Investigation of the physical properties of K₂Co₂(MoO₄)₃ for photocatalytic application

In this contribution, potassium cobalt(II) molybdate K₂Co₂(MoO₄)₃ was synthesized by a solid-state reaction process. The morphology, the microstructure and the optical properties of the prepared compound have been studied by means of scanning probe microscopy, X-ray diffraction (XRD), FTIR and Raman spectroscopy respectively. Also, this material was studied by photoluminescence and UV–Vis spectroscopy. XRD analysis revealed that K₂Co₂(MoO₄)₃ crystallizes in the monoclinic system with P2₁/c space group and lattice parameters: a = 7.038(8) Å, b = 8.987(9) Å, c = 20.573(3) Å, β = 112.19(3)°, V = 1204.9(7) Å³ and Z = 4. This structure can be described by the presence of tetramers linked with each other by MoO₄ tetrahedra giving a three-dimensional crystal structure containing channels in which K⁺ ions reside. Obtained Raman and IR lines were assigned to different normal vibration modes. The photoluminescence spectrum shows several peaks associated mainly with interstitials defects and oxygen vacancies due to a photoinduced charge carrier recombination. It is found that the rate of MB degradation is about 80% for xenon and UV (8 W) lights and it is of about 60% over sunlight during 2 h. This work suggests a good photocatalytic activity of K₂Co₂(MoO₄)₃, which may be of interest to develop a safe, cost-effective solar water treatment process.