Flat-Band Potential Determination and Catalytical Properties of Sn3O4/SnO2 Heterostructures in the Photo-Electrooxidation of Small Organic Molecules under Ultraviolet (370 nm) and Blue (450 nm) Light

Abstract

Sn3O4 are promising semiconductor materials due to their visible light absorption ability. In this work, a series of materials, such as SnO2, Sn3O4 and Sn3O4/SnO2 heterostructures, with different phase ratios were prepared using hydrothermal synthesis. The materials were characterized using X-ray diffraction (XRD), Raman and diffuse reflectance spectroscopy (DRS), high resolution transmission electron microscopy (HRTEM), nitrogen adsorption (BET). Flat-band potentials (EFB) of the samples were determined using the photocurrent onset potential (POP) method. It was shown that the potentials obtained with open circuit potential measurements versus illumination intensity (OCP) likely corresponded to the EFB of SnO2 nanoparticles in heterostructures due to interfacial electron transfer from the conducting band of Sn3O4 to that of SnO2. The photo-electrooxidation processes of a series of organic substrates were studied in the potential range of 0.6–1.4 V vs. RHE under irradiation with ultraviolet (λ = 370 nm) and visible (λ = 450 nm) light. The Sn3O4 sample showed high activity in the photo-electrooxidation of acetone and formic acid in visible light. The Sn3O4/SnO2 samples exhibited noticeable activity only in the oxidation of formic acid. The presence of the SnO2 phase in the Sn3O4/SnO2 samples increased the photocurrent values under ultraviolet illumination, but significantly reduced the oxidation efficiency in visible light.