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

Deadline for manuscript submissions: closed (20 December 2023) | Viewed by 21311

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Dr. Aleksej Zarkov

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Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Naugarduko 24, LT-03225 Vilnius, Lithuania
Interests: functional inorganic materials; mixed metal oxides; nanomaterials; inorganic biomaterials; thin films; ceramics
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Dear Colleagues,

Rapid development of the world highly demands new materials, nanostructures and multicomponent composites with specific chemical and physical properties, which meet the requirements of modern technologies. The employment of appropriate synthetic approaches is crucial for the preparation of inorganic materials with designed microstructure and properties. Among the others, the sol-gel method is very well known for its versatility, simplicity, time- and cost-efficiency. The mixing of starting materials on an atomic level provides high homogeneity and stoichiometry of the products, allowing to obtain high-quality materials at low temperature. The versatility of sol-gel method allows for the development of materials for a wide range of applications in electronics, optoelectronics, catalysis, biomedicine and many other areas. The scope of this Special Issue, “Sol-Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications”, of Materials is focused on, but not limited to, the preparation, characterization and application of functional inorganic materials, as well as hybrid materials, which are important in the field of electronics, optics, biomedicine and others. It is my pleasure to invite you to submit your works in the form of full research articles or reviews related to the investigation of bulk materials, nanomaterials and thin films.

Dr. Aleksej Zarkov
Guest Editor

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Keywords

functional materials
magnetic materials
ferroelectric materials
piezoelectric materials
optical materials
biomaterials
hybrid materials
processing routes
ceramics
thin films

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Published Papers (11 papers)

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Editorial

Jump to: Research

3 pages, 168 KiB

Open AccessEditorial

Sol–Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications

by Aleksej Zarkov

Materials 2024, 17(2), 462; https://doi.org/10.3390/ma17020462 - 18 Jan 2024

Cited by 2 | Viewed by 1353

Abstract

The rapid advances in technologies around the globe necessitate the development of new materials, nanostructures, and multicomponent composites with specific chemical and physical properties that can meet the requirements of modern technologies [...] Full article

(This article belongs to the Special Issue Sol-Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications)

Research

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22 pages, 4675 KiB

Open AccessEditor’s ChoiceArticle

Screening Ba_0.9A_0.1MnO₃ and Ba_0.9A_0.1Mn_0.7Cu_0.3O₃ (A = Mg, Ca, Sr, Ce, La) Sol-Gel Synthesised Perovskites as GPF Catalysts

by Nawel Ghezali, Álvaro Díaz Verde and María José Illán Gómez

Materials 2023, 16(21), 6899; https://doi.org/10.3390/ma16216899 - 27 Oct 2023

Cited by 4 | Viewed by 1123

Abstract

Ba_0.9A_0.1MnO₃ (BM-A) and Ba_0.9A_0.1Mn_0.7Cu_0.3O₃ (BMC-A) (A = Mg, Ca, Sr, Ce, La) perovskite-type mixed oxides were synthesised, characterised, and used for soot oxidation in simulated Gasoline Direct Injection (GDI) engine exhaust conditions. The samples have been obtained by the sol-gel method in an aqueous medium and deeply characterised. The characterization results indicate that the partial substitution of Ba by A metal in BaMnO₃ (BM) and BaMn_0.7Cu_0.3O₃ (BMC) perovskites: (i) favours the hexagonal structure of perovskite; (ii) improves the reducibility and the oxygen desorption during Temperature-Programmed Desorption (O₂-TPD) tests and, consequently, the oxygen mobility; (iii) mantains the amount of oxygen vacancies and of Mn(IV) and Mn(III) oxidation states, being Mn(IV) the main one; and (iv) for Ba_0.9A_0.1Mn_0.7Cu_0.3O₃ (BMC-A) series, copper is partially incorporated into the structure. The soot conversion data reveal that Ba_0.9La_0.1Mn_0.7Cu_0.3O₃ (BMC-La) is the most active catalyst in an inert (100% He) reaction atmosphere, as it presents the highest amount of copper on the surface, and that Ba_0.9Ce_0.1MnO₃ (BM-Ce) is the best one if a low amount of O₂ (1% O₂ in He) is present, as it combines the highest emission of oxygen with the good redox properties of Ce(IV)/Ce(III) and Mn(IV)/Mn(III) pairs. Full article

(This article belongs to the Special Issue Sol-Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications)

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12 pages, 5690 KiB

Open AccessArticle

Fabrication of Europium-Doped CaF₂ Films via Sol-Gel Synthesis as Down-Shifting Layers for Solar Cell Applications

by Anna Lucia Pellegrino, Emil Milan, Adolfo Speghini and Graziella Malandrino

Materials 2023, 16(21), 6889; https://doi.org/10.3390/ma16216889 - 27 Oct 2023

Cited by 1 | Viewed by 1166

Abstract

In the present work, an in-depth study on the sol-gel process for the fabrication of Eu-doped CaF₂ materials in the form of thin films has been addressed for the production of down-shifting layers. Fine-tuning of the operative parameters, such as the annealing temperature, substrate nature and doping ion percentage, has been finalized in order to obtain Eu(III)-doped CaF₂ thin films via a reproducible and selective solution process for down-shifting applications. An accurate balance of such parameters allows for obtaining films with high uniformity in terms of both their structural and compositional features. The starting point of the synthesis is the use of a mixture of Ca(hfa)₂•diglyme•H₂O and Eu(hfa)₃•diglyme adducts, with a suited ratio to produce 5%, 10% and 15% Eu-doped CaF₂ films, in a water/ethanol solution. A full investigation of the structural, morphological and compositional features of the films, inspected using X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX), respectively, has stated a correlation between the annealing temperature and the structural characteristics and morphology of the CaF₂ thin films. Interestingly, crystalline CaF₂ films are obtained at quite low temperatures of 350–400 °C. The down-shifting properties, validated by taking luminescence measurements under UV excitation, have allowed us to correlate the local environment in terms of the degree of symmetry around the europium ions with the relative doping ion percentages. Full article

(This article belongs to the Special Issue Sol-Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications)

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18 pages, 13529 KiB

Open AccessArticle

Influence of the Deposition Parameters on the Properties of TiO₂ Thin Films on Spherical Substrates

by Maria Covei, Cristina Bogatu, Silvioara Gheorghita, Anca Duta, Hermine Stroescu, Madalina Nicolescu, Jose Maria Calderon-Moreno, Irina Atkinson, Veronica Bratan and Mariuca Gartner

Materials 2023, 16(14), 4899; https://doi.org/10.3390/ma16144899 - 8 Jul 2023

Cited by 2 | Viewed by 1296

Abstract

Wastewater treatment targeting reuse may limit water scarcity. Photocatalysis is an advanced oxidation process that may be employed in the removal of traces of organic pollutants, where the material choice is important. Titanium dioxide (TiO₂) is a highly efficient photocatalyst with good aqueous stability. TiO₂ powder has a high surface area, thus allowing good pollutant adsorption, but it is difficult to filter for reuse. Thin films have a significantly lower surface area but are easier to regenerate and reuse. In this paper, we report on obtaining sol-gel TiO₂ thin films on spherical beads (2 mm diameter) with high surface area and easy recovery from wastewater. The complex influence of the substrate morphology (etched up to 48 h in concentrated H₂SO₄), of the sol dilution with ethanol (1:0 or 1:1), and the number of layers (1 or 2) on the structure, morphology, chemical composition, and photocatalytic performance of the TiO₂ thin films is investigated. Etching the substrate for 2 h in H₂SO₄ leads to uniform, smooth surfaces on which crystalline, homogeneous TiO₂ thin films are grown. Films deposited using an undiluted sol are stable in water, with some surface reorganization of the TiO₂ aggregates occurring, while the films obtained using diluted sol are partially washed out. By increasing the film thickness through the deposition of a second layer, the roughness increases (from ~50 nm to ~100 nm), but this increase is not high enough to promote higher adsorption or overall photocatalytic efficiency in methylene blue photodegradation (both about 40% after 8 h of UV-Vis irradiation at 55 W/m²). The most promising thin film, deposited on spherical bead substrates (etched for 2 h in H₂SO₄) using the undiluted sol, with one layer, is highly crystalline, uniform, water-stable, and proves to have good photocatalytic activity. Full article

(This article belongs to the Special Issue Sol-Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications)

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21 pages, 13543 KiB

Open AccessArticle

High NIR Reflectance and Photocatalytic Ceramic Pigments Based on M-Doped Clinobisvanite BiVO₄ (M = Ca, Cr) from Gels

by Guillermo Monrós, Mario Llusar and José A. Badenes

Materials 2023, 16(10), 3722; https://doi.org/10.3390/ma16103722 - 14 May 2023

Cited by 5 | Viewed by 1649

Abstract

Clinobisvanite (monoclinic scheelite BiVO₄, S.G.I2/b) has garnered interest as a wide-band semiconductor with photocatalyst activity, as a high NIR reflectance material for camouflage and cool pigments and as a photoanode for PEC application from seawater. BiVO₄ exists in four polymorphs: orthorhombic, zircon-tetragonal, monoclinic, and scheelite-tetragonal structures. In these crystal structures, V is coordinated by four O atoms in tetrahedral coordination and each Bi is coordinated to eight O atoms from eight different VO₄ tetrahedral units. The synthesis and characterization of doped bismuth vanadate with Ca and Cr are studied using gel methods (coprecipitated and citrate metal–organic gels), which are compared with the ceramic route by means of the UV–vis–NIR spectroscopy of diffuse reflectance studies, band gap measurement, photocatalytic activity on Orange II and its relation with the chemical crystallography analyzed by the XRD, SEM-EDX and TEM-SAD techniques. The preparation of bismuth vanadate-based materials doped with calcium or chromium with various functionalities is addressed (a) as pigments for paints and for glazes in the chrome samples, with a color gradation from turquoise to black, depending on whether the synthesis is by the conventional ceramic route or by means of citrate gels, respectively; (b) with high NIR reflectance values that make them suitable as fresh pigments, to refresh the walls or roofs of buildings colored with them; and (c) with photocatalytic activity. Full article

(This article belongs to the Special Issue Sol-Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications)

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19 pages, 6502 KiB

Open AccessArticle

Zinc Oxide Films Fabricated via Sol-Gel Method and Dip-Coating Technique–Effect of Sol Aging on Optical Properties, Morphology and Photocatalytic Activity

by Katarzyna Wojtasik, Magdalena Zięba, Cuma Tyszkiewicz, Wojciech Pakieła, Grażyna Żak, Olgierd Jeremiasz, Ewa Gondek, Kazimierz Drabczyk and Paweł Karasiński

Materials 2023, 16(5), 1898; https://doi.org/10.3390/ma16051898 - 24 Feb 2023

Cited by 11 | Viewed by 2228

Abstract

Zinc oxide layers on soda-lime glass substrates were fabricated using the sol-gel method and the dip-coating technique. Zinc acetate dihydrate was applied as the precursor, while diethanolamine as the stabilizing agent. This study aimed to determine what effect has the duration of the sol aging process on the properties of fabricated ZnO films. Investigations were carried out with the sol that was aged during the period from 2 to 64 days. The sol was studied using the dynamic light scattering method to determine its distribution of molecule size. The properties of ZnO layers were studied using the following methods: scanning electron microscopy, atomic force microscopy, transmission and reflection spectroscopy in the UV-Vis range, and the goniometric method for determination of the water contact angle. Furthermore, photocatalytic properties of ZnO layers were studied by the observation and quantification of the methylene blue dye degradation in an aqueous solution under UV illumination. Our studies showed that ZnO layers have grain structure, and their physical–chemical properties depend on the duration of aging. The strongest photocatalytic activity was observed for layers produced from the sol that was aged over 30 days. These layers have also the greatest porosity (37.1%) and the largest water contact angle (68.53°). Our studies have also shown that there are two absorption bands in studied ZnO layers, and values of optical energy band gaps determined from positions of maxima in reflectance characteristics are equal to those determined using the Tauc method. Optical energy band gaps of the ZnO layer fabricated from the sol aged over 30 days are E_g^I = 4.485 eV and E_g^II = 3.300 eV for the first and second bands, respectively. This layer also showed the highest photocatalytic activity, causing the pollution to degrade 79.5% after 120 min of UV irradiation. We believe that ZnO layers presented here, thanks to their attractive photocatalytic properties, may find application in environmental protection for the degradation of organic pollutants. Full article

(This article belongs to the Special Issue Sol-Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications)

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10 pages, 2206 KiB

Open AccessArticle

Sol-Gel Synthesis and Characterization of Yttrium-Doped MgFe₂O₄ Spinel

by Dovydas Karoblis, Kestutis Mazeika, Rimantas Raudonis, Aleksej Zarkov and Aivaras Kareiva

Materials 2022, 15(21), 7547; https://doi.org/10.3390/ma15217547 - 27 Oct 2022

Cited by 4 | Viewed by 1604

Abstract

In this study, an environmentally friendly sol-gel synthetic approach was used for the preparation of yttrium-doped MgFe₂O₄. Two series of compounds with different iron content were synthesized and A-site substitution effects were investigated. In the first series, the iron content was fixed and the charge balance was suggested to be compensated by a partial reduction of Fe³⁺ to Fe²⁺ or formation of interstitial O²⁻ ions. For the second series of samples, the iron content was reduced in accordance with the substitution level to compensate for the excess of positive charge, which accumulates due to replacing divalent Mg²⁺ with trivalent Y³⁺ ions. Structural, morphological and magnetic properties were inspected. It was observed that single-phase compounds can only form when the substitution level reaches 20 mol% of Y³⁺ ions and iron content is reduced. The coercivity as well as saturation magnetization decreased with the increase in yttrium content. Mössbauer spectroscopy was used to investigate the iron content in both tetrahedral and octahedral positions. Full article

(This article belongs to the Special Issue Sol-Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications)

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12 pages, 4119 KiB

Open AccessArticle

Reaching Visible Light Photocatalysts with Pt Nanoparticles Supported in TiO₂-CeO₂

by Ixchel Alejandra Mejia-Estrella, Alejandro Pérez Larios, Belkis Sulbarán-Rangel and Carlos Alberto Guzmán González

Materials 2022, 15(19), 6784; https://doi.org/10.3390/ma15196784 - 30 Sep 2022

Cited by 1 | Viewed by 1611

Abstract

Nanostructured catalysts of platinum (Pt) supported on commercial TiO₂, as well as TiO₂-CeO₂ (1, 5 and 10 wt% CeO₂), were synthesized through the Sol-Gel and impregnation method doped to 1 wt% of Platinum, in order to obtain a viable photocatalytic material able to oxidate organic pollutants under the visible light spectrum. The materials were characterized by different spectroscopy and surface techniques such as Specific surface area (BET), X-ray photoelectron spectroscopy (XPS), XRD, and TEM. The results showed an increase in the diameter of the pore as well as the superficial area of the supports as a function of the CeO₂ content. TEM images showed Pt nanoparticles ranking from 2–7 nm, a decrease in the particle size due to the increase of CeO₂. The XPS showed oxidized Pt²⁺ and reduced Pt⁰ species; also, the relative abundance of the elements Ce³⁺/Ce⁴⁻ and Ti⁴⁺ on the catalysts. Additionally, a shift in the Eg band gap energy (3.02–2.82 eV) was observed by UV–vis, proving the facticity of applying these materials in a photocatalytic reaction using visible light. Finally, all the synthesized materials were tested on their photocatalytic oxidation activity on a herbicide used worldwide; 2,4-Dichlorophenoxyacetic acid, frequently use in the agriculture in the state of Jalisco. The kinetics activity of each material was measured during 6 h of reaction at UV–Vis 190–400 nm, reaching a removal efficiency of 98% of the initial concentration of the pollutant in 6 h, compared to 32% using unmodified TiO₂ in 6 h. Full article

(This article belongs to the Special Issue Sol-Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications)

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10 pages, 2425 KiB

Open AccessArticle

Versatile Zirconium Oxide (ZrO₂) Sol-Gel Development for the Micro-Structuring of Various Substrates (Nature and Shape) by Optical and Nano-Imprint Lithography

by Nicolas Crespo-Monteiro, Arnaud Valour, Victor Vallejo-Otero, Marie Traynar, Stéphanie Reynaud, Emilie Gamet and Yves Jourlin

Materials 2022, 15(16), 5596; https://doi.org/10.3390/ma15165596 - 15 Aug 2022

Cited by 8 | Viewed by 2517

Abstract

Zirconium oxide (ZrO₂) is a well-studied and promising material due to its remarkable chemical and physical properties. It is used, for example, in coatings for corrosion protection layer, wear and oxidation, in optical applications (mirror, filters), for decorative components, for anti-counterfeiting solutions and for medical applications. ZrO₂ can be obtained as a thin film using different deposition methods such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). These techniques are mastered but they do not allow easy micro-nanostructuring of these coatings due to the intrinsic properties (high melting point, mechanical and chemical resistance). An alternative approach described in this paper is the sol-gel method, which allows direct micro-nanostructuring of the ZrO₂ layers without physical or chemical etching processes, using optical or nano-imprint lithography. In this paper, the authors present a complete and suitable ZrO₂ sol-gel method allowing to achieve complex micro-nanostructures by optical or nano-imprint lithography on substrates of different nature and shape (especially non-planar and foil-based substrates). The synthesis of the ZrO₂ sol-gel is presented as well as the micro-nanostructuring process by masking, colloidal lithography and nano-imprint lithography on glass and plastic substrates as well as on plane and curved substrates. Full article

(This article belongs to the Special Issue Sol-Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications)

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20 pages, 4610 KiB

Open AccessArticle

Influence of Addition of Antibiotics on Chemical and Surface Properties of Sol-Gel Coatings

by Beatriz Toirac, Amaya Garcia-Casas, Miguel A. Monclús, John J. Aguilera-Correa, Jaime Esteban and Antonia Jiménez-Morales

Materials 2022, 15(14), 4752; https://doi.org/10.3390/ma15144752 - 7 Jul 2022

Cited by 2 | Viewed by 2115

Abstract

Infection is one of the most common causes that leads to joint prosthesis failure. In the present work, biodegradable sol-gel coatings were investigated as a promising controlled release of antibiotics for the local prevention of infection in joint prostheses. Accordingly, a sol-gel formulation was designed to be tested as a carrier for 8 different individually loaded antimicrobials. Sols were prepared from a mixture of MAPTMS and TMOS silanes, tris(tri-methylsilyl)phosphite, and the corresponding antimicrobial. In order to study the cross-linking and surface of the coatings, a battery of examinations (Fourier-transform infrared spectroscopy, solid-state ²⁹Si-NMR spectroscopy, thermogravimetric analysis, SEM, EDS, AFM, and water contact angle, thickness, and roughness measurements) were conducted on the formulations loaded with Cefoxitin and Linezolid. A formulation loaded with both antibiotics was also explored. Results showed that the coatings had a microscale roughness attributed to the accumulation of antibiotics and organophosphites in the surface protrusions and that the existence of chemical bonds between antibiotics and the siloxane network was not evidenced. Full article

(This article belongs to the Special Issue Sol-Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications)

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12 pages, 2296 KiB

Open AccessArticle

Sol-Gel Synthesis and Characterization of the Cu-Mg-O System for Chemical Looping Application

by Timofey M. Karnaukhov, Grigory B. Veselov, Svetlana V. Cherepanova and Aleksey A. Vedyagin

Materials 2022, 15(6), 2021; https://doi.org/10.3390/ma15062021 - 9 Mar 2022

Cited by 9 | Viewed by 2774

Abstract

A sol-gel technique was applied to prepare the two-component oxide system Cu-Mg-O, where MgO plays the role of oxide matrix, and CuO is an active chemical looping component. The prepared samples were characterized by scanning electron microscopy, low-temperature nitrogen adsorption, and X-ray diffraction analysis. The reduction behavior of the Cu-Mg-O system was examined in nine consecutive reduction/oxidation cycles. The presence of the MgO matrix was shown to affect the ability of CuO towards reduction and re-oxidation significantly. During the first reduction/oxidation cycle, the main characteristics of the oxide system (particle size, crystallization degree, etc.) undergo noticeable changes. Starting from the third cycle, the system exhibits a stable operation, providing the uptake of similar hydrogen amounts within the same temperature range. Based on the obtained results, the two-component Cu-Mg-O system can be considered as a prospective chemical looping agent. Full article

(This article belongs to the Special Issue Sol-Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications)

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