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ABSTRACT: A unique nanocomposite C-TiO2 was prepared by the growth of TiO2 on carbon nanoparticles using a simple hydrothermal procedure. Transmission electron microscopic (TEM) measurements showed that the nanocomposites exhibited an average core diameter of approximately 5 nm with a rather well-defined lattice space (0.4 nm) that was somewhat larger than that (0.38 nm) of the (100) crystalline planes of anatase TiO2. This lattice expansion was accounted for by the formation of surface defect dipoles of the nanosized TiO2 particles. X-ray photoelectron spectroscopic (XPS) measurements suggested that partial charge transfer occurred from carbon nanoparticles to TiO2 by the interfacial Ti-O-C linkages, which led to effective diminishment of the C-TiO2 photoluminescence as compared to that of pure TiO2 or carbon nanoparticles, suggesting intimate electronic interactions between the carbon and TiO2 components in the nanocomposites. Such unique characteristics were then exploited for the effective photocatalytic degradation of organic pollutants, as exemplified by methylene blue, by C-TiO2 under UV photoirradiation. Experimental measurements showed that the photocatalytic activity of C-TiO2 nanocomposites was about twice that of TiO2 alone, whereas little activity was observed with carbon nanoparticles. This was attributed to the electron-accepting sites on the carbon nanoparticles that facilitated interfacial charge separation.
Nanoscale 05/2013; · 5.91 Impact Factor
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ABSTRACT: Bimetallic AgAu Janus nanoparticles were prepared by galvanic exchange reactions of 1-hexanethiolate-passivated silver (AgC6) nanoparticles with gold(I)-mercaptopropanediol complex. The AgC6 nanoparticles were deposited onto a solid substrate surface by the Langmuir-Blodgett method such that the galvanic exchange reactions were limited to the top face of the nanoparticles that was in direct contact with the gold(I) complex solution. The resulting nanoparticles exhibited an asymmetrical distribution not only of the organic capping ligands on the nanoparticle surface but also of the metal elements in the nanoparticle cores, in contrast to the bulk-exchange counterparts where these distributions were homogeneous within the nanoparticles, as manifested in contact angle, UV-vis, XPS, and TEM measurements. More interestingly, despite a minimal loading of Au onto the Ag nanoparticles, the bimetallic AgAu nanoparticles exhibited enhanced electrocatalytic activity in oxygen reduction reactions, as compared to the monometal AgC6 nanoparticles. Additionally, the electrocatalytic performance of the Janus nanoparticles was markedly better than the bulk-exchange ones, suggesting that the segregated distribution of the polar ligands from the apolar ones might further facilitate charge transfer from Ag to Au in the nanoparticle cores, leading to additional improvement of the adsorption and reduction of oxygen.
Langmuir 11/2012; · 4.19 Impact Factor
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ABSTRACT: Chlorophenyl-stabilized platinum nanoparticles (1.85 nm) exhibited electrocatalytic activity for oxygen reduction up to 3 times higher than that of commercial Pt/C catalysts. Similar enhancement was observed with naked Pt/C functionalized by the same chlorophenyl fragments, suggesting the important role of organic capping ligands in the manipulation of nanoparticle electrocatalytic performance.
Chemical Communications 04/2012; 48(28):3391-3. · 6.17 Impact Factor
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ABSTRACT: Water-soluble carbon nanoparticles were prepared by refluxing natural gas soot in concentrated nitric acid. The surface of the resulting nanoparticles was found to be decorated with a variety of oxygenated species, as suggested by spectroscopic measurements. Back potentiometric titration of the nanoparticles was employed to quantify the coverage of carboxylic, lactonic, and phenolic moieties on the particle surface by taking advantage of their vast difference of acidity (pK(a)). The results were largely consistent with those reported in previous studies with other carbonaceous (nano)materials. Additionally, the presence of ortho- and para-quinone moieties on the nanoparticle surface was confirmed by selective labelling with o-phenylenediamine, as manifested in X-ray photoelectron spectroscopy, photoluminescence, and electrochemical measurements. The results further supported the arguments that the surface functional moieties that were analogous to 9,10-phenanthrenequinone were responsible for the unique photoluminescence of the nanoparticles and the emission might be regulated by surface charge state, as facilitated by the conjugated graphitic core matrix.
Nanoscale 02/2012; 4(3):1010-5. · 5.91 Impact Factor
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ABSTRACT: Butylphenyl-functionalized Pt nanoparticles (Pt-BP) with an average core diameter of 2.93 ± 0.49 nm were synthesized by the co-reduction of butylphenyl diazonium salt and H(2)PtCl(4). Cyclic voltammetric studies of the Pt-BP nanoparticles showed a much less pronounced hysteresis between the oxidation currents of formic acid in the forward and reverse scans, as compared to that on naked Pt surfaces. Electrochemical in situ FTIR studies confirmed that no adsorbed CO, a poisoning intermediate, was generated on the Pt-BP nanoparticle surface. These results suggest that functionalization of the Pt nanoparticles by butylphenyl fragments effectively blocked the CO poisoning pathway, most probably through third-body effects, and hence led to an apparent improvement of the electrocatalytic activity in formic acid oxidation.
Physical Chemistry Chemical Physics 12/2011; 14(4):1412-7. · 3.57 Impact Factor
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ABSTRACT: A mercapto derivative of diacetylene was used as the hydrophilic ligand to prepare Janus nanoparticles by using hydrophobic hexanethiolate-protected gold (AuC6, diameter 5 nm) nanoparticles as the starting materials. The amphiphilic surface characters of the Janus nanoparticles were verified by contact angle measurements, as compared to those of the bulk-exchange counterparts where the two types of ligands were distributed rather homogeneously on the nanoparticle surface. Dynamic light scattering studies showed that the Janus nanoparticles formed stable superstructures in various solvent media that were significantly larger than those by the bulk-exchange counterparts. This was ascribed to the amphiphilic characters of the Janus nanoparticles that rendered the particles to behave analogously to conventional surfactant molecules. Notably, because of the close proximity of the diacetylene moieties on the Janus nanoparticle surface, exposure to UV irradiation led to effective covalent cross-linking between the diacetylene moieties of neighboring ligands, as manifested in UV-vis and fluorescence measurements where the emission characteristics of dimers and trimers of diacetylene were rather well-defined, in addition to the monomeric emission. In contrast, for bulk-exchange nanoparticles, no trimer emission could be identified, and the intensity of dimer emission was markedly lower (though the intensity increased with increasing diacetylene coverage on the particle surface) under the otherwise identical experimental conditions. This is largely because the diacetylene ligands were distributed on the entire particle surface, and it was difficult to find a large number of ligands situated closely so that the stringent topochemical principles for the polymerization of diacetylene derivatives could be met. Importantly, the cross-linked Janus nanoparticles were found to exhibit marked enhancement of the structural integrity, which was attributable to the impeded surface diffusion of the thiol ligands on the nanoparticle surface, as manifested in fluorescence measurements of aged nanoparticles.
Langmuir 12/2011; 27(23):14581-8. · 4.19 Impact Factor
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ABSTRACT: Monodisperse butylphenyl-functionalized palladium (Pd-BP, dia. 2.24 nm) nanoparticles were synthesized through co-reduction of butylphenyldiazonium and H(2)PdCl(4) by NaBH(4). Because of this unique surface functionalization and a high specific electrochemical surface area (122 m(2) g(-1)), the Pd-BP nanoparticles exhibited a mass activity ∼4.5 times that of commercial Pd black for HCOOH electrooxidation.
Chemical Communications 06/2011; 47(21):6075-7. · 6.17 Impact Factor
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ABSTRACT: Carbon nanoparticles were synthesized from natural gas soot and functionalized with ferrocenyl moieties by using 4-ferrocenylphenyldiazonium as the reactive precursor. The incorporation of the ferrocenyl units onto the carbon nanoparticle surface was confirmed by varied spectroscopic measurements. For instance, in FTIR measurements the characteristic vibrational bands of the ferrocenyl and phenyl moieties could be clearly identified. XPS measurements showed that there were approximately 31.9 ferrocenyl units per nanoparticle. UV-vis spectroscopic measurements displayed an absorption band at ca. 465 nm which was consistent with the optical characteristics of ferrocenyl derivatives. Furthermore, with surface functionalization by the ferrocenyl moieties, the photoluminescence of the carbon nanoparticles was found to diminish in intensity and red-shift in energy with the addition of NOBF(4). This was accounted for by the formation of varied electron-accepting moieties on the particle surface, such as positively charged ferrocenium, quinone-like derivatives, and nitrosation of the aromatic rings of the graphitic cores. Interestingly, in electrochemical studies the nanoparticle-bound ferrocenyl moieties were found to exhibit two pairs of voltammetric waves with a difference of their formal potentials at about 78 mV, suggesting nanoparticle-mediated intraparticle charge delocalization at mixed valence as a result of the strong core-ligand covalent bonds and the conductive sp(2) carbon matrix of the graphitic cores. Consistent behaviors were observed in near-infrared measurements, indicating that the particles behaved analogously to a Class I/II mixed-valence compound.
Nanoscale 02/2011; 3(5):1984-9. · 5.91 Impact Factor
