Papers by Author: Mohammad Reza Vaezi

Abstract: Titanium dioxide is a cheap, chemically stable and non-toxic material. However its photocatalytic properties are unstable and it is a modest semiconductor and a mediocre insulator. For several applications it would be interesting to make it either more insulating or more conducting. The goal of this work was to modify the photocatalytic properties of nano-crystalline TiO2 powders by wet chemical routes and hydrothermal methods to understand the mechanism leading to these modifications The principal factors that influence the photocatalytic properties are on the one hand the concentration and nature of the chemical and physical conditions in TiO2, and on the other hand the morphology of the powders. The study was split into two parts. The fist part describes the modifications of the material obtained by chemical preparation's parameters. Like: preparation method, pH., additives, surfactants, and temperature. The second part describes the modifications obtained by modifying the photo catalysis reactors. Several analysis techniques have been used to characterize the TiO2 samples. They are essentially divided in four categories. The chemical analyses included electron probe microanalyses. The structure and morphology analyses of powders were carried out with x-ray diffraction. The photo catalytically properties in batch or CRS mode were measured in room temperature. Finally optical transmission provided information on the electronic states and morphology of the samples. The results imply that powders with anatase 40% and rutile 60 % with 15nm crystallite size have the optimum properties.

Abstract: Microwave irradiation is a novel method to accelerate the preparation of inorganic nanoparticles as well as various nanostructures such as nanotubes, nanorods, and nanowires. In this research, silver (Ag) nanostructures with various morphologies were prepared via a rapid microwave-assisted technique. The spherical and polygonal Ag nanoparticles were synthesized in the presence of Polyvinilpyroliden (PVP) as stabilizing agent. Ethylene glycol (EG) serves as a solvent. The silver nanoparticles were produced by Continuous and Discontinuous Wave irradiation. The obtained materials were characterized by UV-visible and transmission electron microscopy (TEM). The results present that the size of nanoparticles increase in continuous irradiation. In this process, the morphology of product is polygonal. In the discontinuous process the colloidal particle size is smaller than that obtained from the continuous process. Furthermore, the Ag nanoparticles have spherical shapes. The final data show that microwave processing has unique advantages over conventional heating processes.

Abstract: Nowadays, different production methods of nanoparticles have been developed. Among novel wet-chemical processes, the Chemical Bath Deposition (CBD) method is used to synthesize nanoparticles more easily than the other method. In this investigation, titanium dioxide (TiO2) nanoparticles were synthesized by the Chemical Bath Deposition (CBD) method. Tetraisopropyl titanate (C12H28O4Ti), sodium hydroxide (NaOH) and ethanol were used as initial materials. Appropriate solvents were used for preparation of samples. CBD process was carried out at 50°C for 90 min and the obtained materials washed and then dried at room temperature for 48 hrs. For determining particle size and evaluation of morphological characteristics, X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used. The TEM observation indicated that the average particles size of powder is about 10-30 nm and the shape of product is semi-spherical shape. The final results present that the CBD method is more suitable than the other process because of it showing a low processing cost and fine powders.

Abstract: Current researches show a growing interest in Zinc Oxide (ZnO) nanoparticles. ZnO is a semiconductor with a wide direct band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature. Several methods have been developed in order to synthesize ZnO nanoparticles. Chemical methods, among them sol-gel process, are more convenient. Sol-gel is common for producing metal oxide nanoparticles because of its simplicity, cheapness and high quality products. In this research ZnO nanoparticles were prepared via the sol-gel process. ZnAc2.2H2O as precursor and TEA (Triethanolamine) as a novel surfactant were used in a methanolic solution. MEA (Monoethanolamine) and DEA (Diethanolamine) have been highly used before. In this research, solutions with different weight ratios of ZnAc to TEA (1:2, 1:1 and 2:1) were obtained. After drying, all samples were calcinated at 500 °C for 1 hr. Obtained nanoparticles were characterized with the hope of achieving better properties.

Abstract: The study of mechanical alloying on the Fe–Cu system, as a model system for those with positive heats of mixing, are investigated. In this research work the effects of impact force, such as increasing in the surface temperature of powders, the number of vacancies and pipe diffusion, on the strain and grain size of final powders have been studied. The aim of this research is to find the optimum condition for mechanical alloying of Cu-Fe system by the help of automatic design and analysis of TAGUCHI experiments.

Abstract: ZnO nanoparticles because of their interesting properties and various morphologies, has become one of the most attractive nanomaterials for research objectives. Its significant properties has made it applicable in UV-Light emitters, varistors, transparent high power electronics, gas sensors, etc., [1]. Many approaches have been used to obtain ZnO nanoparticles, including: Hydrothermal [2], Solvothermal [3], Reverse micelles [4], Sol-Gel [4], Sonochemical [5], and Chemical Bath Deposition [6], etc. Among these, hydrothermal and alcohol-thermal methods have been extremely investigated. In this paper, buthanol as a solvent is used for synthesis of Zinc oxide at 130°C and 150°C at different reaction periods. Also the effects of different surfactants including: N_Cetyl_N,N,N,_trimethyl ammonium bromide (CTAB), Poly vinyl pyrolidon-K90 (PVP), Poly ethylene glycol-15000 (PEG) on obtained morphologies were investigated extremely. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were used for characterization of nanoparticles.

Abstract: ZnO as a semiconductor is used in many applications such as gas sensor devices, laser and optoelectronic devices, photocatalysts, solar cells, and varistors. The applications and properties of ZnO nanoparticles highly depend on the size and morphology of these particles. In this research ZnO nanoparticles were prepared via chemical bath deposition at various temperatures in order to see the effects of synthesis temperature and also 2- methoxyethanol (2-ME) as a novel solvent on the morphology of obtained nanoparticles. For synthesizing of ZnO nanostructured materials, 2-ME has been highly used in sol-gel process but it is the first time that it is used in the chemical bath deposition process. For this purpose 1 M solutions of zinc acetate dehydrate in 2-ME were prepared and added to the solution of NaOH in the same solvent dropwisely. Monoethanolamine (MEA) was used as surfactant. The synthesis temperatures were 30°C, 60°C and 90°C. After filtering and drying, morphologies of obtained nanoparticles were characterized and compared.

Abstract: Nanometer oxides e.g. SnO2, ZnO, TiO2, ZrO2, etc. have photocatalytic and gas sensing properties which can be different in nanometer range. They have been produced by several methods such as Chemical Bath Deposition (CBD), Pulsed-laser deposition, Chemical Vapor Deposition (CVD), screen printing and firing process, spray pyrolysis technique, magnetron sputtering, mechanical alloying, etc. It was found that the production method and its parameters would affect the size and morphology of these oxides. By using a composite of these oxides their properties would also be affected. In this paper the effects of sonication and reaction temperatures on SnO/ZnO coupled oxides' morphologies were investigated. These coupled oxides were characterized by X-Ray Diffraction (XRD), X-Ray Florescence (XRF), Scanning Electron Microscopy (SEM), and Differential Thermal Analysis (DTA). As a result of using the ultra sound source, the sizes of nano oxides decreased, which is one of the most important advantages of sonochemical synthesis in comparison with chemical bath deposition synthesis of these nano-composites.

Abstract: Magnetite (Fe3O4) nanoparticles were prepared simply by the reverse co-precipitation method from the solution of ferrous/ferric mixed salt in the presence of cationic surfactant (cetyl trimethyl ammonium bromide, CTAB) and nonionic surfactant (Polyethylene glycol, PEG) in two concentrations. Meanwhile, Fe3O4 nanoparticles without surfactant are also synthesized under the same condition for comparison. In addition via the reverse co-precipitation method, the pH which is an important factor in synthesis of magnetite was controlled at high values easily. The experimental results reveal that addition of surfactants affected on the size and morphology of the nanoparticles based on the X-ray diffraction (XRD) and scanning electron microscope (SEM) characterizations.