Thermogravimetric analysis of selected coal-bearing strata kaolinite

Two kinds of coal-bearing kaolinite from China were analysed by X-ray diffraction (XRD), Thermogravimetric analysis-mass spectrometry (TG-MS), infrared emission spectroscopy. Thermal decomposition occurs in a series of steps attributed to (a) desorption of water at 68 °C for Datong coal bearing strata kaolinite and 56 °C for Xiaoxian with mass losses of 0.36 % and 0.51 % (b) decarbonization at 456 °C for Datong coal bearing strata kaolinite and 431 °C for Xiaoxian kaolinite, (c) dehydroxylation takes place in two steps at 589 and 633 °C for Datong coal bearing strata kaolinite and at 507 °C and 579 °C for Xiaoxian kaolinite. This mineral were further characterised by infrared emission spectroscopy (IES). Well defined hydroxyl stretching bands at around 3695, 3679, 3652 and 3625 cm-1 are observed. At 650 °C all intensity in these bands is lost in harmony with the thermal analysis results. Characteristic functional groups from coal are observed at 1918, 1724 and 1459 cm-1. The intensity of these bands decrease by thermal treatment and is lost by 700 °C.

Raman spectroscopic study of the hydroxy-arsenate mineral geminite Cu(AsO3OH)•H2O

The mineral geminite, an hydrated hydroxy-arsenate mineral of formula Cu(AsO3OH)•H2O, has been studied by Raman and infrared spectroscopy. Two minerals from different origins were investigated and the spectra proved quite similar. In the Raman spectra of geminite, four bands are observed at 813, 843, 853 and 885 cm-1. The assignment of these bands is as follows: (a) The band at 853 cm-1 is assigned to the AsO43- ν1 symmetric stretching mode (b) the band at 885 cm-1 is assigned to the AsO3OH2- ν1 symmetric stretching mode (c) the band at 843 cm-1 is assigned to the AsO43- ν3 antisymmetric stretching mode (d) the band at 813 cm-1 is ascribed to the AsO3OH2- ν3 antisymmetric stretching mode. Two Raman bands at 333 and 345 cm-1 are attributed to the ν2 AsO4 3- bending mode and a set of higher wavenumber bands are assigned to the ν4 AsO43- bending mode. A very complex set of overlapping bands is observed in both the Raman and infrared spectra. Raman bands are observed at 2288, 2438, 2814, 3152, 3314, 3448 and 3521 cm-1. Two Raman bands at 2288 and 2438 cm-1 are ascribed to very strongly hydrogen bonded water. The broader Raman bands at 3152 and 3314 cm-1 may be assigned to adsorbed water and not so strongly hydrogen bonded water in the molecular structure of geminate. Two bands at 3448 and 3521 cm-1 are assigned to the OH stretching vibrations of the (AsO3OH)2- units. Raman spectroscopy identified Raman bands attributable to AsO43- and AsO3OH2- units.

Use of hydrotalcites for the removal of toxic anions from aqueous solutions

The removal of toxic anions has been achieved using hydrotalcite via two methods: (1) coprecipitation and (2) thermal activation. Hydrotalcite formed via the coprecipitation method, using solutions containing arsenate and vanadate up to pH 10, are able to remove more than 95% of the toxic anions (0.2 M) from solution. The removal of toxic anions in solutions with a pH of >10 reduces the removal uptake percentage to 75%. Raman spectroscopy observed multiple A1 stretching modes of V−O and As−O at 930 and 810 cm−1, assigned to vanadate and arsenate, respectively. Analysis of the intensity and position of the A1 stretching modes helped to identify the vanadate and arsenate specie intercalated into the hydrotalcite structure. It has been determined that 3:1 hydrotalcite structure predominantly intercalate anions into the interlayer region, while the 2:1 and 4:1 hydrotalcite structures shows a large portion of anions being removed from solution by adsorption processes. Treatment of carbonate solutions (0.2 M) containing arsenate and vanadate (0.2 M) three times with thermally activated hydrotalcite has been shown to remove 76% and 81% of the toxic anions, respectively. Thermally activated hydrotalcite with a Mg:Al ratio of 2:1, 3:1, and 4:1 have all been shown to remove 95% of arsenate and vanadate (25 ppm). At increased concentrations of arsenate and vanadate, the removal uptake percentage decreased significantly, except for the 4:1 thermally activated hydrotalcite. Thermally activated Bayer hydrotalcite has also been shown to be highly effective in the removal of arsenate and vanadate. The thermal activation of the solid residue component (red mud) removes 30% of anions from solution (100 ppm of both anions), while seawater-neutralized red mud removes 70%. The formation of hydrotalcite during the seawater neutralization process removes anions via two mechanisms, rather than one observed for thermally activated red mud.

Kaolinite platelet orientation for XRD and AFM applications

The structure-building phenomena within clay aggregates are governed by forces acting between clay particles. The nature of such forces is important to understand in order to manipulate the aggregate structure for applications such as settling and dewatering. A parallel particle orientation is required when conducting force measurements acting between the basal planes of clay mineral platelets using atomic force microscopy (AFM). In order to prepare a film of clay particles with the optimal orientation for conducting AFM measurements, the influences of particle concentration in suspension, suspension pH and particle size on the clay platelet orientation were investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. From these investigations, we conclude that high clay (dry mass) concentrations and larger particle diameters (up to 5 µm) in suspension result in random orientation of platelets on the substrate. The best possible laminar orientation in the clay dried film as represented in the XRD by the 001/020 intensity ratio of more than 150 and by SE micrograph assessments, was obtained by drying thin layers from 0.2 wt% of -5 µm clay suspensions at pH 10.5. These dried films are stable and suitable for close-approach AFM studies in solution.

4-Carbamoylpiperidinium 5-nitrosalicylate

In the structure of the title compound, C6H13N2O+ C7H4NO5-, the isonipecotamide cations and the 5-nitrosalicylate anions form hydrogen-bonded chain substructures through head-to-tail piperidinium N---H...O(carboxyl) hydrogen bonds and through centrosymmetric cyclic head-to-head amide-amide hydrogen-bonding associations [graph set R2/2(8)]. These chains are cross linked by amide N---H...O~carboxyl~ and piperidinium N-H...O(nitro) associations to give a two-dimensional sheet structure.

Order and disorder in the structures of two crystal polymorphs of the adduct bis(quinolinium-2-carboxylate) DL-malic acid

The structures of two polymorphs of the anhydrous cocrystal adduct of bis(quinolinium-2-carboxylate) DL-malic acid, one triclinic the other monoclinic and disordered, have been determined at 200 K. Crystals of the triclinic polymorph 1 have space group P-1, with Z = 1 in a cell with dimensions a = 4.4854(4), b = 9.8914(7), c = 12.4670(8)Å, α = 79.671(5), β = 83.094(6), γ = 88.745(6)deg. Crystals of the monoclinic polymorph 2 have space group P21/c, with Z = 2 in a cell with dimensions a = 13.3640(4), b = 4.4237(12), c = 18.4182(5)Å, β = 100.782(3)deg. Both structures comprise centrosymmetric cyclic hydrogen-bonded quinolinic acid zwitterion dimers [graph set R2/2(10)] and 50% disordered malic acid molecules which lie across crystallographic inversion centres. However, the oxygen atoms of the malic acid carboxylic groups in 2 are 50% rotationally disordered whereas in 1 these are ordered. There are similar primary malic acid carboxyl O-H...quinaldic acid hydrogen-bonding chain interactions in each polymorph, extended into two-dimensional structures but in l this involves centrosymmetric cyclic head-to-head malic acid hydroxyl-carboxyl O-H...O interactions [graph set R2/2(10)] whereas in 2 the links are through single hydroxy-carboxyl hydrogen bonds.

Bubble rise velocity and trajectory in xanthan gum crystal suspension

An experimental set-up was used to visually observe the characteristics of bubbles as they moved up a column holding xanthan gum crystal suspensions. The bubble rise characteristics in xanthan gum solutions with crystal suspension are presented in this paper. The suspensions were made by using different concentrations of xanthan gum solutions with 0.23 mm mean diameter polystyrene crystal particles. The influence of the dimensionless quantities; namely the Reynolds number, Re, the Weber number, We, and the drag co-efficient, cd, are identified for the determination of the bubble rise velocity. The effect of these dimensionless groups together with the Eötvös number, Eo, the Froude number, Fr, and the bubble deformation parameter, D, on the bubble rise velocity and bubble trajectory are analysed. The experimental results show that the average bubble velocity increases with the increase in bubble volume for xanthan gum crystal suspensions. At high We, Eo and Re, bubbles are spherical-capped and their velocities are found to be very high. At low We and Eo, the surface tension force is significant compared to the inertia force. The viscous forces were shown to have no substantial effect on the bubble rise velocity for 45 < Re < 299. The results show that the drag co-efficient decreases with the increase in bubble velocity and Re. The trajectory analysis showed that small bubbles followed a zigzag motion while larger bubbles followed a spiral motion. The smaller bubbles experienced less horizontal motion in crystal suspended xanthan gum solutions while larger bubbles exhibited a greater degree of spiral motion than those seen in the previous studies on the bubble rise in xanthan gum solutions without crystal.

Pseudo-merohedral twinning in the structure of the hydrated 1:1 proton-transfer compound of 5-sulfosalicylic acid with 4-aminopyridine

The structure of the pseudo-merohedrally twinned crystal of the 1:1 proton-transfer compound of 5-sulfosalicylic acid (3-carboxy-4-hydroxybenzenesulfonic acid) with 4-aminopyridine: 4-aminopyridinium 3-carboxy-4-hydroxybenzenesulfonate sesquihydrate has been determined at 180 K and the hydrogen-bonding pattern is described. Crystals of the compound are monoclinic with space group P21/c, with unit cell dimensions a = 35.2589(8), b = 7.1948(1), c = 24.5851(5) Å, β = 110.373(2)o, and Z = 16. The monoclinic asymmetric unit comprises four cation-anion pairs and six water molecules of solvation with only the pyridinium cations having pseudo-symmetry as a result of inter-cation aromatic ring π-π stacking effects. Extensive hydrogen bonding gives a three-dimensional framework structure.

Manipulating double-decker molecules at the liquid-solid interface

We have used a scanning tunneling microscope to manipulate heteroleptic phthalocyaninato, naphthalocyaninato, porphyrinato double-decker molecules at the liquid/solid interface between 1-phenyloctane solvent and graphite. We employed nano-grafting of phthalocyanines with eight octyl chains to place these molecules into a matrix of heteroleptic double-decker molecules; the overlayer structure is epitaxial on graphite. We have also used nano-grafting to place double-decker molecules in matrices of single-layer phthalocyanines with octyl chains. Rectangular scans with a scanning tunneling microscope at low bias voltage resulted in the removal of the adsorbed doubledecker molecular layer and substituted the double-decker molecules with bilayer-stacked phthalocyanines from phenyloctane solution. Single heteroleptic double-decker molecules with lutetium sandwiched between naphthalocyanine and octaethylporphyrin were decomposed with voltage pulses from the probe tip; the top octaethylporphyrin ligand was removed and the bottom naphthalocyanine ligand remained on the surface. A domain of decomposed molecules was formed within the double-decker molecular domain, and the boundary of the decomposed molecular domain self-cured to become rectangular. We demonstrated a molecular “sliding block puzzle” with cascades of double-decker molecules on the graphite surface.

Diiodidobis[4-(-nitrobenzyl)pyridine-kN']zinc

In the structure of title compound [ZnI2(C12H10N2O2)2] from the reaction of 4-(4-nitrobenzyl)pyridine with zinc(II) iodide, the asymmetric unit contains two independent discrete distorted tetrahedral complex units [Zn-I range, 2.5472(8)-2.5666(7)A; Zn-N range, 2.044(4)-2.052(4)A], which are essentially identical conformationally and exist in the crystal structure as a racemic twin.

Amine-sssisted route to fabricate LiNbO3 particles with a tunable shape

An ethylenediamine-assisted route has been designed for one-step synthesis of lithium niobate particles with a novel rodlike structure in an aqueous solution system. The morphological evolution for these lithium niobate rods was monitored via SEM: The raw materials form large lozenges first. These lozenges are a metastable intermediate of this reaction, and they subsequently crack into small rods after sufficiently long time. These small rods recrystallize and finally grow into individual lithium niobate rods. Interestingly, shape-controlled fabrication of lithium niobate powders was achieved through using different amine ligands. For instance, the ethylenediamine or ethanolamine ligan can induce the formation of rods, while n-butylamine prefers to construct hollow spheres. These as-obtained lithium niobate rods and hollow spheres may exhibit enhanced performance in an optical application field due to their distinctive structures. This effective ligand-tuned-morphology route can provide a new strategy to facilely achieve the shape-controlled synthesis of other niobates.

2,4,6-Trinitro-N-[4-(phenyldiazenyl)phenyl)phenyl]aniline

The title compound, C18H12N6O6 was prepared from the reaction of 4-(phenyldiazenyl)aniline (aniline yellow) with picrylsulfonic acid. The dihedral angle formed by the two benzene rings of the diphenyldiazenyl ring system 6.55(13)deg. and that formed by the rings of the picrate-aniline ring system is 48.76(12)deg. The molecule contains an intramolecular aniline-nitro N-H...O hydrogen bond.

Evidence of multiwall carbon nanotube deformation caused by poly(3-hexylthiophene) adhesion

We show that when a soft polymer like Poly(3-hexyl-thiophene) wraps multiwall nanotubes by coiling around the main axis, a localized deformation of the nanotube structure is observed. High resolution transmission electron microscopy shows that radial compressions of about 4% can take place, and could possibly lead to larger interlayer distance between the nanotube inner walls and reduce the innermost nanotube radius. The mechanical stress due to the polymer presence was confirmed by Raman spectroscopic observation of a gradual upshift of the carbon nanotube G-band when the polymer content in the composites was progressively increased. Vibrational spectroscopy also indicates that charge transfer from the polymer to the nanotubes is responsible for a peak frequency relative downshift for high P3HT-content samples. Continuously acquired transmission electron microscopy images at rising temperature show the MWCNT elastic compression and relaxation due to polymer rearrangement on the nanotube surface.

Fast hole surface conduction observed for indoline sensitizer dyes immobilized at fluorine-doped tin oxide - TiO2 surfaces

The indoline dyes D102, D131, D149, and D205 have been characterized when adsorved on fluorine-doped tin oxide (FTO) and TiO2 electrode surfaces. Adsorption from 50:50 acetonitrile - tert-butanol onto flourine-doped tin oxide (FTO) allows approximate Langmuirian binding constants of 6.5 x 10(4), 2.01 x 10(3), 2.0 x 10(4), and 1.5 x 10(4) mol-1 dm3, respectively, to be determined. Voltammetric data obtained in acetonitrile/0.1 M NBu4PF6 indicate reversible on-electron oxidation at Emid = 0.94, 0.91, 0.88, and 0.88 V vs Ag/AgCI(3 M KCI), respectively, with dye aggregation (at high coverage) causing additional peak features at more positive potentials. Slow chemical degradation processes and electron transfer catalysis for iodine oxidation were observed for all four oxidezed indolinium cations. When adsorbed onto TiO2 nanoparticle films (ca. 9nm particle diameter and ca.3/um thickness of FTO0, reversible voltammetric responses with Emid = 1.08, 1.156, 0.92 and 0.95 V vs Ag/AgCI(3 M KCI), respectively, suggest exceptionally fast hole hopping diffusion (with Dapp > 5 x 10(-9) m2 s-1) for adsorbed layers of four indoline dyes, presumably due to pie-pie stacking in surface aggregates. Slow dye degradation is shown to affect charge transport via electron hopping. Spectrelectrochemical data for the adsorbed indoline dyes on FTO-TiO2 revealed a red-shift of absorption peaks after oxidation and the presence of a strong charge transfer band in the near-IR region. The implications of the indoline dye reactivity and fast hole mobility for solar cell devices are discussed.

Electron diffusion and back reaction in dye-sensitized solar cells : the effect of nonlinear recombination kinetics

The electron collection efficiency in dye-sensitized solar cells (DSCs) is usually related to the electron diffusion length, L = (Dτ)^1/2, where D is the diffusion coefficient of mobile electrons and τ is their lifetime, which is determined by electron transfer to the redox electrolyte. Analysis of incident photon-to-current efficiency (IPCE) spectra for front and rear illumination consistently gives smaller values of L than those derived from small amplitude methods. We show that the IPCE analysis is incorrect if recombination is not first-order in free electron concentration, and we demonstrate that the intensity dependence of the apparent L derived by first-order analysis of IPCE measurements and the voltage dependence of L derived from perturbation experiments can be fitted using the same reaction order, γ ≈ 0.8. The new analysis presented in this letter resolves the controversy over why L values derived from small amplitude methods are larger than those obtained from IPCE data.