Synthesis of Metal-Organic Framework ZnOx-MOF@MnO2 Composites for Selective Removal of Strontium Ions from Aqueous Solutions

A Zn(II)-based metal-organic framework (MOF) compound and MnO2 were used to prepare ZnOx-MOF@MnO2 composites for selective Sr2+ removal in aqueous solutions. The ZnOx-MOF@MnO2 composites were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and Brunauer-Emmett-Teller surface area analysis. The functional groups, morphologies, thermal stabilities, and specific surface areas of the composites were suitable for Sr2+ adsorption. A maximum adsorption capacity of 147.094 mg g(-1) was observed in batch adsorption experiments, and the sorption isotherms were fit well by the Freundlich model of multilayer adsorption. Adsorption reached equilibrium rapidly in kinetic experiments and followed the pseudo-secondorder kinetic model. The adsorption capacity of the ZnOx-MOF@MnO2 composite with the highest MnO2 content was high over a wide pH range, and the composite was highly selective toward Sr2+ in solutions containing coexisting competing ions. Also, it has a good reusability for removing Sr2+.