Enhanced methylene blue adsorption using zirconate alginate/graphene oxide/UiO-67 aerogel spheres: Synthesis, characterization, kinetic studies, and adsorption mechanisms.

Zirconium alginate/graphene oxide (ZA/GO) hydrogel spheres were prepared by crosslinking sodium alginate and GO with Zr. Then Zr on the surface of the ZA/GO substrate acted as the metal nucleation site of the UiO-67 crystal and interacted with the organic ligand biphenyl 4-4'-dicarboxylic acid (BPDC) to make UiO-67 grow in situ on the surface of the ZA/GO hydrogel sphere by the hydrothermal method. The BET surface areas of ZA/GO, ZA/UiO-67, and ZA/GO/UiO-67 aerogel spheres were 1.29, 47.71, and 89.33 m/g respectively. The maximum adsorption capacities of ZA/GO, ZA/UiO-67, and ZA/GO/UiO-67 aerogel spheres for methylene blue (MB) at room temperature (298 K) were 145.08, 307.49, and 1105.23 mg/g respectively. The kinetic analysis showed that the adsorption process of MB on the ZA/GO/UiO-67 aerogel sphere was consistent with the pseudo-first-order kinetic model. Isotherm analysis showed that MB was adsorbed on ZA/GO/UiO-67 aerogel spheres as a single layer. Thermodynamic analysis showed that the adsorption process of MB on the ZA/GO/UiO-67 aerogel sphere was exothermic and spontaneous. Adsorption of MB on ZA/GO/UiO-67 aerogel spheres is mainly dependent on π-π bond, electrostatic interaction, and hydrogen bond. After 8 cycles, ZA/GO/UiO-67 aerogel spheres still showed high adsorption performance and good reuse ability.