Ultra-High-Capacity Adsorption of Rhodamine B in a Carboxyl-Functionalized Metal–Organic Framework via Surface Adsorption

The adsorption of rhodamine B (RhB) from aqueous solution on a functionalized metal–organic framework UiO-66-(COOH)2 was studied systematically in view of the adsorption isotherm, kinetics, thermodynamics, effect of pH and co-existing salts, and regeneration of the material. The adsorption behavior of RhB on UiO-66-(COOH)2 followed the Langmuir isotherm model and pseudo-second-order model. The thermodynamics study indicates that the adsorption of RhB is mainly controlled by the entropy effect rather than the enthalpy change. The strong electrostatic interaction as well as H-bond interaction contributes to the capture of RhB on the nanoscale UiO-66-(COOH)2 via the surface adsorption manner. UiO-66-(COOH)2 exhibited an ultra-high adsorption capacity of 2200 mg g–1 and excellent continuous removal ability. The high adsorption capacity, strong anti-interference ability, and easy regeneration make UiO-66-(COOH)2 as an ideal adsorbent for RhB removal from aqueous solution.