Daniela Kovacheva

Daniela Kovacheva
Bulgarian Academy of Sciences | BAS · Institute of General and Inorganic Chemistry

Dr.

About

276
Publications
40,793
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4,668
Citations
Citations since 2017
91 Research Items
2544 Citations
20172018201920202021202220230100200300400500
20172018201920202021202220230100200300400500
20172018201920202021202220230100200300400500
20172018201920202021202220230100200300400500
Additional affiliations
October 1984 - present
Bulgarian Academy of Sciences
Position
  • Professor (Full)

Publications

Publications (276)
Article
Full-text available
Mono- and bimetallic Ni- and Ru-modified micro-mesoporous ZSM-5 catalysts were prepared by wet impregnation. The influence of the Ni content, the addition of Ru and the sequence of the modification by two metals on the physicochemical properties of the catalysts were studied. They were characterized by X-ray powder diffraction (XRD), N2 physisorpti...
Article
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The present study is focused on the development of cannabidiol-loaded polymeric nanomicelles as a drug delivery system with neuroprotective effects. Cannabidiol was loaded in Pluronic micelles (Pluronic P123 or its combination with Pluronic F127) possessing an average diameter smaller than 50 nm and high encapsulation efficiency for the hydrophobic...
Article
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ZnO doped with transition metals (Co, Fe, or Ni) that have non-compensated electron spins attracts particular interest as it can induce various magnetic phenomena and behaviors. The advanced atomic layer deposition (ALD) technique makes it possible to obtain very thin layers of doped ZnO with controllable thicknesses and compositions that are compa...
Article
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The present paper reports on MnCoFeO4 spinels with peculiar composition and their catalytic behavior in the reactions of complete oxidation of hydrocarbons. The samples were synthesized by solution combustion method with sucrose and citric acid as fuels. All samples were characterized by powder X-ray diffraction, N2-physisorption, scanning electron...
Article
The focus of our study is the development of novel ceria-based materials that can be successfully used as catalysts in various environmentally friendly processes due to a significant improvement of ceria intrinsic characteristics. In particular, the combination of ceria with low-dimensional carbon materials such as graphene oxide (GO) and nanodiamo...
Article
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Here, we report results on the magnetic and microwave properties of polycrystalline Y-type hexaferrite synthesized by sol-gel auto-combustion and acting as a filler in a composite microwave absorbing material. The reflection losses in the 1-20 GHz range of the Y-type hexaferrite powder dispersed homogeneously in a polymer matrix of silicon rubber w...
Article
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The activated carbons were produced from waste biomass using a mixture of used motor oil and diverse plastic residues, such as high-density polyethylene and thermoplastic phenol formaldehyde resins. They were used as a host matrix of iron and/or chromium oxide nanoparticles. The obtained materials were characterized in details by a complex of physi...
Article
Thermo-responsive copolymer, Agar agar-graft-poly(N-vinylcaproactam) (AA-g-PnVCL) was prepared by grafting N-vinylcaprolactam units onto the Agar backbone. Graft copolymer was synthesized by free-radical polymerization, using 2,2′-Azobis(2,4-dimethylvaleronitrile) (AMVN) as an initiator in the nitrogen atmosphere. In order to evaluate the compositi...
Article
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In the present study, we report on the facile prepared nanocomposites of reduced graphene oxide RGO with Cu and Ag. The synthesis was performed through an environmentally friendly and easy method by simultaneous reduction in solutions containing Cu2+ or Ag+ and graphene oxide (GO) using zinc powder as a reducing agent in aqueous acidic media. The c...
Article
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Rapidly solidified alloys (Al-Cu-Mg) 100-х Zn x , x = 0, 1, 2, 3 at.% were produced by Chill Block Melt Spinning (CBMS) method and their microstructure and crystallization behavior were studied. XRD and TEM analyzes showed that the obtained Al-Cu-Mg ribbon was 98 % amorphous, and the microstructure of the Zn-containing ribbons consisted of an amorp...
Article
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This study is focused on the design control of Cu–Zr–Ti oxide composites by the variation of the Zr/Ti ratio and the copper deposition procedure used. For the first time, these ternary composites were obtained by a combination of template-assisted hydrothermal techniques for the preparation of mesoporous ZrO2–TiO2 mixed oxides with diverse composit...
Conference Paper
Full-text available
We investigated the magnetic properties and magnetic phase transition in Y-type Ba0.5Sr1.5NiMgFe12O22 hexaferrite powder prepared by citrate sol-gel spontaneous combustion. The saturation magnetisation value of 32 emu/g at 4.2 K was lowered to 24 emu/g at 300 K. The magnetisations curves did not saturate even at a magnetic field of 50 kOe for both...
Article
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PdCuNiSb alloys were synthesized in IMSETHAC BAS laboratory. The base alloys were foamed with 2, 3 and 4 mass. % ZrH 2 in an induction furnace in Ar atmosphere. The microstructure and phase composition of the base Pd-42Cu28Ni10Sb20 alloys and the foams PdCuNiSb(Zr) were determined by SEM and XRD. The chemical compositions of the structural componen...
Article
The microstructure of manganese and cerium oxide bi-component materials with different Ce/Mn ratio, obtained by co-precipitation and template assisted hydrothermal techniques, is studied in details by nitrogen physisorption, XRD, SEM, TEM, XPS and Raman spectroscopies and TPR with hydrogen. The catalytic behaviour of the composites in total oxidati...
Article
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Nickel-decorated mesoporous cerium–iron oxide composites were synthesized by a combination of incipient wetness impregnation and template-assisted hydrothermal techniques. The effects of the Fe/Ce ratio and the calcination temperature of cerium–iron oxides on the phase composition, texture, structure, and redox properties of the composites were stu...
Article
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Materials with cation ratio Cu:Ni:Fe = 0.5:0.5:2 were prepared by sol-gel auto-combustion technique using corresponding metal nitrates and citric acid as complexating/fuel agent and ammonia for pH adjustment. For comparison, one sample was synthesised by the same method, but without pH adjustment, and one sample with nominal composition Cu0.5Ni0.5F...
Article
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Oregano oil (OrO) possesses well-pronounced antimicrobial properties but its application is limited due to low water solubility and possible instability. The aim of this study was to evaluate the possibility to incorporate OrO in an aqueous dispersion of chitosan–alginate nanoparticles and how this will affect its antimicrobial activity. The encaps...
Article
Hybrid organic-inorganic perovskites (HOIPs) have attracted considerable attention, especially organometal trihalide perovskite, as promising materials for high-efficient solar cells. An interesting organic cation that can be incorporated in perovskite structure is the guanidinium (GUA) cation. Therefore, a number of investigations have been perfor...
Article
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Carbon foams with different surface functionality and tailored texture characteristics were prepared from mixtures containing coal tar pitch and furfural in different proportions. The obtained materials were used as a host matrix for the preparation of zinc- and cobalt-mixed ferrite nanoparticles. The texture, morphology, phase composition, and the...
Article
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In this work, we continued our systematic investigations on synthesis, structural studies, and electrochemical behavior of Ni-rich materials Li[NixCoyMnz]O2 (x + y + z = 1; x ≥ 0.8) for advanced lithium-ion batteries (LIBs). We focused, herein, on LiNi0.85Co0.10Mn0.05O2 (NCM85) and demonstrated that doping this material with high-charge cation Mo6+...
Article
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Original method for direct preparation of nanocomposites of reduced gra-phene oxide and metal nanoparticles was developed. The technological scheme involves the preparation of graphene oxide by modified Hummers' method and the subsequent composite synthesis by simultaneous reduction of mixture of GO and the appropriate silver and copper salts. The...
Article
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BiFeO3 is an interesting material due to its multiferroic properties. It attracts attention due to its potential applications in spintronics and in microelectronics for data storage, among others. Single-phase bulk material from BiFeO3 is difficult to synthesize. The kinetics of perovskite phase formation most often leads to the presence of impurit...
Article
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This work is focused on the preparation of Ni0.5M0.5Fe2O4 mixed ferrites (M = Zn or Cu), supported on nanoporous carbons materials. The carbon supports are obtained from various waste residues, such as peach stones from the canning industry and by-products from the low rank coals pyrolysis. X-ray diffraction (XRD), nitrogen physisorption, high-reso...
Article
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In this work, the feasibility of atomic layer deposition (ALD) to prepare transition metal (Ni-, Co- or Fe-) doped ZnO thin films have been studied. The effects of dopant on the structure, morphology and optical properties of films have been investigated by a number of various techniques: X-ray diffraction (XRD), X-ray photoelectron spectroscopy (X...
Conference Paper
Full-text available
The effect is reported of substituting the non-magnetic Zn2+ cations with magnetic Ni2+ cations, and of the magnetic Fe3+ cations with non-magnetic Al3+ cations in Ba0.5Sr1.5Zn0.5Ni1.5Fe11.92Al0.08O22 on the resulting magnetic properties. The Y-type hexaferrite powders were synthesized by citric acid sol-gel auto-combustion, followed by appropriate...
Article
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AlN thin films (∼25 nm) have been grown with a Beneq TFS-200 ALD reactor on Si (111) substrates. TMA (trimethylaluminum) and NH 3 were used as precursors. The substrate temperatures were 330°C, ALD cycles 550. In order to study the stoichiometry of AlN film the TMA and NH 3 doses (pulses) were varied from 60 to 180 ms and from 60 to 90 ms, respecti...
Article
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The magneto-optical (MO) properties of ZnO / Ni transition metal oxide (TMO) nano-laminate structures prepared by Atomic Layer Deposition (ALD) have been investigated. The structural (XRD) and chemical composition (XPS) analysis confirm the ZnO formation and corresponding effect of Ni incorporation in the crystal lattice. The XPS identification of...
Article
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We report studies on the effect of substituting the magnetic Fe ³⁺ cations with nonmagnetic Al ³⁺ cations in Y-type hexaferrite Ba 0.5 Sr 1.5 Zn 2 Fe 11.92 Al 0.08 O 22 powders on their magnetic properties and especially on the magnetic phase transitions responsible for observing the magnetoelectric effect. In this research, the Y-type hexaferrite...
Preprint
Full-text available
Reduced graphene oxide (RGO) is a promising material for environmental protection, energy storage, but still very few papers have reported its use as catalyst support. In the present study we report the preparation of novel RGO-supported nickel-zinc ferrite catalyst for hydrogen production from methanol. The catalyst is highly active and reaches 10...
Article
This study presents the potential of Mobil Composition of Matter No.41 (MCM-41) and Hollow Mesoporous Silica (HMS) as an efficient drug delivery system for anticancer drug bicalutamide (BLT). Bicalutamide loaded nanoparticles were characterized by using X-ray diffraction (XRD), N2-physisorption, dynamic light scattering (DLS), TEM and attenuated to...
Article
Full-text available
A series of mesoporous cerium-iron binary oxides was prepared by a hydrothermal technique using CTAB as a template. The influence of the Fe/Ce ratio and the variations in the preparation techniques such as the type of solvent and the precipitation agent, the approach of the template release, and the temperature of calcination on the phase compositi...
Article
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Materials with nominal composition Cu0.5Ni0.5Fe2O4 were prepared by sol-gel auto-combustion technique using corresponding metal nitrates and citric acid as complexating agent/fuel agent. Different ratios between citric acid and metal ions were used to control the combustion reaction. For comparison, Cu0.5Ni0.5Fe2O4 ferrite was also synthesised by c...
Article
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Electrodeposited and physically vapor-deposited Zn-Cr alloy coatings consist of several non-equilibrium Zn-Cr phases – hexagonal η-(Zn, Cr), hexagonal δ-(Zn, Cr), and cubic Γ-(Zn, Cr) – which have different corrosion characteristics. Upon annealing, these non-equilibrium phases transform into ζ-CrZn13 phase and η-Zn or α-Cr, depending on the Cr con...
Article
The synthesis of guanidinium lead iodide, C(NH2)3PbI3 (GUAPbI3), was conducted by slow evaporation of the mixture obtained by dissolving PbI2 and C(NH2)3I in acetonitrile. When the evaporation is done at 40 ºC, a yellow needle-like crystals are being formed. The sample was characterized by elemental analysis, density measurements, scanning electron...
Article
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The present study aims at removal of hexavalent chromium from aqueous solution using manganese ferrite (MnFe 2 O 4) nanoparticles. The investigated material was obtained by solution combustion method using starting reagents Mn(NO 3) 2 .4H 2 O and Fe(NO 3) 3 .9H 2 O (as oxidizers) and citric acid (as a re-ducer). Nanoparticles of MnFe 2 O 4 were cha...
Article
Co-precipitated NiAl and NiMgAl layered double hydroxides (LDHs) were prepared at M²⁺/Al³⁺ molar ratio of 2.5/1 and subsequently promoted with gold targeting to be studied as catalysts and supports of gold particles in the hydrogen production via water-gas shift (WGS) reaction. Powder X-ray diffraction and N2 physisorption before and after WGS test...
Article
A propane combustion catalyst was prepared by supporting of Pd on optimized multiphase composition, containing Al 2 O 3 , La 2 O 3 and CeO 2 aiming for possible application in catalytic converters for abatement of propane in waste gases. The catalyst characterization has been made by N 2 - physisorption, XRD, SEM/EDX, TEM and XPS. The obtained valu...
Article
The present study evaluated the impact of doxorubicin encapsulation in chitosan-alginate nanoparticles on its stability, cytotoxic potential in multidrug resistant lymphoma cells (L5178 MDR1) and toxicity in H9c2 cardioblasts. The results indicated that the encapsulation stabilized the drug against degradation due to its inner location in nanoparti...
Article
Full-text available
The data presented has to do with identifying the various phases arising during the synthesis of the Y-type hexaferrite series Ba0.5Sr1.5Zn2-xNixFe12O22 by auto-combustion that we deem important for their microstructural and magnetic properties. The data and the related analyses support the research paper “Ni-substitution effect on the properties o...
Article
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We report results on the structural and microwave properties and magnetic phase transitions in polycrystalline Sr3Co2Fe24O41 hexaferrite synthesized by sol-gel auto-combustion and acting as a filler in a composite microwave absorbing material. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves revealed a change in the magnetizat...
Article
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Abstract. Ni-, Co- and Fe-doped ZnO films were grown by atomic layer deposition on Si and glass substrates. The structures prepared were studied and characterized by XRD, XPS, ellipsometry and FTIR. The crystalline ZnO structure showed a strong dependence on the substrate used and the type of transition metal ion despite of the low doping levels....
Article
Full-text available
Thin AlN films were grown on Si substrates in a Beneq TFS-200 ALD reactor. The atomic layer deposition (ALD) process consisted of two half cycles – aluminum adsorption and nitridization separated by a purging step. TMA (trimethylaluminum) and NH 3 were used as precursors, and nitrogen (N 2 ), as a carrier gas. The pulse duration, purging time, depo...
Article
Full-text available
We present details of the microstructural properties of Y- (Ba 2 Mg 2 Fe 12 O 22 , Ba 0.5 Sr 1.5 Zn 2 Fe 12 O 22 , Ba 0.5 Sr 1.5 Zn 2 Al 0.08 Fe11.92O 22 ) and Z-type (Sr 3 Co 2 Fe 24 O 41 ) hexaferrite thick films deposited by screen printing and drop casting on unpolished polycrystalline Al 2 O 3 substrates. The hexaferrites thick films obtained...
Article
We consider the influence of the magnetic cation (Ni²⁺) substitution on the structural and magnetic properties of Ba0.5Sr1.5Zn2-xNixFe12O22 (x = 0.8, 1, 1.5) powders. The powders were synthesized by using the citric-acid sol-gel auto-combustion method. Their ac-magnetization was measured in an ac-magnetic field with an amplitude of 10 Oe and a freq...
Article
Hydrothermally obtained mesoporous ceria-titania mixed oxides with different composition are modified with copper using incipient wetness impregnation and “chemisorption-hydrolysis” techniques. Their catalytic properties in methanol decomposition as a source of hydrogen and total oxidation of ethyl acetate as representative volatile organic polluta...
Article
Full-text available
A nanocomposite CrAlSiN–AlSiN coating with periodically modulated composition was developed and investigated regarding the effect of the composition and structure on the mechanical properties. The modulation was performed by variation of the pressure, cathode current and bias voltage during deposition. The structure and composition of the coating w...
Article
The influence of the glycine-glycerol fuel mixing ratio on the structure, morphology, magnetic and catalytic properties of nanosized MnFe2O4 prepared by solution combustion method was investigated. The samples were synthesized using mixture of glycerol and glycine in the reducing power ratios 1:0, 0.75:0.25, 0.5:0.5, and 0.25:0.75. All samples were...
Article
New and complex results on catalytic activity, thermal stability, effect of H 2 O and SO 2 on the Pd/La 2 O 3 -CeO 2 -Al 2 O 3 model system in methane combustion have been obtained. The catalyst characterization has been made by N 2 - physisorption, XRD, SEM/EDX, HRTEM, XPS, TPD, TPR and FTIR methods. The observed high activity is related to the st...
Article
Round-shaped natural graphite is commonly used as anode material for rechargeable lithium-ion batteries. We report atypical electrochemical behavior of round-shaped graphite anodes in Li-ion batteries: an intriguing phenomenon whereby substantial progressive increase in capacity is observed over tens of cycles. To understand the reasons underlying...
Article
High quality activated carbon was prepared using by-products from the pyrolysis of low rank coals as a precursor. The obtained carbon material was applied as a host matrix of nanosized MFe2O4 ferrites (M = Ni, Cu or Zn). XRD, Mössbauer and TPR analyses were performed for samples characterization and their catalytic behavior in methanol decompositio...
Article
Leptothrix genus bacteria were cultivated in Lieske medium in presence of anodic Al2O3/Al to synthesize γ-FeOOH as a biogenic precursor for catalyst preparation. Different amounts of biogenic iron (0.6, 0.9, 9.2% Fe) were deposited. γ-FeOOH deposition on the support was identified the process being determined by the anodic Al2O3 surface structure....
Article
The work reported herein is an important continuation of our recent experimental and computational studies on Li[NixCoyMnz]O2 (x+y+z=1) cathode materials for Li ion batteries, containing minor amounts of multivalent cationic dopants like Al3+, Zr4+, W6+, Mo6+. Based on DFT calculations for LiNi0.8Co0.1Mn0.1O2, it was concluded that Mo6+ cations pre...
Article
We present results from a study on the influence of the preparation technique on the structural and magnetic properties of Ba0.5Sr1.5Zn2Fe12O22 powders synthesized by citric-acid sol-gel auto-combustion and sonochemistry and characterized by X-ray diffraction, scanning electron microscopy and magnetic measurements. Two magnetic intermediate phases...
Article
Full-text available
Ba2Mg0.4Co1.6Fe12O22 was prepared in powder form by sonochemical co-precipitation and examined by X-ray diffraction, Mössbauer spectroscopy and magnetization measurements. Careful XRD data analyses revealed the Y-type hexaferrite structure as an almost pure phase with a very small amount of CoFe2O4 as an impurity phase (about 1.4%). No substantial...
Article
Full-text available
Three samples of NiAl layered double hydroxides with takovite-like structure were prepared by a co-precipitation method at Ni²⁺/Al³⁺ molar ratios of 1.5, 2.5 and 4.0. The samples were investigated as catalysts for hydrogen production by means of water–gas shift reaction (WGSR). The properties and catalytic behavior of the unmodified as-synthesized...
Article
Silver nanoparticles (AgNPs)were synthesized by reduction of Ag ⁺ with four extracts of Rosa damascena waste: post-distillation water (PW), water extract (WE), 30% (30 EE)and 70% (70 EE)ethanol extracts. The ethanolic extracts were rich in polyphenols and particularly catechin and epicatechin (1388.01 ± 2.27 and 677.47 ± 2.03 μgmL ⁻¹ , respectively...
Article
This study is aimed at the development of intelligent approach for clean energy production via valorization of industrial waste by-products. The proposed scheme is based on the preparation of activated carbon based catalysts for methanol decomposition as a source of hydrogen. Peach stones from the canning industry and by-products from low-rank coal...
Article
Lomefloxacin (LF) is interesting as a model molecule from a safety point of view because of its high potential for serious adverse drug effects (i.e. phototoxic reactions). In this study, MCM-41 mesoporous silica nanoparticles (MCM-41) were loaded with lomefloxacin, aiming to overcome the drug’s intrinsic cytotoxicity. The good biocompatibility of...
Conference Paper
We report results from a study on the influence of the substitution of Zn²⁺ cations in the Y-type Ba0.5Sr1.5Zn2Fe12O22 hexaferrite, known for strong magnetoelectric coupling, with magnetic cations, such as Ni²⁺, on its structural and magnetic properties. Polycrystalline samples of Ba0.5Sr1.5ZnNiFe12O22 were synthesized by citric acid sol-gel auto-c...
Conference Paper
Full-text available
The functional properties of dark, milk and white chocolate with 5% cow butter or sesame oil were improved by addition of 2% or 3% conjugated linoleic acid (CLA). Microbiological, rheological, X-ray diffraction and sensory analysis were carried out. A sensory profile of chocolate with (CLA) was recorded. The acid number in percent of oleic acid was...
Article
Herein, we present development of new pH-responsive drug delivery systems for D3-dopamine receptor agonist pramipexole, based on its encapsulation in MCM-41 mesoporous silica particles. Pramipexole loaded particles were further coated with chitosan and/or sodium alginate in order to modify drug release. The prepared pramipexole loaded nanoparticles...
Article
The improvement of the electrochemical properties of Zn-electrode in the Ni-Zn battery cell by adding two types of B(Pb)SrCaCuO conducting ceramics ((Bi1.7Pb0.3Sr2CuOx (B(Pb)SCCO 2201) and Bi1,7Pb0,3Sr2CaCu2Ox (B(Pb)SCO 2212)) is confirmed. Their presence in the zinc electrode mass increases the discharge capacity of the battery, forming a strong c...
Article
Full-text available
In this study, spherical hollow mesoporous silica (HMS) particles with average size of 550 nm were loaded with dopamine-receptor agonist pramipexole, as a model drug. High drug loading (55%) was achieved by its incorporation in the reservoir structure of HMS. The newly developed drug-delivery systems were further double-coated with bioadhesive poly...
Article
Porous inorganic materials have been extensively applied as enzyme carriers due to their high mechanic stability and high specific surface area, resistance to microbial attack, stability in organic solvents, and stability upon heating. In recent years, enzymes immobilised on nanosized materials have attracted scientist attention with regard to new...
Article
A series of titania-tin oxide binary nanosized mesoporous materials with various composition were successfully obtained by template assisted hydrothermal technique. They were characterized by nitrogen physisorption, XRD, TEM, XPS, UV-Vis, FTIR of adsorbed pyridine and Raman spectroscopes. The reduction properties of the composites were studied by T...