Recep Akkaya

Adsorptive features of polyacrylamide–apatite composite for Pb2+, UO22+ and Th4+

Micro-composite of polyacrylamide (PAA) and apatite (Apt) was prepared by direct polymerization of acrylamide in a suspension of Apt and characterized by means of FT-IR, XRD, SEM and BET analysis. The adsorptive features of PAA-Apt and Apt were then investigated for Pb(2+), UO(2)(2+) and Th(4+) in view of dependency on ion concentration, temperature, kinetics, ion selectivity and reusability. Experimentally obtained isotherms were evaluated with reference to Langmuir, Freundlich and Dubinin-Radushkevich (DR) models. Apt in PAA-Apt had higher adsorption capacity (0.81, 1.27 and 0.69 mol kg(-1)) than bare Apt (0.28, 0.41 and 1.33 mol kg(-1)) for Pb(2+) and Th(4+), but not for UO(2)(2+). The affinity to PAA-Apt increased for Pb(2+) and UO(2)(2+) but not changed for Th(4+). The values of enthalpy and entropy changed were positive for all ions for both Apt and PAA-Apt. Free enthalpy change was DeltaG<0. Well compatibility of adsorption kinetics to the pseudo-second-order model predicated that the rate-controlling step was a chemical sorption. This was consistent with the free energy values derived from DR model. The reusability tests for Pb(2+) for five uses proved that the composite was reusable to provide a mean adsorption of 53.2+/-0.7% from 4x10(-3)M Pb(2+) solution and complete recovery of the adsorbed ion was possible (98+/-1%). The results of this investigation suggested that the use of Apt in the micro-composite form with PAA significantly enhanced the adsorptive features of Apt.

Uranium and thorium adsorption from aqueous solution using a novel polyhydroxyethylmethacrylate-pumice composite

Poly(hydroxyethylmethacrylate-pumice), [P(HEMA-Pum)], composite was synthesized by free radical polymerization in aqueous solution. The adsorptive features of P(HEMA-Pum) composite were investigated for UO2(2+) and Th(4+) using a range of pH, concentration, time (kinetics), temperature (thermodynamics), ionic strength and selectivity, and the related parameters were derived from the obtained results. These results indicated that all adsorbents had high affinity to the uranium and thorium ions. The parameters obtained from Langmuir, Freundlich and Dubinin-Radsushkevich models fit the data well. The values of enthalpy and entropy changes showed that the overall adsorption process was endothermic (ΔH > 0) and increasing entropy (ΔS > 0), and it was spontaneous (ΔG < 0) as expected. The adsorption kinetics following the pseudo-second order model indicated that the rate-controlling step was chemical adsorption that occurred by ion exchange process. Reusability of P(HEMA-Pum) was also investigated, and it was found that the composite could be used at least 5 times.

Production and immobilization of a novel thermoalkalophilic extracellular amylase from bacilli isolate

A Thermoalkalophilic amylase was produced from an environmental bacterial isolate. The enzyme was then immobilized through its amino groups onto the epoxy rings of magnetic poly glycidyl methacrylate [m-poly (GMA)] beads. The free enzyme was active within a large pH range, between 7 and 12 and displayed the optimum activity at 95°C and pH 10. The immobilization appeared to increase the stability of the enzyme as its bound form showed optimum activity at 105°C and pH 11.0. Kinetic studies demonstrated that immobilized enzyme had higher K(m) and lower V(max) values. The activity of the free and bound enzyme was determined, at 37°C and pH 10.0 and pH 11.0, respectively, in the presence of various organic solvents and detergents (5%, v/v). Results obtained indicated that detergents, sodium dodecyl sulfate (SDS) and TritonX-100, caused six fold increase and that various organic solvents also increased the activity of the amylase.

Separation of uranium and thorium in aqueous solution using polyhydroxyethylmethacrylate-hydroxyapatite novel composite

Abstract Poly(hydroxyethylmethacrylate-hydroxyapatite) [P(HEMA-Hap)] composite was synthesized by free radical polymerization in aqueous solution. The adsorptive features of P(HEMA-Hap) composite were investigated for and Th4+ using a range of pH, concentration, time, temperature, and ionic strength values. It was observed that P(HEMA-Hap) composite had high affinity to uranium and thorium ions and that the adsorption capacity of the composite increased in proportion to the amount of Hap content. Adsorption data obtained fitted well into the classical Lagmuir, Freundlich, and Dubinin-Radushkevich sorption models. Changes in the enthalpy and entropy values showed that the overall adsorption process was endothermic and spontaneous (ΔG < 0), as expected. The adsorption kinetics following the pseudo-second order model indicated that the rate-controlling step was chemical adsorption that occurred by ion exchange process. Reusability of the composite was also investigated, and it was found that the composite co...

Production, purification, and characterization of metalloprotease from Candida kefyr 41 PSB

A thermostable metalloprotease, produced from an environmental strain of Candida kefyr 41 PSB, was purified 16 fold with a 60% yield by cold ethanol precipitation and affinity chromatography (bentonite-acrylamide-cysteine microcomposite). The purified enzyme appeared as a single protein band at 43kDa. Its optimum pH and temperature points were found to be 7.0 and 105°C, respectively. Km and Vmax values of the enzyme were determined to be 3.5mg/mL and 4.4μmolmL-1min-1, 1.65mg/mL and 6.1μmolmL-1min-1, using casein and gelatine as the substrates, respectively. The activity was inhibited by using ethylenediamine tetraacetic acid (EDTA), indicating that the enzyme was a metalloprotease. Stability of the enzyme was investigated by using thermodynamic and kinetic parameters. The thermal inactivation profile of the enzyme conformed to the first order kinetics. The half life of the enzyme at 95, 105, 115, 125 and 135°C was 1310, 610, 220, 150, and 86min, respectively.

A Crosslinked Carboxylic Acid Containing Cation Exchange Monolithic Cryogel for Human Serum Albumin Separation

For this work, we synthesized poly(N-isopropylacrylamide-acrylamide)-acrylic acid (poly(NIPAM-Am)-AAc) monolithic cryogel for a human serum albumin separation (HSA) from a protein mixture (human serum immunoglobulin, human serum albumin and lysozyme) and performed HSA adsorption studies using the cryogel to do continuous system experiments in a syringe column connected by a peristaltic pump. Poly(NIPAM-Am)-AAc with a pore size of 10–100 μm was produced by free radical polymerization that proceeded in an aqueous solution of monomers frozen inside a syringe column. The monolithic poly(NIPAM-Am)-AAc cryogel was characterized by performing swelling studies, FTIR and SEM that showed a swelling ratio of 6.2 g H2O/g dry cryogel. The maximum HSA adsorption by the cryogel was 42.5 mg/g polymer at pH 4.0 in a 50 mM acetate buffer. We also studied the effect of two different temperatures (25 and 40°C). The higher temperature increased the adsorption capacity of the cryogel. HSA molecules could be reversibly adsorbed and desorbed five times with the same poly(NIPAM-Am)-AAc cryogel without a noticeable loss of their HSA adsorption capacity. The synthesized cryogel was used to separate albumin from the protein mixture. Adsorbed albumin was eluted by changing the pH of the buffer (pH 7.0 and 25°C). Poly(NIPAM-Am)-AAc monolithic cryogel behaved as a cation exchange column because of its functional carboxylic group.

Cross-Linked Bentonite-Acrylamide-histidine-Based Metal-Chelate Affinity Microcomposites for Lysozyme Separation From Egg White

Among different adsorbents, a new support for immobilized metal affinity chromatography was used for lysozyme separation from egg white. For this purpose, acrylamide, bisacrylamide, bentonite, and L-histidine in the presence of an initiator (azobisisobutyronitrile, AIBN) were mixed and bentonite-acrylamide-histidine microcomposites were prepared by bulk polymerization. Characterization studies were performed by SEM, FT-IR, XRD, and BET. Specific surface area of the bentonite and BABH microcomposite was found to be 33.4 and 1.42 m2/g, respectively. Cu2+ ions (20 µmol/g) were chelated on these bentonite-acrylamide-histidine (50 µmol/g L-histidine incorporation) microcomposites. The lysozyme adsorption capacity of the Cu2+ ions chelated microcomposites increased the lysozyme adsorption up to 100 mg/g while the lysozyme adsorption capacity of the bentonite-acrylamide-histidine was 24 mg/g. More than 89% of the adsorbed lysozyme was desorbed in 1 h in the desorption medium containing 1.0 M NaCl. Bentonite-acrylamide-histidine-Cu(II) was used for the purification of lysozyme from chicken egg white. The purity of lysozyme was estimated by SDS-PAGE. Specific activity of the purified lysozyme was found as 50,000 U/mg using Micrococcus lysodeikticus as substrate. The new metal-chelate affinity microcomposites were suitable for repeated use for five cycles without a noticeable loss of capacity.

Terbium adsorption onto polyhydroxyethylmethacrylate–hydroxyapatite composite and its modified composition by phytic acid

AbstractHydroxyapatite (Hap) was entrapped in poly(hydroxyethylmethacrylate) P(HEMA) by direct polymerization and P(HEMA–Hap) was obtained in aqueous solution. Phytate (phy) was immobilized by phytic acid (phy) modification onto the poly(hydroxyethylmethacrylate–hydroxyapatite), P(HEMA–Hap). The adsorptive features of P(HEMA–Hap) composite and its modified form P(HEMA–Hap)–phy, were investigated by using Tb analogues, rare earth elements (REE), by isotopic tracer method, 160Tb was used as the radiotracer. It was observed that P(HEMA–Hap) composite had a higher affinity for Tb3+ than bare Hap, as well as its modified composition P(HEMA–Hap)–phy. Adsorption data obtained, fitted well to the classical Lagmuir, Freundlich, and Dubinin–Radushkevich (D–R) sorption models. Changes in enthalpy and entropy values showed that the overall adsorption process was endothermic (ΔH > 0), increasing entropy (ΔS > 0), and spontaneous (ΔG < 0), as expected. The adsorption kinetics following the pseudo-second order model ind...

New low-cost composite adsorbent synthesis and characterization

Abstract In this research, a novel composite, poly(acrylamide-expanded perlite) [P(AAm-EP)], was synthesized and characterized. The chemical synthesis was achieved by using free-radical polymerization and a number of structural characterization methods, including Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET)-porosity, and swelling tests. Free-radical polymerization of acrylamide (AAm) over expended perlite (EP) was successfully performed. The effect of reaction variables, such as dosage of the initiator, total concentration of the reactants, reactant ratio, mixing time, temperature, and reaction time, were investigated in detail. Expended perlite was cross-linked with acrylamide to enhance its chemical resistance. P(AAm-EP) composite has a specific surface area of 31.7 m2 g−1.

Bentonite-acrylamide-histidine-Cu(II) Microcomposite for Cytochrome c Adsorption

Bentonite-acrylamide-histidine with an average particle diameter of 200-1000 μm was produced by bulk polymerization of bentonite, acrylamide, bisacrylamide, AIBN and histidine. Bentonite-acrylamide-histidine-Cu(II) microcomposite was prepared by loading copper ions. The microcomposite was characterized by scanning electron microscopy (SEM), specific surface area and elemental analysis. Cytochrome c adsorption studies were performed, for the first time, by using the new metal chelated affinity support (bentonite-acrylamide-histidine-Cu(II)) microcomposite in batchwise experiments.