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 TiO2 membrane (NCQDs/TiO2) 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/TiO2 was 2.2 times that observed over TiO2. The UV- vis absorption range of NCQDs/TiO2 was expanded to the visible-light region after being sensitized by the NCQDs. The photoluminescence (PL) intensity of NCQD/TiO2 was weaker than that of either TiO2 or NCQDs, which indicating that the recombination of the photogenerated electrons and holes was suppressed when TiO2 was sensitized by the NCQDs. The different electron migration patterns in the NCQDs/TiO2 composite under ultraviolet (UV) and visible-light (Vis) irradiation were proposed based on the experimental results. Additionally, an SiO2 Opal photonic crystal was also utilized to enhance the light harvesting in this work. An NCQDs/TiO2/SiO2 Opal composite was prepared with the photonic band gap (PBG) of the SiO2 Opal being designed at 455 nm, which is the center of the absorption range of NCQDs/TiO2 in the visible-light region. Due to the PBG reflection and photolocalization effect of the SiO2 Opal photonic crystal, the photocatalytic degradation rate of gaseous acetaldehyde over NCQDs/TiO2/SiO2 Opal was 1.89 times of that observed over NCQDs/TiO2 and 4.15 times of that found over TiO2. The synergistic effect of the NCQDs and SiO2 Opal photonic crystal greatly enhanced the photocatalytic performance of TiO2.