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Inorganics
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Mixed Metal Oxides
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Mixed Metal Oxides

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

Deadline for manuscript submissions: closed (1 December 2018) | Viewed by 48403

Special Issue Editor

Prof. Dr. Aivaras Kareiva

E-Mail Website
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,

Developments in materials science, combining physics, chemistry, theory and even biosciences, have brought us to another level of understanding of properties of mixed-metal oxides. The area of application of mixed-metal oxides concerns all aspects of human life, ranging from novel building materials to medicine. The development of novel materials is a fundamental focal point of chemical research; and this interest is mandated by advancements in all areas of industry and technology. Many synthesis methods used for the fabrication of different multinary oxide systems require extensive procedures, elevated temperatures and lengthy treatments. These processing conditions do not allow facile control over micro-structure, grain size and grain size distribution in the resulting powders or shapes. Owing to such wide and diverse application potentials of mixed-metal oxides, chemical routes for the preparation of pure and/or homogeneously doped different systems are highly desirable.

The scope of this Special Issue of Inorganics is focused on the synthesis, characterization and application of mixed-metal oxides and related materials, which are important in biomedicine, optoelectronics, catalysis, conservation and restoration of cultural heritage, and related industrial areas. The field of the research in application of soft chemistry approaches in the synthesis of various advanced multifunctional materials, bulk and thin films, are very much appreciated.

Prof. Dr. Aivaras Kareiva
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Inorganics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • mixed-metal oxides
  • bioceramics
  • catalysts
  • luminescence materials
  • multifunctional materials
  • thin/thick films
  • processing routes

Related Special Issue

Published Papers (10 papers)

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Research

10 pages, 2775 KiB  
Article
Molecularly Engineered Lithium–Chromium Alkoxide for Selective Synthesis of LiCrO2 and Li2CrO4 Nanomaterials
by Olusola Ojelere, David Graf and Sanjay Mathur
Inorganics 2019, 7(2), 22; https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics7020022 - 14 Feb 2019
Cited by 7 | Viewed by 4713
Abstract
Achieving control over the phase-selective synthesis of mixed metal oxide materials remains a challenge to the synthetic chemist due to diffusion-driven growth, which necessitates the search for new compounds with pre-existent chemical bonds between the phase-forming elements. We report here a simple solvothermal [...] Read more.
Achieving control over the phase-selective synthesis of mixed metal oxide materials remains a challenge to the synthetic chemist due to diffusion-driven growth, which necessitates the search for new compounds with pre-existent chemical bonds between the phase-forming elements. We report here a simple solvothermal process to fabricate LiCrO2 and Li2CrO4 nanoparticles from bimetallic single-source precursors, demonstrating the distinctive influence of molecular design and calcination conditions on the resulting nanomaterials. The chemical identity of [Li2Cr(OtBu)4Cl(THF)2] (1) and [LiCr(OtBu)2(PyCH=COCF3)2(THF)2] (2) was unambiguously established in the solid state by single-crystal X-ray diffraction, revealing the formation of a coordination polymeric chain in compound 1, whereas electron paramagnetic resonance spectroscopy (EPR) studies revealed a monomeric structure in solution. TEM analysis of synthesized LiCrO2 nanoparticles showed nearly uniform particles size of approximately 20 nm. The sensitivity of the LiCrO2 phase towards oxidation was investigated by X-ray diffraction, revealing the formation of the stable Li2CrO4 after calcination in air. Full article
(This article belongs to the Special Issue Mixed Metal Oxides)
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12 pages, 28552 KiB  
Article
Investigation of the Reduction of a Molybdenum/Iron Molecular Nanocluster Single Source Precursor
by Gibran L. Esquenazi and Andrew R. Barron
Inorganics 2018, 6(4), 104; https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics6040104 - 27 Sep 2018
Viewed by 4108
Abstract
The thermolysis of the polyoxometalate cluster [HxPMo12O40⊂H4Mo72Fe30(O2CMe)15O254(H2O)90−y(EtOH)y] (1) under air, argon, and reducing conditions (5%, 10%, [...] Read more.
The thermolysis of the polyoxometalate cluster [HxPMo12O40⊂H4Mo72Fe30(O2CMe)15O254(H2O)90−y(EtOH)y] (1) under air, argon, and reducing conditions (5%, 10%, 50% H2 with Ar balance) has been investigated. The resulting products have been characterized by XRD, SEM, and EDX analysis. Thermolysis in air at 1100 °C yields predominantly Fe2O3, due to sublimation of the molybdenum component; however, under Ar atmosphere, the mixed metal oxide (Fe2Mo3O8) is formed along with Mo and MoO2. Introduction of 5% H2 (1100 °C) results in the alloy Fe2Mo3 in addition to Fe2Mo3O8 and Mo; in contrast, reduction at a lower temperature (900 °C) yields the carbide (Fe3Mo3C) and the analogous oxide (Fe3Mo3O), suggesting that these are direct precursors of Fe2Mo3. Increasing the H2 concentration (10%) promotes carbide rather than oxide formation (Fe3Mo3C and Mo2C), until alloy formation (Fe7.92Mo5.08) predominates under 50% H2 at 1200 °C. The effect of temperature and H2 concentration on the composition, grain size, and morphology has been investigated by EDX, SEM, and XRD. The relationship of the composition of 1 (i.e., Fe:Mo = 30:84) with the product distribution is discussed. Full article
(This article belongs to the Special Issue Mixed Metal Oxides)
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16 pages, 2455 KiB  
Article
Botanically Templated Monolithic Macrostructured Zinc Oxide Materials for Photocatalysis
by Nathan M. Black, David S. Ciota and Edward G. Gillan
Inorganics 2018, 6(4), 103; https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics6040103 - 25 Sep 2018
Cited by 2 | Viewed by 3493
Abstract
With an increased focus on light energy to facilitate catalytic processes, photocatalysts have been intensively studied for a wide range of energy and environmental applications. In this report, we describe the use of chemically dehydrated leaves as sacrificial foam-like templates for the growth [...] Read more.
With an increased focus on light energy to facilitate catalytic processes, photocatalysts have been intensively studied for a wide range of energy and environmental applications. In this report, we describe the use of chemically dehydrated leaves as sacrificial foam-like templates for the growth of monolithic macrostructured semiconducting zinc oxide and nickel or cobalt doped zinc oxide materials. The composition and structure of these templated zinc oxides were characterized using X-ray powder diffraction, scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. Optical properties were examined using solid-state UV–vis diffuse reflectance spectroscopy. The metal-doped ZnO materials have enhanced visible absorption and lower band gaps as compared to ZnO. The botanically templated ZnO materials retain the macroscopic cellular form of the leaf template with fused nanoparticle walls. Their UV photocatalytic oxidative abilities were investigated using methylene blue dye degradation in air. The leaf templated zinc oxides degrade ~85% of methylene blue dye with 30 min of UV illumination. Nickel and cobalt doped zinc oxides showed varying degrees of decreased UV and visible light photocatalytic activity, possibly due to metal-mediated charge recombination. The mild chemical dehydration process here allows complex soft botanical structures to be easily utilized for templating materials. Full article
(This article belongs to the Special Issue Mixed Metal Oxides)
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10 pages, 2497 KiB  
Article
Synthesis of NiFe2O4-LDH Composites with High Adsorption and Photocatalytic Activity for Methyl Orange Degradation
by Cristian D. Valencia-Lopez, Mario Zafra-Calvo, María José Martín de Vidales, Verónica Blanco-Gutierrez, Evangelina Atanes-Sanchez, Noemí Merayo, Francisco Fernandez-Martinez, Antonio Nieto-Marquez and Antonio J. Dos santos-Garcia
Inorganics 2018, 6(3), 98; https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics6030098 - 12 Sep 2018
Cited by 17 | Viewed by 4501
Abstract
The presence of hazardous chemicals in wastewater produced by industrial activities and human metropoles is threating the availability of safe drinking water. The development of a multifunctional material coupling adsorption and photocatalytic activity is hereby particularly promising for the removal of pollutants. We [...] Read more.
The presence of hazardous chemicals in wastewater produced by industrial activities and human metropoles is threating the availability of safe drinking water. The development of a multifunctional material coupling adsorption and photocatalytic activity is hereby particularly promising for the removal of pollutants. We have proved the adsorption and catalytic activity of NiFe2O4-layered double hydroxide (LDH) composite through the degradation of methyl orange (MO) at room temperature under visible light. This degradation is enhanced by using a set of small light-emitting diodes (LEDs) providing a uniform 405 nm UV light. The remediation process is based on a first-step rapid adsorption of MO molecules by the LDH structures followed by the photocatalytic oxidation of the pollutant by the (·OH) radicals produced by the NiFe2O4 semiconductor nanoparticles (NPs). The magnetic properties of the ferrite NPs allow a facile separation of the composite from the liquid media via a simple magnet. NiFe2O4-LDH composite could find wide application as a highly effective adsorbent/oxidizing catalyst operating under visible or near UV light. Full article
(This article belongs to the Special Issue Mixed Metal Oxides)
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13 pages, 4166 KiB  
Article
New Mixed Y0.5R0.5VO4 and RVO4:Bi Materials: Synthesis, Crystal Structure and Some Luminescence Properties
by Leonid Vasylechko, Andrii Tupys, Vasyl Hreb, Volodymyr Tsiumra, Iryna Lutsiuk and Yaroslav Zhydachevskyy
Inorganics 2018, 6(3), 94; https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics6030094 - 10 Sep 2018
Cited by 10 | Viewed by 4128
Abstract
The results are reported on a precise crystal structure and microstructure determination of new mixed YVO4-based orthovanadates of Y0.5R0.5VO4 (R = Sm, Tb, Dy, Ho, Tm, Yb, Lu) as well as some Bi3+-doped [...] Read more.
The results are reported on a precise crystal structure and microstructure determination of new mixed YVO4-based orthovanadates of Y0.5R0.5VO4 (R = Sm, Tb, Dy, Ho, Tm, Yb, Lu) as well as some Bi3+-doped RVO4 (R = La, Gd, Y, Lu) nano- (submicro-) materials. The formation of continuous solid solutions in the YVO4–RVO4 pseudo-binary systems (R = Sm, Tb, Dy, Ho, Tm, Yb, Lu) has been proved. The lattice constants and unit cell volumes of the new mixed orthovanadates were analyzed as a function of R3+ cation radius. The impact of crystal structure parameters on the energy band gap of the materials was studied by means of photoluminescence studies of the Bi3+-doped compounds. Full article
(This article belongs to the Special Issue Mixed Metal Oxides)
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10 pages, 2841 KiB  
Article
Assembly of ZnO Nanoparticles on SiO2@α-Fe2O3 Nanocomposites for an Efficient Photo-Fenton Reaction
by Kasimayan Uma, Sridharan Balu, Guan-Ting Pan and Thomas C.-K. Yang
Inorganics 2018, 6(3), 90; https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics6030090 - 03 Sep 2018
Cited by 14 | Viewed by 4900
Abstract
The SiO2@α-Fe2O3/ZnO metal oxide nanocomposites employed in this study were obtained using the sol-gel method. Their photocatalytic activities were enhanced by photo-Fenton reactions. The metal oxide composite of ZnO and α-Fe2O3 nanoparticles were deposited [...] Read more.
The SiO2@α-Fe2O3/ZnO metal oxide nanocomposites employed in this study were obtained using the sol-gel method. Their photocatalytic activities were enhanced by photo-Fenton reactions. The metal oxide composite of ZnO and α-Fe2O3 nanoparticles were deposited on the SiO2 nanospheres intended for visible light photocatalysis. Further, the as-synthesized SiO2@α-Fe2O3/ZnO nanocomposites exhibited a robust crystallinity and a high adsorption of dye molecules when compared to SiO2@ZnO and SiO2@α-Fe2O3 nanocomposites, respectively. The experimental results demonstrated a rapid Methylene Blue (MB) degradation among these catalysts within short intervals of time with the addition of α-Fe2O3/ZnO mixed metal oxide catalysts on the SiO2 nanospheres. Finally, a photo-Fenton reaction was implemented to confirm the presence of the hydroxyl (OH) radicals, which are powerful agents used for the degradation of organic pollutants. Full article
(This article belongs to the Special Issue Mixed Metal Oxides)
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16 pages, 2857 KiB  
Article
Crystal Structure and Coordination of B-Cations in the Ruddlesden–Popper Phases Sr3−xPrx(Fe1.25Ni0.75)O7−δ (0 ≤ x ≤ 0.4)
by Gunnar Svensson, Louise Samain, Jordi Jacas Biendicho, Abdelfattah Mahmoud, Raphaël P. Hermann, Sergey Ya. Istomin and Jekabs Grins
Inorganics 2018, 6(3), 89; https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics6030089 - 31 Aug 2018
Cited by 3 | Viewed by 6880
Abstract
Compounds Sr3−xPrxFe1.25Ni0.75O7−δ with 0 ≤ x ≤ 0.4 and Ruddlesden–Popper n = 2 type structures were synthesized and investigated by X-ray and neutron powder diffraction, thermogravimetry, and Mössbauer spectroscopy. Both samples, prepared at [...] Read more.
Compounds Sr3−xPrxFe1.25Ni0.75O7−δ with 0 ≤ x ≤ 0.4 and Ruddlesden–Popper n = 2 type structures were synthesized and investigated by X-ray and neutron powder diffraction, thermogravimetry, and Mössbauer spectroscopy. Both samples, prepared at 1300 °C under N2(g) flow and samples subsequently air-annealed at 900 °C, were studied. The structures contained oxygen vacancies in the perovskite layers, and the Fe/Ni cations had an average coordination number less than six. The oxygen content was considerably higher for air-annealed samples than for samples prepared under N2, 7 − δ = ~6.6 and ~5.6 per formula unit, respectively. Mössbauer data collected at 7 K, below magnetic ordering temperatures, were consistent with X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) results. The electrical conductivity was considerably higher for the air-annealed samples and was for x = 0.1~30 S·cm−1 at 500 °C. The thermal expansion coefficients were measured in air between room temperature and 900 °C and was found to be 20–24 ppm·K−1 overall. Full article
(This article belongs to the Special Issue Mixed Metal Oxides)
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13 pages, 4693 KiB  
Article
Gd3Li3Te2O12:U6+,Eu3+: A Tunable Red Emitting Garnet Showing Efficient U6+ to Eu3+ Energy Transfer at Room Temperature
by David Böhnisch, Juri Rosenboom, Thomas Jansen and Thomas Jüstel
Inorganics 2018, 6(3), 84; https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics6030084 - 23 Aug 2018
Cited by 3 | Viewed by 3427
Abstract
Since the invention of fluorescent light sources, there is strong interest in Eu3+ activated phosphors as they are able to provide a high color rendering index (CRI) and luminous efficacy, which will also hold for phosphor converted light emitting diodes. Due to [...] Read more.
Since the invention of fluorescent light sources, there is strong interest in Eu3+ activated phosphors as they are able to provide a high color rendering index (CRI) and luminous efficacy, which will also hold for phosphor converted light emitting diodes. Due to an efficient U6+ to Eu3+ energy transfer in Gd3Li3Te2O12:U6+,Eu3+, this inorganic composition shows red photoluminescence peaking at 611 nm. That means Eu3+ photoluminescence can be nicely sensitized via excitation into the U6+ excitation bands. Therefore, photoluminescence properties, such as temperature dependent emission and emission lifetime measurements, are presented. Charge transfer bands were investigated in detail. Additionally, density functional theory calculations reveal the band structure of the pure, i.e., non-doped host material. Obtained theoretical results were evaluated experimentally by the aid of diffuse UV reflectance spectroscopy. Full article
(This article belongs to the Special Issue Mixed Metal Oxides)
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14 pages, 3857 KiB  
Article
High-Performance La0.5Ba0.5Co1/3Mn1/3Fe1/3O3−δ-BaZr1−zYzO3−δ Cathode Composites via an Exsolution Mechanism for Protonic Ceramic Fuel Cells
by Laura Rioja-Monllor, Sandrine Ricote, Carlos Bernuy-Lopez, Tor Grande, Ryan O’Hayre and Mari-Ann Einarsrud
Inorganics 2018, 6(3), 83; https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics6030083 - 23 Aug 2018
Cited by 14 | Viewed by 4277
Abstract
A novel exsolution process was used to fabricate complex all-oxide nanocomposite cathodes for Protonic Ceramic Fuel Cells (PCFCs). The nanocomposite cathodes with La0.5Ba0.5Co1/3Mn1/3Fe1/3O3−δ-BaZr1−zYzO3−δ nominal composition [...] Read more.
A novel exsolution process was used to fabricate complex all-oxide nanocomposite cathodes for Protonic Ceramic Fuel Cells (PCFCs). The nanocomposite cathodes with La0.5Ba0.5Co1/3Mn1/3Fe1/3O3−δ-BaZr1−zYzO3−δ nominal composition were prepared from a single-phase precursor via an oxidation-driven exsolution mechanism. The exsolution process results in a highly nanostructured and intimately interconnected percolating network of the two final phases, one proton conducting (BaZr1−zYzO3−δ) and one mixed oxygen ion and electron conducting (La0.5Ba0.5Co1/3Mn1/3Fe1/3O3−δ), yielding excellent cathode performance. The cathode powder is synthesized as a single-phase cubic precursor by a modified Pechini route followed by annealing at 700 °C in N2. The precursor phase is exsolved into two cubic perovskite phases by further heat treatment in air. The phase composition and chemical composition of the two phases were confirmed by Rietveld refinement. The electrical conductivity of the composites was measured and the electrochemical performance was determined by impedance spectroscopy of symmetrical cells using BaZr0.9Y0.1O2.95 as electrolyte. Our results establish the potential of this exsolution method where a large number of different cations can be used to design composite cathodes. The La0.5Ba0.5Co1/3Mn1/3Fe1/3O3−δ-BaZr0.9Y0.1O2.95 composite cathode shows the best performance of 0.44 Ω·cm2 at 600 °C in 3% moist synthetic air. Full article
(This article belongs to the Special Issue Mixed Metal Oxides)
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8 pages, 11702 KiB  
Article
Single Crystal Growth of Sillén–Aurivillius Perovskite Oxyhalides Bi4NbO8X (X = Cl, Br)
by Chengchao Zhong, Daichi Kato, Fumitaka Takeiri, Kotaro Fujii, Masatomo Yashima, Emily Nishiwaki, Yasuhiro Fujii, Akitoshi Koreeda, Cédric Tassel, Ryu Abe and Hiroshi Kageyama
Inorganics 2018, 6(2), 41; https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics6020041 - 16 Apr 2018
Cited by 10 | Viewed by 6871
Abstract
Sillén–Aurivillius perovskite Bi4NbO8X (X = Cl, Br) is a promising photocatalyst for water splitting under visible light, as well as a potential ferroelectric material. In this work, we investigate the crystal growth conditions by mainly varying soak temperature, soak [...] Read more.
Sillén–Aurivillius perovskite Bi4NbO8X (X = Cl, Br) is a promising photocatalyst for water splitting under visible light, as well as a potential ferroelectric material. In this work, we investigate the crystal growth conditions by mainly varying soak temperature, soak time and cooling rate. Under the optimal conditions, we successfully obtained yellow platelet single crystals with an in-plane distance of several hundred microns. As opposed to conventional crystal growth, a moderate cooling is essential to suppress an evaporation of the Bi–O–Cl species from a melt zone. The single crystals of Bi4NbO8Br were also grown using a similar condition. We suggest that the knowledge obtained in this study can be generally applied to other Sillén–Aurivillius phases and related oxyhalides. Full article
(This article belongs to the Special Issue Mixed Metal Oxides)
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