Search

Silicene, the ultimate scaling of a silicon atomic sheet in a buckled honeycomb lattice, represents a monoelemental class of two-dimensional (2D) materials similar to graphene but with unique potential for a host of exotic electronic properties. Nonetheless, there is a lack of experimental studies largely due to the interplay between material degradation and process portability issues. This review highlights the state-of-the-art experimental progress and future opportunities in the synthesis, characterization, stabilization, processing and experimental device examples of monolayer silicene and its derivatives. The electrostatic characteristics of the Ag-removal silicene field-effect transistor exhibit ambipolar charge transport, corroborating with theoretical predictions on Dirac fermions and Dirac cone in the band structure. The electronic structure of silicene is expected to be sensitive to substrate interaction, surface chemistry, and spin–orbit coupling, holding great promise for a variety of novel applications, such as topological bits, quantum sensing, and energy devices. Moreover, the unique allotropic affinity of silicene with single-crystalline bulk silicon suggests a more direct path for the integration with or revolution to ubiquitous semiconductor technology. Both the materials and process aspects of silicene research also provide transferable knowledge to other Xenes like stanene, germanene, phosphorene, and so forth. [ABSTRACT FROM AUTHOR]

Extensive research on two-dimensional (2D) materials has triggered the renaissance of an old topic, that is, the intercalation and exfoliation of layer materials. Such top-down exfoliation produced 2D materials and their dispersions have several advantages including low cost, scalable production capability, solution processability, and versatile functionalities stemming from the large number of species of layer materials, and show promising potential in many applications. In recent years, many new methods have been developed for exfoliating layer materials to 2D materials for different application purposes. In this review the different exfoliation approaches are first systematically analyzed from the viewpoint of methodology, and the advantages and disadvantages of each method are compared. Second, the assembly of exfoliated 2D materials into macrostructures by solution-based techniques is summarized. Third, the state-of-the-art applications of 2D material dispersions and their assemblies in electronics and optoelectronics, electrocatalysis, energy storage, etc., are discussed. Finally, insights and perspectives on current research challenges and future opportunities regarding the exfoliation and applications of 2D materials in dispersions are considered. [ABSTRACT FROM AUTHOR]

As a two-dimensional (2D) material, molybdenum disulfide (MoS2) exhibits unique electronic and optical properties useful for a variety of optoelectronic applications including light harvesting. In this article, we review recent progress in the synthesis, properties and applications of MoS2 and related heterostructures. Heterostructured materials are developed to add more functionality or flexibility compared to single component materials. Our focus is on their novel properties and functionalities as well as emerging applications, especially in the areas of light energy harvesting or conversion. We highlight the correlation between structural properties and other properties including electronic, optical, and dynamic. Whenever appropriate, we also try to provide fundamental insight gained from experimental as well as theoretical studies. Finally, we discuss some current challenges and opportunities in technological applications of MoS2. [ABSTRACT FROM AUTHOR]

The discovery of graphene opened a door for manufacturing and investigating two-dimensional (2D) materials. After more than ten years of development, 2D materials have become one of the most important topics in materials research, with dozens of new materials having been synthesized experimentally and even more predicted theoretically. In this review, we provide a comprehensive overview of the fabrication of 2D materials based on epitaxial growth in an ultra-high vacuum (UHV) experimental environment and the investigation of their physical and chemical properties. In particular, we focus on techniques like intercalation, templated molecular adsorption, and direct selenization and tellurization of metal substrates. We discuss progress in fabrication methods of monatomic and binary 2D materials and highlight their interesting and quite unusual physical properties. Finally, we assess future directions of research in this field, where breakthroughs can be expected, and indicate where investments in additional research might be most rewarding scientifically. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) metal–organic framework (MOF) nanosheets are attracting increasing research attention due to their unique properties originating from their ultrathin thickness, large surface area and high surface-to-volume atom ratios. Many great advances have been made in the synthesis and application of 2D MOF nanosheets over the past few years. In this review, we summarize the recent advances in the synthesis of 2D MOF nanosheets by using top-down methods, e.g. sonication exfoliation, mechanical exfoliation, Li-intercalation exfoliation and chemical exfoliation, and bottom-up methods, i.e. interfacial synthesis, three-layer synthesis, surfactant-assisted synthesis, modulated synthesis, and sonication synthesis. In addition, the recent progress in 2D MOF nanosheet-based nanocomposites is also briefly introduced. The potential applications of 2D MOF nanosheets in gas separation, energy conversion and storage, catalysis, sensors and biomedicine are discussed. Finally, we give our personal insights into the challenges and opportunities for the future research of 2D MOF nanosheets and their composites. [ABSTRACT FROM AUTHOR]

Herein, we report the successful application of hybrid Au-Ag nanoparticles (NPs) and nanochains (NCs) in the harvesting of visible light energy for selective hydrogenation reactions. For individual Au@Ag NPs with Au25 cores, the conversion and turnover frequency (TOF) are approximately 8 and 10 times higher than those of Au25 NPs, respectively. Notably, after the self-assembly of the Au@Ag NPs, the conversion and TOF of 1D NCs were approximately 2.5 and 2 times higher than those of isolated Au@Ag NPs, respectively, owing to the coupling of surface plasmon and the increase in the rate at which hot (energetic) electrons are generated with the formation of plasmonic hot spots between NPs. Furthermore, the surface-enhanced Raman scattering (SERS) activity of 1D Au@Ag NCs was strengthened by nearly 2 orders of magnitude. [ABSTRACT FROM AUTHOR]

One of the primary factors affecting the effectiveness of nanomaterials in enhancing cement composites properties is its ability to disperse efficiently without aggregation. To-date a number of methods have been proposed to increase the dispersion of CNTs in the mixes. Studies have shown that the response of cement-based materials to CNT addition can vary depending on the dispersion mechanism employed. Despite the need, there is no standardized methodology used to disperse CNTs, and consequently, it is hard to model the behavior. This study focused on using design of experiments (DOE) to assess the effect of dispersion protocol on the characteristics of cement-based composites. Experiments were carried out with different procedures to compare the effect of wet and dry mixing of CNTs, sonication exposure time, whisking and CNTs concentration on the mechanical properties of mortar blocks. Response Surface Methodology (RSM) was used to model the experimentally determined compressive strength. The model was further validated by comparing its predictions with other experimental scenarios. The model can be used to determine the optimum methodology to disperse CNTs in cement composites. To compare experimental data, there is a need to provide the exact details of all steps involved in a dispersion protocol that is captured by the proposed model. Following the suggested protocol for specimen preparation can ensure achieving a high level of dispersion and superior performance. [ABSTRACT FROM AUTHOR]

Various types of nanomaterials such as magnetic nanoparticles, carbon nanostructures, metal oxides, noble metal nanoparticles, and ion imprinted polymers have been incorporated in new innovative approaches for speciation analysis. Small size, high surface to volume ratio, and high chemical reactivity are the properties which make them ideal sorbents for selective separation of chemical species. Nanostructures based on different modifications of the nanoparticles and combinations between them additionally increased the nano-strategies employed for on-line or off-line determination of particular chemical species of elements. The presented review is focused on the use of nanomaterials for speciation analysis, analytical procedures developed and their application for analysis of environmental, food and biological samples. Critical view points on the current limitations and their future perspective are presented. [ABSTRACT FROM AUTHOR]

Proper understanding of the basic processes and specific properties of engineered nanomaterials (NMs) that modify the fate and effects of NMs is crucial for NM-tailored risk assessment. This in turn requires developers of NMs and for regulators to consider the most important parameters governing the properties, behavior and toxicity of NMs. As fate and effect studies are commonly performed in laboratory settings, mimicking to a varying extent realistic exposure conditions, it is important to be able to extrapolate results of fate and effect studies in synthetic media to realistic environmental conditions. This requires detailed understanding of the processes controlling the fate and behavior of NMs in terrestrial and aquatic media, as dependent on the composition of the medium. It is the aim of this contribution to provide background reading to the NM and media specific properties and processes that affect the fate and behavior of NMs in aquatic environments, focusing on the specific properties of NMs that modulate the interactions in the aquatic environment. A general introduction on the dominant fate determining processes of NMs is supplemented by case studies on specific classes of NMs: metal NMs, stable oxides, iron oxides, and carbon nanotubes. Based on the synthesis of the current knowledge base toward essential data and information needs, the review provides a description of the particle specific properties and the water characteristics that need monitoring in order to allow for future quantification and extrapolation of fate and behavior properties of NMs in freshwater compartments of varying composition. [ABSTRACT FROM AUTHOR]

The interaction of a highly dynamic poly(aryl acetylene) (poly- 1) with Li+, Na+, and Ag+ leads to macroscopically chiral supramolecular nanospheres, nanotubes, toroids, and gels. With Ag+, nanospheres with M helicity and tunable sizes are generated, which complement those obtained from the same polymer with divalent cations. With Li+ or Na+, poly- 1 yields chiral nanotubes, gels, or toroids with encapsulating properties and M helicity. Right-handed supramolecular structures can be obtained by using the enantiomeric polymer. The interaction of poly- 1 with Na+ produces nanostructures whose helicity is highly dependent on the solvation state of the cation. Therefore, structures with either of the two helicities can be prepared from the same polymer by manipulation of the cosolvent. Such chiral nanotubes, toroids, and gels have previously not been obtained from helical polymer-metal complexes. Chiral nanospheres made of poly(aryl acetylene) that were previously assembled with metal(II) species can now be obtained with metal(I) species. [ABSTRACT FROM AUTHOR]

An introduction is presented which discusses several reports published within issue on topics including characterization techniques; the structure-activity-function relationships in small clusters, nanoparticles; application of electron microscopy to investigate the structure of nanoparticles.

Nanostructures, such as carbon nanotubes, are often added to polymers and composites to enhance their strength. The extreme mechanical properties of carbon nanotubes suggest an obvious rationale behind this approach. However as Markus Buehler and Isabelle Su at Massachusetts Institute of Technology in the US highlight in their recent topical review [1] the behaviour that renders nanomaterials soft or strong can be far from trivial, often involving interactions on a range of scales from macrostructures to nanostructures and—in the case of biostructures—the amino acids and proteins they are built from. [ABSTRACT FROM AUTHOR]