A robust ditopic enaminone- and hydrazone-linked amine-functionalized porous organic cage for effective permanganate capture and conversion

Abstract

Potassium permanganate (KMnO₄) is widely employed as an oxidizing agent for water purification and pollutant removal. However, the residual MnO₄⁻ in water presents substantial health risks, and thus the efficient removal of aqueous MnO₄⁻ has emerged as a major research focus. Herein, we present a novel amine-containing triangular prism-shaped [3 + 6] porous organic cage (POC) adsorbent, named DPOC-1. It is assembled from three tetraformyl-functionalized calix[4]resorcinarenes and six heteroditopic 3,4-diaminobenzhydrazide organic synthons through Schiff-base chemistry. SCXRD analysis reveals that DPOC-1 contains a large cavity volume of up to ∼1500 ų, two large guest-accessible windows with a maximum diameter of 0.75 nm, as well as abundant nitrogen and oxygen chelating sites surrounded by its windows. Leveraging these advantageous features, combined with its specific surface area of up to approximately 700 m² g⁻¹, DPOC-1 demonstrates exceptional efficiency in capturing aqueous MnO₄⁻. It achieves a removal rate exceeding 99% within 3 minutes and shows excellent recyclability through a dual adsorption–reduction mechanism. Specifically, the material maintains nearly 90% adsorption efficiency even after 10 consecutive cycles, and a portion of the absorbed MnO₄⁻ is subsequently converted into value-added Mn₂O₃. This study offers a novel strategic approach for utilizing POC adsorbents in the remediation of heavy metal oxyanion pollution, simultaneously enabling resource recovery.