جستجوی مقالات مرتبط با کلیدواژه « graphene nanosheets » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

Hypothesis:

 A nanocomposite layer including graphene nanosheets could be used to enhance the barrier properties of high density polyethylene through a layer-by-layer assembly method. Planar graphene nanoparticles help to decrease the gas permeability of polyethylene substrates by making a tortuous pathway for gas molecules transmittance.

Two different methods were used to increase the barrier properties of high density polyethylene and the results were compared with each other. In the first method, a thin film of polymer nanocomposite including graphene oxide nanoparticles and polyvinyl alcohol was coated on the surface of high density polyethylene film using a film applicator. The effective variables in this method were the weight fraction of graphene oxide particles in polyvinyl alcohol and thickness of the nanocomposite layer. In the second method, a layer-by-layer assembly was used. Chitosan solution acted as a positive charge and graphene oxide suspension in water was utilized as a negative charge.

In high density polyethylene samples coated by polyvinyl alcohol nanocomposite (10 micrometers), the oxygen transmittance rate decreased drastically to 3 cm3m2 bar. This decrease was expected due to the structure of polyvinyl alcohol and its inherent barrier properties. By adding graphene oxide into polyvinyl alcohol, the permeability values showed a slight decrease and reached 0.8 cm3 m2 bar.Statistical analysis based on the surface response method for the layer-by-layer method showed that permeability depends on pH, number of bilayers and graphene concentration. At high pH, the graphene oxide sheets take on a smoother and more stretched shape and are more likely to aggregate, which increases permeability.

By varying the level of graphene's surface oxidation in this paper, the thickness of the interphase region was altered, and its influence on the conductivity was investigated. Due to the similarity of water-based epoxy chemical groups with graphene oxide oxygen groups, the interphase region was reinforced. Infrared spectroscopy and thermal gravimetry were performed to evaluate the graphene oxide synthesis, and Raman spectroscopy was also performed to investigate the structural defects on graphene sheets. At first glance, based on the interphase region theory, it is expected that by increasing the oxidation rate of graphene nanosheets, the electrical conductivity of polymeric coatings will increase, and the percolation threshold will decrease. On the other hand, due to increased oxidation, the structural defect on graphene nanosheets increases, and the conductivity of the coatings is expected to decrease. Due to the opposite effect of the two factors mentioned above, the effectiveness of nanocomposite samples was studied, and the impressment of each factor was investigated in this project.

 The combustion of fossil fuels to supply energy produces large amounts of carbon dioxide. Carbon dioxide emissions have led to rising global temperature and many natural disasters, including floods, hurricanes, rising sea levels, and widespread droughts, that threaten ecological systems and human life. Therefore, the uptake and removal of carbon dioxide from sources or the environment play a key role in countering the threat of global warming.

In this study, a venturi scrubber was utilized to eliminate CO2 from the air stream on a semi-industrial scale. The effects of different parameters including inlet air flow rate to the venturi scrubber, solvent flow rate, and solvent loss during the scrubbing process were investigated on CO2 absorption by a nanofluid solvent containing iron oxide/water at the presence of tetramethylammonium hydroxide (TMAH) as a surface-active material.

The surface-active material of TMAH prevents the agglomeration of nanoparticles in the base fluid and stabilizes the fluid. The maximum efficiency of absorption and the highest molar flux of CO2 were achieved when iron oxide nanoparticles were used along with graphene nanosheets with the ratios of iron oxide nanoparticles (25%) and graphene nanosheets (75%) at the presence of TMAH surface-active material due to their nature. The reason is the better agitation (of the solution) by iron oxide nanoparticles that results in an increased displacement of graphene nanosheets. The random Brownian movements of nanoparticles create micron size eddies that increase mass transfer at the gas-liquid interface. In addition, molar flux and CO2 gas absorption efficiency decreased by increasing the concentration of nanoparticles.

Epoxy resin has remarkable properties including excellent mechanical and electrical properties, thermal and chemical stability, and resistance to creep. On the other side, these resins are brittle with low resistance toward crack initiation and its growth. In order to solve this problem, thermoplastic polysulfone and graphene nanosheets have been used as filler for improving the flexibility of epoxy coatings. The effect of adding different amounts (1, 0.5, 2.5, 5 wt%) of polysulfone and 0.5 wt% of graphene nanosheets on the epoxy properties was investigated by thermal analysis (DSC), tensile strength, impact resistance and determining the gel content of samples. The results showed that the tensile strength of epoxy resin increased by adding polysulfone, and the graphene nanosheets could improve flexibility of the sample containing 1 wt% polysulfone. The study of thermal properties of cured samples by means of DSC analysis showed that the addition of polysulfone into the epoxy network resulted in changing the glass transition (Tg) of the resin. With incorporation of graphene nanosheets into the polymer matrix, the modulus decreased due to the reduction in number of crosslinks. The study in impact resistance of the samples showed that those containing 1 wt% polysulfone and 0.5 wt% graphene displayed high strength and impact resistance. These types of compounds can be used in flexible and anticorrosion coatings.

Today’s, discharge of toxic industrial effluents into the environment is one of the major problems of societies. Recently, graphene as member of carbon allotropes have attracted researcher's attention to color removal due to high surface area. Graphene is a monolayer of sp2-hybridized carbon atoms arranged in a two dimensional lattice. Dyes contain aromatic rings in their chemical structure that can be adsorbed well by grapheme through the π- π interactions. Several researches have been investigated on the use of dispersed graphene nanosheets as an efficient adsorbent for removal of dyes. The results indicated graphene can adsorb dyes very well but their performance has been limited by extend of dispersion. Now, the high cost of production is the major obstacles to its industrial using. In this paper, the commonly used methods for the synthesis of graphene and its application in the removal of color compounds from industrial wastewater have been reviewed.