The recent surge in graphene research has stimulated interest in the investigation of various 2-dimensional (2D) nanomaterials. Among these materials, the 2D boron nitride (BN) nanostructures are in a unique position. This is because they are the isoelectric analogs to graphene structures and share very similar structural characteristics and many physical properties except for the large band gap. The main forms of the 2D BN nanostructures include nanosheets (BNNSs), nanoribbons (BNNRs), and nanomeshes (BNNMs). BNNRs are essentially BNNSs with narrow widths in which the edge effects become significant; BNNMs are also variations of BNNSs, which are supported on certain metal substrates where strong interactions and the lattice mismatch between the substrate and the nanosheet result in periodic shallow regions on the nanosheet surface. Recently, the hybrids of 2D BN nanostructures with graphene, in the form of either in-plane hybrids or inter-plane heterolayers, have also drawn much attention. In particular, the BNNS-graphene heterolayer architectures are finding important electronic applications as BNNSs may serve as excellent dielectric substrates or separation layers for graphene electronic devices. In this article, we first discuss the structural basics, spectroscopic signatures, and physical properties of the 2D BN nanostructures. Then, various top-down and bottom-up preparation methodologies are reviewed in detail. Several sections are dedicated to the preparation of BNNRs, BNNMs, and BNNS-graphene hybrids, respectively. Following some more discussions on the applications of these unique materials, the article is concluded with a summary and perspectives of this exciting new field.

Hexagonal boron nitride (h-BN), the isoelectric analogue of graphite, was functionalized using lipophilic and hydrophilic amine molecules. The functionalization induced the exfoliation of the layered structure of h-BN, resulting in few-layered and monolayered nanosheets soluble in common organic solvents and/or water. The soluble h-BN nanosheets were characterized using various solution-phase and solid-state techniques. For example, the optical extinction coefficients of the h-BN nanosheets in homogeneous dispersions were estimated to be much lower than those of graphene sheets, confirming their low-colored nature. Solution-phase NMR spectroscopy supported the mechanism that the amino groups of the functional molecules complex to the electron-deficient boron atoms on the h-BN nanosheet surfaces in terms of Lewis acid−base interactions. Results from other microscopic and spectroscopic characterizations of these functionalized two-dimensional nanomaterials are also presented, and the implications of the reported versatile and effective functionalization strategy are discussed.

Hexagonal boron nitride (h-BN) is traditionally considered to be insoluble in water. However, here we demonstrate that water is effective to exfoliate the layered h-BN structures with the assistance of bath sonication, forming “clean” aqueous dispersions of h-BN nanosheets without the use of surfactants or organic functionalization. Besides few-layered h-BN nanosheets, there was also evidence on the presence of monolayered nanosheet and nanoribbon species. Most nanosheets were of reduced lateral sizes, which was attributed to the cutting of parent h-BN sheets induced by the sonication-assisted hydrolysis (evidenced by the ammonia test and spectroscopy results). The hydrolysis effect also assisted in the exfoliation of h-BN nanosheets in addition to the solvent polarity effect. The h-BN nanosheets in such “clean” aqueous dispersions were demonstrated to be conveniently processed via solution methods with retained physical properties. The dispersed h-BN nanosheets in water also exhibited strong affinity toward proteins such as ferritin, suggesting that the nanosheet surfaces were available for further bioconjugations. The above findings may pave the way for the applications of these novel 2-dimensional nanomaterials in various fields such as composites, electronics, and biology.

Metal-air batteries, especially Li-air batteries, have attracted significant research attention in the past decade. However, the electrochemical reactions between CO (0.04 % in ambient air) with Li anode may lead to the irreversible formation of insulating Li CO , making the battery less rechargeable. To make the Li-CO batteries usable under ambient conditions, it is critical to develop highly efficient catalysts for the CO reduction and evolution reactions and investigate the electrochemical behavior of Li-CO batteries. Here, we demonstrate a rechargeable Li-CO battery with a high reversibility by using B,N-codoped holey graphene as a highly efficient catalyst for CO reduction and evolution reactions. Benefiting from the unique porous holey nanostructure and high catalytic activity of the cathode, the as-prepared Li-CO batteries exhibit high reversibility, low polarization, excellent rate performance, and superior long-term cycling stability over 200 cycles at a high current density of 1.0 A g . Our results open up new possibilities for the development of long-term Li-air batteries reusable under ambient conditions, and the utilization and storage of CO .

A rapid, solventless method is described for the decoration of carbon nanotubes with metal nanoparticles. The straightforward two-step process utilizes neither reducing agents nor electric current and involves the dry mixing of a precursor metal salt (e.g., a metal acetate) with carbon nanotubes (single- or multi-walled) followed by heating in an inert atmosphere. The procedure is scalable to multigram quantities and generally applicable to various other carbon substrates (e.g., carbon nanofiber, expanded graphite, and carbon black) and many metal salts (e.g., Ag, Au, Co, Ni, and Pd acetates). As a model system, Ag nanoparticle-decorated carbon nanotube samples were prepared under various mixing techniques, metal loading levels, thermal treatment temperatures, and nanotube oxidative acid treatments. These nanohybrids were characterized by a variety of microscopic and spectroscopic techniques. For example, X-ray diffraction and scanning electron microscopy indicated that the average size of the Ag nanoparticles has little to do with the thermal treatment temperature but can be easily controlled by varying the Ag loading. Raman spectroscopy illustrated both the metal-nanotube electronic interactions and the surface enhancement effect from the Ag nanoparticle attachment. High-resolution transmission electron microscopy captured the in situ salt-to-metal conversion events on the nanotube surface. The mechanistic implications from the characterization results are discussed.