Amino acid-modified magnetic covalent organic framework: Synthesis, properties and application in digital detection of trace amounts of chromium (VI) in water and wastewater

Heavy metals are among the most significant pollutants in marine and surface water environments due to their high toxicity, chemical stability, and ability to bioaccumulate. Even at trace levels, these elements can interact with biochemical pathways, disrupt metabolic processes in marine organisms, and cause extensive biological damage, including reduced biodiversity and long-term toxic effects. Among heavy metals, chromium(VI) is recognized as a highly toxic and carcinogenic contaminant because of its strong oxidizing properties, high solubility, and cellular permeability. Its presence in marine waters and industrial effluents poses a serious threat to both ecosystems and human health. Therefore, the development of efficient, sensitive, stable, and reusable materials for the detection and removal of chromium(VI) from aquatic environments is of critical importance. In this study, a magnetic covalent organic framework (COF-Cys_Au@CF) functionalized with the amino acid cysteine and gold nanoparticles was synthesized as a novel platform for the digital sensing and selective adsorption of chromium(VI) in water and marine wastewater samples. The synthesis involved the stepwise assembly of the base COF, incorporation of magnetic and gold nanoparticles, and surface modification with the amino acid. Extensive structural characterization, including FT-IR, XRD, FESEM, EDX, and VSM, confirmed the successful formation of the framework, uniform distribution of nanoparticles, suitable thermal and magnetic stability, and effective interactions among the composite components. FESEM and EDX analyses demonstrated the homogeneous dispersion of magnetic and gold nanoparticles within the COF network, while VSM data confirmed the desired magnetic behavior for rapid separation under an external magnetic field. The adsorption performance and digital sensing of chromium(VI) were evaluated using ۱۵ mg of the adsorbent with samples containing ۰.۰۷ ppm chromium(VI) at pH ۲ and a contact time of ۹۰ seconds. The results revealed that the synthesized material exhibited very high sensitivity, with a limit of detection (LOD) of ۱.۴ μg/L and a limit of quantification (LOQ) of ۴.۹ μg/L. Method reproducibility was confirmed with RSD values of ۵.۳% and ۲.۱% for chromium(VI) concentrations of ۳۰ and ۱۰۰ μg/L, respectively. The adsorption capacity under optimal conditions is [۲۱.۲۲ mg/g], and the recovery of real water and wastewater samples ranged from ۹۷.۲% to ۱۰۴%. The magnetic property of the composite allowed rapid separation and reuse for up to ۷ cycles without significant loss of efficiency. Kinetic and isotherm analyses indicated that the chromium(VI) adsorption process follows a pseudo-second-order kinetic model and the Langmuir isotherm, reflecting strong surface interactions and high adsorption capacity. The combination of the COF structure, amino acid surface functionalization, and gold nanoparticles resulted in high selectivity, rapid adsorption, and facile magnetic separation, highlighting the practical significance of this system for monitoring marine pollution. Overall, the cysteine-functionalized magnetic COF with gold nanoparticles provides a novel, sensitive, and environmentally friendly platform for digital sensing and selective adsorption of chromium(VI), with strong potential for practical applications in monitoring and managing toxic contaminants in water and marine wastewater. This study represents a significant advancement in the design of sustainable, reusable, and high-performance adsorbents for heavy metals in aquatic environments, offering an effective strategy to mitigate the environmental impacts of heavy metal pollution.

کلیدواژه ها:

Reabsorption Chromium(VI) ، Cobalt Ferrite ، Magnetic Covalent Organic Framework (COF) ، Digital sensing ، Amino acid–functionalized nanocomposite