Iodide ion photooxidation on the hetero-system WS2/TiO2 prepared by sol–gel

The photoelectrochemical characterization of the hetero-system x % WS2/TiO2 (x = 0, 10 and 20) is undertaken to assess its photoactivity for iodide ion oxidation. The nanosized catalyst is prepared by sol–gel at 450 °C; the X-ray diffraction shows broad peaks with a specific surface area of 110 m2 g−1. The gap of WS2 (1.72 eV), determined from the diffuse reflectance spectrum, is well matched to the solar spectrum. The flat band potential (−0.83 V SCE ) is more anodic than the I2/I− level (~0.3 V SCE ), thus leading to iodide photooxidation. The electrochemical impedance spectroscopy reveals both the charge transfer and Warburg diffusion. The oxidation is catalyzed by dissolved oxygen through the formation of H2O2 and is optimized with respect to the I− concentration (0.25 M) and catalyst dose (1 mg L−1). A conversion rate of 81 % is reported under solar light within 3 h illumination. Hence, the heterosystem is attractive for the chemical storage through the reaction: (\(2 {\text{ I}}^{ - } + {\text{O}}_{ 2} + 2 {\text{ H}}_{ 2} {\text{O}} \to {\text{I}}_{ 2} + {\text{H}}_{ 2} {\text{O}}_{ 2} + 2 {\text{ OH}}^{ - } ,\Delta {\text{G}}_{\text{R}}^{^\circ } = 3 5. 3 2 \;{\text{kcal}} \;{\text{mol}}^{ - 1}\)).