A new compound Mn5P4O20H8 achieving efficient heavy metal removal to the ppb level through a dual chemisorption–ion exchange pathway

Abstract

Effective removal of heavy metal ions down to the mark of tolerance concentration (parts per billion level) from drinking water remains a great challenge. Metal oxide-related materials have emerged as promising candidates for next-gen high performance adsorbents owing to their flexibility in tuning the chemical composition and surface structure. Herein, we have successfully synthesized a new compound Mn₅P₄O₂₀H₈ through a facile one-pot solvothermal process, which has a lattice structure with a three-dimensional network crosslinked by [PO₄] tetrahedra and [MnO₆] octahedra. A synergistic pathway of surface hydroxyl group trapping and lattice ion-exchange endows the obtained Mn₅P₄O₂₀H₈ with superior removal efficiency (>99%) for Pb²⁺, Cr³⁺, and Fe³⁺ from relatively high concentration (∼5 parts per million, μg L⁻¹) to parts per billion levels (40, 1, and 1 parts per billion for Cr³⁺, Fe³⁺, and Pb²⁺, respectively), much lower than the WHO permitted level for drinking water. The maximum adsorption capacities for Pb²⁺, Cr³⁺, and Fe³⁺ are 1510, 201, and 300 mg g⁻¹, respectively. In addition, the as-prepared Mn₅P₄O₂₀H₈ adsorbent exhibits excellent reusability without significant degradation. These results make the Mn₅P₄O₂₀H₈ material a great adsorbent for the application in remediation of heavy metal polluted water. This work sheds light on extending the design of adsorbent nanomaterials for water treatment to a broader library of synthetic toolboxes and mechanistic ideas.