Emerging Functional Porous Materials for Remediation of Oxo-Pollutants: Unlocking Two Decades of Achievements

In recent years water pollution is considered as the greatest hazard to life among all pollutions. In this regard, water contamination by hazardous heavy metal derived oxo-pollutants, such as CrO42–, Cr2O72–, AsO43–, SeO32–, SeO42–, TcO4–, ReO4–, etc., has been a rapidly expanding worldwide problem for human health and the environment because of their high toxicity after bioaccumulation. Accordingly, the US Environmental Protection Agency (EPA) has classified these oxo-anions as the priority pollutants and it is thus of utmost necessity to remove them from wastewater. Because of their advantages over traditional adsorbents in terms of tunable porosity, high surface area, and an abundance of functional groups, advanced functional porous materials (AFPMs) such as metal–organic frameworks (MOFs), porous organic polymers (POPs), covalent organic frameworks (COFs), and porous hybrid composites have attracted immense attention presently for wastewater treatment. This Review aims to explore the potential of AFPM systems for effectively capturing oxo-anions through the use of appropriate ionic characters and functional groups. In this Review, we provide a comprehensive overview on the most recent developments on the aforementioned porous sorbent materials that can provide a practical solution for wastewater treatment. We summarize various hazardous oxo-anions with respect to their structural variations, pH dependent structural changes, and also their detrimental consequences. We then emphasize the potentials of water stable cationic MOFs for selective removal of Cr(VI)-, Mn(VII)-, Tc(VI)-, Se(IV)-, Se(VI)-, U(VI)-, As(III)-, and As(V)-based oxo-pollutants in aqueous phase. This Review discusses target-specific design strategies for ionic porous organic polymers and hybrid functional materials to remediate toxic oxo-anions. It highlights how the structural design and fine-tuning of AFPMs enhance their ability to efficiently capture oxo-pollutants, particularly through ion-exchange processes. The Review concludes with a discussion on the challenges, opportunities, and future research directions, encouraging further exploration of oxo-pollutant selective AFPMs for improved environmental pollution management.