Comparison study on the adsorption performance of methylene blue and congo red on Cu-BTC

Cu-BTC, one of the metal-organic frameworks (MOFs), has been applied to remove the cationic dye methylene blue (MB) and anionic dye methyl orange (CR) from contaminated water. Liquid phase adsorption experiments were conducted and the maximum adsorptive capacity was determined. Various conditions were evaluated, including initial dye concentration, contact time, solution pH, and temperature. The Langmuir and Freundlich adsorption models were used to describe the equilibrium isotherm and isotherm constant calculation. It was found that the Cu-BTC adsorption capacities of MB and CR are much higher than those of the other types of MOFs and adsorbents. Maximum equilibrium adsorption capacities of 143.27 and 877.19mg/g for MB and CR were achieved. Three simplified kinetic models including pseudo-first-order, pseudo-second-order, and intra-particle diffusion equations were used to investigate the adsorption process. The pseudo-second-order equation was followed for adsorption of MB and CR on Cu-BTC. Temperature-dependent adsorption behaviors of MB and CR show that the adsorption is a spontaneous and endothermic process accompanying an entropy increase. This work indicates that Cu-BTC could be employed as an effective adsorbent in the removal of the textile dyes from effluents.