Characteristics of dextrin adsorption by elemental sulfur

Characteristics of dextrin adsorption by elemental sulfur were investigated by the means of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, total organic carbon (TOC) measurements, BET measurements as well as molecular dynamics simulation (MDS). Adsorption isotherms for dextrin adsorption by sulfur were compared to isotherms for dextrin adsorption by other hydrophilic and hydrophobic surfaces taken from the literature. The three-dimensional structure of dextrin was studied in detail and possible mechanisms of adsorption are discussed. Additionally, molecular dynamics simulations provided further insight into the mechanism of dextrin adsorption by elemental sulfur.     

Ultrafast nonresonant response of TiO2 nanostructured films

We present a detailed study of the nonresonant third-order ultrafast response of TiO(2) nanostructured films, combining a classical heterodyned optical Kerr effect experiment, with two polarization selective Kerr techniques, based on transient lensing and phase modulation effects. The complementarity of these techniques is highlighted and demonstrated with calculations. Different aspects of the experimental results are addressed in detail and, finally, the possibilities of performing experiments on liquid dynamics in the pores of TiO(2) films, are discussed in the light of the present results.     

Efficient oxygen reduction on layers of ordered TiO2 nanotubes loaded with Au nanoparticles

Au nanoparticles dispersed over a self-organized nanotubular TiO₂ matrix can be used as a highly efficient catalyst system for the electrochemical oxygen reduction reaction in aqueous solutions. For the same loading of Au nanoparticles, the nanotubular support provides a manifold increase in the reaction rate in comparison with a flat TiO₂ support, or a pure Au sheet electrode.     

Selective synthesis of organic sulfides and disulfides by the reduction of elemental sulfur with samarium diiodide

Elemental sulfur can be reduced to the corresponding thiolate anion species (S²⁻ and S²⁻₂) selectively by samarium diiodide in the presence and absence of HMPA, respectively. The subsequent alkylation of the thiolate anion species provides a useful synthetic route to dialkyl sulfides and disulfides. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9: 581–584, 1998     

A practical and selective reduction of nitroarenes using elemental sulfur and mild base

A method was developed to reduce aromatic nitro compounds to the corresponding anilines using sulfur and base. The method tolerates a range of functional groups on the benzene ring, avoids the use of hydrogen and transition metals and provides the anilines in moderate to high yields.     

Direct synthesis of isothiocyanates from isonitriles by molybdenum-catalyzed sulfur transfer with elemental sulfur

The direct molybdenum-catalyzed sulfuration of a variety of isonitriles with elemental sulfur or propene sulfide as sulfur donors affords the corresponding isothiocyanates in good yields and under mild reaction conditions. A catalytic cycle is suggested, in which the molybdenum oxo disulfur complex operates as the active sulfur-transferring species. A novel adduct between the isonitrile and the molybdenum complex has been characterized by X-ray analysis and its association constant determined by UV-vis spectroscopy, but this adduct appears not to be involved in the sulfur-transfer process.     

Preparation of highly uniform Ag/TiO2 and Au/TiO2 supported nanoparticle catalysts by photodeposition

Photodeposition of Ag nanoparticles on commercial TiO2 particles and nanoparticles was performed in order to provide direct visualization of the spatial distribution of photoactive sites on sub-micrometer-scale and nanoscale TiO2 particle surfaces and to create materials for potential catalytic applications. HRTEM (high-resolution transmission electron microscopy) and HAADF-STEM (high-angle annular dark-field scanning transmission electron microscopy) were used to characterize these materials. The size and spatial distributions of the Ag nanoparticles on the commercial TiO2 were not uniform; the concentration of Ag was higher on grain boundaries and at the edges of these submicrometer particles. In the case of TiO2 nanoparticles, the size distribution of the Ag nanoparticles deposited was relatively uniform and independent of irradiation time and photon energy. The amount of Ag deposited on TiO2 nanoparticles was at least 6 times higher than that on the commercial samples for comparable irradiation conditions. Compared to the case of Ag photodeposition, the difference in the amount of Au photodeposited on TiO2 particles and nanoparticles was even greater, especially at low precursor concentrations. Photodeposition on TiO2 nanoparticles is suggested as a potential method for the preparation of Au/TiO2 catalysts, as loadings in excess of 10 wt % of uniform 1 nm metal particles were achieved in this work.     

Multiple CO Oxidation Promoted by Au2 Dimers in Au2TiO4− Cluster Anions

Time‐of‐flight mass spectrometry experiments demonstrated that laser ablation generated and mass selected Au₂TiO₄^? cluster anions can unexpectedly oxidize three CO molecules in an ion trap reactor. This is an improvement on the more commonly observed oxidation of at most two CO molecules by a doped cluster. Quantum chemistry calculations were performed to rationalize the reactions. The lowest energy isomer of Au₂TiO₄^? contains a superoxide unit, the participation of which in CO oxidation can be promoted by the Au₂ dimer. The Au₂ dimer functions as a rather flexible electron reservoir in each CO oxidation step in terms of the release and storage of electrons to drive the dissociation of superoxide to peroxide and then to lattice oxygen atoms, which can be removed by reaction with CO molecules. This gas‐phase study enriches our understanding toward the nature of reactive oxygen species involved in gold‐catalyzed oxidation reactions.     

New methodology for the introduction of sulfur into organic molecules : Synthesis of anhydrous Li2S,Li2S2 and LiSr species by lithium triethylborohydride reduction of elemental sulfur and disulfides

Anhydrous THF solutions of Li₂S or Li₂S₂ (or chemically equivalent species) are rapidly and quantitatively formed by the reaction of common yellow sulfur with appropriate stoichiometries of commercially available LiEt₃BH. Only volatile by-products H₂ and Et₃B are produced; however, the Et₃B probably associates with the anionic sulfur species generated. Subsequent reaction with electrophiles (alkylating agents or acylating agents) affords sulfide or disulfide derivatives in high yields. In several cases, literature procedures are substantially improved. Disulfides are cleaved to lithium mercaptides by LiEt₃BH. Subsequent addition of electrophiles affords unsymmetrical sulfides. Trisulfides and tetrasulfides can also be prepared by LiEt₃BH reduction of S_g, but only in low yield.     

Photocatalytic reduction of nitrate over TiO2 and Ag-modified TiO2

This research work presents the efficiency of the TiO₂ and Ag–TiO₂ thin films prepared by the sol–gel method and coated onto the surface of 304 stainless steel sheets used in the photocatalytic nitrate reduction processes. The Ag–TiO₂ thin films had the weight by weight (w/w) ratio of Ag⁺/TiO₂ of 0.1% as Ag atom. The XRD results showed that the crystalline phase structure of TiO₂ on the Ag–TiO₂ thin films was anatase. The optical band gaps of the TiO₂ and 0.1% Ag–TiO₂ thin films were respectively 3.27 and 2.70 eV, while the surface of the prepared catalysts was hydrophobic with the respective average water contact angles of 94.8° and 118.5° for the TiO₂ and 0.1% Ag–TiO₂ thin films. The net efficiencies of photocatalytic nitrate reduction of TiO₂ and 0.1% Ag–TiO₂ were 41.4% and 70.0%, respectively. The loading of Ag only influenced the nitrate removal efficiency without affecting the stoichiometric ratio of formate to nitrate. The net stoichiometric ratio of formate to nitrate of all experiments was 2.8:1.0, which is close to the stoichiometric ratio of 2.5:1.0 of the nitrate reduction to nitrite and then to nitrogen gas.     

Unexpected promotion of Au/TiO2 by nitrate for CO oxidation

The catalytic activity for Au/TiO2 for CO oxidation can be significantly enhanced by the addition of nitrates and this may relate to the variable catalyst performance observed in many studies.     

Fluorination of polyfluoroalkoxy derivatives of sulfur tetrafluoride by elemental fluoride

Conclusions The feasibility was demonstrated for the preparation of mono- and bis(,,-trihydro-perfluoroalkoxy) derivatives of sulfur hexafluoride by the fluorination of the corresponding sulfur tetrafluoride derivatives with elemental fluorine.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1906–1908, August, 1988.     

Reaction of indolizines with elemental sulfur

The fusion of 3,8-diphenyl-, 1,2-diphenyl-, and 6-methyl-2,7-diphenyl-indolizines with sulfur results in the formation of bis(indolizin-3-yl) disulfides with the respective substituents. Bis(2,8-diphenylindolizin-3-yl) disulfide is reduced to the original indolizine, and its treatment with nitric acid gives 2,8-diphenyl-1, 3-dinitroindolizine. Bis(dibenzo[b,g]indolizin-11-yl) disulfide is obtained from dibenzo[b,g]indolizine. The formation of the disulfides is apparently a general region of indolizines without substituents at C₃ or C₁ of the pyrrole ring. The structures of the disulfides obtained have been confirmed by data from x-ray diffraction analysis and NMR spectroscopy.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1371–1375, October, 1984.     

Dissolved organic matter-mediated reduction of ionic Au(III) to elemental Au nanoparticles and their growth to visible granules

The biogeochemical transformation of gold (Au), i.e. its dissolution and re-precipitation, is critical in supergene transport of Au and formation of Au granules. Besides biogenic reduction, the formation Au granules can also be driven by chemical processes. Previous studies have showed the formation of Au nanoparticles (AuNPs) from ionic Au(III) can be mediated by dissolved organic matter under sunlight. In this letter, we further demonstrated that these AuNPs can further slowly (in years) grow into visible Au granules. Different sized nano-flower and fractal dendrite-like branched gold structures (from tens of nanometres to over 100 μm) were observed in the Au granule sample. This growth of AuNPs into visible Au granules may play a critical role in the supergene mineralization and enrichment of secondary Au and drive the biogeochemical cycle of Au.     

Determination of elemental sulfur in coal by gas chromatography-mass spectrometry

A method for the determination of S0 in coal based on the extraction with cyclohexane with subsequent quantitative analysis of elemental sulfur in the extract by GC/MS is described. The quantity of elemental sulfur was determined in four coal samples with different distribution of sulfur forms. The effect of solvent and extraction time on the efficiency of sulfur removal was studied. The elemental sulfur extracted from coal occurred in the form of S6, S7 and S8. Calibration solutions were prepared from freshly recrystalized elemental sulfur. It was found that the injection temperature has a crucial influence on the m/z 64 ion chromatogram.     

Microbial reduction of sulfur dioxide with pretreated sewage sludge and elemental hydrogen as electron donors

It has been demonstrated that heat- and alkali-pretreated sewage sludge may serve as an electron donor and carbon source for SO₂ reduction byDesulfovibrio desulfuricans. A continuousD. desulfuricans culture was operated for 6 mo with complete reduction of SO₂ to H₂S. The culture required only minor amounts of mineral nutrients in addition to pretreated sewage sludge. It has also been shown that the sulfate-reducing bacteriumDesulfotomaculum orientis can be grown on H₂ as an energy source, CO₂ as a carbon source, and SO₂ as a terminal electron acceptor. Complete reduction of SO₂ to H₂S was observed.     

Microstructured Au/TiO2 model catalyst systems

The preparation of microstructured Au/TiO2 model catalysts as a first step toward micrometer-scale parallel studies on model catalysts and toward studies of mesoscopic effects in catalytic reactions was investigated by atomic force microscopy and X-ray photoelectron spectroscopy. The model systems, which consist of micrometer-size active areas covered with Au nanoparticles that are separated by similarly sized inactive areas free of Au particles, are fabricated by combining optical lithography methods for microstructuring and ultrahigh vacuum evaporation for Au nanoparticle deposition and by applying suitable cleaning steps. It is demonstrated that practically perfect microstructures with Au nanoparticles of catalytically relevant sizes (2-3-nm diameter) on a clean TiO2 substrate can be produced this way and that the processing steps do not affect the deposited Au nanoparticles, neither in size nor in lateral distribution.     

Low-dimensional chainlike assemblies of TiO2 nanorod-stabilized Au nanoparticles

A simple and versatile light-based strategy to grow low-dimensional gold superstructures is presented; prolonged UV-irradiation of TiO2 nanorod-stabilized Au nanoparticles in organic media promotes the progressive formation of distinctive chainlike metal assemblies, namely segments of a few gold particles, 2D or quasi-1D large structures composed of interlacing lines of hundreds of metal units over areas of about 500 nm2.