In situ Raman study of laser‐induced stabilization of reduced nanoceria (CeO_2−x) supported on graphene

Abstract

This 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.

Temperature‐induced phonon behavior in titanium disulfide (TiS2) nanosheets

“…In order to further explore the possibilities of TiS 2 applications in above‐mentioned examples, one needs to fully understand the fundamental properties of this material, including phonon properties. Phonon properties can be investigated using Raman spectroscopy, which has been proved to be an excellent tool for characterization of structural, thermal, optical, and electronic properties of layered materials . However, up to date, phonon properties (especially as a function of temperature) in titanium disulfide thin films are still poorly understood or unavailable.…”

Mechanochemical synthesis of carbon-stabilized Cu/C, Co/C and Ni/C nanocomposites with prolonged resistance to oxidation

“…The structure of the nanocomposites were characterized using micro‐Raman spectroscopy at appropriate experimental conditions 63 . The measurements were performed at room temperature in backscattering configuration using a triple Raman spectrometer T‐64000 Horiba Jobin‐Yvon, equipped with electrically cooled charge‐coupled device (CCD) detector and Olympus BX41 microscope.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XIV

“…Their findings for the temperature dependence of the double resonance process in single‐layer MoS 2 can be extended to other classes of transition metal dichalcogenide materials. Nikolenko et al [ 86 ] reported on an in situ Raman study of laser‐induced stabilization of reduced nanoceria (CeO 2‐x ) supported on graphene. They conclude that 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.…”