Synthesis and characterization of a family of layered trichalcogenides for assisted hydrogen photogeneration

Three layered trisulfides (TiS₃, ZrS₃, HfS₃) have been synthesized by solid–gas reaction between metal and sulfur in a vacuum sealed ampoule at 550 °C during 60 h. The samples used in this work were prepared from a colloidal suspension of powder of each one of the metal trisulfides (MS₃, M = Ti, Zr, Hf) in ethanol and deposited on titanium disks and quartz substrates by ”drop coating” technique. These samples have been characterized by X‐ray diffraction, energy dispersive analysis of X‐ray and scanning electron microscopy. The obtained direct optical band gaps are 1.0 ± 0.1 eV, 2.0 ± 0.1 eV and 2.2 ± 0.1 eV for TiS₃, ZrS₃ and HfS₃, respectively. Photoelectrochemical measurements in 0.5 M Na₂SO₃ have been carried out to characterize the MS₃/electrolyte interface. The flat‐band potentials (V_fb) vs. Ag/AgCl measured by electrochemical impedance spectroscopy (EIS) are –0.84 ± 0.02 V (TiS₃), –0.93 ± 0.02 V (ZrS₃) and –0.92 ± 0.02 V (HfS₃). Hydrogen generation was investigated in a photoelectrochemical cell (PEC) with MS₃ as photoanodes under white light illumination of 200 ± 20 mW/cm² at external bias potentials of 0.3 V vs. Ag/AgCl. Hydrogen evolution flows have been quantified by quadrupole mass spectrometry (QMS) reaching instantaneous values up to 19 ± 2 nmol H₂/min cm² with TiS₃ as photoanode.     

Combination of radon and stable isotope analysis as a tool for decision support concerning the remediation of NAPL-contaminated sites

The non-aqueous phase-liquid (NAPL)-contaminated aquifer at a major refinery site in Mexico was investigated. Owing to the depth of the contaminated aquifer section (NAPL source zone) of over 100 m below the surface, the actual aquifer material was not accessible for sampling. Information on the residual NAPL contamination of the aquifer could only be obtained indirectly by analysing groundwater samples from a few wells available at the site. To tackle the problem, an approach alternative to conventional groundwater analysis for dissolved NAPL was chosen. For evaluating the recent contamination and estimating its probable future development, the radioisotope radon-222 and the stable isotopes 13C, 34S and 18O were used as naturally occurring contamination tracers and process indicators. Radon was used as partitioning tracer for the approximate localization and semi-quantitative assessment of the NAPL source zone. The stable isotopes were used as indicators for naturally occurring biodegradation processes, which might potentially be implemented into future remediation schemes.     

On the reactivity of naphthalene and biphenyl dianions: tying up loose ends concerning an SN2‐ET dichotomy in alkylation reactions

Naphthalene and biphenyl dianions are interesting compounds that can be obtained by double reduction of the corresponding arenes in solution with certain alkali metals. These dianions are highly reactive and rather elusive species with very high laying and highly delocalized electrons. They share many aspects of the reactivity of the alkali metal they originated from and consequently behave primarily as strong electron transfer (ET) reagents. We report here kinetic evidence for a different type of reactivity in their alkylation reactions with alkyl fluorides. By using cyclopropylmethyl fluoride (c‐C₃H₅CH₂F) as a very fast radical probe, we were able to settle that this alkylation does not involve the classical electron transfer reaction followed by radical coupling between diffusing radicals, but supports the alternative S_N2 concerted mechanism, discerning thus this mechanistic S_N2‐ET dichotomy. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Environmentally friendly sonocatalysis promoted preparation of 1-thiocarbamoyl-3,5-diaryl-4,5-dihydro-1H-pyrazoles

An efficient and green synthesis of thiocarbamoyl-3,5-diaryl-4,5-dihydro-1H-pyrazoles via the condensation of chalcones with thiosemicarbazide in ethanol and KOH under ultrasound irradiation is reported. The products were isolated in good yields after short reaction times.     

Asymptotics of Sobolev embeddings and singular perturbations for the -Laplacian

We consider the best constant for the embedding of into where , . Here with a smooth, bounded domain in and a large positive number. It is proven by the validity of the expansion

as , where is a positive constant depending on and . The behavior of associated extremals, which satisfy an equation involving the -Laplacian operator, is also analyzed.

     

Fractal scattering of microwaves from soils

Using a combination of laboratory experiments and computer simulation we show that microwaves reflected from and transmitted through soil have a fractal dimension correlated to that of the soil's hierarchic permittivity network. The mathematical model relating the ground-penetrating radar record to the mass fractal dimension of soil structure is also developed. The fractal signature of the scattered microwaves correlates well with some physical and mechanical properties of soils.