One-pot synthesis of (anatase/bronze-type)-TiO2/carbon dot polymorphic structures and their photocatalytic activity for H2 generation

We report the one-pot synthesis of anatase/bronze-type ((A/B)-TiO2) and carbon dots (CDs) via a simple solvothermal method using only TiCl4 and ethylene glycol. Control of the reaction temperature and duration enabled the compositions of pure (B) phase, (A/B)-TiO2/CDs, and (A)-TiO2/CDs to be tuned. A series of experiments on the synthesis conditions was carefully conducted at various temperatures (150-200 degrees C) for various reaction times (5-36 h). Pure phase (B)-TiO2 was obtained at 150 degrees C for all reaction times (5 to 36 h). The (B) phase was transformed to anatase at temperatures from 170 degrees C for reaction times longer than 12 h. At the same time, CDs were formed from the decomposition of ethylene glycol at temperatures greater than 160 degrees C and long reaction times (> 12 h). The photocatalytic activities of the composite catalysts were evaluated by H-2 generation from a water-ethylene glycol mixed solution under UV-visible light. H-2 generation rates were observed in this order: (A/B)-TiO2/CDs > (A)-TiO2/CDs > (B)-TiO2 > (A)-TiO2. This high photocatalytic activity for (A/B)TiO2/CDs is attributed to effective charge-separation and broad-light absorption. The developed method will be important for the facile synthesis of (A/B)-TiO2/CD materials and has more potential than conventional multi step methods.