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    Acid Red 1 and Acid Red 114 decolorization in H2O2-modified subcritical water: process optimization and application on a textile wastewater
    (Desalination Publications, 2017) Kayan, Berkant; Akay, Sema; Kulaksız, Esra; Gözmen, Belgin; Kalderis, Dimitrios
    Solutions of Acid Red 1 and Acid Red 114 were treated in H2O2-modified subcritical water in the temperature range of 100 degrees C-200 degrees C for up to 60 min. Response surface methodology based on the Box-Behnken design was used to optimize the process. For Acid Red 1, optimum decolorization of 97% can be achieved at 192 degrees C, 181 mM H2O2, 51.3 min treatment time, and 121 mg/L dye concentration. For Acid Red 114, the optimum conditions were 195 degrees C, 157 mM H2O2, 38 min treatment time and 110 mg/L dye concentration, where 91% decolorization could be obtained from the proposed model. It was determined that temperature is the most important factor, followed by the oxidant concentration. Degradation was less efficient for AR114 due to the double azo bonds, compared to the single azo bond of AR1. Application of the optimum treatment conditions on real reactive dye wastewater resulted in 92.7, 79.1 and 20.4% removal of BOD5, COD and TSS, respectively.
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    Adsorption of 2,4-dichlorophenol on paper sludge/wheat husk biochar: Process optimization and comparison with biochars prepared from wood chips, sewage sludge and hog fuel/demolition waste
    (Elsevier Ltd., 2017) Kalderis, Dimitrios; Kayan, Berkant; Akay, Sema; Kulaksız, Esra; Gözmen, Belgin
    The adsorption of 2,4-dichlorophenol, a toxic by-product of triclosan commonly found in wastewater treatment plant effluents, was studied on paper sludge/wheat husks biochar. By using response surface methodology, the optimum conditions and effects of pH, temperature, initial 2,4-DCP concentration and time were determined. The solution pH was found to be the most influential parameter whereas the optimum adsorption conditions were predicted as: C-0 = 40.28 mg L-1, T = 326 K, pH = 2.8, t = 143 min, where a 99.95% adsorption could be achieved. Both Langmuir and Freundlich provided a good fit for the experimental data, indicating a surface and multi-layer adsorption. Kinetically, the process primarily followed the pseudo-second order model (chemisorption). By comparing the adsorption capacity at equilibrium of our main biochar (q(e) = 9.28 mg g(-1)) to 3 biochars prepared from different biomasses (q(e) values 1.57-2.96 mg g(-1)), it was concluded that pH-dependent electrostatic interactions and non-covalent pi-electron donor-acceptor mechanisms play the most important role. Finally, there was indication that high concentrations of Ca and K may promote the adsorbate-adsorbent interactions and enhance adsorption.
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    An easily fabricated palladium nanocatalyst on magnetic biochar for Suzuki-Miyaura and aryl halide cyanation reactions
    (Royal Society of Chemistry, 2021) Turunç, Ersan; Akay, Sema; Baran, Talat; Kalderis, Dimitrios; Tsubota, Toshiki; Kayan, Berkant
    Biochar is a carbon-rich solid, the surface of which is covered with a high density of functional carbonyl, hydroxyl and carboxylic acid groups. In this work, palladium nanoparticles were embedded on magnetic biochar and a new reusable and environmentally-friendly catalyst was developed and applied for the promotion of Suzuki-Miyaura C-C coupling and cyanation reactions. The high-carbon (77%), low-ash content (5.8%) and the relatively high surface area (266 m(2) g(-1)) of pine tree biochar (PTB) suggested that it might be highly suitable as a catalyst substrate. The Fe3O4-Pd-biochar nanocomposite was successfully characterized using SEM, TEM, EDX, FT-IR, BET and XRD. Its catalytic role was initially evaluated using p-NO2C6H4I as a model reactant (for both types of reactions) and later for the production of biaryls and benzonitriles from a wide range of aryl halides under mild reaction conditions. Biaryls and benzonitriles were characterized using GC-MS. In the case of the Suzuki-Miyaura reaction, the optimum yield of 98% was obtained with a catalyst concentration of 0.04 mol%, microwave irradiation of 400 W, and a residence time of 5 min, using K2CO3 as the base. With respect to the cyanation reaction, dimethylformamide, Na2CO3 and 6 h were the optimum solvent, base and reaction duration, respectively. Subsequently, the nanocatalyst showed excellent catalytic activity in both reactions, achieving >88% yields in most cases, regardless of the aryl iodide or bromide used and the type of substitution.
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    Aqueous solubility and chromatographic studies of antifungal drug-fluconazole at high temperature conditions
    (Elsevier B.V., 2021) Akay, Sema; Kayan, Berkant
    Fluconazole is a novel triazole antifungistatic drug, which can be administered both orally and intravenously and is currently used for the treatment of systemic and superficial fungal infections. In this study, the solubility of fluconazole in water at elevated temperature and pressure was investigated at temperatures in the range of 298 to 473 K under autogenous- 5.0 MPa pressure. The results showed that the solubility of fluconazole was increased 146-fold at the highest experimental temperature of 473 K. Based on the experimental data, a mathematical model was developed to predict the solubility of fluconazole in subcritical water. The model was validated successfully and the theoretical solubility values matched well with the experimental data. Furthermore, a modified Apelblat equation provided a good fit to the experimental values except at low temperature. The molar enthalpy and the molar entropy of dissolution of fluconazole in subcritical water at temperatures ranging from 298 to 473 K were calculated. The good solubility of fluconazole in subcritical water allowed us to perform high temperature liquid chromatography (HTLC) for the determination of this agent. Moreover, thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis confirmed that fluconazole had excellent thermal stability under subcritical conditions.
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    Assessment of a Pd-Fe3O4-biochar nanocomposite as a heterogeneous catalyst for the solvent-free Suzuki-Miyaura reaction
    (Elsevier, 2021) Akay, Sema; Baran, Talat; Kayan, Berkant; Kalderis, Dimitrios
    The objective of this study was the development of a novel, biochar-based Pd nanocatalyst and its evaluation for the promotion of the Suzuki-Miyaura coupling reaction. The Fe3O4-Pd-biochar composite was successfully characterized through a range of spectroscopic and elemental analysis techniques. Its catalytic activity was initially assessed using p-NO2C6H4I as a model reactant and later for the production of biaryls from a wide range of aryl halides, under microwave irradiation and solvent-free conditions. The optimum yield of 99% was obtained at a catalyst dosage of 8 mg, microwave irradiation of 400 W, 6 min residence time, using K2CO3 as the base. Furthermore, the catalyst promoted the Suzuki-Miyaura reaction of aryl iodides and bromides (yields in the range of 88-97 and 86-97%, respectively), but was less successful for aryl chlorides (yields 78-83%). The presence of Fe3O4 allowed for the quick recovery of the catalyst, whereas repeated runs established its recyclability.
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    Degradation of emerging contaminant coumarin based on anodic oxidation, electro-Fenton and subcritical water oxidation processes
    (Academic Press Inc., 2022) Görmez, Özkan; Akay, Sema; Gözmen, Belgin; Kayan, Berkant; Kalderis, Dimitrios
    The degradation of emerging contaminant coumarin was separately investigated in anodic, electro-Fenton and subcritical water oxidation processes. With respect to the anodic and electro-Fenton oxidation, the influence of constant current, treatment time and initial concentration of coumarin was studied. Regarding subcritical water oxidation, the effect of the oxidant concentration, temperature, treatment time and initial coumarin concentration was investigated. In anodic and electro-Fenton oxidation processes, coumarin degradation proceeded in a similar manner, achieving 99% degradation, after 180 min at a constant current of 200 mA. In both set-ups, further increasing the applied current lowered the degradation efficiency due to the formation of by-products and the increasing occurrence of side-reactions. The highest degradation of 88% was achieved in subcritical conditions, specifically at 200 °C, using 150 mM H2O2 and after 37.5 min of treatment. Under subcritical conditions, temperature was the most prominent parameter, followed by the H2O2 concentration. Under all methodologies, increasing treatment time had a small positive effect on coumarin degradation, indicating that time is not the most influential parameter. A comparison of the three methodologies in terms of performance as well as energy consumption and simplicity of operation highlighted the advantages of subcritical water oxidation.
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    Degradation of nitroaromatic compounds in subcritical water: application of response surface methodology
    (Desalination Publications, 2017) Kayan, Berkant; Akay, Sema; Gözmen, Belgin; Gizir, A. Murat; Demirel, Muhammet; Kalderis, Dimitrios
    In this study, subcritical water has been used as a medium for degradation of 2,4-dinitrotoluene (2,4-DNT), 4-nitrotoluene (4-NT) and 2-amino-4-nitrotoluene (2-A-4-NT). The effect of temperature, oxidant concentration and time were studied and the optimal combination of reaction parameters was established using response surface methodology in a Box-Behnken design. Of all the parameters examined, temperature showed the most positive effect on the degradation of the nitroaromatic compounds. Optimal reaction conditions were found to be a temperature of 240 degrees C, 210 degrees C and 236 degrees C, time of 180, 178 and 172 min, oxidant concentration of 100, 99.64 and 99.61 mM for 2,4-DNT, 4-NT and 2-A-4-NT, respectively. Since high-temperature was applied, the possibility of formation of subcriticaldegradation products existed; therefore, total amounts of degraded nitroaromatic compounds and formed intermediate products were determined by gas chromatographic-mass spectrometric analysis.
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    Degradation, solubility and chromatographic studies of Ibuprofen under high temperature water conditions
    (Elsevier Ltd, 2021) Akay, Sema; Öztürk, Serpil; Kalderis, Dimitrios; Kayan, Berkant
    Ibuprofen (IBP) is an emerging environmental contaminant having low aqueous solubility which negatively affects the application of advanced oxidation and adsorption processes. It was determined that as the temperature increased to 473 K, the mole fraction solubility increased considerably from 0.02 × 10?3 to 212.88 × 10?3 (10600-fold). Calculation of the thermodynamic properties indicated an endothermic process, ?solH > 0, with relatively high ?solS values. Spectroscopic, thermal and chromatographic analyses established the IBP stability at subcritical conditions. In the second part of the study, the degradation of IBP in H2O2-modified subcritical was studied and the effect of each process variable was investigated. The optimum degradation of 88% was reached at an IBP concentration of 15 mg L?1, temperature of 250 °C, 105 min treatment time and 250 mM H2O2. The process was optimized by response surface methodology and a mathematical model was proposed and validated. Temperature was determined as the most influential parameter, followed by H2O2 concentration. At temperatures higher than 230 °C, a small but noticeable reduction in degradation % suggested that the OH· radicals are consumed at a higher rate than they are produced, through side reactions with other radicals and/or IBP by-products. Finally, potential by-products were determined by gas chromatographic-mass spectrometric analysis and potential by-products were proposed.
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    Dissolution thermodynamics and preferential solvation of 2,4-dinitrotoluene in (ethanol + water) mixtures
    (Elsevier B.V., 2021) Akay, Sema; Kayan, Berkant; Martínez, Fleming
    Abstract Author keywords Indexed keywords SciVal Topics Abstract In this research, the equilibrium mole fraction solubility of 2,4-dinitrotoluene (2,4-DNT) in some aqueous-ethanolic mixtures was determined at seven temperatures from (293.15 to 323.15) K. The respective apparent thermodynamic functions (Gibbs energy, enthalpy, and entropy of the dissolution processes) were computed using the van't Hoff and Gibbs equations. The enthalpy-entropy relationship for 2,4-DNT was non-linear in the plot of enthalpy vs. Gibbs energy of solution with negative slope in the composition region 0.00 ? w1 ? 0.40 but positive slope in the region 0.40 ? w1 ? 1.00. Therefore, the driving mechanism for 2,4-DNT transfer processes is the entropy in water-rich mixtures and the enthalpy in ethanol-rich mixtures. In addition, by means of the inverse Kirkwood-Buff integrals is observed that 2,4-DNT is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by ethanol molecules in the mixtures of 0.23 ? x1 ? 1.00.
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    Equilibrium solubility of 6-methylcoumarin in some (ethanol plus water) mixtures: determination, correlation, thermodynamics and preferential solvation
    (Taylor & Francis, 2022) Akay, Sema; Kayan, Berkant; Coşkun, Savaş; Jouyban, Abolghasem; Martinez, Fleming; Acree, William E.
    The solubility of 6-methylcoumarin in water, ethanol and nine aqueous ethanol mixtures was determined from 293.15 to 323.15 K. 6-Methylcoumarin solubility expressed in mole fraction was correlated with some well-known correlation/prediction models. Gibbs energy, enthalpy and entropy, for dissolution and mixing processes, were computed using van't Hoff and Gibbs equations. The plot of enthalpy vs. Gibbs energy of dissolution exhibited negative slopes from water to w(1) = 0.20 and from w(1) = 0.90 to ethanol but positive slopes in the interval 0.20 w(1) w(1) = 0.20 is entropy-driven that could be attributed to water molecules releasing originally bounded as 'icebergs' around the drug-non-polar groups. In mixtures of 0.20 w(1) < 0.90, enthalpy-driving mechanism for drug transfer from more-polar to less-polar systems is observed, probably owing to better solvation by ethanol. Inverse Kirkwood-Buff integrals show that 6-methylcoumarin is preferentially solvated by water in water-rich mixtures but preferentially solvated by ethanol in 0.24 x(1) < 1.00.
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    Equilibrium solubility of vanillin in some (ethanol plus water) mixtures: determination, correlation, thermodynamics and preferential solvation
    (Elsevier, 2021) Akay, Sema; Kayan, Berkant; Jouyban, Abolghasem; Martinez, Fleming; Acree, William E., Jr.
    Equilibrium mole fraction solubility of vanillin in nine aqueous-ethanolic mixtures, as well as in neat water and neat ethanol, was determined at seven temperatures from T = 293.15 to T = 323.15 K. Vanillin solubility in these mixtures was adequately correlated with several well-known correlation models with the mean percentage deviations of 5.9 to 18.3%. Respective apparent thermodynamic functions, i.e. Gibbs energy, enthalpy, and entropy, for the dissolution, mixing and solvation processes, were computed using the van't Hoff and Gibbs equations. The enthalpy-entropy relationship for vanillin was non-linear in the plot of enthalpy vs. Gibbs energy of dissolution with positive slopes from neat water to the mixture of w(1) = 0.10 and the interval 0.50 < w(1) < 0.90 but negative in the interval 0.10 < w(1) < 0.50 and from w(1) = 0.90 to neat ethanol. Accordingly, in the first cases the vanillin transfer from more polar to less polar solvent systems is enthalpy-driven but entropy-driven for the last ones. Moreover, by means of the inverse Kirkwood-Buff integrals is observed that vanillin is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by ethanol molecules in mixtures of 0.23 < x(1) < 1.00.
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    Fabrication of palladium nanocatalyst supported on magnetic eggshell and its catalytic character in the catalytic reduction of nitroarenes in water
    (Journal of Organometallic Chemistry, 2021) Çalışkan, Melike; Akay, Sema; Kayan, Berkant; Baran, Talat
    Aromatic nitro compounds, which have good solubility in water, are highly toxic and non-biodegradable are one of the most important industrial pollutants and have negative effects on human health, aquatic life and the environment. Therefore, the elimination of these harmful organic compounds has become an issue of great importance. For this, in this study we have developed a palladium nanocatalyst supported on Fe3O4-coated eggshell and characterized by FT-IR, XRD, XPS, FE-SEM, TG/DTG, BET, TEM and EDS techniques (Pd-Fe3O4-ES). Also, the quantitative analysis of Pd was determined using ICP-OES. The catalytic behavior of the designed Pd-Fe3O4-ES nanocatalyst was investigated against the catalytic reduction of several highly toxic nitro compounds using NaBH4 in water at room temperature. The progress of the reduction was followed using high performance liquid chromatography (HPLC). The catalytic studies revealed that the nitro compounds were converted into the desired amines by the Pd-Fe3O4-ES nanocatalyst using a very low dose of catalyst (15 mg) and short-duration reactions (81–360 s) in aqueous medium at ambient temperature. Furthermore, the Pd-Fe3O4-ES nanocatalyst showed good catalytic stability by retaining its activity after the fifth catalytic run.
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    Fabrication of palladium nanoparticles supported on natural volcanic tuff/Fe3O4 and Its catalytic role in microwave-assisted suzuki-miyaura coupling reactions
    (Springer, 2021) Baran, Talat; Akay, Sema; Kayan, Berkant
    Natural minerals have a huge potential as stabilizers in the catalytic systems due to their high mechanical durability, porous surface, non-toxicity and abundance in nature. This study aims to the development of a magnetically retrievable, heterogeneous palladium catalytic system derived from volcanic tuff (VT), an abundant form of zeolite, for Suzuki-Miyaura coupling (SMC) reactions. For this purpose, a new catalyst support was designed by loading volcanic tuff with Fe3O4(VT/Fe3O4) and palladium nanoparticles were prepared on VT/Fe3O4 via wet chemical reduction method (Pd NPs@VT/Fe3O4). Then, Pd NPs@VT/Fe3O4 was evaluated as a heterogeneous catalyst in the microwave-assisted production of biaryl via SMC reactions. Pd NPs@VT/Fe3O4 efficiently coupled various substituted aryl iodides, bromides and chlorides in a very short reaction time, solvent-free media and in an air environment. Catalytic tests indicated that Pd NPs@VT/Fe3O4 converted aryl halides into desired biaryls with a high yield up to 99%. Moreover, it was showed that Pd NPs@VT/Fe3O4 retained its stability and catalytic performance by producing 92% yield after eight successive cycles. This study demonstrated that VT can be a good alternative support alongside other known supports such as biopolymers, carbon and silica based materials and it can be utilized for the synthesis of different catalysts. Graphic.
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    Fe-modified hydrochar from orange peel as adsorbent of food colorant Brilliant Black: process optimization and kinetic studies
    (Springer, 2020) Çatlıoğlu, F. N.; Akay, Sema; Gözmen, Belgin; Turunç, Ersan; Anastopoulos, Loannis; Kayan, Berkant; Kalderis, Dimitrios
    Abstract: The main aims of this work were to produce and characterize Fe-modified hydrochar from orange peel waste, optimize the adsorption through response surface methodology, investigate the role of treatment time, dye concentration, adsorbent dose and temperature, and determine the dominant mechanisms through kinetics analysis. Orange peel waste was hydrothermally carbonized at 200 °C for 8 h, and the hydrochar was embedded with magnetite nanoparticles. The composite adsorbent was characterized through spectrometric and surface analytical methods. Subsequently, analysis of variance was used to design the experimental runs, propose a polynomial equation describing the adsorption process and finally optimize the adsorption conditions. The results indicated that 99% removal can be theoretically achieved at the following conditions: dye initial concentration of 6.08 mg/L, treatment time of 26.30 min, temperature of 44.79 °C and adsorbent concentration of 2.27 g/L. The dominant factors were the dye and adsorbent concentration, whereas time and temperature variations had a much lesser impact. Among examined models, the Langmuir model showed a better match to the experimental data. The maximum monolayer adsorption capacity was determined as 10.49 mg/g. The mechanism of interaction was largely based on surface chemisorption between the dye and adsorbent. Fe-modified hydrochar exhibited a positive adsorption behavior, and it was shown that a new valorization option for orange peel waste is available. This option may follow other valorization pathways, such as isolation of biologically active molecules, therefore offering a complete solution to this type of waste. Graphic abstract: [Figure not available: see fulltext.]
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    Fe-modified sporopollenin as a composite biosorbent for the removal of Pb2+ from aqueous solutions
    (Desalination Publications, 2016) Şener, Murat; Kayan, Berkant; Akay, Sema; Gözmen, Belgin; Kalderis, Dimitrios
    The role of Fe-modified sporopollenin (Fe-Sp) biomass in Pb2+ removal from aqueous solutions was investigated by batch biosorption technique. The prepared biosorbent was characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, and Fourier transform infrared spectroscopy. The influence of pH, contact time, biosorbent dose, and initial concentration on biosorption process were optimized by using a four factor Box-Behnken design combined with response surface methodology. The results indicated a positive adsorption behavior of Fe-Sp and a strong pH dependency of the process. The optimum predicted parameters were determined as follows: biosorbent dosage 0.5 g, pH of 6.75, contact time 104 min, and initial Pb2+ concentration of 25.42 ppm. The Freundlich isotherm model provided a better fit (R-2 = 0.994) for the experimental data, indicating biosorption on a heterogeneous surface. Maximum biosorption capacity (q(max)) was 22.72 mg g(-1) as indicated by the Langmuir isotherm. Kinetically, the adsorption process followed a pseudo-second-order model, indicating that chemisorption was the rate-limiting step.
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    Green chromatographic separation of coumarin and vanillins using subcritical water as the mobile phase
    (Oxford Univ Press İnc, 2016) Kayan, Berkant; Akay, Sema; Yang, Yu
    Pure water was used as the eluent for separation of coumarin, vanillin and ethyl vanillin at temperatures ranging from 100 to 200 degrees C using a homemade subcritical water chromatography (SBWC) system. Chromatographic separations were performed on five commercial columns including XTerra MS C18, XBridge C18, Zorbax RRHD Eclipse Plus, Zorbax SB-Phenyl and Zorbax SB-C18 columns. The retention time of all three solutes decreased with increasing water temperature. The shortest retention time among all acceptable separations, less than 4 min, was achieved on the Zorbax SB-C18 column at 200 degrees C. While separations on the XTerra MS C18 column resulted in fronting peaks and a degradation peak from ethyl vanillin on the Zorbax RRHD Eclipse Plus column was observed, all three other columns yielded reasonable separations under SBWC conditions. In addition to separation of the standard test mixture, separation of coumarin contained in a skincare cream sample was also carried out using SBWC.
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    İlaç etken maddelerinin yüksek sıcaklıktaki çözünürlüğünün incelenmesi: çözünürlük modelleri ve kromatografik ayrımlar
    (Aksaray Üniversitesi Fen Bilimleri Enstitüsü, 2020) Akay, Sema; Kayan, Berkant
    Günümüzde, atık sulardaki kirleticiler konusunda tarım uygulamaları, endüstriyel deşarjlar ve insanlar önemli bir rol oynamaktadır. Tüm bu uygulamalar, çeşitli kirleticiler üreterek ve su döngüsünü değiştirerek doğa ve insan sağlığı üzerinde küresel bir endişeye neden olmaktadır. Mikrokirleticiler içerisinde bugün en çok dikkat çekenlerden biri, içme suları vasıtasıyla insan sağlığında risk uyandırma potansiyeline sahip olan ilaç kalıntılarıdır. İlaç kalıntılarının potansiyel sağlık riskleri yanında, sucul ekosisteme ve fiziki çevreye olan zararları da pek çok araştırmanın konusunu oluşturmaktadır. Bu kirleticiler, farklı su kaynaklarında genellikle birkaç ng/L ile ?g/L arasında değişen çok düşük konsantrasyonlarda bulunmaktadır. İlaçların çözünürlüğünde kullanılacak ideal çözücü, ayarlanabilir özelliklere sahip çok yönlü bir çözücü olan 'su'dur. Su, kaynama sıcaklığı ile kritik sıcaklığı arasında subkritik su olarak adlandırılmaktadır. Bu çalışmada, subkritik su kullanılarak ilaç etken maddelerinin çözünürlüğü incelenmiştir. Sonuçlar, ilaç etken maddelerinin yüksek sıcaklıktaki sulu çözünürlüğünün, ortam sıcaklığından daha yüksek olduğunu göstermiştir. 498 K'a kadar artan sıcaklık, 5-Fluorourasil için 12 kat, sülfadiazin için 15 kat, essitalopram okzalat için 55 kat, flukonazol için 147 kat ve ibuprofen için 10600 kat arasında değişen çözünürlük artışlarıyla sonuçlanmıştır. Deneysel verilere dayanarak, subkritik suda ilaç etken maddelerinin çözünürlüğünü tahmin etmek için matematiksel modeller geliştirilmiştir. Modeller başarıyla doğrulanmış ve teorik çözünürlük değerleri deneysel verilerle iyi bir şekilde eşleşmiştir. Ayrıca, Modifiye Apelblat denklemi, yüksek sıcaklıklarda deneysel değerlerle iyi bir uyum sağlamıştır. Subkritik sudaki ilaç etken maddelerinin molar çözünme entalpisi yüksek sıcaklık koşullarında belirlenmiştir. Pozitif entalpi değerleri, işlemin endotermik olduğunu göstermiştir. Sonuç olarak, subkritik sudaki ilaç etken maddelerinin yeterli çözünürlüğü, bu ajanların analizi için yeşil kromatografik teknikler kullanmamıza imkan sunmuştur.
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    Investigation on the solubility of the antidepressant drug escitalopram in subcritical water
    (American Chemical Society, 2021) Akay, Sema; Kayan, Berkant; Yang, Yu
    Escitalopram (ESC), the S-enantiomer of citalopram, is a selective serotonin reuptake inhibitor. Escitalopram is widely used to treat panic disorder, depression, obsessive compulsive disorder, and social anxiety disorder. The main goal of this present research is to determine the aqueous solubility of ESC at temperatures ranging from 298 to 473 K and a pressure of 5.0 MPa. ESC solubility increased significantly from 1.08 × 10-3 to 59.88 × 10-3 (mole fraction) when the temperature was raised from 298 to 473 K. This is a 55-fold enhancement. A mathematical model was developed based on our experimental solubility data. The model was used to successfully predict the solubility of ESC in subcritical water. Furthermore, experimental data were correlated using a modified Apelblat equation. The apparent thermodynamic analysis including apparent dissolution standard enthalpy (?solH) and apparent dissolution standard entropy (?solS) were calculated. Thermodynamic property calculations showed that the process is endothermic ?solH > 0, and the ?solS values were relatively high. Spectroscopic analyses revealed that ESC was stable in subcritical water at temperatures up to 473 K. The enhanced solubility of ESC in subcritical water enabled us to use high-temperature liquid chromatography to separate this antidepressant drug.
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    Kumarinlerin subkritik su kromatografisi ile ayrılması
    (Aksaray Üniversitesi Fen Bilimleri Enstitüsü, 2015) Akay, Sema; Kayan, Berkant
    Bu çalışma iki kısımdan oluşmaktadır. Çalışmanın birinci kısmında, yeni dizayn kromatografi sistemi kullanılarak, kumarin, vanilin ve etil vanilin bileşiklerinin subkritik su kromatografisi ile ayrılması araştırılmıştır. Kromatografik ayrımlar, Waters XTerra MS C18, Zorbax RRHD Eclipse Plus, Zorbax SB-Phenyl, Zorbax SB-C18, and Waters XBridge C18 kolonları içeren beş farklı kolon kullanılarak gerçekleştirilmiştir. Sıcaklığın artmasıyla birlikte çalışılan üç bileşiğinde alıkonma zamanları kısalmıştır. Çalışılan beş farklı kolon içinde Zorbax SB-Phenyl ve Zorbax SB-C18 iyi sonuçlar vermesine rağmen, en iyi ayrım Waters XBridge C18 kolonunda elde edilmiştir. Kumarin, vanilin ve etil vanilin bileşiklerinin subkritik su kromatografisi ile ayrımları 100 ile 200 °C arasında, hem sabit hem değişken akış hızlarında gerçekleştirilmiştir. Sıcaklığın, alıkonma faktörüne etkisi Van't Hoff eşitliği ile incelenmiştir. Çalışmanın ikinci kısmında, subkritik su kromatografisinde kolon dolgu materyali (sabit faz) olarak kullanılacak olan Poli(HEMA-MAH) (PHEMAH) (poli(hidroksietil metakrilat-N-metakriloil-(L-histidin)-metilester) mikroküreleri sentezlenmiştir ve yüksek sıcaklıkta kararlılık ve dayanıklılık testleri yapılmıştır. Bu moleküller yüksek sıcaklıkta kararlılık ve dayanıklılık gösterebilmektedir. Sentezlenen bu kolon dolgu maddesi ile kumarin, vanilin, etil vanilin, 6-metil kumarin ve 7-metil kumarin bileşiklerinin ayrılması 125 ile 200 oC arasında gerçekleştirilmiştir. Metanol/Su karışımı ( %2-97 ve %5-94) mobil faz olarak kullanılmıştır. En iyi ayrım yüksek sıcaklıkta %5-94 metanol/su oranında gözlenmiştir.
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    Poly(benzoxazine-co-sulfur): An efficient sorbent for mercury removal from aqueous solution
    (Wiley-Blackwell, 2017) Akay, Sema; Kayan, Berkant; Kalderis, Dimitrios; Arslan, Mustafa; Yağcı, Yusuf; Kıskan, Barış
    A novel sulfur-rich adsorbent, poly(BA-ala-co-sulfur), was synthesized by reacting allyl functional benzoxazine (BA-ala) and elemental sulfur. Simultaneous inverse vulcanization and ring-opening reactions of benzoxazine generated copolymers in several feed ratios. The adsorption behavior of these copolymers was investigated in aqueous solutions containing Hg2+. A three level Box-Behnken design with four factors was applied in order to examine the interactive effect of Hg2+ concentration (ppm), S % in adsorbent, temperature, and pH. The optimum adsorption conditions were determined as: 10.33 ppm Hg2+, 68% S content, 329 K, and pH 6.3. Common isotherm and kinetic models were applied to the experimental data, where the Langmuir isotherm provided the better fit (q(max)=79.36 mg g(-1)) and the pseudo-second order fit indicated chemisorption as the process-controlling step. (C) 2017 Wiley Periodicals, Inc.