Rice husk-derived cobalt silica as effective peroxymonosulfate activator for degradation of organic pollutants

Abstract

In this study, mesoporous silica was synthesized from rice husks, and subsequently used to prepare a cobalt silica (Co/SiO2) catalyst via a simple sol–gel approach. The synthesized Co/SiO2 catalyst was thoroughly characterized. The analysis of the scanning electron microscopy (SEM) images revealed silica particles with sizes of nearly 20 nm. Energy-dispersive X-ray analysis showed a good Co dispersion on the catalyst surface with a Co content of 7.7 %. The Co/SiO2 catalyst was then utilized as a peroxymonosulfate (PMS) activator to degrade reactive black 5 (RB5). Furthermore, the impact of various parameters on RB5 degradation was analyzed. The Co/SiO2 catalyst demonstrated excellent performance and completely degraded RB5 within 8 min with a rate constant of 5.5 × 10−1 min−1 at an extremely low dosage of 0.05 g/L. Furthermore, the degradation rate increased with temperature, and the activation energy was 51.5 kJ/mol. The analysis of the quenching and electron paramagnetic resonance experiments showed that SO4• −, HO•, 1O2, and O2• − were produced, with 1O2 being the predominant reactive species. Notably, the catalyst remained effective when tested in actual water environments and could degrade various other dyes and tetracycline. To facilitate catalyst recovery through filtration, Co/SiO2 was embedded in crosslinked chitosan beads. The bead catalyst demonstrated comparable performance to pristine Co/SiO2 and could be reused for five cycles.