Research ArticleSURFACE CHEMISTRY

Identification of different oxygen species in oxide nanostructures with 17O solid-state NMR spectroscopy

See allHide authors and affiliations

Science Advances  20 Feb 2015:
Vol. 1, no. 1, e1400133
DOI: 10.1126/sciadv.1400133
  • Fig. 1 Solid-state NMR spectra of nanosized ceria in comparison with DFT calculations.

    (A) 17O NMR spectra for ceria nanoparticles enriched at different temperatures and acquired at different external fields compared with the 17O NMR spectra of micrometer-sized ceria (bulk ceria) and the summary of the chemical shifts predicted using a structural model shown in (B). The spectra obtained at 14.1 and 9.4 T were acquired with spinning speeds of 55 and 20 kHz, respectively. Short pulse lengths of 0.1 to 0.4 μs corresponding to π/72 to π/18 pulses for H217O and optimized recycle delays from 1 to 100 s to ensure quantitative observations of all the resonances were used. Detailed experimental parameters are summarized in table S9. (B) The structural model of ceria used in the DFT calculations. Red and white spheres represent oxygen and cerium ions, respectively. The exposed surface is (111), and the calculated chemical shift of 17O in each layer is shown on the right.

  • Fig. 2 Solid-state NMR spectra of ceria in contact with water.

    (A, bottom to top) 17O MAS NMR spectra of nonenriched ceria nanoparticles adsorbed with nonenriched water; ceria nanoparticles enriched in 17O2 at 573 K and then exposed to air; ceria nanoparticles enriched in 17O2 at 573 K and then adsorbed with nonenriched water (water was added dropwise); the previous sample dried under vacuum at room temperature and at 573 K; and ceria nanoparticles enriched in 17O2 at 573 K. (B, bottom to top) 17O NMR spectra of liquid H217O; 17O MAS NMR spectra of bulk ceria adsorbed with H217O (bulk-H217O); the previous sample dried under vacuum at 373 K; nonenriched ceria nanoparticles adsorbed with H217O by adding water dropwise [nano-H217O(D)]; the previous sample dried under vacuum at 373 K; and nonenriched ceria nanoparticles adsorbed with H217O by adsorbing water through a vacuum line and then dried under vacuum at 373 K [nano-H217O(A)]. The samples of H217O, bulk-H217O, and nano-H217O(D) in (B) were packed into the rotors in air. All the spectra were acquired at 9.4 T. Detailed experimental parameters are summarized in table S10. Asterisks denote spinning sidebands.

  • Fig. 3 Double-resonance solid-state NMR data of ceria nanoparticles.

    (A, top to bottom) 17O MAS NMR spectra of ceria nanoparticles adsorbed with 17O water followed by thermal treatment under vacuum at 373 K at 14.1 and 9.4 T; difference spectrum in 17O-1H REDOR experiments; and 1H-17O CP MAS NMR spectrum with a contact time of 100 μs. (B) The peak intensity in CP MAS NMR experiment as a function of contact time. Spectra were obtained at both 9.4 and 14.1 T under MAS rates of 13 to 14 kHz. One thousand to 40,000 scans were averaged, and recycle delays from 0.2 to 1 s were used. Asterisks denote spinning sidebands.

  • Fig. 4 Solid-state NMR spectra of ceria nanoparticles adsorbed with H217O followed by thermal treatment.

    Top to bottom: 17O NMR spectrum of nonenriched ceria nanoparticles adsorbed with H217O by adding water dropwise, then dried under vacuum at 373, 423, 473, 523, 573, and 773 K. A rotor-synchronized Hahn-echo sequence (π/6 - τ - π/3 - τ - acquisition) was used. Spectra were obtained at 9.4 T under a MAS rate of 20 kHz. Eight thousand to 20,000 scans were collected, and recycle delays from 0.2 to 0.5 s were used. Asterisks denote spinning sidebands.

  • Fig. 5 Solid-state NMR spectra of reduced ceria in comparison with bulk and nanosized ceria.

    (A) 17O NMR spectra of bulk ceria enriched in 17O2 at 1073 K (bottom) and reduced in H2 atmosphere at 1073 K (top). (B) 17O NMR spectra of nanosized ceria enriched in 17O2 at 773 K (bottom), reduced in H2 atmosphere at 773 K (top), and reoxidized in air reduced ceria (middle). Inset shows the full width of the three 17O spectra. A rotor-synchronized Hahn-echo sequence (π/6 - τ - π/3- τ - acquisition) was used. Data were obtained at 9.4 T under a MAS rate of 20 kHz. One hundred thousand (A, bulk), 300,000 (A, reduced), 1024 (B), and 40,000 scans (B, inset) were averaged, and recycle delays of 0.1 s (A), 1 s (B), and 0.01 s (B, inset) were used. Asterisks denote spinning sidebands.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/ content/full/1/1/e1400133/DC1

    Materials and Methods

    Fig. S1. XRD and electron microscopy characterization of ceria nanoparticles.

    Fig. S2. XRD patterns of ceria nanoparticles calcined at different temperatures.

    Fig. S3. Scanning electron microscopy image of the bulk ceria sample.

    Fig. S4. Longitudinal relaxation studies of ceria nanoparticles.

    Fig. S5. Quantification of surface oxygen ions from NMR and BET data.

    Fig. S6. Chemical shift calculations of ceria with different surface slabs.

    Fig. S7. Solid-state NMR of ceria nanoparticles in contact with water at ultrahigh field.

    Fig. S8. DFT calculations for ceria in contact with water.

    Fig. S9. Nutation NMR of ceria nanoparticles.

    Fig. S10. TRAPDOR NMR of ceria nanoparticles.

    Fig. S11. Electron microscopy and solid-state NMR spectra of ceria nanorods.

    Fig. S12. Vacancy formation energies of different oxygen ions.

    Fig. S13. Solid-state NMR spectra of ceria nanoparticles with different surface areas labeled by adsorbing H217O.

    Fig. S14. Ce 3d3/2,5/2 XPS spectra collected for ceria nanoparticles, nanorods, and bulk sample, as well as line fitting results.

    Fig. S15. Molar percentage of Ce3+ as a function of particle size from XPS data.

    Fig. S16. H2 TPR profiles of bulk ceria and ceria nanoparticles.

    Fig. S17. Structure model and chemical shift calculations of ceria with oxygen vacancies.

    Fig. S18. The criterion for NMR calculations and the determination of chemical shift.

    Table S1. Mean diameter of ceria nanoparticles.

    Table S2. BET surface area of ceria samples.

    Table S3. Calculated NMR parameters of quadrupolar interaction for ceria.

    Table S4. Calculated NMR parameters of quadrupolar interaction for ceria in contact with water.

    Table S5. Calculated chemical shifts for ceria in contact with water.

    Table S6. Calculated chemical shifts for ceria with oxygen vacancies in the bulk.

    Table S7. Calculated chemical shifts for ceria with subsurface oxygen vacancies.

    Table S8. Calculated chemical shifts for ceria with surface oxygen vacancies.

    Table S9. Detailed NMR parameters for acquiring 17O MAS NMR data in Fig. 1.

    Table S10. Detailed NMR parameters for acquiring 17O NMR data in Fig. 2.

  • Supplementary Materials

    This PDF file includes:

    • Materials and Methods
    • Fig. S1. XRD and electron microscopy characterization of ceria nanoparticles.
    • Fig. S2. XRD patterns of ceria nanoparticles calcined at different temperatures.
    • Fig. S3. Scanning electron microscopy image of the bulk ceria sample.
    • Fig. S4. Longitudinal relaxation studies of ceria nanoparticles.
    • Fig. S5. Quantification of surface oxygen ions from NMR and BET data.
    • Fig. S6. Chemical shift calculations of ceria with different surface slabs.
    • Fig. S7. Solid-state NMR of ceria nanoparticles in contact with water at ultrahigh field.
    • Fig. S8. DFT calculations for ceria in contact with water.
    • Fig. S9. Nutation NMR of ceria nanoparticles.
    • Fig. S10. TRAPDOR NMR of ceria nanoparticles.
    • Fig. S11. Electron microscopy and solid-state NMR spectra of ceria nanorods.
    • Fig. S12. Vacancy formation energies of different oxygen ions.
    • Fig. S13. Solid-state NMR spectra of ceria nanoparticles with different surface areas labeled by adsorbing H2 17O.
    • Fig. S14. Ce 3d3/2,5/2 XPS spectra collected for ceria nanoparticles, nanorods, and bulk sample, as well as line fitting results.
    • Fig. S15. Molar percentage of Ce3+ as a function of particle size from XPS data.
    • Fig. S16. H2 TPR profiles of bulk ceria and ceria nanoparticles.
    • Fig. S17. Structure model and chemical shift calculations of ceria with oxygen vacancies.
    • Fig. S18. The criterion for NMR calculations and the determination of chemical shift.
    • Table S1. Mean diameter of ceria nanoparticles.
    • Table S2. BET surface area of ceria samples.
    • Table S3. Calculated NMR parameters of quadrupolar interaction for ceria.
    • Table S4. Calculated NMR parameters of quadrupolar interaction for ceria in contact with water.
    • Table S5. Calculated chemical shifts for ceria in contact with water.
    • Table S6. Calculated chemical shifts for ceria with oxygen vacancies in the bulk.
    • Table S7. Calculated chemical shifts for ceria with subsurface oxygen vacancies.
    • Table S8. Calculated chemical shifts for ceria with surface oxygen vacancies.
    • Table S9. Detailed NMR parameters for acquiring 17O MAS NMR data in Fig. 1.
    • Table S10. Detailed NMR parameters for acquiring 17O NMR data in Fig. 2.

    Download PDF

    Files in this Data Supplement:

Navigate This Article