Nature Publishing GroupCorma Canós, A.; Concepción Heydorn, P.; Boronat Zaragoza, M.; Sabater Picot, MJ.; Navas Escrig, J.; Yacaman, MJ.; Larios, E.... (2013). Exceptional oxidation activity with sizecontrolled supported gold clusters of low atomicity. Nature Chemistry. 5 (9) SummaryThe catalyticic activity of gold depends on particle size, with reactivity increasing as particle diameter decreases. Investigation of the trends in the subnanometer regime, where gold exists as small clusters of a few atoms, is now starting thanks to recent advances in synthesis and characterization techniques. An easy method to prepare isolated gold atoms supported on functionalized carbon nanotubes and their performance in the oxidation of thiophenol with O 2 are described. Single gold atoms are not active and they aggregate under reaction conditions into gold clusters of low atomicity, which show a catalytic activity comparable to that sulfhydryl oxidase enzymes. When clusters grow into larger nanoparticles, catalyst activity drops to zero.Theoretical calculations show that gold clusters are able to simultaneously activate thiophenol and O 2 , while larger nanoparticles become passivated by strongly adsorbed thiolates. The combination of an optimum for reactants activation and product desorption makes gold clusters excellent catalysts. Main TextGold has attracted wide interest as catalyst in the last years due to its unexpected activity and, specially, to its high selectivity in organic reactions. [1][2][3] The catalytic properties of gold depend on several factors that in some cases are intimately related:gold particle size and morphology, metal-oxide support interaction, oxidation state of the active sites, etc. 4-8 The influence of particle size has been extensively investigated, and a volcano type curve with a maximum in activity at an optimum diameter has been reported for CO oxidation, 7 alkane oxidation, 9 or propene epoxidation with O 2 and H 2 , 10 while in other cases an exponential increase in activity with decreasing particle size has been observed. 5,11,12 However, the trends in catalytic activity when the particle diameter While it appears that in order to control reactivity, the atomicity control of the gold clusters is crucial, the synthesis of size-selected metal clusters and their deposition over a solid support is a challenging task. 26 The wet-chemistry methods for preparing supported metal clusters involve the anchoring of well defined precursors to an adequate support, 27,28 followed by removal of the ligands by post-synthesis treatments, trying to prevent cluster agglomeration during these steps. 9,[29][30][31]32 Soft landing of monodisperse metal clusters grown in the gas phase and with precise size selection by mass spectrometry is a more straightforward method, but it requires sophisticated equipment, and the scaling up of the process is a major drawback. 20,23,33 In The chemical nature of these isolated atoms has been investigated by X-ray absorption spectroscopy (XAS) and X-ray photoelectron spe...
A facile route is developed to boost the electrocatalytic activity of WS2 by chemically unzipping WS2 nanotubes to form WS2 nanoribbons (NRs) with increased edge content. Analysis indicates that the hydrogen evolution reaction activity is strongly associated with the number of exposed active edge sites. The formation of WS2 NRs is an effective route for controlling the electrochemical properties of the 2D dichalcogenides, enabling their application in electrocatalysis.
SummarySilver nanoparticles offer a possible means of fighting antibacterial resistance. Most of their antibacterial properties are attributed to their silver ions. In the present work, we study the actions of positively charged silver nanoparticles against both methicillin-sensitive Staphylococcus aureus and methicillin-resistant Staphylococcus aureus. We use aberration-corrected transmission electron microscopy to examine the bactericidal effects of silver nanoparticles and the ultrastructural changes in bacteria that are induced by silver nanoparticles. The study revealed that our 1 nm average size silver nanoparticles induced thinning and permeabilization of the cell wall, destabilization of the peptidoglycan layer, and subsequent leakage of intracellular content, causing bacterial cell lysis. We hypothesize that positively charged silver nanoparticles bind to the negatively charged polyanionic backbones of teichoic acids and the related cell wall glycopolymers of bacteria as a first target, consequently stressing the structure and permeability of the cell wall. This hypothesis provides a major mechanism to explain the antibacterial effects of silver nanoparticles on Staphylococcus aureus. Future research should focus on defining the related molecular mechanisms and their importance to the antimicrobial activity of silver nanoparticles.
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