Enhanced near-visible-light photocatalytic removal of formaldehyde over Au-assisted ZnSn(OH)6 microcubes

The increase of formaldehyde in the air causes many problems in the environment. The photocatalytic method is green, inexpensive, high sufficiency, but challenging to use because of photocatalysts’ wide bandgap working only under the UV light, which is accounted for less than 5% of the sunlight. Here, gold-assisted ZnSn(OH)6 microcubes (Au:cZHS) were produced by a hydrothermal process of cZHS, a well-known catalyst for NOx and VOCs removal. The existence and unique morphology of the Au:cZHS composites were confirmed by the characterizations of X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), Raman spectroscopy, field-emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The band structure and charge-transfer processes of the materials were evaluated from the results of the UV–Vis diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS), and Mott–Schottky. These results indicated the Au:cZHS composites have a high sufficiency of charge transport and near-visible light absorption. The electron spin resonance (ESR) was also used to determine reactive oxygen species producing from photocatalytic reactions. In addition, the reaction rates and apparent quantum efficiency (AQE) were calculated for a better comparison with other studies. In addition, the 10% Au:cZHS removed more than 70% of 1 ppb formaldehyde (HCHO) under solar light. These results indicate that the Au:cZHS is a promising photocatalyst for air treatment.