Adsorption separation in-situ synthesis of MIL-101(Cr)/AC composite and its cycling adsorption for Cr(VI) from aqueous solution

Cr(III) was adsorbed and separated by activated carbon (AC) from aqueous solution in order to recycle and reuse it, then MIL-101(Cr)/AC composite was in-situ synthesized by hydrothermal method based on AC adsorbed Cr(III). The structure and morphology of AC, MIL-101(Cr) and MIL-101(Cr)/AC composite were investigated by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller and zeta potential. The factors of time, temperature, pH and adsorbent dosage on Cr(VI) adsorption capacity and the reusability of the materials were studied. The results indicated that the specific surface area of AC, MIL-101(Cr) and MIL-101(Cr)/AC was 950.9, 1,687.1 and 655.9 m2 center dot g-1, respectively. The adsorption capacity of MIL-101(Cr)/AC for Cr(VI) was 47.00 mg center dot g-1, which was higher than that of AC (45.22 mg center dot g-1) but less than that of MIL-101(Cr) (50.5 mg center dot g-1). The adsorption of Cr(VI) on MIL101(Cr)/AC is a spontaneous exothermic process and best fitted with the second-order kinetic model and Langmuir isotherm model. The composite of MIL-101(Cr)/AC, is a green adsorbent and shows good reusability for Cr(VI) removal from water.