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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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    Adsorption of Malachite Green on Fe-modified biochar: Influencing factors and process optimization
    (Desalination Publications, 2017) Kulaksız, Esra; Gözmen, Belgin; Kayan, Berkant; Kalderis, Dimitrios
    Paper sludge and wheat husk biochar was converted to a Fe-composite through a simple co-precipitation process and its adsorption behavior was tested against an emerging pollutant, Malachite Green (MG). Response surface methodology was employed to determine the optimum experimental conditions and the interactions between pH, initial MG concentration, temperature and treatment time. The maximum adsorption percentage obtained experimentally was 97.1%, whereas the Box-Behnken design predicted a maximum adsorption of 98%, at pH 6.16, initial MG concentration of 6.56 ppm, temperature of 34.75 degrees C and treatment time of 22 min. Compared with the original biochar, the Fe-modified sample improved the adsorption of MG by similar to 34%. The adsorption mechanism followed the Langmuir model (q(max) = 172.3 mg/g, correlation coefficient 0.960) and the kinetics of the process were best described by the pseudo-second-order model (correlation coefficient 0.9818), although boundary layer effects were also observed.
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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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    Application of response surface methodology and central composite design for the optimization of textile dye degradation by wet air oxidation
    (Springer Berlin Heidelberg, 2012) Demirel, Muhammet; Kayan, Berkant
    Background: The present study is aimed at investigating the degradation of azo dye solution of AR 274 by wet air oxidation conditions. The central composite design matrix and response surface methodology were applied in designing the experiments to evaluate the interactive effects of the three most important operating variables. Thus, the interactive effects of oxygen pressure (3.0 to 5.0 MPa), temperature (100°C to 250°C), and time (30 to 90 min) on the degradation of dye were investigated. Results: The predicted values were found to be in good agreement with the experimental values (R2 = 0.9981 and Adj-R2 = 0.9965), which define the propriety of the model and the achievement of CCD in the optimization of WAO process. Conclusions: Intermediates of dye degradation were detected by GC-MS, the possible degradation mechanism for the WAO of dye was discussed, and the probable degradation pathway was deduced. © 2012, Demirel and Kayan; licensee Springer.
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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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    Assessment of Orange Peel Hydrochar as a Soil Amendment: Impact on Clay Soil Physical Properties and Potential Phytotoxicity
    (Springer Netherlands, 2019) Kalderis, Dimitrios; Papameletiou, George; Kayan, Berkant
    Purpose: The main objectives of this work were the following: (1) to investigate the applicability of orange peel hydrochar as a soil amendment for improving the physical properties of a compacted, clay soil and (2) to study the growth of maize on substrates composed of clay soil and hydrochar and determine any potential phytotoxic effects. Methods: The effect on soil’s bulk density (BD), aeration, water holding capacity (WHC), and hydraulic conductivity were examined with hydrochar additions of 5, 10 and 15% (w/w) and determined by conventional laboratory methods. Potential phytotoxic effects were determined through the Zucconi germination index on fresh, diluted and 4-week old undiluted hydrochar extracts. The effect of hydrochar on maize growth was studied in clay soil (as reference), clay soil with 5% (w/w) fresh hydrochar, clay soil with 5% (w/w) of 4-week-old hydrochar and clay soil with 5% (w/w) biochar (for comparison). Results: At an application rate of 5% (w/w) hydrochar, the bulk density was reduced from 1.35 to 1.22 g/cm3, the air-filled porosity was increased from 33 to 37% and the saturated hydraulic conductivity from 0.96 to 1.01 cm/h. The water holding capacity remained practically unchanged, however it was considerably reduced at higher application rates. The seed germination test indicated strong phytotoxicity of the fresh, undiluted hydrochar extract, which was reduced when the extract was diluted or the hydrochar allowed to mature for 4 weeks. The pot tests indicated that hydrochar did not improve the yield of maize, probably due to the presence of phytotoxic substances. Conclusions: This study demonstrated a new valorization pathway for a significant agricultural waste. Additionally, it proved the applicability of orange peel hydrochar for improving the physical properties of clay soil. However, due to phytotoxic effects, further work is required before a field application is considered. © 2018 Springer Nature B.V.
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    Biosorption properties of pretreated sporopollenin biomass for lead(II) and copper(II): Application of response surface methodology
    (ELSEVIER SCIENCE BV, 2014) Şener, Murat; Reddy, D. Harikishore Kumar; Kayan, Berkant
    The role of pretreated sporopollenin (PSp) biomass in M(II) (M = Pb, Cu) removal from aqueous solutions was investigated by batch biosorption technique. The chemical properties and morphology of the biosorbent were characterized by means of FT-IR and SEM-EDX techniques. Influence of various operating parameters like pH, contact time, biosorbent dose and initial concentration on biosorption process were optimized by using a quadratic model Box-Behnken design using response surface methodology. The results indicated that Pb(II) and Cu(II) sorption on PSp was strongly dependent on pH. The experimental equilibrium data was analyzed with three isotherm models and the sorption data was better fitted to Langmuir isotherm model, and the order of maximum biosorption capacity (q(max)) was Pb(II) (6.10 mg g(-1))> Cu(II) (4.84 mg g(-1)). FTIR and SEM-EDX was used to identify the biosorption mechanism and it was confirmed from SEM-EDX that metal ions were present in the PSp biomass after biosorption. These results are important for estimating and optimizing the removal of metal ions by PSp biomass. The results demonstrated that PSp was a economic and eco-friendly biosorbent possessed strong sorption characteristics for Pb(II) and Cu(II) ions.
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    CoFe2O4 nanoparticles decorated onto graphene oxide and graphitic carbon nitride layers as a separable catalyst for ultrasound-assisted photocatalytic degradation of Bisphenol-A
    (Elsevier Ltd, 2022) Görmez, Erkan; Yakar, Ezgi; Gözmen, Belgin; Kayan, Berkant; Khataee, Alireza
    The advanced oxidation process (AOP) through ultrasound-assisted photocatalytic degradation has attracted much attention in removing emerging contaminants. Herein, CoFe2O4-GO and CoFe2O4-g-C3N4 nanocomposites were synthesized using the ultrasound-assisted co-precipitation method. TEM, XRD, XPS, EDS, SEM, and FT-IR techniques characterized the structural, morphological, and chemical properties of the synthesized nanocomposites. The analyses showed that CoFe2O4 structure was nano-sized and distributed more homogeneously in graphene oxide (GO) layers with oxygenated functional groups than graphitic carbon nitride (g-C3N4). While the efficiency of composite catalysts, as photocatalysts, for degradation of bisphenol-A (BPA) was low in the visible region in the presence of persulfate, their catalytic efficacy was higher with sonolytic activation. The addition of persulfate as an oxidant remarkably enhanced the target pollutant degradation and TOC removal of BPA solution. Both composite catalysts showed 100 % BPA removal with the synergistic effect of visible region photocatalytic oxidation and sonocatalytic oxidation in the presence of persulfate at pH 6.8. In ultrasound-assisted photocatalytic oxidation of BPA, the highest mineralization efficiencies were obtained at 2 h treatment time, pH 6.8, 16 mM PS, catalyst dosages of 0.1 g/L CoFe2O4-GO, and 0.4 g/L CoFe2O4-g-C3N4 as 62 % and 55 %, respectively. An effective catalyst was obtained by reducing e?/h+ recombination and charge transfer resistance by decorating the GO layers with CoFe2O4.
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    Comparative degradation of 5-fluorouracil in aqueous solution by using H2O2-modified subcritical water, photocatalytic oxidation and electro-Fenton processes
    (Elsevier, 2022) Kulaksız, Esra; Kayan, Berkant; Gözmen, Belgin; Kalderis, Dimitrios; Oturan, Nihal; Oturan, Mehmet A.
    This study investigated the degradation of the antineoplastic agent 5-fluorouracil (5-FU) widely applied to treat different cancers using different advanced oxidation processes such as electro-Fenton (EF), photocatalysis with TiO2, and H2O2-modified subcritical water oxidation. The treatment with the EF process was the most efficient compared to others. Interestingly, in the EF process, the oxidative degradation of 5-FU behaved differently depending on the anode used. At low currents (20 and 40 mA), Pt and DSA anodes performed better than BDD and Ti4O7 anodes. In contrast, at the higher current of 120 mA, the production of heterogeneous hydroxyl radicals (M(•OH)) became important and contributed significantly to the oxidation of 5-FU in addition to homogeneous •OH generated in the bulk solution. These latter have high O2-evolution overpotential leading to the high amount of physisorbed M(•OH) compared to Pt and DSA. The oxidative degradation of 5-FU was then performed by titanium dioxide-based photocatalytic oxidation and subcritical water oxidation processes, both of which showed a lower degradation efficiency and failed to achieve complete mineralization. Finally, a comparison was performed in laboratory-scale, taking into account the following performance indicators: the degradation efficiency, the mineralization power, the cost of equipment and reagents, and the energy required for the treatment of 5-FU.
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    Degradation of Acid Red 274 using H2O2 in subcritical water: Application of response surface methodology
    (Elsevıer Scıence Bv, 2012) Kayan, Berkant; Gözmen, Belgin
    In this research, the degradation of Acid Red 274 (AR 274) was investigated under subcritical water conditions using H2O2, which led to the oxidative degradation of Acid Red 274 up to its 80% of mineralization. The Box-Behnken design matrix and response surface methodology (RSM) were applied in designing the experiments for evaluating the interactive effects of the three most important operating variables. Thus, the interactive effects of temperature (100-250 degrees C), oxidant (H2O2) concentration (50-250 mM), and time (30-60 min.) on the degradation of AR 274 were investigated. A total of 17 experiments were conducted in this research, and the analysis of variance (ANOVA) indicated that the proposed quadratic model could be used for navigating the design space. The proposed model was essentially in accordance with the experimental case with correlation coefficient R-2 = 0.9930 and Adj-R-2 = 0.9839, respectively. The results confirmed that RSM based on the Box-Behnken design was a compatible method for optimizing the operating conditions of AR 274 degradation. (C) 2011 Elsevier B.V. All rights reserved.
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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.