Marjan Bele - Academia.edu (original) (raw)

Drug Delivery by Marjan Bele

ACS Applied Materials & Interfaces, 2013

With the advancement of drug delivery systems based on mesoporous silica nanoparticles (MSNs), a ... more With the advancement of drug delivery systems based on mesoporous silica nanoparticles (MSNs), a simple and efficient method regulating the drug release kinetics is needed. We developed redox-responsive release systems with three levels of hindrance around the disulfide bond. A model drug (rhodamine B dye) was loaded into MSNs' mesoporous voids. The pore opening was capped with β-cyclodextrin in order to prevent leakage of drug. Indeed, in absence of a reducing agent the systems exhibited little leakage, while the addition of dithiothreitol cleaved the disulfide bonds and enabled the release of cargo. The release rate and the amount of released dye were tuned by the level of hindrance around disulfide bonds, with the increased hindrance causing a decrease in the release rate as well as in the amount of released drug. Thus, we demonstrated the ability of the present mesoporous systems to intrinsically control the release rate and the amount of the released cargo by only minor structural variations. Furthermore, an in vivo experiment on zebrafish confirmed that the present model delivery system is nonteratogenic.

Papers by Marjan Bele

ACS Catalysis, 2020

The development of affordable, low-iridium-loading, scalable, active, and stable catalysts for th... more The development of affordable, low-iridium-loading, scalable, active, and stable catalysts for the oxygen-evolution reaction (OER) is a requirement for the commercialization of proton-exchange membrane water electrolyzers (PEMWEs). However, the synthesis of high-performance OER catalysts with minimal use of the rare and expensive element Ir is very challenging and requires the identification of electrically conductive and stable high-surface-area support materials. We developed a synthesis procedure for the production of large quantities of a nanocomposite powder containing titanium oxynitride (TiON x) and Ir. The catalysts were synthesized with an anodic oxidation process followed by detachment, milling, thermal treatment, and the deposition of Ir nanoparticles. The anodization time was varied to grow three different types of nanotubular structures exhibiting different lengths and wall thicknesses and thus a variety of properties. A comparison of milled samples with different degrees of nanotubular clustering and morphology retention, but with identical chemical compositions and Ir nanoparticle size distributions and dispersions, revealed that the nanotubular support morphology is the determining factor governing the catalyst's OER activity and stability. Our study is supported by various state-of-the-art materials' characterization techniques, like X-ray photoelectron spectroscopy, scanning and transmission electron microscopies, Xray powder diffraction and absorption spectroscopy, and electrochemical cyclic voltammetry. Anodic oxidation proved to be a very suitable way to produce high-surface-area powder-type catalysts as the produced material greatly outperformed the IrO 2 benchmarks as well as the Ir-supported samples on morphologically different TiON x from previous studies. The highest activity was achieved for the sample prepared with 3 h of anodization, which had the most appropriate morphology for the effective removal of oxygen bubbles.

Journal of Sol-Gel Science and Technology, 2020

Many groups have already investigated the use of NiCu magnetic nanoparticles (MNPs) as mediators ... more Many groups have already investigated the use of NiCu magnetic nanoparticles (MNPs) as mediators for magnetic fluid hyperthermia, but we were the first to report the potential of NiCu MNPs as bimodal therapeutic systems, capable of simultaneous magnetic hyperthermia (MH) and targeted drug delivery. The superparamagnetic nanoparticles have a magnetic core, which enables their manipulation through an external magnetic field, a biocompatible layer, providing a surface for attachment of suitable receptors for targeting specific tissues, and a therapeutic load either incorporated inside the coating pores or hosted within internal cavities of the particles. In this study, we incorporated three model drugs with different pharmacological activity into superparamagnetic Ni x Cu 1−x nanoparticles. The superparamagnetic Ni x Cu 1−x nanoparticles were prepared using a sol-gel method, and exhibited a Curie temperature (T C) in the therapeutic range for use in MH. The nanoparticles were prepared in a silica matrix to avoid their agglomeration during thermal treatment and to provide suitable compartments for incorporation inside the pores. The release of the incorporated drugs paracetamol, bupivacaine hydrochloride, and pentoxifylline was studied using an in vitro release system, where UV-visible spectrophotometry (UV/Vis) was used for quantification of the released drug. The Ni x Cu 1−x nanoparticles were characterized using X-ray diffraction analysis, thermogravimetric analysis (TGA/SDTA), Fourier transform infrared spectroscopy, scanning electron microscopy, and magnetic measurements. Surface area and pore size were determined by using BET analysis. Finally, the biocompatibility of the samples was tested on human skin-derived fibroblasts.

Environmental Pollution, 2016

Microplastic fibers (MP) from textile weathering and washing are increasingly being recognized as... more Microplastic fibers (MP) from textile weathering and washing are increasingly being recognized as environmental pollutants. The majority of studies on the bioavailability and effects of microplastic focused on small polystyrene spherical plastic particles, while less data are available for fibers and for other materials besides polystyrene. We investigated the ingestion and effects of ground polyethylene terephthalate (PET) textile microfibers (length range: 62e1400 mm, width 31e528 mm, thickness 1 e21.5 mm) on the freshwater zooplankton crustacean Daphnia magna after a 48 h exposure and subsequent 24 h of recovery in MP free medium and algae. The majority of ingested fibers by D. magna were around 300 mm, but also some very large twisted MP fibers around 1400 mm were found inside the gut. Exposure to these fibers results in increased mortality of daphnids after 48 h only in the case where daphnids were not pre-fed with algae prior to experiment, but no effect was found when daphnids were fed before the experiments. Regardless of the feeding regime, daphnids were not able to recover from MP exposure after additional 24 h incubation period in a MP free medium with algae. The uptake and effects of PET textile MP on D. magna are presented here for the first time.

European Microscopy Congress 2016: Proceedings, 2016

Vacuum, 2007

Auger electron spectroscopy (AES) depth profiling was used to study the oxidation phenomena of AI... more Auger electron spectroscopy (AES) depth profiling was used to study the oxidation phenomena of AISI316L stainless steel during treatment with oxygen plasma. Samples were exposed to low-pressure RF plasma with a high dissociation degree, so that the flux of oxygen atoms onto the sample surface exceeded 1024m−2s−1. A set of samples was oxidized 4min at different temperatures up to 1300K

The effect of gelatine on irreversible charge consumption due to the SEI formation is studied usi... more The effect of gelatine on irreversible charge consumption due to the SEI formation is studied using three graphite types from TIMCAL: TIMREX KS44, TIMREX SFG44 and TIMREX E-SLX50. It is shown that in all cases gelatine treatment leads to a decrease in irreversible charge losses with respect to untreated samples. Furthermore, it is shown that gelatine is electrochemically stable, the charge due to gelatine degradation is of the order of 1 mAh/g. Using DEMS it is shown that gelatine-treated samples release CO 2 at voltages negative to +0.5 V versus metallic lithium. This might serve as an additional explanation for the beneficial role of gelatine with respect to irreversible losses of lithium.

Journal of Applied Polymer Science, 2009

Nanocomposite fibers based on polypropylene (PP) polymer were prepared with different content of ... more Nanocomposite fibers based on polypropylene (PP) polymer were prepared with different content of nanofiller. Filaments were spun from an isotactic iPP homopolymer. Montmorillonite modified by N,N-dimethyl-N,N dioctadecylammonium cations was used for preparation of PP nanocomposite fibers. A PP grafted with acrylic acid was added as a coupling agent. Nanocomposite fibers were characterized, i.e., the surface morphology of PP nanocomposite fibers was observed and surface properties were defined by electrokinetic properties determination by zeta potential measurements. For particle distribution observation the plasma etching was involved as a method for sample preparation. The addition of nanoparticles has an impact on ZP value of nanofilled fibers, however, isoelectric point IEP is not significantly influenced by different concentrations of nanofiller. V

Analytica Chimica Acta, 2008

A new type of carbon film electrode, composed of a thin layer of tightly packed carbon black (CB)... more A new type of carbon film electrode, composed of a thin layer of tightly packed carbon black (CB) nanoparticles deposited onto a gelatin-covered indium tin oxide/glass support using the surface-induced deposition (SID) approach, is presented. Some parameters of the novel SID method were optimized and the surface image and functionalization of the investigated carbon black film electrode (CBFE) was inspected by employing scanning electron microscopy and infrared spectroscopy. A cyclic voltammetry (CV) study was conducted in which the electron-transfer kinetics and CBFE interfacial characteristics were evaluated employing several selected reference redox systems, such as [Ru(NH(3))(6)](3+/2+), [Fe(CN)(6)](3-/4-) and Fe(3+/2+) in aqueous, and ferrocene/ferrocenium in acetonitrile media. CV recordings were also performed in order to compare the electrochemical behavior of the CBFE with that of some well-known and established bare carbon-based electrodes. In order to confirm the validity of the CB film preparation method, the electroanalytical performance of the proposed CBFE was examined by carrying out linear sweep voltammetry of ascorbic acid (AA), anodic stripping square-wave voltammetry of Cu(II) in acidic medium, and amperometric measurements of hydrogen peroxide under flow injection conditions. The sensing characteristics of the novel carbon film electrode, demonstrated in this preliminary study, comprise: (i) a wide working potential window ranging from +1.0 to -1.3 V (depending on the solution pH), (ii) a wide applicable pH range (at least from 2 to 12), (iii) low voltammetric background (<5 microA cm(-2)), (iv) a satisfactory linear voltammetric and amperometric response (r(2)>0.99) to various analytes, (v) good reproducibility (for example, r.s.d. of 2% in amperometric detection of H(2)O(2) and r.s.d. of 8.5% for electrode-to-electrode CV runs), and (vi) stable and fast current response (at least 100 CV runs with negligible change in CV response). The main advantages of the proposed CBFE originate from the unique CB film formation procedure that enables fast, simple, inexpensive and non-toxic CBFE preparation, which can find application in advanced electrochemical devices and is suitable for mass production.

Journal of Colloid and Interface Science, 2002

Uniform fluorescent silica-dye microspheres have been prepared by coating preformed monodispersed... more Uniform fluorescent silica-dye microspheres have been prepared by coating preformed monodispersed silica particles with silica layers containing rhodamine 6G or acridine orange. The resulting dispersions exhibit intense fluorescent emission between 500 and 600 nm, over a broad excitation wavelength range of 460 to 550 nm, even with exceedingly small amounts of dyes incorporated into the silica particles (10-30 ppm, expressed as weight of dye relative to weight of dry particles). The fluorescent particles can be prepared in micrometer diameters suitable for analyses using flow cytometry with 488-nm laser excitation.

Nanomaterials

Titanium oxynitride carbon composite nanofibers (TiON/C-CNFs) were synthesised with electrospinni... more Titanium oxynitride carbon composite nanofibers (TiON/C-CNFs) were synthesised with electrospinning and subsequent heat treatment in ammonia gas. In situ four-probe electrical conductivity measurements of individual TiON/C-CNFs were performed. Additionally, the TiON/C-CNFs were thoroughly analysed with various techniques, such as X-ray and electron diffractions, electron microscopies and spectroscopies, thermogravimetric analysis and chemical analysis to determine the crystal structure, morphology, chemical composition, and N/O at. ratio. It was found that nanofibers were composed of 2–5 nm sized titanium oxynitride (TiON) nanoparticles embedded in an amorphous carbon matrix with a small degree of porosity. The average electrical conductivity of a single TiON/C-CNF was 1.2 kS/m and the bulk electrical conductivity of the TiON/C-CNF fabric was 0.053 kS/m. From the available data, the mesh density of the TiON/C-CNF fabric was estimated to have a characteristic length of 1.0 µm and ele...

Electrochimica Acta, 2021

The Journal of Physical Chemistry C, 2021

Electrochemical stability of a commercial Au/C catalyst in an acidic electrolyte has been investi... more Electrochemical stability of a commercial Au/C catalyst in an acidic electrolyte has been investigated by an accelerated stress test (AST), which consisted of 10,000 voltammetric scans (1 V/s) in the potential range between 0.58 and 1.41 V RHE. Loss of Au electrochemical surface area (ESA) during the AST pointed out to the degradation of Au/C. Coupling of an electrochemical flow cell with ICP-MS showed that only a minor amount of gold is dissolved despite the substantial loss of gold ESA during the AST (∼35% of initial value remains at the end of the AST). According to the electrochemical mass spectrometry experiments, carbon corrosion occurs during the AST but to a minor extent. By using identical location scanning electron microscopy and identical location transmission electron microscopy, it was possible to discern that the dissolution of small Au particles (<5 nm) within the polydisperse Au/C sample is the main degradation mechanism. The mass of such particles gives only a minor contribution to the overall Au mass of the polydisperse sample while giving a major contribution to the overall ESA, which explains a significant loss of ESA and minor loss of mass during the AST. The addition of low amounts of chloride anions (10 −4 M) substantially promoted the degradation of gold nanoparticles. At an even higher concentration of chlorides (10 −2 M), the dissolution of gold was rather effective, which is useful from the recycling point of view when rapid leaching of gold is desirable.

Journal of Physics: Energy, 2020

More efficient utilization of iridium is of immense importance for the future development of prot... more More efficient utilization of iridium is of immense importance for the future development of proton exchange membrane electrolyzers. In this study, we introduce a new facile and scalable synthesis of an Ir-based high-performance oxygen evolution reaction (OER) electrocatalytic nanocomposite. The composite consists of Ir nanoparticles with an average size of 3–4 nm, which are effectively anchored on a titanium oxynitride support (TiONx), which is distributed across high-surface-area Ketjen Black carbon (Ir/TiONx/C). We provide complete structural, morphological and compositional characterization (x-ray diffraction, scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy) and propose a proper benchmark protocol to measure true electrochemical performance. Compared to the state-of-the-art Ir Black electrocatalyst, Ir/TiONx/C exhibits approximately three times higher OER performance.

Analytical Chemistry, 2019

The future significance of energy conversion has stimulated intense investigation of various elec... more The future significance of energy conversion has stimulated intense investigation of various electrocatalytic materials. Hence electrocatalysts have become the subject of electrochemical characterization on a daily basis. In certain cases of interest, when measuring electrochemical reactions beyond the onset potentials, however, appropriateness of existing electroanalytical methods may be questioned and alternative approaches need to be developed. The present study highlights some shortcomings in the electrochemical investigation of gas evolving reactions. The oxygen evolution reaction (OER) is selected as a case example with a specific focus on the electrochemical stability of a nanoparticulate iridium catalyst. When conventional electrochemical methods, such as thin film rotating disc electrodes are employed to study the materials' stability, the intrinsic degradation is masked by oxygen bubbles, which are inherently being formed during the reaction, especially when high current densities are used. In this Letter, we present a solution to this issue, the so-called floating electrode arrangement. Its elegant usage enables fast and reliable electrochemical characterization of oxygen evolution electrocatalysts.

Catalysts, 2019

The oxygen reduction reaction (ORR) properties of a proprietary PtCu3/C alloy electrocatalyst pro... more The oxygen reduction reaction (ORR) properties of a proprietary PtCu3/C alloy electrocatalyst produced on a multi-gram scale are characterized by the conventional rotating disc electrode (RDE) method and by constructing a membrane electrode assembly (MEA) proton exchange membrane (PEM) single cell. The PtCu3 nanoparticles become porous, enriched in Pt on the surface, and exhibit a high RDE activity. The single cell electrochemical study reveals that, contrary to most advanced catalysts, the high ORR activity can be transferred from the RDE to the MEA. In the latter case, at 0.9VIRfree, a mass activity of 0.53 A/mgPt, at a Pt electrode loading of 0.2 mg/cm2, is achieved. However, at high current density, oxygen transport becomes limited. This is proven by the analysis of polarization curves and electrochemical impedance spectroscopy (EIS) data with a Kulikovsky (physical) model. These indicate that this limitation is caused by the non-optimal microporosity of our catalyst, which hind...

ACS Applied Energy Materials, 2019

Coatings, 2018

A profound understanding of the Au dissolution process is a prerequisite for optimal utilization ... more A profound understanding of the Au dissolution process is a prerequisite for optimal utilization of Au-based materials. This goes for either increasing the corrosion stability of materials in the sectors where the long-term functionality of Au is needed or decreasing the corrosion stability where the recovery of the Au component is crucial. By employing an extremely sensitive online analytical system, consisting of an electrochemical flow cell coupled to an inductively coupled plasma mass spectrometry, in situ potential-resolved dissolution of Au in the ppb range is enabled. A comparative study of two Au based materials, (i) a polycrystalline Au disk and (ii) carbon-supported Au nanoparticles, is presented. As a probe, chloride ions were used to elucidate the distinct differences in the corrosion behavior of the two analogues.

ACS Applied Materials & Interfaces, 2013

With the advancement of drug delivery systems based on mesoporous silica nanoparticles (MSNs), a ... more With the advancement of drug delivery systems based on mesoporous silica nanoparticles (MSNs), a simple and efficient method regulating the drug release kinetics is needed. We developed redox-responsive release systems with three levels of hindrance around the disulfide bond. A model drug (rhodamine B dye) was loaded into MSNs&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; mesoporous voids. The pore opening was capped with β-cyclodextrin in order to prevent leakage of drug. Indeed, in absence of a reducing agent the systems exhibited little leakage, while the addition of dithiothreitol cleaved the disulfide bonds and enabled the release of cargo. The release rate and the amount of released dye were tuned by the level of hindrance around disulfide bonds, with the increased hindrance causing a decrease in the release rate as well as in the amount of released drug. Thus, we demonstrated the ability of the present mesoporous systems to intrinsically control the release rate and the amount of the released cargo by only minor structural variations. Furthermore, an in vivo experiment on zebrafish confirmed that the present model delivery system is nonteratogenic.

ACS Catalysis, 2020

The development of affordable, low-iridium-loading, scalable, active, and stable catalysts for th... more The development of affordable, low-iridium-loading, scalable, active, and stable catalysts for the oxygen-evolution reaction (OER) is a requirement for the commercialization of proton-exchange membrane water electrolyzers (PEMWEs). However, the synthesis of high-performance OER catalysts with minimal use of the rare and expensive element Ir is very challenging and requires the identification of electrically conductive and stable high-surface-area support materials. We developed a synthesis procedure for the production of large quantities of a nanocomposite powder containing titanium oxynitride (TiON x) and Ir. The catalysts were synthesized with an anodic oxidation process followed by detachment, milling, thermal treatment, and the deposition of Ir nanoparticles. The anodization time was varied to grow three different types of nanotubular structures exhibiting different lengths and wall thicknesses and thus a variety of properties. A comparison of milled samples with different degrees of nanotubular clustering and morphology retention, but with identical chemical compositions and Ir nanoparticle size distributions and dispersions, revealed that the nanotubular support morphology is the determining factor governing the catalyst's OER activity and stability. Our study is supported by various state-of-the-art materials' characterization techniques, like X-ray photoelectron spectroscopy, scanning and transmission electron microscopies, Xray powder diffraction and absorption spectroscopy, and electrochemical cyclic voltammetry. Anodic oxidation proved to be a very suitable way to produce high-surface-area powder-type catalysts as the produced material greatly outperformed the IrO 2 benchmarks as well as the Ir-supported samples on morphologically different TiON x from previous studies. The highest activity was achieved for the sample prepared with 3 h of anodization, which had the most appropriate morphology for the effective removal of oxygen bubbles.

Journal of Sol-Gel Science and Technology, 2020

Many groups have already investigated the use of NiCu magnetic nanoparticles (MNPs) as mediators ... more Many groups have already investigated the use of NiCu magnetic nanoparticles (MNPs) as mediators for magnetic fluid hyperthermia, but we were the first to report the potential of NiCu MNPs as bimodal therapeutic systems, capable of simultaneous magnetic hyperthermia (MH) and targeted drug delivery. The superparamagnetic nanoparticles have a magnetic core, which enables their manipulation through an external magnetic field, a biocompatible layer, providing a surface for attachment of suitable receptors for targeting specific tissues, and a therapeutic load either incorporated inside the coating pores or hosted within internal cavities of the particles. In this study, we incorporated three model drugs with different pharmacological activity into superparamagnetic Ni x Cu 1−x nanoparticles. The superparamagnetic Ni x Cu 1−x nanoparticles were prepared using a sol-gel method, and exhibited a Curie temperature (T C) in the therapeutic range for use in MH. The nanoparticles were prepared in a silica matrix to avoid their agglomeration during thermal treatment and to provide suitable compartments for incorporation inside the pores. The release of the incorporated drugs paracetamol, bupivacaine hydrochloride, and pentoxifylline was studied using an in vitro release system, where UV-visible spectrophotometry (UV/Vis) was used for quantification of the released drug. The Ni x Cu 1−x nanoparticles were characterized using X-ray diffraction analysis, thermogravimetric analysis (TGA/SDTA), Fourier transform infrared spectroscopy, scanning electron microscopy, and magnetic measurements. Surface area and pore size were determined by using BET analysis. Finally, the biocompatibility of the samples was tested on human skin-derived fibroblasts.

Environmental Pollution, 2016

Microplastic fibers (MP) from textile weathering and washing are increasingly being recognized as... more Microplastic fibers (MP) from textile weathering and washing are increasingly being recognized as environmental pollutants. The majority of studies on the bioavailability and effects of microplastic focused on small polystyrene spherical plastic particles, while less data are available for fibers and for other materials besides polystyrene. We investigated the ingestion and effects of ground polyethylene terephthalate (PET) textile microfibers (length range: 62e1400 mm, width 31e528 mm, thickness 1 e21.5 mm) on the freshwater zooplankton crustacean Daphnia magna after a 48 h exposure and subsequent 24 h of recovery in MP free medium and algae. The majority of ingested fibers by D. magna were around 300 mm, but also some very large twisted MP fibers around 1400 mm were found inside the gut. Exposure to these fibers results in increased mortality of daphnids after 48 h only in the case where daphnids were not pre-fed with algae prior to experiment, but no effect was found when daphnids were fed before the experiments. Regardless of the feeding regime, daphnids were not able to recover from MP exposure after additional 24 h incubation period in a MP free medium with algae. The uptake and effects of PET textile MP on D. magna are presented here for the first time.

European Microscopy Congress 2016: Proceedings, 2016

Vacuum, 2007

Auger electron spectroscopy (AES) depth profiling was used to study the oxidation phenomena of AI... more Auger electron spectroscopy (AES) depth profiling was used to study the oxidation phenomena of AISI316L stainless steel during treatment with oxygen plasma. Samples were exposed to low-pressure RF plasma with a high dissociation degree, so that the flux of oxygen atoms onto the sample surface exceeded 1024m−2s−1. A set of samples was oxidized 4min at different temperatures up to 1300K

The effect of gelatine on irreversible charge consumption due to the SEI formation is studied usi... more The effect of gelatine on irreversible charge consumption due to the SEI formation is studied using three graphite types from TIMCAL: TIMREX KS44, TIMREX SFG44 and TIMREX E-SLX50. It is shown that in all cases gelatine treatment leads to a decrease in irreversible charge losses with respect to untreated samples. Furthermore, it is shown that gelatine is electrochemically stable, the charge due to gelatine degradation is of the order of 1 mAh/g. Using DEMS it is shown that gelatine-treated samples release CO 2 at voltages negative to +0.5 V versus metallic lithium. This might serve as an additional explanation for the beneficial role of gelatine with respect to irreversible losses of lithium.

Journal of Applied Polymer Science, 2009

Nanocomposite fibers based on polypropylene (PP) polymer were prepared with different content of ... more Nanocomposite fibers based on polypropylene (PP) polymer were prepared with different content of nanofiller. Filaments were spun from an isotactic iPP homopolymer. Montmorillonite modified by N,N-dimethyl-N,N dioctadecylammonium cations was used for preparation of PP nanocomposite fibers. A PP grafted with acrylic acid was added as a coupling agent. Nanocomposite fibers were characterized, i.e., the surface morphology of PP nanocomposite fibers was observed and surface properties were defined by electrokinetic properties determination by zeta potential measurements. For particle distribution observation the plasma etching was involved as a method for sample preparation. The addition of nanoparticles has an impact on ZP value of nanofilled fibers, however, isoelectric point IEP is not significantly influenced by different concentrations of nanofiller. V

Analytica Chimica Acta, 2008

A new type of carbon film electrode, composed of a thin layer of tightly packed carbon black (CB)... more A new type of carbon film electrode, composed of a thin layer of tightly packed carbon black (CB) nanoparticles deposited onto a gelatin-covered indium tin oxide/glass support using the surface-induced deposition (SID) approach, is presented. Some parameters of the novel SID method were optimized and the surface image and functionalization of the investigated carbon black film electrode (CBFE) was inspected by employing scanning electron microscopy and infrared spectroscopy. A cyclic voltammetry (CV) study was conducted in which the electron-transfer kinetics and CBFE interfacial characteristics were evaluated employing several selected reference redox systems, such as [Ru(NH(3))(6)](3+/2+), [Fe(CN)(6)](3-/4-) and Fe(3+/2+) in aqueous, and ferrocene/ferrocenium in acetonitrile media. CV recordings were also performed in order to compare the electrochemical behavior of the CBFE with that of some well-known and established bare carbon-based electrodes. In order to confirm the validity of the CB film preparation method, the electroanalytical performance of the proposed CBFE was examined by carrying out linear sweep voltammetry of ascorbic acid (AA), anodic stripping square-wave voltammetry of Cu(II) in acidic medium, and amperometric measurements of hydrogen peroxide under flow injection conditions. The sensing characteristics of the novel carbon film electrode, demonstrated in this preliminary study, comprise: (i) a wide working potential window ranging from +1.0 to -1.3 V (depending on the solution pH), (ii) a wide applicable pH range (at least from 2 to 12), (iii) low voltammetric background (&amp;amp;amp;amp;amp;amp;lt;5 microA cm(-2)), (iv) a satisfactory linear voltammetric and amperometric response (r(2)&amp;amp;amp;amp;amp;amp;gt;0.99) to various analytes, (v) good reproducibility (for example, r.s.d. of 2% in amperometric detection of H(2)O(2) and r.s.d. of 8.5% for electrode-to-electrode CV runs), and (vi) stable and fast current response (at least 100 CV runs with negligible change in CV response). The main advantages of the proposed CBFE originate from the unique CB film formation procedure that enables fast, simple, inexpensive and non-toxic CBFE preparation, which can find application in advanced electrochemical devices and is suitable for mass production.

Journal of Colloid and Interface Science, 2002

Uniform fluorescent silica-dye microspheres have been prepared by coating preformed monodispersed... more Uniform fluorescent silica-dye microspheres have been prepared by coating preformed monodispersed silica particles with silica layers containing rhodamine 6G or acridine orange. The resulting dispersions exhibit intense fluorescent emission between 500 and 600 nm, over a broad excitation wavelength range of 460 to 550 nm, even with exceedingly small amounts of dyes incorporated into the silica particles (10-30 ppm, expressed as weight of dye relative to weight of dry particles). The fluorescent particles can be prepared in micrometer diameters suitable for analyses using flow cytometry with 488-nm laser excitation.

Nanomaterials

Titanium oxynitride carbon composite nanofibers (TiON/C-CNFs) were synthesised with electrospinni... more Titanium oxynitride carbon composite nanofibers (TiON/C-CNFs) were synthesised with electrospinning and subsequent heat treatment in ammonia gas. In situ four-probe electrical conductivity measurements of individual TiON/C-CNFs were performed. Additionally, the TiON/C-CNFs were thoroughly analysed with various techniques, such as X-ray and electron diffractions, electron microscopies and spectroscopies, thermogravimetric analysis and chemical analysis to determine the crystal structure, morphology, chemical composition, and N/O at. ratio. It was found that nanofibers were composed of 2–5 nm sized titanium oxynitride (TiON) nanoparticles embedded in an amorphous carbon matrix with a small degree of porosity. The average electrical conductivity of a single TiON/C-CNF was 1.2 kS/m and the bulk electrical conductivity of the TiON/C-CNF fabric was 0.053 kS/m. From the available data, the mesh density of the TiON/C-CNF fabric was estimated to have a characteristic length of 1.0 µm and ele...

Electrochimica Acta, 2021

The Journal of Physical Chemistry C, 2021

Electrochemical stability of a commercial Au/C catalyst in an acidic electrolyte has been investi... more Electrochemical stability of a commercial Au/C catalyst in an acidic electrolyte has been investigated by an accelerated stress test (AST), which consisted of 10,000 voltammetric scans (1 V/s) in the potential range between 0.58 and 1.41 V RHE. Loss of Au electrochemical surface area (ESA) during the AST pointed out to the degradation of Au/C. Coupling of an electrochemical flow cell with ICP-MS showed that only a minor amount of gold is dissolved despite the substantial loss of gold ESA during the AST (∼35% of initial value remains at the end of the AST). According to the electrochemical mass spectrometry experiments, carbon corrosion occurs during the AST but to a minor extent. By using identical location scanning electron microscopy and identical location transmission electron microscopy, it was possible to discern that the dissolution of small Au particles (<5 nm) within the polydisperse Au/C sample is the main degradation mechanism. The mass of such particles gives only a minor contribution to the overall Au mass of the polydisperse sample while giving a major contribution to the overall ESA, which explains a significant loss of ESA and minor loss of mass during the AST. The addition of low amounts of chloride anions (10 −4 M) substantially promoted the degradation of gold nanoparticles. At an even higher concentration of chlorides (10 −2 M), the dissolution of gold was rather effective, which is useful from the recycling point of view when rapid leaching of gold is desirable.

Journal of Physics: Energy, 2020

More efficient utilization of iridium is of immense importance for the future development of prot... more More efficient utilization of iridium is of immense importance for the future development of proton exchange membrane electrolyzers. In this study, we introduce a new facile and scalable synthesis of an Ir-based high-performance oxygen evolution reaction (OER) electrocatalytic nanocomposite. The composite consists of Ir nanoparticles with an average size of 3–4 nm, which are effectively anchored on a titanium oxynitride support (TiONx), which is distributed across high-surface-area Ketjen Black carbon (Ir/TiONx/C). We provide complete structural, morphological and compositional characterization (x-ray diffraction, scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy) and propose a proper benchmark protocol to measure true electrochemical performance. Compared to the state-of-the-art Ir Black electrocatalyst, Ir/TiONx/C exhibits approximately three times higher OER performance.

Analytical Chemistry, 2019

The future significance of energy conversion has stimulated intense investigation of various elec... more The future significance of energy conversion has stimulated intense investigation of various electrocatalytic materials. Hence electrocatalysts have become the subject of electrochemical characterization on a daily basis. In certain cases of interest, when measuring electrochemical reactions beyond the onset potentials, however, appropriateness of existing electroanalytical methods may be questioned and alternative approaches need to be developed. The present study highlights some shortcomings in the electrochemical investigation of gas evolving reactions. The oxygen evolution reaction (OER) is selected as a case example with a specific focus on the electrochemical stability of a nanoparticulate iridium catalyst. When conventional electrochemical methods, such as thin film rotating disc electrodes are employed to study the materials' stability, the intrinsic degradation is masked by oxygen bubbles, which are inherently being formed during the reaction, especially when high current densities are used. In this Letter, we present a solution to this issue, the so-called floating electrode arrangement. Its elegant usage enables fast and reliable electrochemical characterization of oxygen evolution electrocatalysts.

Catalysts, 2019

The oxygen reduction reaction (ORR) properties of a proprietary PtCu3/C alloy electrocatalyst pro... more The oxygen reduction reaction (ORR) properties of a proprietary PtCu3/C alloy electrocatalyst produced on a multi-gram scale are characterized by the conventional rotating disc electrode (RDE) method and by constructing a membrane electrode assembly (MEA) proton exchange membrane (PEM) single cell. The PtCu3 nanoparticles become porous, enriched in Pt on the surface, and exhibit a high RDE activity. The single cell electrochemical study reveals that, contrary to most advanced catalysts, the high ORR activity can be transferred from the RDE to the MEA. In the latter case, at 0.9VIRfree, a mass activity of 0.53 A/mgPt, at a Pt electrode loading of 0.2 mg/cm2, is achieved. However, at high current density, oxygen transport becomes limited. This is proven by the analysis of polarization curves and electrochemical impedance spectroscopy (EIS) data with a Kulikovsky (physical) model. These indicate that this limitation is caused by the non-optimal microporosity of our catalyst, which hind...

ACS Applied Energy Materials, 2019

Coatings, 2018

A profound understanding of the Au dissolution process is a prerequisite for optimal utilization ... more A profound understanding of the Au dissolution process is a prerequisite for optimal utilization of Au-based materials. This goes for either increasing the corrosion stability of materials in the sectors where the long-term functionality of Au is needed or decreasing the corrosion stability where the recovery of the Au component is crucial. By employing an extremely sensitive online analytical system, consisting of an electrochemical flow cell coupled to an inductively coupled plasma mass spectrometry, in situ potential-resolved dissolution of Au in the ppb range is enabled. A comparative study of two Au based materials, (i) a polycrystalline Au disk and (ii) carbon-supported Au nanoparticles, is presented. As a probe, chloride ions were used to elucidate the distinct differences in the corrosion behavior of the two analogues.

Nanoparticles of platinum-group metals (PGM) on carbon supports are widely used as catalysts for ... more Nanoparticles of platinum-group metals (PGM) on carbon supports are widely used as catalysts for a number of chemical and electrochemical conversions on laboratory and industrial scale. The newly emerging field of single atom catalysis focuses on the ultimate level of metal dispersion, i.e. atomically dispersed metal species anchored on the substrate surface. However, the presence of single atoms in traditional nanoparticle-based catalysts remains largely overlooked. In this work we use aberration-corrected scanning transmission electron microscope to investigate four commercially available nanoparticle-based PGM/C catalysts (PGM = Ru, Rh, Pd, Pt). We show that in addition to nanoparticles, single atoms are also present on the surface of carbon substrates. These observations raise questions about the role that single atoms play in conventional nanoparticle PGM/C catalysts. We critically discuss the observations with regard to the quickly developing field of single atom catalysis.