Ünal Geçgel

Removal of Methylene Blue from Aqueous Solution by Activated Carbon Prepared from Pea Shells (Pisum sativum)

An activated carbon was prepared from pea shells and used for the removal of methylene blue (MB) from aqueous solutions. The influence of various factors such as adsorbent concentration, initial dye concentration, temperature, contact time, pH, and surfactant was studied. The experimental data were analyzed by the Langmuir and Freundlich models of adsorption. The adsorption isotherm was found to follow the Langmuir model. The monolayer sorption capacity of activated carbon prepared from pea shell for MB was found to be 246.91 mg g−1 at 25 ∘C. Two simplified kinetic models including pseudo-first-order and pseudo-second-order equation were selected to follow the adsorption processes. Kinetic studies showed that the adsorption followed pseudo-second-order kinetic model. Various thermodynamic parameters such as , , and were evaluated. The results in this study indicated that activated carbon prepared from pea shell could be employed as an adsorbent for the removal of MB from aqueous solutions.

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.

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.

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.