Browsing by Author "Yildirim, Rahel"

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Fabrication and Characterization of Copper Nanoparticles Anchored on Sulfonated Reduced Graphene Oxide as Effective Catalyst for the Reduction of Thioflavine-T Cationic Dye in Aqueous Medium
(Elsevier Science Sa, 2022) Yildirim, Rahel; Karatas, Yasar; Demirci, Umit B.; Gulcan, Mehmet
The development of innovative methods for the effective removal of toxic organic pollutants from wastewater is of paramount importance. Removal of organic pollutants from aqueous media by chemical reduction using low cost metal-based nanocatalysts and in the presence of sodium borohydride (NaBH4), as a reducing agent, has become a very valuable approach in recent years. We report the advanced catalytic property of copper (0) nanoparticles (Cu NPs) supported on sulfonated reduced graphene oxide (Cu@rGO-SO3H) for the catalytic reduction of thioflavine-T (ThT) dye in the presence of NaBH4, at moderate conditions. Cu@rGO-SO3H catalyst was synthesized by the impregnation-reduction method and diverse characterization techniques were applied to explain the structure and morphology. The results show that the Cu NPs are perfectly dispersed on the surface of the rGO-SO3H support surface (d(mean) = 6.9 +/- 0.4 nm). The catalytic activity of the Cu@rGO-SO3H catalyst was tested in the reduction of ThT in water at 298 K in the presence of NaBH4 and the excellent activity of catalyst have been detected against ThT with 30.5 min(-1) initial turn-over frequency (TOFinitial) value. Another important point is that the catalyst has good reusability performance (at 5th reuse 68%) for the catalytic reduction of ThT. Our catalytic studies were also carried out at various temperatures in order to calculate the E-a, Delta H-not equal and Delta S-not equal.
H2 Production From the Hydrolytic Dehydrogenation of Methylamine-Borane Catalyzed by Sulfonated Reduced Graphene Oxide-Aided Synthesis of Ruthenium Nanoparticles
(Pergamon-elsevier Science Ltd, 2021) Yildirim, Rahel; Gulcan, Mehmet
A new catalyst was prepared using sulfonated reduced graphene oxide support with a large surface area containing ruthenium nanoparticles (Ru@rGO-SO3H). The developed Ru@rGO-SO3H catalyst was used in the hydrogen production process from the hydrolytic dehydrogenation of methylamine-borane (MeAB). Sulfonated reduced graphene oxide and the developed catalyst were characterized by Raman and FT-IR spectroscopies, ICP-OES, XRD, XPS, TEM, TEM-EDX, SEM and SEM-EDX techniques. The average particle size of Ru nano particles, which were homogeneously distributed on the sulfonated reduced graphene oxide surface, was found as 2.2 +/- 0.2 nm. After analyzing the effect of nanocatalyst and substrate concentrations on the catalytic reaction, reactions were realized at different temperatures, the efficiency of the Ru@rGO-SO3H nanocatalyst in initial turnover frequency (TOFinitial) and the activation parameters (E-a, Delta H-# and Delta S-#) were calculated. According to the data obtained, the TOFinitial value was calculated as 5300.86 h(-1) (88.35 min(-1)). E-a, Delta H-# and Delta S-# values were also calculated as 53.83 kJ/mol, 50.73 kJ/mol and -51.55 J/mol.K, respectively. Finally, when the reusability performance results of the catalyst are evaluated, it is found that the catalyst is very stable and retains its initial effectiveness to a great extent (>95%) after the 5th reuse. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Investigation of Antibacterial Activity and Polyethersulfone (Pes) Membrane Usability of Delafossite-Type Cumno2 and Cumno2-Nh2 Nanostructures
(Springer, 2025) Yildirim, Rahel; Ozdemir, Sadin; Tollu, Gulsah; Gulcan, Mehmet; Filiz, Volkan; Dizge, Nadir
Membrane fouling is one of the most important issues in membrane studies and remains a current challenge. Therefore, developing composite membranes to reduce fouling is essential. In this study, delafossite-type CuMnO2 and CuMnO2-NH2 nanostructures were synthesized and characterized in detail using various instrumental tools, including SEM, SEM-Elemental Mapping, P-XRD, BET, and FTIR. The biological properties of CuMnO2 and CuMnO2-NH2 nanostructures, including antioxidant, antimicrobial, cell viability, antidiabetic activity, antibiofilm activity, and DNA fragmentation, were examined. Both materials exhibited good antioxidant, antimicrobial, and antibiofilm properties. The highest antioxidant activity for CuMnO2 was 75.93% at 100 mg/L, while the highest antioxidant activity for CuMnO2-NH2 was 92.35% at 100 mg/L. The most effective MIC value of 16 mg/L was obtained for CuMnO2 against Enterococcus hirae and Enterococcus faecalis. The highest amylase activity, at 165.2%, was observed at 100 mg/L for CuMnO2. Both CuMnO2 and CuMnO2-NH2 exhibited complete inhibition of microbial cell viability (100%) at 100 mg/L. Additionally, they demonstrated excellent biofilm inhibition activities against S. aureus and P. aureginosa. Furthermore, the use of polyethersulfone (PES) membranes coated with CuMnO2 and CuMnO2-NH2 compounds for the eradication of Escherichia coli was investigated, along with the antibacterial activities of the membrane surface and permeate.