فصلنامه مواد پیشرفته و پوشش های نوین
پیاپی 6 (پاییز 1392)

PVA/CdS nanocomposite thin films were prepared via electrospinning method at different ratio. Firstly, CdS nanoparticles were synthesized using cadmium nitrate (Cd (NO3)2) and sodium sulphide (Na2S) in a simple and economical way. Then, PVA/CdS nanocomposite were prepared at different CdS nanoparticles ratio (20, 30, 40 and 50) using electrospinning method. The morphology and structure of nanocomposites were characterized by X-ray diffraction and scanning electron microscopy (SEM). The results indicated the formation of CdS nanoparticles with crystalline phase in the PVA matrix and proved that nanoparticles were successfully coated by polyvinyl alcohol molecules. Furthermore, the optical properties were analyzed by diffuse reflectance spectroscopy (DRS). From the shift in optical band gap, particle sizes were calculated using effective mass approximation (EMA) method which were in agreement with the results obtained from XRD observation for 50:50 and 80:20 samples. The film prepared at 50:50 ratio was found to be suitable for application in solar cells as a window layer due to the crystalline phase, favorable band gap and higher optical transmittance.

The aim of this study was to investigate the effects of surfactant concentration on the size and magnetic stability of magnetite nanoparticles produced via chemical co-precipitation method and then, the effects of magnetite nanoparticles on the properties of the emulsion aggregation toner production method. In this study, magnetite nanoparticles were synthesized by using co-precipitation method and magnetite particle size was controlled using lauric acid surface active material. To evaluate the various characteristics of magnetite nanoparticles, DLS, XRD and VSM and for toner properties, PSA, VSM, POM and softening point were carried out. The results showed that, depending upon the saturation concentration of surfactant the magnetite saturation was changed between 28 emu/g and 62 emu/g. Furthermore, increase of surfactant concentration until the optimum point resulted in decrease of the saturation magnetization and particle size and also, the sub-phase of e-Fe2O3 became more intense. Eventually, the produced toner shows appropriate properties compared to the industrial sample.

In this study, a commercial zirconic acid based pretreatment was performed on hot dip galvanized steel sheets via immersion process. The effect of pH on morphology, composition and electrochemical behavior of the conversion layer was investigated. Field emission scanning electron microscopy (FE-SEM) coupled with energy dispersive X-ray spectroscopy (EDS) were carried out to study the morphology and composition of the surface after treatment. Also, DC polarization and EIS were used to evaluate the corrosion behavior of the treated surface in 3.5 wt.% NaCl. Electrochemical results revealed that the best anti-corrosion performance with the lowest current density and highest Rp value, belongs to the conversion coating obtained in acid concentration of 3% and pH= 5 for galvanized steel samples. EDS results disclosed that conversion coating consisted of: Fe, Zn, O, Zr and C confirming a dense ZrO2 layer is formed on galvanized steel samples. Furthermore, FE-SEM images showed that a uniform and compact layer of conversion coating is obtained on galvanized steel surface in pH=5 which corroborates EDS and electrochemical consequences.

In this study, ultrafine PbS nanoparticles were synthesized through wet-chemical synthesis, using 2-mercaptoethanol as a capping agent. It is for the first time that mercaptoenthanol is being used during synthesis of PbS. The structural, electronic/optical and morphological properties of the samples were studied by XRD (X-ray diffraction), UV-Vis spectroscopy and STM (scanning tunneling microscopy). It was found that, the size of the particles is highly dependent on the molarity of the capping agents. Excitonic shoulders along with a large blue shift of the absorption peaks in the optical spectra (due to quantum size effect) were observed to appear when the capping agent (2-mercaptoethanol) concentration increased from 0.1M (on set) to 1M (saturated state). The X-ray diffraction patterns exhibited the PbS characteristic peaks and also specified high purity of the samples. STM measurements were performed to observe the size and morphology of particles, which suggested that the particles are about 1.5-2 nm in size and spherical in shape. Band gap of the obtained PbS nanoparticles was calculated from the optical spectra and was found to be 4.1 eV. The merit of this study is that extremely fine PbS nanoparticles could be achieved with an approximate band gap of 3.5 eV which has not been reported so far.

In this research, the effect of expandable graphite (EG) incorporated into an epoxy aliphatic amine system was investigated. The epoxy/EG systems were prepared by using 0-4 wt% of EG. The morphological structures of expandable and expanded graphite were studied by scanning electron microscopy. The influence of EG content on the thermal, flame retardant and mechanical properties of epoxy resin was investigated using thermogravimetric analysis, oxygen index test, dynamic mechanical analysis, tensile and impact tests. TGA results showed that adding EG increases the initial decomposition and residue weights of the composites. It was found that the oxygen index, glass transition temperature and young’s modulus of epoxy/ EG systems increase up to 60 %, 3% and 50% with increasing EG concentration up to 4%(wt) respectively. On the other hand, maximum value for tensile strength, storage modulus, cross- linking density, ultimate tensile strain and impact strength were obtained when the concentration of EGwas 2wt% in the composite. These characteristics increased up to 30%, 57%, 74%, 14% and 25%, respectively.

Two new organic dyes based on indoline were prepared and phenothiazine was utilized as the electron donor and cyanoacrylic acid as the electron acceptor anchoring groups. All synthesized dyes prepared by standard reactions from phenothiazine as the starting material. To this end, phenothiazine as the starting material was alkylated, further aminated with POCl3 and subsequently nitrated with nitric acid. The obtained compounds were reacted with cyano acetic acid to prepare synthesis dyes. These dyes together with their corresponding intermediates were purified and characterized by FTIR, 1HNMR, 13CNMR, elemental analysis and UV-Visible analytical techniques. Spectrophotometric evaluations of the prepared dyes in solution and on a TiO2 substrate were carried out in order to assess changes in the status of the dyes. The wavelength of maximum absorption for each dyes in solution are 405 nm and 417 nm and on TiO2 films are 422nm and 436 nm, respectively. Finally, dye sensitized solar cells were fabricated in order to determine the current density/photovoltage curves and conversion efficiencies of each dye. The conversion efficiency for each dyes were 3.21% and 3.87%, respectively.

In this study, SiO2/ TiO2/ zeolite tertiary composites with (STZ) high adsorption capability and high photocatalytic activity were synthesized by immobilizing mixed silica and titanium dioxide nanoparticles on modified zeolite via sol-gel method. The characteristics of chemistry and morphology of composites were investigated by Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD) and scanning electron microscope (SEM). Addition of silica particles enhanced the uniform dispersion of titanium dioxide nanoparticles on modified zeolite by changing in surface charge of zeolite.Furthermore, FTIR spectra showed successful immobilizingof SiO2 and TiO2nanoparticlesinto the zeolite with AL (IV) and Si-O-Ti bonds. Surface area of the composites increased significantly after immobilizing of silica and titanium dioxide nanoparticles, and thus greatly improved the photodegradation efficiency. The optimal condition for complete decolorization with STZ0.2-0.4 and STZ 0.4-0.2 composites was found in 30 min.