Physical characterizations of nano-particles α-MoO3: Eosin degradation under visible light

α-MoO₃ was identified by X-ray diffraction (XRD) and the pattern revealed a single phase in the orthorhombic system (SG: Pbnm). Three strong vibrations at 439, 806 and 977 cm⁻¹ in the FT-IR spectrum are associated to the elongation mode of Mo–O, Mo–O-Mo and Mo = O bonds. MoO₃ with a light blue color absorbs in the visible region with a gap (E_g) of 2.77 eV. It corresponds to the electrons transition from the valence band formed by (O₂: 2p) to the conduction band deriving from Mo⁶⁺:4d orbital. A further electronic transition of 1 eV, corresponds to the internal transfer of charges between Mo⁶⁺/Mo⁵⁺. The linearization of the Arrhenius equation: log σ as a function of 10³/T indicated a semiconductor behavior of MoO₃ with an activation energy of 0.036 eV. The variation of the thermoelectric power (S) of MoO₃, in the temperature range studied, indicated an n-type behavior with electrons as majority of carriers. The extrapolation of the fitted line to infinite capacity (C⁻² = 0) yielded a flat band potential (E_fb) of 0.29 V_SCE. The photoactivity of MoO₃ was studied by varying different parameters under visible light: the dose of MoO₃, the initial concentration of EOS, pH of working medium and light intensity. The optimal conditions: 0.7 mg/mL of MoO₃/E0S with intensity of 8.5 mW cm⁻² at pH ~ 4 allowed to obtain a photocatalytic oxidation efficiency of 53%.