Influence of covalent organic framework integrated hybrid PEI membrane on removal of divalent salts-fulvic acid residues

Background

Natural organic matter (NOMs) can form complexes with divalent salts, increasing their bioaccumulation in aquatic systems and posing health risks to aquatic organisms. This study explores the use of triazine-structured Covalent Organic Frameworks (COFs), specifically NENP-1, incorporated into polyetherimide (PEI) membranes to enhance the removal of fulvic acid (FA) with Mg²⁺ and Ca²⁺ from saline wastewater.

Methods

Flat sheet membranes (M2-M5) with varying COF concentrations (0.25 %, 0.5 %, 0.75 %, and 1 %) were fabricated by the phase inversion method. The presence of characteristics peaks at 3486 cm^-1 (secondary amine), 1495 - 1349cm^-1 (triazine structure) functional group in the was confirmed, which confirmed the NENP-1 successful embedding in the matrix of PEI polymer. FESEM analysis revealed that the 0.25 wt.% membrane had uniform nanoparticle dispersion and a thin selective layer, while higher COF content (1 wt.%) caused aggregation and dense layer formation.

Significant Findings

Among the membranes (M1-M5), the M2 (0.25 wt.%) COF membrane showed the best performance, achieving solute fluxes of 180 and 190 L·m⁻²·h⁻¹ for FA+MgCl₂ and FA+CaCl₂, with 72 % and 79 % rejection, respectively. Further, the M2 (0.25 wt.%) membrane also demonstrated good antifouling properties, with a flux recovery ratio of 78.5 %. Overall, NENP-1/PEI membranes present a viable solution for removing NOMs and divalent salts from contaminated water sources.