Adsorption interaction between a metal–organic framework of chromium–benzenedicarboxylates and uranine in aqueous solution

Metal-organic frameworks as novel functional materials, have enjoyed extensive exploration, with applications ranging from gas storage to sensing to adsorbents. Here, the adsorption interaction between a metal-organic framework of chromium-benzenedicarboxylates (MIL-101) and uranine in aqueous solution was studied. The influences of various factors on their adsorption interaction were discussed in view of pH value, contact time and initial concentration of uranine, and then the adsorption kinetics and isotherms were investigated. It was found that the adsorption kinetics obeyed the pseudo-second-order kinetic model and the adsorption isotherms followed the Langmuir model. In addition, the zeta potential of MIL-101 decreased obviously after adsorbing uranine and the adsorption capacity of MIL-101 was greater than that of the zeolitic imidazolate framework of Zn(MeIM)2 [MeIM = imidazolate-2-methyl] (ZIF-8), showing the importance of the electrostatic interactions between MIL-101 and uranine as well as the importance of the large pore aperture of MIL-101 for the adsorption interaction, respectively. The results of the adsorption thermodynamics and related parameters including free energy, enthalpy and entropy changes revealed that the adsorption of uranine on MIL-101 was a spontaneous and endothermic process.