A selective colorimetric and efficient removal strategy for mercury(ii) in aquatic systems using mesoporous Fe3O4-loaded silver probes

Abstract

Mesoporous Fe₃O₄-loaded silver nanocomposites (Fe₃O₄@Ag) were simply fabricated as bi-functional nanozymes for the catalysis-based detection and removal of Hg²⁺ ions. It was found that the as-prepared magnetic Fe₃O₄@Ag could display peroxidase-like catalysis activity that could be rationally enhanced in the presence of Hg²⁺ ions. To our surprise, the shell of the Ag element may decrease the catalysis of the Fe₃O₄ to some degree. However, the Ag particles could serve as the probes for specifically recognizing Hg²⁺ ions and trigger increased catalysis through the formation of Ag–Hg alloys, with a decreased signal background. A high-throughput colorimetric analytical method was thereby developed based on the Fe₃O₄@Ag catalysis for probing Hg²⁺ ions in the muscles of fish by using 96-well plates, at linear Hg²⁺ concentrations ranging from 0.010 to 2.5 mg kg⁻¹. Moreover, the developed colorimetric analytical method was applied to evaluate Hg²⁺ levels in muscle samples of different kinds of fish. Unexpectedly, an obvious difference of Hg²⁺ levels in muscles of four kinds of fish was discovered, with the order of snakehead (Ophicephalus argus) > largemouth bass (Micropterus salmoides) > crucian carp (Carassius auratus) > silver carp (Hypophthalmichthys molitrix), where the carnivorous fish showed higher Hg²⁺ levels than the omnivorous or plant-based ones. Moreover, the as-fabricated Fe₃O₄@Ag adsorbents with their large specific surface area and high environmental robustness could exhibit efficient Hg²⁺ adsorption with capacities of up to 397.60 mg g⁻¹. A removal efficiency of 99.40% can also be expected for Hg²⁺ ions from wastewater, with the magnet-aided recycling of Fe₃O₄@Ag adsorbents. Such an Fe₃O₄@Ag-based colorimetric analysis and removal strategy for Hg²⁺ ions should find wide applications in the fields of aquatic food safety, environmental monitoring, and clinical diagnostics of Hg-poisoning diseases.