Crafting carbon sphere-titania core-shell interfacial structure to achieve enhanced visible light photocatalysis

Anchoring titania on carbon sphere forms a core-shell structure (TiO2@CS) which shows high-performance visible light response photocatalysis. In order to further improve such photocatalysis, herein acrylic acid (AA) is employed to modify the surface chemistry of CS so as to craft the interfacial structure between CS and TiO2. It was found that AA addition leads to morphology change from smooth to rough surface or to aggregates of smaller primary nanoparticles which, however, do not impede formation of the close contact core-shell structure with TiO2. Detailed analysis demonstrates a complex change in surface functional groups of CS in which the acidic -OH is the major type whose quantity shows a peak maximum and a continuous increase at small and large AA addition ranges, respectively. Photocatalysis, photocurrent, and DFT calculation certificate that rather than -COOH, the acidic -OH, particularly, that related to sufficiently conjugated backbone carbon contributes to the formation of the interfacial structure which facilitates better visible light responsive photocatalysis. Benefiting from the improved interfacial charge separation, the visible light photoactivity reaches the highest when the quantity of the conjugated carbon-related -OH becomes the maximum. An explicit charge transfer mechanism is proposed based on both experimental and theoretical calculation results.