Efficient photo‐degradation of cationic dyes by Co₃O₄ and Sr‐Co₃O₄ spinel nanocomposites under solar light irradiation

In the present study Co3O4 and Sr-Co3O4 nanoparticles were prepared by sol-gel and co-precipitation methods and tested as photo-catalysts for the degradation of methylene blue (MB, model molecule of the thiazine dyes class) and malachite green (MG, model molecule of the triphenylmethane category)under solar light irradiation. To study the photocatalytic activity, Co3O4 was doped by three different weight percentages of strontium (5%, 10%, and 15%). Among these, 10 wt% Sr-Co3O4, named as (10)Sr-Co3O4, showed maximum photodegradation efficiency toward both MB and MG. Their structural and morphological characteristics, chemical composition, surface area, and optical properties were investigated by FT-IR spectroscopy, X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy – Energy Dispersive Spectroscopy (FE-SEM-EDX), UV–Vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) analysis. The XRD investigations of Co3O4 and (10)Sr-Co3O4 catalysts indicated retention of structure. The effect of initial pH, initial concentration of the dyes and photocatalysts dose was properly investigated. The results demonstrated the enhanced photocatalytic activity of (10)Sr-Co3O4 compared to that of pristine Co3O4 due to Sr doping that improves electron-hole (e–/h+) pairs separation mediated by charge migration on the Sr-Co3O4 structure. The as-prepared photocatalyst exhibited a remarkable photocatalytic efficiency towards both the dyes. (10)Sr-Co3O4 and Co3O4 degraded 96% and 88% of MB at pH = 11, and 92% and 85% of MG at pH = 9, respectively in 90 min. Moreover, it was demonstrated that the photodegradation of MB and MG by Sr-Co3O4 and Co3O4 followed a pseudo-first-order kinetics. Both the photocatalysts showed good stability during recycling maintaining high performances after five cycles. Finally, the active species were identified using various scavengers by trapping holes and radicals generated during the photocatalytic degradation process