Journal of Nanoanalysis
Volume:1 Issue: 1, Apr 2014

In this study, a new silica gel based adsorbent was fabricated and its ability in separation and quantification of alkanes mixture was investigated. Silica gel (SiO2) is a polar absorbent which is mainly used to separate polar compounds. Also, the carbon materials such as activated carbon and recently carbon nanotube (CNTs), have been widely used for separation of nonpolar materials. Carbon nanotubes are nanosized carbon-based sorbents that have a high surface area and a large aspect ratio and are known to be stable at high temperatures. It is, therefore, conceivable to use of their unique properties in gas chromatography. In this work, a MWCNT-Silica gel nanocomposite was prepared by Sol-Gel process and it was used as stationary phase in gas chromatography for separation of alkanes mixture. In first part, ability of silica gel adsorbent was studied and then results were compared with new MWCNT-Silica gel nanocomposite. Finally, a quantitative investigation was done on a LPG sample and propane, 2-methylpropane, n-butane, 2,2-dimethylpropane, 2-methylbutane and n-pentane were measured by standard addition.

The separations of alcohols with hydrophilic and hydrophobic parts, and the separation of aromatic mixtures, are extremely important processes in gas and petroleum industries. Choosing an adsorbent for performing this separation is the most important part of the process. Silica gel is used as an adsorbent is various techniques such as pressure swing adsorption (PSA) and gas and liquid chromatography. Due to the polarity of silica gel, it is used for the separation of polar molecules. Carbon materials such as activated carbon and recently carbon nanotube (CNTs) are widely used for the separation of nonpolar materials. In the course of this study, a new composite was fabricated using sol-gel methods. Multiwall carbon nanotubes (non-polar carbon-based adsorbents with high surface areas) were mixed with a silica gel base (a strong polar adsorbent). The composite was then used in the separation of mixtures of both aromatic hydrocarbons and alcohols.

An attempt has been made to investigate the effect of SiO2 nanoparticles on the conductivity of polypyrrole conducting polymeric films prepared by an electrochemical method. The obtained nanocomposites were characterized by FTIR, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results indicate that the conductivity of the nanocomposite was significantly increased in comparison to pure polypyrrole. Fitting the impedance results to an equivalent circuit reveals that addition of SiO2 nanoparticles reduces the ohmic resistance due to the better conductivity.

In this study, the adsorption behavior of the primary, secondary and tertiary alcohols over nanoscale (1 0 0) surface of defect spinel γ-alumina was investigated with the aid of density functional theory (DFT) at BLYP/DNP level of calculation. The influence of different substituents including alkyl, cycloalkyl, allyl and aryl were analyzed for free and adsorbed alcohols to shed light the adsorption selectivity of these compounds over γ-alumina surface. These results indicate that more branches at a position of alcohol favor the adsorption, while a decrease in adsorption energy is achieved for the alcohols containing the substituents at the β position. The tertiary alcohols are adsorbed over the surface stronger than secondary and primary alcohols. Alcohols with larger alkyl chains have greater adsorption energies. Also the aryl alcohols are adsorbed over the surface better than the alkyl and allyl moieties.

Infrared (IR) and ultraviolet (UV) spectroscopic analysis of eight structural isomers of C20 carbon nanostructures, i.e. ring, tadpole, bow-tie, dumb-bell, spiro, propellane, bowl and cage, were performed at different levels of theory including semi-empirical (AM1 and PM3), Hartree-Fock (HF/6-31++G, 6-31++G**) and density functional theory (B3LYP/6-31++G, 6-31++G**). A broad range of IR spectra (400-2700 cm-1) is covered by C-C bending vibrations (low frequency region) and C-C stretching vibrations (high frequency region) in almost all isomers. The absorption maximum (λmax) in UV spectra for bowl and cage isomers appears below 300 nm and for cyclic isomers above it. These results show that IR and UV spectra are useful tools for identification of C20 structural isomers.

Silicate mesoporous materials are of the main interesting adsorbents for decreasing of hydrogen sulfide (H2S) from crude oil. In this work zinc impregnated highly ordered MCM-41 was synthesized via post-synthesis functionalization and was used as adsorbent for removal of H2S from crude oil. Also the variation of solvents was mainly adjusted. In  order  to  determine  the  ideal  solvent  for  the  synthesis  of  zinc incorporated MCM-41,  a  few solvents (water, ethanol and THF) has been tried in these experiments. The experiments showed that THF is a better solvent to get better materials.

The acid dissociation constants of the hydroxyl groups in 25, 26, 27, 28-tetrahydroxy-5, 11, 17, 23-tetrasulphonic-calix[4]arene (SC4) were determined at 25οC by a combination of potentiometric and spectrophotometric titration method. The first and second acid dissociation constants (pKa1, pKa2) were found to be 3.19 and 12.1, which demonstrated pKa shift due to intramolecular hydrogen bonding interactions among hydroxyl groups in SC4.