Adsorption studies of tetracycline hydrochloride and diclofenac sodium on NH-MIL-53(Al/Zr) sodium alginate gel spheres.

Metal-organic frameworks are emerging inorganic-organic hybrid materials that can be self-assembled from metal ions and organic ligands via coordination bonds. These materials possess large specific surface area, tunable pore structure, abundant active center, diversity of functional groups as well as high mechanical and thermal stability which promote their applications in adsorption and catalysis studies. In this study, NH-MIL-53(Al/Zr) was prepared and embedded into sodium alginate gel spheres (NH-MIL-53(Al/Zr)-SA) and its adsorption properties towards TC and DCF in solution were investigated. According to XRD and FTIR analysis, the structure of the raw material was not changed after making the gel spheres. The maximum adsorption towards TC (pH =3) and DCF (pH =5) reached 98.5 mg·g and 192 mg·g, respectively. The process was consistent with Langmuir and Freundlich, suggesting that there was both monolayer and multilayer adsorption which infers the presence of physical adsorption (intra-particle diffusion) and non-homogeneous chemical adsorption. The thermodynamic parameters showed that the adsorption process was a spontaneous entropy increasing reaction. The regeneration rate of spent NH-MIL-53(Al/Zr)-SA could still reach 99.1 % after three cycles, indicating good regeneration performance. This study can provide a basis for the application of NH-MIL-53(Al/Zr)-SA in wastewater treatment.