A Review on Iron Oxide‐Based Nanoarchitectures for Biomedical

DOI: 10.1002/smtd.201800512 Article type: Review A Review on Iron Oxide-Based Nanoarchitectures for Biomedical, Energy Storage, and Environmental Applications Shunsuke Tanaka, Yusuf Valentino Kaneti*, Ni Luh Wulan Septiani, Shi Xue Dou, Yoshio Bando, and Md. Shahriar A. Hossain, Jeonghun Kim, and Yusuke Yamauchi* S. Tanaka, Dr. Y. V. Kaneti, Prof. Y. Bando International Research Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan E-mail: [email protected] N. L. W. Septiani Department of Engineering Physics and Research Center for Nanoscience and Nanotechnology, Bandung Institute of Technology, 10 Ganesha Street, Bandung 40132, Indonesia S. Tanaka, Prof. S. X. Dou, Prof. Y. Bando Australian Institute of Innovative Materials (AIIM), University of Wollongong, North Wollongong, New South Wales 2500, Australia Dr. M. S. A. Hossain School of Chemical Engineering and School of Mechanical & Mining Engineering, Faculty of Engineering, Architecture and Information Technology (EAIT), The University of Queensland, Brisbane, QLD 4072, Australia Dr. J. Kim, Prof. Y. Yamauchi This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/smtd.201800512. This article is protected by copyright. All rights reserved. School of Chemical Engineering and School of Mechanical & Mining Engineering, Faculty of Engineering, Architecture and Information Technology (EAIT), The University of Queensland, Brisbane, QLD 4072, Australia E-mail: [email protected] Prof. Y. Yamauchi Key Laboratory of Sensor Analysis of Tumor Marker (Ministry of Education), Shandong Key Laboratory of Biochemical Analysis, and Key Laboratory of Analytical Chemistry for Life Science in Universities of Shandong, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology (QUST), Qingdao 266042, China Keywords: iron oxide nanoparticles, energy storage, biomedical applications, catalysis, surface modification Abstract Iron oxide nanoarchitectures with distinct morphologies from one-dimensional (1D) to three- dimensional (3D) have been developed using various wet chemical methods. They have been employed for a wide range of applications, including energy storage, biomedical, and environmental applications. The functional properties of iron oxide nanoarchitectures depend on the size, shape, composition, magnetic properties and surface modification. To overcome the limitations of pure iron oxide nanostructures, hybridization with various inorganic materials (e.g., silica, metals, metal oxides) and carbon-based materials have been proposed. Herein, the recent advances on the preparation of various iron oxide nanoarchitectures are reviewed along with their functional applications in energy storage, biomedical, and environmental fields. Finally, the effects of various parameters on the functional performance of iron oxide nanostructures for these applications are summarized and the trends and future outlook on the development of iron oxide nanoarchitectures for these applications are also given. This article is protected by copyright. All rights reserved. 1. Introduction Iron is known as the fourth most abundant element on earth. The oxide form of iron is known to exist in 16 different phases. Among them, hematite (α-Fe2O3), maghemite (γ-Fe2O3), and magnetite (Fe3O4)) are by far the most widely studied. Hematite is an n-type semiconductor with an indirect bandgap of 2.1-2.3 eV. Hematite is the most stable form of iron oxide and it can be used as a precursor to obtain Fe3O4 or γ-Fe2O3. Further, hematite is often employed in catalysis and gas sensors owing to their wide abundance, low toxicity, high sensitivity/activity, and high corrosion resistance. In the hematite crystal structure, Fe3+ ions occupy two-thirds of the octahedral sites which are confined by the almost ideal hexagonal [1] close-packed oxygen lattice (Figure 1a). In comparison, Fe3O4 possesses a cubic inverse spinel structure which consists of a cubic close packed array of oxygen ions, in which all of the Fe2+ ions occupy half of the octahedral sites and the Fe3+ are split evenly across the rest of the octahedral sites and the tetrahedral sites (Figure 1b). Fe3O4 has the lowest resistivity [2] among iron oxides as a result of its very narrow bandgap of 0.1 eV. γ-Fe2O3 is the second most stable phase of iron oxide with a narrow bandgap of 2.0 eV. Similar to Fe3O4, γ-Fe2O3 also has a cubic spinel crystal structure, however it contains only Fe3+ ions. In the crystal structure of γ-Fe2O3, the oxygen anions give rise to a cubic close-packed array in which the Fe3+ ions are distributed over tetrahedral sites and octahedral sites (Figure 1c). Typically, α- Fe2O3 can be achieved by the oxidation of γ-Fe2O3 or Fe3O4 in air at temperatures ranging between 400-600 °C. In contrast, γ-Fe2O3 can generally be obtained from the calcination of Fe3O4 in air at temperatures ≤250 °C. To date, iron oxide-based materials have been investigated for a wide range of applications, such as catalysis, biomedicine, environmental remediation and energy storage devices owing to their intrinsic and unique properties (including chemical, thermal, optical, electronic, and magnetic properties (Figure 1).[1, 3] In the past decade, numerous efforts have been carried out to synthesize various iron oxide nanoarchitectures from zero-dimensional (0D) to three-dimensional (3D) through various wet-chemical and gas-phase methods. Many studies have shown that synthetic parameters, such as the choice of iron precursor, type and amount of reducing agent, temperature, pH, etc., can determine the size and morphology of the resulting iron oxide products, which in turn affect their functional properties, including magnetic properties. The size, shape, and composition of the iron oxide nanostructures can affect their magnetic properties. The size determines whether the iron oxide particles display ferromagnetic or superparamagnetic behavior and affects their saturation magnetization (Ms) This article is protected by copyright. All rights reserved. (i.e., the maximum magnetization that nanoparticles (NPs) can exhibit when exposed to an external magnetic field) and blocking temperature (TB) (i.e., the temperature at which the magnetic moments of NPs become blocked during the time scale of the measurement). Further, by manipulating the morphology of iron oxide nanostructures, it is possible to tune the magnetic properties of these materials. For example, cubic Fe3O4 NPs showed a higher TB than spherical Fe3O4 NPs and pseudocubic iron oxide NPs displayed a larger Ms value than pseudospherical ones.[4, 5] Furthermore, the doping of a secondary metal to magnetic iron oxide NPs can also enhance their magnetic properties due to cationic substitution, which in turn enhances their heating efficiency for hyperthermia.[6] Therefore, proper optimization of these parameters is critical for maximizing the functional properties of the iron oxide nanostructures. Porous materials have attracted significant interests in materials research due to their high surface area, large pore volume, narrow pore size distribution, and modifiable surface properties.10, 11 In general, porous materials can be categorized into three classes based on the IUPAC (International Union of Pure and Applied Science) classification: macroporous (>50 nm), mesoporous (2-50 nm) and microporous materials (< 2 nm).12 Mesoporous and microporous materials are often referred to as nanoporous materials. In the last decade, significant research efforts have been devoted into the development of mesoporous iron oxide and ferrites (MFe2O4) through template-based methods, such as hard-templating, soft- templating, and sacrificial-templating methods. The hard-templating methods typically rely on the use of hard templates, such as mesoporous silica (e.g., KIT-6, SBA-15), mesoporous carbon, and anodic aluminium oxide (AAO).[7] Iron oxide NPs play important roles in various biomedical applications, such as magnetic resonance imaging (MRI), drug delivery, hyperthermia, and biosensors, due to their magnetic properties, low toxicity, easy preparation, capabilities to store drugs and to react with certain biomolecules in the body, and unique enzyme-mimicking ability. The size, shape, and composition of iron oxide NPs have profound effects on their saturation magnetization and coercivity, which in turn affect their performance in these applications. For instance, the heating efficiency and contrast ability of iron oxide NPs for MRI and hyperthermia are strongly dependent on the Ms and Hc, with higher Ms leading to higher heating efficiency and contrast ability. To address the limitations of iron oxide NPs in these This article is protected by copyright. All rights reserved. bio-applications, surface modification or functionalization with polymers or biomolecules and hybridization with carbon-based materials and metals have been proposed. Beside biomedical applications, iron oxide nanoarchitectures have also been widely investigated for energy storage devices, such as lithium-ion batteries (LIBs) and supercapacitors (SCs).[3] LIBs are commonly found in portable devices and electric vehicles.[3] For LIBs, iron oxide with porous or hollow nanoarchitectures are generally

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