Nanotechnology has gained much attention for its potential application in medical science. Iron oxide nanoparticles have demonstrated a promising effect in various biomedical applications. In particular, magnetite (Fe3O4) nanoparticles are widely applied due to their biocompatibility, high magnetic susceptibility, chemical stability, innocuousness, high saturation magnetisation, and inexpensiveness. Magnetite (Fe3O4) exhibits superparamagnetism as its size shrinks in the single-domain region to around 20 nm, which is an essential property for use in biomedical applications. In this review, the application of magnetite nanoparticles (MNPs) in the biomedical field based on different synthesis approaches and various surface functionalisation materials was discussed. Firstly, a brief introduction on the MNP properties, such as physical, thermal, magnetic, and optical properties, is provided. Considering that the surface chemistry of MNPs plays an important role in the practical implementation of in vitro and in vivo applications, this review then focuses on several predominant synthesis methods and variations in the synthesis parameters of MNPs. The encapsulation of MNPs with organic and inorganic materials is also discussed. Finally, the most common in vivo and in vitro applications in the biomedical world are elucidated. This review aims to deliver concise information to new researchers in this field, guide them in selecting appropriate synthesis techniques for MNPs, and to enhance the surface chemistry of MNPs for their interests.

The presence of grain boundaries in two-dimensional (2D) materials is known to greatly affect their physical, electrical, and chemical properties. Given the difficulty in growing perfect large single-crystals of 2D materials, revealing the presence and characteristics of grain boundaries becomes an important issue for practical applications. Here, we present a method to visualize the grain structure and boundaries of 2D materials by epitaxially growing transition metal dichalcogenides (TMDCs) over them. Triangular single-crystals of molybdenum disulfide (MoS2) epitaxially grown on the surface of graphene allowed us to determine the orientation and size of the graphene grains. Grain boundaries in the polycrystalline graphene were also visualized reflecting their higher chemical reactivity than the basal plane. The method was successfully applied to graphene field-effect transistors, revealing the actual grain structures of the graphene channels. Moreover, we demonstrate that this method can be extended to determine the grain structure of other 2D materials, such as tungsten disulfide (WS2). Our visualization method based on van der Waals epitaxy can offer a facile and large-scale labeling technique to investigate the grain structures of various 2D materials, and it will also contribute to understand the relationship between their grain structure and physical properties.

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Perfluorosulphonic acid-based membranes such as Nafion are widely used in fuel cell applications. However, these membranes have several drawbacks, including high expense, non-eco-friendliness, and low proton conductivity under anhydrous conditions. Biopolymer-based membranes, such as chitosan (CS), cellulose, and carrageenan, are popular. They have been introduced and are being studied as alternative materials for enhancing fuel cell performance, because they are environmentally friendly and economical. Modifications that will enhance the proton conductivity of biopolymer-based membranes have been performed. Ionic liquids, which are good electrolytes, are studied for their potential to improve the ionic conductivity and thermal stability of fuel cell applications. This review summarizes the development and evolution of CS biopolymer-based membranes and ionic liquids in fuel cell applications over the past decade. It also focuses on the improved performances of fuel cell applications using biopolymer-based membranes and ionic liquids as promising clean energy. Int. J. Mol. Sci. 2020, 21, 632 2 of 52 used to exchange protons from the anode to the cathode [1]. PEMFCs are light, highly efficient, and compact. They operate at relatively low temperatures (≈80 • C), have high power density, and are suitable for various applications. Figure 1 shows that PEMFC consists of various important elements, namely, bipolar plates, diffusion layers, electrodes (anode and cathode), and an electrolyte. The core of a PEMFC is a membrane electrode assembly (MEA) composed of a proton exchange membrane (PEM) placed between two electrodes. Int. J. Mol. Sci. 2019, 20, x FOR PEER REVIEW 2 of 53 Int. J. Mol. Sci. 2020, 21, 632 3 of 52Polysaccharides, such as chitosan (CS) and cellulose, are among the best natural polymer materials because of their abundance in the environment. CS is a linear polysaccharide consisting of randomly distributed β-(1-4)-linked d-glucosamine (deacetylated unit) and N-acetyl-d-glucosamine (acetylated unit), which is produced by the deacetylation of chitin. CS has high water affinity properties as there is the presence of three different polar functional groups, which are hydroxyl (-OH), primary amine (-NH 2 ), and C-O-C groups. CS has a structure that is very similar to cellulose, but the difference among them is that CS contains amine groups and its structure is characterized by its molecular weight and degree of deacetylation, where its solubility is depended on [7].CS has rigid structure and high crystallinity as there are three hydrogen atoms strongly bonded between the amino and hydroxyl groups within the CS monomers, due to the immobilized structure, which leads to its proton conduction limitation. Moreover, CS has attractive physicochemical properties in aqueous solution due to its polycationic nature and this leads to wide range of biological purposes such as antimicrobial activity and disease resistance activities in plants [8]. CS membranes are one of the most preferable and favorable materials to re...

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Graphene nanoribbons (GNRs) are a promising material for electronic applications, because quantum confinement in a one-dimensional nanostructure can potentially open the band gap of graphene. However, it is still a challenge to synthesize high-quality GNRs by a bottom-up approach without relying on lithographic techniques. In this work, we demonstrate lattice-oriented catalytic growth of single-layer GNRs on the surface of a heteroepitaxial Ni film. Catalytic decomposition of a poly(methyl methacrylate) film on the Ni(100) film at 1000 °C gives narrow nanoribbons with widths of 20-30 nm, which are aligned along either [011] or [011] directions of the Ni lattice. Furthermore, low-energy electron microscope (LEEM) analysis reveals that orientation of carbon hexagons in these GNRs is highly controlled by the underlying Ni(100) lattice, leading to the formation of zigzag edges. This heteroepitaxial approach would pave a way to synthesize nanoribbons with controlled orientation for future development of electronic devices based on graphene nanostructures.

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