M. A. Santa Ana

Intercalation chemistry of molybdenum disulfide

Abstract Most relevant features of the fundamental and applied chemistry of MoS 2 are reviewed highlighting the importance of the layered nature of the solid on the optical and catalytic properties of the compounds. Experimental and theoretical aspects related to the 2H-1T-MoS 2 phase change induced by the insertion of lithium are discussed. The principal systems known until this moment, specifically those based on the intercalation of molecular and polymeric organic donors, organometallic species and cations into MoS 2 as well as the methods used for their synthesis, are described. The main characteristic of the products, principally their properties as mixed conductors and the diffusion of lithium inside the interlamellar spaces are discussed.

Vanadate Conformation Variations in Vanadium Pentoxide Nanostructures

We report the comparative structural-vibrational study of nanostructures of nanourchins, nanotubes, and nanorods of vanadium oxide. The tube walls comprise layers of vanadium oxide with the organic surfactant intercalated between atomic layers. Both Raman scattering and infrared spectroscopies showed that the structure of nanourchins, nanotubes, and nanorods of vanadium oxide nanocomposite are strongly dependent on the valency of the vanadium, its associated interactions with the organic surfactant template, and on the packing mechanism and arrangement of the surfactant between vanadate layers. Accurate assignment of the vibrational modes to the V–O coordinations has allowed their comparative classification and relation to atomic layer structure. Although all structures are formed from the same precursor, differences in vanadate conformations due to the hydrothermal treatment and surfactant type result in variable degrees of crystalline order in the final nanostructure. The nanotube-containing nanourchins contain vanadate layers in the nanotubes that are in a distorted –V 5+ conformation, whereas the the nanorods, by comparison, show evidence for V 5+ and V 4+

Mixed conductivity and lithium diffusion in poly(ethylene oxide) molybdenum disulfide nanocomposites

Abstract The electrical conductivity, the lithium diffusion, and the diffusion activation thermodynamics of the nanocomposites arising from the co-intercalation of lithium and poly(ethylene oxide) in molybdenum disulfide, Li 0.1 MoS 2 (PEO) 0.5 and Li 0.1 MoS 2 (PEO) 1.0 , are analyzed and compared with those of pure MoS 2 . According to qualitative galvanostatic relaxation experiments, the products are mixed ionic and electronic conductors with a ratio σ e / σ i of about 10 3 .

Electrical conductivity and lithium diffusion in molybdenum disulfide intercalated with poly(ethylene oxide)

Abstract Electrical conductivity and lithium diffusion coefficients of nanocomposites prepared by intercalation of molybdenum disulfide with poly(ethylene oxide), Li0.1MoS2(PEO)y, are informed. The products show a semiconductor behaviour with relatively high electrical conductivity. Lithium diffusion coefficients are higher than those observed for the disulfide alone.

Atomic Layer Structure of Vanadium Oxide Nanotubes Grown on Nanourchin Structures

Science Foundation Ireland (SFI grant no. 02/IN.1/172); Fondo Nacional de Desarrollo Cientifico y Tecnologico, Chile ( FONDECyT grants 1050344, 1030102, 7050081); University of Chile; Universidad Tecnologica Metropolitana, Chile

Synthesis, functionalization, and properties of intercalation compounds

Abstract Layered compounds are nanostructured, intrinsically anisotropic materials which often undergo intercalation reactions producing host–guest complexes. In this work examples from the molybdenum disulfide chemistry are used for discussing how the properties of the products may be regulated by appropriate selection of the guests species used for functionalizing the pristine sulfide. Special attention is given to new intercalates based in the intercalation of surfactants, which under special conditions may act as template promoting the conversion of the layered products into micro and nanotubes. The form how this kind of surfactants may be used for obtaining laminar derivatives of cadmium disulfide with the sulfide in a confined state is also described.

The oscillopolarographic determination of uranium and thorium in supporting electrolytes containing cupferron

Abstract Uranium(VI and IV) and thorium(IV) give cathodic indentations in supporting electrolytes prepared from 0.1 M perchloric acid, 0.5 M ammonium thiocyanate and 5·10 -3 M cupferron (solution A) or from 0.1 M succinic-succinate buffer pH 4, 0.1 M sodium chloride, 10 -3 M cupferron and 0.05% gelatine (solution B). The uranium indentation on the dE/dt = f(E) curve (Q=0.75 and 0.73) permits its detection at the 3·10 -7 M level. The thorium indentation (Q=0.78) permits its detection at the 4·10 -7 M level in solution B. Methods for the elimination of interfering ions for the uranium determination are described. In the determination of thorium, Ga(III), Fe(III), Ti(IV) and U(VI) interfere.

Lithium-induced self-assembling of poly(ethylene oxide) intercalated in molybdenum disulfide

Static 7 Li and 1 H NMR experiments were performed between 150 and 400 K. The contributions of both 7 Li- 7 Li and 7 Li- 1 H dipolar interactions to the magnetic second moment were determined in the rigid-lattice regime (T < 220 K). Calculated magnetic second moments for different PEO conformations, considering both intra- and inter-molecular interactions, indicate that the polymer in this nanocomposite is compatible with C-C bonds predominately in gauche conformations and the oxygen atoms defining tetrahedral sites hosting the lithium ions. The model adequately satisfies the geometric restrictions determined by the structure and the stoichiometry of the product. Furthermore, the temperature dependence of the 7 Li linewidth and the 7 Li and 1 H spin-lattice relaxations for the nanocomposite and two reference compounds, (PEO) 8 LiClO 4 and Li 0.22 MoS 2 , provided information about the effects of PEO intercalation on the polymer and Li + dynamics and conformation, indicating that Li + mobility is coupled to polymer motion, the polymer motion is restricted by the intercalation process, and the chain conformation inside the interlayer space is in the sequence TGGTGGTGG.

The polarographic determination of traces of titanium-(IV) in the presence of n-benzoyl-n-phenylhydroxylamine

The polarographic behavior of the titanium(IV)-N-benzoyl-N-phenyl-hydroxylamine (BPHA) system in acidic medium and in water-ethanol mixtures has been studied. In (1+3) water-ethanol containing 2 M sulfuric acid and 0.05 M BPHA, titanium(IV) gives a single kinetically controlled wave. Titanium(IV) can be determined at concentrations as low as 5·10-6M, in the presence of Fe(III), Cu(II), V(V), etc., but Cd(II), Sn(II and IV), As(V), U(VI) and Mo(VI) interfere.

Redox properties of 17-electron thiolate complexes of cyclopentadienyl iron (III)

Abstract The redox electrochemistry of iron (III) thiolate complexes of the type [CpFe(dppe)-SR]PF6 R = CH3, C3H7, C6H5, p-C6H4Br and thiobenzothiazole has been examined by cyclic voltammetry, coulometry and spectroelectrochemistry methods. Four redox waves were observed in the range −1.5 to +1.5 V (S.C.E.) in CH2Cl2. Around 0.0 V the metal centered reduction Fe (III)→Fe (II) process was observed, while that around +0.5 V the wave observed was attributed to a ligand centered oxidation. Strongly irreversible waves of oxidation near 1.3 V were assigned to the oxidation of RSSR while a reduction wave also strongly irreversible at very high negative potential was attributed to the reduction of the RSSR free ligand, RSSR + 2e → 2RS−. The redox wave observed for the disulphides compounds are discussed in terms of a reductive elimination of RSSR. Chemical and electrochemical reduction of the complexes [CpFe(dppe)-SR]PF6 was accomplished by the color changes blue → red-brown characteristic of the redox change 17e → 18e.