فصلنامه نانو مواد
پیاپی 26 (تابستان 1395)

In this research work RF Resorcinol formaldehyde (RF) aerogels were synthesized by sol gel method. Using various analyzes such as scanning electron microscope (SEM) and mechanical tests the optimum conditions for composite were obtained. Three samples were prepared in the presence of three different catalysts with R/C molar ratio of 50, 100 and 200. Among them Na2C 3 was the best catalyst with the least shrinkage of 31.87% and low density of 0.6317 g/cm3. Catalyst (C) respectively and the porosity of samples were investigated by SEM images. Furthermore, to find out the effect of catalyst, two other samples at a fixed ratio of R/C=100 and at the presence of NaHCO3 and K2CO3 as catalysts were synthesized. It was found that addition of multi wall carbon nanotubes (MWCNTs) at room temperature to the RF aerogels lead to more shrinkage 46.87%), low density of 0.492 g/cm3 and enhanced mechanical properties with the a Young's module in the order of 300.

Nanocrystalline copper aluminate powder was synthesized by a polyacrylamide gel method using aluminum nitrate, copper nitrate as precursor materials. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV-Vis spectrophotometry (UV-Vis), thermogravimetric and differential thermal analysis (DTA TG) and Fourier transform infrared spectroscopy (FTIR). Crystallized CuAl2O4 was initially observed after calcination at 500 °C and only peaks corresponding to CuAl2O4 spinel crystal were observed at 700 °C. The SEM results showed that the samples have layered morphology. These layered structures are made up of nano particles that are connected together. With increase of temperature, the layered structures are broken into smaller pieces. The results show that different calcination temperatures cause a variation in color.

A green approach by using aqueous extract of Rosmarinus officinalis L. for silver nanoparticles (AgNPs) synthesis was developed and optimized. Parameters affecting the synthesis of AgNPs, such as temperature, extract pH, silver nitrate and extract (ratio of plant mass to extraction solvent volume) concentrations were investigated and optimized. Optimum conditions for the synthesis of silver nanoparticles (AgNPs) are as follows: Ag concentration, 1 mM, extract concentration, 2 g/L, pH=9 and temperature, 45 °C. Biosynthesized silver nanoparticles were characterized using UV Visible absorption spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), dynamic light scattering (DLS) and transmission electron microscopy (TEM). TEM and DLS analyses shown the synthesized AgNPs were predominantly spherical in shape with sizes in the range of 20-40 nm. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of AgNPs were determined for several pathogens include Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Bacillus cereus and Staphylococcus aureus. The antibacterial activity of the synthesized AgNPs was compared with several antibiotic drugs as control. This eco friendly and cost-effective synthesis method can be potentially use for large-scale production of silver nanoparticles.

In this research, nanostructured intermetallic compounds γ-Cu5Zn8 produced by mechanical alloying and mechanical milling. For this purpose, the mechanical alloying was done by pure copper and zinc powder at a suitable weight ratio for forming the composition Cu5Zn8. In mechanical milling, first intermetallic compounds γ-Cu5Zn8 ingot was prepared and then mechanical milling was done by planetary ball mill at different times. Phase analysis and morphology has been made using X-ray diffraction (XRD) and scanning electron microscopy (SEM). After pressing, hardness and electrical conductivity tests were performed on the samples. The hardness for mechanical milling samples were calculated as 463.6 HV, whereas the hardness for mechanical alloying samples was measured as 432.3 HV.

In this study, nanocomposite coating was performed by incorporating nano-titania photocatalyst pigment with rutile and anatase phase in polyurethane (PU) to different loading level ( . , 0.5, 1.0 and 2.0% by weight) and also self-cleaning effect practically assessment. Dispersion of nanoparticles in PU matrix was done by using ultrasonication mixing machine, rotary mixer and finally gas removing. For providing nanocomposites with low agglomerate, shall be use dispersant accordance manufacture instruction. After addition of the appropriate amount of hardener, prepared nanocomposite coating was investigated by applying on steel and glass substrate and after 2weeks time for curing, exposing them to UV weathering and salt spray testing. The dispersion quality and surface morphology of nanocomposite coating was evaluated by using different analytical techniques. Dry film thickness (DFT) of samples was mostly in the range 90 μm. Roughness after exposing of naoncomposites on UV radiation and salt spray measurement by atomic force microscopy (AFM) topography. The results revealed that addition of 0.1 wt.% rutile phase of TiO2 nanoparticles improves the best performance of nanocomposite coatings. According the results adding nanoparticle to PU improve coating lift time and also reduce maintenance and repair costs and help to decrease environment damage.

A chemical nanosensor has been prepared by direct attachment of colored reagent on sol-gel film layer. This nanosensor has been made by direct attachment of Safranin O on the sol-gel film and the sensing layer consists of tetramethoxysilane and methyl-3-methoxysilane. The sol-gel films were placed in the 0.05% w/v Safranin O solution at 25 °C and the solution were stirred by magnet till the reagent completely diffuses in the sol-gel layer and distributes homogeneously. After washing the film by water, the sol-gel layer completely dried. The results film has less than 8 months lifetime and the time response of the film is less than 5 seconds. The linear range and detection limit of nanosensor were 2.00-2200 ng/ml and 2 ng/ml, respectively. This is a simple method and the color that used was cheap and nontoxic and can be used widely.