Efficient removal of dyes from water by zirconium-based metal-organic cages with varying functional groups

The adsorption of organic dyes from wastewater is an efficient approach to reduce dye pollution for water resources and land. Herein, a series of zirconium-based metal-organic cages (Zr-MOCs) with different functional groups, ZrT-1, ZrT-1-Br, ZrT-1-NH2 and ZrT-1-OH, were synthesized by solvothermal that can be applied to remove methyl orange (MO) and rhodamine B (RhB). The adsorption kinetics of Zr-MOCs was fitted well by pseudo-second-order. ZrT-1 exhibits the most excellent adsorption ability for MO and RhB compared with the other Zr-MOCs due to the highest pore volume. Interestingly, Zr-MOCs can remove both anionic dye (MO) and cationic dye (RhB) due to the synergistic interplay between pore volume, electrostatic interaction, π-π interaction and hydrogen bonding. The adsorption behaviors of MO and RhB on ZrT-1 are suitable to the Langmuir model that belong to the monolayer adsorption. The maximum adsorption capacities for MO and RhB towards ZrT-1 are 190 mg/g and 227 mg/g at 25 °C, pH=7 and the initial dye concentration of 80 mg/L, respectively.