In this article, we demonstrate that TiO2@carbon core/shell (TiO2@C) nanocomposite photocatalysts prepared by carbonizing a single molecular layer of aromatic compounds adsorbed on the surface of TiO2 nanoparticles selectively enhance the generation of hydrogen peroxide (H2O2). Atomically thin carbon shells have been formed directly on the surface of TiO2 nanoparticles through pyrolytic decarboxylation of the adsorbed aromatic compounds, benzoic acid (BA), and 1-naphthoic acid (NA), which yields two types of TiO2@C nanocomposites, TiO2@C(BA) and TiO2@C(NA). Raman spectroscopy shows that the as-obtained nanocomposites have similar degrees of graphitization (D/G band ratio), regardless of the type of aromatic precursors, but TiO2@C(NA) contains more oxygenic species than TiO2@C(BA) (D*/G band ratio). Such oxygenic species predominantly exist in the form of epoxide groups, as determined by attenuated total reflection infrared spectroscopy. The sp2 carbon atoms near the epoxide groups in the carbon shell can act as active sites for the two-electron reduction of O2. Therefore, TiO2@C(NA) can generate H2O2 more efficiently than TiO2@C(BA). Furthermore, the carbon shells retard the reconsumption of the generated H2O2 by inhibiting the adsorption of H2O2 on the surface of TiO2 nanoparticles, thereby improving the photocatalytic efficiency of H2O2 generation. Finally, we have shown the durability and reproducibility of our TiO2@C-based photocatalytic systems. We believe that our research may offer a potentially improved strategy for H2O2 generation and other photocatalytic applications.
Keywords: TiO2; carbon shells; hydrogen peroxide; nanocomposites; photocatalysis.