Inspired by rich physics and functionalities of graphenes, scientists have taken an intensive interest in two-dimensional (2D) crystals of h-BN (analogue of graphite, so-called "white" graphite). Recent calculations have predicted the exciting potentials of BN nanoribbons in spintronics due to tunable magnetic and electrical properties; however no experimental evidence has been provided since fabrication of such ribbons remains a challenge. Here, we show that few- and single-layered BN nanoribbons, mostly terminated with zigzag edges, can be produced under unwrapping multiwalled BN nanotubes through plasma etching. The interesting stepwise unwrapping and intermediate states were observed and analyzed. Opposed to insulating primal tubes, the nanoribbons become semiconducting due to doping-like conducting edge states and vacancy defects, as revealed by structural analyses and ab initio simulations. This study paves the way for BN nanoribbon production and usage as functional semiconductors with a wide range of applications in optoelectronics and spintronics.

"White graphenes": boron nitride nanoribbons via boron nitride nanotube unwrapping

In this study, we report nonmetal plasmonic MoS2@TiO2 heterostructures for highly efficient photocatalytic H2 generation. Large area laminated MoS2 in conjunction with TiO2 nanocavity arrays is achieved via carefully controlled anodization, physical vapor deposition, and chemical vapor deposition processes. The broad spectral response ranging from ultraviolet-visible (UV-vis) to near-infrared (NIR) wavelengths and finite element frequency-domain simulations suggest that this MoS2@TiO2 heterostructure enhances photocatalytic activity for H+ reduction. A high H2 yield rate of 181 μmol h−1 cm−2 (equal to 580 mmol h−1 g−1 based on the loading mass of MoS2) is achieved using a low catalyst loading mass. The spatially uniform heterostructure, correlated with plasmon-resonance through the conformal MoS2 coating that effectively regulates charge transfer pathways, is proven to be vitally important for the unique solar energy harvesting and photocatalytic H2 production. As an innovative exploration, our study demonstrates that the photocatalytic activities of nonmetal, earth-abundant materials can be enhanced with plasmonic effects, which may serve as an excellent catalytic agent for solar energy conversion to chemical fuels.

MoS2/TiO2 heterostructures as nonmetal plasmonic photocatalysts for highly efficient hydrogen evolution

Two-dimensional (2D) nanomaterials are currently explored as novel photothermal agents because of their ultrathin structure, high specific surface area, and unique optoelectronic properties. In addition to single photothermal therapy (PTT), 2D nanomaterials have demonstrated significant potential in PTT-based synergistic therapies. In this Minireview, we summarize the recent progress in 2D nanomaterials for enhanced photothermal cancer therapy over the last five years. Their unique optical properties, typical synthesis methods, and surface modification are also covered. Emphasis is placed on their PTT and PTT-synergized chemotherapy, photodynamic therapy, and immunotherapy. The major challenges of 2D photothermal agents are addressed and the promising prospects are also presented.

Two-Dimensional Nanomaterials for Photothermal Therapy

Strain engineering in two-dimensional nanomaterials beyond graphene

Metallic phase 2D molybdenum disulfide (MoS2 ) is an emerging class of materials with remarkably higher electrical conductivity and catalytic activities. The goal of this study is to review the atomic structures and electrochemistry of metallic MoS2 , which is essential for a wide range of existing and new enabling technologies. The scope of this paper ranges from the atomic structure, band structure, electrical and optical properties to fabrication methods, and major emerging applications in electrochemical energy storage and energy conversion. This paper also thoroughly covers the atomic structure-properties-application relationships of metallic MoS2 . Understanding the fundamental properties of these structures is crucial for designing and manufacturing products for emerging applications. Today, a more holistic understanding of the interplay between the structure, chemistry, and performance of metallic MoS2 is advancing actual applications of this material. This new level of understanding also enables a myriad of new and exciting applications, which motivated this review. There are excellent reviews already on the traditional semiconducting MoS2 , and this review, for the first time, focuses on the uniqueness of conducting metallic MoS2 for energy applications and offers brand new materials for clean energy application.

Metallic MoS2 for High Performance Energy Storage and Energy Conversion.

The emergence of two-dimensional (2D) materials has led to tremendous interest in the study of graphene and a series of mono- and few-layered transition metal dichalcogenides (TMDCs). Among these TMDCs, the study of molybdenum disulfide (MoS2) has gained increasing attention due to its promising optical, electronic, and optoelectronic properties. Of particular interest is the indirect to direct band-gap transition from bulk and few-layered structures to mono-layered MoS2, respectively. In this review, the study of these properties is summarized. The use of Raman and Photoluminescence (PL) spectroscopy of MoS2 has become a reliable technique for differentiating the number of molecular layers in 2D MoS2.

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Recent Advancement on the Optical Properties of Two-Dimensional Molybdenum Disulfide (MoS2) Thin Films

We demonstrate a universal approach to extract one- and two-dimensional nanomaterials from contaminated water, which is based on a microscopic oil-water interface trapping mechanism. Results indicate that carbon nanotubes, graphene, boron nitride nanotubes, boron nitride nanosheets, and zinc oxide nanowires can be successfully extracted from contaminated water at a successful rate of nearly 100%. The effects of surfactants, particle shape, and type of organic extraction fluids are evaluated. The proposed extraction mechanism is also supported by in situ monitoring of the extraction process. We believe that this extraction approach will prove important for the purification of water contaminated by nanoparticles and will support the widespread adoption of nanomaterial applications.

Dustin Winslow

Papers

Recent Advancement on the Optical Properties of Two-Dimensional Molybdenum Disulfide (MoS2) Thin Films

A Simple and Universal Technique To Extract One- and Two-Dimensional Nanomaterials from Contaminated Water.

Controlled Synthesis of Functional Boron Nitride Nanostructures for Applications