Sequestering Mercury in Cation Traps of Iron-Phosphate Framework via Isomorphous Substitution Minimizes Microbial Methylation

Abstract

A critical consideration for the design of mercury (Hg)-removal materials is preventing microbial methylation of accumulated Hg, a process that forms the highly neurotoxic and bioaccumulative methylmercury (MeHg) during material disposal or post in situ remediation. Inspired by how natural minerals incorporate Hg impurities within crystalline structures through isomorphous substitution, we design an iron-phosphate framework (NH₄)Fe₂(PO₄)₂(OH)·2H₂O (denoted as NFP) for highly effective Hg sequestration. With its large quantities of negatively charged oxygen-rich channels, NFP effectively attracts Hg and physically entraps the ions by forming Hg–O coordination bonds. Thus, NFP renders fast kinetics and high capacity for Hg adsorption, ensuring extremely low Hg release and minimal microbial methylation potential. Regulating crystal facets decreases the ion exchange energy between NFP and Hg²⁺, further enhancing the effectiveness of NFP. Notably, mimicking natural mineral formation not only endows NFP with high environmental compatibility and versatility. This bionic design offers a new strategy for tackling environmental pollution while avoiding generating secondary problems of even greater health concerns.