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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.

No MeSH data available.


Related in: MedlinePlus

Cu-doped TiO2 nanoparticles formation mechanisms in a FLAR. Top represents TiO2 formation mechanism, middle is for low copper dopant concentration and bottom is for high dopant concentration.
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Figure 2: Cu-doped TiO2 nanoparticles formation mechanisms in a FLAR. Top represents TiO2 formation mechanism, middle is for low copper dopant concentration and bottom is for high dopant concentration.

Mentions: The proposed Cu-doped TiO2 particle formation mechanism is illustrated in Figure 2. This is similar to the pathways proposed by Basak [24] for multi-component nanomaterial systems. To understand the formation mechanism of the Cu-doped TiO2 nanoparticles in the flame aerosol reactor, pristine TiO2 was synthesized first using TTIP only as the precursor. TTIP decomposes to form TiO2 monomers, which then undergo subsequent growth by collision followed by sintering to form nanoparticles (test 1A). For synthesizing Cu-doped TiO2 particles, both the TTIP and copper nitrate precursor are fed to the high-temperature flame. The nanoparticle properties such as size and composition depend on the relative decomposition kinetics and molar feed ratios of the precursors (see Figure 2). The decomposition rate of TTIP is given by, ka = 3.96 × 105 exp((-7.05 × 104)/RTs-1 [29]. Since the kinetic data for copper nitrate precursor is not available, the decomposition rate reported for copper acetyl acetonate was assumed (kb = 3.02 × 107 exp((-1.15 × 105)/RT)s-1) [30]. The two precursors form TiO2 (formed from TTIP molecular decomposition) and CuO (formed by decomposition of copper nitrate followed by evaporation) monomers at similar time instants as their decomposition rates are similar (k1, Cu /k1, Ti to approximately 5, at 2,200°C). Depending on the molar feed ratio of the precursors, a variety of morphologies can be formed, ranging from particles consisting of only copper oxide, particles of only TiO2, and the particles of mixed TiO2 and CuO. At low copper concentrations (1-5 wt.%), CuO monomers are readily incorporated into the higher concentration TiO2 clusters by a scavenging process. This is similar to the phenomenon demonstrated by Wang et al. [22]. Subsequent collisional growth and sintering result in a homogenous mix of Cu-doped TiO2 particles. However, at higher Cu feed concentration (approximately 15wt%), apart from the collision and sintering of the CuO monomers and TiO2 clusters, some of the CuO oxide monomers also condense onto the formed Cu-doped TiO2 particles. The HR-TEM image of the synthesized 15-wt.% Cu-TiO2 nanoparticles indicates regions of amorphous CuO on the particle surface. The explanation of CuO monomer condensation on the particle surface is thus corroborated (test 1F). The nanomaterials synthesized at various dopant concentration were verified by single particle EDS analysis to be comprised of both copper and titania. No particles were found consisting of only Ti or only copper species.


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

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

Cu-doped TiO2 nanoparticles formation mechanisms in a FLAR. Top represents TiO2 formation mechanism, middle is for low copper dopant concentration and bottom is for high dopant concentration.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Cu-doped TiO2 nanoparticles formation mechanisms in a FLAR. Top represents TiO2 formation mechanism, middle is for low copper dopant concentration and bottom is for high dopant concentration.
Mentions: The proposed Cu-doped TiO2 particle formation mechanism is illustrated in Figure 2. This is similar to the pathways proposed by Basak [24] for multi-component nanomaterial systems. To understand the formation mechanism of the Cu-doped TiO2 nanoparticles in the flame aerosol reactor, pristine TiO2 was synthesized first using TTIP only as the precursor. TTIP decomposes to form TiO2 monomers, which then undergo subsequent growth by collision followed by sintering to form nanoparticles (test 1A). For synthesizing Cu-doped TiO2 particles, both the TTIP and copper nitrate precursor are fed to the high-temperature flame. The nanoparticle properties such as size and composition depend on the relative decomposition kinetics and molar feed ratios of the precursors (see Figure 2). The decomposition rate of TTIP is given by, ka = 3.96 × 105 exp((-7.05 × 104)/RTs-1 [29]. Since the kinetic data for copper nitrate precursor is not available, the decomposition rate reported for copper acetyl acetonate was assumed (kb = 3.02 × 107 exp((-1.15 × 105)/RT)s-1) [30]. The two precursors form TiO2 (formed from TTIP molecular decomposition) and CuO (formed by decomposition of copper nitrate followed by evaporation) monomers at similar time instants as their decomposition rates are similar (k1, Cu /k1, Ti to approximately 5, at 2,200°C). Depending on the molar feed ratio of the precursors, a variety of morphologies can be formed, ranging from particles consisting of only copper oxide, particles of only TiO2, and the particles of mixed TiO2 and CuO. At low copper concentrations (1-5 wt.%), CuO monomers are readily incorporated into the higher concentration TiO2 clusters by a scavenging process. This is similar to the phenomenon demonstrated by Wang et al. [22]. Subsequent collisional growth and sintering result in a homogenous mix of Cu-doped TiO2 particles. However, at higher Cu feed concentration (approximately 15wt%), apart from the collision and sintering of the CuO monomers and TiO2 clusters, some of the CuO oxide monomers also condense onto the formed Cu-doped TiO2 particles. The HR-TEM image of the synthesized 15-wt.% Cu-TiO2 nanoparticles indicates regions of amorphous CuO on the particle surface. The explanation of CuO monomer condensation on the particle surface is thus corroborated (test 1F). The nanomaterials synthesized at various dopant concentration were verified by single particle EDS analysis to be comprised of both copper and titania. No particles were found consisting of only Ti or only copper species.

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