In-situ green steam-assisted synthesis of Fe⁰/SCOF-PAN and acidic microenvironment fabrication for anti-passivation and efficient Cr(VI) reduction

To address the challenges posed by both the inherent limitations including aggregation and passivation of nano zero-valent iron (nZVI) and the treatment of acidic chromium-containing wastewater under mild conditions, a three-dimensional sulfonated covalent organic framework (SCOF) polyacrylonitrile (PAN) blended membrane loaded with nZVI (Fe⁰/SCOF-PAN) was fabricated via a green steam-assisted multiphase blending method combined with freeze-drying. Innovatively, SCOF was introduced into the PAN matrix to achieve dual modification, where the electrostatic repulsion provided by sulfonic acid groups significantly improved the dispersion of nZVI. Additionally, the membrane structure created acidic microenvironment within its cavities, effectively mitigating nZVI passivation. Experimental results demonstrated that the Fe⁰/SCOF-PAN composite exhibits excellent nZVI loading capacity and high Cr(VI) removal performance. Compared with unmodified PAN-supported nZVI, the Cr(VI) removal efficiency increased by 33.8%, and the loading capacity improved by 21.9 mg/g, while the removal efficiency remained above 90% in actual wastewater. Based on pseudo-first-order kinetics modeling, Sips isotherm analysis, thermodynamic studies, and XPS characterization, the high removal efficiency of Fe⁰/SCOF-PAN was attributed primarily to the redox reactions involving nZVI and its derived Fe²⁺ species, supplemented by the active sites and functional groups of SCOF, which contributed through electrostatic attraction and chelation. This study presents a low-energy strategy for synthesizing SCOF-PAN blended membranes, offering a novel approach for designing high-performance nZVI supported materials and advancing the treatment of acidic chromium-laden industrial wastewater.