Zirconium based metal-organic framework as highly efficient and acid-stable adsorbent for the rapid removal of Sr2+ and Cs+ from solution

Abstract

Herein we present acid stable [Zr6(µ3-O)4(µ3-OH)4(OBA)4(OH)3(H2O)3(Me2NH2)]n (OBA = 4,4-oxy bis(benzoic acid)) (Zr(OBA) MOF) with the presence of cationic dimethyl ammonium groups were charge balanced with anionic Zr(OBA)nn– that is effective for removing Sr2+ and Cs+. This MOF shows distribution coefficients and record-high absorption capacities (Qm) of 353 mg/g for Sr2+ and 432.91 mg/g for Cs+ at pH 4, 112.75 mg/g for Sr2+ and 141.24 mg/g for Cs+ under 4 M HNO3 circumstances, and 221.5 mg/g for Sr2+ and 253.77 mg/g for Cs+ from simulated seawater. It was demonstrated that a significant excess of complex cations had no substantial influence on the removal of Sr2+ and Cs+ from simulated seawater and nuclear waste, which have been included with Sr2+ and Cs+. The Langmuir isotherm was well suited for Sr2+ and Cs+ adsorption onto MOF, confirming the existence of monolayer adsorption. This finding was made possible by investigating the Langmuir, Freundlich, and Temkin adsorption isotherms. The results of the experiments agree very well with pseudo-second-order kinetic studies, which leads one to believe that chemisorption is the primary mechanism. The measurement of zeta potential has indicated an electrostatic connection between the negatively charged surface of the MOF and positively charged Sr2+/Cs+ at various pH values. This interaction demonstrates that the adsorption capacity is relatively high. SEM-EDS elemental mapping, IR, and XPS analysis confirm the presence of Sr2+ and Cs+ on MOF - of Zr(OBA)@Sr and Zr(OBA)@Cs MOF after adsorption studies. Sr2+/Cs+ exchanged MOF were improved in order to get a clear image of the ion exchange process, and the binding energies of −87.31 for Zr(OBA)@Sr and −113.75 kJ/mol for Zr(OBA)@Cs, respectively. The dose, initial concentration of metal ions, pH solution, contact time, and other ions of Na+, K+, Ca2+, and Mg2+ that were already present affected the adsorption of Sr2+ and Cs+. Recycle studies of Zr(OBA) MOF show 80 % recovery of Sr2+ and Cs+ even after eight cycles.