High efficiency reductive degradation of a wide range of azo dyes by SiO2-Co core-shell nanoparticles

Spherical silica-cobalt (SiO2-Co) core-shell nanoparticles were successfully fabricated for the degradation of a wide range of azo dyes. By introducing (3-Aminopropyl) triethoxysilane (APTES) to SiO2 nanoparticle surface, which served as an amine-functional ligating agent for Cobalt (Co) reduction from Co2+ ions by using sodium borohydride (NaBH4), size-controllable SiO2-Co core-shell nanoparticles were synthesized. These core-shell nanoparticles were found to be highly efficient as catalysts for the degradation of a wide range of. synthetic azo dyes. Methyl Orange, an example of a toxic synthetic azo dye, could be reductively degraded in aqueous solution within one minute by using 50 mg of SiO2-Co core-shell nanoparticles at a dye concentration of 0.076 mM at pH 2.5. Kinetic studies revealed Methyl Orange degradation by SiO2-Co core-shell nanoparticles to be first-order in reaction rate. The highest degradation rate constant k was 69.50 min(-1) for optimized core-shell nanostructure under the above conditions. Other azo dyes, such as Orange G, Amaranth and Congo Red, processing increased complexity and more "-N=N-" double bonds, could also be reductively degraded in acidic aqueous solution by using the SiO2-Co core-shell nanoparticles, at high reaction rates. Congo Red, due to having two "-N=N-" bonds, would need more core-shell nanoparticles in order to achieve the same amount of degradation. These SiO2-Co core-shell nanoparticles could well play an important role as a fast treatment option, when applied to Wastewater treatment. (C) 2016 Elsevier B.V. All rights reserved.