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Photo-catalytic activities of plant hormones on semiconductor nanoparticles by laser-activated electron tunneling and emitting.

Tang X, Huang L, Zhang W, Jiang R, Zhong H - Sci Rep (2015)

Bottom Line: Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules.We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors.By using this approach, photo-activities of phytohormones have been investigated.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Pesticides and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan, Hubei 430079, P. R. China.

ABSTRACT
Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO₂), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi₂O₃)₀.₀₇(CoO)₀.₀₃(ZnO)₀.₉ semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated.

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Related in: MedlinePlus

Mass spectrum of photo-catalytic polymerization of SA on surfaces of bismuth cobalt zinc oxide nanoparticles (A) and formation of negatively charged dimeric (B), trimeric (C) and tetrameric (D) ions.
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f5: Mass spectrum of photo-catalytic polymerization of SA on surfaces of bismuth cobalt zinc oxide nanoparticles (A) and formation of negatively charged dimeric (B), trimeric (C) and tetrameric (D) ions.

Mentions: While photo-catalytic dissociation reactions have been extensively studied, less attention has been paid to photo-catalytic polymerization in the past. We provide here experimental evidences that can demonstrate the formation of dimeric, trimeric and tetrameric ions of salicylic acid (SA) on the solid surfaces of (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor instead of gas phase. As shown in Figure 5 (A), in addition to the molecular ion at m/z 137 as well as other low abundance peaks at m/z 241 and 361, an ion at m/z 481 dominates the mass spectrum. These peaks were considered as the results of photo-catalytic polymerization and the mechanisms were interpreted as Figure 5 (B), (C) and (D) for the formation of dimeric, trimeric and tetrameric ions of SA respectively. Presence of benzene ring in SA makes it have strong absorption in UV region shown in Supplementary Figure 1 (B). Formation of ester bonds between OH and COOH results in the linkage of two, three or four neutral salicylic acids. As illustrated in Figure 5 (B–D), laser activated hot electrons can be captured by charge deficient carbon atoms of carboxylic groups of the polymers of salicylic acid. Subsequent tandem processes include unpaired electron-directed intermolecular substitutions and the formation of negatively charged poly-membered rings with the loss of OH radical ions. The ion at m/z 481 is the largest macrocyclic ion we have detected so far. It shows the strongest stability among all these macrocyclic ions. Ion mobility experiments demonstrate that these ions have different collision cross sections as shown in Supplementary Figure 6. In order to investigate if these ions were formed in the gas phase or on the solid surfaces of nanoparticles, different semiconductors have been studied. It was found that SA cannot undergo polymerization when TiO2 or ZnO material was used as shown in Supplementary Figure 7. This experimental result indicates that the photo-catalytic polymerization reaction indeed occurs on the solid surfaces. Dopping of Bi2O3 in ZnO changes the photo-catalytic properties.


Photo-catalytic activities of plant hormones on semiconductor nanoparticles by laser-activated electron tunneling and emitting.

Tang X, Huang L, Zhang W, Jiang R, Zhong H - Sci Rep (2015)

Mass spectrum of photo-catalytic polymerization of SA on surfaces of bismuth cobalt zinc oxide nanoparticles (A) and formation of negatively charged dimeric (B), trimeric (C) and tetrameric (D) ions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4352873&req=5

f5: Mass spectrum of photo-catalytic polymerization of SA on surfaces of bismuth cobalt zinc oxide nanoparticles (A) and formation of negatively charged dimeric (B), trimeric (C) and tetrameric (D) ions.
Mentions: While photo-catalytic dissociation reactions have been extensively studied, less attention has been paid to photo-catalytic polymerization in the past. We provide here experimental evidences that can demonstrate the formation of dimeric, trimeric and tetrameric ions of salicylic acid (SA) on the solid surfaces of (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor instead of gas phase. As shown in Figure 5 (A), in addition to the molecular ion at m/z 137 as well as other low abundance peaks at m/z 241 and 361, an ion at m/z 481 dominates the mass spectrum. These peaks were considered as the results of photo-catalytic polymerization and the mechanisms were interpreted as Figure 5 (B), (C) and (D) for the formation of dimeric, trimeric and tetrameric ions of SA respectively. Presence of benzene ring in SA makes it have strong absorption in UV region shown in Supplementary Figure 1 (B). Formation of ester bonds between OH and COOH results in the linkage of two, three or four neutral salicylic acids. As illustrated in Figure 5 (B–D), laser activated hot electrons can be captured by charge deficient carbon atoms of carboxylic groups of the polymers of salicylic acid. Subsequent tandem processes include unpaired electron-directed intermolecular substitutions and the formation of negatively charged poly-membered rings with the loss of OH radical ions. The ion at m/z 481 is the largest macrocyclic ion we have detected so far. It shows the strongest stability among all these macrocyclic ions. Ion mobility experiments demonstrate that these ions have different collision cross sections as shown in Supplementary Figure 6. In order to investigate if these ions were formed in the gas phase or on the solid surfaces of nanoparticles, different semiconductors have been studied. It was found that SA cannot undergo polymerization when TiO2 or ZnO material was used as shown in Supplementary Figure 7. This experimental result indicates that the photo-catalytic polymerization reaction indeed occurs on the solid surfaces. Dopping of Bi2O3 in ZnO changes the photo-catalytic properties.

Bottom Line: Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules.We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors.By using this approach, photo-activities of phytohormones have been investigated.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Pesticides and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan, Hubei 430079, P. R. China.

ABSTRACT
Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO₂), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi₂O₃)₀.₀₇(CoO)₀.₀₃(ZnO)₀.₉ semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated.

Show MeSH
Related in: MedlinePlus