From Waste to Catalyst: Cobalt-Functionalized Silica as a Photocatalyst for Water Purification

The repurposing of waste industrial materials for use in environmental remediation is of great interest in terms of the circular economy as well as public health and safety efforts. Herein, an innovative approach is presented to synthesize a cobalt-functionalized waste silica (Co-MS) utilizing a green, solvent-deficient method (SDM), using industrial waste micron-sized silica (MS) as a sustainable support material. The resulting Co-MS composite is evaluated as a photocatalyst for the removal of methylene blue (MB) under natural sunlight, offering an energy-efficient and environmentally friendly treatment method. Comprehensive characterization confirmed the formation of multiple-valence-state cobalt nanoparticlesCo, CoO, and Co₃O₄ on the waste silica support. The resulting optimal composite includes 9.1 wt % cobalt oxide species and shows a polyoxide nature with finely dispersed cobalt oxide nanoparticles that are less aggregated compared to bulk Co₃O₄ and show an improved photocatalytic performance under solar light. Incorporation of cobalt oxide species into MS also results in an S _BET increase from 43 m² g^-1 for bulk Co₃O₄ to 91 m² g^-1 for the Co-MS composite. The selected composite Co-MS thus achieves 87.5% MB removal efficiency within 1 h, demonstrating its potential as a low-cost, sustainable photocatalyst for wastewater treatment applications.