فصلنامه مواد پیشرفته و پوشش های نوین
پیاپی 34 (پاییز 1399)

Due to the severe and harmful effects of chemical pollutants on human health and the environment, researchers have always been looking for effective ways for detoxification of chemical pollutants. In this study, zirconium-based metal-organic framework (UiO-66) nanostructures were synthesized in two gel-based (xerogel) and solvothermal (aerogel) methods. Morphology, crystalline structure, porosity and specific surface area as well as their behavior against degradation of dimethyl methylphosphonate (DMMP) as nerve agent simulant were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD), N2 adsorption isotherms (BET) and gas chromatography-mass spectrometry (GC-MS). The results showed the synthesis of aerogel and xerogel UiO-66 with uniform size distribution and crystalline structure indicating the successful synthesis of these compounds. UiO-66 xerogel also showed higher specific surface area and pore volume than UiO-66 nanocrystals (aerogel). The degradation performance of the synthesized metal-organic framework nanostructures showed that the UiO-66 xerogel with a half-life of 28.6 min had better catalytic properties than the UiO-66 aerogel at 120 min and ambient temperature, as about 80% of DMMP is hydrolyzed.

We prepared samples including nanoparticles of Fe3O4 via co-precipitation method with microwave heating using water and ethylene glycol as solvent. The procedure was repeated with various natural surfactants. XRD and SEM analysis was performed to determine the nanostructural characteristics of nanoparticles. SEM analysis disclosed that the type of surfactant and solvent will affect the nanostructures. In the next stage, Fe3O4/Ag nanocomposite was prepared using magnetite nanoparticles and AgNO3 by microwave method and its nanostructure was defined by SEM and TEM analysis. The mean diameter was determined between 40-55 nm from SEM software and 44-64 nm by Motic software for particles of all samples. Likewise, the purity of Fe3O4 nanoparticles and prepared nanocomposite were documented by FT-IR spectrometry. All the products had pure nanoparticles of Ag and Fe3O4 which was agreed with XRD results. To evaluate the magnetic parameters of samples, VSM analysis were done. Hysteresis curves disclosed that all the products have superparamagnetic properties. We also assessed the photocatalytic potential of prepared nanocomposites using methyl orange and congo red solutions under UV radiation and the effect of concentration of absorbent, pH of solutions and the time of irradiation on the color removing was investigated. This study confirms that these Fe3O4/Ag nanocomposites can be used as recyclable photo-catalysts for water refinery in home and industries. The best result for color removing was for 0.9 gr/lit absorbent, pH=2 and t= 80 min for irradiation.

Harvesting of wasted energies using mechanical to electrical energy nanogenerators has become a major branch of energy research area due to the global energy concerns. Piezoelectric and triboelectric mechanisms are between the two most widely used methods in this field. In this study, different combinations of fibrous nanogenerators including PVDF nanofibers and PVDF / BaTiO3 composite nanofibers with wool fabrics consist of three types of weft knitted fabric and combed wool fibers were prepared, due to their promising position in the triboelectric series. Different configuration of layers were also set to optimize the layer composition for the best electrical output. The electrical output voltage per unit area of different samples were measured after the contact - separation mode of electrification for each sample. Results showed that the arc-shape layer deposition has the best triboelectric layer arrangement to achieve the optimized electrical output at a specified force with the highest output value of 4.35(V/cm2), where the output of PVDF piezoelectric layer was only 0.475(mV/cm2). For a given force, the output of the triboelectric nanogenerator was more than 9000 times higher than that of the pure PVDF/BaTiO3 piezoelectric nanogenerator. These results teach us a first step towards the fabrication of self-chargeable wearable microelectronic devices.

Cathodic protection by using photocatalysts, a new method of metal protection, is known as photoelectrochemical cathodic protection. In this study, at first, hematite nanotubes were prepared by electrochemical anodizing method; and then, using chemical bath deposition method at different times, tungsten trioxide particles were created on the surface of hematite nanotubes. Electron microscopy images confirmed the formation of regular hematite nanotubes on the surface; so by increasing the deposition time, the nanotubes diameter reduced from 40 nm to about 36 nm. The results of XRD, EDX and EDX-Mapping showed the presence of tungsten particles and their uniform distribution on the surface of the nanotubes. In order to study the photoelectrochemical properties of the samples, as photoanode in the photoelectrochemical protection of 403 stainless steel, chronoamprometry, open circuit potential and Tafel methods were used. The results showed that the coated (modified) samples had better performance than the uncoated ones (bare nanotubes), and of all prepared samples, sample T3 (with a deposition time of three hours) has the best performance. Also, the calculation of electron half-life in the samples using OCP tests showed that this value for H, T1, T2 and T3 samples is 0.92, 1.96, 2.12 and 1.99 seconds, respectively.

In this study, self-stratified metallic surface coating based on polyurethane resin consisting of single-layer polymer acrylic with high gloss, without the use of clear coat, with the aim of covering industrial parts, home appliances and even car body repair was designed and formulated. The purpose of the work was to reduce the amount of consumables, work error and coverage time compared to the conventional and traditional coating (two layers of coating consisting of metallic base coat and clear coat). To design the experiments (DOE), the Taguchi method was used to optimize the type and amount of the main raw materials, including polyol acrylic resin type, cellulose acetate butyrate and wax. Various tests such as adhesion, gloss, hardness, abrasion salt fog and immersion were performed on the formulated coatings. The results showed, for example, an optimal adhesion rate of (5B), a gloss about 89%, mottling level of 51, and hardness of 210 seconds. Also, no sedimentation was observed in the liquid state and the results of moisture resistance and water immersion tests were acceptable based on standard criteria, compared to conventional double-layered samples.

In this work, polyaniline (PANI) microcapsules were successfully synthesized by the oxidative polymerization in the direct mini-emulsion method. 8-hydroxyquinoline (8-HQ) was used as a corrosion inhibitor in the core of microcapsules, which can also act as a fluorescent indicator. The synthesized microcapsules were characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Dynamic Light Scattering (DLS), Fourier Transform Infrared spectroscopy (FTIR), Thermal Gravimetric Analysis (TGA) and Ultraviolet-Visible spectroscopy (UV–Vis) techniques. The qualitative study of the corrosion resistance behavior of coatings containing microcapsules was performed using the salt spray test. The FE-SEM images were used to study the morphology of the surface of the microcapsules. According to FE-SEM images, the microcapsules with and without 8-HQ were almost identical in appearance, and the diameter of the spherical microcapsules was approximately 0.6-5 µm. The results of the DLS showed that the synthesized microcapsules are monodisperse and have a narrow distribution of particle size. The chemical structure of the microcapsules was investigated using FTIR spectroscopy. The results of the TGA analysis confirmed the formation of polyaniline microcapsules. The UV–Vis spectroscopy showed that polyaniline microcapsules are sensitive to reducing and oxidizing agents and are released by reduction-oxidation reactions. Since PANI microcapsules can exhibit an oxidation-reduction response to electrical or chemical stimuli, these particles could be an appropriate choice to be used in anti-corrosion and self-healing applications in metallic systems. The results of the salt spray test showed that the epoxy coating containing 5 wt.% of the microcapsules, has better corrosion resistance than the epoxy.

In this paper, starch nanocomposite are synthesized by the addition of nanocrystalline montmorillonite and graphite and identified by various characterization methods. To improve the nanocomposite properties of starch, it is activated using methyl methamethacrylate monomer, and then polymer (methyl methacrylate) polymer is placed on the starch by polymerization reaction on starch. Methylene base-acrylamide mesh agent has been used to make cross-links in polymers and to cross-link them. The composite prepared in this study was identified by various methods, including nuclear magnetic resonance imaging, subcutaneous radiography, scanning electron microscopy imaging, and heat weight analysis. Graphite has been used as a conductive additive in composites and the electrical conductivity of composites has been evaluated by the spectroscopic method of electrochemical impedance. Different amounts of graphite, including 0, 5, 10 and 15% by weight of graphite, were used as additives in the composite, and an electrical conductivity study showed that a composite containing 10% by weight of graphite showed the highest conductivity. The results showed that the starch composite of the grid containing the monoclonal nanofluid additives and graphite had an electrical conductivity.