Amine-Rich Porous MOF Nanocrystals for the Selective Capture of Carcinogenic Anions and Organo-Pollutants from the Waste Water Environment at Neutral pH
Srijan Mukherjee, Subhrajyoti Ghosh, Shyam Biswas
Abstract
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 CrO 4 2–, Cr 2 O 7 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 CrO 4 2–, Cr 2 O 7 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.