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Size-Dependent Effects in Materials for Environmental Protection and Energy Application

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Materials Chemistry".

Deadline for manuscript submissions: closed (31 October 2023) | Viewed by 29958

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Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Interests: solid state chemistry; materials for energy storage; lithium ion batteries; sodium ion batteries; electron paramagnetic resonance spectroscopy; structure characterization; intercalation chemistry
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E-Mail Website
Guest Editor
Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 11 Acad. G. Bonchev Str., 1113 Sofia, Bulgaria
Interests: theoretical and computational chemistry; molecular modeling; molecular and periodic structures; spectroscopis properties; optical materials
Special Issues, Collections and Topics in MDPI journals

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Guest Editor
Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria
Interests: oxide glasses; structural characterization; thermal stability; optical properties; sol–gel synthesis; hybrid materials; photocatalytic properties; antibacterial properties
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleague,

The concept of size-dependent material properties becomes dominant in the materials science community. Understanding the size-dependent properties of materials is the most challenging issue in the advanced Materials science. To a great extent this is a result of the technological requirements concerning the development of materials with controlled properties, as well as of the recent progress in materials science, nanotechnology and computational chemistry.

The aim of this Special Issue is to discuss the dimensional effects in materials for environmental protection and clean energy production as an innovative approach for the development of innovative materials with improved properties. The Special Issue will comprise (but is not limited to) the following three main classes of advanced inorganic materials that form the basis of modern technologies:

  • Materials and thin films for environmental protection;
  • Materials for clean energy storage;
  • Ceramics/Bioceramics and Glasses for Better Living (with applications in optics, molecular electronics and medicine).

Prof. Dr. Radostina Stoyanova
Prof. Dr. Ivelina Georgieva
Dr. Albena Bachvarova-Nedelcheva
Guest Editors

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Keywords

  • advanced inorganic materials
  • chemistry of materials
  • computational chemistry
  • catalysts/sorbents
  • electrode materials for rechargeable batteries
  • hydrogen storage materials
  • glasses and ceramics
  • optics
  • molecular electronics
  • bio-compatible materials

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Related Special Issue

Published Papers (22 papers)

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Research

20 pages, 6220 KiB  
Article
The Beneficial Impact of Mineral Content in Spent-Coffee-Ground-Derived Hard Carbon on Sodium-Ion Storage
by Sonya Harizanova, Ivan Uzunov, Lyubomir Aleksandrov, Maria Shipochka, Ivanka Spassova and Mariya Kalapsazova
Materials 2024, 17(5), 1016; https://doi.org/10.3390/ma17051016 - 22 Feb 2024
Cited by 1 | Viewed by 1484
Abstract
The key technological implementation of sodium-ion batteries is converting biomass-derived hard carbons into effective anode materials. This becomes feasible if appropriate knowledge of the relations between the structure of carbonized biomass products, the mineral ash content in them, and Na storage properties is [...] Read more.
The key technological implementation of sodium-ion batteries is converting biomass-derived hard carbons into effective anode materials. This becomes feasible if appropriate knowledge of the relations between the structure of carbonized biomass products, the mineral ash content in them, and Na storage properties is gained. In this study, we examine the simultaneous impact of the ash phase composition and carbon structure on the Na storage properties of hard carbons derived from spent coffee grounds (SCGs). The carbon structure is modified using the pre-carbonization of SCGs at 750 °C, followed by annealing at 1100 °C in an Ar atmosphere. Two variants of the pre-carbonization procedure are adopted: the pre-carbonization of SCGs in a fixed bed and CO2 flow. For the sake of comparison, the pre-carbonized products are chemically treated to remove the ash content. The Na storage performance of SCG-derived carbons is examined in model two and three Na-ion cells. It was found that ash-containing carbons outperformed the ash-free analogs with respect to cycling stability, Coulombic efficiency, and rate capability. The enhanced performance is explained in terms of the modification of the carbon surface by ash phases (mainly albite) and its interaction with the electrolyte, which is monitored by ex situ XPS. Full article
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13 pages, 1875 KiB  
Article
Water Splitting Reaction Mechanism on Transition Metal (Fe-Cu) Sulphide and Selenide Clusters—А DFT Study
by Ellie Uzunova, Ivelina Georgieva and Tsvetan Zahariev
Materials 2024, 17(1), 56; https://doi.org/10.3390/ma17010056 - 22 Dec 2023
Viewed by 1030
Abstract
The tetracarbonyl complexes of transition metal chalcogenides M2X2(CO)4, where M = Fe, Co, Ni, Cu and X = S, Se, are examined by density functional theory (DFT). The M2X2 core is cyclic with either [...] Read more.
The tetracarbonyl complexes of transition metal chalcogenides M2X2(CO)4, where M = Fe, Co, Ni, Cu and X = S, Se, are examined by density functional theory (DFT). The M2X2 core is cyclic with either planar or non-planar geometry. As a sulfide, it is present in natural enzymes and has a selective redox capacity. The reduced forms of the selenide and sulfide complexes are relevant to the hydrogen evolution reaction (HER) and they provide different positions of hydride ligand binding: (i) at a chalcogenide site, (ii) at a particular cation site and (iii) in a midway position forming equal bonds to both cation sites. The full pathway of water decomposition to molecular hydrogen and oxygen is traced by transition state theory. The iron and cobalt complexes, cobalt selenide, in particular, provide lower energy barriers in HER as compared to the nickel and copper complexes. In the oxygen evolution reaction (OER), cobalt and iron selenide tetracarbonyls provide a low energy barrier via OOH* intermediate. All of the intermediate species possess favorable excitation transitions in the visible light spectrum, as evidenced by TD-DFT calculations and they allow photoactivation. In conclusion, cobalt and iron selenide tetracarbonyl complexes emerge as promising photocatalysts in water splitting. Full article
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17 pages, 6005 KiB  
Article
Corrosion-Resistive ZrO2 Barrier Films on Selected Zn-Based Alloys
by Irina Stambolova, Daniela Stoyanova, Maria Shipochka, Nelly Boshkova, Silviya Simeonova, Nikolay Grozev, Georgi Avdeev, Ognian Dimitrov and Nikolai Boshkov
Materials 2023, 16(24), 7673; https://doi.org/10.3390/ma16247673 - 15 Dec 2023
Cited by 1 | Viewed by 1049
Abstract
This work presents the enhanced corrosion resistance of newly developed two-layer composite coatings deposited on low-carbon steel: electrodeposited zinc alloy coatings (Zn–Ni with 10 wt.% Ni (ZN) or Zn–Co with 3 wt.% Co (ZC), respectively) and a top ZrO2 sol–gel layer. Surface [...] Read more.
This work presents the enhanced corrosion resistance of newly developed two-layer composite coatings deposited on low-carbon steel: electrodeposited zinc alloy coatings (Zn–Ni with 10 wt.% Ni (ZN) or Zn–Co with 3 wt.% Co (ZC), respectively) and a top ZrO2 sol–gel layer. Surface morphology peculiarities and anti-corrosion characteristics were examined using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), atomic force microscopy (AFM), water contact angle (WCA) measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) analyses, potentiodynamic polarization (PDP) curves, corrosion potential (Ecorr), polarization resistance (Rp) measurements (for a prolonged period of 25 days) and open-circuit potential (OCP). The results were compared with the corrosion peculiarities of usual zinc coating. The zirconia top coatings in both systems were amorphous and dense, possessing hydrophobic nature. The experimental data revealed an increased corrosion resistance and protective ability of the ZC system in comparison to that of ZN due to its smooth, homogeneous surface and the presence of poorly crystallized oxides (ZnO and Co3O4), both later playing the role of a barrier for corrosive agents. Full article
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0 pages, 2566 KiB  
Article
Naphthalene Monoimides with Peri-Annulated Disulfide Bridge—Synthesis and Electrochemical Redox Activity
by Monika Mutovska, Natali Simeonova, Stanimir Stoyanov, Yulian Zagranyarski, Silva Stanchovska and Delyana Marinova
Materials 2023, 16(23), 7471; https://doi.org/10.3390/ma16237471 - 1 Dec 2023
Cited by 1 | Viewed by 1121
Abstract
Nowadays, organosulfur compounds provide new options in the development of full organic ion batteries. However, many drawbacks (such as kinetics limitations during the reversible oxidation of disulfides with cleavage of S–S bond, as well as solubility in non-aqueous electrolytes) make their commercialization difficult. [...] Read more.
Nowadays, organosulfur compounds provide new options in the development of full organic ion batteries. However, many drawbacks (such as kinetics limitations during the reversible oxidation of disulfides with cleavage of S–S bond, as well as solubility in non-aqueous electrolytes) make their commercialization difficult. Herein, a new concept for the design of organosulfur compounds with regulated redox properties and limited solubility is proposed. As a proof-of-concept, we designed peri-disulfo-substituted 1,8-naphthalimide derivatives, in which the alkyl chain length and halogen substituents (Cl or Br) at positions 3 and 6 are varied. The compounds were synthesized by an originally developed procedure starting from tetrahalonaphthalic anhydride via nucleophilic substitution at both peri-positions in the respective imide. Using ionic liquid electrolyte, it was found that the new peri-dithiolo-1,8-naphthalimides can participate in n- and p-type redox reactions at about 2.0 V and above 4.0 V vs. Li/Li+, respectively. The redox potentials are sensitive mainly to whether Cl or Br substituents are available in the molecule architecture, while the alkyl chain length determines the kinetics of the redox reactions. Among all compounds, the chloro-substituted compound with the shorter alkyl chain displays the best kinetics for both low- and high-voltage redox reactions. Full article
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16 pages, 7242 KiB  
Article
Graphene-Based Composites for Thermoelectric Applications at Room Temperature
by Sonya Harizanova, Vassil Vulchev and Radostina Stoyanova
Materials 2023, 16(23), 7262; https://doi.org/10.3390/ma16237262 - 21 Nov 2023
Cited by 1 | Viewed by 1196
Abstract
The thermoelectric materials that operate at room temperature represent a scientific challenge in finding chemical compositions with three optimized, independent parameters, namely electrical and thermal conductivity and the Seebeck coefficient. Here, we explore the concept of the formation of hybrid composites between carbon-based [...] Read more.
The thermoelectric materials that operate at room temperature represent a scientific challenge in finding chemical compositions with three optimized, independent parameters, namely electrical and thermal conductivity and the Seebeck coefficient. Here, we explore the concept of the formation of hybrid composites between carbon-based materials and oxides, with the aim of modifying their thermoelectric performance at room temperature. Two types of commercially available graphene-based materials are selected: N-containing reduced graphene oxide (NrGO) and expanded graphite (ExGr). Although the NrGO displays the lowest thermal conductivity at room temperature, the ExGr is characterized by the lowest electrical resistivity and a negative Seebeck coefficient. As oxides, we choose two perspective thermoelectric materials: p-type Ca3Co4O9 and n-type Zn0.995Al0.005O. The hybrid composites were prepared by mechanical milling, followed by a pelleting. The thermoelectric efficiency was evaluated on the basis of its measured electrical resistivity, Seebeck coefficient and thermal conductivity at room temperature. It was found that that 2 wt.% of ExGr or NrGO leads to an enhancement of the thermoelectric activity of Ca3Co4O9, while, for Zn0.995Al0.005O, the amount of ExGr varies between 5 and 20 wt.%. The effect of the composites’ morphology on the thermoelectric properties is discussed on the basis of SEM/EDS experiments. Full article
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11 pages, 4880 KiB  
Article
Synthesis and Luminescent Properties of Barium Molybdate Nanoparticles
by Maria Gancheva, Reni Iordanova, Iovka Koseva, Georgi Avdeev, Gergana Burdina and Petar Ivanov
Materials 2023, 16(21), 7025; https://doi.org/10.3390/ma16217025 - 3 Nov 2023
Cited by 3 | Viewed by 975
Abstract
BaMoO4 was obtained via facile mechanochemical synthesis at room temperature and a solid-state reaction. An evaluation of the phase composition and structural and optical properties of BaMoO4 was conducted. The influence of different milling speeds on the preparation of BaMoO4 [...] Read more.
BaMoO4 was obtained via facile mechanochemical synthesis at room temperature and a solid-state reaction. An evaluation of the phase composition and structural and optical properties of BaMoO4 was conducted. The influence of different milling speeds on the preparation of BaMoO4 was explored. A shorter reaction time for the phase formation of BaMoO4 was achieved using a milling speed of 850 rpm. A milling speed of 500 rpm led to partial amorphization of the initial reagents and to prolongation of the synthesis time of up to 3 h of milling time. Solid-state synthesis was performed via heat treatment at 900 °C for 15 h. X-ray diffraction analysis (XRD), infrared (IR) and UV diffuse reflectance (UV-Vis) and photoluminescence (PL) spectroscopy were carried out to characterize the samples. Independently of the method of preparation, the obtained samples had tetragonal symmetry. The average crystallite sizes of all samples, calculated using Scherrer’s formula, were in the range of 240 to 1540 Å. IR spectroscopy showed that more distorted structural MoO4 units were formed when the compound was synthesized via a solid-state reaction. The optical band gap energy of the obtained materials was found to decrease from 4.50 to 4.30 eV with increasing crystallite sizes. Green- and blue-light emissions were observed for BaMoO4 phases under excitation wavelengths of 330 and 488 nm. It was established that the intensity of the PL peaks depends on two factors: the symmetry of MoO4 units and the crystallite sizes. Full article
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12 pages, 3887 KiB  
Article
Preparation, Characterization, and Antibacterial Properties of Cu-Fibreboards
by Lyubomir Aleksandrov, Nadezhda Rangelova, Nevena Lazarova-Zdravkova, Nelly Georgieva, Mirela Dragnevska and Sanchi Nenkova
Materials 2023, 16(21), 6936; https://doi.org/10.3390/ma16216936 - 28 Oct 2023
Cited by 1 | Viewed by 1274
Abstract
In the present study, copper modified fibreboards were prepared and their existing phase, morphology, and antibacterial behaviour were investigated. The copper content and the physical and mechanical properties of fibreboards (thickness, bending strength, and swelling) were determined. X-ray diffraction analysis (XRD) showing diffraction [...] Read more.
In the present study, copper modified fibreboards were prepared and their existing phase, morphology, and antibacterial behaviour were investigated. The copper content and the physical and mechanical properties of fibreboards (thickness, bending strength, and swelling) were determined. X-ray diffraction analysis (XRD) showing diffraction peaks typical for cellulose, Cu2S, and Na2SO4, depended on the preparation conditions. The average size of the Cu2S crystals varied between 20 and 50 nm. The morphology of the obtained fibreboards, as well as the size and shape of copper particles, were observed by scanning electron microscopy (SEM) and transition electron microscopy (TEM). The antibacterial activity was tested against Gram-positive (Bacillus subtilis 3562) and Gram-negative (Escherichia coli K12 407) bacteria. The tests showed that the materials had higher antibacterial activity against E. coli, which depended on their preparation conditions. Based on these results, the obtained copper fibreboards can be used as antibacterial agents in the packaging and building industry. Full article
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10 pages, 2527 KiB  
Article
Hydrogen Storage Properties of Ball Milled MgH2 with Additives- Ni, V and Activated Carbons Obtained from Different By-Products
by Eli Grigorova, Pavel Markov, Boyko Tsyntsarski, Peter Tzvetkov and Ivanka Stoycheva
Materials 2023, 16(20), 6823; https://doi.org/10.3390/ma16206823 - 23 Oct 2023
Viewed by 1182
Abstract
The hydrogen sorption of materials based on 80 wt.% MgH2 with the addition of 15 wt.% Ni or V and 5 wt.% activated carbons synthesized from polyolefin wax, a waste product from polyethylene production (POW), walnut shells (CAN), and peach stones (CPS) [...] Read more.
The hydrogen sorption of materials based on 80 wt.% MgH2 with the addition of 15 wt.% Ni or V and 5 wt.% activated carbons synthesized from polyolefin wax, a waste product from polyethylene production (POW), walnut shells (CAN), and peach stones (CPS) prepared by milling under an inert Ar atmosphere for a period of 1 h, is investigated. All precursors are submitted to pyrolysis followed by steam activation in order to obtain the activated carbons. The hydrogen sorption evaluations are carried out for absorption at 473 and 573 K with pressure of 1 MPa and for desorption at 623 and 573 K with pressure of 0.15 MPa. The composition of the samples after milling and hydrogenation is monitored by X-ray diffraction analyses. The 80 wt.% MgH2–15 wt. %Ni–5 wt.% POW or CAN after absorption–desorption cycling and in a hydrogenated state at 573 K and 1 MPa are analyzed by TEM. Full article
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23 pages, 9703 KiB  
Article
Effect of TiO2 on Pd/La2O3-CeO2-Al2O3 Systems during Catalytic Oxidation of Methane in the Presence of H2O and SO2
by Ralitsa Velinova, Silviya Todorova, Daniela Kovacheva, Hristo Kolev, Yordanka Karakirova, Pavel Markov, Katerina Tumbalova, Georgi Ivanov and Anton Naydenov
Materials 2023, 16(20), 6784; https://doi.org/10.3390/ma16206784 - 20 Oct 2023
Cited by 1 | Viewed by 1968
Abstract
New results on the effect of TiO2 on Pd/La2O3-CeO2-Al2O3 systems for catalytic oxidation of methane in the presence of H2O and SO2 have been received. Low-temperature N2-adsorption, XRD, [...] Read more.
New results on the effect of TiO2 on Pd/La2O3-CeO2-Al2O3 systems for catalytic oxidation of methane in the presence of H2O and SO2 have been received. Low-temperature N2-adsorption, XRD, SEM, HRTEM, XPS, EPR and FTIR techniques were used to characterize the catalyst. The presence of Ce3+ on the catalytic surface and in the volume near the lantana was revealed by EPR and XPS. After aging, the following changes are observed: (i) agglomeration of the Pd-clusters (from 8 nm to 12 nm); (ii) transformation of part of the TiO2 from anatase to larger particles of rutile; and (iii)—the increase in PdO/Pd—ratio above its optimum. The modification by Ti of the La2O3-CeO2-Al2O3 system leads to higher resistance towards the presence of SO2 most likely due to the prevailing formation of unstable surface sulfites instead of thermally stable sulfates. Based on kinetic model calculations, the reaction pathway over the Pd/La2O3-CeO2-TiO2-Al2O3 catalyst follows the Mars–van Krevelen mechanism. For evaluation of the possible practical application of the obtained material, a sample of Pd/La2O3-CeO2-TiO2-Al2O3, supported on rolled aluminum-containing stainless steel (Aluchrom VDM®), was prepared and tested. Methane oxidation in an industrial-scale monolithic reactor was simulated using a two-dimensional heterogeneous reactor model. Full article
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16 pages, 7283 KiB  
Article
Network Structure and Luminescent Properties of ZnO–B2O3–Bi2O3–WO3:Eu3+ Glasses
by Aneliya Yordanova, Margarita Milanova, Reni Iordanova, Margit Fabian, Lyubomir Aleksandrov and Petia Petrova
Materials 2023, 16(20), 6779; https://doi.org/10.3390/ma16206779 - 20 Oct 2023
Cited by 2 | Viewed by 1339
Abstract
In this study, we investigated the influence of Bi2O3 and WO3 on both structure and optical properties of 50ZnO:(49 − x)B2O3:1Bi2O3:xWO3; x = 1, 5, 10 glasses doped with [...] Read more.
In this study, we investigated the influence of Bi2O3 and WO3 on both structure and optical properties of 50ZnO:(49 − x)B2O3:1Bi2O3:xWO3; x = 1, 5, 10 glasses doped with 0.5 mol% Eu2O3. IR spectroscopy revealed the presence of trigonal BØ3 units connecting superstructural groups, [BØ2O] metaborate groups, tetrahedral BØ4 units in superstructural groupings (Ø = bridging oxygen atom), borate triangles with nonbridging oxygen atoms, [WO4]2− tetrahedral, and octahedral WO6 species. Neutron diffraction experimental data were simulated by reverse Monte Carlo modeling. The atomic distances and coordination numbers were established, confirming the short-range order found by IR spectra. The synthesized glasses were characterized by red emission at 612 nm. All findings suggest that Eu3+ doped zinc borate glasses containing both WO3 and Bi2O3 have the potential to serve as a substitute for red phosphor with high color purity. Full article
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14 pages, 2510 KiB  
Article
Machine Learning Prediction of the Redox Activity of Quinones
by Ilia Kichev, Lyuben Borislavov, Alia Tadjer and Radostina Stoyanova
Materials 2023, 16(20), 6687; https://doi.org/10.3390/ma16206687 - 14 Oct 2023
Cited by 1 | Viewed by 1216
Abstract
The redox properties of quinones underlie their unique characteristics as organic battery components that outperform the conventional inorganic ones. Furthermore, these redox properties could be precisely tuned by using different substituent groups. Machine learning and statistics, on the other hand, have proven to [...] Read more.
The redox properties of quinones underlie their unique characteristics as organic battery components that outperform the conventional inorganic ones. Furthermore, these redox properties could be precisely tuned by using different substituent groups. Machine learning and statistics, on the other hand, have proven to be very powerful approaches for the efficient in silico design of novel materials. Herein, we demonstrated the machine learning approach for the prediction of the redox activity of quinones that potentially can serve as organic battery components. For the needs of the present study, a database of small quinone-derived molecules was created. A large number of quantum chemical and chemometric descriptors were generated for each molecule and, subsequently, different statistical approaches were applied to select the descriptors that most prominently characterized the relationship between the structure and the redox potential. Various machine learning methods for the screening of prospective organic battery electrode materials were deployed to select the most trustworthy strategy for the machine learning-aided design of organic redox materials. It was found that Ridge regression models perform better than Regression decision trees and Decision tree-based ensemble algorithms. Full article
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0 pages, 8562 KiB  
Article
Polycarboxy/Sulfo Betaine—Calcium Phosphate Hybrid Materials with a Remineralization Potential
by Diana Rabadjieva, Rumiana Gergulova, Konstans Ruseva, Alexander Bonchev, Pavletta Shestakova, Marin Simeonov, Radosveta Vasileva, Dragomir Tatchev, Rositsa Titorenkova and Elena Vassileva
Materials 2023, 16(20), 6640; https://doi.org/10.3390/ma16206640 - 11 Oct 2023
Cited by 2 | Viewed by 1325
Abstract
Biomacromolecules control mineral formation during the biomineralization process, but the effects of the organic components’ functionality on the type of mineral phase is still unclear. The biomimetic precipitation of calcium phosphates in a physiological medium containing either polycarboxybetaine (PCB) or polysulfobetaine (PSB) was [...] Read more.
Biomacromolecules control mineral formation during the biomineralization process, but the effects of the organic components’ functionality on the type of mineral phase is still unclear. The biomimetic precipitation of calcium phosphates in a physiological medium containing either polycarboxybetaine (PCB) or polysulfobetaine (PSB) was investigated in this study. Amorphous calcium phosphate (ACP) or a mixture of octacalcium phosphate (OCP) and dicalcium phosphate dihydrate (DCPD) in different ratios were identified depending on the sequence of initial solution mixing and on the type of the negative functional group of the polymer used. The more acidic character of the sulfo group in PSB than the carboxy one in PCB determines the dominance of the acidic solid phases, namely, an acidic amorphous phase or DCPD. In the presence of PCB, the formation of ACP with acicular particles arranged in bundles with the same orientation was observed. A preliminary study on the remineralization potential of the hybrid material with the participation of PSB and a mixture of OCP and DCPD did not show an increase in enamel density, contrary to the materials based on PCB and ACP. Moreover, the latter showed the creation of a newly formed crystal layer similar to that of the underlying enamel. This defines PCB/ACP as a promising material for enamel remineralization. Full article
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16 pages, 3821 KiB  
Article
Mg, Zn Substituted Calcium Phosphates—Thermodynamic Modeling, Biomimetic Synthesis in the Presence of Low-Weight Amino Acids and High Temperature Properties
by Diana Rabadjieva, Rumiana Gergulova, Kostadinka Sezanova, Daniela Kovacheva and Rositsa Titorenkova
Materials 2023, 16(20), 6638; https://doi.org/10.3390/ma16206638 - 11 Oct 2023
Cited by 2 | Viewed by 1282
Abstract
The preparation of specially doped calcium phosphates (CaPs) is receiving a great deal of attention from researchers due to CaPs’ enhanced capabilities for application in medicine. Complexation and precipitation in a complicated electrolyte system including simulated body fluids that are enriched with Mg [...] Read more.
The preparation of specially doped calcium phosphates (CaPs) is receiving a great deal of attention from researchers due to CaPs’ enhanced capabilities for application in medicine. Complexation and precipitation in a complicated electrolyte system including simulated body fluids that are enriched with Mg2+ and Zn2+ ions and modified with glycine, alanine and valine were first evaluated using a thermodynamic equilibrium model. The influence of the type and concentration of amino acid on the incorporation degree of Mg and Zn into the solid phases was predicted. Experimental studies, designed on the basis of thermodynamic calculations, confirmed the predictions. Amorphous calcium phosphates double-doped with Mg and Zn were biomimetically precipitated and transformed into Mg, Zn-β—tricalcium phosphates (TCP) upon calcination. The Rietveld refinement confirmed that Mg2+ and Zn2+ substituted Ca2+ only at the octahedral sites of β-TCP, and in some cases, fully displacing the Ca2+ from them. The resulting Mg, Zn-β–TCP can serve as a reservoir for Mg and Zn ions when included in the formulation of a biomaterial for bone remodeling. The research conducted reveals the effect of combining mathematical models with experimental studies to pre-evaluate the influence of various additives in the design of materials with predetermined properties. Full article
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16 pages, 4532 KiB  
Article
Ultra-Short Laser-Assisted Micro-Structure Formations on Mg/Zn Double-Doped Calcium Phosphate Ceramics for Enhanced Antimicrobial Activity
by Albena Daskalova, Kostadinka Sezanova, Liliya Angelova, Tsvetelina Paunova-Krasteva, Rumiana Gergulova, Daniela Kovacheva and Diana Rabadjieva
Materials 2023, 16(20), 6626; https://doi.org/10.3390/ma16206626 - 10 Oct 2023
Cited by 1 | Viewed by 1150
Abstract
Bacterial infection is one of the most common and harmful medical issues following the implantation of materials and devices in the body leading to antibiotic resistance of diverse bacterial strains. In this work, a novel approach is presented combining adopted laser-based patterning method [...] Read more.
Bacterial infection is one of the most common and harmful medical issues following the implantation of materials and devices in the body leading to antibiotic resistance of diverse bacterial strains. In this work, a novel approach is presented combining adopted laser-based patterning method in addition to doping (Mg and Zn) metal ions to prepare calcium phosphate ceramic substrate, applicable in medicine, with enhanced surface antimicrobial characteristics. The preparation of tablets containing Mg (8.44 mol%) and Zn (2.63 mol%) β-tricalcium phosphate involved biomimetic precipitation of amorphous calcium phosphate in media of simulated body fluid enriched with Mg2+ and Zn2+ ions as well as the presence of valine as an organic additive, followed by step-wise calcination up to 1000 °C. The results from laser processing showed formation of deeper patterns with increased surface roughness (from 4.9 µm to 9.4 µm) as laser power and velocity increase, keeping constant the hatch sizes of 50 µm. The textured surfaces consist of peaks and valleys arrangement that change the morphology of Escherichia coli cells and decrease of cell viability. Our study reveals the possibilities of the application of ultra-short laser radiation as a potential alternative therapy for controlling the antimicrobial effect of the ceramic surface. Full article
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16 pages, 6647 KiB  
Article
Carbon-Based Composites with Mixed Phosphate-Pyrophosphates with Improved Electrochemical Performance at Elevated Temperature
by Sonya Harizanova, Trajche Tushev, Violeta Koleva and Radostina Stoyanova
Materials 2023, 16(19), 6546; https://doi.org/10.3390/ma16196546 - 4 Oct 2023
Cited by 1 | Viewed by 3222
Abstract
Sodium iron phosphate-pyrophosphate, Na4Fe3(PO4)2P2O7 (NFPP) emerges as an excellent cathode material for sodium-ion batteries. Because of lower electronic conductivity, its electrochemical performance depends drastically on the synthesis method. Herein, we provide a [...] Read more.
Sodium iron phosphate-pyrophosphate, Na4Fe3(PO4)2P2O7 (NFPP) emerges as an excellent cathode material for sodium-ion batteries. Because of lower electronic conductivity, its electrochemical performance depends drastically on the synthesis method. Herein, we provide a simple and unified method for synthesis of composites between NFPP and reduced graphene oxide (rGO) and standard carbon black, designed as electrode materials for both sodium- and lithium-ion batteries. The carbon additives affect only the morphology and textural properties of the composites. The performance of composites in sodium and lithium cells is evaluated at elevated temperatures. It is found that NFPP/rGO outperforms NFPP/C in both Na and Li storage due to its hybrid mechanism of energy storage. In sodium half-cells, NFPP/rGO delivers a reversible capacity of 95 mAh/g at 20 °C and 115 mAh/g at 40 °C with a cycling stability of 95% and 88% at a rate of C/2. In lithium half-cells, the capacity reaches a value of 120 mAh/g at 20 and 40 °C, but the cycling stability becomes worse, especially at 40 °C. The electrochemical performance is discussed on the basis of ex situ XRD and microscopic studies. The good Na storage performance of NFPP/rGO at an elevated temperature represents a first step towards its commercialization. Full article
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21 pages, 3651 KiB  
Article
Influence of the Chemical Composition of Ceria Conversion Coatings, Sealed in Solution of NaH2PO4 and Ca(NO3)2, on the Corrosion Behavior of Aluminum
by Aleksandar Tsanev, Reni Andreeva and Dimitar Stoychev
Materials 2023, 16(19), 6499; https://doi.org/10.3390/ma16196499 - 29 Sep 2023
Cited by 1 | Viewed by 1119
Abstract
The corrosion-protective influence of eco-friendly ceria conversion coatings deposited on Al-1050 alloy, additionally treated in mixed NaH2PO4 and Ca(NO3)2 solution, was studied. The main aim of this work was to investigate how the obtained mixed systems of [...] Read more.
The corrosion-protective influence of eco-friendly ceria conversion coatings deposited on Al-1050 alloy, additionally treated in mixed NaH2PO4 and Ca(NO3)2 solution, was studied. The main aim of this work was to investigate how the obtained mixed systems of coatings eliminates the negative role of cracks and pores on the surface formed after deposition only of ceria coating. For this purpose, the growth structure, main components and corrosion resistance of the so formed protective systems were investigated by SEM, EDS, XRD, XPS and electrochemical (PDP, Rp, etc.) methods. The results obtained show that the basic components of the conversion layers (before and after exposure in model corrosion media) are characterized by Al2O3, Al(OH)3, CePO4 and Ca5(PO4)3(OH). Based on these results, the optimal conditions of immersion treatment(s) of Al substrate are established. At these regimes, the relationship of co-deposited Ce3+, PO43+ and Ca2+-containing components of the conversion layers determine the maximum values of their polarization resistance—a basic criterion for corrosion protection of Al. This effect is related to the formation of fill out of the defects of the conversion coatings and additional Ca5(PO4)3(OH), CePO4 AlPO4 and Al(OH)3 deposits, leading to the decrease of the corrosion rate. Full article
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13 pages, 18765 KiB  
Article
Formation of Oriented Nanowires from Mixed Metal Oxides
by Anna Dikovska, Genoveva Atanasova, Rumen Nikov, Georgi Avdeev, Zara Cherkezova-Zheleva, Daniela Paneva and Nikolay Nedyalkov
Materials 2023, 16(19), 6446; https://doi.org/10.3390/ma16196446 - 27 Sep 2023
Cited by 1 | Viewed by 917
Abstract
In this study, we present a physical method for the fabrication of oriented nanowires composed of mixed metal oxides. Pulsed laser deposition carried out in the air under atmospheric pressure was used for the production of samples. Two sets of experiments were performed [...] Read more.
In this study, we present a physical method for the fabrication of oriented nanowires composed of mixed metal oxides. Pulsed laser deposition carried out in the air under atmospheric pressure was used for the production of samples. Two sets of experiments were performed by applying nanosecond and picosecond laser ablation, respectively. The depositions were performed using the laser ablation of mixed targets from iron oxide and zinc oxide as the initial materials in different ratios. The experiments were carried out in a magnetic field, which allowed us to control the morphology of nanostructures. The structure, microstructure, morphology, and composition of the structures obtained were studied in relation to the sample composition and laser ablation regime applied. The morphological analysis revealed that the structure of the samples consisted mainly of nanowire-like features reaching tens of micrometers in length. These nanowires were composed of nanoparticles and oriented predominantly in parallel to magnetic field lines. Nanoparticles produced using ps ablation were, on average, smaller than those obtained by ns ablation of the same target. Using ablation with ps laser pulses, we were able to produce new composite materials or materials containing unstable phases. Full article
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16 pages, 3283 KiB  
Article
Effect of B2O3 on the Structure, Properties and Antibacterial Abilities of Sol-Gel-Derived TiO2/TeO2/B2O3 Powders
by Albena Bachvarova-Nedelcheva, Reni Iordanova, Angelina Stoyanova, Nelly Georgieva, Veronica Nemska and Tsvetelina Foteva
Materials 2023, 16(19), 6400; https://doi.org/10.3390/ma16196400 - 25 Sep 2023
Viewed by 1209
Abstract
This paper studies the influence of B2O3 on the structure, properties and antibacterial abilities of sol-gel-derived TiO2/TeO2/B2O3 powders. Titanium(IV) butoxide, telluric(VI) acid and boric acid were used as precursors. Differences were observed in [...] Read more.
This paper studies the influence of B2O3 on the structure, properties and antibacterial abilities of sol-gel-derived TiO2/TeO2/B2O3 powders. Titanium(IV) butoxide, telluric(VI) acid and boric acid were used as precursors. Differences were observed in the degree of decomposition of Ti butoxide in the presence of H3BO3 and H6TeO6 acids. The phase transformations of the obtained gels in the temperature range of 200–700 °C were investigated by XRD. Composite materials containing an amorphous phase and different crystalline phases (metallic Te, α-TeO2, anatase, rutile and TiTe3O8) were prepared. Heating at 400 °C indicated a crystalline-to-amorphous-phase ratio of approximately 3:1. The scanning electron microscopy (SEM) analysis showed the preparation of plate-like TiO2 nanoparticles. The IR results showed that the short-range order of the amorphous phases that are part of the composite materials consists of TiO6, BO3, BO4 and TeO4 structural units. Free B2O3 was not detected in the investigated compositions which could be related to the better connectivity between the building units as compared to binary TiO2/B2O3 compositions. The UV-Vis spectra of the investigated gels exhibited a red shift of the cut-off due to the presence of boron and tellurium units. The binary sample achieved the maximum photodegradation efficiency (94%) toward Malachite green dye under UV irradiation, whereas the ternary sample photoactivity was very low. The compositions exhibited promising antibacterial activity against E. coli NBIMCC K12 407. Full article
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14 pages, 29175 KiB  
Article
Picosecond Pulsed Laser Deposition of Metals and Metal Oxides
by Anna Dikovska, Genoveva Atanasova, Tina Dilova, Aleksandra Baeva, Georgi Avdeev, Petar Atanasov and Nikolay Nedyalkov
Materials 2023, 16(19), 6364; https://doi.org/10.3390/ma16196364 - 22 Sep 2023
Cited by 2 | Viewed by 1156
Abstract
In this work, we present the fabrication of thin films/nanostructures of metals and metal oxides using picosecond laser ablation. Two sets of experiments were performed: the depositions were carried out in vacuum and in air at atmospheric pressure. The subjects of investigation were [...] Read more.
In this work, we present the fabrication of thin films/nanostructures of metals and metal oxides using picosecond laser ablation. Two sets of experiments were performed: the depositions were carried out in vacuum and in air at atmospheric pressure. The subjects of investigation were the noble metals Au and Pt and the metal oxides ZnO and TiO2. We studied and compared the phase composition, microstructure, morphology, and physicochemical state of the as-deposited samples’ surfaces in vacuum and in air. It was found that picosecond laser ablation performed in vacuum led to the fabrication of thin films with embedded and differently sized nanoparticles. The implementation of the same process in air at atmospheric pressure resulted in the fabrication of porous nanostructures composed of nanoparticles. The ablation of pure Pt metal in air led to the production of nanoparticles with an oxide shell. In addition, more defects were formed on the metal oxide surface when the samples were deposited in vacuum. Furthermore, the laser ablation process of pure Au metal in a picosecond regime in vacuum and in air was theoretically investigated using molecular dynamics simulation. Full article
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18 pages, 3901 KiB  
Article
Study on the Dye Removal from Aqueous Solutions by Graphene-Based Adsorbents
by Paunka Vassileva, Vencislav Tumbalev, Diana Kichukova, Dimitrinka Voykova, Daniela Kovacheva and Ivanka Spassova
Materials 2023, 16(17), 5754; https://doi.org/10.3390/ma16175754 - 22 Aug 2023
Cited by 5 | Viewed by 1256
Abstract
In the current investigation, the removal efficiency regarding a cationic dye, methylene blue (MB), from three graphene-based materials was investigated. The materials’ characterization process involved instrumental methods such as XRD, XPS, SEM, TEM, FTIR, and nitrogen adsorption at 77 K. The survey examined [...] Read more.
In the current investigation, the removal efficiency regarding a cationic dye, methylene blue (MB), from three graphene-based materials was investigated. The materials’ characterization process involved instrumental methods such as XRD, XPS, SEM, TEM, FTIR, and nitrogen adsorption at 77 K. The survey examined how various process factors influenced the ability of the studied materials to adsorb cationic dyes. These parameters encompassed contact time, initial dye concentrations, solution pH, and temperature. The adsorption procedure was effectively explained through the application of pseudo-second-order and Langmuir models. The maximum adsorption capacity for the best adsorbent at 293 K was found to be 49.4 mg g−1. In addition, the study also determined the entropy, enthalpy, and Gibbs free energy values associated with the removal of MB and showed that the adsorption of MB is endothermic, feasible, and spontaneous. The results also revealed that the studied materials are suitable adsorbents for the removal of cationic dyes. Full article
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16 pages, 16702 KiB  
Article
Effect of Cu as a Minority Alloying Element on the Corrosion Behaviour of Amorphous and Crystalline Al-Ni-Si Alloy
by Vanya Dyakova, Yoanna Kostova, Boriana Tzaneva, Hristina Spasova and Daniela Kovacheva
Materials 2023, 16(15), 5446; https://doi.org/10.3390/ma16155446 - 3 Aug 2023
Viewed by 1108
Abstract
The effect of copper as a minority alloying element on the corrosion behaviour of amorphous and crystalline Al74Ni16Si10 and Al74Ni15Si9Cu2 alloys was investigated in this study. Amorphous alloys were produced as [...] Read more.
The effect of copper as a minority alloying element on the corrosion behaviour of amorphous and crystalline Al74Ni16Si10 and Al74Ni15Si9Cu2 alloys was investigated in this study. Amorphous alloys were produced as rapidly solidified ribbons using the Chill Block Melt Spinning (CBMS) method and subsequently annealed to complete crystallisation. The corrosion rate of alloys was obtained through continuous immersion tests in 3.5% NaCl at 25 °C and 50 °C for 360 h. The electrochemical parameters corrosion current density (Jcorr) and corrosion potential (Ecorr) were determined via the potentiodynamic polarisation test. The results showed better corrosion characteristics of amorphous alloys. The addition of 2 at.% copper to the Al74Ni16Si10 alloy improved pitting corrosion resistance without significant effect on the corrosion current and potential. In immersion tests at 25 °C, the presence of copper resulted in an increase in the corrosion rate of about 300% for both amorphous and crystalline alloys. At a temperature of 50 °C, this increase is on average 130%. The apparent difference between the results of the two test methods is discussed in terms of the imperfections on the surface of rapidly solidified ribbons. The results of this study will contribute to a more complex understanding of the nature of amorphous alloys and their application. Full article
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14 pages, 3258 KiB  
Article
Impact of Beam Deflection Geometry on the Surface Architecture and Mechanical Properties of Electron-Beam-Modified TC4 Titanium Alloy
by Maria Ormanova, Borislav Stoyanov, Nikolay Nedyalkov and Stefan Valkov
Materials 2023, 16(15), 5237; https://doi.org/10.3390/ma16155237 - 26 Jul 2023
Viewed by 1008
Abstract
This paper aims to investigate the impact of beam deflection geometry on the structure, surface architecture, and friction coefficient of electron-beam-modified TC4 titanium alloys. During the experiments, the electron beam was deflected in the form of different scanning geometries, namely linear, circular, and [...] Read more.
This paper aims to investigate the impact of beam deflection geometry on the structure, surface architecture, and friction coefficient of electron-beam-modified TC4 titanium alloys. During the experiments, the electron beam was deflected in the form of different scanning geometries, namely linear, circular, and matrix. The structure of the treated specimens was investigated in terms of their phase composition by employing X-ray diffraction experiments. The microstructure was studied by scanning electron microscopy (SEM). The surface architecture was examined by atomic force microscopy (AFM). The friction coefficient was studied by a mechanical wear test. It was found that the linear and circular deflection geometries lead to a transformation of the phase composition, from double-phase α + β to α’ martensitic structure. The application of a linear manner of scanning leads to a residual amount of beta phase. The use of a matrix does not tend to structural changes on the surface of the TC4 alloy. In the case of linear geometry, the thickness of the modified zone is more than 800 μm while, in the case of EBSM using circular scanning, the thickness is about 160 μm. The electron-beam surface modification leads to a decrease in the surface roughness to about 27 nm in EBSM with linear deflection geometry and 31 nm in circular deflection geometry, compared to that of the pure TC4 substrate (about 160 nm). The electron-beam surface modification of the TC4 alloy leads to a decrease in the coefficient of friction (COF), with the lowest COF values obtained in the case of linear deflection geometry (0.32). The results obtained in this study show that beam deflection geometry has a significant effect on the surface roughness and friction coefficient of the treated surfaces. It was found that the application of a linear manner of scanning leads to the formation of a surface with the lowest roughness and friction coefficient. Full article
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