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Publication Metadata only An aerogel-based photocatalytic microreactor driven by light guiding for degradation of toxic pollutants(Elsevier Science Sa, 2021) Jonas, Alexandr; N/A; Department of Chemical and Biological Engineering; Department of Physics; Özbakır, Yaprak; Erkey, Can; Kiraz, Alper; PhD Student; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Department of Physics; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; N/A; 29633; 22542Efficient utilization of light in photocatalytic chemical processes requires careful optimization of the photocatalytic reactor layout to maximize the interaction between the incident light, photocatalyst and reactant molecules. Herein, we report a new type of photocatalytic flow microreactor with an integrated light guide, formed by a channel fabricated inside a hydrophobic composite aerogel monolith made of silica and titania (TiO2). The liquid-filled channel simultaneously acts as a reaction vessel and as a liquid-core optofluidic waveguide, distributing the incident light over the whole reaction volume. Anatase TiO2 nanoparticles embedded in the channel walls then serve as a photocatalyst that can efficiently interact with both the guided light and the reactant solution along the channel length. Composite aerogels were synthesized with TiO2 content between 1 and 50 wt %, retaining their interconnected mesoporous network, low refractive index, and waveguide propagation losses below -3.9 dB/cm over this range of compositions. Using photocatalytic degradation of phenol - an organic compound with harmful environmental effects - as a model chemical reaction, the performance of the microreactor was systematically investigated. Reactant conversion was observed to increase with increasing incident light power, decreasing reactant flow rate and increasing mass fraction of TiO2 in the composite. An analytical model of the reactor/light guide system was developed that predicted successfully the scaling of the reactant conversion with the incident light power and reactant flow rate. The presented concept of aerogel-based optofluidic photocatalytic microreactors is readily scalable and possesses great potential for carrying out other photocatalytic reactions in both polar and non-polar solvents.Publication Metadata only Black phosphorus-based photocatalysts for energy and environmental applications(Elsevier, 2021) Department of Chemistry; N/A; N/A; Department of Physics; Metin, Önder; Küçükkeçeci, Hüseyin; Eroğlu, Zafer; Altan, Orhan; Faculty Member; Researcher; Researcher; Other; Department of Chemistry; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering; N/A; College of Sciences; 46962; N/A; N/A; N/APhotocatalysis using semiconductor materials to conduct chemical reactions more efficiently with the aid of sunlight irradiation is foreseen as a promising solution to combat the energy and environmental pollution crisis that the world is facing at present. Finding a suitable semiconductor material that harvests a large portion of the sunlight spectrum with high photocatalytic efficiency lies in the heart of photocatalysis. In this regard, black phosphorus (BP), a rising star two-dimensional (2D) semiconducting material, has recently been regarded as an abundant, nontoxic, metal-free, and cheap photocatalyst with a suitable bandgap and broad light absorption ability. In this chapter, after the introduction of the general properties and synthesis of BP, the photocatalytic efficiency of BP and BP-based composites in energy and environmental applications are summarized.Publication Metadata only Determination of composition of ethanol-CO2 mixtures at high pressures using frequency response of microcantilevers(Elsevier Science Bv, 2018) Jonas, Alexandr; Department of Physics; Department of Mechanical Engineering; Department of Chemical and Biological Engineering; N/A; Kiraz, Alper; Alaca, Burhanettin Erdem; Erkey, Can; Baloch, Shadi Khan; Faculty Member; Faculty Member; Faculty Member; PhD Student; Department of Physics; Department of Mechanical Engineering; Department of Chemical and Biological Engineering; 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 Sciences; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; 22542; 115108; 29633; N/AThe measurement of the composition of ethanol-CO2 mixtures at high pressures is important in many applications involving supercritical fluids such as drying of alcogels or release of MEMs. Resonant frequency and quality factor (Q-factor) of microcantilevers immersed in ethanol-CO2 mixtures were measured at a temperature of 308 K and pressure range from 8 MPa to 22 MPa. The measurements were carried out for different mixture compositions ranging from 0.91 to 6.16 wt% of ethanol in CO2. At a given pressure and temperature, the resonant frequencies were found to decrease linearly with the increasing ethanol weight percent in the mixture. The sensitivity of the resonant frequency to changes in composition was found to increase with decreasing pressure. The experimental results show that ethanol-CO2 mixture composition can be determined with good accuracy using mainly the measured resonant frequency of microcantilevers.Publication Metadata only Determination of viscosity and density of fluids using frequency response of microcantilevers(Elsevier Science Bv, 2015) Jonas, Alexandr; Department of Chemical and Biological Engineering; Department of Mechanical Engineering; Department of Physics; Department of Chemical and Biological Engineering; Eris, Gamze; Alaca, Burhanettin Erdem; Kiraz, Alper; Erkey, Can; Researcher; Faculty Member; Faculty Member; Faculty Member; Department of Mechanical Engineering; Department of Physics; Department of Chemical and Biological Engineering; College of Engineering; College of Engineering; College of Sciences; College of Engineering; N/A; 115108; 22542; 29633We report on the simultaneous measurement of density and viscosity of nitrogen in gas and supercritical phases at 308.15 K and pressures up to 24 MPa. The density and viscosity were extracted from the measured frequency responses of an oscillated microcantilever immersed in N-2. To this end, a model of oscillatory motion of immersed cantilevers incorporating the effects of hydrodynamic forces was employed. Using argon as a reference fluid of known density and viscosity, cantilever calibration parameters were obtained from nonlinear regression of cantilever resonant frequencies and quality factors recorded in argon. Subsequently, these calibration parameters were used in the model equations to determine the density and viscosity of nitrogen at the given experimental pressure and temperature. In the studied pressure range, the root-mean-square deviations of the measured density and viscosity of nitrogen from the reference values obtained from NIST database were 2.5% and 5.2%, respectively. (C) 2015 Elsevier B.V. All rights reserved.Publication Metadata only Frequency response of microcantilevers immersed in gaseous, liquid, and supercritical carbon dioxide(Elsevier, 2013) N/A; Department of Chemical and Biological Engineering; Department of Physics; N/A; Department of Physics; Department of Mechanical Engineering; Department of Physics; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Uzunlar, Erdal; Beykal, Burcu; Ehrlich, Katjana; Şanlı, Deniz; Jonas, Alexandr; Alaca, Burhanettin Erdem; Kiraz, Alper; Ürey, Hakan; Erkey, Can; Master Student; Undergraduate Student; N/A; Researcher; Other; Faculty Member; Faculty Member; Faculty Member; Faculty Member; Department of Mechanical Engineering; Department of Physics; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; College of Engineering; College of Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; N/A; 115108; 22542; 8579; 29633The frequency response of ferromagnetic nickel microcantilevers with lengths ranging between 200 mu m and 400 mu m immersed in gaseous, liquid and supercritical carbon dioxide (CO2) was investigated. the resonant frequency and the quality factor of the cantilever oscillations in CO2 were measured for each cantilever length in the temperature range between 298 K and 323 K and the pressure range between 0.1 MPa and 20.7 MPa. at a constant temperature, both the resonant frequency and the quality factor were found to decrease with increasing pressure as a result of the increasing CO2 density and viscosity. very good agreement was found between the measured cantilever resonant frequencies and predictions of a model based on simplified hydrodynamic function of a cantilever oscillating harmonically in a viscous fluid valid for Reynolds numbers in the range of [1;1000] (average deviation of 2.40%). at high pressures of CO2, the experimental Q-factors agreed well with the predicted ones. at low CO2 pressures, Additional internal mechanisms of the cantilever oscillation damping caused lowering of the measured Q-factor with respect to the hydrodynamic model predictions.Publication Metadata only Motion of single terrylene molecules in confined channels of poly(butadiene)-poly(ethylene oxide) diblock copolymer(Amer Chemical Soc, 2009) N/A; Department of Physics; Department of Chemistry; Yorulmaz, Mustafa; Kiraz, Alper; Demirel, Adem Levent; Master Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 22542; 6568The motion of terrylene probe molecules in confined PB channels of an asymmetric PB-PEO diblock copolymer has been investigated by single molecule tracking. The one-dimensional diffusion coefficients were found to be significantly smaller and had a narrower distribution compared to two-dimensional diffusion coefficients in PB. The trajectories of some single molecules showed unusual behavior of directed motion where mean square displacement had a parabolic dependence oil lag time. The likely origin of this behavior is discussed in terms of local variations in the PB channel width and the resulting change in the local density. The results show the effect of nonuniformities and heterogeneities in the channels on the motion of single molecules and demonstrate the sensitivity of single molecule tracking in characterizing self-assembled block copolymer morphologies.Publication Metadata only The rational design of a graphitic carbon nitride-based dual S-scheme heterojunction with energy storage ability as a day/night photocatalyst for formic acid dehydrogenation(Elsevier Science Sa, 2022) Department of Physics; Department of Computer Engineering; N/A; Department of Chemistry; Altan, Orhan; Altıntaş, Elvin; Alemdar, Sıla; Metin, Önder; Other; Researcher; Master Student; Faculty Member; Department of Physics; Department of Computer Engineering; Department of Chemistry; College of Sciences; College of Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 46962Photocatalytic formic acid dehydrogenation (FAD) has been regarded as one of the most promising methods of producing H2 in a sustainable manner. In the photocatalytic FAD reaction, photogenerated holes play an important role in the reaction mechanism and thus in the efficiency of photocatalysts. However, the design of photocatalytic systems capable of generating high hole potential without compromising the reducing ability of the photocatalyst is extremely rare for the FAD reaction. In this respect, we report herein a novel and highly efficient heterojunction photocatalyst composed of 2D graphitic carbon nitride, 2D MnO2, 1D MnOOH, and 0D PdAg alloy nanoparticles, denoted as GCN/MnO2/MnOOH-PdAg, that can create high reduction and oxidation potentials via a dual S-scheme heterojunction. The photocatalysts exhibited a superb photocatalytic activity in the FAD with a record turnover frequency (TOF) of 3919 h-1 under visible light irradiation, which was 6-, 5.2and 24-times greater than those of GCN-PdAg, GCN/MnO2-PdAg, and MnO2/MnOOH-PdAg heterojunctions, respectively. The structure and dual S-scheme mechanism of the photocatalyst have been clearly demonstrated by extensive instrumental analysis, radical trapping tests, and scavenger experiments. More importantly, it was discovered that the presented photocatalyst continued to function with comparable activity in dark for a prolonged time using the same photocatalytic mechanism. The activity of the photocatalyst in dark was attributed to the utilization of electrons stored on Mn2O3, which was detected as a 4-5 nm thick layer on the surface of MnOOH nanorods. This study, in addition to being the first example of both a "day/night photocatalyst" for FAD with an S-scheme mechanism, also demonstrates for the first time the boosting of FAD via a dual S-scheme heterojunction photocatalyst.Publication Metadata only Three-dimensional optofluidic waveguides in hydrophobic silica aerogels via supercritical fluid processing(Elsevier, 2013) Jonas, Alexandr; Department of Chemical and Biological Engineering; N/A; N/A; Department of Chemical and Biological Engineering; Department of Physics; Department of Physics; Department of Chemical and Biological Engineering; Eris, Gamze; Şanlı, Deniz; Ülker, Zeynep; Bozbağ, Selmi Erim; Kiraz, Alper; Erkey, Can; Researcher; Researcher; PhD Student; Researcher; Other; Faculty Member; Faculty Member; Department of Physics; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of Engineering; N/A; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; College of Sciences; College of Engineering; N/A; N/A; 262388; N/A; N/A; 22542; 29633Optofluidic components enable flexible routing and transformations of light beams in integrated lab-on-a-chip systems with the use of carefully shaped fluid parcels. For structural integrity reasons, the working fluid is typically contained within a solid-material chip. One of the outstanding challenges in optofluidics is the preparation and processing of optofluidic waveguides. These require solid cladding materials that are sufficiently strong to contain the fluid while possessing optical properties that allow efficient confinement of light within fluidic channels. Here, we report on a new technique to obtain liquid-core optofluidic waveguides based on total internal reflection of light in three-dimensional water-filled channels embedded in hydrophobic silica aerogel. To form the channels, we employ a fiber made of cage-like silicon-oxygen compound - trifluoropropyl polyhedral oligomeric silsesquioxane (trifluoropropyl PUSS) - which has high solubility in supercritical CO2 (scCO(2)). A U-shaped fiber made of trifluoropropyl PUSS is obtained by melt/freeze processing of PUSS powder and subsequently placed in a silicate sol. After gelation of the sol and aging of the gel, scCO(2) extraction is used to dry the wet gel and extract the POSS fiber, yielding a dry silica aerogel with a U-shaped empty channel inside it. Finally, the silanol groups at the surface of the aerogel are reacted with hexamethyldisilazane (HMDS) in the presence of scCO(2) to render the aerogel surface hydrophobic and the channel is filled with water. We demonstrate efficient waveguiding by coupling light into the water-filled channel and monitoring the channel output. The presented procedure opens up new possibilities for creating complex three-dimensional networks of liquid channels in aerogels for optofluidic applications. (C) 2012 Elsevier B.V. All rights reserved.