The preparation and study of quantum dots and quantum wires play a very important role in nanotechnology. In this particular study, we report on the uptake of silver by living alfalfa plants. X-ray absorption spectroscopy and transmission electron microscopy (TEM) studies corroborated silver metal uptake by alfalfa plants from a silver-rich solid medium and the subsequent formation of silver nanoparticles. Silver nanoparticle alignment, structure, and coalescence were observed using TEM with an atomic resolution analysis. Dark field image TEM showed the connection of silver nanoparticles of different sizes by possibly noncrystalline silver atomic wires. To our knowledge, this is the first report on the formation of silver nanoparticles by a living plant system.

Alfalfa sprouts: A natural source for the synthesis of silver nanoparticles

Coordinatively unsaturated (CUS) iron sites are highly active in catalytic oxidation reactions; however, maintaining the CUS structure of iron during heterogeneous catalytic reactions is a great challenge. Here, we report a strategy to stabilize single-atom CUS iron sites by embedding highly dispersed FeN4 centers in the graphene matrix. The atomic structure of FeN4 centers in graphene was revealed for the first time by combining high-resolution transmission electron microscopy/high-angle annular dark-field scanning transmission electron microscopy with low-temperature scanning tunneling microscopy. These confined single-atom iron sites exhibit high performance in the direct catalytic oxidation of benzene to phenol at room temperature, with a conversion of 23.4% and a yield of 18.7%, and can even proceed efficiently at 0°C with a phenol yield of 8.3% after 24 hours. Both experimental measurements and density functional theory calculations indicate that the formation of the Fe═O intermediate structure is a key step to promoting the conversion of benzene to phenol. These findings could pave the way toward highly efficient nonprecious catalysts for low-temperature oxidation reactions in heterogeneous catalysis and electrocatalysis.

A single iron site confined in a graphene matrix for the catalytic oxidation of benzene at room temperature.

Dispersing catalytically active metals as single atoms on supports represents the ultimate in metal utilization efficiency and is increasingly being used as a strategy to design hydrogen evolution reaction (HER) electrocatalysts. Although platinum (Pt) is highly active for HER, given its high cost it is desirable to find ways to improve performance further while minimizing the Pt loading. Here, we use onion-like nanospheres of carbon (OLC) to anchor stable atomically dispersed Pt to act as a catalyst (Pt1/OLC) for the HER. In acidic media, the performance of the Pt1/OLC catalyst (0.27 wt% Pt) in terms of a low overpotential (38 mV at 10 mA cm−2) and high turnover frequencies (40.78 H2 s−1 at 100 mV) is better than that of a graphene-supported single-atom catalyst with a similar Pt loading, and comparable to a commercial Pt/C catalyst with 20 wt% Pt. First-principle calculations suggest that a tip-enhanced local electric field at the Pt site on the curved support promotes the reaction kinetics for hydrogen evolution. Isolating metal atoms on supports is becoming an increasingly studied approach to design water splitting electrocatalysts. Here, the authors prepare a hydrogen evolution catalyst comprising atomically dispersed Pt atoms on curved carbon supports, which outperform similar catalysts where the support is flat.

Atomically dispersed platinum supported on curved carbon supports for efficient electrocatalytic hydrogen evolution

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Reactivity of Surface Species in Heterogeneous Catalysts Probed by In Situ X-ray Absorption Techniques

Concern and interest related to the effects of nanomaterials on living organisms are growing in both the scientific and public communities. Reports have described the toxicity of nanoparticles (NPs) on micro- and macro-organisms, including some plant species. Nevertheless, to the authors’ knowledge there are no reports on the biotransformation of NPs by edible terrestrial plants. Here, shown for the first time, is evidence pertaining to the biotransformation of ZnO and CeO2 NPs in plant seedlings. Although the NPs did not affect soybean germination, they produced a differential effect on plant growth and element uptake. By using synchrotron X-ray absorption spectroscopy we obtained clear evidence of the presence of CeO2 NPs in roots, whereas ZnO NPs were not present. Random amplified polymorphic DNA assay was applied to detect DNA damage and mutations caused by NPs. Results obtained from the exposure of soybean plants to CeO2 NPs show the appearance of four new bands at 2000 mg L−1 and three new bands at ...

Evidence of the differential biotransformation and genotoxicity of ZnO and CeO2 nanoparticles on soybean (Glycine max) plants

WinXAS is a new X-ray absorption spectroscopy (XAS) data-analysis program. It runs under the operating system MS-Windows 95/NT and offers several unique features. It has a user-friendly graphical environment and is capable of reading a variety of data formats. It contains a number of useful numerical algorithms beyond those used in conventional XAS analysis and offers a simple interface to the ab-initio theoretical code FEFF. The availability of fast macros in WinXAS makes it particularly useful for on-line data examination at synchrotron radiation facilities during XAS experiments as well as for the analysis of multiple-scan data such as those from time-resolved experiments.

T. Ressler

Papers

WinXAS: a program for X-ray absorption spectroscopy data analysis under MS-Windows.