In situ Raman study of laser‐induced stabilization of reduced nanoceria (CeO2−x) supported on graphene

Abstract

AbstractThis work demonstrates a novel approach to application of in situ Raman spectroscopy to study laser‐induced stabilization of reduced nanoceria (CeO2−x) supported on graphene—a promising nanocomposite for future development of nanomaterial‐enabled gas sensors or vital catalysts for hydrogenation of alcohols under anaerobic conditions. Structural stabilization of CeO2−x nanoparticles (NPs) on a graphene surface is evidenced by significant modification of Raman spectra—the appearance, increase in relative intensity, and low‐wavenumber shift of CeO2 F2g band at excitation laser powers higher than ~5 mW. The effect is related to the reduction in a number of oxygen vacancies in CeO2−x NPs. Analysis of the graphene 2D and G band wavenumbers through ω2D(ωG) correlation indicated a decrease in p‐type graphene doping attributed to the charge transfer between the stabilizing CeO2−x NPs and the graphene that occurs due to trapping of graphene mobile holes by oxygen vacancies in CeO2−x. High‐resolution transmission electron microscopy analysis supported this idea by showing the increased lattice constant of fluorite‐type hexagonal‐shaped CeO2−x NPs as compared with bulk CeO2 and which could be related to partial reduction of CeO2−x NPs as a result of the Ce4+ transformation to Ce3+ with formation of corresponding oxygen vacancies. X‐ray photoelectron spectroscopy data confirmed the mixed Ce4+/Ce3+ valence state of the CeO2−x NPs. Thus, by combining the structure conversion of nanoceria induced by electromagnetic radiation and its stabilization by the graphene support, this work provides a foundation for advanced concepts in the development of the next‐generation catalysts and sensors.