Amine-Rich Porous MOF Nanocrystals for the Selective Capture of Carcinogenic Anions and Organo-Pollutants from the Waste Water Environment at Neutral pH.

The escalating concentration of hazardous Cr-(VI) and pharmaceutical waste in water bodies underscores the imperative need to advance sustainable, cost-effective, and recyclable technologies to eliminate these pollutants from wastewater, thereby ensuring the safety and purity of drinking water supply. We have constructed an amine-rich, highly robust, reusable, porous three-dimensional nanosized (15–35 nm) Zr-(IV) metal–organic framework (1′) for selective and eco-friendly removal of lethal Cr-(VI) oxo-anions and pharmaceutical waste (i.e., ibuprofen) from the aqueous medium at neutral pH (pH 7). 1′ exhibits a highly positive charged surface, entraps toxic anionic Cr-(VI) oxo-anion pollutants over its surface in a reversible manner, and converts them into less toxic Cr-(III) species, within less than 30 s. The equilibrium adsorption capacities (q_e) of 1′ for CrO₄^2–, Cr₂O₇^2–, and ibuprofen were 223.4, 146.6, and 323.3 mg/g (according to Langmuir fitting), respectively, which are among the highest sorption capacities achieved by MOF adsorbents. With faster adsorption kinetics, 1′ showed a negligible effect in adsorption performance even in the coexistence of 50 times excess concentration of other possible anionic species. Further, the potential removal of CrO₄^2–, Cr₂O₇^2–, and ibuprofen from complicated environmental water samples was executed by 1′ with negligible change in efficiency. Furthermore, an ion exchange silica-based reusable column was constructed with a 1% loading of 1′ for efficient and rapid removal of oxo-anions on a larger scale. The ion exchange column efficiently removes Cr-(VI) oxo-anions and enables us to lower the concentration of Cr-(VI) in drinking water to levels below the prescribed threshold (100 ppb, as per US-EPA recommendation). In addition, the probable mechanisms behind the adsorption-based removal of Cr-(VI) oxo-anions and the organic pollutant ibuprofen by cationic 1′ were systematically inspected through various instrumental techniques. [ABSTRACT FROM AUTHOR]