Kinetics and adsorptive study of organic dye removal using water-stable nanoscale metal organic frameworks

Abstract

Kinetics and isotherms of adsorption behavior of nanoscale Zr-based metal-organic framework for the removal of three organic dyes including acidic, direct and basic ones from aqueous solutions were studied by sorption models. Nanocube-shaped UiO-66 particles with an average edge length of 215 nm, specific surface area of 1215 m2/g, total pore volume of 0.58 cm3/g, and average pore diameter of 1.8 nm were prepared by solvothermal methods. Analyzing of the equilibrium isotherms indicates that direct dye removal is best fitted with the Langmuir isotherm. Study of the adsorption kinetics also determines that direct dye adsorption follows pseudo-first-order model (R2=0.99). The kinetics of basic and acidic dyes are proceeded by intra-particle diffusion and pseudo-second-order models, respectively. The sorption capacity of the nanoscale particles is reduced from 42 to 18.8 mg/g by increasing its concentration form 10–20 mg, owing to aggregation and overlying of their active sites. Under optimum removal condition determined by the response surface methodology (pH = 5, contact time of 40 min, adsorbent amount of 10 mg, and initial dye concentration of 40 ppm), the sorption half-time of adsorption is about 5 min which is much quicker than values reported in literature. Through comparison with the published results, the condition for achieving rapid and highly effective organic dye removal from aqueous solutions is demonstrated.