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Inorganics
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Mixed Metal Oxides II
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Mixed Metal Oxides II

A special issue of Inorganics (ISSN 2304-6740). This special issue belongs to the section "Inorganic Solid-State Chemistry".

Deadline for manuscript submissions: closed (25 June 2024) | Viewed by 15211

Special Issue Editor

Prof. Dr. Aivaras Kareiva

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Guest Editor
Institute of Chemistry, Vilnius University, LT-03225 Vilnius, Lithuania
Interests: multifunctional metal oxides; catalysts; microstructure; physical properties; nanoparticles; nanoclusters; nanocomposites; solid-state chemistry
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The Special Issue “Mixed Metal Oxides”, published in Inorganics in 2020, collected 10 excellent papers and 23,841 views, attracting many potential readers and authors. This encouraged us to build upon the success of the first Issue. Therefore, we would like to extend a second edition in this Special Issue, “Mixed Metal Oxides II”.

Developments in materials and nanomaterials science, combining different sciences, have brought us to another level of understanding of the properties of mixed-metal oxides. As mentioned previously, the area of application of mixed-metal oxides is very broad, and covers almost all aspects of human life. Therefore, the development of novel materials is a fundamental focal point of chemical research, particularly inorganic chemistry. Owing to this wide and diverse application potential of mixed-metal oxides, chemical routes for the preparation of pure and/or homogeneously doped different systems are still highly desirable. The quality of synthetic materials is highly dependent on the overall characteristics and features of the synthesized powders. These attributes include density, purity, phase composition, crystallinity, particle size, particle-size distribution, particle morphology, and specific surface area. Thus, all the mentioned material properties are highly sensitive to processing conditions, which are very much responsible for the crystallinity, crystal shape, crystal size, crystal size distribution and phase purity of the resulting powders.

Many research groups worldwide use exploratory approaches targeting the development of new solid compounds and functional materials. The scope of this Special Issue of Inorganics again is focused on the synthesis, characterization and application of mixed-metal oxides and related materials, which are important in all areas of our life. A detailed understanding of reaction pathways at the level of the most basic steps of the formation of solids by in situ methods (X-ray and neutron diffraction, thermal analysis, Raman spectroscopy, etc.) is very desired. Works describing the research and application of soft chemistry approaches in the synthesis of various advanced multifunctional materials, as well as bulk and thin films, will be very much appreciated. Investigations on the preparation of mixed-metal oxides, biomaterials and nanomaterials using solid-state reaction, sol–gel, co-precipitation, hydrothermal and other synthesis methods are very desired as well.

Prof. Dr. Aivaras Kareiva
Guest Editor

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Keywords

  • multifunctional metal oxides
  • catalysts
  • microstructure
  • physical properties
  • nanoparticles
  • nanoclusters
  • nanocomposites
  • solid-state chemistry

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Related Special Issue

Published Papers (9 papers)

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Research

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15 pages, 10179 KiB  
Article
Adsorption Studies of Ternary Metal Ions (Cs+, Sr2+, and Co2+) from Water Using Zeolite@Magnetic Nanoparticles (Z@Fe3O4 NPs)
by Tung Van Nguyen, Lien Thi Nguyen, Ha Thi Thu Nguyen and Thu-Huong Le
Inorganics 2024, 12(11), 276; https://doi.org/10.3390/inorganics12110276 - 25 Oct 2024
Viewed by 481
Abstract
The mixture of three metal ions (Cs+, Sr2+, and Co2+) is commonly found in radioactive waste, which induces several negative health effects. The removal of multiple metal ions is a true challenge for researchers due to the [...] Read more.
The mixture of three metal ions (Cs+, Sr2+, and Co2+) is commonly found in radioactive waste, which induces several negative health effects. The removal of multiple metal ions is a true challenge for researchers due to the competitive adsorption of ions onto adsorbents. In this study, three metal ions, namely Cs+, Sr2+, and Co2+, have been successfully removed simultaneously from water using zeolite@magnetic nanoparticles (Z@Fe3O4 NPs). The optimized condition for the adsorption of ternary metal ions was obtained at an adsorbent weight of 0.2, pH of 6.0~7.0, and contact time of 60 min. The adsorption mechanism of ternary metal ions onto the surface of Z@Fe3O4 NPs was studied using the Pseudo-first-order, Pseudo-second-order, Elovich, and Intra-particle diffusion models. The Dubinin–Radushkevich Temkin, Freundlich, and Langmuir isotherm models were used to study the isotherm adsorption. The ternary metal ion adsorption (Cs+, Sr2+, and Co2+) on Z@Fe3O4 NPs was followed by the Pseudo-second-order model (PSO) with correlation coefficient (R2) range of 0.9826–0.9997. Meanwhile, the adsorption isotherms of ternary metal ions on Z@Fe3O4 NPs were in line with the Langmuir model with R2 values higher than 0.9206, suggesting monolayer chemisorption with maximum adsorption capacities of 48.31, 15.02, and 10.41 mg/g for Cs+, Sr2+, and Co2+, respectively. Thus, the selectivity trend in the ternary metal ions system towards the Z@Fe3O4 NPs is observed to be Cs+ > Sr2+ > Co2+, which indicates that the competitive effect of Cs+ is the strongest compared to Sr2+ and Co2+ions. Full article
(This article belongs to the Special Issue Mixed Metal Oxides II)
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11 pages, 8759 KiB  
Article
An Investigation of the Interface between Transition Metal Oxides (MnOx, FeOx, CoOx and NiOx)/MoO3 Composite Electrocatalysts for Oxygen Evolution Reactions
by Karmegam Dhanabalan, Mrunal Bhosale, Ganesan Sriram, Thangarasu Sadhasivam and Tae Hwan Oh
Inorganics 2024, 12(9), 241; https://doi.org/10.3390/inorganics12090241 - 2 Sep 2024
Viewed by 877
Abstract
This study presents the synthesis of a multicomponent metal oxide electrocatalyst that increases the activity of the oxygen evolution reaction (OER). We synthesized transition metal oxides (MnOx, FeOx, CoOx, and NiOx) with MoO3 heterostructures [...] Read more.
This study presents the synthesis of a multicomponent metal oxide electrocatalyst that increases the activity of the oxygen evolution reaction (OER). We synthesized transition metal oxides (MnOx, FeOx, CoOx, and NiOx) with MoO3 heterostructures through a solid-state reaction approach at low cost. In comparison to the other compositions, CoOx garnered higher attention and demonstrated superior performance on account of its large surface area and varied crystal facets. The MnOx-MoO3, FeOx-MoO3, CoOx-MoO3, and NiOx-MoO3 compositions attained an overpotential of 390 mV, 350 mV, 310 mV, and 340 mV, respectively, at a current density of 10 mA cm−2 in alkaline solution. The performance of OER was enhanced in CoOx-MoO3 at 10 mA cm−2, while FeOx-MoO3 exhibited a lower current density at 100 mA cm−2 than other metal oxides. The CoOx-MoO3 material exhibited a favorable crystal interface transition due to the presence of MoO3 oxide. For the first time, we report on the MoO3-to-(MnOx, FeOx, CoOx, and NiOx) interface crystal transition and the active surface area for OER catalytic activity in water-splitting processes. This investigation intends to develop an electrocatalyst that is capable of producing hydrogen with the use of heterostructure metal oxides. Full article
(This article belongs to the Special Issue Mixed Metal Oxides II)
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19 pages, 2938 KiB  
Article
Enhancing Supercapacitor Performance with Zero-Dimensional Tin–Niobium Oxide Heterostructure Composite Spheres: Electrochemical Insights
by Vediyappan Thirumal, Bathula Babu, Palanisamy Rajkumar, Jin-Ho Kim and Kisoo Yoo
Inorganics 2024, 12(6), 142; https://doi.org/10.3390/inorganics12060142 - 21 May 2024
Viewed by 860
Abstract
The development of advanced tin and niobium bimetallic composite electrode materials is crucial for enhancing the performance of supercapacitors. In this paper, we present a novel bimetallic composite material consisting of zero-dimensional spherical-like SnNb2O6 nanocomposites synthesized through the reaction of [...] Read more.
The development of advanced tin and niobium bimetallic composite electrode materials is crucial for enhancing the performance of supercapacitors. In this paper, we present a novel bimetallic composite material consisting of zero-dimensional spherical-like SnNb2O6 nanocomposites synthesized through the reaction of tin oxide (SnO2) and niobium pentoxide (Nb2O5) precursors, alongside comparative materials. The morphology of the spherical agglomerates comprising Sn/Nb oxide particles that were nucleated on the SnNb2O6 surface was characterized using field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM). The as-prepared heterostructures of the SnNb2O6 composites were analyzed for elemental composition, including Sn3d, Nb3d, and O1s; moreover, chemical oxidative state analysis was performed through X-ray photoelectron spectroscopy (XPS). Additionally, cyclic voltammetry curves exhibited pseudocapacitive redox behavior for the SnNb2O6 composites, while the galvanostatic charge-discharge (GCD) performance demonstrated a maximum specific capacitance of 294.8 F/g at 1 A/g. Moreover, SnNb2O6 composite electrodes demonstrated rapid charge–discharge kinetics and excellent cycling stability, with a capacitance retention of 95.7% over 10,000 cycles. This study elucidated the synthesis of tin–niobium oxide-based composites, demonstrating their potential for high-performance supercapacitors. Full article
(This article belongs to the Special Issue Mixed Metal Oxides II)
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16 pages, 6318 KiB  
Article
Synthesis, Crystal Structure and Photoluminescent Properties of Red-Emitting CaAl4O7:Cr3+ Nanocrystalline Phosphor
by Leonid Vasylechko, Vitalii Stadnik, Vasyl Hreb, Yaroslav Zhydachevskyy, Andriy Luchechko, Vitaliy Mykhaylyk, Hans Kraus and Andrzej Suchocki
Inorganics 2023, 11(5), 205; https://doi.org/10.3390/inorganics11050205 - 9 May 2023
Cited by 3 | Viewed by 1756
Abstract
Calcium dialuminate, CaAl4O7, nanopowders with a grossite-type structure, doped with chromium ions, were synthesized via the combined sol–gel solution combustion method. The evolution of phase composition, crystal structure, and microstructural parameters of the nanocrystalline materials depending on the temperature [...] Read more.
Calcium dialuminate, CaAl4O7, nanopowders with a grossite-type structure, doped with chromium ions, were synthesized via the combined sol–gel solution combustion method. The evolution of phase composition, crystal structure, and microstructural parameters of the nanocrystalline materials depending on the temperature of the thermal treatment was investigated via X-ray powder diffraction and applying the Rietveld refinement technique. The photoluminescent properties of CaAl4O7 nanophosphors activated with Cr3+ ions were studied over the temperature range of 4.5–325 K. The samples show deep red and near-infrared luminescence due to the 2E → 4A2 and 4T2 → 4A2 energy level transitions of Cr3+ ions under excitation in the two broad emission bands in the visible spectral region. The R lines emission reveals a strong temperature dependence. The feasibility of the material for non-contact luminescence sensing is investigated, and good sensitivity is obtained based on the (R2/R1) luminescence intensity ratio and the lifetime of the emission. Full article
(This article belongs to the Special Issue Mixed Metal Oxides II)
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11 pages, 5024 KiB  
Article
Molten Salt Synthesis of Micro-Sized Hexagonally Shaped REMnO3 (RE = Y, Er, Tm, Yb)
by Dovydas Karoblis, Aleksej Zarkov, Tomas Murauskas and Aivaras Kareiva
Inorganics 2023, 11(5), 178; https://doi.org/10.3390/inorganics11050178 - 23 Apr 2023
Cited by 1 | Viewed by 1566
Abstract
Yttrium manganite (YMnO3) is a compound belonging to the hexagonal rare earth manganites family, which demonstrates multiferroic properties. This material can be prepared by several synthetic approaches, with the most common one being the solid-state synthesis. In this work, we show [...] Read more.
Yttrium manganite (YMnO3) is a compound belonging to the hexagonal rare earth manganites family, which demonstrates multiferroic properties. This material can be prepared by several synthetic approaches, with the most common one being the solid-state synthesis. In this work, we show a possibility of preparing this material via molten salt synthesis using the NaCl-KCl mixture as the reaction medium and yttrium and manganese nitrates as the starting materials. We demonstrate that, by varying the reaction temperature and the nitrates-to-chlorides ratio, it is feasible to synthesize hexagonally shaped particles of microscopic dimensions. A similar synthesis procedure can be successfully applied for the preparation of other hexagonal manganites—ErMnO3, TmMnO3, and YbMnO3. Full article
(This article belongs to the Special Issue Mixed Metal Oxides II)
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10 pages, 5092 KiB  
Article
Sol-Gel Synthesis and Characterization of Novel Y3−xMxAl5−yVyO12 (M—Na, K) Garnet-Type Compounds
by Diana Vistorskaja, Andrius Laurikenas, Alejandro Montejo de Luna, Aleksej Zarkov, Sapargali Pazylbek and Aivaras Kareiva
Inorganics 2023, 11(2), 58; https://doi.org/10.3390/inorganics11020058 - 25 Jan 2023
Cited by 2 | Viewed by 1714
Abstract
In this study, for the first time to the best of our knowledge, the new garnets Y3−xNaxAl5O12, Y3−xKxAl5O12, Y3Al5−yVyO12, and [...] Read more.
In this study, for the first time to the best of our knowledge, the new garnets Y3−xNaxAl5O12, Y3−xKxAl5O12, Y3Al5−yVyO12, and Y3−xNaxAl5−yVyO12 with various stoichiometric compositions were successfully synthesized by the aqueous sol-gel method. All obtained samples were characterized by X-ray diffraction (XRD) analysis, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). It was determined from the XRD results that the formation of monophasic Y3−xNaxAl5O12, Y3−xKxAl5O12, Y3Al5−yVyO12, and Y3−xNaxAl5−yVyO12 garnets is possible only at limited doping levels. The highest substitutional level of doped metal was observed for the YAG doped with sodium (x = 1), and the lowest substitutional level was observed for the YAG doped with vanadium (y = 0.05). Furthermore, the obtained FTIR spectroscopy results were in good agreement with the XRD analysis data, i.e., they confirmed that the YAG is the main crystalline phase in the end products. The SEM was used to study the morphology of the garnets, and the results obtained showed that all synthesized samples were composed of nano-sized agglomerated crystallites. Full article
(This article belongs to the Special Issue Mixed Metal Oxides II)
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11 pages, 3030 KiB  
Article
ZnSnO3 or Zn2SnO4/SnO2 Hierarchical Material? Insight into the Formation of ZnSn(OH)6 Derived Oxides
by Davide Redolfi-Bristol, Lorenzo Branzi, Michele Back, Pietro Riello, Adolfo Speghini, Nicola Pinna and Alvise Benedetti
Inorganics 2022, 10(11), 183; https://doi.org/10.3390/inorganics10110183 - 26 Oct 2022
Viewed by 2333
Abstract
Piezoelectric materials are a class of compounds that is gaining increasing interest in various applications such as energy harvesting. During the last decade, lead-free ZnSnO3 perovskite ceramic has gained attention among the scientific community thanks to its unique symmetry-dependent and spontaneous polarization [...] Read more.
Piezoelectric materials are a class of compounds that is gaining increasing interest in various applications such as energy harvesting. During the last decade, lead-free ZnSnO3 perovskite ceramic has gained attention among the scientific community thanks to its unique symmetry-dependent and spontaneous polarization properties such as piezoelectricity and ferroelectricity. Nevertheless, only a few studies successfully prepared pure ZnSnO3, while most seem to mislead the product for its hydroxide precursor (ZnSn(OH)6) or a mixture of Zn2SnO4 and SnO2. In our work, we investigated the conversion of ZnSn(OH)6 at different temperatures (500, 600, 700, 750 and 800 °C) by X-ray powder diffraction analysis, and in-situ using synchrotron radiation up to 950 °C under ambient atmosphere and in a vacuum, to reproduce conventional reaction conditions. SEM and TEM have been used to understand the evolution of the particle shape and surface structure before and after the thermal treatments. Our results show the instability of the ZnSn(OH)6 phase, which converts into an amorphous structure at low temperature. Above 750 °C, the material segregates into Zn2SnO4 and SnO2, supporting the hypothesis that the thermal treatment of the hydroxide phase under typical conditions results in the formation of an oxide mixture rather than the phase pure ZnSnO3. Full article
(This article belongs to the Special Issue Mixed Metal Oxides II)
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16 pages, 2138 KiB  
Article
Structural Control and Electrical Behavior of Thermally Reduced Graphene Oxide Samples Assisted with Malonic Acid and Phosphorus Pentoxide
by Ruta Aukstakojyte, Justina Gaidukevic, Gediminas Niaura, Martynas Skapas, Virginijus Bukauskas and Jurgis Barkauskas
Inorganics 2022, 10(9), 142; https://doi.org/10.3390/inorganics10090142 - 16 Sep 2022
Cited by 5 | Viewed by 2050
Abstract
We present a detailed study of the structural and electrical changes occurring in two graphene oxide (GO) samples during thermal reduction in the presence of malonic acid (MA) (5 and 10 wt%) and P2O5 additives. The morphology and de-oxidation efficiency [...] Read more.
We present a detailed study of the structural and electrical changes occurring in two graphene oxide (GO) samples during thermal reduction in the presence of malonic acid (MA) (5 and 10 wt%) and P2O5 additives. The morphology and de-oxidation efficiency of reduced GO (rGO) samples are characterized by Fourier transform infrared, X-ray photoelectron, energy-dispersive X-ray, Raman spectroscopies, transmission electron and scanning electron microscopies, X-ray diffraction (XRD), and electrical conductivity measurements. Results show that MA and P2O5 additives are responsible for the recovery of π-conjugation in rGO as the XRD pattern presents peaks corresponding to (002) graphitic-lattice planes, suggesting the formation of the sp2-like carbon structure. Raman spectra show disorders in graphene sheets. Elemental analysis shows that the proposed reduction method in the presence of additives also suggests the simultaneous insertion of phosphorus with a relatively high content (0.3–2.3 at%) in rGO. Electrical conductivity measurements show that higher amounts of additives used in the GO reduction more effectively improve electron mobility in rGO samples, as they possess the highest electrical conductivity. Moreover, the relatively high conductivity at low bulk density indicates that prepared rGO samples could be applied as metal-free and non-expensive carbon-based electrodes for supercapacitors and (bio)sensors. Full article
(This article belongs to the Special Issue Mixed Metal Oxides II)
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Review

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28 pages, 1570 KiB  
Review
Nonstoichiometric Strontium Ferromolybdate as an Electrode Material for Solid Oxide Fuel Cells
by Gunnar Suchaneck and Evgenii Artiukh
Inorganics 2022, 10(12), 230; https://doi.org/10.3390/inorganics10120230 - 29 Nov 2022
Cited by 11 | Viewed by 2360
Abstract
This review is devoted to the application of Sr2FeMoO6−δ (SFM) and Sr2F1.5Mo0.5O6−δ (SF1.5M) in La1−xSrxGa1−yMgyO3−δ (LSGM)-based SOFCs. We consider the most relevant [...] Read more.
This review is devoted to the application of Sr2FeMoO6−δ (SFM) and Sr2F1.5Mo0.5O6−δ (SF1.5M) in La1−xSrxGa1−yMgyO3−δ (LSGM)-based SOFCs. We consider the most relevant physical properties (crystal structure, thermodynamic stability, iron and molybdenum valence states, oxygen vacancy formation and oxygen non-stoichiometry, electrical conductivity), A- and B-site ion substitution, and the performance of SF1+xM SOFCs (polarization resistance, operation with hydrogen, operation with hydrocarbons and methanol). Their properties can be tailored to a particular application by the substitution of different metal cations into their lattices. SF1+xM materials are excellent catalysts in hydrocarbon oxidation and can prevent carbon deposition due to the ability to exchange lattice oxygen with the gaseous phase. Moreover, they are sulfur tolerant. This opens the way to direct hydrocarbon-fueled SOFCs, eliminating the need for external fuel reforming and sulfur removal components. Such SOFCs can be greatly simplified and operate with much higher overall efficiency, thus contributing to the solution to the lack of energy problem in our modern world. Full article
(This article belongs to the Special Issue Mixed Metal Oxides II)
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