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Öğe An approach for prediction of optimum reaction conditions for laccase-catalyzed bio-transformation of 1-naphthol by response surface methodology (RSM)(Elsevier Sci Ltd, 2008) Ceylan, Hasan; Kubilay, Şenol; Aktaş, Nahit; Şahiner, NurettinResponse surface methodology (RSM) was successfully applied to enzymatic bio-transformation of 1-naphthol. The experiments were conducted in a closed system containing acetone and sodium acetate buffer, with laccase enzyme. Laccase enzyme used as catalyst was derived from Trametes versicolor (ATCC 200801). The enzymatic bio-transformation rate of I-naphthol, based oil measurements of initial dissolved oxygen (DO) consumption rate in the closed system, was optimized by the application of RSM. The independent variables, which had been found as the most effective variables on the initial DO consumption rate by screening experiments, were determined as medium temperature, pH and acetone content. A quadratic model was developed through RSM in terms of related independent variables to describe the DO consumption rate as the response. Based on contour plots and variance analysis, optimum operational conditions for maximizing initial DO consumption rate, while keeping acetone content at its minimum value, were 301 K of temperature, pH 6 and acetone content of 7% to obtain 9.17 x 10(-3) mM DO/min for initial oxidation rate. (c) 2007 Published by Elsevier Ltd.Öğe Dichromate and arsenate anion removal by PEI microgel, cryogel, and bulkgel(Elsevier Ltd, 2021) Kubilay, Şenol; Demirci, Şahin; Can, Mehmet; Aktaş, Nahit; Şahiner, NurettinAmong the various metal ions, chromate (Cr(VI)) and arsenate (As(V)) are the two most hazardous toxic ion species and are found in nature in the form of dichromate and arsenate anions. In this investigation, polyethyleneimine (PEI)-based hydrogels were prepared with microgel, cryogel, and bulkgel morphologies employing glycerol diglycidyl ether as a crosslinker. The prepared PEI-based hydrogels were used to remove dichromate and arsenate anions from aqueous media. PEI microgel, cryogel, and bulkgels weighing 50 mg of each adsorbed 84.7 ± 0.8, 76.5 ± 5.2, and 108.9 ± 2.4 mg.g-1 of dichromate anions and 15.9 ± 0.7, 45.4 ± 1.9, and 79.2 ± 11.6 mg.g-1 of arsenate anions in 30, 120, and 240 min, respectively. The dichromate and arsenate anions adsorption of PEI-based hydrogels were found to fit to the pseudo-second-order kinetic, and nonlinear Langmuir isotherm models, respectively with higher R2 values. The highest distribution coefficient (Kd) value of PEI-based hydrogels for dichromate adsorption was obtained on the cryogel forms of PEI as 1.89 ± 0.05. Likewise, the highest Kd value for the arsenate adsorption was calculated on PEI-based bulkgels as 0.46 ± 0.01. The thermodynamic parameters of PEI based hydrogels in the adsorption of dichromate and arsenate anions e.g., ΔG (all negative (except for the arsenate adsorption by PEI microgels), and ΔH that is around 2-10 kJ.mol-1, and ΔS what is around 0.01-0.02 kJ.mol-1. K-1 were calculated. The reusability studies showed that PEI-based hydrogels can be used for at least 5 consecutive adsorption-desorption cycles with almost 70 % anion removal efficiency after the fifth cycle.Öğe Hydrogel-Biochar composites for effective organic contaminant removal from aqueous media(Elsevier, 2011) Karakoyun, Necdet; Kubilay, Şenol; Aktaş, Nahit; Turhan, Ömer; Kasımoğlu, Murat; Yılmaz, Selahattin; Şahiner, NurettinIn this study, p(acrylamide)-chicken biochar (p(AAm)-CB), p(acrylamide)-wood biochar (p(AAm)-WB), and p(acrylamide)-tire biochar (p(AAm)-TB) hydrogel composites were prepared using acrylamide (AAm) as monomer with the corresponding biochars, with N,N'-methylenebisacrylamide (MBA) as crosslinker and ammonium persulfate (APS) as initiator. P(AAm)-CB, p(AAm)-WB, and p(AAm)-TB were used as adsorbents to remove phenol from aqueous environments. The synthesized p(AAm)-CB, p(AAm)-WB, p(AAm)-TB and p(AAm) hydrogel composites had swelling values of 1112, 1045, 847, and 623%, respectively in distilled water. The prepared hydrogel biochar material compositions were examined using an elemental analyzer. Absorption of phenol into p(AAm)-WB was studied at different pHs to determine the optimum pH for maximum removal of phenol. The ionic strength of the medium was varied between 0.01 and 1 mol L-1 to determine the effect of salt (NaCl) on the absorption characteristics and it was found that the absorption of phenol increased with a decrease in the amount of salt. Langmuir and Freundlich isotherms were applied to describe the absorption characteristics and the Langmuir isotherm describes the absorption phenomena in this study much better than the Freundlich isotherm. Pseudo-first-order and pseudo-second-order kinetic studies were also applied to determine absorption characteristic. (C) 2011 Elsevier B.V. All rights reserved.Öğe Utilization of Environmentally Benign Hydrogels and Their Networks as Reactor Media in the Catalytic Reduction of Nitrophenols(Taylor & Francis As, 2011) Özay, Hava; Kubilay, Şenol; Aktaş, Nahit; Şahiner, NurettinIron particles were synthesized inside poly(2-acrylamido-2-methyl-1-propansulfonic acid) (p(AMPS)) and used as a catalyst in the reduction of nitro benzene and 4-nitrophenol to aniline and 4-aminophenol, respectively, in acidic medium. It was demonstrated that hydrogel networks can be used effectively as catalysis media in the reduction of some organic toxic materials. The results verified that iron particles containing p(AMPS) hydrogel networks yield faster conversion rates. Additionally, iron nanoparticles containing p(AMPS) hydrogel networks could catalyze the reaction, giving 32% yield without any added cocatalyst, providing self cocatalyst mission.Öğe Utilization of magnetic hydrogels in the separation of toxic metal ions from aqueous environments(Elsevier, 2010) Özay, Özgür; Ekici, Sema; Baran, Yakup; Kubilay, Şenol; Aktaş, Nahit; Şahiner, NurettinWe report the synthesis of poly(2-acrylamido-2-methyl-1-propansulfonic acid-co-vinylimidazole), p(AMPS-c-VI) hydrogels from various amounts of 2-acrylamido-2-methyl-1-propansulfonic acid (AMPS) and N-vinylimidazole (VI) monomers by photo-polymerization technique. Hydrogel composites with magnetic properties were synthesized in situ by incorporating Fe(II) and Fe(III) ions into p(AMPS-c-VI) hydrogels network and then reducing them with alkaline solution. Hydrogels swellings were performed for both bare and magnetic hydrogels. The selective removal capability of toxic metal ions, Cu(II), Cd(II), Fe(II), and Pb(II) by these hydrogels was studied in aqueous medium. Desorption studies were also performed in weakly acidic media to observe whether these hydrogel composites can be utilized as reusable tool for the toxic metal ion removal. The effects of the gel amount, contact time with metal ions, metal species and metal ion concentrations on absorption phenomena were evaluated. The equilibrium removal process of metal ions by the composite hydrogels complies well with the Langmuir adsorption isotherm model. (C) 2010 Elsevier B.V. All rights reserved.
