Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

To solve the problem of the global energy shortage and the pollution of the environment, in recent years, semiconductor photocatalytic technology that converts solar energy into chemical fuel has been widely studied. Regarding semiconductor-based photocatalysts, CdS has attracted extensive attention due to its relatively narrow bandgap for visible-light response and sufficiently negative potential of the conduction band edge for the reduction of protons. Studies have shown that CdS-based photocatalysts possess excellent photocatalytic performance in terms of solar-fuel generation and environmental purification. This critical review presents the recent advances and progress in the design and synthesis of various CdS and CdS-based photocatalysts. The basic physical and chemical properties of CdS and the related growth mechanism have been briefly summarized. Moreover, the applications of CdS-based photocatalysts have been discussed such as in photocatalytic hydrogen production, reduction of CO2 to hydrocarbon fuels and degradation of pollutants. Finally, a brief perspective on the challenges and future directions for the development of CdS and CdS-based photocatalysts are also presented.

CdS-Based photocatalysts

Two dimensional hexagonal boron nitride (2D-hBN), an isomorph of graphene with a very similar layered structure, is uniquely featured by its exotic opto-electrical properties together with mechanical robustness, thermal stability, and chemical inertness. It is thus extensively studied for application in field effect transistors (FETs), tunneling devices, deep UV emitters and detectors, photoelectric devices, and nanofillers. 2D-hBN is considered as one of the most promising materials that can be integrated with other 2D materials, such as graphene and transition metal dichalcogenides (TMDCs), for the next generation microelectronic and other technologies. Although it is by itself an insulator, it can well be tuned by several strategies in terms of properties and functionalities, such as by doping, substitution, functionalization and hybridization, making 2D-hBN a truly versatile type of functional materials for a wide range of applications. In this review, the distinct structural characteristics of 2D-hBN, doping- and defect-induced variations in energy bands and structures, and resultant properties, are presented. There are a wide variety of processing routes that have been developed for 2D-hBN, including also those for doping, substitution, functionalization and combination with other materials to form heterostructures or h-BNC hybrid nanosheets, which are systematically elaborated for novel functions. The comprehensive overview provides the types of the state-of-the-art 2D-hBN made by new synthesis strategies, where the mainstream approaches include exfoliation, chemical vapor deposition, and gas phase epitaxy, together with several other new methods that have been successfully developed in the past few years. On the basis of the extraordinary electrical and functional properties and thermal–mechanical stability, the applications of hBN-based nanosheets as substrates and dielectrics, passivation layers, and nanofillers in nanodevices and nanocomposites are discussed, together with the peculiar optical and wetting characteristics.

Two dimensional hexagonal boron nitride (2D-hBN): synthesis, properties and applications

Graphitic carbon nitride (g–C3N4)–based metal-free photocatalysts for water splitting: A review

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

Construction of Longan–like hybrid structures by anchoring nickel hydroxide on yolk–shell polypyrrole for asymmetric supercapacitors

Efficiency and stability are the two key elements for photocatalyst. The application of CdS, as a classical photocatalyst, has been seriously restricted because of the inherent photocorrosion issue. Based on the rate-theory analysis, in this paper, we propose the photocorrosion and recrystallization of CdS on the surface of WS2 nanosheets under visible light irradiation to resolve the photocorrosion issue. A highly stable and efficient CdS/WS2 photocatalyst has been obtained following this strategy for the first time. The rate of H2 evolution distinctly increases (56.2 times) compared with that in pure CdS nanoparticles, and keeps excellent stability in hydrogen generation for more than 200 h without any decrease, which are superior to any other previously reported CdS based photocatalysts. This new approach has potential application in designing and fabricating more stable and efficient composite chalcogenide photocatalysts.

Utilizing photocorrosion-recrystallization to prepare a highly stable and efficient CdS/WS2 nanocomposite photocatalyst for hydrogen evolution

Recent advances in the improvement of g-C3N4 based photocatalytic materials

Based on the phase transformation of phosphorus and Gibbs free energy theory, a new mild method to fabricate black phosphorus nanosheets from their red phosphorus microsphere counterparts is proposed. Interestingly, the as-prepared black phosphorus nanosheets, as a kind of novel metal-free photocatalyst, exhibit excellent photocatalytic H2 production performance owing to their intrinsic layered polycrystalline structure. Besides, the nanosheet is also a kind of potential anode material in lithium-ion batteries and shows good electrochemical performance.

A Novel Mild Phase-Transition to Prepare Black Phosphorus Nanosheets with Excellent Energy Applications

CdS is a photocatalyst known for its desirable bandgap and availability but it is limited by photocorrosion and inefficiency issues in practical applications. According to band engineering theory, regulating the width of bonding region that exists between cubic phase and hexagonal phase, we design a suitable phase junction and achieve effective separation of electron-hole pairs. Thus, the problems caused by photocorrosion and phase exclusion can be resolved. The optimal photocatalytic activity of the prepared material is 4.9 mmol h −1  g −1 with 41.5% quantum efficiency at the wavelength of 420 nm, which is 60 times higher than that of the initial samples (cubic or hexagonal phase), and keeps high photocatalytic stability. This novel construction approach can be useful in designing ideal band structures and matching the phase bandgap of other binary sulfides.

Gang Zhao

Papers

Construction of Longan–like hybrid structures by anchoring nickel hydroxide on yolk–shell polypyrrole for asymmetric supercapacitors

Utilizing photocorrosion-recrystallization to prepare a highly stable and efficient CdS/WS2 nanocomposite photocatalyst for hydrogen evolution

Recent advances in the improvement of g-C3N4 based photocatalytic materials

A Novel Mild Phase-Transition to Prepare Black Phosphorus Nanosheets with Excellent Energy Applications

Phase junction CdS: High efficient and stable photocatalyst for hydrogen generation