Exploration of octahedrally shaped MnCo2O4 catalyst particles for visible light driven photocatalytic water splitting reaction

Abstract

MnCo₂O₄ catalyst with a smooth octahedral geometry and a band gap of 2.11 eV was developed for a visible light driven photocatalytic water splitting process considering the crucial role of Co(III)OH centres in Co₃O₄ catalysts, as well as cobalt(II) oxide and Mn³⁺ centres in the most active Mn₂O₃ catalyst towards photocatalytic water splitting process. The formation of the MnCo₂O₄ catalyst was confirmed by XRD, EDAX and XPS. The smooth octahedral geometry of most of the crystals synthesized was visualized via FE-SEM analysis. The photocatalytic efficiency of the catalyst was analyzed with respect to time, presence of sacrificial agent (methanol) and in presence of direct sunlight. 0.08 g of the catalyst produced about 33 mL of gaseous products from 20 mL of water after 95 minutes of visible light irradiation (λ > 420 nm). The overall water splitting efficiency was increased in the presence of a small amount of methanol; hydrogen GC spectra revealed that evolved hydrogen gas produced in the presence of methanol was extra pure. The reusability analysis revealed that the synthesized catalyst could be reused after the activation process possibly due to the surface restructuring of the active centres of the catalyst during the continuous water splitting process. There was a slight decrease in the activity of the reused catalyst due to the decrease in concentration of the octahedrally shaped crystals, as evidenced by the FE-SEM analysis. These results revealed that the developed octahedrally shaped MnCo₂O₄ catalyst will be an essential part for the future generation of visible light driven water splitting catalysts.