Yazar "Özekmekçi, Mehtap" seçeneğine göre listele

Listeleniyor 1 - 5 / 5
  • Küçük Resim Yok
    Öğe
    A density functional theory study of molecular H2S adsorption on (4,0) SWCNT doped with Ge, Ga and B
    (Elsevier B.V., 2021) Geçim, Gözde; Özekmekçi, Mehtap
    The molecular adsorption of hydrogen sulfide has been investigated theoretically by using Density Functional Theory for gallium (Ga), germanium (Ge) and boron (B) doped (4,0) single-walled carbon nanotubes (SWCNTs). The method of B3LYP was utilized with basis sets of 6-31G(d,p) and LANL2DZ. Adsorption energy and adsorption enthalpy, HOMO and LUMO energy values, HOMO-LUMO energy gap, chemical hardness, chemical potential, electronegativity and Gibbs free energy values have been evaluated in this study. All doped SWCNT structures have negative Gibbs free energy and adsorption energy values which make these clusters promising for the removal of H2S by adsorption. However, Ge doped SWCNT cluster has the lowest HOMO-LUMO energy gap and chemical potential, highest electronegativity with minimum adsorption energy values when compared to other clusters. Furthermore, it is softer than other metal doped SWCNT clusters due to the lower chemical hardness value.
  • Küçük Resim Yok
    Öğe
    Ga and Ge-doped graphene structures: A DFT study of sensor applications for methanol
    (Elsevier, 2020) Geçim, Gözde; Özekmekçi, Mehtap; Fellah, Mehmet Ferdi
    Density functional theory calculations have been carried out to investigate the adsorption of methanol on the surface of Ga and Ge-doped graphene clusters and in order to explore the potential of doped graphene as a gas sensor. The hybrid B3LYP method with 6-31G (d,p) and LANL2DZ basis sets were used in this study. The charge distributions of structures show that both Ga-doped and Ge-doped graphene structures are sensitive to methanol molecule. The HOMO-LUMO gap of the Ga-doped and Ge-doped graphene structures decreased when methanol adsorbed on these structures. This result indicates that electrical conductivity of both structures have increased. Hence, Ga-doped and Ge-doped graphene structures could be utilized as a gas sensing material in order to detect methanol. Furthermore, the higher electrical conductivity and the smaller recovery time of Ge-doped graphene than those of Ga-doped graphene make it more sensitive and useful in terms of methanol sensing.
  • Küçük Resim Yok
    Öğe
    Removal of boron from industrial wastewater using PVP/PVDF blend membrane and GO/PVP/PVDF hybrid membrane by pervaporation
    (Springer, 2021) Özekmekçi, Mehtap; Ünlü, Derya; Çopur, Mehmet
    Removal of boron from water is a significant issue worldwide. Boron levels in waters containing high concentrations should be kept under control. Boron removal from the industrial wastewater released from Eti Mine Boron plants was investigated by using blend and hybrid membranes in a laboratory-scale pervaporation system. Polyvinylpyrrolidone/Polyvinylidene fluoride blend membrane and Graphene oxide/Polyvinylpyrrolidone/Polyvinylidene fluoride hybrid membranes were synthesized for this process. The membranes were characterized by using scanning electron microscopy, Fourier transform infrared, X-ray diffraction and contact angle measurements. Separation performance was evaluated in terms of flux, removal ratio of boron, and boron concentration in permeate within the membrane. Membranes showed higher separation performance in industrial wastewater. The highest boron removal was obtained as 99.86% with a flux of 0.755 kg/m2h when the 8 wt% graphene oxide loaded hybrid membrane was used. This study indicates that the Polyvinylpyrrolidone and Graphene oxide addition improved the membrane features and separation performances of the pervaporation process with improved hydrophilic membrane features can be preferred as an innovative water treatment method for the removal of boron from industrial wastewater. The obtained results show that pervaporation can be readily adapted to the removal of boron species by appropriate membrane selection.
  • Küçük Resim Yok
    Öğe
    Synthesis of CaCO3 and trimethyl borate by reaction of ulexite and methanol in the presence of CO2
    (Elsevier Sci Ltd, 2020) Özekmekçi, Mehtap; Çopur, Mehmet
    Developing CO2 capture and use of technologies to reduce anthropogenic emissions can be part of the solution against climate change. The purpose of this study is to develop a novel method to synthesize CaCO3 and trimethyl borate solution by utilizing and capturing carbon dioxide in a high pressure reactor. Dissolution of ulexite has been investigated to determine the effect of important working parameters by using Taguchi method. The parameters and their ranges were given as follows: reaction temperature, 80-120 degrees C; pressure, 10-30 bar; solid-to liquid ratio, 5/100-20/100 g/mL; particle size,-106 + 75 mu m-212 + 154 mu m; stirring speed, 500-750 rpm; reaction time, 20-60 min. The findings of this research were given as follows: (1) the optimum operational conditions were found to be reaction temperature 120 degrees C, pressure 30 bar, solid to liquid ratio 0.05 g/ml, stirring speed 750 rpm, reaction time 60 min, particle size -154 + 106 mu m, (2) 92.94 %of B2O3 was taken into solution under optimum condition (2) the sequestration capacity of CO2 was found to be 188 kg per ton ulexite (3) characterization of products by FTIR, SEM, XRD and ICP-OES confirmed that trimethyl borate and CaCO3 were synthesized. The utilization of CO2 in this process could sequester a considerably amount of CO2, therefore it can be contribute to decrease CO2 emission that causes greenhouse effect.
  • Küçük Resim Yok
    Öğe
    Use of zeolites for the removal of H2S: A mini-review
    (Elsevier, 2015) Özekmekçi, Mehtap; Salkıç, Gözde; Fellah, Mehmet Ferdi
    Being a successful adsorbent for removal of hydrogen sulfide, zeolites should have good sulfur loading capacity, good regenerability and stable structure. These are natural zeolites having high adsorption capacity compared to other zeolites and synthetic zeolites. Zeolites can be modified by metals or metal oxides in order to increase their adsorption capacity. Removal of H2S is an essential process because it leads to corrosion in transport lines and poisoning of many catalysts even in low levels. Different types of adsorption methods such as fixed bed adsorption, pressure swing adsorption and sequential bed methods were experimentally used to investigate the removal of hydrogen sulfide. Computational methods (DFT) were also utilized theoretically. ETS-2 zeolite can be good choice to remove H2S due to its adsorbent properties. However this material has not been studied so much. Therefore more studies should be done experimentally and theoretically to examine the removal of hydrogen sulfide on excellent metal exchange forms of ETS-2. Consequently zeolites that have sulfur capacity increasing with modifications of metals or metal oxides are promising materials due to their high surface volume ratio which is one of the most important factors in adsorption. (C) 2015 Elsevier B.V. All rights reserved.