Interface-Engineered CDC@ZIF-8 hybrids for sustainable phosphate Sequestration from aqueous media

Excessive phosphate (PO₄³⁻) discharge into aquatic ecosystems is a critical environmental issue due to its role in triggering eutrophication and degrading water quality. In this work, we report the synthesis and evaluation of a novel hybrid adsorbent composed of carbide-derived carbon (CDC) integrated into a ZIF-8-based metal–organic framework (MOF) for efficient PO₄³⁻ removal from aqueous solutions. The CDC@MOF composites were synthesized via a hydrothermal route using various CDC loadings (60, 120, and 180 mg) to optimize their structural and functional performance. Detailed physicochemical characterization was performed using SEM, TEM/SAED, XRD, FTIR, XPS, BET, TGA, and point of zero charge analysis. Among the prepared composites, CDC@MOF-2 (120 mg CDC) exhibited superior characteristics, including well-developed micro-mesoporosity, enhanced crystallinity, and increased active surface area. Batch adsorption experiments revealed a high PO₄³⁻ uptake of 85.79 mg P/g at pH 4.1 and 22 °C. Nonlinear kinetic modeling showed that the Elovich and fractal-like Vermeulen models best described the adsorption mechanism, indicating concurrent physical and chemical interactions with a significant role of surface heterogeneity and diffusion control. Additionally, CDC@MOF-2 showed remarkable selectivity toward PO₄³⁻ in the presence of coexisting anions (NO₃^–, Cl^–, SO₄^2–, HCO₃^–, Br^–), and retained over 85 % of its adsorption capacity after five regeneration cycles. The results highlight CDC@MOF-2 as a robust and regenerable adsorbent with promising applicability for sustainable PO₄³⁻ removal from contaminated water.