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    Experimental and computational (DFT) study of a binary system of triethanolamine and ethanol at temperatures from 293.15 to 323.15 K under 101.3 kPa
    (Academic Press Ltd- Elsevier Science Ltd, 2025) Muzhaqi, Evis; Kavakli, Aycan Altun; Sara, Osman Nuri; Fellah, M. Ferdi
    In this study, the density and viscosity of binary mixtures of triethanolamine (TEA) and ethanol were measured over the entire composition range at temperatures of 293.15 and 323.15 K under a pressure of 101.3 kPa. Correlations were obtained expressing density and viscosity values as a function of temperature. Excess molar volume (VE) and viscosity deviation (Delta eta) were calculated from the measured values. These properties were further fitted to the Redlich-Kister polynomial equation. Thermodynamic parameters such as partial molar volumes, apparent molar volumes, coefficients of thermal expansion, and excess Gibbs free energy of activation for viscous flow were also determined. Moreover, activation enthalpy and entropy values for viscous flow were evaluated. The experimental results and the Density Functional Theory (DFT) calculations were used to discuss the molecular interactions for binary mixtures of TEA and ethanol. Negative values of VE and Delta eta were observed across all studied temperatures and compositions, indicating strong specific interactions between TEA and ethanol molecules. There is a distinct difference in the temperature dependence of VE and Delta eta. As the temperature increases, the VE values become increasingly negative, while the Delta eta values decrease. Both experimental results and Density Functional Theory (DFT) calculations confirm the presence of intermolecular hydrogen bonding in the binary mixtures. Furthermore, FTIR spectroscopy suggests the possible presence of intermolecular interactions between the components.
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    The effects of diethyl ether, diethylene glycol dimethyl ether, and dimethyl carbonate addition on the physical and thermodynamic properties of biodiesel
    (Springer, 2024) Osman, Sibel; Sara, Osman Nuri; Kavakli, Aycan Altun; Lungu, Mioara-Jeanina
    In the present study, density, viscosity, surface tension, and refractive indices of binary mixtures of biodiesel + diethyl ether (DEE), diethylene glycol dimethyl ether (DEGDME), and dimethyl carbonate (DMC), which are used as biodiesel additives, have been measured over the whole range of concentration from 288.15 to 323.15 K and at atmospheric pressure. The density and kinematic viscosity values of the binary mixtures, prepared with different mole fractions of DEE, DEGDME, and DMC, were compared with the limits specified by the biodiesel fuel standard (EN14214). Furthermore, experimentally measured density values were utilized to define a first-order polynomial equation for estimating the densities of the prepared binary mixtures. Excess molar volumes (VE), excess thermal expansion coefficient (alpha pE), excess Gibbs energy of activation of the viscous flow (triangle G*E), deviations in kinematic viscosity (Delta nu), surface tension (Delta sigma), and refractive index (Delta nD) values were calculated. These deviation values from ideality were adjusted to a Redlich-Kister (R-K) polynomial equation and the obtained coefficients in the equation were reported. VE values were negative for biodiesel + DEE while positive values were obtained for biodiesel + DEGDME and DMC. Moreover, the values of Delta nu were negative for all mixtures of biodiesel + DEE, DEGDME, and DMC. The obtained results were analyzed with regard to intermolecular interactions and structural effects between both similar and dissimilar molecules.
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    The influence of surfactant type and calcination temperature on the formation of nickel oxide nanoparticles by chemical precipitation method
    (Springer, 2025) Abdulkarim, Alaa; Kavakli, Aycan Altun; Sara, Osman Nuri
    In this study, the synthesis of NiO nanoparticles was carried out using a sequential precipitation and thermal degradation method. Nickel nitrate hexahydrate (Ni(NO3)26H2O) served as the precursor, while sodium hydroxide (NaOH) was used as the precipitating agent in a stoichiometric ratio. Various surfactants, including SDS, CTAB, Tween 80, PVP, NP-10 and PEG, were used as stabilizing agents. The obtained precipitates were calcined at different temperatures ranging from 300 to 600 degrees C. The effects of surfactant type and calcination temperature on the synthesized NiO morphology, particle size, and distribution were investigated. SEM, XRD, FT-IR, and BET analyses were used for product characterization. XRD analysis confirmed that the synthesized samples had a cubic (Fm-3 m) structure. The majority of the synthesized NiO particles have an average particle size of less than 60 nm, with nearly spherical shapes except for the CTAB-assisted sample, which also displayed rod-shaped structures. Besides, calcination temperature was found to play a critical role in tailoring particle size, surface area, and pore structure. As the calcination temperature increases, the average particle size and pore distribution increase, while the surface area decreases. The BET surface areas of NiO NPs range from 44 to 110 m2 g-1, with the highest value observed in the SDS-stabilized sample, which also has the smallest particle size. According to the BET analysis, the isotherms correspond to type IV(a) based on the hysteresis loop observed in the high relative pressure region (P/P-0) between 0.6 and 1.