Author: Mario Kotlár

Cobalt-doped WSe2@conducting polymer nanostructures as bifunctional electrocatalysts for overall water splitting

Posted on by Mario Kotlár

Sadik Cogal, Gamze Celik Cogal, Matej Mičušík, Mário Kotlár, Maria Omastová

In: International Journal of Hydrogen Energy, (2023)

https://doi.org/10.1016/j.ijhydene.2023.09.002

Abstract

Designing of high-performance, low-cost, and nonprecious metal-based bifunctional electrocatalysts is highly significant for the development of water splitting process and expanding the practical application of green hydrogen production. Transition metal dichalcogenides (TMDs) with intrinsic physical and chemical properties have been considered potential catalytic materials for electrode fabrication. However, it has remained challenging to develop TMD catalysts that have bifunctional properties for overall water splitting. Herein, WSe2, as a typical representative of TMDs, was utilized to design electrocatalysts using polypyrrole (PPy) or polyaniline (PANI) as a conducting polymer (CP) and cobalt doping. A facile hydrothermal preparation of WSe2 in the presence of CP enabled the construction of cobalt-doped WSe2@CP electrocatalysts. Morphological analysis indicated that the CP played an important role as a conductive template to enhance the distribution of WSe2 nanosheets, leading to higher surface area. In addition, cobalt doping led to the formation of defect structures and boosted the electrocatalytic activities of the catalysts for oxygen evolution reaction (OER).

Tailoring the electronic properties of the SnO2 nanoparticle layer for n-i-p perovskite solar cells by Ti3C2TX MXene

Posted on by Mario Kotlár

Muhammad Faraz Ud Din, Shima Sousani, Mario Kotlar, Sami Ullah, Maros Gregor, Tomas Scepka, Yaryna Soyka, Anastasiia Stepura, Ashin Shaji, Femi Igbari, Karol Vegso, Vojtech Nadazdy, Peter Siffalovic, Matej Jergel, Maria Omastova, Eva Majkova

In: Materials Today Communications, Volume 36, (2023)

https://doi.org/10.1016/j.mtcomm.2023.106700

Abstract

The effect of the Ti3C2Tx MXene modification of the SnO2 electron transport layer (ETL) was studied for the concentration range 0–7.4 wt% MXene. The electronic properties of the MXene-modified ETL were studied by the electrical conductivity measurements, density of states mapping by the energy-resolved electrochemical impedance spectroscopy, ultraviolet photoelectron spectroscopy, and photoluminescence. The structure and morphology of the MXene-modified ETL and the top perovskite layer were analyzed by the scanning electron microscopy (SEM), scanning transmission electron microscopy, grazing-incidence X-ray diffraction and in situ grazing-incidence wide-angle X-ray scattering (GIWAXS). The increased electrical conductivity and electron selectivity for the MXene-modified SnO2 ETL was confirmed up to 1 wt% MXene. For 7.4 wt% MXene, significant suppression of the hole blocking property of the ETL was found. The in situ GIWAXS was performed during the post-deposition annealing of the perovskite layer. The increased perovskite grain size on the SnO2 ETL modified by MXene compared to the pure SnO2 ETL visible by SEM was confirmed. The uniaxial texture of the perovskite crystals was revealed in both cases with an increased misorientation angle for the MXene-modified ETL. The grain size and misorientation angle do not exhibit any systematic temporal changes during the post-deposition annealing. The increasing number of the grains during the annealing was observed. These results are explained using the nucleation and growth model. The increased power conversion efficiency from 17.4% to 18.3% of the archetypal methylammonium-lead-iodide perovskite solar cell after the modification of the SnO2 ETL with 0.1 wt% MXene is the effect of two contributions – increased electrical conductivity of the ETL and improved crystallinity and larger grain size compared to the pure SnO2 ETL, which lowers the total boundary area and charge recombination at trap states typically formed at grain boundaries.

Thermoplastic starch/bentonite clay nanocomposite reinforced with vitamin B2: Physicochemical characteristics and release behavior

Posted on by Mario Kotlár

Abolfazl Heydari, Milad KhajeHassani, Haniyeh Daneshafruz, Sepideh Hamedi, Faeze Dorchei, Mário Kotlár, Fahimeh Kazeminava, Samahe Sadjadi, Farideh Doostan, Ivan Chodak, Hassan Sheibani

In: International Journal of Biological Macromolecules. Vol. 242, (2023)

https://doi.org/10.1016/j.ijbiomac.2023.124742

Abstract

This study presents the development and characterization of a nanocomposite material, consisting of thermoplastic starch (TPS) reinforced with bentonite clay (BC) and encapsulated with vitamin B2 (VB). The research is motivated by the potential of TPS as a renewable and biodegradable substitute for petroleum-based materials in the biopolymer industry. The effects of VB on the physicochemical properties of TPS/BC films, including mechanical and thermal properties, water uptake, and weight loss in water, were investigated. In addition, the surface morphology and chemical composition of the TPS samples were analyzed using high-resolution SEM microscopy and EDS, providing insight into the structure-property relationship of the nanocomposites. The results showed that the addition of VB significantly increased the tensile strength and Young’s modulus of TPS/BC films, with the highest values observed for nanocomposites containing 5 php of VB and 3 php of BC. Furthermore, the release of VB was controlled by the BC content, with higher BC content leading to lower VB release. These findings demonstrate the potential of TPS/BC/VB nanocomposites as environmentally friendly materials with improved mechanical properties and controlled release of VB, which can have significant applications in the biopolymer industry.

Electrochemical modified Pt nanoflower @ rGO for non- enzymatic electrochemical sensing of glucose

Posted on by Mario Kotlár

Saravanan Gengan, R.M. Gnanamuthu, Sanjay Sankaranarayanan, Venumbaka Maneesh Reddy, Bhanu Chandra Marepally, Ravi Kumar Biroju

Sensors and Actuators A: Physical, Volume 353, (2023)

https://doi.org/10.1016/j.sna.2023.114232

Abstract

Since lower danger of biorecognition element degradation, enzymes-less glucose have the potential for more reliable in vivo activity, but it suffers due to lack of linear response and poor selectivity. We made attempt to improve selectivity, linear response and stability, environmentally benign electrochemical method adopted to fabricate Pt nanoflowers (PtNF) anchored on rGO modified GCE (PtNF-rGO/GCE). The PtNF-rGO/GCE electrode demonstrated good glucose electrooxidation in alkaline solution, with a linear range, sensitivity and detection limit are up to 3.5 mM, 335.5 μA mM−1 cm−1 and 53 μM (S/N = 3) respectively. The PtNF-rGO/GCE electrode is not only selective also inhibit interfering molecules like uric, dopamine, ascorbic acid. This allows for broadly sensitive, work at low-potential, stable, and quick glucose current detection, which is capable for the expansion of non-enzymatic glucose detectors.

Defective Graphene/Plasmonic Nanoparticle Hybrids for Surface-Enhanced Raman Scattering Sensors

Posted on by Mario Kotlár

Biroju Ravi K., Marepally Bhanu Chandra, Malik Pariksha, Dhara Soumen, Gengan Saravanan, Maity Dipak, Narayanan Tharangattu N., Giri Pravat K.

In: ACS Omega 2023, 8, 4, 4344–4356, (2023)

https://doi.org/10.1021/acsomega.2c07706

Abstract

Two-dimensional–zero-dimensional plasmonic hybrids involving defective graphene and transition metals (DGR-TM) have drawn significant interest due to their near-field plasmonic effects in the wide range of the UV–vis–NIR spectrum. In the present work, we carried out extensive investigations on resonance Raman spectroscopy (RRS) and localized surface plasmon resonance (LSPR) from the various DGR-TM hybrids (Au, Ag, and Cu) using micro-Raman, spatial Raman mapping analysis, high-resolution transmission electron microscopy (HRTEM), and LSPR absorption measurements on defective CVD graphene layers. Further, electric field (E) mappings of samples were calculated using the finite domain time difference (FDTD) method to support the experimental findings. The spatial distribution of various in-plane and edge defects and defect-mediated interaction of plasmonic nanoparticles (NPs) with graphene were investigated on the basis of the RRS and LSPR and correlated with the quantitative analysis from HRTEM, excitation wavelength-dependent micro-Raman, and E-field enhancement features of defective graphene and defective graphene-Au hybrids before and after rapid thermal annealing (RTA). Excitation wavelength-dependent surface-enhanced Raman scattering (SERS) and LSPR-induced broadband absorption from DGR-Au plasmonic hybrids reveal the electron and phonon interaction on the graphene surface, which leads to the charge transfer from TM NPs to graphene. This is believed to be responsible for the reduction in the SERS signal, which was observed from the wavelength-dependent Raman spectroscopy/mappings. We implemented defective graphene and DGR-Au plasmonic hybrids as efficient SERS sensors to detect the Fluorescein and Rhodamine 6G molecules with a detection limit down to 10–9 M. Defective graphene and Au plasmonic hybrids showed an impressive Raman enhancement in the order of 108, which is significant for its practical application.

Correlated reflectance and Raman spectroscopy in substrates with coherent transparent layers

Posted on by Mario Kotlár

VANČO, Ľubomír – KOTLÁR, Mário – VRETENÁR, Viliam – KADLEČÍKOVÁ, Magdaléna – VOJS, Marian – VOGRINČIČ, Peter

In Surfaces and Interfaces. Vol. 34, (2022)

https://doi.org/10.1016/j.surfin.2022.102309

Abstract

Intensity of Raman bands in substrates covered with transparent overlayers can be enhanced due to optical interference, leading to incorrect quantitative interpretation of Raman signals. If thickness and optical properties of the overlayer are known, correction can be done using appropriate models. We theoretically discuss and experimentally evaluate a model where thickness and refractive index of the overlayer remain unknown and determination of enhancement factor is possible via linear relationship to reflectance-related response of the whole structure. Correct interpretation of the spectra is then possible since refractive index and thickness of the transparent layer are implicitly introduced in the measured reflectance. For experimental evidence we exploit SiNx/Si and SiO2/Si structures to find a significant correspondence with the model, aiming toward correlative reflectance and Raman spectroscopy.

Raman spectroscopy of silicon with nanostructured surface

Posted on by Mario Kotlár

KADLEČÍKOVÁ, Magdaléna – VANČO, Ľubomír – BREZA, Juraj – MIKOLÁŠEK, Miroslav – HUŠEKOVÁ, Kristína – FRÖHLICH, Karol – PROCEL, Paul – ZEMAN, Miro – ISABELLA, Olindo

In Optik. Vol. 257, (2022)

https://doi.org/10.1016/j.ijleo.2022.168869

Abstract

We compared the morphology and Raman response of nanoscale shaped surfaces of Si substrates versus monocrystalline Si. Samples were structured by reactive ion etching, and four of them were covered by a RuO2-IrO2 layer. Raman bands, centred at approx. 520 cm–1, belonging to samples processed by etching the Si surface have intensities higher by approximately one order of magnitude than those of reference non-etched samples. For nanostructured samples, the rise in the Raman signal was 12–14 × , which is in agreement with the model of the electric field at the tips of Si due to their geometry. This phenomenon is related to the high absorption of excitation radiation. Nanostructured surfaces of samples containing a layer of RuO2-IrO2 give rise to the phenomenon of surface enhancement of the Raman response most likely due to the charge transfer at the interface between silicon and conductive oxides. The nanostructured surface of Si without a metal layer behaves as a SERS substrate and detects the analytes at a low concentration.

Mesoporous SnO2 Nanoparticle-Based Electron Transport Layer for Perovskite Solar Cells

Posted on by Mario Kotlár

ULLAH, Sami – FARAZ, Muhammad Ud Din – KHAN, Kasi Jafar – KHAN, Kasi Ajab – VÉGSÖ, Karol – KOTLÁR, Mário – MIČUŠÍK, Matej – JERGEL, Matej – NÁDAŽDY, Vojtech – ŠIFFALOVIČ, Peter – MAJKOVÁ, Eva – FAKHARUDDIN, Azhar

In ACS Applied Nano Materials. Vol. 5, iss. 6 (2022)

https://doi.org/10.1021/acsanm.2c00840

Abstract

A perovskite solar cell (PSC) featuring a mesoporous architecture can facilitate perovskite layer formation over a large area via increasing the number of heterogeneous nucleation sites. The morphology of the electron transport layer (ETL) and its interface with the perovskite layer is one of the key factors to boost the performance of a PSC. Tin dioxide (SnO2) is considered as a promising ETL in PSCs owing to its high carrier mobility, good transmittance, deep conduction band level, and efficient photoelectron extraction. Generally, the mesoporous SnO2 (m-SnO2) ETL has a higher surface-to-volume ratio compared to a compact SnO2 layer. Herein, we report on an m-SnO2 ETL prepared by anodizing a metallic tin film on a fluorine-doped tin oxide (FTO) substrate in NaOH solution under an ambient atmosphere. In particular, we developed a bilayer architecture of the m-SnO2 ETL based on the fabrication of two consecutive m-SnO2 layers. The morphology of each layer was controlled by varying the anodization voltage and time at a constant solution concentration during the growth process. This unique approach enabled the deposition of an m-SnO2 ETL with sufficient coverage of the FTO substrate, which is difficult to achieve with a single layer of m-SnO2. In particular, the scanning electron and atomic force microscopy analyses confirmed that the m-SnO2 layer covers completely the FTO substrate. The device fabricated with this bilayer m-SnO2 ETL achieved a 27% improvement in power conversion efficiency compared to that with a single layer of m-SnO2.

Contribution of photocatalytic and Fenton-based processes in nanotwin structured anodic TiO2 nanotube layers modified by Ce and V

Posted on by Mario Kotlár

THIRUNAVUKKARASU,  Guru Karthikeyan – GOWRISANKARAN, Sridhar – ČAPLOVIČOVÁ, Mária – SATRAPINSKYY, Leonid – GREGOR, Maroš – LAVRIKOVA, Aleksandra Y. – GREGUŠ, Ján – HALKO, Radoslav – PLESCH, Gustav – MOTOLA, Martin – MONFORT, Olivier

In Dalton Transactions. Vol. 51, iss. 28 (2022)

https://doi.org/10.1039/D2DT00829G

Abstract

In the present work, nanotwin structured TiO2 nanotube (TNT) layers are prepared by the electrochemical anodization technique to form the anatase phase and by surface modification via spin-coating of Ce and V precursors to form Ce-TNT and V-TNT, respectively. The surface and cross-sectional images by SEM revealed that the nanotubes have an average diameter of ∼130 nm and a length of ∼14 μm. In addition, the TEM images revealed the nanotwin structures of the nanotubes, especially the anatase (001) and (112) twin surfaces, that increase the transport of photogenerated charges. The photoinduced degradation of caffeine (CAF) by TNT, Ce-TNT, and V-TNT led to a degradation extent of 16%, 26% and 33%, respectively, whereas it increased to 26%, 38%, and 46% in the presence of H2O2, owing to the involvement of Fenton-based processes (in addition to photocatalysis). The effect of the Fenton-based processes accounts for about 10% of the total degradation extent of CAF. Finally, the mechanism of the photoinduced degradation of CAF was investigated. The main oxidative species were the hydroxyl radicals, and the better efficiency of V-TNT over Ce-TNT and TNT was ascribed to its negative surface, thus improving the interactions with CAF.

Ni-Fe Cathode Catalyst in Zero-Gap Alkaline Water Electrolysis

Posted on by Mario Kotlár

ZÁCHENSKÁ, Jana – JORÍK, Vladimír – VANČO, Ľubomír – MIČUŠÍK, Matej – ZEMANOVÁ, Matilda

In Electrocatalysis. Vol. 13, iss. 4 (2022)

https://doi.org/10.1007/s12678-022-00734-6

Abstract

Ni–Fe cathode catalyst for zero-gap alkaline water electrolysis was studied. Ni–Fe coatings on nickel foam were prepared by direct current (DC) and pulse current (PC) electrodeposition. The influence of different plating conditions and composition of the electrolyte on the morphology of the samples was studied. It was found that under DC electrodeposition, iron is dominant in the coating. Under PC plating conditions, Ni is the dominant element in Ni–Fe coatings. Ni–Fe coatings prepared under DC electrodeposition provide an effective catalyst in zero-gap electrolysis. Increasing Fe content in the coatings improves the catalytic activity of Ni–Fe catalyst. The study of convenient parameters of PC electrodeposition seems to be complex to reach a highly active surface area.