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Öğe A Facile Approach to Produce Activated Carbon from Waste Textiles via Self-Purging Microwave Pyrolysis and FeCl3 Activation for Electromagnetic Shielding Applications(Mdpi, 2024) Sert, Sema; Siyahjani Gültekin, Şirin; Gültekin, Burak; Kaya, Deniz Duran; Korlu, AyşegülThis study aims to convert composite textile structures composed of nonwoven and woven fabrics produced from cotton-jute wastes into activated carbon textile structures and investigate the possibilities of using them for electromagnetic shielding applications. To this end, the novel contribution of this study is that it shows that directly carbonized nonwoven textile via self-purging microwave pyrolysis can provide Electromagnetic Interference (EMI) shielding without any processing, including cleaning. Textile carbonization is generally achieved with conventional heating methods, using inert gas and long processing times. In the present study, nonwoven fabric from cotton-jute waste was converted into an activated carbon textile structure in a shorter time via microwaves without inert gas. Due to its polar structure, FeCl3 has been used as a microwave absorbent, providing homogeneous heating in the microwave and acting as an activating agent to serve dual purposes in the carbonization process. The maximum surface area (789.9 m(2)/g) was obtained for 5% FeCl3. The carbonized composite textile structure has a maximum of 39.4 dB at 1 GHz of EMI shielding effectiveness for 10% FeCl3, which corresponds to an excellent grade for general use and a moderate grade for professional use, exceeding the acceptable range for industrial and commercial applications of 20 dB, according to FTTS-FA-003.Öğe Dopant Free Donor-Acceptor Type Polymer Hole Transport Materials for Efficient and Stable Perovskite Solar Cells(Amer Chemical Soc, 2024) Akın Kara, Duygu; Turgut, Sevdiye Başak; Çırak, Dilek; Karaman, Merve; Can, Mustafa; Koyuncu, Sermet; Gültekin, BurakA new donor-acceptor type polymers containing benzothiadiazole (HB1) and benzoselenidiazole (HB2) as acceptor units were prepared or use as hole transport layers in perovskite solar cells (PSCs). It was observed that the electrochemical HOMO-LUMO band gap narrowed from 2.74 to 1.88 depending on the variation in the acceptor unit. In addition, the charge-transfer band at 580 nm undergoes a 30 nm red-shift and broadens to the near-infrared region. HB1 and HB2 were introduced as dopant-free HTMs to replace the commonly used 2,2 ',7,7 '-tetrakis[N,N-di(4-methoxyphenyl)amino]-9-9 '-spirobifluorene (spiro-OMeTAD) in planar heterojunction n-i-p type of PSCs. Compared with HB2, HB1 exhibited better film morphology and mobility, resulting in improved charge-carrier extraction and transport. Dopant-free HB1 devices fabricated using the Cs0.05FA0.79MA0.16-Pb (IxBr1-x)3 triple cation perovskite displayed a champion power conversion efficiency of 11.69% under one sun illumination (100 mW cm(-2)) which is higher than the efficiency of HB2-based devices. The inflated performance was attributed to the reduced charge recombination and improved conductivity. In addition, these new HTMs exhibited higher hydrophobicity and thermal stability than their doped spiro-OMeTAD counterpart, making it possible to achieve good stability.Öğe Electrochemical and optical properties of biphenyl bridged-dicarbazole oligomer films: Electropolymerization and electrochromism(Pergamon-Elsevier Science Ltd, 2009) Koyuncu, Sermet; Gültekin, Burak; Zafer, Ceylan; Bilgili, Hakan; Can, Mustafa; Demic, Şerafettin; Kaya, İsmet4,4'-Di(N-carbazoyl)biphenyl monomer (CBP) was synthesized and coated onto ITO-glass surface by electrochemical oxidative polymerization. Its CV shows two distinct one-electron and stepwise oxidation processes occurred at 1.29 and 1.61 V. By using this property, the monomer was electrochemically polymerized separately at these oxidation states and thus, two different oligomer films were obtained afterwards. Their spectro-electrochemical and electrochromic properties were also investigated. Switching ability of the oligomers was evaluated by kinetic studies upon measuring the percent transmittance (%T) at their maximum contrast point, indicating that these oligomers were found to be suitable material for electrochromic devices. (C) 2009 Elsevier Ltd. All rights reserved.Öğe Kendiliğinden Organize Olabilen Donör-Akseptör Tipi Konjuge Polimerler ve Fotovoltaik Uygulamaları(2016) Koyuncu, Sermet; Bilgili, Hakan; Gültekin, Burak; Zafer, CeylanBu projede, ilk olarak kendiliğinden organize olabilen yan zincirler ile fonksiyonlandırılmış, du?şu?k bant aralığına sahip bir seri donör-akseptör tipi polimer tasarlanmış ve sentezlenmiştir. Sentezlenen bu polimerlerin optik ve elektrokimyasal özellikleri UV-Vis absorbsiyon ve döngu?sel voltametri ölçu?mleri vasıtasıyla incelenmiştir. Daha sonra ise sentezlenen yarıiletken polimerlerden hem siloksan içerenleri hem de siloksanlamadan önceki basamak olan allil grubu içeren polimerlerle, hacimsel heteroeklemli organik fotovoltaik hu?cre denemeleri gerçekleştirilmiştir. Denemelerde en yu?ksek gu?ç dönu?şu?m verimi, %6,06 (ortalama: %5,74) ile allil içeren diketopirolpirol ve karbazol tu?revi, BP-3 polimeri ile elde edilmiştir. Elde edilen yu?ksek verimin nedenleri, sonuç ve artışma bölu?mu?nde morfoloji analizleriyle açıklanmıştır. Polimerlerin yan zincirleri u?zerinde bulunan siloksan gruplarının film fazında kendiliğinden organize olmaları sayesinde, fotovoltaik hu?crenin aktif tabakasında, donör ve akseptör arasında bir nanofaz ayrımının sağlanması ve moleku?ller arasındaki etkileşimin artırılması ile hu?cre kararlılığın iyileştirilmesi amaçlanmıştır. Film morfolojisi optimizasyonu, diferansiyel taramalı kalorimetre (DSC) ile belirlenen camsı geçiş sıcaklıkları (Tg) kullanılarak yapılmıştır. Termal tavlama (thermal annealing) sonucunda, aktif tabakada gözlenen değişimler, atomik kuvvet mikroskopu (AFM) ve X-ışını difraktometresi ile takip edilmiştir. Son olarak, analiz sonuçları kullanılarak, polimerlerin fotovoltaik performansları değerlendirilmiştir.Öğe Stable Efficient Solid-State Supercapacitors and Dye-Sensitized Solar Cells Using Ionic Liquid-Doped Solid Biopolymer Electrolyte(Amer Chemical Soc, 2024) Konwar, Subhrajit; Siyahjani Gültekin, Şirin; Gültekin, Burak; Kumar, Sushant; Punetha, Vinay Deep; Yahya, Muhd Zu Azhan Bin; Diantoro, MarkusAs synthetic and nonbiodegradable compounds are becoming a great challenge for the environment, developing polymer electrolytes using naturally occurring biodegradable polymers has drawn considerable research interest to replace traditional aqueous electrolytes and synthetic polymer-based polymer electrolytes. This study shows the development of a highly conducting ionic liquid (1-hexyl-3-methylimidazolium iodide)-doped corn starch-based polymer electrolyte. A simple solution cast method is used to prepare biopolymer-based polymer electrolytes and characterized using different electrical, structural, and photoelectrochemical studies. Prepared polymer electrolytes are optimized based on ionic conductivity, which shows an ionic conductivity as high as 1.90 x 10(-3) S/cm. Fourier transform infrared spectroscopy (FTIR) confirms the complexation and composite nature, while X-ray diffraction (XRD) and polarized optical microscopy (POM) affirm the reduction of crystallinity in biopolymer electrolytes after doping with ionic liquid (IL). Thermal and photoelectrochemical studies further affirm that synthesized material is well stable above 200 degrees C and shows a wide electrochemical window of 3.91 V. The ionic transference number measurement (t ion) confirms the predominance of ionic charge carriers in the present system. An electric double-layer capacitor (EDLC) and a dye-sensitized solar cell (DSSC) were fabricated by using the highest conducting corn starch polymer electrolyte. The fabricated EDLC and DSSC delivered an average specific capacitance of 130 F/g and an efficiency of 1.73% in one sun condition, respectively.
