Limits...
CdSe/TiO2 core-shell nanoparticles produced in AOT reverse micelles: applications in pollutant photodegradation using visible light.

Fontes Garcia AM, Fernandes MS, Coutinho PJ - Nanoscale Res Lett (2011)

Bottom Line: CdSe quantum dots with a prominent band-edge photoluminescence were obtained by a soft AOT water-in-oil (w/o) microemulsion templating method with an estimated size of 2.7 nm.The CdSe particles were covered with a TiO2 layer using an intermediate SiO2 coupling reagent by a sol-gel process.The resulting CdSe/TiO2 core/shell nanoparticles showed appreciable photocatalytic activity at λ = 405 nm which can only originate because of electron injection from the conduction band of CdSe to that of TiO2.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre of Physics (CFUM), University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal. pcoutinho@fisica.uminho.pt.

ABSTRACT
CdSe quantum dots with a prominent band-edge photoluminescence were obtained by a soft AOT water-in-oil (w/o) microemulsion templating method with an estimated size of 2.7 nm. The CdSe particles were covered with a TiO2 layer using an intermediate SiO2 coupling reagent by a sol-gel process. The resulting CdSe/TiO2 core/shell nanoparticles showed appreciable photocatalytic activity at λ = 405 nm which can only originate because of electron injection from the conduction band of CdSe to that of TiO2.

No MeSH data available.


Related in: MedlinePlus

Photodegradation kinetics of MB using either Degussa TiO2 at 340 nm (open circles) and 405 nm (filled circles) or CdSe/TiO2 core-shell nanoparticles at 340 nm (open square) and 405 nm (filled square). The lines represent first-order exponential kinetics. Control experiments without any photocatalyst at 340 nm (open triangle) and 405 nm (filled triangle) are also shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3211843&req=5

Figure 5: Photodegradation kinetics of MB using either Degussa TiO2 at 340 nm (open circles) and 405 nm (filled circles) or CdSe/TiO2 core-shell nanoparticles at 340 nm (open square) and 405 nm (filled square). The lines represent first-order exponential kinetics. Control experiments without any photocatalyst at 340 nm (open triangle) and 405 nm (filled triangle) are also shown.

Mentions: In Figure 4, the photodegradation of MB effected by the prepared CdSe/TiO2 core shell nanoparticles is shown. The fraction of the remaining MB in each irradiation time is obtained by subtracting the background from dispersion and comparing the 665 nm absorption peak with the spectrum of pure MB in aqueous solution. The results are shown in Figure 5 for the CdSe/TiO2 nanoparticles and for commercial TiO2 Degussa (25 nm TiO2 nanoparticles) at 340 and 405 nm. The lines represent an exponential decay of MB concentration corresponding to a first-order kinetics. As expected, plain TiO2 shows a very inefficient photodegradation rate at 405 nm irradiation. However, at 340 nm, a wavelength well below TiO2 band gap, the photodegradation occurs at a rate of 7.0 × 10-3 min-1. CdSe/TiO2 shows a photodegradation rate of 2.7 × 10-3 min-1 at 405 nm. At 340 nm, a biphasic behaviour occurs at a very fast initial photodegradation rate of 4.0 × 10-2 min-1 followed by slower process at a rate of 3.9 × 10-3 min-1. As the TiO2 shell cannot absorb blue light, the observed photodegradation process at 405 nm must originate from absorption caused by the CdSe core. This process could be occurring in remaining CdSe QDs that did not couple with TiO2 by the sol-gel process [6]. However, the lack of PL contradicts this possibility. On the other hand, if only plain TiO2 particles were responsible for the photocatalytic effect, then the dependence of the remaining MB fraction on irradiation time at 340 nm should be similar for Degussa TiO2 and CdSe/TiO2. This similarity was not observed, as also confirmed in Figure 5, with the photodegradation efficiency of the core-shell nanoparticles being higher than that of Degussa TiO2. Thus, we have strong indications that a synergistic effect exists between CdSe and TiO2 in the prepared nanoparticles. This effect has been reported in the photoreduction of methyl viologen by CdSe and TiO2 nanoparticles confined in the aqueous pools of AOT reversed micelles [7]. A possible mechanism for the photodegradation of MB mediated by CdSe in core-shell CdSe/TiO2 involves an electron transfer step from the conduction band of excited CdSe to the conduction band of TiO2. This electron may reduce oxygen-generating superoxide anion radical (O2•-) that in turn may originate OH• radicals. These highly reactive oxygen species can then oxidize MB resulting in its decomposition. The resulting hole in CdSe must be filled to regenerate the catalyst. This can also be accomplished by superoxide radical acting as a reductant and regenerating O2.


CdSe/TiO2 core-shell nanoparticles produced in AOT reverse micelles: applications in pollutant photodegradation using visible light.

Fontes Garcia AM, Fernandes MS, Coutinho PJ - Nanoscale Res Lett (2011)

Photodegradation kinetics of MB using either Degussa TiO2 at 340 nm (open circles) and 405 nm (filled circles) or CdSe/TiO2 core-shell nanoparticles at 340 nm (open square) and 405 nm (filled square). The lines represent first-order exponential kinetics. Control experiments without any photocatalyst at 340 nm (open triangle) and 405 nm (filled triangle) are also shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211843&req=5

Figure 5: Photodegradation kinetics of MB using either Degussa TiO2 at 340 nm (open circles) and 405 nm (filled circles) or CdSe/TiO2 core-shell nanoparticles at 340 nm (open square) and 405 nm (filled square). The lines represent first-order exponential kinetics. Control experiments without any photocatalyst at 340 nm (open triangle) and 405 nm (filled triangle) are also shown.
Mentions: In Figure 4, the photodegradation of MB effected by the prepared CdSe/TiO2 core shell nanoparticles is shown. The fraction of the remaining MB in each irradiation time is obtained by subtracting the background from dispersion and comparing the 665 nm absorption peak with the spectrum of pure MB in aqueous solution. The results are shown in Figure 5 for the CdSe/TiO2 nanoparticles and for commercial TiO2 Degussa (25 nm TiO2 nanoparticles) at 340 and 405 nm. The lines represent an exponential decay of MB concentration corresponding to a first-order kinetics. As expected, plain TiO2 shows a very inefficient photodegradation rate at 405 nm irradiation. However, at 340 nm, a wavelength well below TiO2 band gap, the photodegradation occurs at a rate of 7.0 × 10-3 min-1. CdSe/TiO2 shows a photodegradation rate of 2.7 × 10-3 min-1 at 405 nm. At 340 nm, a biphasic behaviour occurs at a very fast initial photodegradation rate of 4.0 × 10-2 min-1 followed by slower process at a rate of 3.9 × 10-3 min-1. As the TiO2 shell cannot absorb blue light, the observed photodegradation process at 405 nm must originate from absorption caused by the CdSe core. This process could be occurring in remaining CdSe QDs that did not couple with TiO2 by the sol-gel process [6]. However, the lack of PL contradicts this possibility. On the other hand, if only plain TiO2 particles were responsible for the photocatalytic effect, then the dependence of the remaining MB fraction on irradiation time at 340 nm should be similar for Degussa TiO2 and CdSe/TiO2. This similarity was not observed, as also confirmed in Figure 5, with the photodegradation efficiency of the core-shell nanoparticles being higher than that of Degussa TiO2. Thus, we have strong indications that a synergistic effect exists between CdSe and TiO2 in the prepared nanoparticles. This effect has been reported in the photoreduction of methyl viologen by CdSe and TiO2 nanoparticles confined in the aqueous pools of AOT reversed micelles [7]. A possible mechanism for the photodegradation of MB mediated by CdSe in core-shell CdSe/TiO2 involves an electron transfer step from the conduction band of excited CdSe to the conduction band of TiO2. This electron may reduce oxygen-generating superoxide anion radical (O2•-) that in turn may originate OH• radicals. These highly reactive oxygen species can then oxidize MB resulting in its decomposition. The resulting hole in CdSe must be filled to regenerate the catalyst. This can also be accomplished by superoxide radical acting as a reductant and regenerating O2.

Bottom Line: CdSe quantum dots with a prominent band-edge photoluminescence were obtained by a soft AOT water-in-oil (w/o) microemulsion templating method with an estimated size of 2.7 nm.The CdSe particles were covered with a TiO2 layer using an intermediate SiO2 coupling reagent by a sol-gel process.The resulting CdSe/TiO2 core/shell nanoparticles showed appreciable photocatalytic activity at λ = 405 nm which can only originate because of electron injection from the conduction band of CdSe to that of TiO2.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre of Physics (CFUM), University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal. pcoutinho@fisica.uminho.pt.

ABSTRACT
CdSe quantum dots with a prominent band-edge photoluminescence were obtained by a soft AOT water-in-oil (w/o) microemulsion templating method with an estimated size of 2.7 nm. The CdSe particles were covered with a TiO2 layer using an intermediate SiO2 coupling reagent by a sol-gel process. The resulting CdSe/TiO2 core/shell nanoparticles showed appreciable photocatalytic activity at λ = 405 nm which can only originate because of electron injection from the conduction band of CdSe to that of TiO2.

No MeSH data available.


Related in: MedlinePlus