Enhanced photocatalytic performance of visible-light-driven CuO x /TiO 2-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 (CuO ) synergistically modified TiO (CuO /TiO ) 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 CuO /TiO in 150 min visible light irradiation. Characterization results explored the complementary effect of OVs and CuO systematically. The OVs increased the separation efficiency of photogenerated charge carriers and act as adsorption/active sites in HCHO photocatalytic oxidation. The moisture and O were adsorbed and actived by OVs to generate reactive oxygen species (ROS). After doped CuO on the surface of TiO , the photoexcited electrons in Cu O could transfer to the conduction band (CB) of TiO and the photoexcited electrons of TiO could be captured by Cu nanoparticles. Therefore, more ROS were generated due to the synergistic effect of OVs and CuO . The In-situ Fourier transform infrared (in-situ FTIR) measurements show the hydroxyl radical (•OH) was the dominant radical in HCHO photocatalytic oxidation, while •O 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 CuO /TiO nanocomposites displayed a stable and high photoactivity in volatile organic compounds (VOCs) decomposition.