G. V. Avdeev

Bulgarian Academy of Sciences | BAS · Rostislav Kaishev Institute of Physical Chemistry

The chemical interactions of two types of graphite and two types of carbon black (CB) with acetone, toluene, and phenol were studied in order to evaluate the influence of chemical treatment on the structure and morphology of the carbon phases. The experimental treatment of carbon phases was carried out at room temperature for 1 hour. The chemical a...

This study aimed to present the differences in the corrosion properties and protective ability of two bi-layer systems obtained on low-carbon steel in a model corrosive medium of 5% NaCl solution. These newly developed systems consist of Zn-Co (3 wt.%) or Zn-Ni (10 wt.%) alloy coatings as under-layers and a very thin TiO2 sol-gel film as a top-laye...

Increased levels and detrimental effects of volatile organic compounds (VOCs) stimulate research efforts to develop catalysts with high efficiency in complete hydrocarbon oxidation. This work is focused on the complete oxidation of benzene as a probe reaction for VOCs elimination over alumina-supported CuO-CeO2 mixed oxide promoted by gold. The ben...

Dielectric glass-ceramic materials find various applications as parts of sensors, electronic components and even in biomedicine. The present work reports on the synthesis of glass-ceramic materials in the complex oxide system (23.1-z)Na 2 O/17.1BaO/6SrO/23TiO 2 /17.4SiO 2 /7.6B 2 O 3 /5.8Fe 2 O 3 /zAl 2 O 3 , z = 0 and 3 mol %. The melts show spont...

The aim of the present research is to study some aspects of the carbon doping of TiO2 thin films and the influence of low temperature thermal annealing on the phase precipitation in thin films. Тhin films of heavily doped with carbon TiO2 (up to 3 at % C) were deposited on (15 × 25 × 1 mm) glass substrates by r.f. magnetron co-sputtering of TiO2 ta...

Formaldehyde (HCHO) is recognized as one of the most emitted indoor air pollutants with high detrimental effect on human health. Significant research efforts are focused on HCHO removal to meet emission regulations in an effective and economically profitable way. For over three decades, the unique electronic properties and catalytic abilities of na...

Temporary scaffolds that mimic the extracellular matrix’s structure and provide a stable substratum for the natural growth of cells are an innovative trend in the field of tissue engineering. The aim of this study is to obtain and design porous 2D fibroin-based cell matrices by femtosecond laser-induced microstructuring for future applications in m...

Dispersed NiMo sulfide catalysts were synthesized by hydrothermal deposition method with the assistance of thioglycolic acid (TGA) as sulfiding agent ex situ at 160 °C. The prepared samples were characterized by SBET, XRD, SEM, FTIR, XPS, TPR/TPS, TPD-NH3. The catalyst activity was investigated during hydrodesulfurization (HDS) of thiophene (TH) at...

Samarium doped (0.5-5 at.%) ZrO2 films with high surface and optical quality were obtained by sol-gel method using inorganic zirconium precursor. The morphology and roughness of the samples were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). A phase transition following the doping with Sm³⁺ ions was registered...

Hexagonal boron-nitride nanoparticle coating was deposited on AISI 1045 steel surface. The deposition process included a transformation of B-containing thin organic film into nanocrystalline BN using two methods: thermal annealing at 450–850 °C and reactive ion etching in Ar/N2 plasma. The film structure, phases, and film morphology of deposited na...

Thin films of TiO2 doped with carbon were deposited on 15×25×1 mm 3 glass substrates by r.f. magnetron co-sputtering of TiO2 target and carbon plates on their erosion zone in Ar + air atmosphere (0.5 Pa and 0.6 Pa, respectively). Two different process parameters were varied in different experiments: the total area of the carbon plates (84 mm 2 , 56...

This paper presents the process of preparation and characterisation of chemically deposited copper coatings on ZrW2O8 particles. The interest in this topic is driven by the possibility of using such a material in the preliminary stage of obtaining metal-ceramic composites of Cu/ZrW2O8 type with low or zero CTE (coefficient of thermal expansion). A...

The use of laser processing for the creation of diverse morphological patterns onto the surface of polymer scaffolds represents a method for overcoming bacterial biofilm formation and inducing enhanced cellular dynamics. We have investigated the influence of ultra-short laser parameters on 3D-printed poly-ε-caprolactone (PCL) and poly-ε-caprolacton...

Considerable efforts to reduce the harmful emissions of volatile organic compounds (VOCs) have been directed towards the development of highly active and economically viable catalytic materials for complete hydrocarbon oxidation. The present study is focused on the complete benzene oxidation as a probe reaction for VOCs abatement over Co3O4-CeO2 mi...

The aim of our work was to obtain graphene-like phases (defected graphene, graphene oxide and reduced graphene oxide) as fine suspensions by applying pulsed laser ablation (PLA) to microcrystalline graphite suspension in water medium. The fundamental (λ = 1064 nm), second (λ= 532 nm), third (λ= 355 nm) as well as the fourth harmonic (λ= 266 nm) of...

Enhanced corrosion efficiency of low-carbon steel was achieved by newly developed hybrid multilayers, composed of low-carbon steel coated with an electrodeposited zinc sublayer (1 µm), a chitosan (CS) middle layer and ZrO2 coating by the sol–gel method (top-layer). The middle chitosan layer was obtained by dipping galvanized steel substrate in 3% t...

In this paper, we present an original study on metamorphic GaAsSb layers grown by liquid phase epitaxy (LPE) on GaAs substrates for photovoltaic applications. To ensure a controlled growth of the layers with reproducible composition and properties a low-temperature (below 600 °C) variant of LPE was used combined with a precise choice of the technol...

Pyridinium hydrogen sulfate ionic liquid (PHS) heterogenized on activated carbon (AC) is investigated for the first time in the current paper. For that purpose, the xPHS/AC (x = 8, 17, 33 and 66 wt.%) samples are analyzed by a number of physicochemical methods such as N2 adsorption-desorption measurements, X-ray diffraction, X-ray photoelectron spe...

Peculiarities of mechanically assisted thermal synthesis of cuprorivaite (CaCuSi4O10) were described. For the sake of comparison, the classical thermal synthesis of the same product was performed using the same reagents. X‒ray diffraction (XRD) method was used to characterize the products obtained. Phase changes were registered as a result of the m...

Glasses with the mol % composition 20.1Na2O/23TiO2/23.1BaO/3Al2O3/7.6B2O3/17.4SiO2/5.8Fe2O3 were synthesized. During heat treatment at 550°C for 5 min to 7 h, cubic BaTiO3 crystallized. The microstructure of the glass-ceramics was studied by scanning electron microscopy. The average size of the crystalline particles varied from 190 to 790nm, depend...

Using RF magnetron sputtering, we deposited Bi1 2 TiO 20 (BTO) thin films on various substrates (glass, quartz, stainless steel (SS304), (001) and (111) Si and sital-ceramics, Al and Cu foils). The films had a constant thickness of 1.3 μm. The as-deposited films were studied by Raman spectroscopy, scanning electron microscopy (SEM) and energy dispe...

We modified single- and few-layer nano-sized graphene films deposited by pulsed laser deposition (PLD) on ∼300-nm-thick SiO 2 /Si substrates. The samples were irradiated by a UV C lamp (wavelength of 254 nm) for 15 and 30 minutes in air atmosphere. The light was directed almost parallel (about 2 - 2.5 arcdeg declination angle) to the films’ surface...

The aim of this work was to obtain graphene-like phases (defected graphene, graphene oxide and reduced graphene oxide) as fine suspensions by applying pulsed laser ablation (PLA) of micro-crystalline graphite suspension in water medium. The fundamental (λ = 1064 nm), second (λ = 532 nm), third (λ = 355 nm) and fourth harmonics (λ = 266 nm) of a Nd:...

We report on the fabrication of highly porous metal-oxide nanostructures by pulsed laser deposition performed in air at atmospheric pressure. The depositions were performed by ablating synthesized ZnO and a mixed target of ZnO and TiO 2 as initial materials. The attention was focused on the structure, morphology, optical and photocatalytic properti...

In this study two hybrid organic–inorganic ureasilicate monomers with different length of polymer segments were chosen for preparation of sol–gel material that includes two moieties blended on the molecular scale. The first monomer was obtained by crosslinking a double terminated polyoxyalkyleneamine with an isocyanate modified silicone ethoxide an...

The presence of triple phase TiO2 new mixture (Magneli of higher order homologous series, brookite and anatase) containing P dopant ensures positive changes in the structure, in the phase composition and in the chemical composition. These changes explained the reasons for the enhanced UV/Vis photocatalytic efficiency towards oxidative degradation o...

The paper presents experimental results on fabricating composite nanostructures consisting of magnetic and non-magnetic metal oxide nanoparticles. The samples were produced by a single-step process of pulsed laser deposition carried out in air at atmospheric pressure in the presence of a magnetic field. Part of the depositions was performed by abla...

This paper investigated thermal properties of natural thaumasite, such as phase composition and reaction mechanism of thermal decomposition using simultaneous TG-DTGDSC in Ar and Air medium up to 1673 K, coupled with masspectrometer for analysis of evolving gases, and in-situ powder X-ray diffraction measurements. The transitional solid phases, gro...

Worldwide disposal of multi-tonnage solid waste from coal-burning thermal power plants (TPPs) creates serious environmental and economic problems, which necessitate the recovery of industrial waste in large quantities and at commercial prices. Fly ashes (FAs) and slag from seven Bulgarian TPPs have been successfully converted into valuable zeolite-...

The effect of Zn/Al ratio and addition of silica to Al–Znx oxides on the structure and catalytic properties of supported NiMo catalysts in hydrodesulfurization reaction of thiophene was studied. NiMo catalysts were synthesized by simultaneous impregnation of Ni acetate and 12-molybdophosphoric acid on Al–Znx and Al–Zn0.16–Si mixed oxide (with x = Z...

Glass-ceramics with cubic BaTiO3 as a major and hexagonal BaTi1-xFexO3-δ as a second phase were prepared by crystallization at 560°C in a glass with the composition 20.1Na2O/23TiO2/23.1BaO/3Al2O3/7.6B2O3/17.4SiO2/5.8Fe2O3. X-ray photoelectron spectroscopy revealed presence of Ti⁴⁺ and Fe³⁺ ions in tetrahedral and octahedral coordination. Ba²⁺ occur...

In this work, we demonstrate a novel way of fabricating oriented composite nanowires consisting of arranged nanoparticles. The structures are produced by an advanced pulsed laser deposition technology involving the simultaneous ablation of two metal targets, Fe and Ag. The depositions are carried out in air at atmospheric pressure in the presence o...

A new trend in production of aluminum alloys used in construction in the automotive and aerospace industries is manufacture of composite materials. The structure and connection between matrix and particles are studied. This article considers the effect of TiC particles on the structure and properties of nano-microcrystalline alloys based on the Al–...

Glasses are synthesized in the system Na2O/BaO/TiO2/SiO2/B2O3/Al2O3 for different Na2O/Al2O3 ratios. X-ray photoelectron spectroscopy is utilized for the estimation of the valence states of titanium and the occurrence of solely Ti4+ is observed. The presence of bonds from the type Si-O-Al, Si-O-Si and Na-O-Si is detected in the glasses and it is co...

From a glass with the mol% composition 20.1 Na2O-3 Al2O3-23.1 BaO-23 TiO2-7.6 B2O3-17.4 SiO2-5.8 Fe2O3 cubic barium titanate was crystallized. Scanning and transmission electron microscopy micrographs of the prepared glass-ceramics show fine crystals agglomerated to globular particles. With increasing crystallization time, their volume concentratio...

The crystal and magnetic structures of the frustrated Co3O4 spinel oxide have been studied by means of neutron diffraction at high pressures up to 8.7 GPa in the temperature range 5 – 300 K. At ambient pressure, a coexistence of the long range ordered antiferromagnetic (AFM) phase and short range disordered phase below TN = 33 K was observed. At pr...

We modified by UV C light single to few-layered nano-sized graphene films deposited by pulsed laser deposition (PLD) on ~300-nm SiO 2 /Si substrates. The samples were irradiated by UV C lamps (wavelength of 254 nm) for 15, 30, 60 and 90 minutes in air. The influence of the modification was evaluated by following the changes in the X-ray photoelectr...

We modified carbon black (CB) with a large surface area (ENSACO 350 GRANULAR) by acetone and further thermal treatment. The pristine and the modified CB were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and Raman spectroscopy. The acetone treatment increases the content...

We present a microstructural study of nanocomposite samples based on iron oxide and a noble or a transition metal. The samples were produced by laser ablation in air at atmospheric pressure in the presence of a magnetic field. This technology allows production of oriented nanowires composed by nanoparticles. We applied a simultaneous laser ablation...

The protection of environment and human health stimulates intensive research for abatement of volatile organic compounds (VOCs) in the atmosphere. Complete catalytic oxidation is an efficient, environmentally friendly and economically feasible method for elimination of VOCs. This study aims to design high performing and cost-effective catalytic for...

In this work, we present fabrication and studies of pure and Pd-decorated ZnO nanostructures on Ag-coated substrates in view of gas-sensing application. The sensor elements consist of a dense structure of ZnO nanobelts. The chemical composition of the surface and gas-sensing properties of pure and Pd-doped nanostructures were studied and compared....

We present an original study of bulk epitaxial GaAsSb:N layers in view of photovoltaic applications of this material. The layers are grown on n-GaAs substrates by low-temperature liquid phase epitaxy (LPE). The grown GaAsSb:N layers exhibit reproducible properties and good optical quality. A number of experimental methods including x-ray diffractio...

Electrоdeposited Zn–Cr alloy coatings, containing 3.6, 5.4 and 9.4 mass % Cr were analysed by DSC and XRD. X-ray diffraction patterns of the samples show that when they are annealed to selected temperatures before and after the heat flow peaks of the DSC curve, there is an irreversible transition in all three alloys from η-(Zn, Cr) to ζ-CrZn13 phas...

The initial stages of deposition of graphene-like thin films have been studied by X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy and ellipsometry. The deposition process has been performed by sublimation of amorphous carbon on 330 nm SiO2/ (001) Si substrates with surface area of 15× 15 mm². The sublimation proce...

The modification of Cabot Corporation SPHERON 5000 carbon black by thermal treatment has been studied by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. The thermal annealing was performed at temperatures ranging from 500°C to 1150°C for 3 hours in an air-atmosphere. XPS established that th...

Pulsed laser deposition (PLD) of thin carbon films on SiO 2 /Si substrates was performed and the resulting films were examined by X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), Raman spectroscopy and ellipsometry. The deposition process was accomplished by laser ablation with Nd:YAG laser (third harmonic λ = 355 nm, pulse...

This paper presents an experimental investigation on laser-assisted fabrication of oriented nanowires composed by magnetic nanoparticles. The nanowires were produced by implementation of pulsed laser deposition in presence of a magnetic field. The application of an external magnetic field led to the formation of nanowires with a length of several m...

In situ time-resolved powder X-ray diffraction technique has been applied to investigate the structural evolution of Zn-exchanged polycrystalline titanosilicate ETS-4 upon heating within the temperature interval from 25 to 375 °C. The facilities of the Rietveld method as implemented in the software package GSAS have been used to control the plau-si...

The water-gas shift (WGS) reaction is a well-known industrial process used for the production of hydrogen. During the last few decades, it has attracted renewed attention due to the need for high-purity hydrogen for fuel-cell processing systems. The aim of the present study was to develop a cost-effective and catalytically efficient formulation tha...

In this work, we report fabrication of highly porous metal-oxide nanostructures by pulsed laser deposition performed in air at atmospheric pressure. The attention was focused on the structure, morphology, and composition of ZnO, TiO2, SnO2 and MoO3 metal oxides. The technology applied leads to formation of nanostructures composed by nanoparticles....

A laser-based technology is presented for fabrication of oriented nanowires composed by nanoparticles. The nanowires were produced by nanosecond pulsed laser deposition in air at atmospheric pressure in the presence of an external magnetic field. The technology described is relevant to the preparation of nanowires of magnetic materials. Applying an...

Glasses were prepared in the system (100 - x)(0.16Na2O/0.10MnO/0.74SiO2)/xFe2O3, (x = 15 and 25 in mol %) by the traditional melt-quenching technique. Some of them were subsequently crystallized at temperatures in the range from 520 to 700 °C for times from 10 min to 100 h. The valence states of Fe and Mn in selected glasses and glass-ceramics were...

The present work reports on the synthesis of glasses in the system Na2O/Al2O3/BaO/SrO/TiO2/B2O3/SiO2/Fe2O3 from which, after appropriate thermal treatment, barium titanate and strontium-substituted barium titanate glass-ceramics are crystallized. The characteristic temperatures of the glasses are determined by differential scanning calorimetry DSC...

Transparent organic-inorganic ureasilicate materials (ureasils) were synthesized by hydrolysis and co-condensation of two organic – inorganic precursors, obtained by reactions between 3-isocyanatepropyltriethoxysilane (ICPTES) and double terminated polyetheramine (Jeffamine), and between ICPTES and 3-aminopropyl triethoxysilane (APTES), respectivel...