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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Materials Chemistry".

Deadline for manuscript submissions: closed (31 October 2022) | Viewed by 14592

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Prof. Dr. Igor Djerdj

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Department of Chemistry, Josip Juraj Strossmayer University of Osijek, Cara Hadrijana 8/a, HR-31000 Osijek, Croatia
Interests: solid state chemistry; materials chemistry; condensed matter physics; magnetic properties; structure–property relationship; bandstructure calculation; sol-gel synthesis; crystal structure determination; three-way catalysts; functional materials; nanomaterials; perovskites; multiferroicity; metal–organic frameworks
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Dear Colleagues,

The sol–gel process (also known as inorganic polymerization) has emerged as one of the most important routes for the preparation of functional materials. It has an important track record in producing functional materials for diverse applications in optics, electronics, energy, biosensors, medicine (e.g., controlled drug release), reactive material, and separation (e.g., chromatography) technology. Controlled morphologies can be produced at all length scales, from ordered mesoporous arrays to thin films, fibers, and monoliths. A variety of chemical compositions can be produced by such a route, including well-studied metal oxides, nitrides, carbides, and innovative hybrid materials. It is, thus, important for journal Molecules to dedicate a Special Issue to this topic, since it perfectly fits all areas of chemistry. This Special Issue will contain contributions discussing any of the aspects broadly indicated by the keywords.

Prof. Dr. Igor Djerdj
Guest Editor

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Keywords

Sol–gel
Functional materials
Heterogeneous catalysis
Dielectrics
Magnetic materials
Optical materials

Related Special Issue

Sol-Gel Chemistry. From Molecule to Functional Materials in Molecules (22 articles)

Published Papers (7 papers)

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Research

16 pages, 4454 KiB

Open AccessArticle

Highly Stretchable, Self-Adhesive, Antidrying Ionic Conductive Organohydrogels for Strain Sensors

by Xinmin Huang, Chengwei Wang, Lianhe Yang and Xiang Ao

Molecules 2023, 28(6), 2817; https://doi.org/10.3390/molecules28062817 - 21 Mar 2023

Cited by 4 | Viewed by 1787

Abstract

As flexible wearable devices, hydrogel sensors have attracted extensive attention in the field of soft electronics. However, the application or long-term stability of conventional hydrogels at extreme temperatures remains a challenge due to the presence of water. Antifreezing and antidrying ionic conductive organohydrogels were prepared using cellulose nanocrystals and gelatin as raw materials, and the hydrogels were prepared in a water/glycerol binary solvent by a one-pot method. The prepared hydrogels were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The mechanical properties, electrical conductivity, and sensing properties of the hydrogels were studied by means of a universal material testing machine and LCR digital bridge. The results show that the ionic conductive hydrogel exhibits high stretchability (elongation at break, 584.35%) and firmness (up to 0.16 MPa). As the binary solvent easily forms strong hydrogen bonds with water molecules, experiments show that the organohydrogels exhibit excellent freezing and drying (7 days). The organohydrogels maintain conductivity and stable sensitivity at a temperature range (−50 °C–50 °C) and after long-term storage (7 days). Moreover, the organohydrogel-based wearable sensors with a gauge factor of 6.47 (strain, 0−400%) could detect human motions. Therefore, multifunctional organohydrogel wearable sensors with antifreezing and antidrying properties have promising potential for human body monitoring under a broad range of environmental conditions. Full article

(This article belongs to the Special Issue Sol-Gel Functional Materials)

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10 pages, 1444 KiB

Open AccessFeature PaperArticle

Conditions for Shake-Gel Formation: The Relationship between the Size of Poly(Ethylene Oxide) and the Distance between Silica Particles

by Yi Huang, Shunsuke Sato and Motoyoshi Kobayashi

Molecules 2022, 27(22), 7770; https://doi.org/10.3390/molecules27227770 - 11 Nov 2022

Cited by 1 | Viewed by 1345

Abstract

Colloidal silica suspensions are widely used in many fields, including environmental restoration, oil drilling, and food and medical industries. To control the rheological property of suspensions, poly(ethylene oxide) (PEO) polymers are often used. Under specific conditions, the silica-PEO suspension can create a phenomenon called a shake-gel. Previous works discussed the conditions necessary to form a shake-gel and suggested that the bridging effect of the polymer is one of the important mechanisms for shake-gel formation. However, we noted that the influence of PEO size compared to the separation distance between silica particles regarding shake-gel formation has not been systematically investigated, while the PEO size should be larger than the particle–particle separation distance for polymer bridging in order to form gels. Thus, we conducted a series of experiments to examine the effects of the radius of gyration of the PEO and the distance between the silica particles by controlling the PEO molecular weight and the silica concentration. Our results elucidated that the radius of gyration of the PEO should be 2.5 times larger than the distance between the silica surfaces in order to promote the formation of a shake-gel. This result supports the hypothesis that the bridging effect is the main cause of shake-gel formation, which can help us to understand the conditions necessary for shake-gel preparation. Full article

(This article belongs to the Special Issue Sol-Gel Functional Materials)

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9 pages, 707 KiB

Open AccessArticle

Screen Printable Sol-Gel Materials for High-Throughput Borosilicate Glass Film Production

by Jonas D. Huyeng, Raphael Efinger, David Bruge, Oliver Doll, Roman J. Keding and Florian Clement

Molecules 2022, 27(17), 5408; https://doi.org/10.3390/molecules27175408 - 24 Aug 2022

Viewed by 970

Abstract

The use of sol-gel materials can simplify the industrial fabrication of high-efficiency silicon solar cells if a suitable deposition method is established. In this work, we investigate the possibilities to adapt a borosilicate glass sol-gel to provide a stable screen printing process. This material has previously been used as a boron dopant source for silicon solar cells. We now use an adjusted synthesis process, with an increased gelling time and different additives. This changes the rheological properties (i.e., the elastic and viscous moduli G′ and G″) in a way that avoids the dripping of paste through the screen and that stabilizes the material transfer in subsequent printing steps. Using this synthesis process, we were able to show a printing process with long-term stability of more than 500 prints. When comparing the adjusted to the initial paste, we show that, after thermal treatment, the obtained thin films are very similar in terms of their constitution, with a refractive index between n = 1.47 (initial) and n = 1.55 (adjusted). We also show that they provide the same amount of doping under the tested conditions (950 °C, 30 min), resulting in sheet resistances of R_□ = (42.5 ± 2.6) Ω/□ (initial) and R_□ = (46.4 ± 3.6) Ω/□ (adjusted). Full article

(This article belongs to the Special Issue Sol-Gel Functional Materials)

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19 pages, 5508 KiB

Open AccessFeature PaperArticle

Periodic Mesoporous Organosilica Nanoparticles for CO₂ Adsorption at Standard Temperature and Pressure

by Paul Kirren, Lucile Barka, Saher Rahmani, Nicolas Bondon, Nicolas Donzel, Philippe Trens, Aurélie Bessière, Laurence Raehm, Clarence Charnay and Jean-Olivier Durand

Molecules 2022, 27(13), 4245; https://doi.org/10.3390/molecules27134245 - 30 Jun 2022

Cited by 4 | Viewed by 1687

Abstract

(1) Background: Due to human activities, greenhouse gas (GHG) concentrations in the atmosphere are constantly rising, causing the greenhouse effect. Among GHGs, carbon dioxide (CO₂) is responsible for about two-thirds of the total energy imbalance which is the origin of the increase in the Earth’s temperature. (2) Methods: In this field, we describe the development of periodic mesoporous organosilica nanoparticles (PMO NPs) used to capture and store CO₂ present in the atmosphere. Several types of PMO NP (bis(triethoxysilyl)ethane (BTEE) as matrix, co-condensed with trialkoxysilylated aminopyridine (py) and trialkoxysilylated bipyridine (Etbipy and iPrbipy)) were synthesized by means of the sol-gel procedure, then characterized with different techniques (DLS, TEM, FTIR, BET). A systematic evaluation of CO₂ adsorption was carried out at 298 K and 273 K, at low pressure. (3) Results: The best values of CO₂ adsorption were obtained with 6% bipyridine: 1.045 mmol·g⁻¹ at 298 K and 2.26 mmol·g⁻¹ at 273 K. (4) Conclusions: The synthetized BTEE/aminopyridine or bipyridine PMO NPs showed significant results and could be promising for carbon capture and storage (CCS) application. Full article

(This article belongs to the Special Issue Sol-Gel Functional Materials)

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13 pages, 2929 KiB

Open AccessArticle

Structure and Population of Complex Ionic Species in FeCl₂ Aqueous Solution by X-ray Absorption Spectroscopy

by Uroš Luin, Iztok Arčon and Matjaz Valant

Molecules 2022, 27(3), 642; https://doi.org/10.3390/molecules27030642 - 19 Jan 2022

Cited by 2 | Viewed by 2089

Abstract

Technologies for mass production require cheap and abundant materials such as ferrous chloride (FeCl₂). The literature survey shows the lack of experimental studies to validate theoretical conclusions related to the population of ionic Fe-species in the aqueous FeCl₂ solution. Here, we present an in situ X-ray absorption study of the structure of the ionic species in the FeCl₂ aqueous solution at different concentrations (1–4 molL⁻¹) and temperatures (25–80 °C). We found that at low temperature and low FeCl₂ concentration, the octahedral first coordination sphere around Fe is occupied by one Cl ion at a distance of 2.33 (±0.02) Å and five water molecules at a distance of 2.095 (±0.005) Å. The structure of the ionic complex gradually changes with an increase in temperature and/or concentration. The apical water molecule is substituted by a chlorine ion to yield a neutral Fe[Cl₂(H₂O)₄]⁰. The observed substitutional mechanism is facilitated by the presence of the intramolecular hydrogen bonds as well as entropic reasons. The transition from the single charged Fe[Cl(H₂O)₅]⁺ to the neutral Fe[Cl₂(H₂O)₄]⁰ causes a significant drop in the solution conductivity, which well correlates with the existing conductivity models. Full article

(This article belongs to the Special Issue Sol-Gel Functional Materials)

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12 pages, 3104 KiB

Open AccessArticle

Brownmillerites CaFeO_2.5 and SrFeO_2.5 as Catalyst Support for CO Oxidation

by Pierre-Alexis Répécaud, Monica Ceretti, Mimoun Aouine, Céline Delwaulle, Emmanuel Nonnet, Werner Paulus and Helena Kaper

Molecules 2021, 26(21), 6413; https://doi.org/10.3390/molecules26216413 - 23 Oct 2021

Viewed by 2046

Abstract

The support material can play an important role in oxidation catalysis, notably for CO oxidation. Here, we study two materials of the Brownmillerite family, CaFeO_2.5 and SrFeO_2.5, as one example of a stoichiometric phase (CaFeO_2.5, CFO) and one existing in different modifications (SrFeO_2.75, SrFeO_2.875 and SrFeO₃, SFO). The two materials are synthesized using two synthesis methods, one bottom-up approach via a complexation route and one top-down method (electric arc fusion), allowing to study the impact of the specific surface area on the oxygen mobility and catalytic performance. CO oxidation on ¹⁸O-exchanged materials shows that oxygen from SFO participates in the reaction as soon as the reaction starts, while for CFO, this onset takes place 185 °C after reaction onset. This indicates that the structure of the support material has an impact on the catalytic performance. We report here on significant differences in the catalytic activity linked to long-term stability of CFO and SFO, which is an important parameter not only for possible applications, but equally to better understand the mechanism of the catalytic activity itself. Full article

(This article belongs to the Special Issue Sol-Gel Functional Materials)

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14 pages, 3008 KiB

Open AccessArticle

Sol-Gel Synthesis of Ceria-Zirconia-Based High-Entropy Oxides as High-Promotion Catalysts for the Synthesis of 1,2-Diketones from Aldehyde

by Dalibor Tatar, Jelena Kojčinović, Berislav Marković, Aleksandar Széchenyi, Aleksandar Miletić, Sándor Balázs Nagy, Szilveszter Ziegenheim, Imre Szenti, Andras Sapi, Ákos Kukovecz, Kristijan Dinjar, Yushu Tang, David Stenzel, Gábor Varga and Igor Djerdj

Molecules 2021, 26(20), 6115; https://doi.org/10.3390/molecules26206115 - 10 Oct 2021

Cited by 10 | Viewed by 3256

Abstract

Efficient Lewis-acid-catalyzed direct conversion of aldehydes to 1,2-diketones in the liquid phase was enabled by using newly designed and developed ceria–zirconia-based high-entropy oxides (HEOs) as the actual catalysts. The synergistic effect of various cations incorporated in the same oxide structure (framework) was partially responsible for the efficiency of multicationic materials compared to the corresponding single-cation oxide forms. Furthermore, a clear, linear relationship between the Lewis acidity and the catalytic activity of the HEOs was observed. Due to the developed strategy, exclusively diketone-selective, recyclable, versatile heterogeneous catalytic transformation of aldehydes can be realized under mild reaction conditions. Full article

(This article belongs to the Special Issue Sol-Gel Functional Materials)

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