Redox-Active Metal–Organic Framework Nanocrystals for the Simultaneous Adsorption, Detection, and Detoxification of Heavy Metal Cations

The widespread contamination of water by heavy metals requires materials capable of efficient capture, in situ detoxification, and real-time monitoring. This work examines a series of redox-active metal-organic frameworks (MOFs) constructed from hexahydroxytriphenylene (HHTP) ligands coordinated to cobalt, nickel, and copper (Co-HHTP, Ni-HHTP, and Cu-HHTP), revealing how framework architecture and metal coordination environment dictate adsorption capacity, redox activity, and detection performance toward cadmium (Cd²⁺), mercury (Hg²⁺), and lead (Pb²⁺) ions. Among the series, Co-HHTP exhibits the highest uptake capacities of 169, 733, and 554 mg g^-1 for Cd²⁺, Hg²⁺, and Pb²⁺, respectively, attributed to its trigonal stacking and intercalated layers that expose labile water-capped metal sites. These sites facilitate electron transfer, enabling a redox-active capture pathway in which heavy metal cations are partially reduced, with concurrent oxidation of the HHTP ligand. In contrast, Cu-HHTP, with an eclipsed stacking arrangement and limited redox complementarity to the heavy metal ions examined, remains redox-inert and exhibits the lowest performance. Deposition of Co-HHTP onto cotton, silk, and polyester yields MOF@textile composites that retain adsorption efficiency and enable rapid detection of heavy metals at low-ppm concentrations. These findings establish a structure-function correlation, emphasizing how stacking configuration, metal accessibility, and redox-active ligands collectively govern multimechanistic heavy metal remediation.