Improved activity of SnO for the photocatalytic oxygen evolution

SnO prepared by soft chemistry exhibits a black color and semiconducting properties. The X-ray diffraction indicates a tetragonal symmetry (SG: P4/nmm) with nano crystallites of an average size of 85 nm. The forbidden band, determined from the diffuse reflectance is found to be 1.46 eV. The electrical conductivity occurs by polaron hopping and follows an Arrhenius type law with activation energy of 0.21 eV, the change in the slope at 526 K is attributed to the oxidation to SnO2. The photo-electrochemical study shows n type conduction with a flat band potential of −0.45 V, close to the photocurrent onset potential (−0.40 V). The electrochemical impedance spectroscopy shows the bulk contribution of SnO (Rb = 1.7 kΩ cm2) and decreases down to 1.89 kΩ cm2 under illumination. The photocatalytic properties have been evaluated for the first time for to the oxygen evolution. The valence band, deriving from Sn2+: 5p orbital with a potential (−0.80 VSCE/5.55 eV), is suitably positioned with respect to O2/H2O level (∼0.6 VSCE), leading to water oxidation under visible light. The best performance occurs at pH ∼ 7 with an oxygen liberation rate of 23 µmol mL h−1 (mg catalyst)−1 and a quantum efficiency of 1.2%. An improvement of ∼13% is observed on the system SnO/clay.