Electron competitive migration regulating for dual maxima of water photolysis

Electron competitive migration between the conduction band and charge trap centre is the key in governing the catalytic activity and the relevant applications of semiconductor nanomaterials, which is however poorly understood yet. Herein, we systematically studied the electron competitive migration in defective SnO2 nanoparticles through hybridizing with a polymer electron donor, graphitic carbon nitride (g-C3N4). When varying the mass ratio of defective SnO2 from 5% to 70%, an increase of surface-charge trapping centres (oxygen vacancies) in SnO2 effectively regulated the electron competitive migration. As a consequence, dual catalytic activity maxima were observed in hydrogen generation from water splitting under visible light irradiation (lambda > 420 nm). For instance, the relative mass ratios at 10% and 40% yielded maximum hydrogen generation rates of 54.3 mu mol h(-1) g(-1) and 44.3 mu mol h(-1) g(-1), respectively, far beyond that of 27.9 mu mol h(-1) g(-1) for pure g-C3N4. Strikingly, the photon-hydrogen conversion efficiency also showed dual maxima values as SnO2 mass ratio changes. These abnormal observations were comparatively investigated via XPS, EPR and photoluminescence spectra in solid state and aqueous environments. It is demonstrated that electron competitive migration was primarily caused by oxygen vacancies on the SnO2 surface, which plays a key role in creating the dual catalytic activity maxima in water splitting.