Enhanced Visible-Light Photocatalytic Activity of a TiO2 Membrane-Assisted with N-Doped Carbon Quantum Dots and SiO2 Opal Photonic Crystal

A N-doped carbon quantum dots sensitized TiO 2 membrane (NCQDs/TiO 2 ) was fabricated, and the photocatalytic performance of the resulting composites with various sensitization times was studied. The results showed that the photocatalytic degradation rate of gaseous acetaldehyde over NCQDs/TiO 2 was 2.2 times that observed over TiO 2 . The UV–vis absorption range of NCQDs/TiO 2 was expanded to the visible-light region after being sensitized by the NCQDs. The photoluminescence (PL) intensity of NCQD/TiO 2 was weaker than that of either TiO 2 or NCQDs, which indicating that the recombination of the photogenerated electrons and holes was suppressed when TiO 2 was sensitized by the NCQDs. The different electron migration patterns in the NCQDs/TiO 2 composite under ultraviolet (UV) and visible-light (Vis) irradiation were proposed based on the experimental results. Additionally, an SiO 2 Opal photonic crystal was also utilized to enhance the light harvesting in this work. An NCQDs/TiO 2 /SiO 2 Opal composite was prepared with the photonic band gap (PBG) of the SiO 2 Opal being designed at 455 nm, which is the center of the absorption range of NCQDs/TiO 2 in the visible-light region. Due to the PBG reflection and photolocalization effect of the SiO 2 Opal photonic crystal, the photocatalytic degradation rate of gaseous acetaldehyde over NCQDs/TiO 2 /SiO 2 Opal was 1.89 times of that observed over NCQDs/TiO 2 and 4.15 times of that found over TiO 2 . The synergistic effect of the NCQDs and SiO 2 Opal photonic crystal greatly enhanced the photocatalytic performance of TiO 2 .