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    Influence of the Medium Conditions on Enzymatic Oxidation of Bisphenol A
    (Wiley, 2014) Yalcinkaya, Zeki; Gun, Selim; Sahan, Tekin; Birhanli, Emre; Şahiner, Nurettin; Aktas, Nahit; Yesilada, Ozfer
    A multistep response surface methodology (RSM) was successfully applied to optimise the medium conditions for the enzymatic polymerisation of bisphenol A (BPA). The laccase enzyme used as the catalyst was derived from Funalia trogii (ATCC 200800) yeast culture. The enzymatic polymerisation rate of BPA, based on the measurements of the initial dissolved oxygen (DO) consumption rate in a closed batch system, was studied through RSM. Initially the most effective medium factors, which are monomer concentration (mg/L), temperature (degrees C) and solvent content (% methanol), were determined through Plackett-Burman Design (PBD), then the steepest ascent combined with central composite design (CCD) steps were applied to evaluate the optimal reaction conditions for the enzymatic polymerisation. The optimal conditions were evaluated to be 748.46mg/L, 32.24 degrees C and 15.92% for monomer concentration, temperature and solvent content, respectively. A quadratic model was developed through RSM to represent DO consumption in the medium. The maximum DO consumption rate was calculated to be 0.093mg DO/Lmin. Several repetitions were conducted at the optimal conditions to validate the system performance. The data evaluated from the quadratic model were in good agreement with those measured experimentally. The variations between the values did not exceed 10%. The correlation coefficient, R-2, was calculated to be 0.95, which indicates that 95% of results can be explained by model.
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    Magnetic hydrogel syntheses and their applications in the environment for the removal of toxic metal ions
    (Amer Chemical Soc, 2009) Özay, Özgür; Onder, Alper; Sahan, Tekin; Aktas, Nahit; Baran, Yakup; John, Vijay T.; Şahiner, Nurettin
    [Anstract Not Available]
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    Öğe
    Optimization of removal conditions of copper ions from aqueous solutions by Trametes versicolor
    (Elsevier Sci Ltd, 2010) Sahan, Tekin; Ceylan, Hasan; Şahiner, Nurettin; Aktas, Nahit
    A multi-step response surface methodology was successfully applied to optimize the biosorption conditions for the maximum removal of Cu(II) ions from aqueous solutions using Trametes versicolor fungi as a biosorbent. In the first step, the most effective medium factors, which are pH, temperature and initial Cu(II) concentration, on biosorption of Cu(II), were determined through Plackett-Burman Design. Then steepest accent followed by central composite design steps were utilized to evaluate the optimum biosorption conditions for the maximum Cu(II) ions removal. Based on the statistic analysis; the optimum conditions were obtained 5.51, 20.13 degrees C and 60.98 mg/L as medium pH, medium temperature and initial Cu(II) concentration, respectively. Finally the analysis of variance (ANOVA) of central composite design showed the proposed quadratic model fitted experimental data very well. (C) 2010 Elsevier Ltd. All rights reserved.
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    Reusable Soft Hydrogels for Gold Recovery from Acidic Environments
    (Taylor & Francis Inc, 2013) Şahiner, Nurettin; Karakoyun, Necdet; Sahan, Tekin; Butun, Sultan; Aktas, Nahit
    In this study, poly((N-(hydroxymethyl) acrylamide) co-1-allyl-2-thiourea) hydrogels were synthesized by free radical crosslinking copolymerization of N-(hydroxymethyl) acrylamide monomer with the addition of a co-monomer 1-allyl-2-thiourea, and N, N'-methylenebisacrylamide as the crosslinker. The copolymer, poly((N-(hydroxymethyl) acrylamide) co-1-allyl-2-thiourea), was used as a specific sorbent for the recovery of gold. The characteristics of the hydrogels were examined by elemental analyzer and swelling experiments. The effect of pH on the absorption of gold, and the separation and recovery of gold ions from ore samples were investigated. Measurement of absorbed gold was determined by using F-AAS and GF-AAS.
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    Uptake of As(V) and Cr(VI) from aqueous environment by cationic poly(Acrylonitril-co-3-Acrylamidopropyl)trimethylammonium chloride) hydrogels
    (Amer Chemical Soc, 2013) Ersen, Tuba; Alpaslan, Duygu; Sahan, Tekin; Aktaş, Nahit; Şahiner, Nurettin