Adsorption of Pd(II) onto Zr(IV) Based Metal-Organic Framework UIO-66-NH<sub>2</sub> from Hydrochloric Acid Solution

Abstract

Metal-organic frameworks are used in many applications, such as gas separation, catalysis, and the synthesis of nanomaterials. Metal-organic frameworks show superior stability at high temperature, which makes them potentially useful for the adsorption of metal ions from leaching solutions at high temperature. In this work, UIO-66-NH2, a zirconium(IV) based metal-organic framework, was employed for the adsorption of Pd(II) from hydrochloric acid solutions. The adsorption percentage of Pd(II) decreased rapidly as HCl concentration increased from 0.2 M to 1 M and was negligible beyond 3 M. It was found that some of the UIO-66-NH2 was disrupted in the strong HCl solution and released Zr(IV) into the solution. The effect of chloride ion concentration on the adsorption of Pd(II) was investigated. The adsorption percentage of Pd(II) by UIO-66-NH2 decreased rapidly as chloride ion concentration increased. The adsorption of Pd(II) onto UIO-66-NH2 followed the Langmuir isotherm and reached equilibrium within 2 hours under these experimental conditions. The kinetic data for the adsorption of Pd(II) onto UIO-66-NH2 agreed well with a pseudo-second order kinetic model. The initial rate constant at 0.2 M HCl was 15.2 mg/g·min and decreased to 2.7 mg/g·min at 1.0 M HCl. More work is necessary to improve the stability of UIO-66-NH2 in strong HCl solution and to make the metalorganic framework at lower cost. Key words: metal-organic framework, palladium(II), HCl, adsorption