using the Freundlich and pseudo-first-order kinetic models, the thermodynamic parameters revealed that the adsorption process of dyes on CRPM is a spontaneous endothermic reaction. The membrane exhibited excellent adsorption performance for cationic dyes, with RhB displaying a higher maximum adsorption capacity than previously reported porous membranes. Notably, dynamic adsorption-desorption filtration demonstrated a rapid removal efficiency, with RhB, MB, and CV achieving removal rates of 99.09%, 98.63%, and 99.14% respectively, after five cycles. The filtration volume of the CRPM membrane was 2.4-fold greater than that of a traditional PVDF membrane when applied to actual dyeing wastewater. DFT theoretical calculations were employed to elucidate the adsorption mechanism. These calculations confirmed the significant roles of electrostatic interactions, H-bonds and π-π interactions in facilitating the high-efficiency adsorption of cationic dyes. These findings highlight the potential of the crown ether-containing copolymer as a promising material for adsorption separation membranes in the treatment of dyeing wastewater.

A review on polyester and polyester-amide thin film composite nanofiltration membranes: Synthesis, characteristics and applications

Nanofiltration (NF) membranes have been widely used in various fields including water treatment and other separation processes, while conventional thin film composite (TFC) membranes with polyamide (PA) selective layers suffer the problems of fouling and chlorine intolerance. Due to the abundant hydrophilic hydroxyl groups and ester bonds free from chlorine attack, the TFC membranes composed of polyester (PE) or polyester-amide (PEA) selective layers have been proven to possess enhanced anti-fouling properties and superior chlorine resistance. In this review, the research progress of PE and PEA nanofiltration membranes is systematically summarized according to the variety of hydroxyl-containing monomers for membrane fabrication by the interfacial polymerization (IP) reaction. The synthesis strategies as well as the mechanisms for tailoring properties and performance of PE and PEA membranes are analyzed, and the membrane application advantages are demonstrated. Moreover, current challenges and future perspectives of the development of PE and PEA nanofiltration membranes are proposed. This review can offer guidance for designing high-performance PE and PEA membranes, thereby further promoting the efficacy of nanofiltration.

Novel Poly(ester amide) Membranes with Tunable Crosslinked Structures for Nanofiltration

Tuning the crosslinking density of interfacial-polymerized nanofiltration (NF) membranes varying from loose to dense structures can make them meet the demand of various applications. The properties (e.g., pore size and porosity) of NF membranes can be tuned by choosing monomers with different structures and reactivities. Herein, tris(hydroxymethyl)aminomethane (THAM), a low-cost and green monomer, is first employed for the preparation of poly(ester amide) (PEA) thin-film composite membranes via interfacial polymerization. The moderate reactivity of THAM enables rational regulation of the crosslinking density of PEA membranes from loose to dense structures by varying the THAM concentration, which can hardly be achieved for traditional polyamide or polyester membranes. The developed PEA membranes with a wide tunability range of crosslinking densities broaden their potential utility in NF. PEA membranes with dense structures show exceptional desalination performance with a water permeance of 11.1 L m^-2 h^-1 bar^-1 and a Na₂SO₄ rejection of 97.1%. However, loose PEA membranes exhibit good dye/salt separation performance with a dye removal rate over 95.0% and negligible NaCl rejection (<7.5%), as well as high water permeance (>45 L m^-2 h^-1 bar^-1). This work implies that PEA membranes with tunable crosslinked structures provide new possibilities for the development of task-specific separation membranes.