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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access High-quality MgB2 nanocrystals synthesized by using modified amorphous nano-boron powders: study of defect structures and superconductivity properties(American Institute of Physics (AIP) Publishing, 2019) Erdem, Emre; Hassler, Wolfgang; Department of Chemistry; N/A; Somer, Mehmet Suat; Bateni, Ali; Faculty Member; PhD Student; Department of Chemistry; College of Sciences; Graduate School of Sciences and EngineeringNano sized magnesium diboride (MgB2) samples were synthesized using various high-quality nano-B precursor powders. The microscopic defect structures of MgB2 samples were systematically investigated using X-ray powder diffraction, Raman, resistivity measurements and electron paramagnetic resonance spectroscopy. A significant deviation in the critical temperature T-c was observed due to defects and crystal distortion. The symmetry effect of the latter is also reflected on the vibrational modes in the Raman spectra. Scanning electron microscopy analysis demonstrate uniform and ultrafine morphology for the modified MgB2. Defect center in particular Mg vacancies influence the connectivity and the conductivity properties which are crucial for the superconductivity applications.Publication Open Access Locked and loaded: ?-galactosidase activated photodynamic therapy agent enables selective imaging and targeted treatment of glioblastoma multiforme cancer cells(American Chemical Society (ACS), 2022) Elmazoğlu, Z.; Atakan, G.; Kepil, D.; Aykent, G.; Günbaş, G.; Department of Chemistry; Kölemen, Safacan; Almammadov, Toghrul; Faculty Member; Researcher; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); College of Sciences; 272051; N/ASelective detection and effective therapy of brain cancer, specifically, the very aggressive glioblastoma multiforme (GBM), remains one of the paramount challenges in clinical settings. While radiotherapy combined surgery is proposed as the main treatment course, it has several drawbacks such as complexity of the operation and common development of recurrent tumors in this course of patient care. Unique opportunities presented by photodynamic therapy (PDT) offer promising, effective, and precise therapy against GBM cells along with simultaneous imaging opportunities. However, activatable, theranostic molecular systems in PDT modality for GBM remained scarce. Specifically, even though elevated fi-galactosidase (fi-gal) activity in glioblastoma cells is well-documented, targeted, activatable therapeutic PDT agents have not been realized. Herein, we report a fi-galactosidase (fi-gal) activatable phototheranostic agent based on an iodinated resorufin core (RB-1) which was realized in only three steps with commercial reagents in 29% overall yield. RB-1 showed very high singlet oxygen (1O2) quantum yield (54%) accompanied by a remarkable turn-on response in fluorescence upon enzymatic activation. RB-1 was tested in different cell lines and revealed selective photocytotoxicity in U-87MG glioblastoma cells. Additionally, thanks to almost 7% fluorescence quantum yield (phi F) despite extremely high 1O2 generation yield, RB-1 was also demonstrated as a successful agent for fluorescence imaging of U-87MG cells. Due to significantly lower (fi-gal) activity in healthy cells (NIH/3T3), RB-1 stayed in a passive state and showed minimal photo and dark toxicity. RB-1 marks the first example of a fi- gal activatable phototheranostic agent toward effective treatment of glioblastoma.Publication Open Access Guide to water free lithium bis(oxalate) borate (LiBOB)(American Chemical Society (ACS), 2021) Zor, Ceren; Afyon, Semih; N/A; Department of Chemistry; Haciu, Durata; Subaşı, Yaprak; Somer, Mehmet Suat; Teaching Faculty; Researcher; Department of Chemistry; Koç University AKKİM Boron-Based Materials _ High-technology Chemicals Research _ Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM); Graduate School of Sciences and Engineering; College of SciencesLithium bis(oxalate) borate, LiB(C2O4)(2) (LiBOB), is one of the most important electrolyte additives for Li-ion batteries (LIBs) due to its numerous advantages such as thermal stability, good solubility in organic solvents, high conductivity, and low cost as well as providing safer operations with superior electrochemical performance compared to conventional electrolyte combinations. However, the use of LiBOB is limited due to slight instability issues under ambient conditions that might require extra purification steps and result in poorer performances in real systems. Here, we address some of these issues and report a high purity water free LiBOB synthesized with fewer processing steps, employing lithium carbonate, oxalic acid, and boric acid as low-cost starting materials, and via ceramic processing methods under protective atmosphere. The physical and chemical characterizations of both anhydrous and monohydrate phases are performed with X-ray powder diffraction (XRPD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and scanning electron microscopy (SEM) analyses to determine the degree of the purity and the formation of impurities, such as LiBOB center dot H2O, HBO2, and Li2C2O4, as a result of the aging investigations where the as-synthesized salt was exposed to ambient conditions for different durations. Differential thermal analysis (DTA) is applied to determine the optimum synthesis conditions for anhydrous LiBOB and to analyze the water loss and the decomposition of LiBOB center dot H2O. Aging experiments with the water free LiBOB are carried out to evaluate the effect of humidity on the phase changes and resulting impurities under various conditions. The detrimental effect of even slightest humidity conditions is shown, and protective measures during and after the synthesis of LiBOB are discussed. Anhydrous LiBOB could be widely used as an electrolyte additive to improve the overall electrochemical performances for LIBs through development of a protective solid electrolyte interface (SEI) on the surface of high voltage cathodes and by bringing about superior electrochemical properties with increased cycling stability, rate capability, and Coulombic efficiency, if synthesized, purified, and handled properly before use in real electrochemical systems.Publication Open Access High thermoelectric performance enabled by convergence of nested conduction bands in Pb7Bi4Se13 with low thermal conductivity(Nature Publishing Group (NPG), 2021) Hu, Lei; Fang, Yue Wen; Qin, Feiyu; Cao, Xun; Zhao, Xiaoxu; Luo, Yubo; Repaka, Durga Venkata Maheswar; Luo, Wenbo; Suwardi, Ady; Soldi, Thomas; Huang, Yizhong; Liu, Zheng; Hippalgaonkar, Kedar; Snyder, G. Jeffrey; Xu, Jianwei; Yan, Qingyu; Department of Chemistry; Aydemir, Umut; Faculty Member; Department of Chemistry; Koç University AKKİM Boron-Based Materials _ High-technology Chemicals Research _ Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM); College of Sciences; 58403Thermoelectrics enable waste heat recovery, holding promises in relieving energy and environmental crisis. Lillianite materials have been long-term ignored due to low thermoelectric efficiency. Herein we report the discovery of superior thermoelectric performance in Pb7Bi4Se13 based lillianites, with a peak figure of merit, zT of 1.35 at 800 K and a high average zT of 0.92 (450-800 K). A unique quality factor is established to predict and evaluate thermoelectric performances. It considers both band nonparabolicity and band gaps, commonly negligible in conventional quality factors. Such appealing performance is attributed to the convergence of effectively nested conduction bands, providing a high number of valley degeneracy, and a low thermal conductivity, stemming from large lattice anharmonicity, low-frequency localized Einstein modes and the coexistence of high-density moire fringes and nanoscale defects. This work rekindles the vision that Pb7Bi4Se13 based lillianites are promising candidates for highly efficient thermoelectric energy conversion.Publication Open Access An integrated computational-experimental hierarchical approach for the rational design of an IL/UiO-66 composite offering infinite CO2 selectivity(Wiley, 2022) Department of Chemical and Biological Engineering; Department of Chemistry; Zeeshan, Muhammad; Gülbalkan, Hasan Can; Durak, Özce; Haşlak, Zeynep Pınar; Ünal, Uğur; Keskin, Seda; Uzun, Alper; PhD Student; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Engineering; College of Sciences; Graduate School of Sciences and Engineering; N/A; N/A; N/A; N/A; 42079; 40548; 59917Owing to the possibility of generating theoretically unlimited numbers of ionic liquid (IL)-metal-organic framework (MOF) combinations, experimental studies on IL/MOF composites for gas separation applications are mostly conducted on a trial-and-error basis. To address this problem, an integrated computational-experimental hierarchical approach is presented for selecting the best IL-MOF combination for a target gas separation application. For this purpose, UiO-66 and pyrrolidinium-based ILs are chosen as the parent MOF and IL family, respectively, and three powerful computational tools, Conductor-like Screening Model for Realistic Solvents calculations, density functional theory calculations, and grand canonical Monte Carlo simulations, are integrated to identify the most promising IL-UiO-66 combination as 1-n-butyl-1-methylpyrrolidinium dicyanamide/UiO-66, [BMPyrr][DCA]/UiO-66. Then, this composite is synthesized, characterized in deep detail, and tested for CO2/N-2, CO2/CH4, and CH4/N-2 separations. Results demonstrate that [BMPyrr][DCA]/UiO-66 offers an extraordinary gas separation performance, with practically infinite CO2 and CH4 selectivities over N-2 at 15 degrees C and at low pressures. The integrated hierarchical approach proposed in this work paves the way for the rational design and development of novel IL/MOF composites offering exceptional performance for any desired gas separation application.Publication Open Access High performance white light-emitting diodes over 150 lm/W using near-unity-emitting quantum dots in a liquid matrix(American Chemical Society (ACS), 2022) N/A; N/A; Department of Electrical and Electronics Engineering; Department of Chemistry; Önal, Asım; Eren, Güncem Özgün; Sadeghi, Sadra; Melikov, Rustamzhon; Han, Mertcan; Karatüm, Onuralp; Özer, Melek Sermin; Jalali, Houman Bahmani; Doğru-Yüksel, Itır Bakış; Yılgör, İskender; Metin, Önder; Nizamoğlu, Sedat; PhD Student; PhD Student; Master Student; PhD Student; Faculty Member; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; N/A; N/A; N/A; N/A; N/A; N/A; N/A; N/A; 24181; 46962; 130295In the next decade, we will witness the replacement of a majority of conventional light sources with light-emitting diodes (LEDs). Efficient LEDs other than phosphors can enhance their functionality and meet different lighting needs. Quantum dots (QDs) have high potential for future LED technology due to their sensitive band-gap tuning via the quantum confinement effect and compositional control, high photoluminescence quantum yield (PLQY), and mass-production capacity. Herein, we demonstrate white LEDs using QDs that reach over 150 lumens per electrical Watt. For that we synthesized green-and red-emitting ZnCdSe/ZnSe core/shell QDs by low-temperature nucleation, high-temperature shell formation, and postsynthetic trap-state removal. Their cadmium concentration is lower than 100 ppm, satisfying the current EU RoHS regulations, and their PLQY reaches a high level of 94%. The PLQY of QDs is maintained within the device on blue LED via liquid injection, and their integration at optimized optical densities leads to 129.6 and 170.4 lm/W for red-green-blue (RGB)-and green-blue (GB)-based white LEDs, respectively. Our simulations further showed that an efficiency level of over 230 lm/W is achievable using ultraefficient blue LED pumps. The simple fabrication and high performance of white LEDs using QD liquids show high promise for next-generation lighting devices.Publication Open Access A new type of microphotoreactor with integrated optofluidic waveguide based on solid-air nanoporous aerogels(Royal Society of Chemistry (RSC), 2018) Jonas, Alexandr; Department of Chemistry; Department of Electrical and Electronics Engineering; Department of Physics; Özbakır, Yaprak; Erkey, Can; Kiraz, Alper; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; Department of Electrical and Electronics Engineering; Department of Physics; College of Engineering; College of Sciences; N/A; 29633; 22542In this study, we developed a new type of microphotoreactor based on an optofluidic waveguide with aqueous liquid core fabricated inside a nanoporous aerogel. To this end, we synthesized a hydrophobic silica aerogel monolith with a density of 0.22 g cm(-3) and a low refractive index of 1.06 that-from the optical point of view-effectively behaves like solid air. Subsequently, we drilled an L-shaped channel within the monolith that confined both the aqueous core liquid and the guided light, the latter property arising due to total internal reflection of light from the liquid-aerogel interface. We characterized the efficiency of light guiding in liquid-filled channel and-using the light delivered by waveguiding-we carried out photochemical reactions in the channel filled with aqueous solutions of methylene blue dye. We demonstrated that methylene blue could be efficiently degraded in the optofluidic photoreactor, with conversion increasing with increasing power of the incident light. The presented optofluidic microphotoreactor represents a versatile platform employing light guiding concept of conventional optical fibres for performing photochemical reactions.Publication Open Access Metal doped layered MgB2 nanoparticles as novel electrocatalysts for water splitting(Nature Publishing Group (NPG), 2021) Khatamian, Masoumeh; N/A; Department of Chemistry; Sadeghi, Ebrahim; Peighambardoust, Naeimeh Sadat; Ünal, Uğur; Aydemir, Umut; PhD Student; Researcher; Faculty Member; Faculty Member; Department of Chemistry; Koç University AKKİM Boron-Based Materials _ High-technology Chemicals Research _ Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 42079; 58403Growing environmental problems along with the galloping rate of population growth have raised an unprecedented challenge to look for an ever-lasting alternative source of energy for fossil fuels. The eternal quest for sustainable energy production strategies has culminated in the electrocatalytic water splitting process integrated with renewable energy resources. The successful accomplishment of this process is thoroughly subject to competent, earth-abundant, and low-cost electrocatalysts to drive the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), preferably, in the same electrolyte. The present contribution has been dedicated to studying the synthesis, characterization, and electrochemical properties of newfangled electrocatalysts with the formal composition of Mg1-xTMxB2 (x=0.025, 0.05, and 0.1; TM (transition metal)=Fe and Co) primarily in HER as well as OER under 1 M KOH medium. The electrochemical tests revealed that among all the metal-doped MgB2 catalysts, Mg0.95Co0.05B2 has the best HER performance showing an overpotential of 470 mV at-10 mA cm(-2) and a Tafel slope of 80 mV dec(-1) on account of its high purity and fast electron transport. Further investigation shed some light on the fact that Fe concentration and overpotential for HER have adverse relation meaning that the highest amount of Fe doping (x=0.1) displayed the lowest overpotential. This contribution introduces not only highly competent electrocatalysts composed of low-cost precursors for the water-splitting process but also a facile scalable method for the assembly of highly porous electrodes paving the way for further stunning developments in the field.Publication Open Access Cetuximab-Ag2S quantum dots for fluorescence imaging and highly effective combination of ALA-based photodynamic/chemo-therapy of colorectal cancer cells(Royal Society of Chemistry (RSC), 2021) Mohammad Hadi, Layla; Yaghini, Elnaz; Loizidou, Marilena; MacRobert, Alexander J.; Department of Chemistry; N/A; Department of Physics; Acar, Havva Funda Yağcı; Bayır, Ali; Hashemkhani, Mahshid; Demirci, Gözde; Muti, Abdullah; Sennaroğlu, Alphan; Researcher; PhD Student; Master Student; PhD Student; Faculty Member; Department of Chemistry; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; Graduate School of Sciences and Engineering; 178902; N/A; N/A; N/A; N/A; 23851Colorectal cancer (CRC) has a poor prognosis and urgently needs better therapeutic approaches. 5-Aminolevulinic acid (ALA) induced protoporphyrin IX (PpIX) based photodynamic therapy (PDT) is already used in the clinic for several cancers but not yet well investigated for CRC. Currently, systemic administration of ALA offers a limited degree of tumour selectivity, except for intracranial tumours, limiting its wider use in the clinic. The combination of effective ALA-PDT and chemotherapy may provide a promising alternative approach for CRC treatment. Herein, theranostic Ag2S quantum dots (AS-2MPA) optically trackable in near-infrared (NIR), conjugated with endothelial growth factor receptor (EGFR) targeting Cetuximab (Cet) and loaded with ALA for PDT monotherapy or ALA/5-fluorouracil (5FU) for the combination therapy are proposed for enhanced treatment of EGFR(+) CRC. AS-2MPA-Cet exhibited excellent targeting of the high EGFR expressing cells and showed a strong intracellular signal for NIR optical detection in a comparative study performed on SW480, HCT116, and HT29 cells, which exhibit high, medium and low EGFR expression, respectively. Targeting provided enhanced uptake of the ALA loaded nanoparticles by strong EGFR expressing cells and formation of higher levels of PpIX. Cells also differ in their efficiency to convert ALA to PpIX, and SW480 was the best, followed by HT29, while HCT116 was determined as unsuitable for ALA-PDT. The therapeutic efficacy was evaluated in 2D cell cultures and 3D spheroids of SW480 and HT29 cells using AS-2MPA with either electrostatically loaded, hydrazone or amide linked ALA to achieve different levels of pH or enzyme sensitive release. Most effective phototoxicity was observed in SW480 cells using AS-2MPA-ALA-electrostatic-Cet due to enhanced uptake of the particles, fast ALA release and effective ALA-to-PpIX conversion. Targeted delivery reduced the effective ALA concentration significantly which was further reduced with codelivery of 5FU. Delivery of ALA via covalent linkages was also effective for PDT, but required a longer incubation time for the release of ALA in therapeutic doses. Phototoxicity was correlated with high levels of reactive oxygen species (ROS) and apoptotic/necrotic cell death. Hence, both AS-2MPA-ALA-Cet based PDT and AS-2MPA-ALA-Cet-5FU based chemo/PDT combination therapy coupled with strong NIR tracking of the nanoparticles demonstrate an exceptional therapeutic effect on CRC cells and excellent potential for synergistic multistage tumour targeting therapy.Publication Open Access Nanoparticle and gelation stabilized functional composites of an ionic salt in a hydrophobic polymer matrix(Public Library of Science, 2014) Department of Chemistry; Demirel, Adem Levent; Kanyas, Selin; Aydın, Derya; Kızılel, Rıza; Kızılel, Seda; Faculty Member; Researcher; Researcher; Faculty Member; Department of Chemistry; The Center for Computational Biology and Bioinformatics (CCBB); College of Engineering; College of Sciences; 6568; N/A; N/A; N/A; 28376Polymer composites consisted of small hydrophilic pockets homogeneously dispersed in a hydrophobic polymer matrix are important in many applications where controlled release of the functional agent from the hydrophilic phase is needed. As an example, a release of biomolecules or drugs from therapeutic formulations or release of salt in anti-icing application can be mentioned. Here, we report a method for preparation of such a composite material consisted of small KCOOH salt pockets distributed in the styrene-butadiene-styrene (SBS) polymer matrix and demonstrate its effectiveness in anti-icing coatings. The mixtures of the aqueous KCOOH and SBS-cyclohexane solutions were firstly stabilized by adding silica nanoparticles to the emulsions and, even more, by gelation of the aqueous phase by agarose. The emulsions were observed in optical microscope to check its stability in time and characterized by rheological measurements. The dry composite materials were obtained via casting the emulsions onto the glass substrates and evaporations of the organic solvent. Composite polymer films were characterized by water contact angle (WCA) measurements. The release of KCOOH salt into water and the freezing delay experiments of water droplets on dry composite films demonstrated their anti-icing properties. It has been concluded that hydrophobic and thermoplastic SBS polymer allows incorporation of the hydrophilic pockets/phases through our technique that opens the possibility for controlled delivering of anti-icing agents from the composite.