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Supported quantum clusters of silver as enhanced catalysts for reduction.

Leelavathi A, Bhaskara Rao TU, Pradeep T - Nanoscale Res Lett (2011)

Bottom Line: We used the conversion of nitro group to amino group as a model reaction to study the catalytic reduction activity of the QCs.The turn-over frequency was 1.87 s-1 per cluster for the reduction of 4-np at 35°C.Among the substrates investigated, the kinetics followed the order, SiO2 > TiO2 > Fe2O3 > Al2O3.

View Article: PubMed Central - HTML - PubMed

Affiliation: DST Unit of Nanoscience (DST UNS), Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India. pradeep@iitm.ac.in.

ABSTRACT
Quantum clusters (QCs) of silver such as Ag7(H2MSA)7, Ag8(H2MSA)8 (H2MSA, mercaptosuccinic acid) were synthesized by the interfacial etching of Ag nanoparticle precursors and were loaded on metal oxide supports to prepare active catalysts. The supported clusters were characterized using high resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and laser desorption ionization mass spectrometry. We used the conversion of nitro group to amino group as a model reaction to study the catalytic reduction activity of the QCs. Various aromatic nitro compounds, namely, 3-nitrophenol (3-np), 4-nitrophenol (4-np), 3-nitroaniline (3-na), and 4-nitroaniline (4-na) were used as substrates. Products were confirmed using UV-visible spectroscopy and electrospray ionization mass spectrometry. The supported QCs remained active and were reused several times after separation. The rate constant suggested that the reaction followed pseudo-first-order kinetics. The turn-over frequency was 1.87 s-1 per cluster for the reduction of 4-np at 35°C. Among the substrates investigated, the kinetics followed the order, SiO2 > TiO2 > Fe2O3 > Al2O3.

No MeSH data available.


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UV-vis spectrum and luminescence spectra of the QC solution. (A) UV-vis spectrum of Ag7,8 QCs. Inset of (a) shows the corresponding luminescence spectrum collected at 273 K along with a photograph of the red emitting crude cluster solution under UV-lamp at 273 K. (b) Decreasing intensity of luminescence spectra of the QC solution with increase in time, after alumina powders were added. Photograph in the inset shows the decrease in the intensity of the color of the solution with time as clusters are loaded on alumina (under white light illumination).
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Figure 1: UV-vis spectrum and luminescence spectra of the QC solution. (A) UV-vis spectrum of Ag7,8 QCs. Inset of (a) shows the corresponding luminescence spectrum collected at 273 K along with a photograph of the red emitting crude cluster solution under UV-lamp at 273 K. (b) Decreasing intensity of luminescence spectra of the QC solution with increase in time, after alumina powders were added. Photograph in the inset shows the decrease in the intensity of the color of the solution with time as clusters are loaded on alumina (under white light illumination).

Mentions: The as-synthesized QCs of Ag were characterized by optical absorption studies. The corresponding absorption spectra are shown in Figure 1a, and the peak around 550 nm is due to HOMO-LUMO transitions from the 4d valence band to the 5sp conduction band-derived states of QCs [34,38,39]. These were observed after 48 h of etching process [34] and the absence of nanoparticles was confirmed using high resolution transmission electron microscopy of the etched materials. This confirmed that the peak around 550 nm was due to clusters. Inset of Figure 1a shows the photoluminescence spectrum of Ag7,8 QCs having an excitation at 675 nm and emission at 772 nm; these data were collected at 273 K, and the photograph in the inset corresponds to red emission from the as-prepared crude mixture of the QC solutions under UV light irradiation. Figure 1b shows that the emission intensity of the solution decreased with the addition of alumina powder. As QCs got coated on alumina, the concentration of QCs in the solution decreases, and finally, the solution turned colorless as shown in the inset of Figure 1b.


Supported quantum clusters of silver as enhanced catalysts for reduction.

Leelavathi A, Bhaskara Rao TU, Pradeep T - Nanoscale Res Lett (2011)

UV-vis spectrum and luminescence spectra of the QC solution. (A) UV-vis spectrum of Ag7,8 QCs. Inset of (a) shows the corresponding luminescence spectrum collected at 273 K along with a photograph of the red emitting crude cluster solution under UV-lamp at 273 K. (b) Decreasing intensity of luminescence spectra of the QC solution with increase in time, after alumina powders were added. Photograph in the inset shows the decrease in the intensity of the color of the solution with time as clusters are loaded on alumina (under white light illumination).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211169&req=5

Figure 1: UV-vis spectrum and luminescence spectra of the QC solution. (A) UV-vis spectrum of Ag7,8 QCs. Inset of (a) shows the corresponding luminescence spectrum collected at 273 K along with a photograph of the red emitting crude cluster solution under UV-lamp at 273 K. (b) Decreasing intensity of luminescence spectra of the QC solution with increase in time, after alumina powders were added. Photograph in the inset shows the decrease in the intensity of the color of the solution with time as clusters are loaded on alumina (under white light illumination).
Mentions: The as-synthesized QCs of Ag were characterized by optical absorption studies. The corresponding absorption spectra are shown in Figure 1a, and the peak around 550 nm is due to HOMO-LUMO transitions from the 4d valence band to the 5sp conduction band-derived states of QCs [34,38,39]. These were observed after 48 h of etching process [34] and the absence of nanoparticles was confirmed using high resolution transmission electron microscopy of the etched materials. This confirmed that the peak around 550 nm was due to clusters. Inset of Figure 1a shows the photoluminescence spectrum of Ag7,8 QCs having an excitation at 675 nm and emission at 772 nm; these data were collected at 273 K, and the photograph in the inset corresponds to red emission from the as-prepared crude mixture of the QC solutions under UV light irradiation. Figure 1b shows that the emission intensity of the solution decreased with the addition of alumina powder. As QCs got coated on alumina, the concentration of QCs in the solution decreases, and finally, the solution turned colorless as shown in the inset of Figure 1b.

Bottom Line: We used the conversion of nitro group to amino group as a model reaction to study the catalytic reduction activity of the QCs.The turn-over frequency was 1.87 s-1 per cluster for the reduction of 4-np at 35°C.Among the substrates investigated, the kinetics followed the order, SiO2 > TiO2 > Fe2O3 > Al2O3.

View Article: PubMed Central - HTML - PubMed

Affiliation: DST Unit of Nanoscience (DST UNS), Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India. pradeep@iitm.ac.in.

ABSTRACT
Quantum clusters (QCs) of silver such as Ag7(H2MSA)7, Ag8(H2MSA)8 (H2MSA, mercaptosuccinic acid) were synthesized by the interfacial etching of Ag nanoparticle precursors and were loaded on metal oxide supports to prepare active catalysts. The supported clusters were characterized using high resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and laser desorption ionization mass spectrometry. We used the conversion of nitro group to amino group as a model reaction to study the catalytic reduction activity of the QCs. Various aromatic nitro compounds, namely, 3-nitrophenol (3-np), 4-nitrophenol (4-np), 3-nitroaniline (3-na), and 4-nitroaniline (4-na) were used as substrates. Products were confirmed using UV-visible spectroscopy and electrospray ionization mass spectrometry. The supported QCs remained active and were reused several times after separation. The rate constant suggested that the reaction followed pseudo-first-order kinetics. The turn-over frequency was 1.87 s-1 per cluster for the reduction of 4-np at 35°C. Among the substrates investigated, the kinetics followed the order, SiO2 > TiO2 > Fe2O3 > Al2O3.

No MeSH data available.


Related in: MedlinePlus