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    A novel amperometric H2O2 biosensor constructed by cress peroxidase entrapped on BiFeO3 nanoparticles
    (Elsevier Science Sa, 2021) Caglar, Bulent; Icer, Fatih; Ozdokur, Kemal Volkan; Caglar, Sema; Ozdemir, Agah Oktay; Guner, Eda Keles; Beser, Burcu Meryem
    Herein, we synthesized ferromagnetic BiFeO3 nanoparticles with sizes of 20-60 nm and rhombohedral distorted perovskite structure without any co-formed impurity phases by sol-gel method. Structural, morphological, magnetic, electronic and textural properties of BiFeO3 nanoparticles were characterized by using XRD, SEM-EDX, TEM, FTIR, XPS, VSM, UV-DRS, PL and BET techniques. The peroxidase was isolated from the Cress (Lepidium sativum) and purified by using precipitation of ammonium sulfate and chromatographic techniques; gel filtration and ion exchange chromatography which is showed wide range of thermal stability, maximum activity in the acidic environment and close to the body temperature. Afterwards, a novel amperometric biosensor based on Cress peroxidase entrapped on BiFeO3 nanoparticles modified carbon paste electrode was prepared for the first time to sensitive detection of H2O2. The prepared H2O2 biosensor was operated with the aid of chomamperometry technique by applying -0.8 V vs Ag/AgCl electrode. The developed biosensor exhibited a linear response towards to H2O2 in the concentration range of 2.0 10(-7) to 1.0 10(-5) M under the optimal conditions and limit of detection and quantification were estimated as 7.0 10(-8)M (2.7 mu g L-1) and 2.0 10(-7) M (8.7 mu g L-1), respectively. The repeatability of the electrode was calculated as 19.2 for 2.0 10(-7) M (N = 7) and the accuracy was 81.2% for this concentration. In addition, the H2O2 biosensor exhibited excellent stability up to ten days. Finally, the sensor developed was used for the analysis of H2O2 in milk samples and satisfactory recoveries were obtained under the operating conditions.
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    Öğe
    Application of BiFeO3 and Au/BiFeO3 decorated kaolinite nanocomposites as efficient photocatalyst for degradation of dye and electrocatalyst for oxygen reduction reaction
    (Elsevier Science Sa, 2021) Caglar, Bulent; Guner, Eda Keles; Ozdokur, Kemal Volkan; Ozdemir, Agah Oktay; Icer, Fatih; Caglar, Sema; Dogan, Bilge
    To improve the photocatalytic performance and solve the aggregation problem of BiFeO3 nanoparticles, kaolinite-BiFeO3 photocatalyst was successfully prepared for the first time by decoration of ferromagnetic BiFeO3 nanoparticles onto kaolinite surface. Comparative characteristics of kaolinite, bare BiFeO3 and kaolinite-BiFeO3 photocatalyst were investigated in detail by XRD, TEM, SEM-EDX, XPS, FTIR, VSM, UV-DRS, PL, zeta potential and BET techniques. The photocatalytic activities of the samples were also evaluated by photodegradation of rhodamine B as a model reaction under different irradiations like UVA, visible and sunlight. The kaolinite-BiFeO3 exhibited more superior photocatalytic activity as compared with other samples, which is best fitted to pseudofirst-order kinetic. The reactive species trapping experiments indicated that photogenerated-holes play major roles in the degradation process whereas superoxide radicals possess a secondary effect. Enhanced photocatalytic activity of kaolinite-BiFeO3 is attributed to its kaolinite platform that reduces the recombination opportunities of the photogenerated holes and electrons as well as increases the surface area, decreases the particle size and aggregation of nanoparticles. In addition, we also designed a novel electrocatalytic platform based on gold nanoparticles loaded on kaolinite-BiFeO3 modified carbon paste electrode surface for the examination of electrocatalytic activity for oxygen reduction reaction in alkaline medium. Electrochemical characterizations of the Au/BiFeO3/kaolinite modified carbon paste electrode and other bare surfaces were comparatively carried out with the aid of cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. Au/ BiFeO3/kaolinite modified carbon paste electrode exhibited 15-fold current enhancement together with 100 mV anodic potential shift compared with bare carbon paste electrode.