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Abstract Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia. The present work was performed to understand thermal oxidation and metal-insertion processes of molybdenite surfaces. The analysis was performed using atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA). Structural studies using SEM and TEM indicate the local-disordering of the structure as a result of charge-transfer process between the inserted lithium and the molybdenite layer. Selected area electron diffraction measurements indicate the large variations in the diffusivity of lithium confirming that the charge-transfer is different along and perpendicular to the layers in molybdenite. Thermal heating of molybenite surface in air at 400°C induces surface oxidation, which is slow during the first hour of heating and then increases significantly. The SEM results indicate that the crystals formed on the molybdenite surface as a result of thermal oxidation exhibit regular thin-elongated shape. The average size and density of the crystals on the surface is dependent on the time of annealing; smaller size and high density during the first one-hour and significant increase in size associated with a decrease in density with further annealing.

We report the formation of core--shell diamond particles for solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) made by layer-by-layer (LbL) deposition. Their synthesis begins with the amine functionalization of microdiamond by its immersion in an aqueous solution of a primary amine-containing polymer (polyallylamine (PAAm)). The amine-terminated microdiamond is then immersed in an aqueous suspension of nanodiamond, which leads to adsorption of the nanodiamond. Alternating (self-limiting) immersions in the solutions of the amine-containing polymer and the suspension of nanodiamond are continued until the desired number of nanodiamond layers is formed around the microdiamond. Finally, the core--shell particles are cross-linked with 1,2,5,6-diepoxycyclooctane or reacted with 1,2-epoxyoctadecane. Layer-by-layer deposition of PAAm and nanodiamond is also studied on planar Si/Si[O.sub.2] surfaces, which were characterized by scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA). Core--shell particles are characterized by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), environmental scanning electron microscopy (ESEM), and Brunauer--Emmett--Teller (BET) surface area and pore size measurements. Larger (ca. 50 [micro]m) core--shell diamond particles have much higher surface areas and analyte loading capacities in SPE than nonporous solid diamond particles. Smaller (ca. 3 [micro]m), normal and reversed-phase, core--shell diamond particles have been used for HPLC, with 36 300 plates/m for mesitylene in a separation of benzene and alkyl benzenes and 54 800 plates/m for diazinon in a similar separation of two pesticides on a [C.sub.18] adsorbent. 10.1021/ac1002068

We report on the microstructure, dopant-induced changes in the chemical bonding, and electronic structure, chemical valence states of cations in Sn-incorporated gallium oxide (Ga2O3). Spectroscopic characterization of Sn-mixed Ga2O3 compounds (Ga2−2xSnxO3, 0.00 ≤ x ≤ 0.3, Ga–Sn–O), which were produced by the high-temperature solid-state chemical reaction method, indicates that the Sn-mixing-induced changes in the microstructure and electronic structure are significant. X-ray photoelectron spectroscopic (XPS) analyses, which considered the Ga 2p doublet (Ga 2p3/2 and Ga 2p1/2 peaks), indicate that the Ga exists in its highest chemical valence state (Ga3+) in all of the samples, irrespective of Sn-content. The evolution of Sn peaks in XPS data indicates progressive increase in the Sn-content in Ga–Sn–O samples as x increases from 0.0 to 0.3. However, while no significant changes are seen in the Ga chemistry, formation of SnO2 secondary phase was evident, especially with increasing Sn-concentration. The XPS data confirm the Sn4+ chemical valence state of Sn-ions in all of the Ga–Sn–O samples. The energy-dispersive X-ray spectroscopic (EDS) mapping analyses reveal the localization of SnO2 secondary phase in the parent matrix of Ga2O3. Combined EDS and XPS analyses indicate the secondary phase (SnO2) formation becomes dominant for higher Sn-content. Corroborated with chemical analyses made by EDS and XPS, the Fourier infrared (FTIR) spectroscopic analyses also reveal the evolution of Sn–O bonds, which is reflected in the shift for the high-frequency stretching and bending of the GaO4 tetrahedra, which structurally form the β-Ga2O3 phase. The detailed analysis of the FTIR data and peak evolution suggests a stronger interaction of Sn with Ga2O3 for x ≥ 0.15. A correlation between composition, crystal chemistry, and electronic properties is established in Ga–Sn–O compounds. [ABSTRACT FROM AUTHOR]