Highly efficient K_0.4Na_3.6Co(MoO₄)₃ new alluaudite type structure for photocatalytic degradation of methylene blue and green diamine B dyes

A novel alluaudite framework K_0.4Na_3.6Co(MoO₄)₃ photocatalyst has been synthesized by a solid-state reaction for degradation of both methylene blue (MB) and green diamine B (GDB) organic pollutants under sunlight. The sample was characterized using X-ray diffraction (XRD), transmission electron microscope, infrared spectroscopy and Raman spectroscopy, as well as by means of photoluminescence probing, impedance spectroscopy and UV–vis–NIR spectrophotometry. The XRD analysis reveals that such alluaudite type structure crystallizes in the monoclinic system with space group C2/c. Emissions of this material have been observed in a visible region at 290 nm excitation with a broad long-wave luminescence band from oxygen vacancies. UV–vis absorption spectrum measurements showed an efficient optical absorption in UV–vis region with a direct band gap of 3.37 eV. The complex impedance spectra suggested that the ac conductivity is a power law (Aω^s) derived by the correlated barrier hopping conduction mechanism. The efficiency of the dyes removal in the presence of K_0.4Na_3.6Co(MoO₄)₃ particles reaches 83% for MB and 53% for GDB under sunlight irradiation. The current studies establish interesting possibilities for investigating catalytic cycles of these solar light activated photocatalysts.