Highly Stable Water‐Soluble Platinum Nanoparticles Stabilized by Hydrophilic N‐Heterocyclic Carbenes

Controlling the synthesis of stable metal nanoparticles in water is a current challenge in nanochemistry. The strategy presented herein uses sulfonated N‐heterocyclic carbene (NHC) ligands to stabilize platinum nanoparticles (PtNPs) in water, under air, for an indefinite time period. The particles were prepared by thermal decomposition of a preformed molecular Pt complex containing the NHC ligand and were then purified by dialysis and characterized by TEM, high‐resolution TEM, and spectroscopic techniques. Solid‐state NMR studies showed coordination of the carbene ligands to the nanoparticle surface and allowed the determination of a ¹³C–¹⁹⁵Pt coupling constant for the first time in a nanosystem (940 Hz). Additionally, in one case a novel structure was formed in which platinum(II) NHC complexes form a second coordination sphere around the nanoparticle.     

ZIF-Induced d-Band Modification in a Bimetallic Nanocatalyst: Achieving Over 44 % Efficiency in the Ambient Nitrogen Reduction Reaction

The electrochemical nitrogen reduction reaction (NRR) offers a sustainable solution towards ammonia production but suffers poor reaction performance owing to preferential catalyst–H formation and the consequential hydrogen evolution reaction (HER). Now, the Pt/Au electrocatalyst d-band structure is electronically modified using zeolitic imidazole framework (ZIF) to achieve a Faradaic efficiency (FE) of >44 % with high ammonia yield rate of >161 μg mg_cat⁻¹ h⁻¹ under ambient conditions. The strategy lowers electrocatalyst d-band position to weaken H adsorption and concurrently creates electron-deficient sites to kinetically drive NRR by promoting catalyst–N₂ interaction. The ZIF coating on the electrocatalyst doubles as a hydrophobic layer to suppress HER, further improving FE by >44-fold compared to without ZIF (ca. 1 %). The Pt/Au-N_ZIF interaction is key to enable strong N₂ adsorption over H atom.     

Kinetics and Mechanism of Mineral Respiration: How Iron Hemes Synchronize Electron Transfer Rates

Anaerobic microorganisms of the Geobacter genus are effective electron sources for the synthesis of nanoparticles, for bioremediation of polluted water, and for the production of electricity in fuel cells. In multistep reactions, electrons are transferred via iron/heme cofactors of c‐type cytochromes from the inner cell membrane to extracellular metal ions, which are bound to outer membrane cytochromes. We measured electron production and electron flux rates to 5×10⁵ e s^?1 per G. sulfurreducens. Remarkably, these rates are independent of the oxidants, and follow zero order kinetics. It turned out that the microorganisms regulate electron flux rates by increasing their Fe²⁺/Fe³⁺ ratios in the multiheme cytochromes whenever the activity of the extracellular metal oxidants is diminished. By this mechanism the respiration remains constant even when oxidizing conditions are changing. This homeostasis is a vital condition for living systems, and makes G. sulfurreducens a versatile electron source.     

Precipitation of inorganic salts inside hollow micrometer-sized polyelectrolyte shells

Hollow polymer shells formed by layer-by-layer adsorption of oppositely charged polyelectrolytes onto micrometer-sized colloidal particles with subsequent decomposition of the colloidal core were employed as a model system for the study of inorganic crystallization reactions in restricted volumes. The size-selective permeability of shells is used for spatially controlling the precipitation of inorganic salts CaCO3 and BaCO3 into the shell interior. Outside the shells the precipitation was suppressed by the polymers, which are unable to penetrate the shell wall. The precipitates were studied by scanning electron microscopy and atomic force microscopy. The fundamental and applied aspects of research on spatially confined synthesis of inorganic particles are under discussion.     

Unique charge-separated pyridinium-barbituric acid zwitterions

A synthetic procedure for the preparation of the unusual charge-separated pyridinium barbiturate zwitterion 2 from 1,3-dimethylbarbituric acid and 2-pyridinecarbaldehyde in methanol was developed. The structure of the compound was confirmed with X-ray analysis to demonstrate the strong charge separation throughout the molecule. One would expect that this charge separation would increase its reactivity; however, contrary to this expectation, the compound is very stable in acidic media, and in the presence of a base, decarbonylation occurs on one barbituric acid while the zwitterionic moiety of the molecule stays intact.     

Synthesis of nopol over MCM-41 catalysts

MCM-41 was found to be an active heterogeneous catalyst for the synthesis of nopol by the Prins condensation of beta-pinene and paraformaldehyde, but Sn-MCM-41 in which Sn has been grafted on MCM-41 by chemical vapor deposition is far more active and combines high efficiency and recyclability.