Alexander A Guda

Alexander A Guda
Southern Federal University | sfedu · Faculty of Physics

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99
Publications
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Publications

Publications (99)
Article
We report an eco-friendly, simple, and scalable method of FeF2 cathode production. MIL-88A was synthesized in a water medium without any additives. It was used as a source of iron (3+) ions during pyrolysis. The porous structure of such a sacrificial agent allowed us to incorporate poly-vinylidene fluoride molecules as a guest component into a host...
Article
We report the synthesis of a new effective cobalt-based composite for catalytic reduction of water pollutant - p-nitrophenol. ZIF-67 and its Zn-substituted analog have been used as precursors for the catalyst preparation. Their pyrolysis has resulted in cobalt nanoparticles embedded into N-doped carbon substrates. We have used polyvinylidene fluori...
Article
This work establishes structure-property relationships in Ru-based catalytic systems for selective hydrodeoxygenation of ketones to alkenes by combining extensive catalytic testing, in situ X-ray absorption spectroscopy (XAS) under high pressures...
Article
Cu diimine complexes present a noble metal free alternative to classical Ru, Re, Ir and Pt based photosensitizers in solution photochemistry, photoelectrochemical or dye-sensitized solar cells. Optimization of these dyes requires understanding of factors governing the key photochemical properties: excited state lifetime and emission quantum yield....
Article
X‐ray absorption spectroscopy (XAS) was used to characterize the structure of the photoactive Co(II) azobenzene complex. Optical absorption spectra show that photoinduced changes occur only in dimethylformamide (DMF) solvent, while in acetonitrile, this complex is photochemically inactive. Co K‐edge XAS spectra indicate 6‐coordinated species in ace...
Chapter
In this work, we propose a new method for the analysis of time-resolved X-ray absorption near edge structure (XANES) spectra. It allows to decompose an experimental dataset as the product of two matrices: a pure spectral matrix, composed by XANES spectra associable to well-defined chemical species/sites, and their related concentration profiles. Th...
Article
Pure zinc oxide and gallium-doped ZnO films have been deposited on a glass substrate using a sol-gel assisted spin coating technique. The prepared films were characterized by structural, morphological, optical, and the effect of doping is studied. XRD analyses of the films confirm amorphous nature. Raman studies give support to XRD and confirm seco...
Article
Spin‐crossover metal complexes represent important building blocks for a future generation of electronic and optical devices. Pentacoordinated o‐iminosemiquinonate iron(III) complexes are able to demonstrate spin transitions between high spin (HS) and intermediate spin (IS) states under the influence of temperature or irradiation. Studied (MeimSQ)2...
Article
Full-text available
LiCoPO4 (LCP) is a promising high voltage cathode material but suffers from low conductivity and poor electrochemical properties. These properties can be improved by coating with a conductive carbon layer. Ongoing research is focused on the protective layer with good adhesion and inhibition of electrolyte decomposition reactions. In the present wor...
Article
Full-text available
The formation of palladium hydrides is a well-known phenomenon, observed for both bulk and nanosized samples. The kinetics of hydrogen adsorption/desorption strongly depends on the particle size and shape, as well as the type of support and/or coating of the particles. In addition, the structural properties of hydride phases and their distribution...
Article
Constructing excellent heterojunction to improve the photocatalytic performance of materials is critically important. Herein, we report an effective simple, easy preparation method for α-Fe2O3@MoS2QDs nanocomposite via two two-step process, including hydrothermal and ultrasonication approaches. The as-prepared materials were characterized using X-r...
Article
Lithium-excess disordered rock-salt oxides have opened up a new vista in search of high-capacity cathodes, resulting in a variety of new materials with versatile elemental compositions. This work introduces W⁶⁺ as a possible charge-compensator and explores the solid-solution series Li1+x/100Ni1/2−x/120Ti1/2−x/120Wx/150O2 (x = 0, 5, 10, 15, 20), whi...
Article
Copper-ceria finds applications in various energy-related and environmental catalysts. However, the versatile structure and complex redox activity of this material entangle uncovering structure-activity relationships and distinguishing active species from spectators. In this work, we monitored the dynamic structure of the active sites in a catalyst...
Article
Full-text available
Element selectivity and possibilities for in situ and operando applications make X-ray absorption spectroscopy a powerful tool for structural characterization of catalysts. While determination of coordination numbers and interatomic distances from extended spectral region is rather straightforward, analysis of X-ray absorption near-edge structure (...
Article
A novel mixed-ligand Fe(II) complex based on dihydro-bis(pyrazolyl)borate and 1,10-phenanthroline-5,6-dione Fe[(H2B(Pz)2]2[phen-dione] was synthesized. Its local atomic structure and magnetic properties were characterized by means of X-ray absorption and Mössbauer spectroscopies in the temperature range of 8–300 K. According to the experimental dat...
Article
X-ray absorption near-edge spectroscopy (XANES) is becoming an extremely popular tool for material science thanks to the development of new synchrotron radiation light sources. It provides information about charge state and local geometry around atoms of interest in operando and extreme conditions. However, in contrast to X-ray diffraction, a quant...
Article
The set of compositions with Fe²⁺ in the system NaxFex/2Ti2–x/2O4 has been prepared by solid-state reactions in the inert atmosphere at 1050 °С. The oxidation state of iron was confirmed using the XANES method. Na0.88Fe0.44Ti1.56O4 is the new four-element compound in Na2O–“FeO”–TiO2 system. According to the X-ray powder data, it is orthorhombic, Pn...
Article
Li2VO2F with the cation-disordered rock-salt structure is an attractive high-energy-density positive electrode material but suffers from severe capacity fading upon cycling. The underlying reasons are yet unclear. In this study, we unveil the overlooked role of vanadium dissolution and electrode-electrolyte interactions and provide insight into the...
Article
We have synthesized NaCoPO4 and LiCoPO4 via microwave-assisted solvothermal synthesis. The local atomic structure around Co atoms was characterized by means of Co K-edge XANES spectroscopy. Using X-ray diffraction, we have identified two NaCoPO4 phases with Pnma and P65 space groups (lattice parameters a=10.26 Å, b=5.93 Å , c=4.74 Å, and a=10.1...
Article
Full-text available
We report a series of Pd K-edge and Pt L3-edge X-ray absorption spectra (XAS) collected in situ during thermal treatment of functionalized UiO-67-Pd and UiO-67-Pt metal-organic frameworks in inert and reducing atmospheres. We present raw synchrotron data from three subsequent experiments at different beamlines, normalized XAS spectra and k2-weighte...
Article
We have tested for iodine sorption properties a variety of samples with ZIF-8 structure and various Zn/Co ratios (100/0, 95/5, 75/25, 50/50 and 0/100 in mol%). For iodine saturation, an excess of sublimated iodine crystals was used. We have observed that the prevailing trend for all compositions is adsorption of most of the iodine molecules by the...
Article
Full-text available
We report the series of Pd K-edge X-ray absorption spectra collected during hydrogenation of ethylene with variable ethylene/hydrogen ratio over carbon supported palladium nanoparticles. The data presented in this article includes normalized X-ray absorption spectra, k ² -weighted oscillatory χ(k)functions extracted from the extended X-ray absorpti...
Article
Palladium nanoparticles (NPs) find numerous applications as catalysts for hydrogenation of hydrocarbons. Under reaction conditions, formation of palladium hydrides and carbides may occur, which affects the catalytic properties of the catalyst. Unlike pure hydride phase, whose phase diagram is well-studied, conditions of formation of palladium carbi...
Article
Thermal and photoinduced processes accompanied complexation of photochromic spiropyrans (SPP) with Zn ions in acetone solution were characterized by means of UV-Vis and X-ray absorption spectroscopies in operando regime. SPP ligands are usually transparent at λ > 350 nm but, after mixing with Zn ions, they produce a stable colored (ε=32000-38000 M-...
Article
We describe the synthesis and corresponding full characterization of the set of UiO-66 metal-organic frameworks (MOFs) with 1,4-benzenedicarboxylate (C6H4(COOH)2, hereafter H2BDC) and 1,4-naphthalenedicarboxylate (C10H6(COOH)2, hereafter H2NDC) mixed linkers with NDC contents of 0, 25, 50, and 100%. Their structural (powder X-ray diffraction, PXRD)...
Article
X-ray absorption spectroscopy (XAS) has been used to analyze the change in iron oxidation state and coordination numbers of impact glasses from the Zhamanshin crater. Series of samples, specifically aerodynamically shaped small glassy bodies – irghizites, and silica-rich and silica-poor glasses – zhamanshinites, have been investigated. The Fe2.2+ o...
Article
In the last decade the appearance of progressively more sophisticated codes, together with the increased computational capabilities, has made XANES a spectroscopic technique able to quantitatively confirm (or discard) a structural model, thus becoming a new fundamental diagnostic tool in catalysis, where the active species are often diluted metal c...
Article
Formation of gold nanoparticles (NPs) from the mixture containing NaAuCl4 as a precursor, octadecene as a solvent and oleylamine as a reducing agent was studied in situ by means of optical and X-ray spectroscopies. Dynamic light scattering (DLS) revealed the presence of initial aggregates of 500 nm average size which split into nanoparticles of abo...
Article
The bimetallic Zn/Co-ZIF MOFs with different Zn:Co ratio were produced by microwave-assisted solvothermal synthesis. The morphological, structural and electronic properties of the obtained materials were probed with different experimental techniques (XRD, TEM, TGA, BET, UV-Vis, IR, Co and Zn K-edge XANES). The result of the overall characterization...
Article
The bimetallic Zn/Co-ZIF MOFs with different Zn:Co ratio were produced by microwave-assisted solvothermal synthesis. The morphological, structural and electronic properties of the obtained materials were probed with different experimental techniques (XRD, TEM, TGA, BET, UV-Vis, IR, Co and Zn K-edge XANES). The result of the overall characterization...
Article
We report a two-step room temperature protocol for functionalization of copper-based metal–organic framework MOF-199, also known as HKUST-1, with gold nanoparticles. The resulted material is characterized with XRD, TEM, BET, UV–Vis and FTIR techniques building up a complete picture of its structural, electronic and vibrational properties. We also f...
Article
After a short introduction highlighting the potentialities of metal–organic frameworks (MOFs) and the power of X-ray absorption spectroscopies (XAS), a list of selected examples follows. The first part of this review provides the basic concepts that are behind the most used XAS techniques: Extended X-ray Absorption Fine Structure (EXAFS) and X-ray...
Article
Full-text available
A setup for fluorescence-detected X-ray absorption spectroscopy (XAS) with sub-second time resolution has been developed. This technique allows chemical speciation of low-concentrated materials embedded in highly absorbing matrices, which cannot be studied using transmission XAS. Using this setup, the reactivity of 1.5 wt% Pt/CeO 2 catalyst was stu...
Article
The mechanoactivation of ferroelectric materials with perovskite structure is performed. Structural changes of the ferroelectric materials after mechanoactivation based on X-ray absorption spectra (XAFS) and X-ray diffraction data (XRD) are studied. The Fourier analysis of EXAFS spectra allows quantitative estimates to be obtained for the local ato...
Article
Cation-disordered oxides have been ignored as positive electrode material for a long time, due to structurally limited lithium insertion/extraction capabilities. In this work, a case study is carried out on nickel based cation-disordered Fm-3m LiNi0.5M0.5O2 positive electrode materials. The present investigation targets tailoring the electrochemica...
Article
A set of Sm-doped iron oxide magnetic nanoparticles (FexOy NPs) of different size was synthesized by means of microware-assisted methods. Powder X-ray diffraction and transmission electron microscopy showed FexOy NPs with inverse spinel structure and high number of defects which are typical for small NPs. Mössbauer and X-ray absorption spectroscopy...
Article
The presence of a core/shell behavior in Pd nanoparticles (NPs) during the formation of the metal- hydride phase has recently been highlighted combining X-ray absorption and scattering experiments [J. Phys. Chem. C 2017, 121, 18202]. In this work, we focus on formation of the carbide phase in the bulk region and on the surface of supported palladiu...
Chapter
The first part of this chapter provides a simple, but general, description on the physical phenomena that are behind the interaction of probe beams (photons, electrons, or neutrons) with condensed matter. The differences in penetration depth, de Broglie wavelength, and requested sample environment for the three kinds of beams are stressed. The diff...
Article
The thermal decomposition of manganese borohydride Mn(BH4)2 was studied by means of synchrotron-based X-ray absorption spectroscopy (XAS), X-ray powder diffraction (XRPD) and theoretical density functional (DFT) modeling aiming to elucidate changes of the local atomic structure upon hydrogen desorption and to determine possible decomposition reacti...
Article
We used Ni K-edge resonant-valence-to-core X-ray emission spectroscopy (RVtC-XES, also referred to as direct RIXS), an element-selective bulk-sensitive synchrotron-based technique, to investigate the electronic structure of the CPO-27-Ni metal-organic framework (MOF) upon molecular adsorption of significant molecular probes: H2O, CO, H2S, and NO. W...
Chapter
In this chapter, we introduce MOFs as the new class of crystalline porous materials of remarkable potentialities. We underline the flexibility in the realization of different MOFs and the fact that they are ideal materials for performing X-ray absorption experiments at the metal K or L3 edges in transmission mode. A selection of relevant results ap...
Article
Using microwave-assisted synthesis in organic solution, we produced magnetic γ-Fe2O3 nanoparticles covered with oleylamine and oleic acid.
Article
A zirconium metal organic framework with UiO-66 topology was synthesized using 1,4-naphthalenedicarboxylic acid linker (UiO-66-NDC). From synchrotron XRPD we found that the naphthalene rings of the NDC linker is out of (a,c)-plane equilibrium by 30 °, similar to the situation found by single crystal XRD for the benzene rings in UiO-67 [Cryst. Growt...
Article
We report an in situ, temperature and H2 pressure-dependent, characterization of (2.6  0.4) nm palladium nanoparticles supported on active carbon during the process of hydride phase formation. For the first time the core-shell structure is highlighted in the single-component particles on the basis of a different atomic structure and electronic con...
Article
The exceptional thermal and chemical stability of the UiO-66, -67 and -68 classes of isostructural MOFs [J. Am. Chem. Soc., 2008, 130, 13850] makes them ideal materials for functionalization purposes aimed at introducing active centres for potential application in heterogeneous catalysis. We previously demonstrated that a small fraction (up to 10%)...
Article
An end-on superoxido complex with formula {[CoIII(OH2)(trpy)][CoIII(OO·)(trpy)](m-bpp)}4+ , 34+, (bpp- is bis-2-pyridyl-3,5-pyrazolate; trpy is 2,2’;6’:2”-terpyridine) has been characterized by resonance Raman, electron paramagnetic resonance and x-ray absorption spectroscopies. These results together with on-line mass spectrommetry experiments usi...
Article
We report the light-induced electronic and geometric changes taking place in “real time” of a multimolecular [Ru(bpy)3]2+/[Ni(PPh2NPh2)2(CH3CN)]2+/ascorbic acid photocatalytic system by time-resolved X-ray absorption spectroscopy (tr-XAS) in the nano- to microsecond time regime. Using tr-XAS allows us to observe the diffusion-governed electron tran...
Article
Time resolved X-ray absorption spectroscopy (X-TAS) has been used to study the light induced hydrogen evolution reaction catalyzed by a tetradentate macrocyclic cobalt complex with the formula [LCoIIICl2]+ (L = macrocyclic ligand), [Ru(bpy)3]2+ photosensitizer and an equimolar mixture of sodium ascorbate/ascorbic acid electron donor in pure water....
Article
A facile water based synthesis method for HTB-FeF3/rGO and r-FeF3/rGO composites was developed using FeF3 nanoparticles prepared by ball-milling and aqueous graphene oxide precursor. Electrodes of HTB-FeF3/rGO were cast in ambient air and the calendered electrode shows a stable specific energy of 470 Wh kg−1 (210 mA h g−1, 12 mA g−1) after 100 cycl...
Article
A peculiar property of ceria is the ease to form oxygen vacancies, producing reactive sites or facilitating ionic diffusion. For these reasons ceria promotes catalytic activities for a number of important reactions when it is used as a support for transition metals. In our work we study the temporal evolution of oxygen vacancies formation by time-r...
Article
Lanthanide silicates have been hydrothermally synthesized using Cu and Ni containers. Chemical formulae of the synthesized compounds correspond to K3Eu[Si6O15] 2H2O, HK6Eu[Si10O25], K7Sm3[Si12O32], K2Sm[AlSi4O12] 0.375H2O, K4Yb2[Si8O21], K4Ce2[Al2Si8O24]. The oxidation state of lanthanides (Eu, Ce, Tb, Sm, Yb) in these silicates has been determined...
Article
Finite difference method (FDM) implemented in the FDMNES software [Phys. Rev. B, 2001, 63, 125120] was revised. Thorough analysis shows, that the calculated diagonal in the FDM matrix consists of about 96% zero elements. Thus a sparse solver would be more suitable for the problem instead of traditional Gaussian elimination for the diagonal neighbou...
Article
The development of the next generation synchrotron radiation sources - free electron lasers - is approaching to become an effective tool for the time-resolved experiments aimed to solve actual problems in various fields such as chemistry' biology' medicine' etc. In order to demonstrate' how these experiments may be performed for the real systems to...
Article
In the current work we present a detailed analysis of the hydride phase formation in industrial Pd/C nanocatalysts by means of combined in situ X-ray absorption spectroscopy (EXAFS), X-ray diffraction (XRD) and volumetric measurements for the temperatures from - 10 to 50 °C in the hydrogen pressure range from 0 to 1000 mbar. α- and β- hydride phase...
Article
We synthesized UiO-67 Metal Organic Frameworks (MOFs) functionalized with bpydcPt(II)Cl2 and bpydcPt(IV)Cl4 complexes (bpydc = bipyridine-dicarboxylate), as attractive candidates for the heterogenization of homogeneous catalytic reactions. Pt L3-edge XAFS experiments allowed us to thoroughly characterize these materials, in the local environment of...
Article
Full-text available
This review deals with key methods of synthesis and characterization of metal-organic frameworks (MOFs). The modular structure affords a wide variety of MOFs with different active metal sites and organic linkers. These compounds represent a new stage of development of porous materials in which the pore size and the active site structure can be modi...
Article
Potassium and rare-earth (Eu, Sm, Yb, Ce) silicate and aluminosilicate crystals are hydrothermally synthesized under isothermal conditions at 500°C and a pressure of 100 MPa. The chemical and structural formulas of the synthesized compounds HK6Eu[Si10O25], K7Sm3[Si12O32], K2Sm[AlSi4O12] · 0.375H2O, K4Yb2[Si8O21], and K4Ce2[Al2Si8O24] are determined...
Article
Rational development of efficient photocatalytic systems for hydrogen production requires understanding the catalytic mechanism and detailed information about the structure of intermediates in the catalytic cycle. We demonstrate how time-resolved X-ray absorption spectroscopy in the microsecond time range can be used to identify such intermediates...
Article
A Pd K-edge X-ray absorption near edge structure (XANES) analysis for palladium hydride and carbide nanoparticles is presented. It is shown that the presence of H and C atoms changes the Pd unoccupied p-electronic states, affecting the near-edge fine structure. Quantitative XANES analysis is performed using a multidimensional interpolation approach...