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Öğe Enhanced Photocatalytic Hydrogen Evolution by Star-Shaped Viologen-Sensitized TiO2 Nanoparticles(American Chemical Society, 2023) Turgut, Kubra; Altınışık, Sinem; Yanalak, Gizem; Koyuncu, Sermet; Hatay Patir, ImrenViologens are well-suited for serving as electron-transfer mediators in redox systems due to their low reduction potential and ability to form stable radical cations. Because of this feature, viologens can play a key role in modifying semiconductors toward enhanced photocatalytic performance. Herein, a series of hybrid photocatalysts composed of TiO2 nanoparticles and star-shaped viologen derivatives with different alkyl chains [TPCBP-X_TiO2; X: ethyl (E), butyl (B), hexyl (H) and octyl (O)] were prepared for the photocatalytic hydrogen evolution from water under visible-light irradiation. The TPCBP-X molecules not only provide photosensitization of TiO2 nanoparticles in the visible-light region but also act as an efficient electron-transfer mediator for the transfer of photoinduced electrons to TiO2 and Pt. Among these photocatalysts, TPCBP-E_TiO2 exhibited a 1.013 mmol g(-1) h(-1) H-2 evolution rate with an apparent quantum yield (AQY) of 20.15% (470 nm), which dramatically improved hydrogen evolution activity among the other structures [TPCBP-X_TiO2 (X; B, H, O)] due to the more porous and uniform surface, resulting in its low barrier effect for electron transfer. In addition, in the presence of a Pt cocatalyst, TPCBP-E_TiO2 yielded a H-2 evolution rate of 17.7 mmol g(-1), which is about 2.2 times higher than that of pure TPCBP-E_TiO2 (8.1 mmol g(-1)) after 8 h of visible-light illumination.Öğe Photoinduced step-growth polymerizations of thiophene-carbazole based covalent organic polymer(Elsevier Sci Ltd, 2023) Çeliker, Tuğba; Altınışık, Sinem; Yağcı, Yusuf; Koyuncu, SermetA novel metal-free photochemical method for the synthesis of porous conjugated polymers was used to investigate the effects of introducing thiophene co-monomer to the carbazole-based polymer, 4,4′-bis(3,6-di(thiophen-2-yl)-9H-carbazol-9-yl)-1,1′-biphenyl (CBP–Th), in terms of its structural, optical, electrochemical and morphological properties. Irradiation of a CBP-Th monomer solution led to the formation of a dark-colored polymer, PCBP-Th, and the role of thiophene on polymerization was investigated, involving electron transfer between CBP-Th and the iodonium ion in the exciplex produced by proton release and radical coupling reactions. The UV–Vis spectra broadened and redshifted due to the elongation of conjugation and solid-state π-π interactions by extra thiophene additive after the polymerization process. The addition of thiophene co-monomer also resulted in decreasing the onset potentials and thus slightly raised HOMO positions determined by the DPV technique. In theoretical calculations, it has been observed that the charge distribution of PCBP-Th at HOMO is over the entire conjugated structure and it has localization in thiophene-thiophene bridges at LUMO. Since the thiophene co-monomer changes the intermolecular distance, the thermal stability of PCBP-Th polymers decreases and accordingly increases the amorphous characters. According to AFM, TEM and SEM images, introducing the thiophene co-monomer led to the formation of larger clusters, resulting in a more pronounced surface texture on both the powders and thin films.Öğe Hydrothermal Synthesis of CuO Nanoparticles: Tailoring Morphology and Particle Size Variations for Enhanced Properties(Çanakkale Onsekiz Mart University, 2024) Akarken, Gürkan; Cengiz, Uğur; Bektaş, Tijen EnnilTransition metal oxides, particularly copper oxides, have garnered significant attention due to their intriguing photochemical, photomagnetic, photo-thermal, and photoconductive properties. Among these, CuO stands out as a p-type semiconductor having narrow bandgap energy ranges from 1.2 to 2 eV, finding versatile applications such as gas sensing, magnetic storage, solar energy conversion, photocatalysis, supercapacitors, field-emission emitters, and optical switches. Additionally, it serves as a crucial component in materials designed for lithium-ion electrodes. In this study, five different CuO nanoparticles were synthesized by simple and cost-effective hydrothermal method with various reaction temperatures and times in a teflon lined stainless steel autoclave. Copper (II) chloride dihydrate was used as copper source in this process. Various characterization techniques were conducted including X-ray powder diffraction (XRD), Raman spectroscopy, and transmitting electron microscopy (TEM). The effect of temperature and time on synthesis process was characterized and discussed. TEM images show that particle size of CuO increase with the temperature and reaction time. First reaction had the smallest particle sizes (mostly around 9-11 nm). This can be attributed to its lowest reaction temperature and shortest reaction time. For the other reactions, two of them accumulate around 19-35 nm and two around 27-45 nm range. However, the rise in the particle’s diameters is not directly proportional to temperature and time. As a result, CuO nanoparticles have been produced with simple method for the market. It can be produced in large quantities for heat exchangers, gas sensing, magnetic storage, solar energy conversion, photocatalysts, supercapacitors, etc.
