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    Dichromate and arsenate anion removal by PEI microgel, cryogel, and bulkgel
    (Elsevier Ltd, 2021) Kubilay, Şenol; Demirci, Şahin; Can, Mehmet; Aktaş, Nahit; Şahiner, Nurettin
    Among 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.
  • Küçük Resim
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    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, Nurettin
    In 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.