Article

Identification of the structural phases of Ce(x)Zr(1-x)O2 by Eu(III) luminescence studies.

Chemistry Department, ICCOM-CNR, INSTM, Center of Excellence for Nanostructured Materials (CENMAT), University of Trieste, via L. Giorgieri 1, 34127 Trieste, Italy.
Journal of the American Chemical Society (Impact Factor: 10.68). 09/2009; 131(36):13155-60. DOI: 10.1021/ja905158p
Source: PubMed

ABSTRACT Despite the wide application of ceria-zirconia based materials in Three Way Catalysts (TWCs), Solid Oxides Fuel Cells (SOFCs), and H(2) production and purification reactions, an active debate is still open on the correlation between their structure and redox/catalytic performances. Existing reports support the need of either (i) a homogeneous solid solution or (ii) materials with nanoscale heterogeneity to obtain high activity and stability. Here we report on a simple and inexpensive approach to solve this problem taking advantage of the luminescence properties of Eu(III), used as a structural probe introduced either in the bulk or on the surface of the samples. In this way, the real structure of ceria-zirconia materials can be revealed even for amorphous high surface area samples. Formation of small domains is observed in catalytically important metastable samples which appear homogeneous by conventional XRD.

0 Bookmarks
 · 
99 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this article, we discuss the microwave synthesis of sodium dodecyl sulphate (SDS) stabilized Ln(3+)-doped CaMoO4 nanocrystals (Ln(3+) = Eu(3+), Er(3+)/Yb(3+)). The nanocrystals are quite monodispersed with an average size close to 100 nm. FTIR and TGA analyses suggest strong binding of the SDS molecules to the CaMoO4 nanocrystals surface. The high dispersibility of the nanocrystals in water implies that SDS stabilizes the nanocrystals as a bilayer structure. The SDS coating also assists in the easy dispersion of the nanocrystals in toluene without any additional surface chemistry. The Eu(3+) ions doped in the CaMoO4 nanocrystals display very strong red luminescence with a quantum yield close to 40%. Under 980 nm excitation, Er(3+)/Yb(3+)-doped CaMoO4 nanocrystals display Er(3+) emissions at 550 and 650 nm. In addition, interestingly, a NIR peak at around 833 nm is observed, which occurred via a three photon process. Furthermore, the CaMoO4 nanocrystals exhibit photocatalytic activity which is studied through the degradation of Rhodamine B (RhB) dye in neutral conditions. The RhB dye is significantly degraded by ∼80% under UV illumination within 4 h and the rate of degradation is comparable to that observed for well known ZnO nanoparticles. The high luminescence quantum efficiency and strong photocatalytic activity of the Ln(3+)-doped CaMoO4 nanocrystals make them a potential material for dual applications such as bio-imaging and photocatalysis.
    Dalton Transactions 03/2014; · 3.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this article, we report a facile microwave-assisted green synthetic route for colloidal poly(vinylalcohol) (PVA)-coated europium (Eu3+)-doped luminescent heavy metal bismuth oxyhalide (BiOX; X = Cl, Br, I) nanoflakes at low temperature and examine their structural, optical and photocatalytic characteristics. PVA coating onto the surface of the nanoflakes endow them with hydrophilic nature. Both Eu3+-doped BiOCl and BiOBr nanoflakes exhibit strong optical properties related to Eu3+ and Bi3+ which are quenched in case of Eu3+-doped BiOI matrix. These results are supported by Eu3+ photoluminescence lifetime values of 0.61 ms, 0.59 ms and 8.9 s, respectively. The former two matrices have quite similar crystal field environments as deduced from the asymmetric ratios of 5D0 → 7F2 (614 nm) and 5D0→ 7F1 (591 nm) transitions. In addition to possessing interesting photoluminescence properties, all the three nanoflakes exhibit photocatalytic activity. A comparison of the photocatalytic activity of Eu3+-doped BiOX (X = Cl, Br, I) nanoflakes, with corresponding estimated band gaps of 3.36, 2.74 and 1.67 eV, has been evaluated using Rhodamine B (RhB) dye under visible light irradiation. Eu3+-doped BiOCl and BiOBr nanoflakes manifested higher photocatalytic efficiency compared to the Eu3+-doped BiOI nanoflakes.
    Langmuir 01/2014; · 4.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The atomic scale homogeneity of Ce and Zr oxygen bonds represents the main reason for enhanced total oxygen storage capability of CeO2-ZrO2 (Ce/Zr = 1) as compared to that of CeO2. Here, we demonstrate that the addition of 10% Eu(3+) by wet impregnation on preformed nanosized CeO2-ZrO2 (Ce/Zr = 1) followed by calcination induces a remarkable homogeneity of 10% Eu(3+)-CeO2-ZrO2 solid solution. By use of time-resolved emission and excitation spectroscopies, the improvement of the nanoscale chemical and structural homogeneity of 10% Eu(3+)-CeO2-ZrO2 calcined at 1000 as compared to sample calcined at 750 °C is demonstrated. Based on the comparison of luminescence properties of 10% Eu(3+) impregnated on preformed nanosized CeO2-ZrO2 and CeO2, we also show that the presence of zirconium does not only preserve the ability of cerium oxide to "dissolve" lanthanide oxide, but also determines an important stabilization of defects (oxygen vacancies) generated upon Eu(3+) doping.
    Dalton Transactions 04/2014; · 3.81 Impact Factor

Full-text (2 Sources)

View
12 Downloads
Available from
May 31, 2014