Preparation and characterization of chitosan-clay nanocomposites with antimicrobial activity

Chitosan-montmorillonite nanocomposites were prepared by an ion exchange reaction between water soluble oligomeric chitosan and a Na⁺-montmorillonite. The chitosan-montmorillonite nanocomposites were rapidly prepared within 1 h due to the high affinity between the chitosan and the montmorillonite clay host. The basal spacings of the composites were in a range of 14.5-19.6 Å depending on the mixing ratio of chitosan to clay. According to the thermogravimetric analysis (TG) and powder X-ray diffraction analysis the thermal stability of chitosan was remarkably improved in the interlayer space due to the strong electrostatic interaction of cationic chitosan molecules with anionic silicate layers. From the antimicrobial activity test it was found that the nanocomposites showed a synergistic effect in the antimicrobial activity against to Escherichia coli and Staphylococcus aureus.     

Gallate-Zn-Al-layered double hydroxide as an intercalated compound with new controlled release formulation of anticarcinogenic agent

A new organic-clay material, in which the organic moiety is intercalated into the inorganic interlayer, was prepared using gallate anion (GA) as a guest, and Zn-Al-layered double hydroxide, as clay host. The ion-exchange technique was found to be effective for the intercalation process in the formation of the compound. Although the basal spacings of the LDH and its intercalated product were fairly similar, FTIR, CHNS and TGA/DTG results indicated that the GA was actually intercalated into the interlayer of the host in parallel orientation. The resulting nanostructure material possessed a well ordered layered structure with 42.2% GA loading (w/w). The release of the anion from the interlayer of the intercalated compound was found to be of controlled manner, governed by the first order kinetic and it was also concentration dependent. The material has potential as a nano-storage of anticarcenogenic agent with controlled delivery capability.     

Deep desulfurization of model gasoline over photoirradiated titanium-pillared montmorillonite

The activity of Ti-pillared montmorillonite for photocatalytic oxidative desulfurization using 2,5-dimethylthiophene dissolved in n-octane as a model organosulfur compound in gasoline was investigated. Using Ti-pillared montmorillonite and an oil/acetonitrile two-phase extraction, deep desulfurization of sulfur-containing compounds was achieved. During this process, O₂ was used as the oxygen source and photoirradiation was achieved by UV light. Using this approach, 97.4% of the sulfur compounds were oxidized and successfully removed from the model gasoline system under mild reaction conditions. Montmorillonite was prepared by sol–gel method and characterized by XRD, N₂ absorption and UV–vis spectroscopy. The characterization indicates that Ti component enters the interlayer of montmorillonite, working as an active component in the crystal phase of anatase. Deep desulfurization experiments show that the activity of Ti-pillared montmorillonite is obviously better than P25.     

Supramolecular structural control and characteristics of p-hydroxybenzoate intercalated hydrotalcite

p-Hydroxybenzoate pillared layered double hydroxides with different Zn/Al mole ratios have been prepared by three different methods: rehydration of calcined LDH precursor, coprecipitation and anion exchange. The products have been characterized by several experimental techniques: PXRD, FT-IR, TG-DTA and UV-vis. PXRD patterns show that the interlayer distance of p-hydroxybenzoic acid (PHBA)-Zn/Al-LDH varies with ratio Zn/Al, from 14.8 to 15.3 Å, indicating that altering Zn/Al ratios can change the arrangement of the intercalated PHBA anions. Not only do infrared spectra display the characteristic absorption of both the PHBA anion and the Zn/Al layer, but also provide further evidence of the interaction between these two parts. Thermal analysis confirms that the intercalation can make PHBA stable up to 434 °C, which is 213 °C higher than that for pure PHBA. By UV-vis it is found that such a product can control blocking of UV radiation in a wider range of wavelength.     

Large scale intercalated growth of short aligned carbon nanotubes among vermiculite layers in a fluidized bed reactor

Short aligned carbon nanotubes (CNTs) were intercalated grown among vermiculite layers from ethylene using a simple fluidized bed chemical vapor deposition (CVD) process. The length of CNTs ranged from 0.5 to 1.5 μm after a synthesizing duration of 1-5 min at 650 °C. The as-grown CNTs vertically aligned to the vermiculite layers were with the mean outer and inner diameter of 6.7 and 3.7 nm, respectively. A CNT yield of 0.22 g/g_cat was obtained for a 5-min growth. Those indicated that the fluidized bed CVD was an effective way for mass production of short CNTs.     

High temperature-pressure processing of mixed alanate compounds

Mixtures of light-weight hydrides and elements were investigated to increase the understanding of the chemical reactions that take place between various materials. This report details investigations we have made into mixtures that include NaAlH₄, LiAlH₄, MgH₂, Mg₂NiH₄, alkali(ne) hydrides, and early third row transition metals (V, Cr, Mn). Experimental parameters such as stoichiometry, heat from ball milling versus hand milling, and varying the temperature of high pressure molten state processing were studied to examine the effects of these parameters on the reactions of the complex metal hydrides.     

Reactions of chlorine and related molecules with graphite intercalation compounds

K-graphite intercalation compounds (GICs), metal chloride-GICs and reduced products of CuCl₂-GICs were allowed to react with chlorine. Decomposition of K-GICs took place through the reaction with chlorine. The extent of the decomposition was found to be dependent not on the gas pressure of the chlorine but on the stage number of the starting GIC. Metal chloride-GICs were unreactive with chlorine, whereas chlorine could react with copper particles generated in the interlayer of graphite through the reduction of CuCl₂-GICs. The reaction products were CuCl and CuCl₂; the former exists as crystals in the interlayer, and the latter can form CuCl₂-GICs. Also reported on are reactions of GICs with chlorobenzene, benzoyl bromide and iodine monochloride.     

Spray drying: An alternative synthesis method for polycationic oxide compounds

Synthesis of polycationic compounds by the spray-drying technique is an interesting alternative in the domain of aqueous precursor synthesis methods. Spray drying yields high quality samples with good reproducibility. The possibility of scaling up for production of large quantities with fast processing time is well established by the commercial availability of powders of various compositions. In this paper, we have discussed the advantages and limitations of this method and demonstrated its interest by synthesizing a few polycationic compounds selected for their attractive properties of thermoelectricity [Bi_1.68Ca₂Co_1.69O₈, La_0.95A_0.05CoO₃ (A=Ca, Sr, Ba)] or magnetoresistance [La_0.70A_0.30MnO₃ (A=Sr, Ba)]. We have confirmed the quality of these samples by reporting their structure, magnetic and transport properties.     

Preparation and thermal decomposition studies of l-tyrosine intercalated MgAl, NiAl and ZnAl layered double hydroxides

l-Tyrosine (represented as l-Tyr) intercalated MgAl, NiAl and ZnAl layered double hydroxides (LDHs) have been obtained by the method of coprecipitation. In situ FT-IR, in situ HT-XRD and TG-DTA measurements allow a detailed understanding of the thermal decomposition process for the three intercalated composites. In situ HT-XRD reveals that the layered structure of l-Tyr/MgAl-LDH collapses completely at 450 °C with the first appearance of reflections of a cubic MgO phase, while the corresponding temperature for l-Tyr/NiAl-LDH is some 50 °C lower. In contrast, there is a major structural change in l-Tyr/ZnAl-LDH at 250 °C as shown by the disappearance of its (0 0 6) and (0 0 9) reflections at this temperature accompanied by the appearance of reflections of ZnO. In situ FT-IR experiments give information about the decomposition of the interlayer -Tyr ions. The decomposition temperature of l-Tyr in the ZnAl host is about 50 °C lower than the corresponding values for the MgAl and NiAl hosts. TG-DTA curves show a significant weight loss step (170-260 °C) in l-Tyr/ZnAl-LDH which is due to the dehydroxylation of the host layers, with a corresponding weak endothermic peak at 252 °C. This temperature range is much lower than that observed for MgAl and NiAl hosts, indicating that the ZnAl-LDH layers are relatively unstable. The data indicate that the order of thermal stability of the three intercalates is: l-Tyr/MgAl-LDH > l-Tyr/NiAl-LDH > l-Tyr/ZnAl-LDH.     

Effect of donor-acceptor defect pairs on the crystal structure of In and Ga rich ternary compounds of Cu-In(Ga)-Se(Te) systems

A comparative study of the effect of donor-acceptor defect pairs on the unit cell parameters a, c and V of the ordered defect compounds that are intermediate phases of the pseudo-binary [Cu₂(Se,Te)]_1−X[(In₂,Ga₂)(Se₃,Te₃)]_X system has been carried out. It is found that a, c and V decrease linearly with the increase in the fraction of cation vacancies to the total number of cation positions, m, or the fraction of the interacting donor-acceptor defect l per unit, respectively, in the chemical formula. The reduction in the unit cell dimensions is explained as due to the decrease in the effective cation radius r_eff caused by the increase in m or l or decrease in n. The linear dependence of r_eff on a, c, and V has important consequences. This behavior can be used to predict the unit cell parameters of other ODCs that may have chalcopyrite-related structure and have not been reported so far.     

Synthesis of dimethyl carbonate from methyl carbamate and methanol catalyzed by mixed oxides from hydrotalcite-like compounds

A series of mixed oxides calcined from hydrotalcite-like compounds with different cations were prepared and their catalytic activities were studied by the synthesis of dimethyl carbonate (DMC) from methyl carbamate and methanol. Among them, ZnFe mixed oxide possessed the best catalytic ability. Furthermore, the zinc-based mixed oxides as well as the corresponding hydrotalcite-like compounds were characterized by using ICP, TGA, CO₂-TPD and N₂ adsorption/desorption techniques.     

Synthesis of earth-abundant Cu2SnS3 powder using solid state reaction

Cu₂SnS₃ (CTS) powder has been synthesized at 200 °C by solid state reaction of pastes consisting of Cu and Sn salts and different sulphur compounds in air. The compositions of the products is elucidated from XRD and only thiourea is found to yield CTS without any unwanted CuS_x or SnS_y. Rietveld analysis of Cu₂SnS₃ is carried out to determine the structure parameters. XPS shows that Cu and Sn are in oxidation states +1 and +4, respectively. Morphology of powder as revealed by SEM shows the powder to be polycrystalline with porous structure. The band gap of CTS powder is found to be 1.1 eV from diffuse reflectance spectroscopy. Cu₂SnS₃ pellets are p-type with electrical conductivity of 10⁻² S/cm. The thermal degradation and metal–ligand coordination in CTS precursor are studied with TGA/DSC and FT-IR, respectively, and a probable mechanism of formation of CTS has been suggested.     

Electron density distribution in GaAs using MEM

Electron density distribution of GaAs is determined by means of the maximum entropy method (MEM) using reasonably good X-ray data collected at room temperature and 200 K. The bonding electron distributions are clearly visible in the MEM map and the mixed covalent-ionic character in GaAs is evidenced. The density distributions at 200 K show more condensed electronic clouds as compared to the room temperature map, preserving the trend in the bonding characters. The electron densities at the middle of the bond are 0.79 and 0.70 e/ų at 200 K and at room temperature, respectively. The refined harmonic thermal factors are in good agreement with the published values.     

Observations on the influence of pH control on the properties of chemically deposited CdS films in an ammonia-free system

In this work we report on the properties of chemically deposited CdS thin films in an ammonia-free cadmium-sodium citrate system. We studied the influence on the properties of the films of the pH control of the reaction solution. For this, we deposited two types of CdS films employing two different types of reaction solutions. The only difference between both reaction solutions was the addition of a pH buffer in one of them in order to control its pH throughout the deposition process. Several sets of CdS films were deposited from growth solutions with different contents of Cd to determine also the influence of this parameter on the properties of the films. The CdS films were studied by X-ray diffraction, optical transmission and reflection spectroscopy and scanning electron microscopy measurements. We found that the properties of the films depend both on the amount of Cd in the growth solutions and on their pH control. The increase in Cd in the reaction solution yields to films with shorter lattice constant and then higher energy band gap. On the other hand, the pH control of the reaction produces higher deposition rate, larger final thickness and higher energy band gaps in the CdS films.     

Temperature dependent transport properties of CuInSe2-ZnO heterostructure solar Cell

Experimental study of dc and ac transport properties of CuInSe₂/ZnO heterostructure is presented. The current-voltage (I-V) and frequency dependent capacitance (C-f) characteristics of CuInSe₂/ZnO heterostructure were investigated in the temperature range 160-393 K. The heterostructure showed non-ideal behavior of I-V characteristics with an ideality factor of 3.0 at room temperature. Temperature dependent dc conductivity studies exhibited Arrhenius type behavior and revealed the presence of trap level. The C⁻²-V plot measured at frequency 50 kHz had shown non-linear behavior. An increase in capacitance with temperature was observed. The capacitance-frequency characteristics exhibited a transition between low frequency and the high frequency capacitance. As the temperature was lowered the transition occurred at lower frequencies. The frequency and temperature dependent device capacitance had shown a defect state having activation energy of 108 meV.     

Preparation and visible light photocatalytic performance of methylene blue intercalated K4Nb6O17

K₄Nb₆O₁₇ was prepared by hydrothermal treatment of Nb₂O₅ in KOH solution at 180 °C, and then Methylene blue (MB) intercalated K₄Nb₆O₁₇ (K₄Nb₆O₁₇-MB) was prepared by one-pot reaction in which n-propylamine (PA) was used as an intercalation compound. The MB intercalated structure of K₄Nb₆O₁₇-MB was characterized by HRTEM and XRD measurements. K₄Nb₆O₁₇-MB shows good absorption in the visible region and is thermally stable up to 328 °C. By extending the hydrothermal time and selecting the K₄Nb₆O₁₇ with high crystallinity, the K₄Nb₆O₁₇-MB prepared by one-pot reaction showed higher visible light (λ>550 nm) photocatalytic activity than that prepared by traditional two-step electrostatic self-assembly deposition (ESD) method for the degradation of methyl orange (MO).     

Characterization of Cu(In,Ga)Se2 thin films prepared by evaporationfrom ternary compounds

Thin films of Cu(In,Ga)Se₂ were fabricated by evaporation from ternary CuGaSe₂ and CuInSe₂ compounds for photovoltaic device applications and their properties were investigated. From XRF analysis, the Cu:(In+Ga):Se atomic ratio in all thin films was approximately 1:1:2. The Ga/(In+Ga) atomic ratio in the thin films changed linearly from 0 to 1.0 with increasing the [CGS]/([CGS]+[CIS]) mole ratio in the evaporating materials. However, for thin films prepared at the [CGS]/([CGS]+[CIS]) mole ratio above 0.4, the composition by EPMA analysis was not consistent with that by XRF analysis. The result of EPMA analysis showed that the surface of a thin film was Cu-rich. XRD studies demonstrated that the thin films prepared at the [CGS]/([CGS]+[CIS]) mole ratio under 0.2 had a chalcopyrite Cu(In,Ga)Se₂ structure and the preferred orientation to the 112 plane. On the other hand, XRD patterns of the thin films produced at the [CGS]/([CGS]+[CIS]) mole ratio above 0.6 showed the diffraction lines from a chalcopyrite Cu(In,Ga)Se₂ and a foreign phase. The separation of a peak was observed near 2θ=27°, indicative the graded Ga concentration in Cu(In,Ga)Se₂ thin film.     

The effect of aminoalcohols (MEA, DEA and TEA) on morphological control of nanocrystalline ZnO powders and its optical properties

The potential of using encapsulation by MEA, DEA and TEA to control the morphology of ZnO powders was investigated. The crystallite and particle size decreased as a function of aminoalcohol concentration. We found that aminoalcohols can inhibit the crystal growth of ZnO along the c-axis. A steric effect by TEA more strongly influenced the formation of different ZnO shapes than did MEA and DEA. The value of the band gap was dependent on the crystallite size, particle size and particle shape.     

Deformation of single crystal sample using D-DIA apparatus coupled with synchrotron X-rays: In situ stress and strain measurements at high pressure and temperature

We present a technique for high pressure and high temperature deformation experiment on single crystals, using the Deformation-DIA apparatus at the X17B2 beamline of the NSLS. While deformation experiments on polycrystalline samples using D-DIA in conjunction with synchrotrons have been previously reported, this technical paper focuses on single crystal application of the technique. Our single crystals are specifically oriented such that only [1 0 0] slip or [0 0 1] slip in (0 1 0) plane is allowed. Constant applied stress (sigma <300 MPa) and specimen strain rates were monitored using in situ time-resolved X-ray diffraction and radiography imaging, respectively. Rheological properties of each activated slip system in the crystals can be revealed using this technique. In this paper, we describe the principle of sample preparation (e.g. [1 1 0]_c and [0 1 1]_c orientations) to activate specific slip systems (i.e. [1 0 0](0 1 0) and [0 0 1](0 1 0), respectively), stress measurement and procedures of the deformation experiments.     

Preparation of CuInGeSe4 thin films by selenization method using the Cu-In-Ge evaporated layer precursors

CuInGeSe₄ quaternary compounds are known to have a chalcopyrite-like structure and have band gaps of about 1.3 eV, suitable for optimum conversion efficiency for solar cells. We have prepared the CuInGeSe₄ thin films by the selenization method using the Cu-In-Ge evaporated layer precursors. The analyses of X-ray diffraction show that the single phase of CuInGeSe₄ is obtained by the selenization of precursors at 450-500 °C. The SEM observation of film surface shows that the grain sizes are in the order of 1-2 μm. The band gaps of selenized films close to 1.6 eV are wider than that of bulk crystals (about 1.3 eV). These films have p-type conduction and higher electrical resistivities than more 10⁵ Ω cm at room temperature.