Facet-dependent photocatalytic and photoelectric properties of CQDs/TiO2 composites under visible irradiation

The construction of photocatalytic heterostructures and the study of carrier kinetics are significant for developing novel functional materials and understanding catalytic mechanisms. Here, we synthesized the heterostructural composites of carbon quantum dots (CQDs) and TiO2 nanoparticles with (101) or (001) as the main exposed facets by hydrothermal method, named CQDs/TiO2(101) and CQDs/TiO2(001). The facet-dependent sensitization and photocatalysis properties of these composites have been investigated using steady-state and time-resolved spectroscopy. The results indicate that the electron transfer process between CQDs and TiO2 is associated with the exposed facet of TiO2. The electron transfer rate from CQDs to TiO2(101) is two orders of magnitude larger than that to TiO2(001). The CQDs/TiO2(101) composite also demonstrates three times higher photoelectric conversion than CQDs/TiO2(001). The facet-dependent catalytic performances of CQDs/TiO2 composites have been evaluated by the degradation of Rhodamine B (RhB) under visible light irradiation. The rate constant of CQDs/TiO2(101) for the degradation of intermediates (Rh-110) shows 1.82 times higher than that of CQDs/TiO2(001). These findings indicate the effective loading of CQDs on TiO2(101) nanoparticles can be expected to efficiently improve the photoelectric and photocatalytic properties of TiO2-based heterostructure under visible irradiation, and are significant for deep understanding the facet-dependent photocatalytic mechanism and property.