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Single-step processing of copper-doped titania nanomaterials in a flame aerosol reactor.

Sahu M, Biswas P - Nanoscale Res Lett (2011)

Bottom Line: This has been feasible by a detailed understanding of the formation and growth of nanoparticles in the high-temperature flame region.Annealing the Cu-doped TiO2 nanoparticles increased the crystalline nature and changed the morphology from spherical to hexagonal structure.Measurements indicate a band gap narrowing by 0.8 eV (2.51 eV) was achieved at 15-wt.% copper dopant concentration compared to pristine TiO2 (3.31 eV) synthesized under the same flame conditions.

View Article: PubMed Central - HTML - PubMed

Affiliation: Aerosol and Air Quality Research Laboratory, Department of Energy, Environmental and Chemical Engineering, Washington University in St, Louis, St, Louis, MO 63130, USA. pbiswas@wustl.edu.

ABSTRACT
Synthesis and characterization of long wavelength visible-light absorption Cu-doped TiO2 nanomaterials with well-controlled properties such as size, composition, morphology, and crystal phase have been demonstrated in a single-step flame aerosol reactor. This has been feasible by a detailed understanding of the formation and growth of nanoparticles in the high-temperature flame region. The important process parameters controlled were: molar feed ratios of precursors, temperature, and residence time in the high-temperature flame region. The ability to vary the crystal phase of the doped nanomaterials while keeping the primary particle size constant has been demonstrated. Results indicate that increasing the copper dopant concentration promotes an anatase to rutile phase transformation, decreased crystalline nature and primary particle size, and better suspension stability. Annealing the Cu-doped TiO2 nanoparticles increased the crystalline nature and changed the morphology from spherical to hexagonal structure. Measurements indicate a band gap narrowing by 0.8 eV (2.51 eV) was achieved at 15-wt.% copper dopant concentration compared to pristine TiO2 (3.31 eV) synthesized under the same flame conditions. The change in the crystal phase, size, and band gap is attributed to replacement of titanium atoms by copper atoms in the TiO2 crystal.

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TEM images and particle size distributions of as synthesized Cu-doped TiO2 nanoparticles. (a) 1 wt.% Cu-TiO2 and (b) 15 wt.% Cu-TiO2. Inset is the HR-TEM image of the crystal fringes (test 1). Size distribution of particles is determined from measurement of 200 particles from representative TEM images (test 1B, F).
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Figure 3: TEM images and particle size distributions of as synthesized Cu-doped TiO2 nanoparticles. (a) 1 wt.% Cu-TiO2 and (b) 15 wt.% Cu-TiO2. Inset is the HR-TEM image of the crystal fringes (test 1). Size distribution of particles is determined from measurement of 200 particles from representative TEM images (test 1B, F).

Mentions: Figure 3 shows the TEM, HR-TEM images, and primary particle size distribution of 1 wt.% Cu-TiO2 (test 1B) and 15 wt.% Cu-TiO2 (test 1F) samples. The particle size distribution was obtained by measuring the diameter of 200 particles from representative TEM images. As shown in the size distribution of these samples (see Figure 3), the particles were spherical and size decreased with increasing doping concentration. The geometric mean primary particle size obtained at 1 wt.% doping was approximately 47 nm compared to approximately 33 nm obtained at 15 wt.% doping. The peak broadening observed in XRD pattern (see Figure 4) also qualitatively explained the change in particle size and lattice expansion with doping. The crystallite size was estimated from the XRD pattern obtained using Scherrer formula. The crystallite size obtained at 1 wt.% doping was 33 nm compared to 25 and 23 nm at 5 and 15-wt.% doping concentration. It is important to note that crystallite size estimation from XRD is different from the particle size observed from the microscopic analysis. XRD measures the size of the small domains within the grains and one particle may consist of several crystallites based on the preparation methods [31]. The decreased particle size with increasing doping concentration is due to the inhibition of the grain growth. As evident from the HR-TEM images of the 15 wt.% Cu-TiO2 (see Figure 3), an enhanced amorphous layer is observed on the surface. The excess CuO monomers condense on to the existing Cu-doped TiO2 particles. Thus, particle crystallinity decreases and also prevents grain growth. Wang et al. [22] observed an amorphous crystal structure and decreased grain size with an increasing Fe2+/Ti4+ ratios consistent with our Cu-doped TiO2 materials. Reduction in size was also observed when Li et al. [3] synthesized Zn-doped SnO2 nanomaterials. Norris et al. [27] proposed a process called self-purification by which dopants diffuse from inside to the surface sites of TiO2 nanocrystals. This change in particle size with doping concentration is fundamentally a very important phenomenon for electronic structure modification. These results indicate that the particle size of the Cu-doped TiO2 can be controlled by manipulating the dopant concentration in addition to the methods demonstrated by other researchers by controlling the precursor feed concentration and residence time of the particle in the high-temperature flame [26,32].


Single-step processing of copper-doped titania nanomaterials in a flame aerosol reactor.

Sahu M, Biswas P - Nanoscale Res Lett (2011)

TEM images and particle size distributions of as synthesized Cu-doped TiO2 nanoparticles. (a) 1 wt.% Cu-TiO2 and (b) 15 wt.% Cu-TiO2. Inset is the HR-TEM image of the crystal fringes (test 1). Size distribution of particles is determined from measurement of 200 particles from representative TEM images (test 1B, F).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211860&req=5

Figure 3: TEM images and particle size distributions of as synthesized Cu-doped TiO2 nanoparticles. (a) 1 wt.% Cu-TiO2 and (b) 15 wt.% Cu-TiO2. Inset is the HR-TEM image of the crystal fringes (test 1). Size distribution of particles is determined from measurement of 200 particles from representative TEM images (test 1B, F).
Mentions: Figure 3 shows the TEM, HR-TEM images, and primary particle size distribution of 1 wt.% Cu-TiO2 (test 1B) and 15 wt.% Cu-TiO2 (test 1F) samples. The particle size distribution was obtained by measuring the diameter of 200 particles from representative TEM images. As shown in the size distribution of these samples (see Figure 3), the particles were spherical and size decreased with increasing doping concentration. The geometric mean primary particle size obtained at 1 wt.% doping was approximately 47 nm compared to approximately 33 nm obtained at 15 wt.% doping. The peak broadening observed in XRD pattern (see Figure 4) also qualitatively explained the change in particle size and lattice expansion with doping. The crystallite size was estimated from the XRD pattern obtained using Scherrer formula. The crystallite size obtained at 1 wt.% doping was 33 nm compared to 25 and 23 nm at 5 and 15-wt.% doping concentration. It is important to note that crystallite size estimation from XRD is different from the particle size observed from the microscopic analysis. XRD measures the size of the small domains within the grains and one particle may consist of several crystallites based on the preparation methods [31]. The decreased particle size with increasing doping concentration is due to the inhibition of the grain growth. As evident from the HR-TEM images of the 15 wt.% Cu-TiO2 (see Figure 3), an enhanced amorphous layer is observed on the surface. The excess CuO monomers condense on to the existing Cu-doped TiO2 particles. Thus, particle crystallinity decreases and also prevents grain growth. Wang et al. [22] observed an amorphous crystal structure and decreased grain size with an increasing Fe2+/Ti4+ ratios consistent with our Cu-doped TiO2 materials. Reduction in size was also observed when Li et al. [3] synthesized Zn-doped SnO2 nanomaterials. Norris et al. [27] proposed a process called self-purification by which dopants diffuse from inside to the surface sites of TiO2 nanocrystals. This change in particle size with doping concentration is fundamentally a very important phenomenon for electronic structure modification. These results indicate that the particle size of the Cu-doped TiO2 can be controlled by manipulating the dopant concentration in addition to the methods demonstrated by other researchers by controlling the precursor feed concentration and residence time of the particle in the high-temperature flame [26,32].

Bottom Line: This has been feasible by a detailed understanding of the formation and growth of nanoparticles in the high-temperature flame region.Annealing the Cu-doped TiO2 nanoparticles increased the crystalline nature and changed the morphology from spherical to hexagonal structure.Measurements indicate a band gap narrowing by 0.8 eV (2.51 eV) was achieved at 15-wt.% copper dopant concentration compared to pristine TiO2 (3.31 eV) synthesized under the same flame conditions.

View Article: PubMed Central - HTML - PubMed

Affiliation: Aerosol and Air Quality Research Laboratory, Department of Energy, Environmental and Chemical Engineering, Washington University in St, Louis, St, Louis, MO 63130, USA. pbiswas@wustl.edu.

ABSTRACT
Synthesis and characterization of long wavelength visible-light absorption Cu-doped TiO2 nanomaterials with well-controlled properties such as size, composition, morphology, and crystal phase have been demonstrated in a single-step flame aerosol reactor. This has been feasible by a detailed understanding of the formation and growth of nanoparticles in the high-temperature flame region. The important process parameters controlled were: molar feed ratios of precursors, temperature, and residence time in the high-temperature flame region. The ability to vary the crystal phase of the doped nanomaterials while keeping the primary particle size constant has been demonstrated. Results indicate that increasing the copper dopant concentration promotes an anatase to rutile phase transformation, decreased crystalline nature and primary particle size, and better suspension stability. Annealing the Cu-doped TiO2 nanoparticles increased the crystalline nature and changed the morphology from spherical to hexagonal structure. Measurements indicate a band gap narrowing by 0.8 eV (2.51 eV) was achieved at 15-wt.% copper dopant concentration compared to pristine TiO2 (3.31 eV) synthesized under the same flame conditions. The change in the crystal phase, size, and band gap is attributed to replacement of titanium atoms by copper atoms in the TiO2 crystal.

No MeSH data available.


Related in: MedlinePlus