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 (λ > 400 nm) compared to pure TiO2 (inactive). The DFT study revealed that o-xylene strongly adsorb on TiO2 (001) surface than (101) through π 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 π 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.