Publications by authors named "Sotirios Baskoutas"

14 Publications

  • Page 1 of 1

Exciton-Related Raman Scattering, Interband Absorption and Photoluminescence in Colloidal CdSe/CdS Core/Shell Quantum Dots Ensemble.

Nanomaterials (Basel) 2021 May 12;11(5). Epub 2021 May 12.

Institute of Engineering and Physics, Russian-Armenian University, Yerevan 0051, Armenia.

By using the numerical discretization method within the effective-mass approximation, we have theoretically investigated the exciton-related Raman scattering, interband absorption and photoluminescence in colloidal CdSe/CdS core/shell quantum dots ensemble. The interband optical absorption and photoluminescence spectra have been revealed for CdSe/CdS quantum dots, taking into account the size dispersion of the ensemble. Numerical calculation of the differential cross section has been presented for the exciton-related Stokes-Raman scattering in CdSe/CdS quantum dots ensemble with different mean sizes.
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http://dx.doi.org/10.3390/nano11051274DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8151553PMC
May 2021

Direct sunlight-driven enhanced photocatalytic performance of VO nanorods/ graphene oxide nanocomposites for the degradation of Victoria blue dye.

Environ Res 2021 Aug 24;199:111369. Epub 2021 May 24.

Department of Materials Science, University of Patras, 26504, Rio, Patras, Greece. Electronic address:

Herein, we report the synthesis and characterizations of Vanadium pentoxide (VO) nanorods/graphene oxide (GO) nanocomposite as efficient direct solar light driven photocatalyst for the enhanced degradation of victoria blue (VB) dye. The nanocomposite was synthesized by sonochemical process and characterized using several analytical methods in order to study the structural, morphological, compositional, optical and photocatalytic properties. The X-ray diffraction studies confirmed the orthorhombic structure of VO while the morphological examinations revealed the growth of VO nanorods and 2D GO sheets. Interestingly, the UV studies ratify that the bandgap of the nanocomposite was reduced compared to pure GO and VO. Interestingly, the interaction of the VO nanorods with the graphene oxide substrate and its effect on the electronic properties of the combined system, have been examined by means of theoretical calculations, based on the so called Geometry, Frequency, Noncovalent, eXtended Tight Binding (GFN-xTB) method. Studying the photocatalytic behavior of nanocomposite, we observe an almost complete degradation (97.95%) of Victoria Blue (VB) dye under direct sunlight illumination within just 90 min. The outstanding nanocomposite photocatalytic efficiency was due to the excellent transfer of interfacial charge and the suppressed recombination of charge-carrier. The kinetics of the degradation process was also analyzed by calculating the rate constant and half-life time. Finally, a possible mechanism has also been discussed for the degradation process of VB dye using nanocomposite under direct sunlight irradiation.
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http://dx.doi.org/10.1016/j.envres.2021.111369DOI Listing
August 2021

Adsorptive removal of antibiotic ofloxacin in aqueous phase using rGO-MoS heterostructure.

J Hazard Mater 2021 May 5;417:125982. Epub 2021 May 5.

Department of Materials Science, University of Patras, Greece.

This paper reports the synthesis, characterization and detailed adsorption studies of rGO-MoS heterostructure. The heterostructure was explored for the adsorption of ofloxacin from the aqueous phase. Detailed studies were conducted to study the effect of crucial parameters such as pH of drug solution, adsorbent dose, temperature and initial drug concentration on the adsorption capacity. Even with a low surface area of 17.17 m/g, the adsorbent exhibited maximum removal efficiency of 95% at a dose of 0.35 g/L and an initial drug concentration of 10 mg/L in 240 min. Thermodynamic study revealed the values for ∆H and ∆G to be - 101.15 and - 7.47 kJ/mol respectively, indicating that the process is spontaneous and exothermic in nature. The heterostructure adsorbent exhibited remarkable reusability and stability up to five cycles. The heterostructure combines excellent adsorption capabilities arising from the two-dimensional structures of rGO and MoS with the stronger and more specific interaction with the drug molecules which results in better performance towards the removal of the drug. The excellent performance of the heterostructure indicates that combining 2D materials can be a good strategy for producing highly efficient materials towards the adsorptive removal of pollutants.
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http://dx.doi.org/10.1016/j.jhazmat.2021.125982DOI Listing
May 2021

Band Gap Measurements of Nano-Meter Sized Rutile Thin Films.

Nanomaterials (Basel) 2020 Nov 29;10(12). Epub 2020 Nov 29.

Materials Science Department, University of Patras, 26504 Patras, Greece.

Thin Titanium films were fabricated on quartz substrates by radio frequency magnetron sputtering under high vacuum. Subsequent annealing at temperatures of 600 ∘C in air resulted in single-phase TiO2 with the structure of rutile, as X-ray diffraction experiment demonstrates. Atomic-force microscopy images verify the high crystalline quality and allow us to determine the grain size even for ultrathin TiO2 films. Rutile has a direct energy band gap at about 3.0-3.2 eV; however, the transitions between the valence and conduction band are dipole forbidden. Just a few meV above that, there is an indirect band gap. The first intense absorption peak appears at about 4 eV. Tauc plots for the position of the indirect band gap show a "blue shift" with decreasing film thickness. Moreover, we find a similar shift for the position of the first absorbance peak studied by the derivative method. The results indicate the presence of quantum confinement effects. This conclusion is supported by theoretical calculations based on a combination of the effective mass theory and the Hartree Fock approximation.
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http://dx.doi.org/10.3390/nano10122379DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7761142PMC
November 2020

BiWO/C-Dots/TiO: A Novel Z-Scheme Photocatalyst for the Degradation of Fluoroquinolone Levofloxacin from Aqueous Medium.

Nanomaterials (Basel) 2020 May 8;10(5). Epub 2020 May 8.

Department of Materials Science, University of Patras, 26504 Rio Achaia, Patras, Greece.

Photocatalytic materials and semiconductors of appropriate structural and morphological architectures as well as energy band gaps are materials needed for mitigating current environmental problems, as these materials have the ability to exploit the full spectrum of solar light in several applications. Thus, constructing a Z-scheme heterojunction is an ideal approach to overcoming the limitations of a single component or traditional heterogeneous catalysts for the competent removal of organic chemicals present in wastewater, to mention just one of the areas of application. A Z-scheme catalyst possesses many attributes, including enhanced light-harvesting capacity, strong redox ability and different oxidation and reduction positions. In the present work, a novel ternary Z-scheme photocatalyst, i.e., BiWO/C-dots/TiO has been prepared by a facile chemical wet technique. The prepared solar light-driven Z-scheme composite was characterized by many analytical and spectroscopic practices, including powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), N adsorption-desorption isotherm, Fourier-transform infrared spectroscopy (FT-IR), photoluminescence (PL) and UV-vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the BiWO/C-dots/TiO composite was evaluated by studying the degradation of fluoroquinolone drug, levofloxacin under solar light irradiation. Almost complete (99%) decomposition of the levofloxacin drug was observed in 90 min of sunlight irradiation. The effect of catalyst loading, initial substrate concentration and pH of the reaction was also optimized. The photocatalytic activity of the prepared catalyst was also compared with that of bare BiWO, TiO and TiO/C-dots under optimized conditions. Scavenger radical trap studies and terephthalic acid (TPA) fluorescence technique were done to understand the role of the photo-induced active radical ions that witnessed the decomposition of levofloxacin. Based on these studies, the plausible degradation trail of levofloxacin was proposed and was further supported by LC-MS analysis.
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http://dx.doi.org/10.3390/nano10050910DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7279409PMC
May 2020

Electronic and Optical Properties of Ultrasmall ABX (A = Cs, CHNH/B = Ge, Pb, Sn, Ca, Sr/X = Cl, Br, I) Perovskite Quantum Dots.

ACS Omega 2018 Dec 31;3(12):18917-18924. Epub 2018 Dec 31.

Department of Materials Science, School of Natural Sciences, University of Patras, 26504 Patras, Greece.

Perovskite quantum dots (QDs) constitute a novel and rapidly developing field of nanotechnology with promising potential for optoelectronic applications. However, few perovskite materials for QDs and other nanostructures have been theoretically explored. In this study, we present a wide spectrum of different hybrid halide perovskite cuboid-like QDs with the general formula of ABX with varying sizes well below the Bohr exciton radius. Density functional theory (DFT) and time-dependent DFT calculations were employed to determine their structural, electronic, and optical properties. Our calculations include both stoichiometric and nonstoichiometric QDs, and our results reveal several materials with high optical absorption and application-suitable electronic and optical gaps. Our study highlights the potential as well as the challenges and issues regarding nanostructured halide perovskite materials, laying the background for future theoretical and experimental work.
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http://dx.doi.org/10.1021/acsomega.8b02525DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6643916PMC
December 2018

Special Issue: Zinc Oxide Nanostructures: Synthesis and Characterization.

Materials (Basel) 2018 May 23;11(6). Epub 2018 May 23.

Department of Materials Science, University of Patras, 26500 Patras, Greece.

Zinc oxide (ZnO) is a wide band gap semiconductor with an energy gap of 3.37 eV at room temperature. It has been used considerably for its catalytic, electrical, optoelectronic, and photochemical properties. ZnO nanomaterials, such as quantum dots, nanorods, and nanowires, have been intensively investigated for their important properties. Many methods have been described in the literature for the production of ZnO nanostructures, such as laser ablation, hydrothermal methods, electrochemical deposition, sol⁻gel methods, Chemical Vapour Deposition, molecular beam epitaxy, the common thermal evaporation method, and the soft chemical solution method. The present Special Issue is devoted to the Synthesis and Characterization of ZnO nanostructures with novel technological applications.
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http://dx.doi.org/10.3390/ma11060873DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6025422PMC
May 2018

A Study of Quantum Confinement Effects in Ultrathin NiO Films Performed by Experiment and Theory.

Materials (Basel) 2018 Jun 4;11(6). Epub 2018 Jun 4.

Department of Materials Science, University of Patras, 26504 Patras, Greece.

Ultrathin NiO films in the thickness range between 1 and 27 nm have been deposited on high-quality quartz substrates by direct magnetron sputtering under a rough vacuum with a base pressure of 2 × 10 mbar. The sputtering target was metallic Ni; however, due to the rough vacuum a precursor material was grown in which most of Ni was already oxidized. Subsequent short annealing at temperatures of about 600 °C in a furnace in air resulted in NiO with high crystallinity quality, as atomic force microscopy revealed. The images of surface morphology showed that the NiO films were continuous and follow a normal grain growth mode. UV-Vis light absorption spectroscopy experiments have revealed a blue shift of the direct band gap of NiO. The band gap was determined either by Tauc plots (onset) or by the derivative method (highest rate of absorbance increase just after the onset). The experimental results are interpreted as evidences of quantum confinement effects. Theoretical calculations based on Hartree Fock approximation as applied for an electron-hole system, in the framework of effective mass approximation were carried out. The agreement between theory and experiment supports the quantum confinement interpretation.
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http://dx.doi.org/10.3390/ma11060949DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6025098PMC
June 2018

Chemical Sensing Applications of ZnO Nanomaterials.

Materials (Basel) 2018 Feb 12;11(2). Epub 2018 Feb 12.

Department of Materials Science, University of Patras, Patras GR 26504, Greece.

Recent advancement in nanoscience and nanotechnology has witnessed numerous triumphs of zinc oxide (ZnO) nanomaterials due to their various exotic and multifunctional properties and wide applications. As a remarkable and functional material, ZnO has attracted extensive scientific and technological attention, as it combines different properties such as high specific surface area, biocompatibility, electrochemical activities, chemical and photochemical stability, high-electron communicating features, non-toxicity, ease of syntheses, and so on. Because of its various interesting properties, ZnO nanomaterials have been used for various applications ranging from electronics to optoelectronics, sensing to biomedical and environmental applications. Further, due to the high electrochemical activities and electron communication features, ZnO nanomaterials are considered as excellent candidates for electrochemical sensors. The present review meticulously introduces the current advancements of ZnO nanomaterial-based chemical sensors. Various operational factors such as the effect of size, morphologies, compositions and their respective working mechanisms along with the selectivity, sensitivity, detection limit, stability, etc., are discussed in this article.
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http://dx.doi.org/10.3390/ma11020287DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5848984PMC
February 2018

In-Doped ZnO Hexagonal Stepped Nanorods and Nanodisks as Potential Scaffold for Highly-Sensitive Phenyl Hydrazine Chemical Sensors.

Materials (Basel) 2017 Nov 21;10(11). Epub 2017 Nov 21.

Department of Materials Science, University of Patras, Patras 26504, Greece.

Herein, we report the growth of In-doped ZnO (IZO) nanomaterials, i.e., stepped hexagonal nanorods and nanodisks by the thermal evaporation process using metallic zinc and indium powders in the presence of oxygen. The as-grown IZO nanomaterials were investigated by several techniques in order to examine their morphological, structural, compositional and optical properties. The detailed investigations confirmed that the grown nanomaterials, i.e., nanorods and nanodisks possess well-crystallinity with wurtzite hexagonal phase and grown in high density. The room-temperature PL spectra exhibited a suppressed UV emissions with strong green emissions for both In-doped ZnO nanomaterials, i.e., nanorods and nanodisks. From an application point of view, the grown IZO nanomaterials were used as a potential scaffold to fabricate sensitive phenyl hydrazine chemical sensors based on the I-V technique. The observed sensitivities of the fabricated sensors based on IZO nanorods and nanodisks were 70.43 μA·mM cm and 130.18 μA·mM cm, respectively. For both the fabricated sensors, the experimental detection limit was 0.5 μM, while the linear range was 0.5 μM-5.0 mM. The observed results revealed that the simply grown IZO nanomaterials could efficiently be used to fabricate highly sensitive chemical sensors.
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http://dx.doi.org/10.3390/ma10111337DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5706284PMC
November 2017

Morphology control of exciton fine structure in polar and nonpolar zinc sulfide nanorods.

Sci Rep 2017 08 24;7(1):9366. Epub 2017 Aug 24.

Department of Chemistry, University of Hamburg, D-20146, Hamburg, Germany.

Electron-hole exchange interaction in semiconductor quantum dots (QDs) splits the band-edge exciton manifold into optically active ("bright") and passive ("dark") states, leading to a complicated exciton fine structure. In the present work, we resolve by atomistic million-atom many-body pseudopotential calculations the exciton fine structure in colloidal polar and nonpolar zinc sulfide (ZnS) nanorods (NRs). We explore that polar NRs with high symmetry exhibit vanishing fine structure splitting (FSS), and are therefore ideal sources of entangled photon pairs. In contrast, nonpolar NRs grown along [Formula: see text] and [Formula: see text] directions with reduced symmetries have significant FSS, which can even reach up to a few mili electron volts. However, such large FSS can be effectively minimized to a few micro electron volts, or even less, by a simple morphology control.
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http://dx.doi.org/10.1038/s41598-017-09812-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5571107PMC
August 2017

Excitonic optical properties of wurtzite ZnS quantum dots under pressure.

J Chem Phys 2015 Mar;142(11):114305

Institut für Physikalische Chemie, Universität Hamburg, 20146 Hamburg, Germany.

By means of atomistic empirical pseudopotentials combined with a configuration interaction approach, we have studied the optical properties of wurtzite ZnS quantum dots in the presence of strong quantum confinement effects as a function of pressure. We find the pressure coefficients of quantum dots to be highly size-dependent and reduced by as much as 23% in comparison to the bulk value of 63 meV/GPa obtained from density functional theory calculations. The many-body excitonic effects on the quantum dot pressure coefficients are found to be marginal. The absolute gap deformation potential of quantum dots originates mainly from the energy change of the lowest unoccupied molecular orbital state. Finally, we find that the exciton spin-splitting increases nearly linearly as a function of applied pressure.
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http://dx.doi.org/10.1063/1.4914473DOI Listing
March 2015

Near-band-edge exciton polarization change in ZnO nanowires.

Phys Chem Chem Phys 2015 Jan 24;17(2):1197-203. Epub 2014 Nov 24.

Materials Science Department, University of Patras, 26504 Patras, Greece.

Using the atomistic pseudopotential method complemented by configuration interaction calculations, we have studied the electronic and optical properties of ZnO nanowires (NWs) in the presence of quantum confinement effects. Our results indicate that the near-band-edge exciton experiences a crossover from an in-plane polarized A-exciton (for D≥ 3 nm) to an out-of-plane polarized C-exciton (for D < 3 nm) due to quantum confinement. This transition leads to a non-monotonic variation of Stokes shift, exhibiting a maximum value around the critical diameter of 3 nm. The observed behavior is analyzed by a stepwise inclusion of correlation effects, leading to a comprehensive description of the excitonic fine structure.
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http://dx.doi.org/10.1039/c4cp04551cDOI Listing
January 2015

Effective band gap of Si nanocrystals embedded in SiO2 matrix.

J Nanosci Nanotechnol 2006 Jul;6(7):2037-41

Materials Science Department, University of Patras, Greece.

Using a formulation of the Hartree-Fock formalism with the potential morphing method in the effective mass approximation, we calculate the effective band gap of Si nanocrystals embedded in SiO2 matrix without the existence of polysilane, as a function of their diameter in the size range 1-3.5 nm. Our results are in better agreement with the experimental data, in comparison with other existing theoretical data. For diameter smaller than 2 nm our results have the same tendency with the existing theoretical results, e.g., the discrepancy between theory and experiment seems to be essential.
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http://dx.doi.org/10.1166/jnn.2006.333DOI Listing
July 2006