فصلنامه مواد پیشرفته و پوشش های نوین
پیاپی 32 (بهار 1399)

In this study, nitrogen-doped porous carbon was prepared using a nitrogen containing polymer (polyaniline) as a precursor with KOH activation at activation temperature of 800°C. The porous structure of polyaniline and synthesized adsorbent were analyzed with atomic force microscopy (AFM), N2 adsorption-desorption isotherm, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The adsorption of CO2 and N2 by nitrogen-doped porous carbon were measured and correlated Sips model. The BET surface area and CO2 adsorption of prepared adsorbent (at 298K and 1ba) was achieved 723 m2/g and 1.90 mmol/g, respectively. The selectivity of CO2 over N2 (CO2: N2 =50: 50, 298 K, 1 bar), predicted by the ideal adsorbed solution theory (IAST) model, was achieved 3.02. The isostrict heat of adsorption was calculated by using Clausius-Clapiron equation and the results confirmed the exothermic nature of adsorption for both gases. Also, the higher value of heat of adsorption CO2 than N2, showed the stronger interaction between CO2 molecules with the nitrogen-doped porous carbon surface. Results obtained from gas adsorption and heat of adsorption proved the suitability of nitrogen-doped carbon in cyclic processes such as the PSA process.

Sol-gel protective coatings draw many attentions since they are low temperature productive, versatile chemically structure and user-friendly. Protective self-healing coatings provide longer life-time and less maintenance and repair's cost via healing the damages autonomically and non-autonomically. In this study, self-healing hybrid sol-gel coatings containing reversible tetra sulfide, synthesized and studied. The effect of the reversible group’s content and the crosslinking density on the thermal, mechanical and healing properties of the developed sol-gel polymers are presented. The prepared hybrid sol-gel polymers exhibited thermal stability in the S-S bond cleavage temperature window and a significant gap closure capability at modest temperatures. The gap closure efficiency of prepared polymer was strongly affected by healing temperature, crosslinking density and content of reversible tetra-sulfide groups. Investigation of self-healing hybrid sol-gel showed that regardless of mechanical properties' effect on the performance of healing properties, the content of reversible tetra sulfide groups was the main factor in the healing properties.

Production of hydrogen through photoelectrochemical water splitting using a semiconductor is a promising method for production of clean and renewable energy. Cu2O is a positive semiconductor that its conduction band position is suitable for photoelectrochemical reduction of water. In this study, Cu2O was synthesized using electrochemical deposition and it was heat treated at 450 °C for 30 min to obtain two layer Cu2O-CuO and improve its photoelectrochemical property. Oxidation of Cu2O resulted in two layer Cu2O-CuO. The x-ray pattern of the electrodeposited layer showed a pure Cu2O layer. Scanning electron microscopy showed a microstructure change after heat treatment and the particle size was in nanometer scale. Photocurrent density was measured using linear sweep voltammetry under chopped illumination and it was concluded that the photocurrent density of the heat treated sample at 450 °C was increased to 731 μA.cm-2. Electrochemical impedance spectroscopy at constant potential and frequency range of 0.1-105 Hz and also at fixed frequency and potential range of -0.3V up to 0.5V was performed to study charge transfer characteristic of the photocathode and to determine the flat band potential and carrier density. Carrier density of Cu2O and Cu2O-CuO was determined to be 1.3×1018 cm-3 and 3.05×1018 cm-3, respectively and the flat bend potential of Cu2O and Cu2O-CuO was determined to be 0.19V and 0.23V, respectively.

Nowadays, because of the growing of industrial process, environment contamination increased. Industrial waste waters and the resultant diseases that threaten today’s world; human knowledge leads to build a green and unpolluted world; and they are looking to use natural resources instead of chemicals.In the natural dyeing, which is very important in the art-industry of carpet production, the use of natural materials rather than chemicals is considered. In the past, natural dyes were used to dye the required fibers for the carpet. Blue is one of the main colors in the hand-made carpet, which is produced by Woad and indigo in the past and synthetic Indigo nowadays. This research attempts to utilize natural blue color, by using available herbal resources. Plant used in this research is “Indigofera tinctoria”. The primary method of experimentation is extraction of blue pigment (Indigo) from the plant by hot water procedure. Also, the impacts of plant-drying methods on the amount of Indigo extraction from the plant were examined; including: drying in sunlight, in shadow, by microwave and in the oven. The results show that the most amount of Indigo extraction increased when the PH value is about 9. The extracted solution examination was stabilized for 7 days; and the heating temperature was 80 centigrade. Fastness of dyed fibers with extracted dye compare to synthetic Indigofera was acceptable.

Polymer electrolyte membrane fuel cells have received more attention than other fuel cells because of their advantages such as low operating temperature, high power density and short startup time. One of the most important components of a polymer electrolyte membrane fuel cell is bipolar plate which has various types. Metallic bipolar plates have advantages such as higher strength, lower thickness and lower weight than graphite-based composite bipolar plates. Corrosion resistance and interfacial contact resistance of metallic bipolar plates are some of the challenges of using metallic bipolar plates. For this reason, metallic bipolar plates are coated to increase corrosion resistance and reduce contact resistance. In this study, the properties and morphologies of gold coating on copper and stainless steel substrates were studied by using electroplating and sputtering methods. The surface morphologies of the specimens were investigated by scanning electron microscopy. In addition, interfacial contact resistance tests were used to evaluate contact resistance of coated and uncoated specimens. Finally, corrosion resistances of the specimens were studied using galvanostatic and potentiostatic tests. The results showed that the use of electroplating method produces many holes and pores in the specimen surface. It was also found that using sputtering method significantly resulted in an increase in corrosion resistance and decrease in contact resistance of coated specimens.

Dye-sensitized solar cells have been attracting much attention due to their proper efficiency, ease and low-cost manufacturing. In the dye-sensitized solar cells, photosensitizers play an important role in the light absorption and conversion of solar energy into electrical energy. In this work, we have tried to use natural dyes as sensitizers in the manufacture of color-sensitive solar cells. The natural dyes were extracted from plants such as Artemisia absinthinum, Verbascum thapsus, Heracleum persicum, Viola odorata, Matricaria chamomilla, Juglans regia, Corianderum sativum, Punica granatum, Rubia tinctorum, Rheum rhaponticum, Quercus, Lavandula officinalis. Initially, the working electrodes were fabricated using titanium dioxide nanoparticles according to the electrophoresis method and then the sensitization of the electrodes was done by natural dyes. In the final step, the effect of natural dyes on improving the efficiency of solar cells was investigated. The results showed that Lavandula aficinalis (Lavender) absorbed more visible light due to its hydroxyl and carboxyl groups and had the highest efficiency (0.053%) among the other cells.

In this study, the relationship between the color contrast of urban advertising designs with the readability of the designs at different speeds (highways, arteries, squares) as well as the relation between figurative, real and cartoon designs in readability and audience attraction is investigated. Due to the varying speed of the car, rider audiences have a different opportunity to view urban advertising in the around squares, arteries, and highways. Thus, the relationship between color contrast quality variables in two states (low and high), projection time factor (4,8, 12 seconds), and the effect of figurative, real and cartoon designs on the readability of drawings in the case of computer simulation Evaluation. The results show that high contrast designs have better readability. And the longer it takes from four seconds to twelve seconds to see the designs, the readability of the designs increases. On the other hand, the low viewing time limitations of designs can be offset by increased contrast. Using realistic images is more effective in reading high contrast design. Due to the good readability in low speed passages, there is no need to use high contrast in the design. This research shows that high contrast, used to enhance the readability of highway designs, is unnecessary in historical contexts around squares to reduce visual pollution in urban landscapes.