Metal Oxide Nanomaterials: From Fundamental to Applications

A special issue of Nanomaterials (ISSN 2079-4991). This special issue belongs to the section "Synthesis, Interfaces and Nanostructures".

Deadline for manuscript submissions: closed (31 May 2022) | Viewed by 28984

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Special Issue Editors

Department of Chemistry, Illinois Institute of Technology, Chicago, IL 60616, USA
Interests: metal oxide nanomaterials; solid state inorganic/materials chemistry; optical spectroscopy; phosphors; scintillators; catalysts
Dr. Santosh Kumar Gupta
E-Mail Website1 Website2
Guest Editor
Scientific Officer (E), Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai-400085, India
Interests: Ln/An photoluminescence; structure-property correlation; defect spectroscopy; persistent/upconversion PL; nano photonics

Special Issue Information

Dear Colleagues,

The fundamental understanding and application exploration of metal oxide nanomaterials have been expanded extensively over the past couple of decades and continuously with global, creative and diligent work by researchers like you. However, there are no recent collections, such as books, connecting their fundamental aspects and application perspectives in a concise fashion to give a broad view of the current status of this fascinating field. Therefore, we invite authors to contribute either comprehensive review articles or original research articles covering the most recent progress and new developments in the fundamental understanding of the synthesis and properties and the exploration of the utilization of metal oxide nanomaterials. Review articles are preferred, while full papers and communications are also welcomed. Potential topics of this Special Issue include, but are not limited to:

  1. Fundamental science of metal oxide nanomaterials, including their local, long-range and electronic structures, quantum-mechanicals, thermodynamics, defects, and traps characterized by sophisticated experimental techniques and state-of-the-art theory;
  2. Underlying principles and mechanisms of the physicochemical properties of metal oxide nanomaterials understood by experimental studies, theoretical calculations, and machine learning;
  3. Fundamentals on the synthesis of metal oxide nanomaterials, including and thermodynamic aspects that determine their growth modes and probing phase behavior and synthetic pathways via in situ techniques;
  4. Exemplary real-world applications of metal oxide nanomaterials as catalysts, photonics, sensors, electronics, sorbents, etc.

Thank you in advance for your contribution to making this Special Issue a success that consolidates current fundamental knowledge alongside practical applications of metal oxide nanomaterials. We hope that this will be one of the most comprehensive resources for researchers to draw from and build on. 

Prof. Dr. Yuanbing Mao
Dr. Santosh Kumar Gupta
Guest Editors

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Keywords

  • Metal Oxides
  • Nanomaterials
  • Fundamental Understanding
  • Applications

Published Papers (11 papers)

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Editorial

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3 pages, 195 KiB  
Editorial
Metal Oxide Nanomaterials: From Fundamentals to Applications
Nanomaterials 2022, 12(23), 4340; https://doi.org/10.3390/nano12234340 - 06 Dec 2022
Viewed by 1038
Abstract
This Special Issue of Nanomaterials, “Metal Oxide Nanomaterials: From Fundamentals to Applications”, highlights the development and understanding of different types of metal oxide nanoparticles and their use for applications in luminescence, photocatalysis, water–oil separation, optoelectronics, gas sensors, energy-saving smart windows, etc [...] Full article
(This article belongs to the Special Issue Metal Oxide Nanomaterials: From Fundamental to Applications)

Research

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16 pages, 3074 KiB  
Article
Excitation-Dependent Photoluminescence of BaZrO3:Eu3+ Crystals
Nanomaterials 2022, 12(17), 3028; https://doi.org/10.3390/nano12173028 - 31 Aug 2022
Cited by 6 | Viewed by 1652
Abstract
The elucidation of local structure, excitation-dependent spectroscopy, and defect engineering in lanthanide ion-doped phosphors was a focal point of research. In this work, we have studied Eu3+-doped BaZrO3 (BZOE) submicron crystals that were synthesized by a molten salt method. The [...] Read more.
The elucidation of local structure, excitation-dependent spectroscopy, and defect engineering in lanthanide ion-doped phosphors was a focal point of research. In this work, we have studied Eu3+-doped BaZrO3 (BZOE) submicron crystals that were synthesized by a molten salt method. The BZOE crystals show orange–red emission tunability under the host and dopant excitations at 279 nm and 395 nm, respectively, and the difference is determined in terms of the asymmetry ratio, Stark splitting, and intensity of the uncommon 5D07F0 transition. These distinct spectral features remain unaltered under different excitations for the BZOE crystals with Eu3+ concentrations of 0–10.0%. The 2.0% Eu3+-doped BZOE crystals display the best optical performance in terms of excitation/emission intensity, lifetime, and quantum yield. The X-ray absorption near the edge structure spectral data suggest europium, barium, and zirconium ions to be stabilized in +3, +2, and +4 oxidation states, respectively. The extended X-ray absorption fine structure spectral analysis confirms that, below 2.0% doping, the Eu3+ ions occupy the six-coordinated Zr4+ sites. This work gives complete information about the BZOE phosphor in terms of the dopant oxidation state, the local structure, the excitation-dependent photoluminescence (PL), the concentration-dependent PL, and the origin of PL. Such a complete photophysical analysis opens up a new pathway in perovskite research in the area of phosphors and scintillators with tunable properties. Full article
(This article belongs to the Special Issue Metal Oxide Nanomaterials: From Fundamental to Applications)
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15 pages, 3388 KiB  
Article
UV-Vis Activated Cu2O/SnO2/WO3 Heterostructure for Photocatalytic Removal of Pesticides
Nanomaterials 2022, 12(15), 2648; https://doi.org/10.3390/nano12152648 - 01 Aug 2022
Cited by 4 | Viewed by 1379
Abstract
A three-steps sol–gel method was used to obtain a Cu2O/SnO2/WO3 heterostructure powder, deposited as film by spray pyrolysis. The porous morphology of the final heterostructure was constructed starting with fiber-like WO3 acting as substrate for SnO2 [...] Read more.
A three-steps sol–gel method was used to obtain a Cu2O/SnO2/WO3 heterostructure powder, deposited as film by spray pyrolysis. The porous morphology of the final heterostructure was constructed starting with fiber-like WO3 acting as substrate for SnO2 development. The SnO2/WO3 sample provide nucleation and grew sites for Cu2O formation. Diffraction evaluation indicated that all samples contained crystalline structures with crystallite size varying from 42.4 Å (Cu2O) to 81.8 Å (WO3). Elemental analysis confirmed that the samples were homogeneous in composition and had an oxygen excess due to the annealing treatments. Photocatalytic properties were tested in the presence of three pesticides—pirimicarb, S-metolachlor (S-MCh), and metalaxyl (MET)—chosen based on their resilience and toxicity. The photocatalytic activity of the Cu2O/SnO2/WO3 heterostructure was compared with WO3, SnO2, Cu2O, Cu2O/SnO2, Cu2O/WO3, and SnO2/WO3 samples. The results indicated that the three-component heterostructure had the highest photocatalytic efficiency toward all pesticides. The highest photocatalytic efficiency was obtained toward S-MCh (86%) using a Cu2O/SnO2/WO3 sample and the lowest correspond to MET (8.2%) removal using a Cu2O monocomponent sample. TOC analysis indicated that not all the removal efficiency could be attributed to mineralization, and by-product formation is possible. Cu2O/SnO2/WO3 is able to induce 81.3% mineralization of S-MCh, while Cu2O exhibited 5.7% mineralization of S-MCh. The three-run cyclic tests showed that Cu2O/SnO2/WO3, WO3, and SnO2/WO3 exhibited good photocatalytic stability without requiring additional procedures. The photocatalytic mechanism corresponds to a Z-scheme charge transfer based on a three-component structure, where Cu2O exhibits reduction potential responsible for O2 production and WO3 has oxidation potential responsible for HO· generation. Full article
(This article belongs to the Special Issue Metal Oxide Nanomaterials: From Fundamental to Applications)
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19 pages, 3310 KiB  
Article
Sputtering-Assisted Synthesis of Copper Oxide–Titanium Oxide Nanorods and Their Photoactive Performances
Nanomaterials 2022, 12(15), 2634; https://doi.org/10.3390/nano12152634 - 30 Jul 2022
Cited by 8 | Viewed by 1503
Abstract
A TiO2 nanorod template was successfully decorated with a copper oxide layer with various crystallographic phases using sputtering and postannealing procedures. The crystallographic phase of the layer attached to the TiO2 was adjusted from a single Cu2O phase or [...] Read more.
A TiO2 nanorod template was successfully decorated with a copper oxide layer with various crystallographic phases using sputtering and postannealing procedures. The crystallographic phase of the layer attached to the TiO2 was adjusted from a single Cu2O phase or dual Cu2O–CuO phase to a single CuO phase by changing the postannealing temperature from 200 °C to 400 °C. The decoration of the TiO2 (TC) with a copper oxide layer improved the light absorption and photoinduced charge separation abilities. These factors resulted in the composite nanorods demonstrating enhanced photoactivity compared to that of the pristine TiO2. The ternary phase composition of TC350 allowed it to achieve superior photoactive performance compared to the other composite nanorods. The possible Z-scheme carrier movement mechanism and the larger granular size of the attached layer of TC350 under irradiation accounted for the superior photocatalytic activity in the degradation of RhB dyes. Full article
(This article belongs to the Special Issue Metal Oxide Nanomaterials: From Fundamental to Applications)
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15 pages, 4697 KiB  
Article
Experimental Study on the Stability of a Novel Nanocomposite-Enhanced Viscoelastic Surfactant Solution as a Fracturing Fluid under Unconventional Reservoir Stimulation
Nanomaterials 2022, 12(5), 812; https://doi.org/10.3390/nano12050812 - 28 Feb 2022
Cited by 3 | Viewed by 1445
Abstract
Fe3O4@ZnO nanocomposites (NCs) were synthesized to improve the stability of the wormlike micelle (WLM) network structure of viscoelastic surfactant (VES) fracturing fluid and were characterized by Fourier transform infrared spectrometry (FT-IR), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), [...] Read more.
Fe3O4@ZnO nanocomposites (NCs) were synthesized to improve the stability of the wormlike micelle (WLM) network structure of viscoelastic surfactant (VES) fracturing fluid and were characterized by Fourier transform infrared spectrometry (FT-IR), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). Then, an NC-enhanced viscoelastic surfactant solution as a fracturing fluid (NC-VES) was prepared, and its properties, including settlement stability, interactions between NCs and WLMs, proppant-transporting performance and gel-breaking properties, were systematically studied. More importantly, the influences of the NC concentration, shear rate, temperature and pH level on the stability of NC-VES were systematically investigated. The experimental results show that the NC-VES with a suitable content of NCs (0.1 wt.%) shows superior stability at 95 °C or at a high shear rate. Meanwhile, the NC-VES has an acceptable wide pH stability range of 6–9. In addition, the NC-VES possesses good sand-carrying performance and gel-breaking properties, while the NCs can be easily separated and recycled by applying a magnetic field. The temperature-resistant, stable and environmentally friendly fracturing fluid opens an opportunity for the future hydraulic fracturing of unconventional reservoirs. Full article
(This article belongs to the Special Issue Metal Oxide Nanomaterials: From Fundamental to Applications)
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13 pages, 6082 KiB  
Article
Wettability Improvement in Oil–Water Separation by Nano-Pillar ZnO Texturing
Nanomaterials 2022, 12(5), 740; https://doi.org/10.3390/nano12050740 - 22 Feb 2022
Cited by 4 | Viewed by 1666
Abstract
The nanostructure-based surface texturing can be used to improve the materials wettability. Regarding oil–water separation, designing a surface with special wettability is as an important approach to improve the separation efficiency. Herein, a ZnO nanostructure was prepared by a two-step process for sol–gel [...] Read more.
The nanostructure-based surface texturing can be used to improve the materials wettability. Regarding oil–water separation, designing a surface with special wettability is as an important approach to improve the separation efficiency. Herein, a ZnO nanostructure was prepared by a two-step process for sol–gel process and crystal growth from the liquid phase to achieve both a superhydrophobicity in oil and a superoleophobic property in water. It is found that the filter material with nanostructures presented an excellent wettability. ZnO-coated stainless-steel metal fiber felt had a static underwater oil contact angle of 151.4° ± 0.8° and an underoil water contact angle of 152.7° ± 0.6°. Furthermore, to achieve water/oil separation, the emulsified impurities in both water-in-oil and oil-in-water emulsion were effectively intercepted. Our filter materials with a small pore (~5 μm diameter) could separate diverse water-in-oil and oil-in-water emulsions with a high efficiency (>98%). Finally, the efficacy of filtering quantity on separation performance was also investigated. Our preliminary results showed that the filtration flux decreased with the collection of emulsified impurities. However, the filtration flux could restore after cleaning and drying, suggesting the recyclable nature of our method. Our nanostructured filter material is a promising candidate for both water-in-oil and oil-in-water separation in industry. Full article
(This article belongs to the Special Issue Metal Oxide Nanomaterials: From Fundamental to Applications)
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18 pages, 2053 KiB  
Article
Investigation of the Effects of Rapid Thermal Annealing on the Electron Transport Mechanism in Nitrogen-Doped ZnO Thin Films Grown by RF Magnetron Sputtering
Nanomaterials 2022, 12(1), 19; https://doi.org/10.3390/nano12010019 - 22 Dec 2021
Cited by 7 | Viewed by 2603
Abstract
Nitrogen-doped ZnO (ZnO:N) thin films, deposited on Si(100) substrates by RF magnetron sputtering in a gas mixture of argon, oxygen, and nitrogen at different ratios followed by Rapid Thermal Annealing (RTA) at 400 °C and 550 °C, were studied in the present work. [...] Read more.
Nitrogen-doped ZnO (ZnO:N) thin films, deposited on Si(100) substrates by RF magnetron sputtering in a gas mixture of argon, oxygen, and nitrogen at different ratios followed by Rapid Thermal Annealing (RTA) at 400 °C and 550 °C, were studied in the present work. Raman and photoluminescence spectroscopic analyses showed that introduction of N into the ZnO matrix generated defects related to oxygen and zinc vacancies and interstitials. These defects were deep levels which contributed to the electron transport properties of the ZnO:N films, studied by analyzing the current–voltage characteristics of metal–insulator–semiconductor structures with ZnO:N films, measured at 298 and 77 K. At the appliedtechnological conditions of deposition and subsequent RTA at 400 °C n-type ZnO:N films were formed, while RTA at 550 °C transformed the n-ZnO:N films to p-ZnO:N ones. The charge transport in both types of ZnO:N films was carried out via deep levels in the ZnO energy gap. The density of the deep levels was in the order of 1019 cm−3. In the temperature range of 77–298 K, the electron transport mechanism in the ZnO:N films was predominantly intertrap tunneling, but thermally activated hopping also took place. Full article
(This article belongs to the Special Issue Metal Oxide Nanomaterials: From Fundamental to Applications)
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22 pages, 6097 KiB  
Article
Silica@zirconia Core@shell Nanoparticles for Nucleic Acid Building Block Sorption
Nanomaterials 2021, 11(9), 2166; https://doi.org/10.3390/nano11092166 - 25 Aug 2021
Cited by 2 | Viewed by 2201
Abstract
The development of delivery systems for the immobilization of nucleic acid cargo molecules is of prime importance due to the need for safe administration of DNA or RNA type of antigens and adjuvants in vaccines. Nanoparticles (NP) in the size range of 20–200 [...] Read more.
The development of delivery systems for the immobilization of nucleic acid cargo molecules is of prime importance due to the need for safe administration of DNA or RNA type of antigens and adjuvants in vaccines. Nanoparticles (NP) in the size range of 20–200 nm have attractive properties as vaccine carriers because they achieve passive targeting of immune cells and can enhance the immune response of a weakly immunogenic antigen via their size. We prepared high capacity 50 nm diameter silica@zirconia NPs with monoclinic/cubic zirconia shell by a green, cheap and up-scalable sol–gel method. We studied the behavior of the particles upon water dialysis and found that the ageing of the zirconia shell is a major determinant of the colloidal stability after transfer into the water due to physisorption of the zirconia starting material on the surface. We determined the optimum conditions for adsorption of DNA building blocks, deoxynucleoside monophosphates (dNMP), the colloidal stability of the resulting NPs and its time dependence. The ligand adsorption was favored by acidic pH, while colloidal stability required neutral-alkaline pH; thus, the optimal pH for the preparation of nucleic acid-modified particles is between 7.0–7.5. The developed silica@zirconia NPs bind as high as 207 mg dNMPs on 1 g of nanocarrier at neutral-physiological pH while maintaining good colloidal stability. We studied the influence of biological buffers and found that while phosphate buffers decrease the loading dramatically, other commonly used buffers, such as HEPES, are compatible with the nanoplatform. We propose the prepared silica@zirconia NPs as promising carriers for nucleic acid-type drug cargos. Full article
(This article belongs to the Special Issue Metal Oxide Nanomaterials: From Fundamental to Applications)
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12 pages, 1231 KiB  
Article
Effect of Cu2O Substrate on Photoinduced Hydrophilicity of TiO2 and ZnO Nanocoatings
Nanomaterials 2021, 11(6), 1526; https://doi.org/10.3390/nano11061526 - 09 Jun 2021
Cited by 4 | Viewed by 1977
Abstract
The effect of a Cu2O substrate on the photoinduced alteration of the hydrophilicity of TiO2 and ZnO surfaces was studied. It was demonstrated that the formation of heterostructures Cu2O/TiO2 and Cu2O/ZnO strongly changed the direction [...] Read more.
The effect of a Cu2O substrate on the photoinduced alteration of the hydrophilicity of TiO2 and ZnO surfaces was studied. It was demonstrated that the formation of heterostructures Cu2O/TiO2 and Cu2O/ZnO strongly changed the direction of the photoinduced alteration of surface hydrophilicity: while both TiO2 and ZnO demonstrate surface transition to superhydrophilic state under UV irradiation and no significant alteration of the surface hydrophilicity under visible light irradiation, the formation of Cu2O/TiO2 and Cu2O/ZnO heterostructures resulted in photoinduced decay of the surface hydrophilicity caused by both UV and visible light irradiation. All observed photoinduced changes of the surface hydrophilicity were compared and analyzed in terms of photoinduced alteration of the surface free energy and its polar and dispersive components. Alteration of the photoinduced hydrophilic behavior of TiO2 and ZnO surfaces caused by formation of the corresponding heterostructures with Cu2O are explained within the mechanism of electron transfer and increasing of the electron concentration on the TiO2 and ZnO surfaces. Full article
(This article belongs to the Special Issue Metal Oxide Nanomaterials: From Fundamental to Applications)
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Review

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40 pages, 6810 KiB  
Review
The Combination of Two-Dimensional Nanomaterials with Metal Oxide Nanoparticles for Gas Sensors: A Review
Nanomaterials 2022, 12(6), 982; https://doi.org/10.3390/nano12060982 - 16 Mar 2022
Cited by 114 | Viewed by 7813
Abstract
Metal oxide nanoparticles have been widely utilized for the fabrication of functional gas sensors to determine various flammable, explosive, toxic, and harmful gases due to their advantages of low cost, fast response, and high sensitivity. However, metal oxide-based gas sensors reveal the shortcomings [...] Read more.
Metal oxide nanoparticles have been widely utilized for the fabrication of functional gas sensors to determine various flammable, explosive, toxic, and harmful gases due to their advantages of low cost, fast response, and high sensitivity. However, metal oxide-based gas sensors reveal the shortcomings of high operating temperature, high power requirement, and low selectivity, which limited their rapid development in the fabrication of high-performance gas sensors. The combination of metal oxides with two-dimensional (2D) nanomaterials to construct a heterostructure can hybridize the advantages of each other and overcome their respective shortcomings, thereby improving the sensing performance of the fabricated gas sensors. In this review, we present recent advances in the fabrication of metal oxide-, 2D nanomaterials-, as well as 2D material/metal oxide composite-based gas sensors with highly sensitive and selective functions. To achieve this aim, we firstly introduce the working principles of various gas sensors, and then discuss the factors that could affect the sensitivity of gas sensors. After that, a lot of cases on the fabrication of gas sensors by using metal oxides, 2D materials, and 2D material/metal oxide composites are demonstrated. Finally, we summarize the current development and discuss potential research directions in this promising topic. We believe in this work is helpful for the readers in multidiscipline research fields like materials science, nanotechnology, chemical engineering, environmental science, and other related aspects. Full article
(This article belongs to the Special Issue Metal Oxide Nanomaterials: From Fundamental to Applications)
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22 pages, 4817 KiB  
Review
Recent Advances in Fabrication of Flexible, Thermochromic Vanadium Dioxide Films for Smart Windows
Nanomaterials 2021, 11(10), 2674; https://doi.org/10.3390/nano11102674 - 11 Oct 2021
Cited by 24 | Viewed by 4251
Abstract
Monoclinic-phase VO2 (VO2(M)) has been extensively studied for use in energy-saving smart windows owing to its reversible insulator–metal transition property. At the critical temperature (Tc = 68 °C), the insulating VO2(M) (space group P21/c) is transformed into [...] Read more.
Monoclinic-phase VO2 (VO2(M)) has been extensively studied for use in energy-saving smart windows owing to its reversible insulator–metal transition property. At the critical temperature (Tc = 68 °C), the insulating VO2(M) (space group P21/c) is transformed into metallic rutile VO2 (VO2(R) space group P42/mnm). VO2(M) exhibits high transmittance in the near-infrared (NIR) wavelength; however, the NIR transmittance decreases significantly after phase transition into VO2(R) at a higher Tc, which obstructs the infrared radiation in the solar spectrum and aids in managing the indoor temperature without requiring an external power supply. Recently, the fabrication of flexible thermochromic VO2(M) thin films has also attracted considerable attention. These flexible films exhibit considerable potential for practical applications because they can be promptly applied to windows in existing buildings and easily integrated into curved surfaces, such as windshields and other automotive windows. Furthermore, flexible VO2(M) thin films fabricated on microscales are potentially applicable in optical actuators and switches. However, most of the existing fabrication methods of phase-pure VO2(M) thin films involve chamber-based deposition, which typically require a high-temperature deposition or calcination process. In this case, flexible polymer substrates cannot be used owing to the low-thermal-resistance condition in the process, which limits the utilization of flexible smart windows in several emerging applications. In this review, we focus on recent advances in the fabrication methods of flexible thermochromic VO2(M) thin films using vacuum deposition methods and solution-based processes and discuss the optical properties of these flexible VO2(M) thin films for potential applications in energy-saving smart windows and several other emerging technologies. Full article
(This article belongs to the Special Issue Metal Oxide Nanomaterials: From Fundamental to Applications)
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