Heterogeneous activation of oxone with CoMg/SBA-15 for the degradation of dye Rhodamine B in aqueous solution

A novel heterogeneous Co catalyst CoMg/SBA-15 was prepared through a two-step incipient wetness impregnation of Mg and Co into mesoporous silica SBA-15 and used for the activation of oxone to generate sulphate radicals for degrading Rhodamine B (RhB) in aqueous solution. The CoMg/SBA-15 was characterized by several techniques such as XRD, N2 adsorption–desorption, CO2-TPD, TEM and SEM. It was found that the CoMg/SBA-15 existed as agglomerates with the particle size more than 0.3 μm, and Co and Mg occurred mainly both inside and outside the support pores in the form of cubic spinel Co3O4 and Mg oxide crystallites, respectively. Loading Mg into the support increased the dispersion of Co3O4 on the support and generated the remarkable basicity of the catalyst surface promoting the formation of surface Co–OH complex. The CoMg/SBA-15 still displayed the long-range ordered arrangement of the channels in structure with the reduced pore diameter and surface area compared with the SBA-15. The Co/SBA-15–oxone–RhB system, as a test control, was demonstrated to be efficient for the activation of oxone producing sulphate radicals for the degradation of RhB in solution. And the increase of Co/SBA-15 and oxone dosages had the positive effect on the degradation efficiency and rate, with the almost complete RhB degradation in 60 min and the Co leaching concentration less than 43 μg/L and the leaching percent less than 0.40% at appropriate Co/SBA-15 and oxone dosages. In addition, the degradation followed the first-order kinetics. The CoMg/SBA-15 exhibited much higher activity than Co/SBA-15 and Co/MgO with the same Co loading in degrading RhB by sulphate radicals from oxone, with nearly 100% degradation in 5 min, the Co leaching concentration of 80 μg/L and the leaching percent of 0.96%, and almost 100% TOC removal under appropriate conditions achieved. The CoMg/SBA-15 also displayed stable performance during 25 runs of reuse. Based on the UV–vis spectra and TOC measurement, the degradation mechanism of RhB in the presence of CoMg/SBA-15 and oxone was proposed. It is believed that CoMg/SBA-15 can be widely applied in the catalytic oxidation with oxone for the degradation of the refractory organic pollutants such as dye RhB in water.

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► Co/SBA-15 was effective for the activation of oxone to generate sulphate radicals for degradation of the refractory Rhodamine B.
► Recyclable CoMg/SBA-15 showed much higher catalytic activity and acceptable Co leaching compared with Co/SBA-15 and Co/MgO.
► The first-order kinetics was established in heterogeneous cobalt catalyst–oxone–Rhodamine B system.