Centrum pre Nanodiagnostiku Materiálov

Rahul Sharma, Henry Nameirakpam, David Muradas Belinchón, Prince Sharma, Ulrich Noumbe, Daria Belotcerkovtceva, Elin Berggren, Viliam Vretenár, Ľubomir Vančo, Matúš Maťko, Ravi K. Biroju, Soumitra Satapathi, Tomas Edvinsson, Andreas Lindblad, M. Venkata Kamalakar*

In: ACS Applied Materials & Interfaces, Vol 16, Issue 29

https://doi.org/10.1021/acsami.4c07028

Abstract

Two-dimensional (2D) van der Waals heterostructures combine the distinct properties of individual 2D materials, resulting in metamaterials, ideal for emergent electronic, optoelectronic, and spintronic phenomena. A significant challenge in harnessing these properties for future hybrid circuits is their large-scale realization and integration into graphene interconnects. In this work, we demonstrate the direct growth of molybdenum disulfide (MoS2) crystals on patterned graphene channels. By enhancing control over vapor transport through a confined space chemical vapor deposition growth technique, we achieve the preferential deposition of monolayer MoS2 crystals on monolayer graphene. Atomic resolution scanning transmission electron microscopy reveals the high structural integrity of the heterostructures. Through in-depth spectroscopic characterization, we unveil charge transfer in Graphene/MoS2, with MoS2 introducing p-type doping to graphene, as confirmed by our electrical measurements. Photoconductivity characterization shows that photoactive regions can be locally created in graphene channels covered by MoS2 layers. Time-resolved ultrafast transient absorption (TA) spectroscopy reveals accelerated charge decay kinetics in Graphene/MoS2 heterostructures compared to standalone MoS2 and upconversion for below band gap excitation conditions. Our proof-of-concept results pave the way for the direct growth of van der Waals heterostructure circuits with significant implications for ultrafast photoactive nanoelectronics and optospintronic applications.

Andrii Lys, Viktor Zabolotnii, Mária Čaplovičová, Iryna Tepliakova, Agris Berzins, Martin Sahul, Ľubomír Čaplovič, Alexander Pogrebnjak, Igor Iatsunskyi, Roman Viter

In: Journal of Alloys and Compounds,Volume 984, 2024, 173885

https://doi.org/10.1016/j.jallcom.2024.173885

Abstract

Recent research places significant importance on the development of innovative nanocomposites for photoelectrochemical applications. This paper presents the fabrication, characterization, and possible photoelectrochemical applications of novel ZnFe₂O₄/ZnO core-shell nanofibers. These core-shell nanofibers were fabricated through co-axial electrospinning using PVP solutions containing iron and zinc nitrate precursors for the core and shell. The structural and optical properties of ZnFe₂O₄/ZnO core-shell nanofibers were examined through TEM, SEM, XRD, FTIR, Raman spectroscopy, and diffuse reflectance spectroscopy. This comprehensive analysis unveiled that the development of core and shell characteristics was notably influenced by the interdiffusion of [Fe]/[Zn] during the annealing process. The photoelectrochemical properties of ZnFe₂O₄/ZnO core-shell nanofibers were assessed through electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and the Mott-Schottky method. These core-shell nanofibers demonstrated a robust electrochemical response to visible light. Photocurrent and photoconversion efficiency of the core-shell nanofibers were calculated and compared with the corresponding values for core-shell nanoparticles. The mechanisms underlying the structural, optical, and photoelectrochemical properties of ZnFe₂O₄/ZnO core-shell nanofibers were discussed. These advanced nanofibers hold potential applications in photocatalysis, photovoltaics, and energy storage, making this research timely and crucial for advancing sustainable energy technologies and environmental remediation efforts.

Fahimeh Gholami, Arash Ghazitabar, Malek Naderi, Aylar Hoviatdoost, Delasa Ali Jani Ashna, Kiarash Ghazitabar, Bogumił Brycki, Viliam Vretenár

In: Surfaces and Interfaces, (2024)

https://doi.org/10.1016/j.surfin.2024.103936

Abstract

In this study, N-doped cobalt-decorated graphene/carbon nanotube/cellulose microfiber composite aerogels were synthesised and used as oil sorbent. In the current approach, graphene aerogel nanocomposites containing carbon nanotubes and cellulose microfibres were synthesised through a chemical reduction process using ascorbic acid and sodium bisulphite as reducing agents. Subsequently, N-doping was performed using ammonium treatment. The microstructure of these composites was characterised by field emission and conventional scanning electron microscopy, and transmission electron microscopy measurements. The molecular bonding and composition of the composites were analysed using energy-dispersive spectroscopy, Fourier Transform Infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The hydrophobicity of the composites was characterised by a water contact angle test. Finally, the oil sorption performance of the samples was evaluated through a self-design procedure based on a combination of ASTM F716 and 726 standards and Bazargan et al. report. The N-doped Co decorated graphene/carbon nanotube/cellulose microfiber sample with a GO:CNT:CMF mass ratio of 4:2:1 (CGCMF-24) demonstrated the highest hydrophobicity and oil sorption capacity in comparison with other samples. CGCMF-24 adsorbed up to 30, 44, and 54 g/g toluene, cyclohexane, and hexane, respectively. Meanwhile, the most durable adsorbent was CGCMF-24, with 74% durability after five sorption-desorption cycles, and it maintained this capacity for up to 10 cycles.

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).