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.