Construction of homojunction-adsorption layer on anatase TiO2 to improve photocatalytic mineralization of volatile organic compounds

The separation and injection of photogenerated charge carriers significantly affect the mineralization efficiency of volatile organic compounds (VOCs). These two processes can be optimized by enhancing the separation of charge carriers and the adsorption of VOCs via material engineering. However, obtaining both high adsorption ability and photoactivity of VOCs simultaneously at the ppm level is difficult. In this work, we grew microporous TiO2 onto the surface of anatase TiO2 to construct a homojunction-adsorption layer, enhancing both the adsorption and photodegradation of low concentration of toluene, which was chosen as model VOC. N2 adsorption/desorption, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), GC-flame ionization detection, and surface photovoltage spectroscopy (SPS) were employed to analyze the physical properties and mineralization of toluene. Results showed that growth of microporous TiO2 increased the surface area of the catalyst by 160% compared with anatase TiO2, as well as induced microporous structure. This phenomenon significantly enhanced the adsorption of toluene at a low concentration of 5.5 mg/m3 and limited the release of the adsorbed organic compounds. Moreover, SPS and XPS results proved that a homojunction was constructed at the interface of microporous TiO2 and anatase TiO2, greatly improving the separation of photogenerated charge carriers. Owing to the enhanced adsorption ability and photoactivity, the mineralization efficiency of toluene over micropore-anatase TiO2 composite was 1.78 and 2.12 times higher than that over M-TiO2 and anatase TiO2, respectively.