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Ultrasmall silver nanoparticles (2 nm) were prepared by reduction with sodium borohydride (NaBH4) and stabilized by the ligand glutathione (a tripeptide: glycine–cysteine–glutamic acid). NMR spectroscopy and optical spectroscopy (UV and fluorescence) revealed that these particles initially consist of silver nanoparticles and fluorescing silver nanoclusters, both stabilized by glutathione. Over time, the silver nanoclusters disappear and only the silver nanoparticles remain. Furthermore, the capping ligand glutathione eliminates hydrogen sulfide (H2S) from the central cysteine and is released from the nanoparticle surface as tripeptide glycine–dehydroalanine–glutamic acid. Hydrogen sulfide reacts with the silver core to form silver sulfide. After four weeks in dispersion at 4 °C, this process is completed. These processes cannot be detected by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), or differential centrifugal sedimentation (DCS) as these methods cannot resolve the mixture of nanoparticles and nanoclusters or the nature of the nanoparticle core. X-ray photoelectron spectroscopy showed the mostly oxidized state of the silver nanoparticle core, Ag(+I), both in freshly prepared and in aged silver nanoparticles. These results demonstrate that ultrasmall nanoparticles can undergo unnoticed changes that considerably affect their chemical, physical, and biological properties. In particular, freshly prepared ultrasmall silver nanoparticles are much more toxic against cells and bacteria than aged particles because of the presence of the silver clusters. [ABSTRACT FROM AUTHOR]

Metal phosphides have been hailed as potential replacements for scarce noble metal catalysts in many aspects of the hydrogen economy from hydrogen evolution to selective hydrogenation reactions. But the need for dangerous and costly phosphorus precursors, limited support dispersion, and low stability of the metal phosphide surface toward oxidation substantially lower the appeal and performance of metal phosphides in catalysis. We show here that a 1‐step procedure that relies on safe and cheap precursors can furnish an air‐stable Ni2P/Al2O3 catalyst containing 3.2 nm nanoparticles. Ni2P/Al2O3 1‐step is kinetically competitive with the palladium‐based Lindlar catalyst in selective hydrogenation catalysis, and a loading corresponding to 4 ppm Ni was sufficient to convert 0.1 mol alkyne. The 1‐step synthetic procedure alters the surface ligand speciation of Ni2P/Al2O3, which protects the nanoparticle surface from oxidation, and ensures that 85 % of the initial catalytic activity was retained after the catalyst was stored under air for 1.5 years. Preparation of Ni2P on a variety of supports (silica, TiO2, SBA‐15, ZrO2, C and HAP) as well as Co2P/Al2O3, Co2P/TiO2 and bimetallic NiCoP/TiO2 demonstrates the generality with which supported metal phosphides can be accessed in a safe and straightforward fashion with small sizes and high dispersion. [ABSTRACT FROM AUTHOR]

Ultrasmall nanoparticles (diameter 2 nm) of silver, platinum, and bimetallic nanoparticles (molar ratio of Ag:Pt 0:100; 20:80; 50:50; 70:30; 100:0), stabilized by the thiolated ligand glutathione, were prepared and characterized by transmission electron microscopy, differential centrifugal sedimentation, X-ray photoelectron spectroscopy, small-angle X-ray scattering, X-ray powder diffraction, and NMR spectroscopy in aqueous dispersion. Gold nanoparticles of the same size were prepared as control. The particles were fluorescently labeled by conjugation of the dye AlexaFluor-647 via copper-catalyzed azide-alkyne cycloaddition after converting amine groups of glutathione into azide groups. All nanoparticles were well taken up by HeLa cells. The cytotoxicity was assessed with an MTT test on HeLa cells and minimal inhibitory concentration (MIC) tests on the bacteria Escherichia coli and Staphylococcus xylosus. Notably, bimetallic AgPt nanoparticles had a higher cytotoxicity against cells and bacteria than monometallic silver nanoparticles or a physical mixture of silver and platinum nanoparticles. However, the measured release of silver ions from monometallic and bimetallic silver nanoparticles in water was very low despite the ultrasmall size and the associated high specific surface area. This is probably due to the surface protection by a dense layer of thiolated ligand glutathione. Thus, the enhanced cytotoxicity of bimetallic AgPt nanoparticles is caused by the biological environment in cell culture media, together with a polarization of silver by platinum. [ABSTRACT FROM AUTHOR]

Perovskites have emerged as potential catalysts for the alkaline oxygen evolution reaction. Iron impurities in the electrolyte play an important role in enhancing the catalytic activity of Ni centres, but the nature of active sites is elusive. In this article, we report a detailed study of iron incorporation dynamics and provide direct spectroscopic evidence for surface re-construction and dynamic active site evolution in LaNiO3 perovskite using identical location scanning transmission electron microscopy, electron energy loss spectroscopy and in situ electrochemical Raman spectroscopy. We demonstrate that the electrocatalytic activity is enhanced up to an amount of 7.5 ppm Fe traces in the electrolyte by lowering the Tafel slope from 115 to 49 mV dec−1. The iron impurities in the electrolyte enter the perovskite structure, leading to the dissolution of the A-site, vacancy formation, and amorphization of surface layers. The origin of activity arises from these amorphous layers which are ∼5 nm thick and rich in Ni oxyhydroxides, Fe oxyhydroxides, and a Ni–O–Fe coordinated environment. Together with pH-dependent studies, we confirm the lattice oxygen mechanism in the presence of Fe impurities. Our work provides new insights into the design and a deeper understanding of Ni–Fe synergetics in perovskite-based catalysts for alkaline OER. [ABSTRACT FROM AUTHOR]

This work addresses the formation of ammonia (NH3) decomposition catalysts derived from perovskites ABO3 (A=La, Ca, Sr, and B=Fe, Co, Ni) precursors via operando synchrotron X‐ray diffraction experiments. During the reaction in NH3, the perovskite precursors are decomposed and the transition metals are reduced. Depending on their reduction properties, active metallic catalysts are formed in situ on La2O3 as support. The reduction behavior of the perovskites, formation of intermediate phases during activation, and catalytic performance was studied in detail. In addition, microstructure properties such as crystallite sizes and particle morphology were analyzed. Co‐/Ni‐based perovskites decomposed completely during activation to Co0/Ni0 supported on La2O3 while Fe‐based perovskites were fully stable but inactive in catalysis. This difference is due to varying electronic properties of the transition metals, e. g. decreasing electronegativity from Ni to Fe. With decreasing reducibility, the intermediate phases during activation formed more distinct. La3+ was partially substituted by Ca2+/Sr2+ in LaCoO3 to test for advantageous effects in NH3 decomposition. The best performance was observed using the precatalyst La0.8Sr0.2CoO3 with a conversion of 86 % (100 % NH3, 15000 mL g−1 h−1) at 550 °C. [ABSTRACT FROM AUTHOR]