The Electrochemical Synthesis of the Graphite Intercalation Compounds Containing Tetra-n-alkylammonium Cations

The electrochemical intercalation of tetra-n-alkylammonium (TAA) cations into graphite is investigated using galvanostatic reduction and cyclic voltammetry in TAABr/ dimethylsulfoxide (DMSO) electrolytes. Structural and compositional analyzes by X-ray diffraction, thermogravimetric and elemental analyzes show that stable graphite intercalation compounds (GICs) are formed with highly-flattened TAA cation bilayers for (C₅H₁₁)₄N⁺, (C₆H₁₃)₄N⁺, (C₇H₁₅)₄N⁺, (C₈H₁₇)₄N⁺, with gallery expansions of 0.81 nm. (C₄H₉)₄N⁺ forms a mixed-phase product including a stable GIC with monolayer TAA arrangement and a gallery expansion of 0.48 nm. The GICs with bilayer galleries incorporate 0.7–1.2 DMSO co-intercalate molecules per cation; the monolayer galleries contain relatively little DMSO. Although cyclic voltammetry shows that TAA cations smaller than (C₄H₉)₄N⁺ do intercalate into graphite, they do not form stable GICs. The GICs obtained by galvanostatic reduction are compared to those prepared using chemical ion-exchange reactions. A surface passivation model is introduced to explain the relative stabilities of GICs formed with larger TAA cation intercalates

Single stage electrochemical exfoliation method for the production of few-layer graphene via intercalation of tetraalkylammonium cations

We present a non-oxidative production route to few layer graphene via the electrochemical intercalation of tetraalkylammonium cations into pristine graphite. Two forms of graphite have been studied as the source material with each yielding a slightly different result. Highly orientated pyrolytic graphite (HOPG) offers greater advantages in terms of the exfoliate size but the source electrode set up introduces difficulties to the procedure and requires the use of sonication. Using a graphite rod electrode, few layer graphene flakes (2 nm thickness) are formed directly although the flake diameters from this source are typically small (ca. 100–200 nm). Significantly, for a solvent based route, the graphite rod does not require ultrasonication or any secondary physical processing of the resulting dispersion. Flakes have been characterized using Raman spectroscopy, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS)

Preparation, Characterization, and Structure Trends for Graphite Intercalation Compounds Containing Pyrrolidinium Cations

New graphite intercalation compounds (GICs) containing N,N-n-alkyl substituted pyrrolidinium cation intercalates (Py[subscript n.m], n, m = alkyl chain lengths) are obtained via cationic exchange from stage-1 donor-type GIC [Na(ethylenediamine)₁.₀]C₁₅. Powder X-ray diffraction and thermogravimetric analyses are used to determine the GIC structures and compositions. [Py₄.₈]C₄₇·0.71DMSO and [Py₈.₈]C₄₈ with intercalate monolayers are obtained as stage-1 GICs with gallery expansions of 0.48 nm, whereas [Py₁.₁₈]C₄₇ and [Py₁₂.₁₂]C₈₀·0.25DMSO form stage-1 GICs with intercalate bilayers and gallery expansions of 0.81 nm. The gallery dimensions require that alkyl chain substituents orient parallel to the encasing graphene sheets. Smaller intercalate cations such as Py₁.₄, Py₄.₄, and Py₁.₈ either form high-stage GICs or do not form stable intercalation compounds. These results, along with those reported for graphite intercalation of other quaternary ammonium cations, indicate trends in graphite chemistry where larger intercalates form more stable and lower-stage GICs, and the graphene sheet charge densities can be correlated to the intercalate footprint areas

Efficient Fabrication of Nanoporous Si and Si/Ge Enabled by a Heat Scavenger in Magnesiothermic Reactions

Magnesiothermic reduction can directly convert SiO₂ into Si nanostructures. Despite intense efforts, efficient fabrication of highly nanoporous silicon by Mg still remains a significant challenge due to the exothermic reaction nature. By employing table salt (NaCl) as a heat scavenger for the magnesiothermic reduction, we demonstrate an effective route to convert diatom (SiO₂) and SiO₂/GeO₂ into nanoporous Si and Si/Ge composite, respectively. Fusion of NaCl during the reaction consumes a large amount of heat that otherwise collapses the nano-porosity of products and agglomerates silicon domains into large crystals. Our methodology is potentially competitive for a practical production of nanoporous Si-based materials.Keywords: Energy storage, Nanoparticles, Porous silicon, Nanowires, Chemical reduction, Dioxide, Electrodes, Anode materials, Lithium ion batteries, Crystallin

Rapid Degradation of Phenanthrene by Using Sphingomonas sp. GY2B Immobilized in Calcium Alginate Gel Beads

The strain Sphingomonas sp. GY2B is a high efficient phenanthrene-degrading strain isolated from crude oil contaminated soils that displays a broad-spectrum degradation ability towards PAHs and related aromatic compounds. This paper reports embedding immobilization of strain GY2B in calcium alginate gel beads and the rapid degradation of phenanthrene by the embedded strains. Results showed that embedded immobilized strains had high degradation percentages both in mineral salts medium (MSM) and 80% artificial seawater (AS) media, and had higher phenanthrene degradation efficiency than the free strains. More than 90% phenanthrene (100 mg·L−1) was degraded within 36 h, and the phenanthrene degradation percentages were >99.8% after 72 h for immobilized strains. 80% AS had significant negative effect on the phenanthrene degradation rate (PDR) of strain GY2B during the linear-decreasing stage of incubation and preadsorption of cells onto rice straw could improve the PDR of embedded strain GY2B. The immobilization of strain GY2B possesses a good potential for application in the treatment of industrial wastewater containing phenanthrene and other related aromatic compounds

Enhancement of tributyltin degradation under natural light by N-doped TiO2 photocatalyst

Photo-degradation of tributyltin (TBT) has been enhanced by TiO(2) nanoparticles doped with nitrogen (N-doped TiO(2)). The N-doped catalyst was prepared by a sol-gel reaction of titanium (IV) tetraisopropoxide with 25% ammonia solution and calcined at various temperatures from 300 to 600°C. X-ray diffraction results showed that N-doped TiO(2) remained amorphous at 300°C. At 400°C the anatase phase occurred then transformed to the rutile phase at 600°C. The crystallite size calculated from Scherrer's equation was in the range of 16-51 nm which depended on the calcination temperature. N-doped TiO(2) calcined at 400°C which contained 0.054% nitrogen, demonstrated the highest photocatalytic degradation of TBT at 28% in 3h under natural light when compared with undoped TiO(2) and commercial photocatalyst, P25-TiO(2) which gave 14.8 and 18% conversion, respectively