Adsorptive removal of toluene from aqueous solution using metal–organic framework MIL-101(Cr): removal optimization by response surface methodology

Toluene is a typical volatile organic compound present in petroleum, gasoline and industrial wastewater which has harmful effects on human health. In this study, metal–organic framework MIL-101(Cr) was synthesized and used to remove toluene from aqueous solution. Synthesized MIL-101(Cr) was characterized using X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy and nitrogen adsorption–desorption techniques. We used experimental design methodology in order to develop a model for toluene removal and optimize the operational parameters. Effect of five operational parameters of temperature, contact time, adsorbent dosage, the initial concentration of toluene and pH was investigated on removal percentage. Toluene removal of 97% was achieved at the obtained optimum condition. The number of recycles that MIL-101(Cr) can be used without regeneration was investigated, and it was found that this adsorbent can be used for five successive recycles without regeneration or a significant decrease in removal percentage. According to the adsorption experiments, the adsorption of toluene on the MIL-101(Cr) was correlated well with the Freundlich isotherm model. The kinetics of the adsorption process was investigated and the result showed that kinetic data followed the pseudo-second-order model. Thermodynamic studies also showed that the adsorption process was spontaneous and endothermic.