Browsing by Author "Özensoy, Emrah"
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Item Open Access All-solution-processed, oxidation-resistant copper nanowire networks for optoelectronic applications with year-long stability(American Chemical Society, 2020) Polat-Genlik, S.; Tigan, D.; Koçak, Yusuf; Ercan, Kerem Emre; Çiçek, Melih Ogeday; Tunca, S.; Koylan, S.; Coşkun, Ş.; Özensoy, Emrah; Ünalan, H. E.Copper nanowires (Cu NWs) hold promise as they possess equivalent intrinsic electrical conductivity and optical transparency to silver nanowires (Ag NWs) and cost substantially less. However, poor resistance to oxidation is the historical challenge that has prevented the large-scale industrial utilization of Cu NWs. Here, we use benzotriazole (BTA), an organic corrosion inhibitor, to passivate Cu NW networks. The stability of BTApassivated networks under various environmental conditions was monitored and compared to that of bare Cu NW control samples. BTA passivation greatly enhanced the stability of networks without deteriorating their optoelectronic performance. Moreover, to demonstrate their potential, BTA-passivated networks were successfully utilized in the fabrication of a flexible capacitive tactile sensor. This passivation strategy has a strong potential to pave the way for large-scale utilization of Cu NW networks in optoelectronic devices.Item Open Access CdTe quantum dot-functionalized P25 titania composite with enhanced photocatalytic NO2 storage selectivity under UV and vis irradiation(American Chemical Society, 2019) Balcı-Leinen, Merve; Dede, Didem; Khan, Münir Ullah; Çağlayan, Mustafa; Koçak, Yusuf; Demir, Hilmi Volkan; Özensoy, EmrahComposite systems of P25 (titania) functionalized with thioglycolic acid (TGA)-capped CdTe colloidal quantum dots (QDs) were synthesized, structurally characterized, and photocatalytically tested in the photocatalytic NOx oxidation and storage during NO(g) + O2(g) reaction. Pure P25 yielded moderate-to-high NO conversion (31% in UV-A and 40% in visible (vis)) but exhibited extremely poor selectivity toward NOx storage in solid state (25% in UV-A and 35% in vis). Therefore, P25 could efficiently photooxidize NO(g) + O2(g) into NO2; however, it failed to store photogenerated NO2 and released toxic NO2(g) to the atmosphere. CdTe QD-functionalized P25 revealed a major boost in photocatalytic performance with respect to pure P25, where NO conversion reached 42% under UV-A and 43% under vis illumination, while the respective selectivity climbed up to 92 and 97%, rendering the CdTe/P25 composite system an efficient broad-band photocatalyst, which can harvest both UV-A and vis light efficiently and display a strong NOx abatement effect. Control experiments suggested that photocatalytic active sites responsible for the NO(g) + O2(g) photooxidation and formation of NO2 reside mostly on titania, while the main functions of the TGA capping agent and the CdTe QDs are associated with the photocatalytic conversion of the generated NO2 to the adsorbed NOx species, significantly boosting the selectivity toward solid-state NOx storage. Reuse experiments showed that photocatalytic performance of the CdTe/P25 system can be preserved to a reasonable extent with only a moderate decrease in the photocatalytic performance. Although some decrease in the photocatalytic activity was observed after aging, CdTe/P25 could still outperform P25 benchmark photocatalyst. Increasing CdTe QDs loading from the currently optimized minuscule concentrations could be a useful strategy to increase further the catalytic lifetime/stability of the CdTe/P25 system with only a minor penalty in catalytic activity.Item Open Access Controlling the surface dispersion of BaO domains on NOx storage materials via TiO2 anchoring sites(ACS, 2010) Andonova, Stanislava M.; Şentürk, Göksu S.; Özensoy, EmrahIn an attempt to control the surface dispersion and the mobility of BaO domains on NOx storage materials, TiO2/TiOx anchoring sites were introduced on/inside the conventional γ-Al2O3 support matrix. BaO/TiO2/γ-Al2O3 ternary oxide materials were synthesized via two different sol-gel preparation techniques, with varying surface compositions and morphologies. The synthesized NOx storage materials were studied via XRD, Raman spectroscopy, BET surface area analysis, TPD, XPS, SEM, EDX-mapping and in situ FTIR spectroscopy of adsorbed NO2. NOx uptake properties of the BaO/TiO2/γ-Al2O3 materials were found to be strongly influenced by the morphology and the surface structure of the TiO2/TiOx domains. The presence of Ti4+ surface sites provide additional NOx adsorption sites which can store NOx predominantly in the form of bridged/bidentate nitrates. An improved Ba surface dispersion was observed for the BaO/TiO2/γ-Al2O3 materials synthesized via the co-precipitation of alkoxide precursors which was found to originate mostly from the increased fraction of accessible TiO2/TiOx sites on the surface. These TiO2/TiOx sites function as strong anchoring sites for surface BaO domains and can be tailored to enhance surface dispersion of BaO. TPD experiments suggested the presence of at least two different types of NOx species adsorbed on the TiO2/TiOx sites, with distinctively different thermal stabilities. The relative stability of the NOx species adsorbed on the BaO/TiO2/γ-Al2O3 system was found to increase in the following order: NO+/N2O3 on alumina < nitrates on alumina < surface nitrates on BaO < bridged/bidentate nitrates on large/isolated TiO2 clusters < bulk nitrates on BaO on alumina surface and bridged/bidentate nitrates on small TiO2 crystallites homogenously distributed on the surface < bulk nitrates on the BaO sites located on the TiO2 domains.Item Open Access Core-crown quantum nanoplatelets with favorable type-II heterojunctions boost charge separation and photocatalytic NO oxidation on TiO2(Wiley, 2020-09) Ebrahimi, Elnaz; İrfan, Muhammad; Shabani, Farzan; Koçak, Yusuf; Karakurt, Bartu; Erdem, E.; Demir, Hilmi Volkan; Özensoy, EmrahFunctionalization of TiO2 (P25) with oleic acid‐capped CdSe(core)/CdSeTe(crown) quantum‐well nanoplatelets (NPL) yielded remarkable activity and selectivity toward nitrate formation in photocatalytic NOx oxidation and storage (PHONOS) under both ultraviolet (UV‐A) and visible (VIS) light irradiation. In the NPL/P25 photocatalytic system, photocatalytic active sites responsible for the NO(g) photo‐oxidation and NO2 formation reside mostly on titania, while the main function of the NPL is associated with the photocatalytic conversion of the generated NO2 into the adsorbed NO3− species, significantly boosting selectivity toward NOx storage. Photocatalytic improvement in NOx oxidation and storage upon NPL functionalization of titania can also be associated with enhanced electron‐hole separation due to a favorable Type‐II heterojunction formation and photo‐induced electron transfer from the CdSeTe crown to the CdSe core of the quantum well system, where the trapped electrons in the CdSe core can later be transferred to titania. Re‐usability of NPL/P25 system was also demonstrated upon prolonged use of the photocatalyst, where NPL/P25 catalyst surpassed P25 benchmark in all tests.Item Open Access Dry reforming of glycerol over Rh-based ceria and zirconia catalysts: New insights on catalyst activity and stability(Elsevier B.V., 2018) Bulutoğlu, P. S.; Say, Zafer; Bac, S.; Özensoy, Emrah; Avcı, A. K.Effects of reaction temperature and feed composition on reactant conversion, product distribution and catalytic stability were investigated on syngas production by reforming of glycerol, a renewable waste, with CO2 on Rh/ZrO2 and Rh/CeO2 catalysts. For the first time in the literature, fresh and spent catalysts were characterized by in-situ FTIR, Raman spectroscopy, transmission electron microscopy and energy dispersive X-ray analysis techniques in order to unravel novel insights regarding the molecular-level origins of catalytic deactivation and aging under the conditions of glycerol dry reforming. Both catalysts revealed increased glycerol conversions with increasing temperature, where the magnitude of response became particularly notable above 650 and 700 °C on Rh/ZrO2 and Rh/CeO2, respectively. In accordance with thermodynamic predictions, CO2 transformation occurred only above 700 °C. Syngas was obtained at H2/CO ∼0.8, very close to the ideal composition for Fischer-Tropsch synthesis, and carbon formation was minimized with increasing temperature. Glycerol conversion decreased monotonically, whereas, after an initial increase, CO2 conversion remained constant upon increasing CO2/glycerol ratio (CO2/G) from 1 to 4. In alignment with the slightly higher specific surface area of and smaller average Rh-particle size on ZrO2, Rh/ZrO2 exhibited higher conversions and syngas yields than that of Rh/CeO2. Current characterization studies indicated that Rh/CeO2 revealed strong metal-support interaction, through which CeO2 seemed to encapsulate Rh nanoparticles and partially suppressed the catalytic activity of Rh sites. However, such interactions also seemed to improve the stability of Rh/CeO2, rendering its activity loss to stay below that of Rh/ZrO2 after 72 h time-on-stream testing at 750 °C and for CO2/G = 4. Enhanced stability in the presence of CeO2 was associated with the inhibition of coking of the catalyst surface by the mobile oxygen species and creation of oxygen vacancies on ceria domains. Deactivation of Rh/ZrO2 was attributed to the sintering of Rh nanoparticles and carbon formation.Item Open Access Effects induced by interaction of the Pt/CeO x /ZrO x /γ-Al 2 O 3 ternary mixed oxide DeNO x catalyst with hydrogen(Elsevier, 2020) Andonova, S.; Ok, Zehra Aybegüm; Özensoy, Emrah; Hadjiivanov, K.Effects of H2/D2 adsorption on the surface chemistry of Pt/CeOx-ZrOx/γ-Al2O3 DeNOx catalyst were investigated. In-situ FTIR spectroscopy and NOx-TPD techniques were utilized to monitor changes in the surface chemistry of studied materials. Adsorption studies of CO and O2 revealed that the Pt/Ce-Zr/Al sample, initially reduced with H2 at 723 K, is characterized by the presence of oxygen vacancies in close vicinity of Ce3+ centres and metallic Pt sites. Adsorption of O2 occurred through the formation of superoxide (O2 −)ads species and oxidation of Ce3+ to Ce4+ ions. The ability of the catalyst to activate molecular O2 originates from its relatively high population of oxygen vacancies located on/near the surface. Interaction of Pt/Ce-Zr/Al system with H2 or D2 takes place through heterolytic dissociation at ambient temperature. D2 adsorption leads to the reduction of Ce4+ to Ce3+ ions and formation of adsorbed molecular heavy water and gradual D/H exchange with the existing surface hydroxyl groups. Generated D2O interacts with isolated hydroxyls/deuteroxyls through H-bonding and this provokes the formation of H-bonded OeH/OeD groups. These later species are relatively stable and gradually vanish with increasing temperatures above 523 K, leaving behind only isolated hydroxyls. Surfaces enriched with H-bonded hydroxyls are characterized with an enhanced NOx storage ability revealing their significant role in low-temperature NOx adsorption mechanism.Item Open Access The effects of Co / Ce loading ratio and reaction conditions on CDRM performance of Co-Ce / ZrO2 catalysts(Elsevier, 2018) Paksoy, A. İ.; Çağlayan, B. S.; Özensoy, Emrah; Ökte, A. N.; Aksoylu, A. E.This work mainly aims to establish a link between Co/Ce loading ratio in Co-Ce/ZrO2 catalysts and their Carbon Dioxide Reforming of Methane (CDRM) performance. In this context, catalysts with different Co and Ce loadings were prepared and characterized via BET, XRD, HRTEM-EDX, XPS and Raman, and parametrically tested under different CDRM conditions. Dispersion of Co particles was nonhomogeneous on all samples. For the sample with the highest Co/Ce ratio (10%Co-2%Ce/ZrO2), higher amount of lattice oxygen vacancies and lowest degree of ceria reduction were determined. Raman analysis showed that graphitic carbon coexisted with amorphous carbon on the surface of all spent samples. The extent of side reactions prevailed in determining selectivity. It was expressed that both Co-Ce synergistic interaction and synchronous contribution of Ce and ZrO2 were enhanced for the samples having lower Co/Ce ratio. It was confirmed that Ce is only responsible for oxygen transfer but not its formation.Item Open Access Enhanced photocatalytic NOx oxidation and storage under visible-light irradiation by anchoring Fe3O4 nanoparticles on mesoporous graphitic carbon nitride (mpg-C3N4)(Elsevier, 2019) Irfan, Muhammad; Sevim, M.; Koçak, Yusuf; Balcı, Merve; Metin, Ö.; Özensoy, EmrahSeveral mesoporous graphitic carbon nitride (mpg-C3N4) photocatalysts were synthesized by using a hard-templating method comprising thermal polycondensation of guanidine hydrochloride over silica spheres at three different temperatures (450, 500 and 550 ℃). After structural characterization of these mpg-C3N4 photocatalysts, they were tested in NO(g) photo-oxidation under visible (VIS) light. The effects of polycondensation temperature on the structure and photocatalytic performance of mpg-C3N4 in NO photo-oxidation were studied. The results revealed that polycondensation temperature has a dramatic effect on the photocatalytic activity of mpg-C3N4 in NO photo-oxidation, where mpg-C3N4 synthesized at 500 ℃ (mpg-CN500) showed the best performance in NOx abatement as well as a high selectivity towards solid state NOx storage under VIS light illumination. Photocatalytic performance of the mpg-CN500 was further enhanced by the anchoring of 8.0 ± 0.5 wt.% Fe3O4 nanoparticles (NPs) on it. Fe3O4/mpg-CN500 photocatalyst showed both high activity and high selectivity along with extended reusability without a need for a regeneration step. Enhanced photocatalytic NOx oxidation and storage efficiency of Fe3O4/mpg-CN500 photocatalyst was attributed to their mesoporous structure, high surface area and slow electron-hole recombination kinetics, efficient electron-hole separation and facile electron transfer from mpg-CN500 to Fe3O4 domains enhancing photocatalytic O2 reduction, while simultaneously suppressing nitrate photo-reduction and decomposition to NO2(g).Item Open Access Enhancement of formic acid dehydrogenation selectivity of Pd(111) single crystal model catalyst surface via Brønsted bases(American Chemical Society, 2019) Karakurt, Bartu; Koçak, Yusuf; Özensoy, EmrahThe influence of ammonia (NH3) on the doubly deuterated formic acid (DCOOD, FA) dehydrogenation selectivity for a Pd(111) single crystal model catalyst surface was investigated under ultrahigh vacuum conditions using temperature-programmed desorption and temperature-programmed reaction spectroscopy techniques. NH3 adsorption on Pd(111) revealed reversible, molecular desorption without any significant decomposition products, while DCOOD adsorption on Pd(111) yielded D2, D2O, CO, and CO2 as a result of dehydration and dehydrogenation pathways. Functionalizing the Pd(111) surface with ammonia suppressed the FA dehydration and enhanced the dehydrogenation pathway. The boost in the FA dehydrogenation of Pd(111) in the presence of NH3 can be linked to the ease of FA deprotonation as well as the stabilization of the decomposition intermediate (i.e., formate) due to the presence of ammonium counterions on the surface. In addition, the presence of a H-bonded ammonia network on the Pd(111) surface increased the hydrogen atom mobility and decreased the activation energy for molecular hydrogen desorption. In the presence of NH3, catalytic FA decomposition on Pd(111) also yielded amidation reactions, which further suppressed CO liberation and prevented poisoning of the Pd(111) active sites due to strongly bound CO species.Item Open Access Enhancement of photocatalytic NOx abatement on titania via additional metal oxide NOx-storage domains: Interplay between surface acidity, specific surface area, and humidity(Elsevier, 2020) Çağlayan, Mustafa; Irfan, Muhammad; Ercan, Kerem Emre; Koçak, Yusuf; Özensoy, EmrahIn this work, we propose a simple and effective preparation procedure to obtain ternary mixed oxides composed of titania (TiO2, P25), alumina (γ-Al2O3) and calcium oxide (CaO) functioning as efficient photocatalytic NOx oxidation and storage (PHONOS) catalysts that are capable of facile NOx abatement under ambient conditions in the absence of elevated temperatures and pressures with UVA irradiation. In this architecture, titania was the photocatalytic active component and CaO and/or γ-Al2O3 provided NOx storage domains revealing dissimilar specific surface areas (SSA) and surface acidities. We show that photocatalyst formulation can be readily fine-tuned to achieve superior photocatalytic performance surpassing conventional P25 benchmark in short (1 h) and long term (12 h), as well as humidity-dependent photocatalytic tests. We demonstrate the delicate interplay between the surface acidity, SSA and humidity and provide detailed mechanistic insights regarding the origin of photocatalytic activity, selectivity and deactivation pathways.Item Open Access Exceptionally active and stable catalysts for CO2 reforming of glycerol to syngas(Elsevier, 2019) Bac, S.; Say, Zafer; Koçak, Yusuf; Ercan, Kerem E.; Harfouche, M.; Özensoy, Emrah; Avcı, A. K.CO2 reforming of glycerol to syngas was studied on Al2O3-ZrO2-TiO2 (AZT) supported Rh, Ni and Co catalysts within 600–750 °C and a molar inlet CO2/glycerol ratio (CO2/G) of 1–4. Glycerol and CO2 conversions decreased in the following order: Rh/AZT > Ni/AZT > Co/AZT. Reactant conversions on Rh/AZT exceeded 90% of their thermodynamic counterparts at 750 °C and CO2/G = 2–4 at which the activity of Ni/AZT was boosted to ˜95% of the thermodynamic CO2 conversion upon increasing the residence time. The loss in CO2 conversions was below 13% during the 72 h longevity tests confirming the exceptional stability of Rh/AZT and Ni/AZT. However, Co/ AZT suffered from sintering, carbon deposition and oxidation of Co sites, demonstrated via TEM-EDX, XPS, XANES and in-situ FTIR experiments. Characterization of Rh/AZT revealed no significant signs of deactivation. Ni/AZT preserved most of its original metallic pattern and gasified carbonaceous deposits during earlier stages of the reactionItem Open Access Formaldehyde selectivity in methanol partial oxidation on silver: effect of reactive oxygen species, surface reconstruction, and stability of intermediates(American Chemical Society, 2021-05-21) Karatok, Mustafa; Şensoy, M. G.; Vovk, Evgeny I.; Üstünel, H.; Toffoli, D.; Özensoy, EmrahSelective oxidation reactions on heterogeneous silver catalysts are essential for the mass production of numerous industrial commodity chemicals. However, the nature of active oxygen species in such reactions is still debated. To shed light on the role of different oxygen species, we studied the methanol oxidation reaction on Ag(111) single-crystal model catalyst surfaces containing two dissimilar types of oxygen (electrophilic, Oe and nucleophilic, On). X-ray photoelectron spectroscopy and low energy electron diffraction experiments suggested that the atomic structure of the Ag(111) surface remained mostly unchanged after accumulating low Oe coverage at 140 K. Temperature-programmed reaction spectroscopic investigation of low coverages of Oe on Ag(111) revealed that Oe was active for methanol oxidation on Ag(111) with a high selectivity toward formaldehyde (CH2O) production. High surface oxygen coverages, on the other hand, triggered a reconstruction of the Ag(111) surface, yielding Ag oxide domains, which catalyzes methanol total oxidation to CO2 and decreases the formaldehyde selectivity. This important finding indicates a trade-off between CH2O selectivity and methanol conversion, where 93% CH2O selectivity can be achieved for an oxygen surface coverage of θO = 0.08 ML (ML = monolayer) with moderate methanol conversion, while methanol conversion could be boosted by a factor of ∼4 for θO = 0.26 ML with a suppression of CH2O selectivity to 50%. Infrared reflection absorption spectroscopy results and density functional theory calculations indicated that Ag oxide contains dissimilar adsorption sites for methoxy intermediates, which are also energetically less stable than that of the unreconstructed Ag(111). The current findings provide important molecular-level insights regarding the surface structure of the oxidized Ag(111) model catalyst directly governing the competition between different reaction pathways in methanol oxidation reaction, ultimately dictating the reactant conversion and product selectivity.Item Open Access From aluminum foil to two-dimensional nanocrystals using ultrasonic exfoliation(American Chemical Society, 2021-04-15) Lu, W.; Birmingham, B.; Voronine, D. V.; Stolpman, D.; Ambardar, S.; Erdoğan, Deniz Altunöz; Özensoy, Emrah; Zhang, Z.; Solouki, T.Al nanostructures have unique optical properties such as widely tunable surface plasmon resonances from deep UV to NIR that can be used for label-free fluorescence enhancement and surface-enhanced Raman scattering. Various Al nanostructures have been fabricated using sophisticated “top-down” lithographic and “bottom-up” colloidal methods. Here, we developed a simple and efficient method of synthesizing two-dimensional (2D) aluminum (Al) nanocrystals from commercially available Al foil using ultrasonic exfoliation under ambient environment. 2D Al nanocrystals with sizes from a few hundred nanometers to several micrometers and thickness in the tens of nanometers were isolated through centrifugation separation. The exfoliated 2D Al nanocrystals are covered with a passivated Al2O3 nanolayer. The determined exfoliation mechanism is a combination of the preferred cleavage along the (111) surface planes and layer-by-layer Al2O3 exfoliation from the surface of the 2D Al nanocrystals. We demonstrate that the 2D Al nanocrystals can be assembled at water/air interface and transferred to different substrates to form 2D Al nanocrystal films. These 2D Al nanocrystal films exhibit surface plasmon resonance in the visible spectral range and show enhanced Raman signals of adenine using a 532 nm excitation. These 2D Al nanocrystal films could be further developed for new optical and sensing applications.Item Open Access Interaction of CO2 with MnOx/Pd(111) reverse model catalytic interfaces(Wiley, 2023-07-03) Anıl, Arca; Sadak, Ömer Faruk; Karakurt, Bartu; Koçak, Yusuf; Lyubinetsky, Igor; Özensoy, EmrahUnderstanding the activation of CO2 on the surface of the heterogeneous catalysts comprised of metal/metal oxide interfaces is of critical importance since it is not only a prerequisite for converting CO2 to value-added chemicals but also often, a rate-limiting step. In this context, our current work focuses on the interaction of CO2 with heterogeneous bi-component model catalysts consisting of small MnOx clusters supported on the Pd(111) single crystal surface. These metal oxide-on-metal ‘reverse’ model catalyst architectures were investigated via temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) techniques under ultra-high vacuum (UHV) conditions. Enhancement of CO2 activation was observed upon decreasing the size of MnOx nanoclusters by lowering the preparation temperature of the catalyst down to 85 K. Neither pristine Pd(111) single crystal surface nor thick (multilayer) MnOx overlayers on Pd(111) were not capable of activating CO2, while CO2 activation was detected at sub-monolayer (∼0.7 ML) MnOx coverages on Pd(111), in correlation with the interfacial character of the active sites, involving both MnOx and adjacent Pd atoms. © 2023 The Authors. ChemPhysChem published by Wiley-VCH GmbH.Item Open Access Low-pressure deuterium storage on palladium-coated titanium nanofilms: a versatile model system for tritium-based betavoltaic battery applications(American Chemical Society, 2023-08-30) Ghobadi, Türkan Gamze Ulusoy; Koçak, Yusuf; Jalal, Ahsan; Altınkaynak, Yağmur; Çelik, Gülşah; Semiz, Tolga; Çakır, Cihan; Bütün, Bayram; Özbay, Ekmel; Karadaş, Ferdi; Özensoy, EmrahDeuterium (D2(g)) storage of Pd-coated Ti ultra-thin films at relatively low pressures is fine-tuned by systematically controlling the thicknesses of the catalytic Pd overlayer, underlying Ti ultra-thin film domain, D2(g) pressure (PD2), duration of D2(g) exposure, and the thin film temperature. Structural properties of the Ti/Pd nanofilms are investigated via XRD, XPS, AFM, SEM, and TPD to explore new structure-functionality relationships. Ti/Pd thin film systems are deuterated to obtain a D/Ti ratio of up to 1.53 forming crystallographically ordered titanium deuteride (TiDx) phases with strong Tix+–Dy– electronic interactions and high thermal stability, where >90% of the stored D resides in the Ti component, thermally desorbing at >460 °C in the form of D2(g). Electronic interaction between Pd and D is weak, yielding metallic (Pd0) states where D storage occurs mostly on the Pd film surface (i.e., without forming ordered bulk PdDx phases) leading to the thermal desorption of primarily DOH(g) and D2O(g) at <265 °C. D-storage typically increases with increasing Ti film thickness, PD2, T, and t, whereas D-storage is found to be sensitive to the thickness and the surface roughness of the catalytic Pd overlayer. Optimum Pd film thickness is determined to be 10 nm providing sufficient surface coverage for adequate wetting of the underlying Ti film while offering an appropriate number of surface defects (roughness) for D immobilization and a relatively short transport pathlength for efficient D diffusion from Pd to Ti. The currently used D-storage optimization strategy is also extended to a realistic tritium-based betavoltaic battery (BVB) device producing promising β-particle emission yields of 164 mCi/cm2, an open circuit potential (VOC) of 2.04 V, and a short circuit current (ISC) of 7.2 nA.Item Open Access Multichromic vanadium pentoxide thin films through ultrasonic spray deposition(Electrochemical Society, Inc., 2021-10-27) Tutel, Yusuf; Durukan, Mete Batuhan; Koç, Şeyma; Koylan, Serkan; Çakmak, Hüseyin; Koçak, Yusuf; Hekmat, Farzaneh; Özensoy, Emrah; Özbay, Ekmel; Arslan Udum, Yasemin; Toppare, Levent; Unalan, Husnu EmrahVanadium pentoxide (V2O5) is a highly promising material for optoelectronic applications due to its wide optical band gap, significant thermal/chemical stability, and intriguing multichromic properties. Nonetheless, the production of uniform and crack-free V2O5 thin films over large areas via conventional deposition methods remain to be a challenge. In this work, we demonstrate deposition of microscopically uniform, large area (15 cm × 15 cm), nanocrystalline and multichromic V2O5 thin films onto fluorine-doped tin oxide (FTO) coated glass substrates via ultrasonic spray deposition (USD) method. Thin-film formation behavior, microstructural and optoelectronic properties of the deposited films were investigated as a function of post-deposition annealing temperature. Electrochromic performance of the fabricated films up to an area of 15 cm × 15 cm was monitored using cyclic voltammetry (CV), where 3 different coloration states of V2O5 were observed under different applied potentials. Electrochromic devices fabricated with the deposited V2O5 thin films were found to be stable up to 1000 cycles. Results presented herein provide a new roadmap for the large area deposition of V2O5 through USD method, which can be readily extended to a vast number of other functional metal oxide systems.Item Open Access Origins of the photocatalytic NOx oxidation and storage selectivity of mixed metal oxide photocatalysts: prevalence of electron-mediated routes, surface area, and basicity(American Chemical Society, 2024-01-23) Ebrahimi, Elnaz; Irfan, Muhammad; Koçak, Yusuf; Rostas, A. M.; Erdem, E.; Özensoy, EmrahMgO, CaO, SrO, or BaO-promoted TiO2/Al2O3 was utilized in the photocatalytic NOx oxidation and storage reaction. Photocatalytic performance was investigated as a function of catalyst formulation, calcination temperature, and relative humidity. Onset of the photocatalytic activity in TiO2/Al2O3 coincides with the transition from the anatase to rutile phase and increasing number of paramagnetic active centers and oxygen vacancies. Disordered AlOx domains enable the formation of oxygen vacancies and paramagnetic centers on titania domains, hindering the nucleation and growth of titania particles, as well as increasing specific surface area (SSA) to store oxidized NOx species away from titania active sites. Both e-- and h+-mediated pathways contribute to photocatalytic NO conversion. Experiments performed using an e- scavenger (i.e., H2O2), suppressing the e--mediated route, attenuated the photocatalytic selectivity by triggering NO2(g) release. Superior NOx storage selectivity of 7.0Ti/Al-700 as compared to other TiO2/Al2O3 systems in the literature was attributed to an interplay between the presence of electrons trapped at oxygen vacancies and superoxide species allowing a direct pathway for the complete NO oxidation to HNO3/NO3- species, and the relatively large SSA of the photocatalyst prevents the rapid saturation of the photocatalyst with oxidation products. Longevity of the 7.0Ti/Al-700 was improved by the incorporation of CaO, emphasizing the importance of the surface basicity of the NOx storage sites.Item Open Access Precious metal-Free LaMnO3 perovskite catalyst with an optimized nanostructure for aerobic C–H bond activation reactions: alkylarene oxidation and naphthol dimerization(American Chemical Society, 2021-02-03) Şahin, Yeşim; Sika-Nartey, Abel Tetteh; Ercan, Kerem Emre; Koçak, Yusuf; Senol, Sinem; Özensoy, Emrah; Türkmen, Yunus EmreIn this article, we describe the development of a new aerobic C–H oxidation methodology catalyzed by a precious metal-free LaMnO3 perovskite catalyst. Molecular oxygen is used as the sole oxidant in this approach, obviating the need for other expensive and/or environmentally hazardous stoichiometric oxidants. The electronic and structural properties of the LaMnO3 catalysts were systematically optimized, and a reductive pretreatment protocol was proved to be essential for acquiring the observed high catalytic activities. It is demonstrated that this newly developed method was extremely effective for the oxidation of alkylarenes to ketones as well as for the oxidative dimerization of 2-naphthol to 1,1-binaphthyl-2,2-diol (BINOL), a particularly important scaffold for asymmetric catalysis. Detailed spectroscopic and mechanistic studies provided valuable insights into the structural aspects of the active catalyst and the reaction mechanism.Item Open Access Pt/CeOx/ZrOx/γ-Al2O3 ternary mixed oxide DeNOx catalyst: surface chemistry and NOx interactions(American Chemical Society, 2018) Andonova, S.; Ok, Zehra Aybegüm; Drenchev, N.; Özensoy, Emrah; Hadjiivanov, K.Surface chemistry and the nature of the adsorbed NOx species on a Pt/CeO2-ZrO2/Al2O3 catalyst were investigated by IR spectroscopy, X-ray diffraction, H2-temperature programmed reduction, and NOx-temperature programmed desorption. Parallel studies were also carried out with benchmark samples such as CeO2/Al2O3, ZrO2/Al2O3, CeO2-ZrO2/Al2O3 and Pt-supported versions of these materials. All samples were studied in their reduced and nonreduced forms. The use of CO as a probe molecule revealed that during the synthesis of the mixed-metal oxide systems, deposited zirconia preferentially interacted with the alumina hydroxyls, while deposited ceria was preferentially located at the Lewis acid sites. Despite the limited extent of Zr4+ ions incorporated into the CeO2 lattice, the reduction of ceria was promoted and occurred at lower temperatures in the presence of zirconia. When deposited on ZrO2/Al2O3, platinum formed relatively big particles and existed in metallic state even in the nonreduced samples. The presence of ceria hindered platinum reduction during calcination and yielded a high platinum dispersion. Subsequent reduction with H2 led to the production of metallic Pt particles. Consequently, NO adsorption on nonreduced Pt-containing materials was negligible but was enhanced on the reduced samples because of Pt0-promoted NO disproportionation. The nature of the nitrogen-oxo species produced after NO and O2 coadsorption on different samples was similar. Despite the high thermal stability of the NOx adsorbed species on the ceria and zirconia adsorption sites, the NOx reduction in the presence of H2 was much more facile over Pt/CeO2-ZrO2/Al2O3. Thus, the main differences in the NOx reduction functionalities of the investigated materials could be related to the ability of the catalysts to activate hydrogen at relatively lower temperatures.Item Open Access Significance of the Mn-Oxidation state in catalytic and noncatalytic promotional effects of MnOx domains in formic acid dehydrogenation on Pd/MnOx interfaces(American Chemical Society, 2020) Karakurt, Bartu; Koçak, Yusuf; Lyubinetsky, Igor; Özensoy, EmrahThe influence of MnOx overlayers/nanoclusters deposited on the Pd(111) single-crystal model catalyst surface on the catalytic dehydrogenation of double-deuterated formic acid (FA, DCOOD) was studied under ultrahigh vacuum conditions via temperature-programmed desorption and X-ray photoelectron spectroscopy techniques. A significant boost in D2 generation was observed in the catalytic FA dehydrogenation on MnOx/Pd(111) as compared to that of a clean Pd(111) model catalyst, demonstrating the cooperative interaction between Pd(111) and MnOx sites. Maximum FA conversion was observed at a submonolayer MnOx surface coverage of 0.25 ML (monolayer) on Pd(111), whereas D2 formation was found to be suppressed when the Pd(111) surface was entirely covered with relatively thick (15 ML) MnOx overlayers. A direct correlation between increasing relative abundance of oxidized Mn surface states (i.e., Mn2+, Mn3+, and Mn4+) and increasing catalytic FA dehydrogenation was observed. Different modes of promotion of FA dehydrogenation via MnOx (i.e., catalytic promotion versus noncatalytic/stoichiometric promotion) were discussed as a function of the differences in the model catalyst preparation and the extent of oxidation of the MnOx overlayer.