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Inorganics
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Mixed Metal Oxides, 3rd Edition
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Mixed Metal Oxides, 3rd Edition

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

Deadline for manuscript submissions: 31 May 2026 | Viewed by 8353

Special Issue Editors

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
Dr. Greta Inkrataitė

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Guest Editor Assistant
Institute of Chemistry, Vilnius University, LT-03225 Vilnius, Lithuania
Interests: luminescence; sol-gel synthesis; inorganics compounds; materials research; garnets
Dr. Dovydas Karoblis

E-Mail Website
Guest Editor Assistant
Institute of Chemistry, Vilnius University, Naugarduko 24, LT-03225 Vilnius, Lithuania
Interests: sol-gel synthesis; molten salt synthesis; multiferroics; magnetism; phase transitions; manganites; ferrites

Special Issue Information

Dear Colleagues,

The Special Issue, “Mixed Metal Oxides”, published in Inorganics in 2018, collected ten excellent papers and attracted many potential readers and authors. Meanwhile, the second edition of this Special Issue, entitled “Mixed Metal Oxides II”, published in 2024, collected nine papers and received more than 19,000 views (as of 7 April 2025). This has encouraged us to build upon the success of the previous two Issues. Therefore, we would like to open a third edition in this Special Issue, “Mixed Metal Oxides, 3rd Edition”.

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 is once again focused on the synthesis, characterization and application of mixed-metal oxides and related materials, which are important in all areas of our life. Contributions offering a detailed understanding of reaction pathways at the level of the most basic steps of the formation of solids via in situ methods (X-ray and neutron diffraction, thermal analysis, Raman spectroscopy, etc.) are sought after. 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. Furthermore, 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 also desired. We look forward to your contributions.

Prof. Dr. Aivaras Kareiva
Guest Editor

Dr. Greta Inkrataitė
Dr. Dovydas Karoblis
Guest Editor Assistants

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

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 2200 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

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

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Published Papers (7 papers)

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Research

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25 pages, 3543 KB  
Article
B-Doped ZnO Nanoparticles: Defect Chemistry, Tensile Strain, and Tunable Optical Response
by Lütfi Arda, Merve Mine Seker Perez, Ersin Ozugurlu and Ilke Tascioglu
Inorganics 2026, 14(2), 60; https://doi.org/10.3390/inorganics14020060 - 16 Feb 2026
Cited by 1 | Viewed by 785
Abstract
ZnO and ZnO:5%B nanoparticles produced by sol–gel synthesis exhibit a single-phase wurtzite structure. X-ray diffraction (XRD) investigation reveals crystallite sizes in the range of 32.37–39.63 nm and microstrain values on the order of [...] Read more.
ZnO and ZnO:5%B nanoparticles produced by sol–gel synthesis exhibit a single-phase wurtzite structure. X-ray diffraction (XRD) investigation reveals crystallite sizes in the range of 32.37–39.63 nm and microstrain values on the order of (1.98–8.03)×10−4, despite the Uniform Stress Deformation Model (USDM) indicating the presence of considerable tensile stress. Significant band-tail states are introduced via boron doping, resulting in Urbach energies ranging from 110 to 193 meV and a narrowed optical band gap of 3.216 eV. With a refractive index range of 2.05–2.71, the material exhibits tunable optical characteristics. Violet and blue emissions originating predominantly from zinc interstitials (Znᵢ) and zinc vacancies (VZn) dominate the photoluminescence spectra, while oxygen interstitial-related contributions remain relatively weak. A high spin density is confirmed by electron spin resonance measurements, which reveal a strong defect-related signal at g≈2.294. The formation of Znᵢ/VZn defect centers due to charge compensation and ionic size mismatch induced by B3+ substitution for Zn2+ significantly modifies the band-edge states and optical constants. These defect-engineered properties render the material promising for applications in ultraviolet (UV) photodetectors, transparent conducting oxides, and electron transport layers in organic photovoltaic devices. Full article
(This article belongs to the Special Issue Mixed Metal Oxides, 3rd Edition)
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17 pages, 3381 KB  
Article
Hydrothermally Constructed ZnIn2S4/SrSnO3 Type-II Heterojunction for Highly Efficient Photocatalytic Hydrogen Evolution
by Zhang-Yi Xiong, Hao Liu, Yan Zhong, Chao-Hao Hu, Dian-Hui Wang, Tian Sang, Shi-Mei Liu, Ke-Wei Chen and Xian-Fu Pan
Inorganics 2026, 14(2), 57; https://doi.org/10.3390/inorganics14020057 - 12 Feb 2026
Viewed by 755
Abstract
To achieve high-performance photocatalysts, efficient separation of photogenerated charge carriers is critical to prolonging their lifetime and thereby enhancing the activity of the hydrogen evolution reaction. In this work, we rationally designed and synthesized a nanoflower-like SrSnO3/ZnIn2S4 heterostructure [...] Read more.
To achieve high-performance photocatalysts, efficient separation of photogenerated charge carriers is critical to prolonging their lifetime and thereby enhancing the activity of the hydrogen evolution reaction. In this work, we rationally designed and synthesized a nanoflower-like SrSnO3/ZnIn2S4 heterostructure by in situ embedding SrSnO3 nanorods within the layered framework of ZnIn2S4. Experimental results demonstrate that the 0.8%-SrSnO3/ZnIn2S4 composite exhibits a hydrogen evolution rate 13.79 times higher than that of pure ZnIn2S4 under simulated solar irradiation. This dramatic enhancement stems from the formation of a Type-II heterojunction at the interface, where the staggered band alignment generates an internal electric field that drives spatial separation of electrons and holes, effectively suppressing recombination and promoting charge utilization. This study validates that the strategic incorporation of a small amount of SrSnO3 into ZnIn2S4 represents a highly effective approach to significantly boost photocatalytic hydrogen production performance. Full article
(This article belongs to the Special Issue Mixed Metal Oxides, 3rd Edition)
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21 pages, 3261 KB  
Article
First-Principles Study on the Enhancement of Formaldehyde Adsorption on Graphene-like ZnO via Doping Au and Vacancy Defects
by Jingze Yao, Chao Ma, Xuefeng Xiao, Weiyin Li, Yujie He and Hao Zhang
Inorganics 2026, 14(2), 53; https://doi.org/10.3390/inorganics14020053 - 11 Feb 2026
Viewed by 504
Abstract
Graphene-like 2D ZnO (g-ZnO), a wide-bandgap semiconductor, shows great potential for gas sensing, owing to its high surface area and carrier mobility. However, the practical use of it is hampered by its intrinsic chemical inertness. In this study, density functional theory was first [...] Read more.
Graphene-like 2D ZnO (g-ZnO), a wide-bandgap semiconductor, shows great potential for gas sensing, owing to its high surface area and carrier mobility. However, the practical use of it is hampered by its intrinsic chemical inertness. In this study, density functional theory was first used to study the effects of zinc vacancies (VZn), oxygen vacancies (VO), and Au doping on formaldehyde (CH2O) sensing. The results show that engineering of the defects and the Au doping both significantly improve the reactivity of the material. Specifically, the VZn system promotes dissociative chemisorption (Eads = −5.55 eV) of CH2O to CO and H atoms. Charge compensation effectively passivates the vacancy states and returns the direct bandgap semiconducting nature of the system. Furthermore, Au doping raises the conduction band and enlarges the bandgap, while the charge accumulation around Au atoms activates the surrounding sites, causing the adsorption mechanism to change from physisorption to chemisorption. Overall, the introduction of VZn and Au doping is an efficient way to overcome the surface inertness and improve sensing sensitivity, offering a theoretical framework for the design of high-performance 2D gas sensors. Full article
(This article belongs to the Special Issue Mixed Metal Oxides, 3rd Edition)
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12 pages, 5443 KB  
Article
Novel SrSnO3/AgBr Heterojunction for Dye Degradation Under Simulated Sunlight
by Si-Hao Tian-Wu, Shi-Mei Liu, Yan Zhong, Chao-Hao Hu, Dian-Hui Wang, Hao Liu, Zhang-Yi Xiong, Tian Sang, Bing-Sen Zeng and Qi Zhang
Inorganics 2025, 13(12), 406; https://doi.org/10.3390/inorganics13120406 - 12 Dec 2025
Viewed by 628
Abstract
Photocatalysis represents an efficient and environmentally friendly technology for wastewater treatment. In this study, a novel composite material, comprising AgBr nanospheres anchored on the surface of SrSnO3 nanorods, was synthesized via a co-precipitation method. Its photocatalytic activity was evaluated using Methyl Orange [...] Read more.
Photocatalysis represents an efficient and environmentally friendly technology for wastewater treatment. In this study, a novel composite material, comprising AgBr nanospheres anchored on the surface of SrSnO3 nanorods, was synthesized via a co-precipitation method. Its photocatalytic activity was evaluated using Methyl Orange as the target pollutant. The results demonstrated that the composite photocatalyst achieved a degradation efficiency of 92% within 40 min, which is 7.16 times higher than AgBr. XPS analysis confirmed the successful construction of a built-in electric field between SrSnO3 and AgBr. Photoelectrochemical experiments further verified a significant enhancement in the charge carrier dynamics of the composite catalyst. Full article
(This article belongs to the Special Issue Mixed Metal Oxides, 3rd Edition)
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20 pages, 7705 KB  
Article
Synthesis and Properties of *BEA Zeolite Modified with Iron(III) Oxide
by Giovana Magalhães dos Santos, Mateus Freitas Paiva, Juliene Oliveira Campos de França, Sílvia Cláudia Loureiro Dias and José Alves Dias
Inorganics 2025, 13(12), 383; https://doi.org/10.3390/inorganics13120383 - 24 Nov 2025
Cited by 2 | Viewed by 1399
Abstract
Modification of zeolitic structures through the incorporation of transition metal oxides has proven to be a promising approach for heterogeneous catalysis. In the present study, *BEA zeolite was modified using the incipient wetness impregnation method with varying amounts (10, 20, and 40 wt.%) [...] Read more.
Modification of zeolitic structures through the incorporation of transition metal oxides has proven to be a promising approach for heterogeneous catalysis. In the present study, *BEA zeolite was modified using the incipient wetness impregnation method with varying amounts (10, 20, and 40 wt.%) of iron(III) oxide to investigate its structural and physicochemical properties. Characterization techniques such as XRD, UV–Vis DRS, FT–IR, Raman spectroscopy, SEM/EDS, TEM/EDS, and SAED, as well as textural and thermal analyses, were employed to assess the main changes. Different iron species were detected, including isolated iron(III) and well-dispersed Fe2O3 nanoparticles coating the zeolite surface. Under the synthesis conditions, increased Fe2O3 loading promoted hematite nanocrystal growth and the formation of the α-Fe2O3 phase, as demonstrated by XRD, Raman, and SAED analyses. Key observations included the preservation of the zeolite framework, high relative crystallinity (ranging from 70% to 85%), and a band gap of approximately 2.0 eV. Furthermore, a general increase in mesoporosity and external surface area was observed, along with a reduction in the number of acidic sites. This decrease may be attributed to restricted accessibility of the probe molecule (pyridine) to Brønsted sites due to micropore blockage in *BEA. These results demonstrate that the adopted synthesis method effectively produced α-Fe2O3/BEA catalysts, with no other crystalline phases of iron(III) oxide detected. Full article
(This article belongs to the Special Issue Mixed Metal Oxides, 3rd Edition)
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12 pages, 2734 KB  
Article
Effect of CaO/SiO2 and MgO/Al2O3 on the Metallurgical Properties of Low Boron-Bearing High-Alumina Slag
by Ye Sun, Zuoliang Zhang, Chunlei Wu and Zhenggen Liu
Inorganics 2025, 13(11), 346; https://doi.org/10.3390/inorganics13110346 - 24 Oct 2025
Viewed by 1305
Abstract
For optimizing the operational efficiency and productivity within blast furnace processes, a profound understanding of the viscous flow characteristics of CaO–SiO2–MgO–Al2O3–B2O3 slag systems is of paramount importance. In this study, we conducted a comprehensive [...] Read more.
For optimizing the operational efficiency and productivity within blast furnace processes, a profound understanding of the viscous flow characteristics of CaO–SiO2–MgO–Al2O3–B2O3 slag systems is of paramount importance. In this study, we conducted a comprehensive investigation into the influence of the CaO/SiO2 and MgO/Al2O3 ratios on the viscosity, break point temperature (TBr), and activation energy (Eη) of low boron-bearing high-alumina slag. Concurrently, we elucidated the underlying mechanisms through which these ratios affect the viscous behavior of the slag by employing a combination of analytical techniques, including X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and thermodynamic modeling using the Factsage software. The experimental findings reveal that, as the CaO/SiO2 ratio increases from 1.10 to 1.30, the slag viscosity at 1773 K decreases from 0.316 Pa·s to 0.227 Pa·s, while both the TBr and Eη exhibit an upward trend, rising from 1534 K and 117.01 kJ·mol−1 to 1583 K and 182.86 kJ·mol−1, respectively. Conversely, an elevation in the MgO/Al2O3 ratio from 0.40 to 0.65 results in a reduction in slag viscosity at 1773 K from 0.290 Pa·s to 0.208 Pa·s, accompanied by a decrease in TBr from 1567 K to 1542 K. The observed deterioration in slag flow properties can be attributed to an enhanced polymerization degree of complex viscous structural units within the slag matrix. Ultimately, our study identifies that an optimal viscous performance of the slag is achieved when the CaO/SiO2 ratio is maintained at 1.25 and the MgO/Al2O3 ratio is maintained at 0.55, providing valuable insights for the rational design and control of blast furnace slag systems. Full article
(This article belongs to the Special Issue Mixed Metal Oxides, 3rd Edition)
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Review

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17 pages, 1113 KB  
Review
Towards Sustainable Processing of Chromite Resources: A Review of Methods for Magnesium and Platinum-Group Metal Extraction
by Rinat Abdulvaliyev, Yerkezhan Abikak, Nazym Akhmadiyeva, Sergey Gladyshev, Alfiyam Manapova and Asiya Kasymzhanova
Inorganics 2025, 13(11), 353; https://doi.org/10.3390/inorganics13110353 - 27 Oct 2025
Cited by 2 | Viewed by 2319
Abstract
This article provides a review of modern technologies for processing chromite ores and beneficiation wastes, with a focus on the recovery of magnesium and platinum-group metals (PGMs). It reveals that the traditional use of chromites solely as a source of chromium limits the [...] Read more.
This article provides a review of modern technologies for processing chromite ores and beneficiation wastes, with a focus on the recovery of magnesium and platinum-group metals (PGMs). It reveals that the traditional use of chromites solely as a source of chromium limits the potential of this raw material, whereas comprehensive processing enables the recovery of associated components, including serpentine minerals, which are widely present in chromite ores and tailings. Pyrometallurgical, hydrometallurgical, plasma-arc, and biotechnological methods are examined, as well as their integration into combined flowsheets. Particular attention is given to sulfation, chloridization, and carbochlorination processes, which ensure a high degree of PGM recovery. Economic and environmental aspects of comprehensive processing are discussed, including carbon footprint reduction, waste minimization, and prospects for the development of “green metallurgy.” It is concluded that the further advancement of resource-efficient and environmentally safe technologies for chromite processing will increase production efficiency, ensure resource independence, and support compliance with global carbon neutrality requirements. Full article
(This article belongs to the Special Issue Mixed Metal Oxides, 3rd Edition)
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