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    Effects of stirring and aeration rates on lipase production and growth of R. delemar
    (ELSEVIER SCIENCE BV, 2012) Ersan, Mehtap; Acikel, Unsal; Acikel, Yesim Sag
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    Equilibrium, hysteresis and kinetics of cadmium desorption from sodium-feldspar using rhamnolipid biosurfactant
    (TAYLOR & FRANCIS LTD, 2012) Asci, Yeliz; Acikel, Unsal; Acikel, Yesim Sag
    In this study, the sorption/desorption equilibruim and the desorption kinetics of Cd by rhamnolipid biosurfactant from Na-feldspar as a soil component were investigated. The linear, Langmuir and Freundlich isotherms adequately fitted the equilibrium sorption data with regression coefficients ranging from 0.9836-0.9879. However, both the sorption/desorption equilibria were well characterized by the Freundlich model. The extent of hysteresis was quantified based on the differences obtained from sorption and desorption isotherms regarding the quantity of Cd(II) sorbed, the Freundlich exponent, concentration-dependent metal distribution coefficients, and the irreversibility index based on the metal distribution coefficient. The kinetics of desorption of Cd from Na-feldspar was investigated using 77 mM rhamnolipid and at pH 6.8. The first-order, an empirical first-order desorption model (two-coefficient), Lagergren-pseudo-first-order, pseudo-second-order, Elovich and modified Freundlich models were used to describe the kinetic data to estimate the rate constants. To determine the rate-controlling step, the intra-particle diffusion model was also applied to the desorption process. The desorption kinetics of Cd(II) on Na-feldspar was represented better by the pseudo-second-order, Elovich and modified Freundlich equations with correlation coefficients ranging from 0.9941-0.9982 than by first-order equations. The rate-controlling stage was suggested to be mainly the surface reaction mechanism.
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    Green Synthesis of ZnO Nanoparticles from Onion Peel Wastes
    (Mehmet Sinan Bilgili, 2020) Canbaz, Gamze Topal; Acikel, Unsal; Acikel, Yesim Sag
    Onion peel and Zn(CH3COO)(2). 2H(2)O were used as a starting material for the synthesis of zinc oxide nanoparticles (ZnONPs). The formation of ZnONPs was first observed by changing the color of the Zn(CH3COO)(2). 2H(2)O solution from colorless to yellow. The Zn-extract solution was tested by a UV-Vi spectrophotometer, and the maximum absorbance peak formation at 362 nm, which belongs to ZnONPs, was observed. For the synthesis of ZnONPs, the optimum Zn(CH3COO)(2). 2H(2)O concentration was determined to be 0.2 M, the optimum temperature was 60 degrees C, the optimum pH was 12.0, and the optimum extract volume was 10 mL. The formation of ZnONPs was identified with the evaluation of SEM images and UV spectra. It was shown that agricultural wastes are re-used and onion peel waste is suitable for the production of ZnONPs.
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    Phenol Removal from Aqueous Environments with ZnO Nanoparticles Produced from Onion Peel Wastes by Green Synthesis
    (Mehmet Sinan Bilgili, 2020) Canbaz, Gamze Topal; Acikel, Unsal; Acikel, Yesim Sag
    Phenolic compounds are important industrial wastes and are classified as hazardous substances polluting seas, streams, stagnant waters, and groundwater resources. Therefore, they must be reduced to the permissible levels before being released into natural environments. The removal of nanomaterials and various pollutants by the adsorption method is gradually becoming more important with new technologies developed. In this study, the phenol adsorption capacity of ZnO nanoparticles (NPs) produced from onion peel wastes by the green synthesis method was investigated. In order to determine the optimum adsorption conditions of phenol to ZnO NPs, the effects of the ambient pH, contact time, initial phenol concentration, and temperature were investigated.
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    Removal of heavy metal by using green synthesis ZnO NPs and ZnO-HNT composite
    (Springer Heidelberg, 2023) Canbaz, Gamze Topal; Acikel, Unsal; Acikel, Yesim Sag
    In this study, Copper (II) adsorption from an aqueous solution with nanoparticles synthesized using organic waste was investigated. For this purpose, the extract obtained from Allium cepa (A. cepa) peel was used as a reducing agent, and zinc oxide nanoparticles (ZnO NPs) were synthesized by the green synthesis method. The synthesized ZnO NPs were obtained as composite adsorbents with halloysite (HNT), a type of clay. The adsorbents were characterized by Fourier transform infrared spectroscopy (FT-IR), energy dispersive X-ray (EDX), scanning electron microscopy (SEM), X-ray diffractometer (XRD), dynamic light scattering spectrometry (DLS), N-2 adsorption-desorption analysis and zero charge point (pH(PZC)) analysis. Parameters affecting the adsorption process such as pH, adsorbent dose, contact time, initial metal concentration, and temperature were investigated. According to the correlation coefficient, the data obtained with ZnO NPs were best summarized by the Langmuir isotherm with an adsorption capacity of 500 mg g(-1). The kinetic description of the adsorption system was performed by pseudo-second-order kinetic and intraparticle diffusion kinetic models. Thermodynamic parameters were calculated and the adsorption process was found to be spontaneous and exothermic.