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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access Emergence of near-infrared photoluminescence via ZnS shell growth on the AgBiS2 nanocrystals(American Chemical Society, 2024) Department of Chemistry; Department of Electrical and Electronics Engineering; Önal, Asım; Kaya, Tarık Safa; Metin, Önder; Nizamoğlu, Sedat; Department of Chemistry; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of EngineeringAgBiS2 nanocrystals (NCs), composed of nontoxic, earth-abundant materials and exhibiting an exceptionally high absorption coefficient from visible to near-infrared (>105 cm(-1)), hold promise for photovoltaics but have lack of photoluminescence (PL) due to intrinsic nonradiative recombination and challenging shell growth. In this study, we reported a facile wet-chemical approach for the epitaxial growth of ZnS shell on AgBiS2 NCs, which triggered the observation of PL emission in the near-infrared (764 nm). Since high quality of the core is critical for epitaxial shell growth, we first obtained rock-salt structured AgBiS2 NCs with high crystallinity, nearly spherical shape and monodisperse size distribution (<6%) via a dual-ligand approach reacting Ag-Bi oleate with elemental sulfur in oleylamine. Next, a zincblende ZnS shell with a low-lattice mismatch of 4.9% was grown on as-prepared AgBiS2 NCs via a highly reactive zinc (Zn(acac)(2)) precursor that led to a higher photoluminescence quantum yield (PLQY) of 15.3%, in comparison with a relatively low reactivity precursor (Zn(ac)(2)) resulting in reduced PLQY. The emission from AgBiS2 NCs with ultrastrong absorption, facilitated by shell growth, can open up new possibilities in lighting, display, and bioimaging.Publication Open Access Enhanced sinterability, thermal conductivity and dielectric constant of glass-ceramics with PVA and BN additions(Multidisciplinary Digital Publishing Institute (MDPI), 2022) Akkasoğlu, Ufuk; Çiçek, Buğra; N/A; Department of Chemistry; Arıbuğa, Dilara; Balcı, Özge; 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 Sciences; N/A; 295531With the rapid development of the microelectronics industry, many efforts have been made to improve glass-ceramics' sinterability, thermal conductivity, and dielectric properties, which are essential components of electronic materials. In this study, low-alkali borosilicate glass-ceramics with PVA addition and glass-BN composites were prepared and successfully sintered at 770 degrees C. The phase composition, density, microstructure, thermal conductivity, and dielectric constant were investigated. It was shown that PVA addition contributes to the densification process of glass-ceramics (~88% relative density, with closed/open pores in the microstructure) and improves the thermal conductivity of glass material from 1.489 to 2.453 W/K.m. On the other hand, increasing BN addition improves microstructures by decreasing porosities and thus increasing relative densities. A glass-12 wt. % BN composite sample exhibited almost full densification after sintering and presented apparent and open pores of 2.6 and 0.08%, respectively. A high thermal conductivity value of 3.955 W/K.m and a low dielectric constant of 3.00 (at 5 MHz) were observed in this material. Overall, the resulting glass-ceramic samples showed dielectric constants in the range of 2.40-4.43, providing a potential candidate for various electronic applications.Publication Open Access Highly sensitive optical sensor for hydrogen gas based on a polymer microcylinder ring resonator(Elsevier, 2020) Eryürek, Mustafa; Department of Physics; Department of Chemistry; Department of Electrical and Electronics Engineering; Bavili, Nima; Balkan, Timuçin; Morova, Berna; Uysallı, Yiğit; Kaya, Sarp; Kiraz, Alper; Researcher; Researcher; PhD Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Department of Electrical and Electronics Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; N/A; N/A; N/A; 116541; 22542A highly sensitive platform is demonstrated for hydrogen gas (H-2) sensing based on a polymer microcylinder ring resonator (PMRR) obtained by an optical fiber coated with an inner nanofilm of amorphous palladium (Pd) and an outer polymer layer of polydimethylsiloxane (PDMS) permeable to H-2. The sensing scheme is based on monitoring the spectral shifts of high-quality optical resonances called whispering gallery modes (WGMs) that propagate in the vicinity of the outer rim of the PDMS layer without being affected by the absorption and scattering losses caused by the Pd nanofilm. WGMs are excited by a single-mode tapered optical fiber evanescently coupled to the PMRR. The observed reversible spectral shifts of the WGMs are induced by changes in the diameter of the PDMS layer caused by expansion or contraction of the Pd nanofilm exposed to varying concentrations of H-2. Maximum spectral shift sensitivity of 140 pm/% H-2, a minimum response time of 95 s, and minimum limit of detection of similar to 60 ppm were measured for sensors prepared with different thicknesses of the amorphous Pd nanofilm and tested in the H-2 concentration range up to 1%, having nitrogen gas (N-2) as a carrier. Experiments were also conducted with Pd nanofilms annealed in air or N-2 atmosphere after the deposition. In both cases, smaller sensitivities were observed due to the formation of larger grains within the film, resulting in slower diffusion and reduced solubility of H in the Pd layer. The impacts of oxygen gas and humidity on sensor performance were also studied.Publication Open Access Synthesis of stable gold nanoparticles using linear polyethyleneimines and catalysis of both anionic and cationic azo dye degradation(Royal Society of Chemistry (RSC), 2020) Abkenar, Sirous Khabbaz; Ow-Yang, Cleva W.; N/A; Department of Chemistry; Çavuşlar, Özge; Acar, Havva Funda Yağcı; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 178902Reduction of auric acid with polyethyleneimine (PEI) provides a simple, low-cost alternative for the production of cationic gold nanoparticles (GNPs). However, linear PEI (lPEI) failed to produce small, colloidally stable GNPs, so far. Since lPEI is a polyelectrolyte, pH should be an important factor both in reduction and stabilization of GNPs and may be optimized to produce small and stable lPEI/GNPs. Cationic GNPs were produced by the direct reduction of auric acid in water with lPEI utilizing two different methods to dissolve the polymer: by protonation or at high temperature. The influence of pH on the particle formation and properties was studied over a wide pH range (3.5 to 10). The impacts of the PEI/Au mass ratio, polymer molecular weight (2.5 and 25 kDa) and post-synthetic pH on the particle properties were also studied. Best is to dissolve lPEI by protonation and to clean the GNPs via controlled centrifugal precipitation. The MW did not influence the hydrodynamic size, stability or particle shape, but low MW lPEI provided faceted particles. This simple one pot synthesis of small, stable cationic GNPs in water is a valuable, simple alternative for producing new cationic GNPs with even low molecular weight lPEI. Additionally, these GNPs were evaluated as catalysts in the degradation of methyl orange (MO) (anionic-zwitterionic) and methylene blue (MB) (cationic) azo dyes at different pH values. The fastest degradation of MO and MB was recorded at pH 7.5 and 3.5, respectively. Overall, this is a rare case where a single catalyst quickly and effectively catalyzes the degradation of both cationic and anionic dyes.Publication Open Access HIPPIE: a new platform for ambient-pressure X-ray photoelectron spectroscopy at the MAX IV Laboratory(International Union of Crystallography (IUCr), 2021) Zhu, Suyun; Scardamaglia, Mattia; Kundsen, Jan; Sankari, Rami; Tarawneh, Hamed; Temperton, Robert; Pickworth, Louisa; Cavalca, Filippo; Wang, Chunlei; Tissot, Heloise; Weissenrieder, Jonas; Hagman, Benjamin; Gustafson, Johan; Lindgren, Fredrik; Kallquist, Ida; Maibach, Julia; Hahlin, Maria; Boix, Virginia; Gallo, Tamires; Rehman, Foqia; D'Acunto, Giulio; Schnadt, Joachim; Shavorskiy, Andrey; Department of Chemistry; Kaya, Sarp; Faculty Member; Department of Chemistry; College of Sciences; 116541HIPPIE is a soft X-ray beamline on the 3 GeV electron storage ring of the MAX IV Laboratory, equipped with a novel ambient-pressure X-ray photoelectron spectroscopy (APXPS) instrument. The endstation is dedicated to performing in situ and operando X-ray photoelectron spectroscopy experiments in the presence of a controlled gaseous atmosphere at pressures up to 30 mbar [1 mbar = 100 Pa] as well as under ultra-high-vacuum conditions. The photon energy range is 250 to 2200 eV in planar polarization and with photon fluxes >10(12) photons s(-1) (500 mA ring current) at a resolving power of greater than 10000 and up to a maximum of 32000. The endstation currently provides two sample environments: a catalysis cell and an electrochemical/liquid cell. The former allows APXPS measurements of solid samples in the presence of a gaseous atmosphere (with a mixture of up to eight gases and a vapour of a liquid) and simultaneous analysis of the inlet/outlet gas composition by online mass spectrometry. The latter is a more versatile setup primarily designed for APXPS at the solid-liquid (dip-and-pull setup) or liquid-gas (liquid microjet) interfaces under full electrochemical control, and it can also be used as an open port for ad hoc-designed non-standard APXPS experiments with different sample environments. The catalysis cell can be further equipped with an IR reflection-absorption spectrometer, allowing for simultaneous APXPS and IR spectroscopy of the samples. The endstation is set up to easily accommodate further sample environments.Publication Open Access Rotational-state-changing collisions between N-2(+) and Rb at low energies(American Physical Society (APS), 2020) Doerfler, A. D.; Villarreal, P.; Gonzalez-Lezana, T.; Gianturco, F. A.; Willitsch, S.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129We present a theoretical study of rotationally elastic and inelastic collisions between molecular nitrogen ions and Rb atoms in the sub-Kelvin temperature regime prevalent in ion-atom hybrid trapping experiments. The cross sections for rotational excitation and de-excitation collisions were calculated using quantum-scattering methods on ab initio potential energy surfaces for the energetically lowest singlet electronic channel of the system. We find that the rotationally inelastic collision rates are at least an order of magnitude smaller than the charge-exchange rates found in this system, rendering inelastic processes a minor channel under the conditions of typical hybrid trapping experiments.Publication Open Access One-step aqueous synthesis of anionic and cationic AgInS2 quantum dots and their utility in improving the efficacy of ALA-based photodynamic therapy(American Chemical Society (ACS), 2022) Loizidou, Marilena; MacRobert, Alexander J.; Department of Chemistry; Acar, Havva Funda Yağcı; Hashemkhani, Mahshid; PhD Student; Department of Chemistry; College of Sciences; Graduate School of Sciences and Engineering; 178902; N/ASilver-indium-sulfide quantum dots (AIS QDs) have potential applications in many areas, including biomedicine. Their lack of regulated heavy metals, unlike many commercialized QDs, stands out as an advantage, but the necessity for alloyed or core-shell structures and related costly and sophisticated processes for the production of stable and high quantum yield aqueous AIS QDs are the current challenges. The present study demonstrates the one-step aqueous synthesis of simple AgInS2 QD compositions utilizing for the first time either a polyethyleneimine/2-mercaptopropionic acid (AIS-PEI/2MPA) mixture or only 2-mercaptopropionic acid (AIS-2MPA) as the stabilizing molecules, providing a AgInS2 portfolio consisting of cationic and anionic AIS QDs, respectively, and tuneable emission. Small AIS QDs with long-term stability and high quantum yields (19-23%) were achieved at a molar ratio of Ag/In/S 1/10/10 in water without any dopant or a semiconductor shell. The theranostic potential of these cationic and anionic AIS QDs was also evaluated in vitro. Non-toxic doses were determined, and fluorescence imaging potential was demonstrated. More importantly, these QDs were electrostatically loaded with zwitterionic 5-aminolevulinic acid (ALA) as a prodrug to enhance the tumor availability of ALA and to improve ALA-induced porphyrin photodynamic therapy (PDT). This is the first study investigating the influence of nanoparticle charge on ALA binding, release, and therapeutic efficacy. Surface charge was found to be more critical in cellular internalization and dark toxicity rather than drug loading and release. Both QDs provided enhanced ALA release at acidic pH but protected the prodrug at physiological pH, which is critical for tumor delivery of ALA, which suffers from low bioavailability. The PDT efficacy of the ALA-loaded AIS QDs was tested in 2D monolayers and 3D constructs of HT29 and SW480 human colon adenocarcinoma cancer cell lines. The incorporation of ALA delivery by the AIS QDs, which on their own do not cause phototoxicity, elicited significant cell death due to enhanced light-induced ROS generation and apoptotic/necrotic cell death, reducing the IC50 for ALA dramatically to about 0.1 and 0.01 mM in anionic and cationic AIS QDs, respectively. Combined with simple synthetic methods, the strong intracellular photoluminescence of AIS QDs, good biocompatibility of especially the anionic AIS QDs, and the ability to act as drug carriers for effective PDT signify that the AIS QDs, in particular AIS-2MPA, are highly promising theranostic QDs.Publication Open Access Protocol on synthesis and characterization of copper-doped InP/ZnSe quantum dots as ecofriendly luminescent solar concentrators with high performance and large area(Elsevier, 2021) Department of Electrical and Electronics Engineering; N/A; N/A; Department of Chemistry; Nizamoğlu, Sedat; Sadeghi, Sadra; Eren, Güncem Özgün; Shahzad, Mehwish; Faculty Member; PhD Student; Department of Electrical and Electronics Engineering; Department of Chemistry; College of Engineering; Graduate School of Sciences and Engineering; 130295; N/A; N/A; N/ALuminescent solar concentrators (LSCs) are simple and cost-effective solar energy-harvesting devices. Indium phosphide (InP)-based colloidal quantum dots (QDs) are promising QDs for efficient LSC devices due to their environmentally benign nature. One major challenge in LSC devices is reabsorption losses. To minimize the reabsorption, Stokes shift engineering is a critical process to designing the QD material. Here, we present a protocol that contains the preparation of structurally engineered copper-doped InP/ZnSe QDs and their LSC application.Publication Open Access A new class of porous materials for efficient CO2 separation: ionic liquid/graphene aerogel composites(Elsevier, 2021) Department of Chemical and Biological Engineering; N/A; Department of Chemistry; Zeeshan, Muhammad; Yalçın, Kaan; Keskin, Seda; Uzun, Alper; Öztuna, Feriha Eylül Saraç; Ünal, Uğur; 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); Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; N/A; N/A; 40548; 59917; N/A; 42079Here, we report a new post-synthesis modification strategy for functionalizing reduced graphene aerogels (rGAs) towards an exceptional CO2 separation performance. 1-N-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) was impregnated on a rGA, prepared by reducing GA at 700 degrees C, at various ionic liquid (IL) loadings of 5, 10, 30, and 50 wt%. The resulting composites were characterized in deep detail by X-ray photoelectron spectroscopy, X-ray diffraction, N-2 physical adsorption measurements, scanning electron microscopy, Fourier transform infrared and Raman spectroscopies, and thermogravimetric analysis. Results indicated the presence of interactions between the rGA surface and the anion of the IL, potentially improving the CO2 affinity. Volumetric gas adsorption measurements using these materials showed that the deposition of [BMIM][PF6] on rGA surface at an IL loading of 50 wt% boosts the CO2/CH4 selectivity by more than 20-times, exceeding an absolute value of 120, a remarkably higher CO2/CH4 selectivity compared to that of other functionalized materials under similar operating conditions. Tunability of both the IL structure and the surface characteristics of rGA offer a tremendous degree of flexibility for the rational design of these IL/rGA composites towards high performance in gas separation applications.Publication Open Access Cationic [6]helicenes: tuning (chir)optical properties up to the near infra-red(Elsevier, 2022) Labrador, Geraldine M.; Jacquemin, Denis; Lacour, Jerome; Department of Chemistry; Bosson, Johann; Department of Chemistry; College of SciencesThe intramolecular condensation of ortho substituents of triaryl carbenium ions can lead to the formation of cationic helicenes. These chiral and configurationally stable molecules exhibit extended optical properties reminiscent of their parent methylium ions. Among them, cationic [6]helicenes are particularly interesting as orthogonal late-stage functionalization strategies allow the introduction of a variety of auxochromes with different regiochemistry. Intense chiroptical properties can thus be tailored in the far red and up to the near infra-red (NIR) spectral windows. A wealth of applications can be foreseen, in particular in material sciences.