Unraveling the Hydrogenation of TiO₂ and Graphene Oxide/TiO₂ Composites in Real Time by in Situ Synchrotron X-ray Powder Diffraction and Pair Distribution Function Analysis

The functionalization of graphene oxide (GO) and graphene by TiO₂ and other metal oxides has attracted considerable attention due to numerous promising applications in catalysis, energy conversion, and storage. Hydrogenation of this class of materials has been proposed as a promising way to tune catalytic properties by altering the structural and chemical transformations that occur upon H incorporation. Herein, we investigate the structural changes that occur during the hydrogenation process using in situ powder X-ray diffraction and pair distribution function analysis of GO-TiO₂ and TiO₂ under H₂ reduction. Sequential Rietveld refinement was employed to gain insight into the evolution of crystal growth of TiO₂ nanoparticles in the presence of two-dimensional (2D) GO nanosheets. GO sheets not only significantly retarded the nucleation and growth of rutile impurities, stabilizing the anatase structure, but was also partially reduced to hydrogenated graphene by the introduction of atomic hydrogen into the honeycomb lattice. We discuss the hydrogenation processes and the resulting composite structure that occurs during the incorporation of atomic H and the dynamic structural transformations that leads to a highly active photocatalyst.