Selective removal of anionic ions from aqueous environment using iron-based metal-organic frameworks and their mechanistic investigations

Abstract

The increasing demand of superior adsorbents towards the elimination of anionic contaminants from the aqueous environment, in this work we have designed the iron-supported metal-organic framework (MOF) such as Fe-MIL-88B towards the remediation of nitrate and phosphate ions from the aqueous region. The effect of solution chemistry on the adsorption of above anions using Fe-MIL-88B was investigated. Chemical structure and morphology of the Fe-MIL-88B was effectively studied using various analytical techniques such as PXRD, FTIR, SEM with EDX, TGA-DTA, XPS and BET analysis. The experimental studies confirmed that Fe-MIL-88B was dominantly reducing the anionic concentration under optimized conditions. The competitive anions study showed that the as-synthesized adsorbent demonstrated significant adsorption efficiency and selectivity towards nitrate and phosphate ions, and the co-anions reveal negligible effects on nitrate and phosphate removal capacities and rate. The removal mechanism exhibited that both anionic ions were adsorbed mainly through complexation mechanism and electrostatic interaction. The anionic nature of both contaminants helps to enhance the adsorption by the synthesized MOF by effectively moving towards the adsorption spots available on Fe-MIL-88B. Additionally, the removal mechanism of nitrate and phosphate onto Fe-MIL-88B was examined using adsorption isotherm and kinetic parameters. Equilibrium analysis revealed that the maximum adsorption efficiency for nitrate and phosphate was 92.59 and 103.09 mg/g, respectively. Accordingly, spent adsorbent could be successfully regenerated using NaOH solution and showed constant adsorption-desorption performance. The results investigate in this present study highlight the feasibility of Fe-MIL-88B as a potential candidate for the elimination of both anions from wastewater.