Revealing adsorption and the photodegradation mechanism of gas phase o-xylene on carbon quantum dots modified TiO2 nanoparticles

Here, we report the photocatalytic oxidation (PCO) of o-xylene on carbon quantum dots (CQDs) modified TiO2 nanoparticles. The results demonstrated that with 1 wt% CQDs loading, 87 % of o-xylene (50 ppm) can be photodegraded, which is 55.3 % higher than pure TiO2 (56 %) under UV/visible light. This improved photocatalytic activity is associated with the important role of CQDs on TiO2 surface, which increased the o-xylene adsorption and facilitated the photogenerated hole-electron separation process. Also, the 1 wt%CQDs/TiO2 nanocomposite showed photocatalytic activity in the visible region (lambda > 400 nm) compared to pure TiO2 (inactive). The DFT study revealed that o-xylene strongly adsorb on TiO2 (001) surface than (101) through pi electrons of the aromatic ring. The in situ DRIFTS study showed that free OH groups on the photocatalyst surface could act as effective Lewis sides for the o-xylene adsorption. The interaction of pi electrons of the aromatic ring and isolated OH groups was also observed. The FTIR peaks for CO2 increased in the case of CQDs/TiO2 nanocomposite contrasted to pure TiO2, which suggested that the presence of CQDs improved the mineralization potency of TiO2. These findings should affect the quest for a better photocatalyst to photodegrade VOCs.