Origin of Visible Light Photoactivity of Reduced Graphene Oxide/TiO₂ by in Situ Hydrothermal Growth of Undergrown TiO₂ with Graphene Oxide

Graphene-related–TiO₂ (G–TiO₂) nanocomposites show enhanced photocatalytic performance, not only due to promoting photogenerated electrons migration but also by extending optical absorption to the visible light range. However, little is known about the origin of the visible light activity, which seems to depend much on the precursor of the titanium source. In this study, an efficient visible light active G–TiO₂-413 was prepared by hydrothermally treating a graphene oxide (GO) suspension and TiO₂ sol with undergrown TiO₂ nanoparticles at 413 K. According to XRD, DRS, TEM, FTIR, Raman, and ESR analyses, when in situ growing TiO₂ nanoparticles from hydrolyzed titanium alkoxides in hydrothermal conditions, a strong chemical interaction appears at the interface of GO sheets and the underdeveloped loosely packed polymeric Ti–O–Ti skeletons, so as to facilitate retaining more alkoxyl groups, inducing crystal disorders, and creating oxygen vacancies. All of these contribute to the significantly enhanced visible light activity of G–TiO₂-413. This sheds new light on the development of visible light responsive TiO₂-based photocatalysts via surface modification approaches