Department of Chemistry

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  • ItemOpen Access
    Subwavelength densely packed disordered semiconductor metasurface units for photoelectrochemical hydrogen generation
    (American Chemical Society, 2022-03-10) Ulusoy Ghobadi, T. Gamze; Ghobadi, Amir; Odabaşı, Oğuz; Karadaş, Ferdi; Özbay, Ekmel; Ulusoy Ghobadi, T. Gamze; Ghobadi, Amir; Karadaş, Ferdi; Özbay, Ekmel
    For most semiconductors, especially the visible-light-absorbing ones, the carrier diffusion length is significantly shorter than the light penetration depth, limiting their photoactivities. This limitation could be mitigated through the use of subwavelength semiconductor-based metasurfaces and metamaterials. In this paper, a large-scale compatible metasurface photocathode, made of densely packed disordered p-type chromium oxide (CrOX), is developed to be utilized in photoelectrochemical (PEC) hydrogen generation. For this purpose, first, tightly packed random Cr nanorods are fabricated using an oblique angle deposition technique. Afterward, an annealing step is applied to the sample to transform these metallic units into a semiconducting p-type CrOX-based metasurface. Based on the experimental characterization results and numerical simulations, the proposed design can provide strong light-matter interactions in an ultra-broadband-wavelength range, mainly due to its multidimensional random geometry and ultrasmall gap sizes. Finally, to substantiate the activity of the CrOXnanorods, a core-crown geometry is developed where the NiOXcapping layer catalyzes the hydrogen evolution reaction (HER). The proposed heterostructure metasurface absorber can impose photocurrent values as large as 50 μA cm-2with a photocurrent spectral response extended up to 500 nm. Moreover, the electrode shows outstanding operation under light irradiation for 9 hours. This work demonstrates a simple, scalable design strategy to fabricate low-cost and stable photocathodes for PEC hydrogen evolution. © 2022 American Chemical Society. All rights reserved.
  • ItemOpen Access
    Selective glucose sensing under physiological pH with flexible and binder-free prussian blue coated carbon cloth electrodes
    (Wiley-VCH Verlag GmbH & Co. KGaA, 2022-01-27) Oglou, Ramadan Chalil; Ulusoy Ghobadi, T. Gamze; Özbay, Ekmel; Karadaş, Ferdi; Oglou, Ramadan Chalil; Ulusoy Ghobadi, T. Gamze; Özbay, Ekmel; Karadaş, Ferdi
    The frequent detection of physiological glucose levels from human blood or sweat requires the development of low-cost electrodes with high sensitivity and selectivity. In this work, we prepared a series of Prussian blue (PB) modified carbon cloth (CC) electrodes with different cyanoferrate groups. We achieved a sensitivity as high as 145.43 μA mm−1cm−2 in a 0.1–6.5 mm concentration range with a response time below 2 s under physiological pH. The electrodes exhibited a superior selectivity of glucose in the presence of interfering agents, including sucrose, lactose, NaCl, ascorbic acid, and uric acid. The electrodes also showed outstanding long-term stability over 15 days. Furthermore, we performed comprehensive electrochemical and characterization studies to elucidate the role of the cyanoferrate group on the morphologic and electronic properties of non-enzymatic glucose sensors.
  • ItemOpen Access
    RuO2 supercapacitor enables flexible, safe, and efficient optoelectronic neural interface
    (Wiley-VCH Verlag GmbH & Co. KGaA, 2022-08-01) Karatum, O.; Yildiz, E.; Kaleli, H. N.; Sahin, A.; Ulgut, Burak; Nizamoglu, S.; Ulgut, Burak
    Optoelectronic biointerfaces offer a wireless and nongenetic neurostimulation pathway with high spatiotemporal resolution. Fabrication of low-cost and flexible optoelectronic biointerfaces that have high photogenerated charge injection densities and clinically usable cell stimulation mechanism is critical for rendering this technology useful for ubiquitous biomedical applications. Here, supercapacitor technology is combined with flexible organic optoelectronics by integrating RuO2 into a donor–acceptor photovoltaic device architecture that facilitates efficient and safe photostimulation of neurons. Remarkably, high interfacial capacitance of RuO2 resulting from reversible redox reactions leads to more than an order-of-magnitude increase in the safe stimulation mechanism of capacitive charge transfer. The RuO2-enhanced photoelectrical response activates voltage-gated sodium channels of hippocampal neurons and elicits repetitive, low-light intensity, and high-success rate firing of action potentials. Double-layer capacitance together with RuO2-induced reversible faradaic reactions provide a safe stimulation pathway, which is verified via intracellular oxidative stress measurements. All-solution-processed RuO2-based biointerfaces are flexible, biocompatible, and robust under harsh aging conditions, showing great promise for building safe and highly light-sensitive next-generation neural interfaces.
  • ItemOpen Access
    Unraveling molecular fingerprints of catalytic sulfur poisoning at the nanometer scale with near-field infrared spectroscopy
    (American Chemical Society, 2022-04-29) Say, Zafer; Kaya, Melike; Kaderoǧlu, Çağıl; Koçak, Yusuf; Ercan, Kerem Emre; Sika-Nartey, Abel Tetteh; Jalal, Ahsan; Türk, Ahmet Arda; Langhammer, Christoph; Jahangirzadeh Varjovi, Mirali; Durgun, Engin; Özensoy, Emrah; Koçak, Yusuf; Ercan, Kerem Emre; Sika-Nartey, Abel Tetteh; Jalal, Ahsan; Türk, Ahmet Arda
    Fundamental understanding of catalytic deactivation phenomena such as sulfur poisoning occurring on metal/metal-oxide interfaces is essential for the development of high-performance heterogeneous catalysts with extended lifetimes. Unambiguous identification of catalytic poisoning species requires experimental methods simultaneously delivering accurate information regarding adsorption sites and adsorption geometries of adsorbates with nanometer-scale spatial resolution, as well as their detailed chemical structure and surface functional groups. However, to date, it has not been possible to study catalytic sulfur poisoning of metal/metal-oxide interfaces at the nanometer scale without sacrificing chemical definition. Here, we demonstrate that near-field nano-infrared spectroscopy can effectively identify the chemical nature, adsorption sites, and adsorption geometries of sulfur-based catalytic poisons on a Pd(nanodisk)/Al2O3 (thin-film) planar model catalyst surface at the nanometer scale. The current results reveal striking variations in the nature of sulfate species from one nanoparticle to another, vast alterations of sulfur poisoning on a single Pd nanoparticle as well as at the assortment of sulfate species at the active metal-metal-oxide support interfacial sites. These findings provide critical molecular-level insights crucial for the development of long-lifetime precious metal catalysts resistant toward deactivation by sulfur. ©
  • ItemOpen Access
    Light-driven water oxidation with ligand-engineered Prussian blue analogues
    (American Chemical Society, 2022-02-24) Ahmad, Aliyu Aremu; Ulusoy Ghobadi, Türkan Gamze; Büyüktemiz, Muhammed; Özbay, Ekmel; Dede, Yavuz; Karadaş, Ferdi; Ahmad, Aliyu Aremu; Ulusoy Ghobadi, Türkan Gamze; Büyüktemiz, Muhammed; Özbay, Ekmel; Karadaş, Ferdi
    The elucidation of the ideal coordination environment of a catalytic site has been at the heart of catalytic applications. Herein, we show that the water oxidation activities of catalytic cobalt sites in a Prussian blue (PB) structure could be tuned systematically by decorating its coordination sphere with a combination of cyanide and bidentate pyridyl groups. K0.1[Co(bpy)]2.9[Fe(CN)6]2([Cobpy-Fe]), K0.2[Co(phen)]2.8[Fe(CN)6]2([Cophen-Fe]), {[Co(bpy)2]3[Fe(CN)6]2}[Fe(CN)6]1/3([Cobpy2-Fe]), and {[Co(phen)2]3[Fe(CN)6]2}[Fe(CN)6]1/3Cl0.11([Cophen2-Fe]) were prepared by introducing bidentate pyridyl groups (phen: 1,10-phenanthroline, bpy: 2,2′-bipyridine) to the common synthetic protocol of Co-Fe Prussian blue analogues. Characterization studies indicate that [Cobpy2-Fe] and [Cophen2-Fe] adopt a pentanuclear molecular structure, while [Cobpy-Fe] and [Cophen-Fe] could be described as cyanide-based coordination polymers with lower-dimensionality and less crystalline nature compared to the regular Co-Fe Prussian blue analogue (PBA), K0.1Co2.9[Fe(CN)6]2([Co-Fe]). Photocatalytic studies reveal that the activities of [Cobpy-Fe] and [Cophen-Fe] are significantly enhanced compared to those of [Co-Fe], while molecular [Cobpy2-Fe] and [Cophen2-Fe] are inactive toward water oxidation. [Cobpy-Fe] and [Cophen-Fe] exhibit upper-bound turnover frequencies (TOFs) of 1.3 and 0.7 s-1, respectively, which are ∼50 times higher than that of [Co-Fe] (1.8 × 10-2s-1). The complete inactivity of [Cobpy2-Fe] and [Cophen2-Fe] confirms the critical role of aqua coordination to the catalytic cobalt sites for oxygen evolution reaction (OER). Computational studies show that bidentate pyridyl groups enhance the susceptibility of the rate-determining Co(IV)-oxo species to the nucleophilic water attack during the critical O-O bond formation. This study opens a new route toward increasing the intrinsic water oxidation activity of the catalytic sites in PB coordination polymers. © 2022 American Chemical Society. All rights reserved.
  • ItemOpen Access
    Operando investigations of the interfacial electrochemical kinetics of metallic lithium anodes via temperature-dependent electrochemical impedance spectroscopy
    (American Chemical Society, 2022-06-28) Zabara, Mohammed Ahmed; Katırcı, Gökberk; Ülgüt, Burak; Zabara, Mohammed Ahmed; Katırcı, Gökberk; Ülgüt, Burak
    One of the major hurdles in the utilization of metallic lithium anodes is understanding the Li+transfer kinetics through the solid electrolyte interface (SEI) in addition to Li oxidation. Electrochemical impedance spectroscopy (EIS) combined with temperature variation provides deeper comprehension and reveals kinetic parameters of individual processes separately. In this study, we report temperature-dependent EIS analysis of metallic Li anodes to shed light on the kinetics of anodic/interfacial processes at different states of charge and wide temperature ranges (-25 to 75 °C), utilizing lithium thionyl chloride (Li/SOCl2) and lithium manganese dioxide (Li/MnO2) primary batteries as model systems. We found in both batteries that the impedance of the SEI processes is highly temperature-dependent with non-Arrhenius behavior at temperatures greater than 35 °C. Conversely, the kinetics of the anodic process showed small temperature dependence that is explained by the Arrhenius equation throughout the temperature range studied. The results provide a deeper understanding of the underlying processes separately in metallic Li anodes under operando and real-time conditions. © 2022 American Chemical Society. All rights reserved.
  • ItemOpen Access
    “Plug and Play” photosensitizer–catalyst dyads for water oxidation
    (American Chemical Society, 2022-04-28) Chalil Oglou, Ramadan; Ulusoy Ghobadi, T. Gamze; Özbay, Ekmel; Karadaş, Ferdi; Chalil Oglou, Chalil Oglou, Ramadan; Ulusoy Ghobadi, T. Gamze; Özbay, Ekmel; Karadaş, Ferdi
    We present a simple and easy-to-scale synthetic method to plug common organic photosensitizers into a cyanide-based network structure for the development of photosensitizer-water oxidation catalyst (PS-WOC) dyad assemblies for the photocatalytic water oxidation process. Three photosensitizers, one of which absorbs red light similar to P680 in photosystem II, were utilized to harvest different regions of the solar spectrum. Photosensitizers are covalently coordinated to CoFe Prussian blue structures to prepare PS-WOC dyads. All dyads exhibit steady water oxidation catalytic activities throughout a 6 h photocatalytic experiment. Our results demonstrate that the covalent coordination between the PS and WOC group not only enhances the photocatalytic activity but also improves the robustness of the organic PS group. The photocatalytic activity of “plug and play” dyads relies on several structural and electronic parameters, including the position of the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the PS with respect to the HOMO level of the catalytic site, the intensity and wavelength of the absorption band of the PS, and the number of catalytic sites.
  • ItemOpen Access
    Chemical tracking of temperature by concurrent periodic precipitation pattern formation in polyacrylamide gels
    (American Chemical Society, 2022-01-20) Khan, Muhammad Turab Ali; Kwiczak-Yiğitbaşı, Joanna; Tootoonchian, Pedram; Morsali, Mohammad; Lagzi, Istvan; Baytekin, Bilge; Khan, Muhammad Turab Ali; Kwiczak-Yiğitbaşı, Joanna; Tootoonchian, Pedram; Morsali, Mohammad; Baytekin, Bilge
    In nature, nonequilibrium systems reflect environmental changes, and these changes are often “recorded” in their solid body as they develop. Periodic precipitation patterns, aka Liesegang patterns (LPs), are visual sums of complex events in nonequilibrium reaction–diffusion processes. Here we aim to achieve an artificial system that “records” the temperature changes in the environment with the concurrent LP formation. We first illustrate the differences in 1-D LPs developing at different temperatures in terms of band spacings, which can demonstrate the time, ramp steepness, and extent of a temperature change. These results are discussed and augmented by a mathematical model. Using scanning electron microscopy, we show that the average size of the CuCrO4 precipitate also reflects the temperature changes. Finally, we show that these changes can also be “recorded” in the 2-D and 3-D LPs, which can have applications in long-term temperature tracking and complex soft material design.
  • ItemOpen Access
    Effect of the polarity of solvents on periodic precipitation: Formation of hierarchical revert liesegang patterns
    (American Chemical Society, 2022-10-11) Holló, Gábor; Zámbó, Dániel; Deák, András; Rossi, Federico; Rossi, Federico; Cucciniello, Raffaele; Nostro, Pierandrea Lo; Nabika, Hideki; Baytekin, Bilge; Lagz, István; Itatani, Masaki; Baytekin, Bilge
    Liesegang pattern (LP) is one example of self-organized periodic precipitation patterns in nonequilibrium systems. Several studies have demonstrated that the LP morphology can track physicochemical environmental conditions (e.g., temperature); however, the polarity effect has not been explored to date. In this study, a copper chromate system is used to reveal the impact of solvent polarity on the evolving LP structure using water/organic solvent mixtures. In the typical case of using water/dimethyl sulfoxide (DMSO) mixtures, two drastic changes in LP morphology with increasing DMSO contents were found: (i) increasing frequency of the original structure and (ii) formation of a hierarchical pattern with the appearance of another, lower-frequency structure. Furthermore, the simulation model operating with a bimodal size distribution, allowing both homogeneous and heterogeneous precipitations showed good agreement with the experimental results. Therefore, this study demonstrated that LP can be tailored by solvent polarity and can be used for designing hierarchical precipitation patterns in a straightforward manner.
  • ItemOpen Access
    Rapid access to hydroxyfluoranthenes via a domino Suzuki–Miyaura/intramolecular Diels–Alder/ring-opening reactions sequence
    (American Chemical Society, 2022-04-07) Ahmadli, Dilgam; Şahin, Yeşim; Çalıkyılmaz, Eylül; Şahin, Onur; Türkmen, Yunus E.; Ahmadli, Dilgam; Şahin, Yeşim; Çalıkyılmaz, Eylül; Şahin, Onur; Türkmen, Yunus E.
    In this work, we developed an efficient method for the rapid construction of fluoranthene skeleton to access a variety of substituted hydroxyfluoranthenes. The 1-iodo-8-alkynylnaphthalene derivatives, which serve as substrates for the key fluoranthene-forming step, were prepared via selective monoalkynylative Sonogashira reactions of 1,8-diiodonaphthalene. The domino reaction sequence which involves a sequential Suzuki–Miyaura coupling, an intramolecular Diels–Alder reaction, and an aromatization-driven ring-opening isomerization has been shown to give substituted hydroxyfluoranthenes in up to 92% yield. This work demonstrates the utility of designing new domino reactions for rapid access to substituted polycyclic aromatic hydrocarbons (PAHs).
  • ItemOpen Access
    Methods-employing multisine electrochemical impedance spectroscopy for batteries ın galvanostatic mode
    (Electrochemical Society, Inc., 2022-11-07) Ülgüt, Burak; Ülgüt, Burak
    Electrochemical Impedance Spectroscopy(EIS) is a standard technique for analyzing batteries in detail. It is immensely powerful as it can yield separate information about various components and interfaces inside while the battery is intact and operational. One drawback of the EIS measurement is the relatively large time it requires.One potential way to improve this issue is the use of the multisine, a technique akin to Fourier Transform techniques in various spectroscopies. In this manuscript, it will be shown that through judicious preparation of excitation signal, proper parameter choice and tweaking, the measurement can be sped up. Under the best conditions, the measurement can be completed within the shortest possible time that transforms to the lowest desired frequency.
  • ItemOpen Access
    Methods—unexpected effects in galvanostatic EIS of randles' cells: Initial transients and harmonics generated
    (Electrochemical Society, Inc., 2022-03-17) Katırcı, Gökberk; Zabara, Mohammed Ahmed; Ülgüt, Burak; Katırcı, Gökberk; Zabara, Mohammed Ahmed; Ülgüt, Burak
    Non-linear EIS analysis is gaining wider attention and interest due to the deeper understanding that is provided especially when combined with linear EIS. The nonlinear part of the data can get corrupted due to a number of effects. One of these is the initial transient, which is the response right after excitation signal is applied before a steady-state is reached. In this study, we demonstrate this phenomenon through analyzing simplified Randles' cells via Kirchoff's laws. To get rid of the effects of the initial transient, instrument manufacturers typically discard some fraction of the response, the effectiveness of which, as demonstrated here has to be checked.
  • ItemOpen Access
    Regulating the solvation structure of potassium Ions using a multidentate ether in potassium metal batteries
    (American Chemical Society, 2022-09-26) Chen, C.; Zhou, J.; Wenbinb, F.; Xueyinga, M.; Chen, S.; Sun, L.; Meng, Y.; Tao, K.; Ülgüt, Burak; Sun, P.; Bielawski, C.; Bielawski, C. W.; Geng, J.; Ülgüt, Burak
    Potassium (K) is regarded as an alternative to lithium (Li) for use in contemporary energy storage devices owing to its high abundance and low electrochemical potential. However, because K ions are larger than Li ions, they exhibit different solvation properties that can ultimately affect device performance. Herein, a multidentate ether-based electrolyte is demonstrated to effectively solvate K ions and the solvation structures can be further modulated with cosolvents. The use of the multidentate ether-based electrolyte also suppresses the formation of K dendrites and significantly enhances the cycling stability of K//K symmetric cells (e.g., over 2000 h at 0.25 mA cm-2). © 2022 American Chemical Society. All rights reserved.
  • ItemOpen Access
    6p valence relativistic effects in 5d photoemission spectrum of Pb atom and bonding properties of Pb-dimer using Dirac–Hartree–Fock formalism including many-body effects
    (AVS, 2022-06-22) Süzer, Şefik; Bagus, Paul S.; Süzer, Şefik
    There has been strong recent interest related to the large spin–orbit coupling in Pb monolayers on various properties of graphene and other 2D-materials. The underlying physical/chemical origin of the spin–orbit splitting has been discussed in terms of the valence 6p atomic level of the lead atom. Indeed, the photoelectron spectra of the Pb atom were the subject of investigations about 50 years ago in Dave Shirley’s laboratory at UC Berkeley. In a paper published in 1975, using He-I UV photoelectron spectroscopy, we reported an unexpected relative intensity ratio for the observed atomic Pb peaks (2P1/2 and 2P3/2) after removal of a 6p valence electron and attributed it to the large spin–orbit interaction in that level. In this contribution, we use the Dirac–Hartree–Fock formalism to reanalyze the complex spectral features reported five years later, for the 5d He-II UV photoelectron spectrum of atomic lead, to extract the 6p valence contribution, which turns out to be significant. Furthermore, we calculate the energy levels of the Pb-dimer at the experimental equilibrium geometry of the molecule to also find the significant contribution of the spin–orbit splitting of the atomic 6p levels in the composition of the valence molecular orbitals of the dimer. Such an approach can be extended to larger systems like monolayers containing lead or other heavy atoms, thus helping in designing 2D-materials with controlled and better targeted properties.
  • ItemOpen Access
    Electrochemical noise analysis in batteries
    (Elsevier, 2022-12-10) Karaoğlu, Gözde; Hatipoğlu, Gizem; Ulgut, Burak; Karaoğlu, Gözde; Hatipoğlu, Gizem; Ulgut, Burak
    Electrochemical noise is invaluable in the investigations of stochastic electrochemical processes. Though historically it has been applied almost exclusively to crevice and pitting corrosion studies, application to batteries is interesting for basic science and shows a huge potential for non-perturbing real-time sensor development. Given this promise, noise studies on batteries are starting to appear in the literature. In this manuscript, we are going to critically evaluate the small but emerging body of literature and investigate the mathematical methods employed. We will discuss the intricacies of electrochemical noise applied to batteries both in measurements and in analysis in order to initiate a deeper discussion. In conclusion, we argue that reliance on mathematical methods alone is not the answer, as all mathematical methods use require parameters to guide the analysis. Instead, post-mortem characterizations of batteries can guide the understanding of noise signals measured in batteries, guiding potential mathematical analysis methods and their steps.
  • ItemOpen Access
    Non-linear harmonics in EIS of batteries with lithium anodes: Proper controls and analysis
    (Elsevier, 2022-10-10) Zabara, Mohammed Ahmed; Katırcı, Gökberk; Ülgüt, Burak; Zabara, Mohammed Ahmed; Katırcı, Gökberk; Ülgüt, Burak
    Non-linear Harmonic Analysis is used to investigate the distortions accompanying the Electrochemical Impedance Spectroscopy (EIS) measurements. The distortions emerge from non-linearity and non-stationarity due to the underlying redox reactions as well as the capacitance. Identifying each response and its source is crucial to correlate the obtained harmonics to their corresponding electrochemical processes. In this study, we identify the distortions of Galvanostatic-EIS measurements of Lithium Primary Batteries by means of comparing mathematical simulations and experimental measurements. The simulations were performed on RC-based equivalent circuit models, which showed the presence of certain distortions. The experimental measurements displayed distortions in the form of both non-linearity and non-stationarity in the case of batteries. The level of the harmonics in the measurements is either similar or higher than the harmonics simulated in the RC equivalent circuits at different frequencies. The obtained harmonics compared to simulations highlights the importance of control measurements before the analysis of non-linear harmonics of EIS measurements galvanostatically excited.
  • ItemOpen Access
    Poly(vinyl amine) microparticles derived from N-Vinylformamide and their versatile use
    (Springer, 2021-09-03) Demirci, S.; Sütekin, S.Duygu; Kurt, S.B.; Güven, O.; Sahiner, N.; Sütekin, S.Duygu
    Cationic polymers with primary amine groups that can easily be functionalized or coupled with substrates by complexation or hydrogen bonding are especially advantageous in preparing particles for biomedical applications. Poly(vinyl amine) (PVAm) is a cationic polyelectrolyte containing the highest number of primary amine groups among any other polymers. Here, we introduce a general method in synthesizing PVAm microparticles via a surfactant-free water-in-oil emulsion technique using cyclohexane as the oil phase and aqueous PVAm solution as the dispersed phase. PVAm particles were prepared to employ two different bifunctional chemical crosslinkers, divinyl sulfone (DVS) and poly(ethylene glycol) diglycidyl ether (PEGGE). The prepared particles were further treated with HCl to protonate the amine groups of PVAm within particles. The effect of crosslinker types and pH on the hydrolytic degradation of PVAm particles were also investigated at three different solution pHs, 5.4, 7.4, and 9, to simulate the skin, blood, and intestinal pH environments, respectively. The blood compatibility of the PVAm particles was evaluated by in vitro hemolysis and blood clotting assays. Furthermore, antifungal and antibacterial efficacy of PVAm-based particles and their protonated forms were tested against C. albicans yeast and E. coli, S. aureus, B. subtilis, and P. aeruginosa bacterial strains. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
  • ItemOpen Access
    Laser-ablation assisted strain engineering of gold nanoparticles for selective electrochemical CO2 reduction
    (Royal Society of Chemistry, 2022-04-19) Zhang, C.; Zhang, W.; Karadaş, Ferdi; Low, J.; Long, R.; Liang, C.; Wang, J.; Li, Z.; Xiong, Y.; Karadaş, Ferdi
    Strain engineering can endow versatile functions, such as refining d-band center and inducing lattice mismatch, on catalysts for a specific reaction. To this end, effective strain engineering for introducing strain on the catalyst is highly sought in various catalytic applications. Herein, a facile laser ablation in liquid (LAL) strategy is adopted to synthesize gold nanoparticles (Au NPs) with rich compressive strain (Au-LAL) for electrochemical CO2 reduction. It is demonstrated that the rich compressive strain can greatly promote the electrochemical CO2 reduction performance of Au, achieving a CO partial current density of 24.9 mA cm−2 and a maximum CO faradaic efficiency of 97% at −0.9 V for Au-LAL, while it is only 2.77 mA cm−2 and 16.2% for regular Au nanoparticles (Au-A). As revealed by the in situ Raman characterization and density functional theory calculations, the presence of compressive strain can induce a unique electronic structure change in Au NPs, significantly up-shifting the d-band center of Au. Such a phenomenon can greatly enhance the adsorption strength of Au NPs toward the key intermediate of CO2 reduction (i.e., *COOH). More interestingly, we demonstrate that, an important industrial chemical feedstock, syngas, can be obtained by simply mixing Au-LAL with Au-A in a suitable ratio. This work provides a promising method for introducing strain in metal NPs and demonstrates the important role of strain in tuning the performance and selectivity of catalysts.
  • ItemOpen Access
    Selective photocatalytic CO2 reduction by cobalt dicyanamide
    (Royal Society of Chemistry, 2022-07-29) Akbari, Sina Sadigh; Karadaş, Ferdi; Akbari, Sina Sadigh; Karadaş, Ferdi
    Photocatalytic conversion of CO2 into chemical fuels is a promising approach to tackle carbon emission and global warming. Herein, we promote a cobalt dicyanamide coordination compound, Co-dca, for the first time, as a selective catalyst to reduce CO2 to CO in the presence of a ruthenium photosensitizer (Ru PS) under visible light irradiation. Co-dca was prepared by a facile precipitation method and characterized by Infrared, UV-Vis, XRD, SEM, TEM, and XPS studies. A series of photocatalytic experiments under various reaction conditions were performed to reveal the role of the PS, the scavenger, and the solvent in the selectivity and the activity of the photocatalytic process. We find that Co-dca exhibits an activity of 254 μmol h−1 g−1 and a CO selectivity as high as 93%.
  • ItemOpen Access
    Dynamic environment at the Zr6 oxo cluster surface is key for the catalytic formation of amide bonds
    (Royal Society of Chemistry, 2022-10-22) Zhang, Y.; Kökçüler, İsmail Yaşar; Azambuja, F.; Parac-Vogt, T.N.; Kökçüler, İsmail Yaşar
    Zirconium compounds are an attractive alternative to costly, low abundant metals for the development of inexpensive, readily available, and robust catalysts. The air and moisture stable Zr oxo clusters such as the Zr6O8 species, are of particular interest as they are key building blocks of several Zr-based metal–organic framework (Zr-MOF) catalysts. However, broader use of these cluster-based materials as catalysts is still hampered by the modest understanding of their fundamental reactivity. To bridge this gap, we report on the activity of a soluble Zr6O8 cluster, [Zr6(OH)4O4(OMc)12] (OMc = methacrylate) (Zr6), as a discrete molecular catalyst for the atom-economic formation of amide bonds. This reaction demands two completely different substrates interacting with the Zr6 catalyst, a key step rarely addressed in MOF catalyzed reactions. Remarkably, Zr6 catalyzes the formation of amide bonds directly from non-activated carboxylic acid and amine substrates in ethanol, without requiring anhydrous conditions or water scavenging to achieve good yields. As shown by a series of kinetic, and mechanistic experiments, this promising reactivity arises from a dynamic environment at the cluster surface, where the essential coordination of both substrates requires an excess of amine to enhance the reaction output. Strikingly, Zr6 catalyst tolerates a range of substrates, including (hetero)aromatic, aliphatic, and α-branched acids, even though their nature directly impacts the reaction efficiency. Further, insights for the future design of catalysts based on Zr oxo cluster are discussed through a detailed comparison of Zr6 reactivity with a related Zr12 cluster, and Zr-MOF catalysts. Considering the advantages of zirconium, and the relevance of discrete Zr oxo clusters as building blocks of several MOF materials of varied utility, the molecular level understanding disclosed here contributes at large to the development of novel catalytic entities, and sustainable approaches to synthetic chemistry.