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    Investigation of photocatalytic activity of TiO2 nanotubes synthesized by hydrothermal method
    (Taylor & Francis Inc, 2023) Karakurt, Huseyin; Kartal, Ozlem Esen
    TiO2 nanotubes were synthesized by hydrothermal reaction using commercially available TiO2 powder at 150 degrees C for 24 h. The transmission electron microscopy, X-ray diffraction, nitrogen adsorption-desorption isotherms and Fourier Transform-Infrared spectroscopy were used to characterize the nanotubes. Anatase phase was not transformed into rutile phase in the range of calcination temperature studied. Increase in calcination temperature result in enhancement of crystallinity and reduction in BET surface area. Photocatalytic removal of Reactive Red 239 (RR239) was investigated using prepared TiO2 nanotubes. Effects of pH, TiO2 nanotube dosage, initial RR239 concentration and calcination temperature were studied. 99%, 97% and 55% of removal efficiency values were attained at pH = 3, 5 and 7, respectively within 60 min or reaction time. With an increase in dosage of TiO2 nanotube in the range of 0.25-0.75 g dm(-3), removal rate increased by a steeper slope. Complete removal of RR239 was observed at 20 mg dm(-3) RR239 concentrations within 30 min but longer time was required for complete removal at higher concentrations. Langmuir-Hinshelwood kinetic expression was proposed based on nonlinear regression analysis. The removal efficiency of nanotubes calcined at 300 - 450 degrees C significantly increased but further increase in calcination temperature caused to decrease the efficiency.100% and 85% removal efficiency values were observed using actual solar light within 120 min of reaction time in July and January, respectively. Experiments conducted with scavengers showed that holes and adsorbed hydroxyl radicals were the major species involved in removal of RR239. A pathway for degradation of RR239 was suggested according to detected intermediate compounds.
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    Removal of Reactive Black 5 by UV-C assisted peroxydisulfate process: Effect of parameters, kinetic study, and phytotoxicity assessment
    (Taylor & Francis Ltd, 2024) Omac, Feyza; Karakurt, Huseyin; Kartal, Ozlem Esen
    Photochemical removal of Reactive Black 5 (RB5) was investigated by the UV-C assisted peroxydisulfate (UV-C/PDS) process. Parameters affecting the removal of RB5 were examined. Activation of PDS by UV-C light significantly improved the removal efficiency compared to direct photolysis or PDS alone. The removal of RB5 by UV-C/PDS process fitted well with the pseudo first-order kinetic model under all tested conditions. Almost complete removal of RB5 was achieved at the end of 120 min within the pH range of 3-7, whereas 90.7 and 89.4% removal efficiency values were observed at pH = 9 and 11, respectively. An increase in PDS dosage in the range of 0.25-1 mM led to a rise in removal from 48.5 to 97.3% after 120 min, and a complete removal was observed with a dosage higher than 2 mM. Pseudo firstorder rate constant (kobs) increased linearly with PDS dosage from 0.0058 to 0.0518 min-1 in the 0.25 mM - 2.3 mM concentration range. The removal efficiency decreased with an increase in the initial concentration of RB5 from 20 to 50 mg L-1 and an exponential correlation was observed between kobs and initial concentration of RB5. Scavenging experiments conducted using t-butyl alcohol and ethyl alcohol implied that both sulphate and hydroxyl radicals were involved in the removal of RB5. Adding HCO3- decreased the removal of RB5 within the range of 1-30 mM. The presence of CI- showed a negative impact on the removal at low concentrations (1-15 mM) and NO3- slightly inhibited the removal of RB5. With corresponding stoichiometric PDS dosage, almost a complete mineralisation was achieved for RB5 solution and simulated dyebath effluent after 720 min of reaction time. EE/O values were determined to be 91.0, 76.8, and 41.1 kWh m-3 order-1 for UV-C/H2O2, UV-C/PMS, and UV-C/PDS processes, respectively. The phytotoxicity tests indicated that the intermediates could be more toxic than the parent compound.
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    Removal of Reactive Red 120 using immobilized TiO2 in the presence of UV light
    (Springer, 2022) Karakurt, Huseyin; Kartal, Ozlem Esen
    Removal of Reactive Red 120 (RR120) dye in aqueous solution was investigated using immobilized TiO2 in the presence of UV light. TiO2 was deposited onto microscope slides by heat attachment method. SEM analyses confirmed that all microscope slides were coated with TiO2 particles completely after single, two, three and four layers coating. The removal efficiency increased with repetitive coating up to three layers. The highest removal efficiency of 94% was obtained at pH 3 within 300 min of reaction time. Complete removal was observed with 5 and 10 mg dm(-3) dye concentrations whereas removal efficiency decreased from 96 to 52% when initial RR120 concentration increased 15 mg dm(-3) to 30 mg dm(-3). The results of nonlinear optimization showed that the kinetics of removal of RR120 in the range of concentration studied described by L-H kinetic expression. The experiments conducted with radical scavengers indicated that hydroxyl radicals and photogenerated hole and electrons were main reactive species in photocatalytic removal of RR120. The photonic efficiency of immobilized system was lower than that of suspended system. Minor drop (6%) in the removal of RR120 with three layers coated slide after four consecutive cycles of 300 min indicated the reusability and stability of coated slides. A possible degradation mechanism for degradation of RR120 was proposed according to detected intermediate compounds. Mineralization of RR120 was monitored by generation of NO3- and SO42- ions in solution during photocatalytic reaction.