Enhanced adsorption of dyes by functionalized UiO-66 nanoparticles: Adsorption properties and mechanisms

UiO-66-based metal-organic framework (MOF) materials are a class of porous crystalline materials consisting of Zr metal clusters compounded with organic ligands of terephthalic acid group. In this study, functionalized UiO-66-X (X=H, NH2, (COOH)2) nanoparticles were synthesized. The morphology of UiO-66-X nanoparticles were characterized by SEM, while the crystal structure was analyzed using XRD and TGA. Chemical composition of UiO-66-X nanoparticles were analyzed through TFIR and XPS. The adsorption capacities of UiO-66-X nanoparticles for anionic dye of Congo red (CR), and cationic dyes of methylene blue (MB) and rhodamine B (Rh B) dyes were evaluated. Furthermore, the adsorption mechanisms of UiO-66-X nanoparticles for dyes were analyzed and summarized. Results showed that the adsorption capacities of UiO-66 and UiO-66-NH2 on CR were 93.05 mg/g and 94.20 mg/g, respectively. In particular, the adsorption capacities of UiO-66-(COOH)2 on MB and Rh B were significantly increased with the adsorption capacities of 80.66 mg/g and 72.64 mg/g, respectively. Due to the strong π-π effect and hydrogen bonding interactions between UiO-66 and CR dyes. UiO-66-NH2 has stronger hydrophilicity and has electrostatic interactions, Lewis acid-base interactions and hydrogen bonds with CR. The abundant -COOH groups and higher negative Zeta potential (-23.43 mV) in UiO-66-(COOH)2 led to strong electrostatic interactions and Lewis acid-base interactions with the cationic dyes MB and Rh B. Therefore, the adsorption performance of UiO-66-(COOH)2 on cationic dyes was improved.