Heavy Metal-Based\nToxic Oxo-Pollutants Sequestration\nby Advanced Functional Porous Materials for Safe Drinking Water

ConspectusWater scarcity as a consequence\nof either environmental or economic\nactions is the most compelling global concern of the 21st century,\nas ∼2 billion people (26% of the total population) struggle\nto access safe drinking water and ∼3.6 billion (46% of the\ntotal population) lack access to clean water sanitation. In this context,\ngroundwater pollution by toxic heavy metals and/or their oxo-pollutants,\nsuch as CrO<sub>4</sub><sup>2–</sup>, Cr<sub>2</sub>O<sub>7</sub><sup>2–</sup>, AsO<sub>4</sub><sup>3–</sup>, SeO<sub>3</sub><sup>2–</sup>, SeO<sub>4</sub><sup>2–</sup>,\nTcO<sub>4</sub><sup>–</sup>, UO<sub>2</sub><sup>2+</sup>, etc.,\nhave been becoming rapidly growing global concerns. The severe toxicity\nupon bioaccumulation of these oxo-anions has prompted the US Environment\nProtection Agency (EPA) to mark these persistent and hazardous substances\nas priority pollutants. Additionally, the heavy-metal-based pollutants\nare difficult to transform into eco-friendly substances, thus presenting\nserious challenges toward human health and environmental preservation.\nTo this end, the emergence of advanced functional porous materials\n(AFPMs), including metal–organic frameworks (MOFs), covalent\norganic frameworks (COFs), metal–organic polyhedrons (MOPs),\nporous organic polymers (POPs), etc., have presented extraordinary\nopportunities in material research and water treatment applications.\nThe liberty in designing and structural tunability of AFPMs, facilitated\nby utilization of structure-encoded molecular building blocks, enables\nprecise control over target-specificity and structure–property\ncorrelations. Bridging the gap between strategic material design and\non-demand real-world application can facilitate the development of\nnext-generation sorbents/ion-exchangers for efficient water treatment.In this Account, we summarize the recent advancements from our\ngroup toward the development of cutting-edge multifunctional ionic-porous\nsorbents, offering viable solutions toward providing clean and safe\ndrinking water. Our vision allows us to comprehend this challenge\nthrough two strategic factors: efficient oxo-anion capture via ion-exchange\nand specific host–guest interactions via installation of modular\nfunctional groups. To provide an overview, we first highlight the\ndifferent structural variants and coexistance of various toxic oxo-anions\ndepending on the pH of the medium and their adverse effects. Next,\nwe highlight the promising potential of water stable cationic MOFs\ntoward selective remediation of toxic Cr(VI), Mn(VII), Tc(VI), Se(IV),\nSe(VI), U (VI), As(III), and As(V)-based toxic oxo-pollutants from\nwater. In the subsequent sections, we summarize the target-specific\ndesign strategies and oxo-anion remediation performances of ionic\nporous organic polymers and hybrid functional porous materials. The\nkey role of target-specific designability and/or structural fine-tuning\nof AFPMs toward preferential sorption of oxo-pollutants is systematically\ndemonstrate. Particularly, the role of ion-exchange (anion-exchange)\nprocesses toward targeted oxo-pollutant capture by ionic AFPMs has\nbeen discussed in details. In several examples, the AFPMs were successful\nin reducing the toxic oxo-anion concentration levels lower than the\npermitted values for drinking water by the World Health Organizing\nCommittee (WHO), showcasing their real-world applicability potency.Our contemporaneous endeavors in exploring ionic AFPMs for selective\ntoxic oxo-anion sequestration may serve as a blueprint to researchers\nfor future development of the next generation sorbent materials for\nenergy-economically feasible water treatment methods.