Enhancement of adsorption performance for I2 and Cr(VI) by the metal-organic framework UiO-66-NH2 via post-synthetic modification

Abstract

Excessive emissions of radioactive I2 and toxic Cr(VI) have been a significant threat to the environment and human health. Thus, the adsorption of I2 and Cr(VI) has attracted great attention. Here a new functionalized UiO-66-NH2 MOF with pyrazole and amide groups were fabricated through postsynthetic modification (PSM) (denoted as UiO-66-AMmpz) and used to study the adsorption of gaseous I2 and aqueous phase Cr(VI). UiO-66-AMmpz exhibited good adsorption capacities of 1.21 g·g−1 for I2 at 75 °C and 291.2 mg·g−1 for Cr(VI) at pH 2, which significantly surpasses the pristine UiO-66-NH2. By analyzing the IR, XPS, EPR, Raman spectra of UiO-66-AMmpz before and after I2 adsorption, it was deduced that the good adsorption performance was attributed to the strong interactions between the adsorbed I2 and abundant N and O sites in the surface and pores of UiO-66-AMmpz, which mainly came from post-introduced the pyrazole and amide groups. In addition, the Cr(VI) adsorption process followed the pseudo-second-order kinetics and its adsorption data also fit well the Langmuir model. Simultaneously, the thermodynamic parameters suggested that the Cr(VI) adsorption process is spontaneous and endothermic process. Moreover, XPS and IR analysis revealed that the adsorbed Cr(VI) was partially reduced to Cr(III) and then fixed on UiO-66-AMmpz. This work can aid us to appreciate the surface interaction between I2 and Cr(VI) and the framework of MOFs and provide a promising MOF material to adsorb gaseous I2 and remove Cr(VI) from water.