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Klara Castkova

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Muhammad Akhyar Farrukh

Central University of Punjab

PROF. OM PRAKASH SINHA

Amity University

Sandip Chakrabarti

Amity University

Prof.Dr. İbrahim USLU

Gazi University

Kenneth Vecchio

University of California, San Diego

Rodrigo Feitosa

Universidade Federal do Paraná

University of Illinois at Urbana-Champaign

Massachusetts Institute of Technology (MIT)

Dinesh Rangappa

Visvesvaraya Technological University

Parmendra Bajpai

Guru Ghasidas University

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Papers by Klara Castkova

Piezo-Enhanced Photocatalytic Activity of the Electrospun Fibrous Magnetic PVDF/BiFeO3 Membrane

Polymers

Creating stimulus-sensitive smart catalysts capable of decomposing organic dyes with high efficie... more Creating stimulus-sensitive smart catalysts capable of decomposing organic dyes with high efficiency is a critical task in ecology. Combining the advantages of photoactive piezoelectric nanomaterials and ferroelectric polymers can effectively solve this problem by collecting mechanical vibrations and light energy. Using the electrospinning method, we synthesized hybrid polymer-inorganic nanocomposite fiber membranes based on polyvinylidene fluoride (PVDF) and bismuth ferrite (BFO). The samples were studied by scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), total transmittance and diffuse reflectance, X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vibrating-sample magnetometer (VSM), and piezopotential measurements. It has been demonstrated that the addition of BFO leads to an increase in the proportion of the polar phase from 86.5% to 96.1% due to the surface ion–dipole interactio...

Electrode Spacing as a Determinant of the Output Performance of Planar-Type Photodetectors Based on Methylammonium Lead Bromide Perovskite Single Crystals

Methylammonium lead bromide is a very perspective hybrid semiconductor material, suitable for hig... more Methylammonium lead bromide is a very perspective hybrid semiconductor material, suitable for high-sensitive, filter-free photodetection of electromagnetic radiation. Herein, we studied the effect of electrode spacing on the output performance and stability of planar-type photodetectors based on high-quality MAPbBr3 single crystals. Such crystals, as large as 4.5×4.5×1.2 mm3 were synthesized via the inverse temperature crystallization method and were further used for the fabrication of planar Au/MAPbBr3/Au photodetectors with variable electrode spacing (in the range between 125 and 25 μm). We report that the electrode spacing has a profound impact on photocurrent densities and key detector parameters (responsivity R, external quantum efficiency EQE, and specific detectivity D*). In the studied fivefold electrode spacing, the photocurrent density increased over 4 times, with decreasing active area of the devices. This effect is attributed to intrinsic photocurrent amplification. Based on the transient photocurrent measurements and calculated key parameters, we determined the device sample with the best output performance. The champion sample with an electrode spacing of 50 μm exhibited great detection ability, especially for a low light intensity of 200 nWcm-2, for which we calculated the R of 19.55 A W-1, EQE of 4253%, and D* of 3.42 × 1012 Jones (cm Hz1/2 W-1). Moreover, the functional stability of this device showed a minimal reduction of photodetection ability after 2000 cycles, which makes it very promising for the next generation of optoelectronic devices.

Influence of LA/Ti molar ratio on the complex synthesis of anatase/brookite nanoparticles and their hydrogen production

International Journal of Hydrogen Energy, 2021

Abstract Heterophase TiO2 nanoparticles formed in the presence of a very low concentration of a s... more Abstract Heterophase TiO2 nanoparticles formed in the presence of a very low concentration of a substance with two donor groups were studied and the mechanism of their formation was proposed. The TiO2 nanoparticles were prepared by low-temperature hydrolysis and polycondensation of Ti (IV) n-propoxide in the presence of lactic acid (LA). The phase composition of the nanoparticles was controlled by the LA/Ti molar ratio ranging from 0.02 to 3.0. At low LA/Ti molar ratios, biphasic anatase-brookite was formed, at average LA/Ti molar ratios, anatase-brookite-rutile particles were formed, and at high molar ratios, pure anatase was formed. By using the low LA/Ti molar ratios, the low-temperature colloidal synthesis made it possible to control the composition of heterophase mesoporous TiO2 nanoparticles with a high specific surface area and high photocatalytic activity in the production of hydrogen by water splitting. The highest photocatalytic activity was exhibited by anatase-brookite nanoparticles containing 46–65% brookite, synthesized at LA/Ti molar ratios in the range of 0. 033 to 0.1.

Piezoelectric PVDF Elements and Systems for Mechanical Engineering Applications

2020 19th International Conference on Mechatronics - Mechatronika (ME), 2020

This paper deals with a review of potential technical applications of piezoelectric polymer syste... more This paper deals with a review of potential technical applications of piezoelectric polymer systems for Industry 4.0 applications. Polyvinylidene difluoride (PVDF) is a highly non-reactive thermoplastic fluoropolymer produced by the polymerization of vinylidene difluoride. Copolymers of PVDF with beta phase could be used in piezoelectric and triboelectric applications which are presented in this paper. PVDF is a candidate for harvesters and sensors that cannot be realized with piezoceramics or single crystals. Both technical applications for sensing and energy harvesting are presented in this paper. These technologies could be useful in mechanical engineering applications like a strain sensor, strain energy harvesting, vibration energy harvester, load sensing and triboelectric sensors/generators. The opportunity for future usage in Industry 4.0 devices is outlined and experimental results of individual systems are presented.

SEM imaging and XPS characterization of doped PVDF fibers

E3S Web of Conferences, 2021

Polyvinylidene fluoride (PVDF) is one of the most promising electroactive polymers; it exhibits e... more Polyvinylidene fluoride (PVDF) is one of the most promising electroactive polymers; it exhibits excellent electroactive behaviours, good biocompatibility, excellent chemical resistance, and thermal stability, rendering it an attractive material for biomedical, electronic, environmental and energy harvesting applications. This work aims to further improve its properties by the inclusion of powders of piezoactive materials. Polyvinylidene fluoride was formed by electrospinning into fibres with a thickness of 1.5-0.3 µm and then examined in a scanning electron microscope. The work offers a description of the current procedure in the preparation of samples and their modification for examination in a scanning electron microscope, characterizes the individual components of doped fibres and deals with specific instruments used for various analytical methods. The work contains a theoretical introduction to the analytical methods to which the samples will be further subjected, such as energy...

Structure Tuning and Electrical Properties of Mixed PVDF and Nylon Nanofibers

Materials, 2021

The paper specifies the electrostatic spinning process of specific polymeric materials, such as p... more The paper specifies the electrostatic spinning process of specific polymeric materials, such as polyvinylidene fluoride (PVDF), polyamide-6 (PA6, Nylon-6) and their combination PVDF/PA6. By combining nanofibers from two different materials during the spinning process, new structures with different mechanical, chemical, and physical properties can be created. The materials and their combinations were subjected to several measurements: scanning electron microscopy (SEM) to capture topography; contact angle of the liquid wettability on the sample surface to observe hydrophobicity and hydrophilicity; crystallization events were determined by differential scanning calorimetry (DSC); X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FT-IR) to describe properties and their changes at the chemical level. Furthermore, for the electrical properties of the sample, the dielectric characteristics and the piezoelectric coefficient were measur...

Case Study of Polyvinylidene Fluoride Doping by Carbon Nanotubes

Materials, 2021

Modern material science often makes use of polyvinylidene fluoride thin films because of various ... more Modern material science often makes use of polyvinylidene fluoride thin films because of various properties, like a high thermal and chemical stability, or a ferroelectric, pyroelectric and piezoelectric activity. Fibers of this polymer material are, on the other hand, much less explored due to various issues presented by the fibrous form. By introducing carbon nanotubes via electrospinning, it is possible to affect the chemical and electrical properties of the resulting composite. In the case of this paper, the focus was on the further improvement of interesting polyvinylidene fluoride properties by incorporating carbon nanotubes, such as changing the concentration of crystalline phases and the resulting increase of the dielectric constant and conductivity. These changes in properties have been explored by several methods that focused on a structural, chemical and electrical point of view. The resulting obtained data have been documented to create a basis for further research and t...

Water‐born 3D nanofiber mats using cost‐effective centrifugal spinning: comparison with electrospinning process: A complex study

Journal of Applied Polymer Science, 2020

A comparison of the electrostatic and centrifugal spinning of poly(vinyl alcohol) and poly(vinyl ... more A comparison of the electrostatic and centrifugal spinning of poly(vinyl alcohol) and poly(vinyl pyrrolidone) is shown in terms of the resulting fiber morphology and the process conditions. Specific parameters of centrifugal spinning, such rotational speed of spinneret and the relative humidity, were extensively investigated in details. Morphologies and diameters of resulting fiber mats were investigated by a scanning electron microscopy and compared between the two spinning techniques. The results revealed that formation of fibers is mainly affected by the initial polymer concentrations (and resulting viscosities) of polymeric solutions, which is in line with previous reports. However, the key novel finding of this work is that increasing relative humidity during centrifugal spinning process leads to greatly reduced fiber diameters to the levels typical for electrospinning. The obtained comparison is discussed and clearly shows technological advantages of the centrifugal spinning o...

High strength alumina tapes prepared by gel-tape casting method

Ceramics International, 2021

Abstract In the current work, high strength alumina (Al2O3) thin tapes were prepared by a novel g... more Abstract In the current work, high strength alumina (Al2O3) thin tapes were prepared by a novel gel-tape casting method. The water-based slurries were gelled by the polymerization of the epoxy monomers. Low viscosity slurries consisting of nanometer-sized alumina particles were prepared with a solid loading reaching 42 vol%. Sodium and ammonium polyacrylate dispersants were used for alumina particle dispersion and stabilization. The individual Al2O3 tapes reached a relative density of over 99.5% and a grain size between 1.1 and 1.3 μm after pressureless sintering at 1450 °C. The biaxial strength of sintered samples was measured in the ball-on-three-balls setup and the values of characteristic Weibull strength up to 1400 MPa were obtained for as-sintered tapes with a thickness of about 190 μm. The effect of sodium and ammonium-based polyacrylate dispersants on tape processing and properties of the Al2O3 tapes were investigated and explained.

Influence of Hydroxyapatite Nanoparticles and Surface Plasma Treatment on Bioactivity of Polycaprolactone Nanofibers

Polymers, 2020

Nanofibers are well known as a beneficial type of structure for tissue engineering. As a result o... more Nanofibers are well known as a beneficial type of structure for tissue engineering. As a result of the high acquisition cost of the natural polymers and their environmentally problematic treatment (toxic dissolution agents), artificial polymers seem to be the better choice for medical use. In the present study, polycaprolactone nano-sized fibrous structures were prepared by the electrospinning method. The impact of material morphology (random or parallelly oriented fibers versus continuous layer) and the presence of a fraction of hydroxyapatite nanoparticles on cell proliferation was tested. In addition, the effect of improving the material wettability by a low temperature argon discharge plasma treatment was evaluated, too. We have shown that both hydroxyapatite particles as well as plasma surface treatment are beneficial for the cell proliferation. The significant impact of both influences was evident during the first 48 h of the test: the hydroxyapatite particles in polycaprolact...

Investigation of Detergent-Modified Enzymomimetic Activities of TEMED-Templated Nanoceria Towards Fluorescent Detection of Their Cellular Uptake

ChemistrySelect, 2018

Ceria nanoparticles can catalyze many redox reactions that resemble reactions catalyzed by natura... more Ceria nanoparticles can catalyze many redox reactions that resemble reactions catalyzed by naturally occurring enzymes, such as peroxidase, catalase, haloperoxidase or phosphatase. This makes nanoceria an attractive material for biomedical and sensing applications. Presence of detergents dramatically affects the catalytic activity of nanoceria. The catalytic activity is also strongly influenced by biogenic compounds present in the sample. Furthermore, biomedical applications are hindered by the difficulties to detect nanoceria uptake by cells. Therefore, we have developed a new fast and sensitive fluorescent haloperoxidase assay based on fluorescein bromination in presence of CTAB to detect uptake of CeO 2 nanoparticles by cells in vitro. Moreover, catalytic activities of standard nanoceria (CeO 2 ) were compared to nanoceria hydrates (CeO 2 .xH 2 O) that are easier for preparation and might be stabilized by biologically relevant molecules allowing for a specific targeting to cells or tissues. We have developed a new approach to produce CeO 2 .xH 2 O in presence of TEMED and analyzed whether the presence of H 2 O 2 during the synthesis influences the catalytic activity of produced particles.

Processing of 0.55(Ba0.9Ca0.1)TiO3‐0.45Ba(Sn0.2Ti0.8)O3 lead‐free ceramics with high piezoelectricity

Journal of the American Ceramic Society, 2020

We report a large piezoelectric constant (d33), 720 pC/N and converse piezoelectric constant (d33... more We report a large piezoelectric constant (d33), 720 pC/N and converse piezoelectric constant (d33*), 2215 pm/V for 0.55(Ba0.9Ca0.1)TiO3‐0.45Ba(Sn0.2Ti0.8)O3 ceramics; the biggest value achieved for lead‐free piezoceramics so far. The ceramic powders were calcined between 1050°C‐1350°C and sintered at 1480°C. The best properties were obtained at a calcination temperature (CT) of 1350°C. The fitting combination of processing and microstructural parameters for example, initial powder particle size >2 µm, ceramics density ~95%, and grain size ~40 µm led to a formation of orthorhombic‐tetragonal‐pseudo‐cubic (O‐T‐PC) mixed phase boundary near room temperature, supported by Raman spectra, pointed to the extremely high piezoelectric activity. These conditions significantly increase piezoelectric constants, together with high relative permittivity (εr) >5000 and a low loss tangent (tan δ) of 0.029. In addition, the d33 value stabilizes in the range of 400‐500 pC/N for all samples calc...

Prevalent anatase crystalline phase increases the cytotoxicity of biphasic titanium dioxide nanoparticles in mammalian cells

Colloids and Surfaces B: Biointerfaces, 2019

Nanoparticular form of titanium dioxide (TiO 2 NPs) belongs to important industrial material. Des... more Nanoparticular form of titanium dioxide (TiO 2 NPs) belongs to important industrial material. Despite being widely used, serious contradictions regarding biosafety of TiO 2 NPs remain. We anticipate that such discrepancies could be due to a lack of understanding of a linkage between TiO 2 NPs phase composition and cytotoxicity. Therefore, we synthesized two types of biphasic TiO 2 NPs differing in an anatase-brookite phase composition. The study presents an array of in vitro data suggesting that TiO 2 NPs with a prevailing anatase phase composition possess higher cytotoxicity compared to TiO 2 NPs with an equal anatase-brookite crystallinity. This phenomenon was evidenced by significantly higher inhibition of metabolic activity and growth of epithelial and neuroblast-like cells. Moreover, anatase-prevailing TiO 2 NPs tend to produce higher amount of reactive oxygen species resulting in DNA fragmentation. Further insights into the molecular aspects of cytotoxicity of anatase-prevailing TiO 2 NPs were obtained by comparative proteomics delineating that TiO 2 NPs deregulate expression of a variety of proteins and associated pathways. This inevitably results in a decreased cellular ability to detoxify reactive oxygen species and respond to various stress conditions. The study provides novel data that add another piece to the jigsaw of the relation between structural features of NPs and biosafety.

Synthesis and characterization of Na2Ti6O13 and Na2Ti6O13/Na2Ti3O7 sodium titanates with nanorod-like structure as negative electrode materials for sodium-ion batteries

Journal of Energy Storage, 2017

In this work, we report microwave assisted hydrothermal synthesis of monoclinic sodium titanates ... more In this work, we report microwave assisted hydrothermal synthesis of monoclinic sodium titanates with either tunnel or with mixed tunnel/layered structure. Single phase Na 2 Ti 6 O 13 and mixed phase Na 2 Ti 6 O 13 / Na 2 Ti 3 O 7 titanates were studied by electrochemical measurements with cyclic voltammetry, impedance spectroscopy and galvanostatic cycling. SEM images revealed that all the synthesized materials consist of rods with widths in the range of tenths to hundreds nanometers. XRD analysis was used for determination of the phase composition and crystallite size. It was shown that mixed phase electrode material reveals higher capacity and wider active voltage range but has also lower cycling stability. The insertion potential of layered titanate Na 2 Ti 3 O 7 is much lower than in the case of Na 2 T i6 O 9 and the specific capacity of mixed titanate in the first cycle is double the capacity of pure Na 2 Ti 6 O 9 . Although presence of layered titanate contributed to high specific capacity in early cycling, it allowed a considerable decrease in specific capacity at higher numbers of cycles.

The Effect of the Thermosensitive Biodegradable PLGA–PEG–PLGA Copolymer on the Rheological, Structural and Mechanical Properties of Thixotropic Self-Hardening Tricalcium Phosphate Cement

International Journal of Molecular Sciences, 2019

The current limitations of calcium phosphate cements (CPCs) used in the field of bone regeneratio... more The current limitations of calcium phosphate cements (CPCs) used in the field of bone regeneration consist of their brittleness, low injectability, disintegration in body fluids and low biodegradability. Moreover, no method is currently available to measure the setting time of CPCs in correlation with the evolution of the setting reaction. The study proposes that it is possible to improve and tune the properties of CPCs via the addition of a thermosensitive, biodegradable, thixotropic copolymer based on poly(lactic acid), poly(glycolic acid) and poly(ethylene glycol) (PLGA–PEG–PLGA) which undergoes gelation under physiological conditions. The setting times of alpha-tricalcium phosphate (α-TCP) mixed with aqueous solutions of PLGA–PEG–PLGA determined by means of time-sweep curves revealed a lag phase during the dissolution of the α-TCP particles. The magnitude of the storage modulus at lag phase depends on the liquid to powder ratio, the copolymer concentration and temperature. A sha...

Effect of transition metal on stability and activity of La-Ca-M-(Al)-O (M = Co, Cr, Fe and Mn) perovskite oxides during partial oxidation of methane

International Journal of Hydrogen Energy, 2017

Perovskite oxides of the type of La x Ca 1-x M y Al 1-y O 3-d (M ¼ Co, Cr, Fe, Mn; x ¼ 0.5; y ¼ 0... more Perovskite oxides of the type of La x Ca 1-x M y Al 1-y O 3-d (M ¼ Co, Cr, Fe, Mn; x ¼ 0.5; y ¼ 0.7e1.0) were prepared using the polymerization methods and evaluated via N 2 adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), energy dispersive X-ray (EDX) spectroscopy, temperature-programmed reduction by hydrogen (TPR-H 2 ) and temperature-programmed oxidation by oxygen (TPO-O 2 ). Catalytic behaviour of the perovskite oxides during methane oxidation was studied using a tubular fixed-bed reactor. In a partial oxidation, which proceeded in two steps, there was total oxidation in the first step and CO 2 and H 2 O were formed; in the second step, the total oxidation products oxidized methane by (dry and wet) reforming reactions to yield CO and H 2 . Total oxidation and the two reforming reactions proceeded on two types of an active centre formed by transition metal ions, oxygen vacancies and oxide ions. The catalytic system La-Ca-Co-Al-O which contained aluminium, decomposed in partial oxidation of methane (POM) into a composite that contained firmly bonded cobalt nanoparticles in the surface of a substrate made up of La 2 O 3 , CaO and Al 2 O 3 which catalysed POM with a high methane conversion and hydrogen selectivity.

Mixed Sodium Titanate As an Anode for a Sodium-Ion Battery

ECS Transactions, 2016

Sodium-ion batteries are very promising complementary power sources usable in applications where ... more Sodium-ion batteries are very promising complementary power sources usable in applications where cost of starting materials and battery itself is more important than its energy density. Mixed sodium titanate anode material with two electroactive crystallographic phases was successfully synthesized via microwave assisted hydrothermal synthesis. The electrochemical performance of Na2Ti3O7/Na2Ti6O13 mixed material is reported together with its structural characterization. SEM images revealed that the final product has nanorods-like structure. The widths of the particles are in the range of hundreds of nanometers and are strongly dependent on calcination temperature unlike the particle lengths remain almost unchanged with the temperature and are in the range of several microns. The initial discharge capacity of the material is 90 mAh/g.

Electrospinning and thermal treatment of yttria doped zirconia fibres

Ceramics International, 2017

As compared to a bulk material, the fibres exhibit novel physical and chemical properties arising... more As compared to a bulk material, the fibres exhibit novel physical and chemical properties arising from their unique geometric features such as high surface area, surface to volume ratio and small fibre diameter. This paper is focused on the fabrication of nanosized 8 mol% yttria doped zirconia fibres by electrospinning from propoxide/polyvinylpyrrolidonebased precursors and physical-chemical characterization of the ceramic fibres with an energy application potential. Fully crystalline composition of cubic zirconia was detected after fibre heat treatment at 700 °C. The fibre morphology was changed with increasing temperature from flexible nonsintered nanoparticle system at 700 °C through porous nanograin structure at 900 °C and nonporous structure with coarser nanograins at 1100 °C to fragile chain-like fibre structure formed of elongated submicrometer grains at 1300-1450 °C. The densification and grain growth kinetics were described in two stages in the temperature range from 700 °C up to 1450 °C.

Case study: Reinforcement of 45S5 bioglass robocast scaffolds by HA/PCL nanocomposite coatings

Journal of the mechanical behavior of biomedical materials, Nov 8, 2017

The purpose of this study is to analyze the mechanical enhancement provided by nanocomposite coat... more The purpose of this study is to analyze the mechanical enhancement provided by nanocomposite coatings deposited on robocast 45S5 bioglass (BG) scaffolds for bone tissue regeneration. In particular, a nanocomposite layer consisting of hydroxyapatite (HA) nanoparticles, as reinforcing phase, in a polycaprolactone (PCL) matrix was deposited onto the surface of the BG struts conforming the scaffold. Three different HA nanopowders were used in this study. The effect of particle size and morphology of these HA nanopowders on the mechanical performance of 45S5 BG scaffolds is evaluated.

Synthesis of calcium phosphates from alkyl phosphates by the sol-gel method

Ceramics, 1998

Syntheses of calcium phosphates from methyl-, ethyl-, i-propyl and n-butyl phosphates and calcium... more Syntheses of calcium phosphates from methyl-, ethyl-, i-propyl and n-butyl phosphates and calcium acetate in acidic and basic water-alcoholic solutions were studied. The composition of calcium phosphates depended mainly on the type of the used catalyst. Mixture of hydroxyapatite and β-tricalcium phosphate (β-TCP) was received by reaction of all alkylphosphates with calcium acetate in acidic solution. Calcium pyrophosphate was received when reaction proceeded in the presence of amonium hydroxide. Hydroxyapatite with admixture of calcium pyrophosphate or β-TCP were prepared by means of monoethanolamine or diethanolamine catalysts. It was found that the hydrolysis of P-OR bound played important role in calcium phosphate syntheses. The mechanism of the syntheses was proposed.

Piezo-Enhanced Photocatalytic Activity of the Electrospun Fibrous Magnetic PVDF/BiFeO3 Membrane

Polymers

Creating stimulus-sensitive smart catalysts capable of decomposing organic dyes with high efficie... more Creating stimulus-sensitive smart catalysts capable of decomposing organic dyes with high efficiency is a critical task in ecology. Combining the advantages of photoactive piezoelectric nanomaterials and ferroelectric polymers can effectively solve this problem by collecting mechanical vibrations and light energy. Using the electrospinning method, we synthesized hybrid polymer-inorganic nanocomposite fiber membranes based on polyvinylidene fluoride (PVDF) and bismuth ferrite (BFO). The samples were studied by scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), total transmittance and diffuse reflectance, X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vibrating-sample magnetometer (VSM), and piezopotential measurements. It has been demonstrated that the addition of BFO leads to an increase in the proportion of the polar phase from 86.5% to 96.1% due to the surface ion–dipole interactio...

Electrode Spacing as a Determinant of the Output Performance of Planar-Type Photodetectors Based on Methylammonium Lead Bromide Perovskite Single Crystals

Methylammonium lead bromide is a very perspective hybrid semiconductor material, suitable for hig... more Methylammonium lead bromide is a very perspective hybrid semiconductor material, suitable for high-sensitive, filter-free photodetection of electromagnetic radiation. Herein, we studied the effect of electrode spacing on the output performance and stability of planar-type photodetectors based on high-quality MAPbBr3 single crystals. Such crystals, as large as 4.5×4.5×1.2 mm3 were synthesized via the inverse temperature crystallization method and were further used for the fabrication of planar Au/MAPbBr3/Au photodetectors with variable electrode spacing (in the range between 125 and 25 μm). We report that the electrode spacing has a profound impact on photocurrent densities and key detector parameters (responsivity R, external quantum efficiency EQE, and specific detectivity D*). In the studied fivefold electrode spacing, the photocurrent density increased over 4 times, with decreasing active area of the devices. This effect is attributed to intrinsic photocurrent amplification. Based on the transient photocurrent measurements and calculated key parameters, we determined the device sample with the best output performance. The champion sample with an electrode spacing of 50 μm exhibited great detection ability, especially for a low light intensity of 200 nWcm-2, for which we calculated the R of 19.55 A W-1, EQE of 4253%, and D* of 3.42 × 1012 Jones (cm Hz1/2 W-1). Moreover, the functional stability of this device showed a minimal reduction of photodetection ability after 2000 cycles, which makes it very promising for the next generation of optoelectronic devices.

Influence of LA/Ti molar ratio on the complex synthesis of anatase/brookite nanoparticles and their hydrogen production

International Journal of Hydrogen Energy, 2021

Abstract Heterophase TiO2 nanoparticles formed in the presence of a very low concentration of a s... more Abstract Heterophase TiO2 nanoparticles formed in the presence of a very low concentration of a substance with two donor groups were studied and the mechanism of their formation was proposed. The TiO2 nanoparticles were prepared by low-temperature hydrolysis and polycondensation of Ti (IV) n-propoxide in the presence of lactic acid (LA). The phase composition of the nanoparticles was controlled by the LA/Ti molar ratio ranging from 0.02 to 3.0. At low LA/Ti molar ratios, biphasic anatase-brookite was formed, at average LA/Ti molar ratios, anatase-brookite-rutile particles were formed, and at high molar ratios, pure anatase was formed. By using the low LA/Ti molar ratios, the low-temperature colloidal synthesis made it possible to control the composition of heterophase mesoporous TiO2 nanoparticles with a high specific surface area and high photocatalytic activity in the production of hydrogen by water splitting. The highest photocatalytic activity was exhibited by anatase-brookite nanoparticles containing 46–65% brookite, synthesized at LA/Ti molar ratios in the range of 0. 033 to 0.1.

Piezoelectric PVDF Elements and Systems for Mechanical Engineering Applications

2020 19th International Conference on Mechatronics - Mechatronika (ME), 2020

This paper deals with a review of potential technical applications of piezoelectric polymer syste... more This paper deals with a review of potential technical applications of piezoelectric polymer systems for Industry 4.0 applications. Polyvinylidene difluoride (PVDF) is a highly non-reactive thermoplastic fluoropolymer produced by the polymerization of vinylidene difluoride. Copolymers of PVDF with beta phase could be used in piezoelectric and triboelectric applications which are presented in this paper. PVDF is a candidate for harvesters and sensors that cannot be realized with piezoceramics or single crystals. Both technical applications for sensing and energy harvesting are presented in this paper. These technologies could be useful in mechanical engineering applications like a strain sensor, strain energy harvesting, vibration energy harvester, load sensing and triboelectric sensors/generators. The opportunity for future usage in Industry 4.0 devices is outlined and experimental results of individual systems are presented.

SEM imaging and XPS characterization of doped PVDF fibers

E3S Web of Conferences, 2021

Polyvinylidene fluoride (PVDF) is one of the most promising electroactive polymers; it exhibits e... more Polyvinylidene fluoride (PVDF) is one of the most promising electroactive polymers; it exhibits excellent electroactive behaviours, good biocompatibility, excellent chemical resistance, and thermal stability, rendering it an attractive material for biomedical, electronic, environmental and energy harvesting applications. This work aims to further improve its properties by the inclusion of powders of piezoactive materials. Polyvinylidene fluoride was formed by electrospinning into fibres with a thickness of 1.5-0.3 µm and then examined in a scanning electron microscope. The work offers a description of the current procedure in the preparation of samples and their modification for examination in a scanning electron microscope, characterizes the individual components of doped fibres and deals with specific instruments used for various analytical methods. The work contains a theoretical introduction to the analytical methods to which the samples will be further subjected, such as energy...

Structure Tuning and Electrical Properties of Mixed PVDF and Nylon Nanofibers

Materials, 2021

The paper specifies the electrostatic spinning process of specific polymeric materials, such as p... more The paper specifies the electrostatic spinning process of specific polymeric materials, such as polyvinylidene fluoride (PVDF), polyamide-6 (PA6, Nylon-6) and their combination PVDF/PA6. By combining nanofibers from two different materials during the spinning process, new structures with different mechanical, chemical, and physical properties can be created. The materials and their combinations were subjected to several measurements: scanning electron microscopy (SEM) to capture topography; contact angle of the liquid wettability on the sample surface to observe hydrophobicity and hydrophilicity; crystallization events were determined by differential scanning calorimetry (DSC); X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FT-IR) to describe properties and their changes at the chemical level. Furthermore, for the electrical properties of the sample, the dielectric characteristics and the piezoelectric coefficient were measur...

Case Study of Polyvinylidene Fluoride Doping by Carbon Nanotubes

Materials, 2021

Modern material science often makes use of polyvinylidene fluoride thin films because of various ... more Modern material science often makes use of polyvinylidene fluoride thin films because of various properties, like a high thermal and chemical stability, or a ferroelectric, pyroelectric and piezoelectric activity. Fibers of this polymer material are, on the other hand, much less explored due to various issues presented by the fibrous form. By introducing carbon nanotubes via electrospinning, it is possible to affect the chemical and electrical properties of the resulting composite. In the case of this paper, the focus was on the further improvement of interesting polyvinylidene fluoride properties by incorporating carbon nanotubes, such as changing the concentration of crystalline phases and the resulting increase of the dielectric constant and conductivity. These changes in properties have been explored by several methods that focused on a structural, chemical and electrical point of view. The resulting obtained data have been documented to create a basis for further research and t...

Water‐born 3D nanofiber mats using cost‐effective centrifugal spinning: comparison with electrospinning process: A complex study

Journal of Applied Polymer Science, 2020

A comparison of the electrostatic and centrifugal spinning of poly(vinyl alcohol) and poly(vinyl ... more A comparison of the electrostatic and centrifugal spinning of poly(vinyl alcohol) and poly(vinyl pyrrolidone) is shown in terms of the resulting fiber morphology and the process conditions. Specific parameters of centrifugal spinning, such rotational speed of spinneret and the relative humidity, were extensively investigated in details. Morphologies and diameters of resulting fiber mats were investigated by a scanning electron microscopy and compared between the two spinning techniques. The results revealed that formation of fibers is mainly affected by the initial polymer concentrations (and resulting viscosities) of polymeric solutions, which is in line with previous reports. However, the key novel finding of this work is that increasing relative humidity during centrifugal spinning process leads to greatly reduced fiber diameters to the levels typical for electrospinning. The obtained comparison is discussed and clearly shows technological advantages of the centrifugal spinning o...

High strength alumina tapes prepared by gel-tape casting method

Ceramics International, 2021

Abstract In the current work, high strength alumina (Al2O3) thin tapes were prepared by a novel g... more Abstract In the current work, high strength alumina (Al2O3) thin tapes were prepared by a novel gel-tape casting method. The water-based slurries were gelled by the polymerization of the epoxy monomers. Low viscosity slurries consisting of nanometer-sized alumina particles were prepared with a solid loading reaching 42 vol%. Sodium and ammonium polyacrylate dispersants were used for alumina particle dispersion and stabilization. The individual Al2O3 tapes reached a relative density of over 99.5% and a grain size between 1.1 and 1.3 μm after pressureless sintering at 1450 °C. The biaxial strength of sintered samples was measured in the ball-on-three-balls setup and the values of characteristic Weibull strength up to 1400 MPa were obtained for as-sintered tapes with a thickness of about 190 μm. The effect of sodium and ammonium-based polyacrylate dispersants on tape processing and properties of the Al2O3 tapes were investigated and explained.

Influence of Hydroxyapatite Nanoparticles and Surface Plasma Treatment on Bioactivity of Polycaprolactone Nanofibers

Polymers, 2020

Nanofibers are well known as a beneficial type of structure for tissue engineering. As a result o... more Nanofibers are well known as a beneficial type of structure for tissue engineering. As a result of the high acquisition cost of the natural polymers and their environmentally problematic treatment (toxic dissolution agents), artificial polymers seem to be the better choice for medical use. In the present study, polycaprolactone nano-sized fibrous structures were prepared by the electrospinning method. The impact of material morphology (random or parallelly oriented fibers versus continuous layer) and the presence of a fraction of hydroxyapatite nanoparticles on cell proliferation was tested. In addition, the effect of improving the material wettability by a low temperature argon discharge plasma treatment was evaluated, too. We have shown that both hydroxyapatite particles as well as plasma surface treatment are beneficial for the cell proliferation. The significant impact of both influences was evident during the first 48 h of the test: the hydroxyapatite particles in polycaprolact...

Investigation of Detergent-Modified Enzymomimetic Activities of TEMED-Templated Nanoceria Towards Fluorescent Detection of Their Cellular Uptake

ChemistrySelect, 2018

Ceria nanoparticles can catalyze many redox reactions that resemble reactions catalyzed by natura... more Ceria nanoparticles can catalyze many redox reactions that resemble reactions catalyzed by naturally occurring enzymes, such as peroxidase, catalase, haloperoxidase or phosphatase. This makes nanoceria an attractive material for biomedical and sensing applications. Presence of detergents dramatically affects the catalytic activity of nanoceria. The catalytic activity is also strongly influenced by biogenic compounds present in the sample. Furthermore, biomedical applications are hindered by the difficulties to detect nanoceria uptake by cells. Therefore, we have developed a new fast and sensitive fluorescent haloperoxidase assay based on fluorescein bromination in presence of CTAB to detect uptake of CeO 2 nanoparticles by cells in vitro. Moreover, catalytic activities of standard nanoceria (CeO 2 ) were compared to nanoceria hydrates (CeO 2 .xH 2 O) that are easier for preparation and might be stabilized by biologically relevant molecules allowing for a specific targeting to cells or tissues. We have developed a new approach to produce CeO 2 .xH 2 O in presence of TEMED and analyzed whether the presence of H 2 O 2 during the synthesis influences the catalytic activity of produced particles.

Processing of 0.55(Ba0.9Ca0.1)TiO3‐0.45Ba(Sn0.2Ti0.8)O3 lead‐free ceramics with high piezoelectricity

Journal of the American Ceramic Society, 2020

We report a large piezoelectric constant (d33), 720 pC/N and converse piezoelectric constant (d33... more We report a large piezoelectric constant (d33), 720 pC/N and converse piezoelectric constant (d33*), 2215 pm/V for 0.55(Ba0.9Ca0.1)TiO3‐0.45Ba(Sn0.2Ti0.8)O3 ceramics; the biggest value achieved for lead‐free piezoceramics so far. The ceramic powders were calcined between 1050°C‐1350°C and sintered at 1480°C. The best properties were obtained at a calcination temperature (CT) of 1350°C. The fitting combination of processing and microstructural parameters for example, initial powder particle size >2 µm, ceramics density ~95%, and grain size ~40 µm led to a formation of orthorhombic‐tetragonal‐pseudo‐cubic (O‐T‐PC) mixed phase boundary near room temperature, supported by Raman spectra, pointed to the extremely high piezoelectric activity. These conditions significantly increase piezoelectric constants, together with high relative permittivity (εr) >5000 and a low loss tangent (tan δ) of 0.029. In addition, the d33 value stabilizes in the range of 400‐500 pC/N for all samples calc...

Prevalent anatase crystalline phase increases the cytotoxicity of biphasic titanium dioxide nanoparticles in mammalian cells

Colloids and Surfaces B: Biointerfaces, 2019

Nanoparticular form of titanium dioxide (TiO 2 NPs) belongs to important industrial material. Des... more Nanoparticular form of titanium dioxide (TiO 2 NPs) belongs to important industrial material. Despite being widely used, serious contradictions regarding biosafety of TiO 2 NPs remain. We anticipate that such discrepancies could be due to a lack of understanding of a linkage between TiO 2 NPs phase composition and cytotoxicity. Therefore, we synthesized two types of biphasic TiO 2 NPs differing in an anatase-brookite phase composition. The study presents an array of in vitro data suggesting that TiO 2 NPs with a prevailing anatase phase composition possess higher cytotoxicity compared to TiO 2 NPs with an equal anatase-brookite crystallinity. This phenomenon was evidenced by significantly higher inhibition of metabolic activity and growth of epithelial and neuroblast-like cells. Moreover, anatase-prevailing TiO 2 NPs tend to produce higher amount of reactive oxygen species resulting in DNA fragmentation. Further insights into the molecular aspects of cytotoxicity of anatase-prevailing TiO 2 NPs were obtained by comparative proteomics delineating that TiO 2 NPs deregulate expression of a variety of proteins and associated pathways. This inevitably results in a decreased cellular ability to detoxify reactive oxygen species and respond to various stress conditions. The study provides novel data that add another piece to the jigsaw of the relation between structural features of NPs and biosafety.

Synthesis and characterization of Na2Ti6O13 and Na2Ti6O13/Na2Ti3O7 sodium titanates with nanorod-like structure as negative electrode materials for sodium-ion batteries

Journal of Energy Storage, 2017

In this work, we report microwave assisted hydrothermal synthesis of monoclinic sodium titanates ... more In this work, we report microwave assisted hydrothermal synthesis of monoclinic sodium titanates with either tunnel or with mixed tunnel/layered structure. Single phase Na 2 Ti 6 O 13 and mixed phase Na 2 Ti 6 O 13 / Na 2 Ti 3 O 7 titanates were studied by electrochemical measurements with cyclic voltammetry, impedance spectroscopy and galvanostatic cycling. SEM images revealed that all the synthesized materials consist of rods with widths in the range of tenths to hundreds nanometers. XRD analysis was used for determination of the phase composition and crystallite size. It was shown that mixed phase electrode material reveals higher capacity and wider active voltage range but has also lower cycling stability. The insertion potential of layered titanate Na 2 Ti 3 O 7 is much lower than in the case of Na 2 T i6 O 9 and the specific capacity of mixed titanate in the first cycle is double the capacity of pure Na 2 Ti 6 O 9 . Although presence of layered titanate contributed to high specific capacity in early cycling, it allowed a considerable decrease in specific capacity at higher numbers of cycles.

The Effect of the Thermosensitive Biodegradable PLGA–PEG–PLGA Copolymer on the Rheological, Structural and Mechanical Properties of Thixotropic Self-Hardening Tricalcium Phosphate Cement

International Journal of Molecular Sciences, 2019

The current limitations of calcium phosphate cements (CPCs) used in the field of bone regeneratio... more The current limitations of calcium phosphate cements (CPCs) used in the field of bone regeneration consist of their brittleness, low injectability, disintegration in body fluids and low biodegradability. Moreover, no method is currently available to measure the setting time of CPCs in correlation with the evolution of the setting reaction. The study proposes that it is possible to improve and tune the properties of CPCs via the addition of a thermosensitive, biodegradable, thixotropic copolymer based on poly(lactic acid), poly(glycolic acid) and poly(ethylene glycol) (PLGA–PEG–PLGA) which undergoes gelation under physiological conditions. The setting times of alpha-tricalcium phosphate (α-TCP) mixed with aqueous solutions of PLGA–PEG–PLGA determined by means of time-sweep curves revealed a lag phase during the dissolution of the α-TCP particles. The magnitude of the storage modulus at lag phase depends on the liquid to powder ratio, the copolymer concentration and temperature. A sha...

Effect of transition metal on stability and activity of La-Ca-M-(Al)-O (M = Co, Cr, Fe and Mn) perovskite oxides during partial oxidation of methane

International Journal of Hydrogen Energy, 2017

Perovskite oxides of the type of La x Ca 1-x M y Al 1-y O 3-d (M ¼ Co, Cr, Fe, Mn; x ¼ 0.5; y ¼ 0... more Perovskite oxides of the type of La x Ca 1-x M y Al 1-y O 3-d (M ¼ Co, Cr, Fe, Mn; x ¼ 0.5; y ¼ 0.7e1.0) were prepared using the polymerization methods and evaluated via N 2 adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), energy dispersive X-ray (EDX) spectroscopy, temperature-programmed reduction by hydrogen (TPR-H 2 ) and temperature-programmed oxidation by oxygen (TPO-O 2 ). Catalytic behaviour of the perovskite oxides during methane oxidation was studied using a tubular fixed-bed reactor. In a partial oxidation, which proceeded in two steps, there was total oxidation in the first step and CO 2 and H 2 O were formed; in the second step, the total oxidation products oxidized methane by (dry and wet) reforming reactions to yield CO and H 2 . Total oxidation and the two reforming reactions proceeded on two types of an active centre formed by transition metal ions, oxygen vacancies and oxide ions. The catalytic system La-Ca-Co-Al-O which contained aluminium, decomposed in partial oxidation of methane (POM) into a composite that contained firmly bonded cobalt nanoparticles in the surface of a substrate made up of La 2 O 3 , CaO and Al 2 O 3 which catalysed POM with a high methane conversion and hydrogen selectivity.

Mixed Sodium Titanate As an Anode for a Sodium-Ion Battery

ECS Transactions, 2016

Sodium-ion batteries are very promising complementary power sources usable in applications where ... more Sodium-ion batteries are very promising complementary power sources usable in applications where cost of starting materials and battery itself is more important than its energy density. Mixed sodium titanate anode material with two electroactive crystallographic phases was successfully synthesized via microwave assisted hydrothermal synthesis. The electrochemical performance of Na2Ti3O7/Na2Ti6O13 mixed material is reported together with its structural characterization. SEM images revealed that the final product has nanorods-like structure. The widths of the particles are in the range of hundreds of nanometers and are strongly dependent on calcination temperature unlike the particle lengths remain almost unchanged with the temperature and are in the range of several microns. The initial discharge capacity of the material is 90 mAh/g.

Electrospinning and thermal treatment of yttria doped zirconia fibres

Ceramics International, 2017

As compared to a bulk material, the fibres exhibit novel physical and chemical properties arising... more As compared to a bulk material, the fibres exhibit novel physical and chemical properties arising from their unique geometric features such as high surface area, surface to volume ratio and small fibre diameter. This paper is focused on the fabrication of nanosized 8 mol% yttria doped zirconia fibres by electrospinning from propoxide/polyvinylpyrrolidonebased precursors and physical-chemical characterization of the ceramic fibres with an energy application potential. Fully crystalline composition of cubic zirconia was detected after fibre heat treatment at 700 °C. The fibre morphology was changed with increasing temperature from flexible nonsintered nanoparticle system at 700 °C through porous nanograin structure at 900 °C and nonporous structure with coarser nanograins at 1100 °C to fragile chain-like fibre structure formed of elongated submicrometer grains at 1300-1450 °C. The densification and grain growth kinetics were described in two stages in the temperature range from 700 °C up to 1450 °C.

Case study: Reinforcement of 45S5 bioglass robocast scaffolds by HA/PCL nanocomposite coatings

Journal of the mechanical behavior of biomedical materials, Nov 8, 2017

The purpose of this study is to analyze the mechanical enhancement provided by nanocomposite coat... more The purpose of this study is to analyze the mechanical enhancement provided by nanocomposite coatings deposited on robocast 45S5 bioglass (BG) scaffolds for bone tissue regeneration. In particular, a nanocomposite layer consisting of hydroxyapatite (HA) nanoparticles, as reinforcing phase, in a polycaprolactone (PCL) matrix was deposited onto the surface of the BG struts conforming the scaffold. Three different HA nanopowders were used in this study. The effect of particle size and morphology of these HA nanopowders on the mechanical performance of 45S5 BG scaffolds is evaluated.

Synthesis of calcium phosphates from alkyl phosphates by the sol-gel method

Ceramics, 1998

Syntheses of calcium phosphates from methyl-, ethyl-, i-propyl and n-butyl phosphates and calcium... more Syntheses of calcium phosphates from methyl-, ethyl-, i-propyl and n-butyl phosphates and calcium acetate in acidic and basic water-alcoholic solutions were studied. The composition of calcium phosphates depended mainly on the type of the used catalyst. Mixture of hydroxyapatite and β-tricalcium phosphate (β-TCP) was received by reaction of all alkylphosphates with calcium acetate in acidic solution. Calcium pyrophosphate was received when reaction proceeded in the presence of amonium hydroxide. Hydroxyapatite with admixture of calcium pyrophosphate or β-TCP were prepared by means of monoethanolamine or diethanolamine catalysts. It was found that the hydrolysis of P-OR bound played important role in calcium phosphate syntheses. The mechanism of the syntheses was proposed.