Adsorption kinetics and mechanisms of carbohydrate/UiO-66 composites for cationic/anionic dye removal

Developing efficient strategies for the removal of organic dyes from aqueous systems remains crucial for environmental remediation. Metal-organic frameworks (MOFs), particularly UiO-66, show exceptional promise as adsorbents; however, they suffer from limited dye uptake capacity. This study addresses this limitation through strategic hybridization of UiO-66 with renewable carbohydrates (glucose and fructose), achieving enhanced performance while reducing costs. The optimized glucose/UiO-66 and fructose/UiO-66 composites demonstrated superior adsorption capacities compared to pristine UiO-66 across multiple dyes: methylene blue (76/69 mg/g), malachite green (73/67 mg/g), rhodamine B (50/59 mg/g), methyl orange (81/169 mg/g), and Congo red (99/198 mg/g). Adsorption efficiency correlated with dye molecular dimensions and the composite's phenolic hydroxyl content. Kinetic analysis revealed pseudo-second-order adsorption behavior dominated by chemisorption via electrostatic and π–π interactions. Notably, fructose-modified composites exhibited exceptional performance for anionic dyes (methyl orange and Congo red), suggesting charge-selective adsorption mechanisms. This work establishes carbohydrate-MOF hybridization as an effective strategy for designing multifunctional adsorbents, providing fundamental insights into structure-performance relationships for environmental applications.