Nanoscience & Nanotechnology-Asia - Volume 2, Issue 1, 2012

A fundamental understanding of the physical and chemical properties of gold clusters, namely, the size dependence of these properties, is necessary for developing wide range of gold clusters’ applications. Having this purpose in mind, the structural and energetic properties, such as binding energies, relative stability and band gaps ΔEHL (HOMOLUMO gaps) are evaluated. The gold clusters in a wide range of sizes, Aun (n=2 - 2016), were constructed and studied by Density Functional Theory and Extended Hückel Theory approaches. It was shown that the high values of ΔEHL for the clusters with n= 2, 6, 8, 20 correlate with the highest stability. This finding explains the existence of magic numbers for gold clusters. The 20 atom tetrahedral cluster stands out as particularly stable, comparing to the other small clusters. The binding energy EB is found to increase with the cluster size. The second difference in energy - Δ2E(n) value is used as the criterion of stability, in addition to ΔEHL and also shows a tendency to increase with the cluster size. This behavior suggests a transition of larger clusters towards bulk metallic properties. Both curves - Δ2E(n) and ΔEHL show sharp transformation from high values to close to 0 eV at n=252-504 cluster sizes (it relates to ca 2 nm cluster size).

Zinc oxide (ZnO) is a wide-band gap IIb-I compound with wurtzite crystal structure, and possesses semiconducting, pyroelectric, piezoelectric, biosafe and biocompatible properties. With these unique characteristics, ZnO becomes one of the most important nanomaterials in scientific research and applications nowadays. The diversity of ZnO nanostructures gives the promising solution to many fields of nanotechnology research, such as dye-sensitized solar cells (DSSCs). As a low-cost alternative to conventional silicon-based or TiO2-based photovoltaic, one-dimensional (1D) ZnO nanomaterials exhibit remarkable potentials and meet the clean energy demand. The aim of this review is to present a brief overview for the preparation methods and properties of 1D ZnO nanotructures and describe their integration into the DSSCs field. In the end, the perspectives of the 1D ZnO nanostructures applied in DSSCs field are introduced.

In the present work, colon specific drug delivery systems have been selected, to deliver the drug locally to colon for longer period of time. Cross-linked guar gum microspheres of model drug secnidazole were prepared by emulsification method and were evaluated for size and surface morphology by SEM, encapsulation efficiency, yield, swelling study. In vitro drug-release studies were performed in conditions simulating stomach-to-colon transit in the presence and absence of rat cecal contents. The marketed product was also compared for drug release profiles. The guar gum microspheres retard the release of drug in stomach but it facilitates the release of large amount of drug in the colon in the presence of rat cecal contents, as these have polysaccharides enzymes that degrade the guar gum in the colon. The release data shows that 44.4% of drug was released in the presence of rat cecal content release medium in 24 hours. Drug release data were fitted to different mathematical model to find release kinetic of drug. The stability studies were performed by storing the microspheres at different conditions of storage. The significance of differences was evaluated by analysis of variance (ANOVA). Differences were considered statistically significant at P < 0.05.

Amphiphilic chitosan-graft-polylactide copolymers (CS-g-PLA) were synthesized via coupling reaction of monocarboxyl-ended polylactide with the amine group of chitosan in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide. The composition of CS-g-PLA copolymers was confirmed by 1H NMR and FTIR. Self-assembled micelles were prepared by direct dissolution of the copolymers in aqueous medium. TEM and DLS were used to determine the morphology and size distribution of micelles. The average diameter of micelles determined by DLS was in the range of 100-120nm, which is much larger than that estimated by TEM. The stereocomplexation between CS-g-PLLA and CS-g-PDLA seemed to enhance the stability of mixed micelles. Paclitaxel was loaded inside micelles by stirring for two days in the micellar solution. Release properties were examined by using high performance liquid chromatography. Micelles with lower initial drug load exhibited faster release rate. After 15 days, the cumulative release percentages from micelles with 5% and 10% initial drug loads reached 11% and 6%, respectively.

Particles with a nanoscale cubic structure, termed nano-cubes, in addition to nanoscale ball-shaped structures (nano-balls) were produced by electric arc discharge with a carbon electrode containing silicon, oxygen, sodium, and fluorine. The nano-cubes have a crystalline structure similar to the nano-balls. Two types of nano-cubes were produced by the electric arc discharge, the first composed only of silicon, and the second containing silicon, oxygen, carbon, sodium and fluorine. The nano-cubes were subjected to compression strength tests by the application of a load to the nano-cubes inserted between two polished sample stages with nano-level surface roughness. The nano-cubes containing silicon, oxygen, carbon, sodium and fluorine collapsed on the aluminum alloy sample stage. On the other hand, the silicon nanocubes were buried in the titanium alloy sample stage.

The asymmetry porphyrin incorporates into mesoporous molecular sieves SBA-15 which through the reaction of the OH group of SBA-15 with the fluorine group of the porphyrin. The resultant material was characterized by means of XRD, TEM, solid UV/Vis, FTIR and nitrogen adsorption. Results indicate that the channels of SBA-15 have been filled with porphyrins. Luminescent property was studied by solid fluorescent emission and excitation spectra. Result indicates that the property of SBA-15/porphyrin is better than that of the pure porphyrin.

Porous TiO2-Al2O3 composites were prepared by sol-gel method using tetrabutyl titanate and aluminum isopropoxide as the sol precursors. PEG1000 was used as the pore forming template. The materials were composed of anatase TiO2 and amorphous Al2O3. Long grooves distributed on the rough surfaces of the materials. FT-IR and XPS spectra indicated that the samples were composed of TiO2 and Al2O3. The porous TiO2-Al2O3 composite calcinated at 500 °C had average pore diameter of 14.56 nm, total pore volume of 0.3945 cm3·g-1, and specific surface area of 128.4 m2·g-1. Meanwhile, it had the maximum adsorption capacity and photocatalytic degradation activity. The maximum adsorption rate was 18.6% when methyl orange adsorption on the material reached the adsorption equilibrium in 30 min. After 90 min of irradiation, methyl orange photocatalytic degradation rate was 77.0%, while the total decoloration rate was 95.6% that was complicated by both photocatalytic degradation and adsorption.

For ultimate commercialization of carbon nanotubes, a cheap catalyst, a simple and large scale synthesis method and a cheap carbon source are necessary for their preparation at low cost. Here, an alternative way of preparing multi walled carbon nanotubes (MWNTs) on a large scale with low cost using conventional hydrocarbon source i.e., liquefied petroleum gas as carbon precursor (LPG) is presented. MWNTs were synthesized using LPG as carbonaceous precursor on Fe and Ni based catalyst on MgO substrate through chemical vapor deposition route. Since LPG is very cheap and has wide reserves, the results suggest that effective catalyst systems will allow the preparation of CNTs with yield up to 58% at low cost. The low ID/IG ratios for Fe/MgO and Fe-Ni/MgO were 0.41 and 0.43 respectively. This shows that CNTs synthesized with this system not only have a good yield but also good crystallinity too. The use of MgO as support minimizes the formation of amorphous carbon as the main impurity and deters the metal particles from aggregating. In this paper, results have been presented on the systematic study for the optimization of several growth parameters. The influences of various parameters such as nature of catalyst-substrate, gas flow rates, influence of hydrogen were investigated. This paper also includes the characterization of these CNTs by scanning electron microscope (SEM), transmission electron microscope (TEM), Raman microscope, thermo gravimetric (TG) analyzer etc.