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    Biodegradation of 2,4,6-Trinitrotoluene (TNT) with Bacteria Isolated from TNT-polluted Waste Pink Water
    (Budapest Univ Technology Economics, 2019) Gok, Zehra Gun; Inal, Murat; Yigitoglu, Mustafa
    In this study, bacterial strains that can use TNT as a nitrogen source isolated from TNT contaminated pink water. We isolated 5 bacterial strains and the isolated bacteria were cultured in medium containing TNT and TNT degradation capacities of isolates were determined by spectrophotometric analysis. According to the results of the analysis that have done, 3 bacterial isolates that have high TNT degradation capacity were selected and the isolates were identified with firstly Gram-staining then with 16S rRNA sequence analysis method. According to the sequence of 16S rRNA, water isolates were identified as Stenotrophomonas maltophilia (SU K2), Klebsiella pneumoniae (SU K3), Raoultella planticola (SU K4). During the TNT degradation studies, at the end of 24 h incubation time, in the medium containing 100 mg/L TNT, TNT degradation rate for SU K2, SU K3 and SU K4 were determined 70 %, 96 % and 93 % respectively. 4-aminodinitrotoluene and 2-aminodinitrotoluene accumulations were detected in the culture medium of all isolates as intermediate products formed during the degradation of TNT by HPLC analysis. Additionally, nitrite accumulation was detected in the culture medium of all isolates and the influence of temperature and pH on the degradation of TNT was also investigated. It was determined that SU K2 isolates have the highest TNT degradation capacity at 35 degrees C, the others have at 30 degrees C and all isolates degraded TNT fastest at pH 7. The results of the study show that the new isolates can be useful for the removal of TNT in a wastewater treatment system.
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    Coating of modified poly(ethylene terephthalate) fibers with sericin-capped silver nanoparticles for antimicrobial application
    (Springer, 2020) Gok, Zehra Gun; Gunay, Kubra; Arslan, Metin; Yigitoglu, Mustafa; Vargel, Ibrahim
    In this work, a kind of amine-type PET fibers was synthesized by reacting hexamethylenediamine (HMDA) with methacrylic acid-g-poly(ethylene terephthalate) (PET-g-MAA) fibers for the adsorption of silk sericin-capped silver nanoparticles (S-AgNPs) to produce antimicrobial fibers. Firstly, PET fibers were grafted MAA by using free radical polymerization technique and HMDA was covalently connected to the grafted PET fibers. Then, for S-AgNPs synthesis, 10 mL of AgNO3 solution (1 mM, 5 mM and 10 mM) was mixed with 10 mL of 1% sericin solution at pH 11. The obtained solution was stirred at room temperature for 24 h. The color change from transparent to yellow-brown indicated the formation of S-AgNPs. AgNPs formation was also determined by measuring the absorbance spectra of S-AgNPs between 300 and 600 nm using UV-Vis spectrophotometer. To determine the antimicrobial properties of S-AgNPs, agar-well diffusion tests were performed. 5 mM and 10 mM S-AgNPs groups showed antimicrobial activity on Escherichia coli and Staphylococcus aureus. After characterization of the synthesized S-AgNPs with UV-Vis spectrophotometer, Zetasizer, FTIR and TEM, the modified PET fibers were coated with S-AgNPs (5 mM and 10 mM). The S-AgNPs coated PET fibers were characterized by FTIR, SEM and X-ray fluorescence spectroscopy. The antimicrobial activities of the obtained PET fibers were investigated on S. aureus and E. coli bacteria by using disk diffusion test. It was found that the S-AgNPs coated modified PET fibers exhibited antimicrobial activities toward both gram-positive and gram-negative bacteria. The resulting polymeric PET fibers containing nano-silver can be used as an antimicrobial surface for many applications such as wound dressing.
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    Effective adsorption of bovine serum albumin by polyethylene terephthalate (PET) fibers modified with glycidyl methacrylate grafting, hexamethylenediamine attachment and Cu2+ adsorption
    (Springer, 2023) Tastan, Samet; Gunay, Kubra; Arslan, Metin; Yigitoglu, Mustafa; Gok, Zehra Gun
    In this work, the glycidyl methacrylate-grafted (GMA) PET fibers were modified with hexamethylenediamine (HMDA) attachment and Cu2+ adsorption to synthesize an effective adsorbent for removal of bovine serum albumin (BSA) from the aqueous environment. The original PET fibers were grafted with GMA monomers (PET-g-GMA) at 30%, 50%, 100%, 150% and 200% grafting yields, and HMDA was covalently connected to the fibers through to the epoxy groups. The obtained fibers were characterized with the scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and nuclear magnetic resonance spectroscopy (C-13-NMR) techniques. Afterward, Cu2+ ions were adsorbed to graft copolymers modified with HMDA and it was observed that the protein adsorption ability of Cu2+ ions containing fibers increased. In the adsorption study performed with PET-g-GMA and PET-g-GMA fibers modified with HMDA, the highest Q value was found to be 1.7 and 1.98, respectively, while this value was found to be 16.4 for HMDA-modified PET fibers containing Cu2+ ions. In the adsorption experiments, it was observed that the fibers with the highest BSA adsorption capacity were those modified (with HMDA and Cu2+) PET-g-GMA fibers that have 200% grafting yield. The effects of various parameters on BSA adsorption with the fibers with the highest adsorption capacity were investigated. In the experiment carried out with the selected fibers, pH optimization was made in the range of pH 3-9 and the optimum pH value was found to be pH 5. The Q value of the fiber at this pH was found to be 24.85 mg/g. During the adsorption process carried out at pH 5, it was found that the amount of adsorbed BSA reached equilibrium after the 9 h. Temperature optimization was carried out between 25 and 55 & DEG;C at optimum pH and incubation time. Q values were found as 24.8 mg/g at 25 & DEG;C, 44 mg/g at 35 & DEG;C, 47 mg/g at 45 & DEG;C and 22 mg/g at 55 & DEG;C. According to these results, the temperature at which the maximum adsorption took place was determined as 45 & DEG;C. In the next step where the initial protein concentration upon adsorption was investigated, it was concluded that the fibers reached saturation after an initial concentration of 200 ppm BSA concentration. As a result of the desorption study carried out for 2 h in acetate buffer containing 1 M NaCl at 25 & DEG;C, it was observed that approximately 85% of the loaded protein desorbed from the fibers after 75 min. It has been seen that the modified PET-g-GMA fibers used as adsorbent in this study can be used in separation and purification processes of BSA by adsorption process, due to its advantages such as high production, low cost, high processability, and easy modification.
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    Elimination of carcinogenic bromate ions from aqueous environment with 4-vinyl pyridine-g-poly(ethylene terephthalate) fibers
    (Springer Heidelberg, 2019) Gunay, Kubra; Arslan, Metin; Bozkaya, Ogun; Aluc, Yasar; Gok, Zehra Gun
    In this study, poly(ethylene terephthalate) fibers grafted with 4-vinyl pyridine (PET-g-4VP) was synthesized with using a radical polymerization method and its removal capacity for bromate ions in the aqueous solution was explored. The synthesized graft copolymer was structurally characterized by scanning electron microscopy (SEM) and Fourier transformed infrared spectroscopy (FTIR). The effect of some parameters such as pH, grafting rate, processing time, and ion concentration on bromate removal was examined with batch experiments. The sorptions of bromate onto the PET-g-4VP fibers were both verified with FTIR and X-ray fluorescence analysis (XRF) and the remaining amount of bromate after adsorption process was determined with an ion chromatography (Shimadzu). Moreover, kinetic and isotherm studies were also performed for adsorption of bromate with the grafted fibers. The point of zero charge (pH(pzc)) of the PET-g-4VP fibers was found to be 7.5 and the fibers removed maximum amount of bromate from aqueous solution at pH 3. Equilibrium time of adsorption was determined to be 75 min and the adsorption kinetic was found to be pseudo-second-order model. It was observed that the increase in the amount of grafted 4VP onto the PET fibers increased the bromate removal capacity of the fibers; however, when the grafting yield of 4VP was over 80%, the bromate removal ability of the fibers decreased. The maximum bromate removal capacity of the PET-g-4VP was determined to be 183 mg/g when the initial bromate amount was 800 mg/L, treatment time was 75 min, pH of the solution was 3, and 4VP grafting yield was 80%. When the initial bromate concentration was higher than 800 mg/L, the removal rate of the PET-g-4VP fibers was not changed. In addition, bromate ion adsorption data indicated compliance with the Freundlich isotherm. The adsorbent fibers obtained by this study may be promising candidates for the removal of bromate ions from the aqueous media.
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    One-pot facile synthesis of silk sericin-capped gold nanoparticles by UVC radiation: Investigation of stability, biocompatibility, and antibacterial activity
    (Wiley, 2019) Akturk, Omer; Gok, Zehra Gun; Erdemli, Ozge; Yigitoglu, Mustafa
    Herein, an easy one-pot synthesis method for gold nanoparticles (AuNPs), involving only gold salt and sericin extracted from silkworm cocoon in the presence of ultraviolet C (UVC) radiation, was developed. Nanoparticle formation was confirmed by characteristic surface plasmon resonance peaks at 520-540 nm wavelengths, and the influence of silk sericin on enhancing the colloidal stability of AuNPs was confirmed. Transmission electron microscopy examination showed the average size (<10 nm) and size distribution decreased significantly with higher sericin concentration. No antibacterial activity was observed on Gram-positive Bacillus subtilis or Gram-negative Escherichia coli for sole AuNPs (0.065-0.26 mg/ml), but the conjugation of AuNPs with streptomycin antibiotic decreased significantly the required minimum inhibitory concentration doses, as also confirmed with agar plating, Scanning Electron Microscopy and Atomic Force Microscopy analyses. Furthermore, sericin-capped AuNPs showed high cell viabilities (>100%) and no sign of any detectable apoptosis or necrosis in 1-day incubation. Also, high real-time cell proliferation results of AuNPs competitive with positive control groups implied excellent in vitro biocompatibility. These results evidenced that sericin enhanced the colloidal stability of AuNPs and the biological activities of sericin-capped AuNPs reported here could render them suitable nanoscale vehicles for biomedical applications.
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    Production of 2-hydroxyethyl methacrylate-g-poly(ethylene terephthalate) nanofibers by electrospinning and evaluation of the properties of the obtained nanofibers
    (WILEY, 2020) Gok, Zehra Gun; Inal, Murat; Bozkaya, Ogun; Yigitoglu, Mustafa; Vargel, Ibrahim
    Nanofiber production was investigated from poly(ethylene terephthalate) (PET) polymers functionalized with hydroxyethyl methacrylate (HEMA) by grafting of HEMA monomers onto the PET fibers. HEMA grafted PET (PET-g-HEMA) copolymers were analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy. PET and PET-g-HEMA were dissolved in trifluoroacetic acid and nanofibers were obtained by electrospinning. It was found that the PET and PET-g-HEMA polymers having grafting yield 20 and 55% could be converted to continuous, smooth, and beadles nanofibers. For characterization of the nanofiber membranes, thermogravimetric analysis, differential scanning calorimeter analysis, surface contact angle measurement, porosity analysis, and mechanical tests were applied. When compared with the original PET nanofibers, the thermal properties and degradation process of PET-g-HEMA nanofibers changed according to the amount of HEMA present in the structure of nanofibers. The contact angles of the nanofibers obtained from PET-g-HEMA polymers decreased whereas the water retention ability of the nanofibers increased compared to original PET nanofibers. The porosity of PET-g-HEMA nanofibers was found be high compared to PET nanofibers and whereas the mechanical properties of PET was higher than PET-g-HEMA nanofibers. The obtained nanofibers can be used in many fields such as biomaterial applications.
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    Removing of Congo red from aqueous solution by 2-hydroxyethyl methacrylate-g-poly(ethylene terephthalate) fibers
    (Springer, 2019) Gok, Zehra Gun; Gunay, Kubra; Arslan, Metin; Yigitoglu, Mustafa
    Grafting of 2-hydroxyethyl methacrylate (HEMA) on poly(ethylene terephthalate) (PET) fibers was carried out via free-radical polymerization technique using benzoyl peroxide as initiator. The obtained copolymers were examined by scanning electron microscope and Fourier-transform infrared spectroscopy analysis, and it was proved that HEMA was successfully grafted onto the PET structure. The synthesized fibrous adsorbents were used to remove Congo red (CR) from aqueous solutions by batch adsorption method. The effects of pH, grafting yield, operation time and dye concentration were studied to find optimal conditions for adsorption of CR by the HEMA-grafted PET (PET-g-HEMA). The obtained results showed that the amounts of adsorbed dye on the PET-g-HEMA lowered with increasing pH. At pH 2, the dye amount adsorbed by the fibers increased with increasing dye concentration up to 70 ppm and grafting yield up to 110%. It was also seen that the adsorption had considerably rapid kinetic and achieved equilibrium within 60 min. The maximum removing abilities of the grafted fibers was found to be 16 mg/g when the beginning concentration of CR was 70 ppm at pH 2. The dye was desorbed from the loaded fibers with 1 M NaOH solution, and it was found that 83% of the adsorbed dye was recovered. The investigations on reusability of the PET-g-HEMA fibers showed that the constructed fibers can be used at least five times without losing adsorption capacities for CR. All these results indicate that the grafting can be used to remove the anionic dyes from the aqueous solution.