Browsing by Author "Aydemir, Murat"

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Amine-Functionalized Graphene Nanosheet-Supported Pdauni Alloy Nanoparticles: Efficient Nanocatalyst for Formic Acid Dehydrogenation
(Royal Soc Chemistry, 2018) Bulut, Ahmet; Yurderi, Mehmet; Kaya, Murat; Aydemir, Murat; Baysal, Akin; Durap, Feyyaz; Zahmakiran, Mehmet
Formic acid (HCOOH), a major by-product of biomass processing with high energy density, stability and non-toxicity, has a great potential as a safe and a convenient liquid hydrogen (H-2) storage material for combustion engines and fuel cell applications. However, high-purity hydrogen release from the catalytic decomposition of aqueous formic acid solution at desirable rates under mild conditions stands as a major challenge that needs to be solved for the practical use of formic acid in on-demand hydrogen generation systems. Described herein is a new nanocatalyst system comprised of 3-aminopropyltriethoxysilane-functionalized graphene nanosheet-supported PdAuNi alloy nanoparticles (PdAuNi/f-GNS), which can reproducibly be prepared by following double solvent method combined with liquid-phase chemical reduction, all at room temperature. PdAuNi/f-GNS selectively catalyzes the decomposition of aqueous formic acid through the dehydrogenation pathway (similar to 100% H-2 selectivity), in the absence of any promoting additives (alkali formates, Bronsted bases, Lewis bases, etc.). PdAuNi/f-GNS nanocatalyst provides CO-free H-2 generation with a turnover frequency of 1090 mol H-2 mol metal(-1) h(-1) in the additive-free dehydrogenation of formic acid at almost complete conversion (>= 92%) even at room temperature. The catalytic activity provided by PdAuNi/f-GNS nanocatalyst is higher than those obtained with the heterogeneous catalysts reported to date for the additive-free dehydrogenation of formic acid. Moreover, PdAuNi/f-GNS nanoparticles show high durability against sintering, clumping and leaching throughout the catalytic runs, so that the PdAuNi/f-GNS nanocatalyst retains almost its inherent catalytic activity and selectivity at the end of the 10th recycle.
Effects of Asymmetric Acceptor and Donor Positioning in Deep Blue Pyridyl-Sulfonyl Based Tadf Emitters
(Elsevier Sci Ltd, 2021) Haykir, Gulcin; Aydemir, Murat; Danos, Andrew; Gumus, Selcuk; Hizal, Gurkan; Monkman, Andrew P.; Turksoy, Figen
In this work, we report synthesis and photophysical properties of deep-blue emitting donor-acceptor (D-A) and donor-acceptor-donor (D-A-D) thermally activated delayed fluorescence (TADF) molecules, where the molecules designed using carbazole as a donor (D) and a pyridyl (a)-sulfonyl (A) based bifunctional group as an acceptor. The work reveals how structural changes favor reverse intersystem crossing (rISC) by forming emissive charge transfer (CT) state, which is thoroughly investigated in different donor and asymmetric acceptor positions. Three comparison sets of regioisomers are investigated. 2,5-substituted pyridine derivatives in Set-1, are D-Aa, D-aA and D-Aa-D structures with asymmetric acceptor systems, revealing that the donor nearer to the pyridine group substantially controls the TADF properties In Set-2, modified the D-Aa-D structures reveal how ortho and meta positioned a relative to A (keeping the carbazole at meta to the A) affects the emission properties, deactivating TADF and promotion triplet-triplet annihilation. In the final set, 2,4-substituted pyridyl-sulfonyl derivatives show that the positioning of the donor far from the pyridine group has minimal influence. This final set of molecules show superior optical and physical properties though, indicating the importance of correct positioning between D, a, and A.
Investigating the Relationships Among Students' Self-Efficacy Beliefs, Their Perceptions of Classroom Learning Environment, Gender, and Chemistry Achievement Through Structural Equation Modeling
(Routledge Journals, Taylor & Francis Ltd, 2016) Boz, Yezdan; Yerdelen-Damar, Sevda; Aydemir, Nurdane; Aydemir, Murat
Background: Investigating factors contributing to chemistry achievement is important since it enables us to make more concrete instructional decisions related to improving students? chemistry achievement.Purpose: This study aimed to investigate how students? perceptions of learning environment, self-efficacy and gender are related to chemistry achievement.Sample: Three hundred fifty six high school students with the age range of 14 and 19 from three different schools in the same district were the participants.Design and methods: A structural equation model was designed and tested. Constructivist learning environment survey, self-efficacy scale were the instruments of the study. Information about students? gender and their chemistry grades belonging to the previous semester were also collected.Results: The model testing showed that chemistry self-efficacy beliefs, students? perceptions of constructivist learning environment (through chemistry-self efficacy) and gender were significantly related to chemistry achievement. Moreover, the findings showed that students? chemistry self-efficacy beliefs mediated the relation of students? learning environment perceptions to their chemistry achievement.Conclusions: The present study has some educational implications for teachers, teacher educators and curriculum developers. First of all, self-efficacy was found to have an effect on students? achievement. Therefore, teachers should consider students? self-efficacy beliefs and devise their instruction accordingly. Another implication of this study is the necessity of considering gender differences in designing teachers? instruction.
The Investigation of Sky-Blue Emitting Anthracene-Carbazole Derivatives: Synthesis, Photophysics and Oled Applications
(Elsevier, 2018) Haykir, Gulcin; Aydemir, Murat; Han, Si Hyun; Gumus, Selcuk; Hizal, Gurkan; Lee, Jun Yeob; Turksoy, Figen
New well-defined structurally different 9,10-bis(9-hexyl-6-((E)-styryl)-9H-carbazol-3-yl)anthracene derivatives, shortly named "6a, 6b and 6c", with side groups having electron donating and withdrawing were systematically synthesized using Suzuki cross-coupling and Vilsmeier-Haack reactions. The impact of electron donating and withdrawing groups and their influence on the molecules photophysical properties has been investigated. The materials showed sky-blue emissions with high internal quantum efficiencies. Based on photophysical investigations the most promising molecule (6a) has been selected and high efficiency OLEDs with external quantum efficiency at very low current efficiency (similar to 1 mA/cm(2)) reaching 5% (doped) were obtained.
Palladium Nanoparticles Supported on Hydroxyapatite Nanospheres: Highly Active, Reusable and Green Catalyst for Suzuki - Miyaura Cross Coupling Reactions Under Aerobic Conditions
(Wiley-v C H verlag Gmbh, 2018) Bulut, Ahmet; Aydemir, Murat; Durap, Feyyaz; Gulcan, Mehmet; Zahmakiran, Mehmet
The development of simply prepared, highly active and reusable nanocatalysts for Suzuki-Miyaura cross coupling reactions under mild and green conditions remains a challenge in the field of synthetic organic chemistry. Herein, we describe a new nanocatalyst comprising of palladium nanoparticles supported on hydroxyapatite nanospheres, which can reproducibly be formed in-situ during the Suzuki-Miyaura coupling reactions starting with Pd(II)-exchanged nanohydroxyapatite. The characterization of the resulting catalyst by using ICP-OES, P-XRD, XPS, TEM, HRTEM, SEM and N-2-adsorption-desorption analyses revealed that the formation of 3.7 +/- 1.3nm palladium(0) nanoparticles (Pd(0)(similar to 430) nanoclusters) on the surface of nano-sized (similar to 50nm) hydroxyapatite (nano-HAp) support by keeping the host framework intact. This previously unappreciated combination of Pd NPs and nano-HAp (PdNPs@nano-HAp) shows excellent activities (TOF's > 3x10(5) h(-1)) in the Suzuki-Miyaura cross coupling reactions of different arylbromides with phenylboronic acid under mild, green and aerobic conditions. More importanly, these new supported palladium(0) nanoparticles were found to be highly durable nanocatalyst throughout the reusability experiments, they maintain almost their inherent activity after 10(th) catalytic cycle at high conversion (> 98%).
Synthesis and Investigation of Intra-Molecular Charge Transfer State Properties of Novel Donor-Acceptor Pyridine Derivatives: the Effects of Temperature and Environment on Molecular Configurations and the Origin of Delayed Fluorescence
(Royal Soc Chemistry, 2015) Aydemir, Murat; Haykir, Gulcin; Turksoy, Figen; Gumus, Selcuk; Dias, Fernando B.; Monkman, Andy P.
A novel series of donor-acceptor-donor (D-A-D) structured pyridine derivatives were synthesised and detailed photo-physical investigations were made using mainly steady-state and time-resolved spectroscopy techniques at varying temperatures. The investigations showed that the molecules have solvent polarity and temperature dependent excited-state configurations, confirmed in two different polarity solvents (295-90 K), i.e. methyl cyclohexane (MCH) and 2-methyltetrahdrofurane (2-MeTHF). In MCH, the investigations revealed dual fluorescence over the temperature range of 295-90 K. At 295 K, the ground-state configuration of the molecules has a partially twisted geometry as determined by DFT calculation, yet the emission originates totally from a locally excited (LE) state, however once the temperature is lowered to 90 K, the twisted molecular configuration is stabilised, and the emission originates from a fully-relaxed intramolecular charge transfer state (ICT), this is contrary to the systems where structural reorganisation stabilises ICT and this is frozen out at low temperatures. The DFT calculations revealed different ground state molecular configurations due to the presence of different electron-donating groups, e.g. the molecule including anthracene groups has a near 901 twisted geometry whereas the triphenylamine including molecule has a pyramidal geometrical folding, therefore, the decrease in temperature restricts the donor degree of rotational freedom. In 2-MeTHF solution, the fluorescence spectrum of both molecules is always of ICT character, but gradually red-shifts through the fluid to glass transition temperature (B135 K), in this case, the fluorescence occurs after structural and solvent-shell relaxations, however, upon cooling below 135 K, the spectra dramatically shift back to blue giving rise to strong emission from an ICT excited-state (but not the LE state) where the molecules have unrelaxed geometries. This significant change in the nature of the emitting species was explained with specific solvent-solute dynamic interactions in the vicinity of the solvation shell and the effect of thermal excitation of molecular vibrational modes of the C-C bond linking donor and acceptor units. Finally, we confirmed that the molecules have ICT ground-state geometry in the solid-state phase (spin-coated films), and the time-resolved decay dynamics were investigated comparing the spin-coated films (at RT and 25 K) and MCH solutions (at 295 K and 90 K).