Synthesis and immobilization of MnO₂ nanoparticles on bio-silica for the efficient degradation of an azo dye in the aqueous solution

In this study, MnO₂ nanoparticles were synthesized on bio-silica by a simple one-step procedure using permanganate in the acidic medium. The synthesized catalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The obtained results confirmed the nanostructure of MnO₂ and its stabilization on the bio-silica as the support. The removal efficiency of acid orange 7 (AO7), using bare bio-silica and MnO₂ coated bio-silica, was found to be 5 and 95%, respectively. The effect of operational parameters including AO7 concentration, catalyst dosage and process time of treatment process was also studied on the basis of efficiency. The results demonstrated that the color removal efficiency was decreased by increasing AO7 concentration, and increased by the enhancement of the process time. The optimal dosage of 0.8 g/L was chosen for the catalyst amount. Hydroxyl radicals played a significant role in the process based on the proposed mechanism. The spectral changes of AO7 during the process in UV-Vis region showed not only the efficient decolorization, but also the degradation of the dye after 50 min of the treatment.