Effect of light irradiation on heightened adsorption of dyes by hydrothermal carbon microspheres

Abstract

Monodisperse carbon microspheres (CMSs) with various diameters were prepared from glucose under controllable hydrothermal conditions at mild temperature. The as-synthesized CMSs were mainly characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and Raman spectrometer. Their adsorption capacity was evaluated by the measurements of relative concentrations of methyl orange (MO), Rhodamine B (RhB) and methylene blue (MB) in the solution under UV and/or visible light irradiation, respectively. By UV and/or visible light irradiation after the saturation of adsorption in the dark, a marked decrease in concentration of RhB and MB was observed, which recovered a heightened adsorption capacity of CMSs. With the decrease of dye concentration, the relative removal of dye increased. Moreover, the diameter of CMSs affected the irradiation-heightened adsorption, which the smaller ones improved the enhancement. The adsorption capacities of the studied CMSs for MB and RhB are estimated to be from 12.08 mg g−1 in the dark to 24.28 mg g−1 after irradiation and from 6.83 mg g−1 in the dark to 21.47 mg g−1 after irradiation, respectively. The adsorption kinetics obeys pseudo-first-order kinetics following the Freundlich isotherm. A possible mechanism for the irradiation-heightened adsorption property of CMSs was discussed.