Trifunctionalized Ionic Covalent Organic Framework-Engineered Mixed-Matrix Membranes for Rapid and High-Performance Adsorptive Separation of Charged Aqua Pollutants

Abstract

Water contamination by inorganic and organic pollutants is one of the most contentious global environmental issues. However, conventional scavenging materials often exhibit poor selectivities and limited adsorption capabilities. By contrast, an ionic covalent organic framework (iCOF) with functionalized pores promises effective capture of harmful oxo-anions and carcinogenic dyes and can benefit their removal over a practical platform. We employ facile Schiff base condensation to devise a thermochemically robust guanidinium-based iCOF via the incisive amalgamation of anion exchange, hydrogen bonding, and electrostatic interaction sites. Building on such trifunctionality, the material demonstrates efficient sequestration of dichromate oxoanions and Congo Red (CR) dye in water with rapid kinetics and superior scavenging capacity (Cr 2 O 7 2− : 412 mg/g, CR: 316.3 mg/ g) compared to other porous crystalline materials. Apart from the high selectivity in the presence of interfering anions/dyes, the adsorptive capacities remain unaltered (>90%) for five cycles with postrelease stability. In-depth analysis corroborates that the removal of oxo-anions is driven by the ion-exchange phenomena, while electrostatic, hydrogen bonding, and π−π stacking interactions play a role in dye adsorption, as also supported by density functional theory studies. The real-time potential of iCOF for long-term water purification has been established via the fabrication of a polysulfone (PSF)-based mixed-matrix membrane. The iCOF@PSF ultrafiltration membrane exhibits high water permeance and rejection of both dichromate (87%) and CR (99.9%) with excellent recyclability. Notably, a high permeate flux of the iCOF@PSF membrane for dichromate (88.6 ± 1.8 L/m 2 h bar) and CR dye (86.2 ± 1.5 L/m 2 h bar) validate effective synergism between iCOF functionalities and the PSF matrix in sieving both the anionic pollutants and provide valuable insights into the development of porous charged materials for wastewater remediation over a practical platform.