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Photo-catalytic activity of Zn1-xMnxS nanocrystals synthesized by wet chemical technique.

Chitkara M, Singh K, Sandhu IS, Bhatti HS - Nanoscale Res Lett (2011)

Bottom Line: Atomic absorption spectrometer has been used for qualitative and quantitative analysis of synthesized nanomaterials.Energy resolved luminescence spectra have been recorded for the detailed description of radiative and non-radiative recombination mechanisms.Photo-catalytic activity dependence on dopant concentration and luminescence quantum yield has been studied in detail.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, Punjabi University, Patiala, Punjab 147 002, India. dhaliwalkaramjit@gmail.com.

ABSTRACT
Polyvinyl pyrrolidone capped Zn1-xMnxS (0 ≤ x ≤ 0.1) nanocrystals have been synthesized using wet chemical co-precipitation method. Crystallographic and morphological characterization of the synthesized materials have been done using X-ray diffraction and transmission electron microscope. Crystallographic studies show the zinc blende crystals having average crystallite size approx. 3 nm, which is almost similar to the average particle size calculated from electron micrographs. Atomic absorption spectrometer has been used for qualitative and quantitative analysis of synthesized nanomaterials. Photo-catalytic activity has been studied using methylene blue dye as a test contaminant. Energy resolved luminescence spectra have been recorded for the detailed description of radiative and non-radiative recombination mechanisms. Photo-catalytic activity dependence on dopant concentration and luminescence quantum yield has been studied in detail.

No MeSH data available.


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Photodegradation of MB dye with time.
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Figure 7: Photodegradation of MB dye with time.

Mentions: Figure 7 shows the Zn1-xMnxS (0 ≤ x ≤ 0.1) nanocrystals sensitized photo-degradation of MB dye under UV-radiation exposure. It can be clearly seen that MB dye is degraded to maximum extent in case of Zn0.9900Mn0.0100S nanocrystals, whereas it is degraded to minimum extent for Zn0.9000Mn0.1000S nanophoto-catalyst. Photoredox chemistry occurring at nanocrystal surface emanates from trapped charge carriers. Incorporation of Mn2+ in ZnS nanocrystal lattice significantly influences the photo-catalytic activity. Addition of Mn2+ ions lengthens the lifetime of excited charge carriers, which results the enhanced photo-catalytic activity. Various charge carrier recombination and charge carrier trapping processes are shown in Figure 5. The competition between the charge carrier recombination and charge carrier trapping followed by the competition between recombination of trapped carriers and interfacial charge transfer determine the overall quantum efficiency for interfacial charge transfer. Doping of Mn2+ up to optimal concentration increases the interfacial charge transfer probability, due to which photo-catalytic activity of ZnS nanocrystals is enhanced. As shown in Figure 7, photo-catalytic activity enhances with increasing value of 'x' only in the range x = 0 to x = 0.01, further increase of dopant concentration, i.e., x = 0.01 to x = 0.1 deteriorates photo-catalytic activity of Zn1-xMnxS nanocrystals. It is due to the fact that up to optimal Mn2+ concentration (x = 0.01), Mn2+ ions lengthens the charge carrier recombination, but at higher dopant concentrations although the possibility of charge carrier trapping is high, but the charge carriers may recombine through quantum tunneling. Moreover, increasing concentration of Mn2+ ions may cause the increased interaction between neighboring Zn2+ ions and the Mn2+ luminescence centre that enhances the spin-orbit coupling of Mn2+ ions, which leads to the relaxation of the spin selection rules [24]. This lowers the radiative recombination time for 4T1 →6A1 transitions, so the recombination of trapped carriers dominates interfacial charge transfer at the higher dopant concentrations. Due to enhanced recombination rate luminescence quantum yield increases to large extent as shown in Figure 4. Figure 8 shows the absorption spectrum of MB dye solution for different durations of UV-radiation exposure in the presence of Zn0.9900Mn0.0100S nanocrystals (optimal dopant concentration). Zn0.9900Mn0.0100S nanocrystal photo-catalyst is efficiently degrading the dye, only negligible amount of dye is present in the solution after 80 min. There is a concentration dependent slight spectral shift in MB dye absorption spectra as the UV irradiation time changes from 0 to 80 min. Red shift in the absorption peak with increasing dye concentration has been observed due to augmented optical density. Moreover, at higher concentrations, aggregation can take place, which affects the optical behaviour. These non-toxic, stable, inexpensive nanocrystalline photo-catalyst having high-redox potentials can be efficiently used for environmental cleaning, water purification, and H2 production. Moreover, due to non-dissolving nature in aqueous media, these photo-catalysts can be easily recovered after use.


Photo-catalytic activity of Zn1-xMnxS nanocrystals synthesized by wet chemical technique.

Chitkara M, Singh K, Sandhu IS, Bhatti HS - Nanoscale Res Lett (2011)

Photodegradation of MB dye with time.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211856&req=5

Figure 7: Photodegradation of MB dye with time.
Mentions: Figure 7 shows the Zn1-xMnxS (0 ≤ x ≤ 0.1) nanocrystals sensitized photo-degradation of MB dye under UV-radiation exposure. It can be clearly seen that MB dye is degraded to maximum extent in case of Zn0.9900Mn0.0100S nanocrystals, whereas it is degraded to minimum extent for Zn0.9000Mn0.1000S nanophoto-catalyst. Photoredox chemistry occurring at nanocrystal surface emanates from trapped charge carriers. Incorporation of Mn2+ in ZnS nanocrystal lattice significantly influences the photo-catalytic activity. Addition of Mn2+ ions lengthens the lifetime of excited charge carriers, which results the enhanced photo-catalytic activity. Various charge carrier recombination and charge carrier trapping processes are shown in Figure 5. The competition between the charge carrier recombination and charge carrier trapping followed by the competition between recombination of trapped carriers and interfacial charge transfer determine the overall quantum efficiency for interfacial charge transfer. Doping of Mn2+ up to optimal concentration increases the interfacial charge transfer probability, due to which photo-catalytic activity of ZnS nanocrystals is enhanced. As shown in Figure 7, photo-catalytic activity enhances with increasing value of 'x' only in the range x = 0 to x = 0.01, further increase of dopant concentration, i.e., x = 0.01 to x = 0.1 deteriorates photo-catalytic activity of Zn1-xMnxS nanocrystals. It is due to the fact that up to optimal Mn2+ concentration (x = 0.01), Mn2+ ions lengthens the charge carrier recombination, but at higher dopant concentrations although the possibility of charge carrier trapping is high, but the charge carriers may recombine through quantum tunneling. Moreover, increasing concentration of Mn2+ ions may cause the increased interaction between neighboring Zn2+ ions and the Mn2+ luminescence centre that enhances the spin-orbit coupling of Mn2+ ions, which leads to the relaxation of the spin selection rules [24]. This lowers the radiative recombination time for 4T1 →6A1 transitions, so the recombination of trapped carriers dominates interfacial charge transfer at the higher dopant concentrations. Due to enhanced recombination rate luminescence quantum yield increases to large extent as shown in Figure 4. Figure 8 shows the absorption spectrum of MB dye solution for different durations of UV-radiation exposure in the presence of Zn0.9900Mn0.0100S nanocrystals (optimal dopant concentration). Zn0.9900Mn0.0100S nanocrystal photo-catalyst is efficiently degrading the dye, only negligible amount of dye is present in the solution after 80 min. There is a concentration dependent slight spectral shift in MB dye absorption spectra as the UV irradiation time changes from 0 to 80 min. Red shift in the absorption peak with increasing dye concentration has been observed due to augmented optical density. Moreover, at higher concentrations, aggregation can take place, which affects the optical behaviour. These non-toxic, stable, inexpensive nanocrystalline photo-catalyst having high-redox potentials can be efficiently used for environmental cleaning, water purification, and H2 production. Moreover, due to non-dissolving nature in aqueous media, these photo-catalysts can be easily recovered after use.

Bottom Line: Atomic absorption spectrometer has been used for qualitative and quantitative analysis of synthesized nanomaterials.Energy resolved luminescence spectra have been recorded for the detailed description of radiative and non-radiative recombination mechanisms.Photo-catalytic activity dependence on dopant concentration and luminescence quantum yield has been studied in detail.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, Punjabi University, Patiala, Punjab 147 002, India. dhaliwalkaramjit@gmail.com.

ABSTRACT
Polyvinyl pyrrolidone capped Zn1-xMnxS (0 ≤ x ≤ 0.1) nanocrystals have been synthesized using wet chemical co-precipitation method. Crystallographic and morphological characterization of the synthesized materials have been done using X-ray diffraction and transmission electron microscope. Crystallographic studies show the zinc blende crystals having average crystallite size approx. 3 nm, which is almost similar to the average particle size calculated from electron micrographs. Atomic absorption spectrometer has been used for qualitative and quantitative analysis of synthesized nanomaterials. Photo-catalytic activity has been studied using methylene blue dye as a test contaminant. Energy resolved luminescence spectra have been recorded for the detailed description of radiative and non-radiative recombination mechanisms. Photo-catalytic activity dependence on dopant concentration and luminescence quantum yield has been studied in detail.

No MeSH data available.


Related in: MedlinePlus