Yüksel Bayrak

Effect of hydrogenation on density and viscosity of sunflowerseed oil

The densities and viscosities of unhydrogenated and hydrogenated sunflowerseed oils have been determined at temperatures ranging from 25 to 50°C at 5°C intervals. The densities of these oils vary linearly with temperature. The values of the parameters for the density equation have been calculated. Smooth curves were obtained when the changes in viscosity with temperature were plotted in the form of ln η vs. 1/T. The energy of activation, the free energy of activation, and the entropy of activation have been calculated at 25°C, and they decreased with the degree of unsaturation in the fatty acid chains of the sunflowerseed oil.

Adsorptive Removal of Rhodamine B with Activated Carbon Obtained from Okra Wastes

This study aimed at preparing and optimizing an activated carbon (OAC) obtained from dry okra wastes by chemical activation with zinc chloride. Also, Rhodamine B removal performance from aqueous solution was analyzed by using this optimized activated carbon. The characterization of the resultant activated carbon, with a high surface area of 1044 m2/g, was carried out using thermogravimetric analysis, Brunauer–Emmett–Teller model, t-plot, N2 adsorption/desorption isotherms, density functional theory, elemental analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, and the point of zero charge. Furthermore, the effects of operating conditions (contact time, initial concentration, adsorbent dosage, temperature, and pH) on Rhodamine B adsorption onto OAC were investigated. Langmuir model was determined to be the best adsorption process, and the maximum adsorption capacity was calculated to be 321.50 mg/g at 25°C. Also, the intraparticle diffusion and boundary layer diffusion were involved in RhB adsorption onto OAC. Moreover, OAC adsorption curves of Rhodamine B followed pseudo second-order model. At 25°C, Gibbs free energy, enthalpy, and entropy obtained from thermodynamic studies were determined to be −27.87 kJ/mol, 13.03 kJ/mol, and 0.15 kJ/mol K, respectively. These thermodynamic values revealed that Rhodamine B adsorption onto OAC was feasible, endothermic, physical, and spontaneous.

Removal of Remazol Black B Textile Dye from Aqueous Solution by Adsorption: Equilibrium and Thermodynamic Studies

The use of low-cost, easy obtained, high-efficiency, and eco-friendly adsorbents has been investigated as an ideal alternative to the current expensive methods of removing dyes from aqueous solution. This study investigates the potential use of activated carbon prepared from orange peel for the removal of Remazol Black B (RB) dye from aqueous solution. It was seen that the removal of RB increased with increasing solution pH (4–10), solution temperature (25–55°C) and adsorbent dose (0.1–1 g/20 mL). The maximum dye removal was reached at 90 minutes. Adsorption isotherms were analyzed by Langmuir and Freundlich models at different temperatures of 25°C, 35°C, 45°C, and 55°C, and the results were discussed in detail. Moreover, the thermodynamics of adsorption were also studied. It was found that the values of standard free energy (ΔG°) were negative for activated carbon. The values of standard enthalpy (ΔH°) and entropy (ΔS°) were found to be positive, and the obtained results were interpreted in detail. Activated carbon developed from orange peel can be attractive options for dye removal from diluted industrial effluents since test reaction made on simulated dyeing aqueous solution show better removal percentage of RB.

Active carbon/graphene hydrogel nanocomposites as a symmetric device for supercapacitors

ABSTRACT Activated carbons (ACs) are successfully synthesized from Elaeagnus grain by a simple chemical synthesis methodology and demonstrated as novel, suitable supercapacitor electrode materials for graphene hydrogel (GH)/AC nanocomposites. GH/AC nanocomposites are synthesized via hydrothermal process at temperature of 180°C. The low-temperature thermal exfoliation approach is convenient for mass production of graphene hydrogel (GH) at low cost and it can be used as electrode material for energy storage applications. The GH/AC nanocomposites exhibit better electrochemical performances than the pure GH. Electrochemical performance of the electrodes is studied by cyclic voltammetry, and galvanostatic charge-discharge measurements in 1.0 M H2SO4 solution. A remarkable specific capacitance of 602.36 Fg−1 (based on GH/AC nanocomposites for 0.4 g AC) is obtained at a scan rate of 1 mVs−1 in 1 M H2SO4 solution and 155.78 Fg−1 for GH. The specific capacitance was increased 3.87 times for GH/AC compared to GH electrodes. Moreover, the GH/AC nanocomposites for 0.2 g AC present excellent long cycle life with 99.8% specific capacitance retained after 1000 charge/discharge processes. Herein, ACs prepared from Elaeagnus grain are synthesized GH and AC supercapacitor device for high-performance electrical energy storage devices as a promising substitute to conventional electrode materials for EDLCs.

Kinetics and Thermodynamics of Cr(VI), Cu(II), and Ni(II) Adsorption on Activated Carbon Prepared from Rice Hulls

First, activated carbon was prepared by various ammonium compounds such as NH4NO3, NH4Cl, NH4Br, NH4I, NH4HCO3, and (NH4)2HPO4. The pore properties such as surface areas, pore volumes and pore sizes of them were compared under same activation conditions (600°C, 5 g of rice hull, 20 g of ammonium compound, within a half-hour activation time). The highest surface area by Brunauer-Emmett-Teller (BET) method was obtained as 456.7667 m2 g−1 by ammonium nitrate compared to other ammonium compounds, and then the kinetics and thermodynamics of Cr(VI), Cu(II), and Ni(II) ions removal from aqueous solutions on this activated carbon were studied. The adsorption data was found to follow second order kinetic model to explan the kinetics of Cr(VI), Cu(II), and Ni(II) ions adsorption, and rate constants were evaluated with the help of this kinetic model. Activation energy and other activation thermodynamic parameters (ΔS≠, ΔH≠, and ΔG≠) were determined by means of the rate constants at different temperatures. Equilibrium data were fitted to the Langmuir and Freundlich adsorption isotherms. Freundlich isotherm best fits the experimental results. Thermodynamic parameters such as KC, ΔG, ΔH, and ΔS were also calculated. The positive value of ΔS and negative values of ΔG showed the spontaneous of this adsorption system, while the positive value of ΔH pointed out this is an endothermic process.

Adsorption of cationic dyes on activated carbon obtained from waste Elaeagnus stone

Activated carbon was obtained from waste Elaeagnus stone by a chemical activation method utilizing ZnCl2. The resultant Elaeagnus activated carbon (EAC) with a high activated specific surface area of 1588 m2/g was characterized using Brunauer–Emmett–Teller method, Fourier transform infrared spectra, point of zero charge, and scanning electron microscopy. The removals of cationic dyes, i.e., malachite green (MG), rhodamine B (RB), and methylene blue (MB) from aqueous solutions via EAC adsorption were characterized by investigating the effects of adsorbent concentration, contact time, initial dye concentration, and temperature. Langmuir model provided the most appropriate fit for all EAC dye adsorption processes, and the adsorption capacities for MB, RB, and MG at 25℃ were calculated to be 288.18, 281.69, and 432.90 mg/g, respectively. The EAC adsorption curves of MB, RB, and MG follow a pseudo second-order kinetic model, and the calculated thermodynamic parameters, i.e., ΔG°, ΔH°, and ΔS° revealed that the synthetic dye adsorptions from aqueous solution were endothermic and spontaneous.

Thermodynamıc Studıes of Interactıon Between CTAB and Carboxymethylcellulose Usıng Different Techniques

Mixtures of carboxymethyl cellulose (carboxyMC) and cethyltrimethyl ammonium bromide (CTAB) were investigated using surface tension, specific conductivity and density measurements. The parameters of the surfactant to polymer association processes such as the critical aggregation concentration (cac) and the polymer saturation point (psp) were determined from the plots of surface tension, specific conductivity and density versus surfactant concentration. The thermodynamic parameters of polymer-surfactant interaction were calculated at different temperatures. The results showed that the standard Gibbs free energy , the enthalpy and the entropy of the aggregation process were found negative in all cases.

Phase Behavior of Oil/Water/Nonionic Surfactant Systems

The phase behavior of oil/water/nonionic surfactant systems under the effect of temperature is usually only measured at an oil‐to‐water ratio of 1:1 (α = 0.5). It was found that with increasing oil‐chain length and increasing hydrophilicity of the surfactant (Triton X‐114 to Triton X‐100), the three‐phase region widens toward higher temperatures. The clear inclination of the “fishes” at constant oil‐to‐water ratios shows that the surfactant becomes more hydrophobic with increasing temperature. It was observed that the phase behavior of systems changes with the amount and kinds of added salts. The description of the experiments by the modified Landau‐type model is satisfactory.