Transforming Coal Byproducts into a Novel Oxidase-Mimetic Nanozyme for Colorimetric Detection of Mercury Ions

Coal waste generated during the production of graphene-related materials (GRMs) presents substantial environmental challenges. This study presents a novel, one-step, low-temperature, wet chemical method for the efficient utilization of coal waste comprising iron-oxyhydroxide (FeOOH) and graphene oxide (GO) to fabricate an innovative silver-nanoparticle-decorated iron-oxyhydroxide-graphene oxide (Ag@FeOOH-GO) nanozyme. The synthesized nanozyme (Ag@FeOOH-GO) demonstrates exceptional oxidase-mimetic catalytic activity in the oxidation of the chromogenic 3,3′,5,5′-tetramethylbenzidine (TMB) substrate to produce a blue-colored oxidized TMB product (ox-TMB) without the need for additional oxidizing agents. Notably, in the presence of Hg2+, the Ag@FeOOH-GO nanozyme enhances the oxidation process of TMB, turning the blue color of ox-TMB into a deep blue color. This phenomenon is used to develop a colorimetric detection method for Hg(II) ions with a limit of detection (LOD) of 5.4 μM within the linear range of 5–30 μM. This study offers a promising solution for valorizing coal waste as a nanozyme for rapidly detecting Hg2+.