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

Abstract

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 Na 2 SO 4 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.

Planting Anion Channels in a Negatively Charged Polyamide Layer for Highly Selective Nanofiltration Separation

“…FT-IR and XPS were employed to prove the occurrence of polymerization and infer the possible microstructure of the separation layer based on changes in the characteristic peaks. As shown in Figure a, the peaks located at 1750 and 1620 cm –1 are due to the stretching vibration of CO originating from the ester and amide linkages, respectively. , The peak intensity of ester stretching vibration is strong for the pristine membrane; however, it becomes weak and even disappears after alkaline treatment, attesting to the obvious hydrolysis of the ester linkages . The broad absorbance around 3400 cm –1 should be ascribed to −OH stretching vibrations, which are derived from the hydrolysis of the unreacted acyl chloride and the unoxidized phenolic hydroxyl groups of TA.…”

“…As shown in Figure 1a, the peaks located at 1750 and 1620 cm −1 are due to the stretching vibration of C�O originating from the ester and amide linkages, respectively. 38,39 The peak intensity of ester stretching vibration is strong for the pristine membrane; however, it becomes weak and even disappears after alkaline treatment, attesting to the obvious hydrolysis of the ester linkages. 40 The broad absorbance around 3400 cm −1 should be ascribed to −OH stretching vibrations, 38 which are derived from the hydrolysis of the unreacted acyl chloride and the unoxidized phenolic hydroxyl groups of TA.…”

Alternative materials for interfacial polymerization: recent approaches for greener membranes

“…Tris(hydroxymethyl)aminomethane or THAM, a low-cost and green monomer was reported used to prepare poly(ester amide) (PEA) thin-film composite membranes via IP. 85 THAM contains one amino group and three hydroxyl groups and exhibits tetrahedral-like geometry which is uncommon among most of the monomers as they are either linear or planar. Moreover, THAM is extensively used in the medical field, specifically in molecular biology or biochemistry, and is featured as an integral component in buffer solutions.…”

“…Moreover, THAM is extensively used in the medical field, specifically in molecular biology or biochemistry, and is featured as an integral component in buffer solutions. 93 Furthermore, THAM demonstrated high water solubility and thus, Zhang et al 85 were particularly interested to investigate the relationship between membrane structures and aqueous monomer concentration for IP with TMC in the organic phase. Additionally, detailed experimental work revealed that the coexistence of functional groups with different reactivities enabled THAM to showcase moderate reactivity which in turn was beneficial for tuning the crosslinking density of the resultant polymeric network.…”