Enhanced photocatalytic performance of visible-light-driven CuOx/TiO2-x for degradation of gaseous formaldehyde: Roles of oxygen vacancies and nano copper oxides

Photocatalysis is an effective method for the removal of formaldehyde (HCHO), and high-efficiency visible-light-driven photocatalysts were urgently required. Herein, oxygen vacancies (OVs) and nano copper oxides (CuOx) synergistically modified TiO2 (CuOx/TiO2-x) photocatalysts were synthesized by one-step hydrothermal followed by impregnation method. The photocatalytic decomposition of HCHO reached 100% at initial concentration of 180 ppm under relative humidity (RH) = 60% by 0.1g CuOx/TiO2-x in 150 min visible light irradiation. Characterization results explored the complementary effect of OVs and CuOx systematically. The OVs increased the separation efficiency of photogenerated charge carriers and act as adsorption/active sites in HCHO photocatalytic oxidation. The moisture and O2 were adsorbed and actived by OVs to generate reactive oxygen species (ROS). After doped CuOx on the surface of TiO2-x, the photoexcited electrons in Cu2O could transfer to the conduction band (CB) of TiO2-x and the photoexcited electrons of TiO2-x could be captured by Cu nanoparticles. Therefore, more ROS were generated due to the synergistic effect of OVs and CuOx. The In-situ Fourier transform infrared (in-situ FTIR) measurements show the hydroxyl radical (•OH) was the dominant radical in HCHO photocatalytic oxidation, while •O2- could also upgrade the photodegradation efficiency of HCHO. Furthermore, the stability tests showed the degradation efficiency of HCHO still reached 90% after five recycles, indicating that CuOx/TiO2-x nanocomposites displayed a stable and high photoactivity in volatile organic compounds (VOCs) decomposition.