Display omitted
Two-dimensional (2D) materials have shown outstanding properties that make them the materials of choice for future semiconductor and flexible nanoelectronics. Hexagonal boron nitride ...nanosheet (BNNS) is one of the most studied 2D materials due to its extraordinary properties and potential applications. The synthesis of large, homogeneous, and few-layered BNNS, however, remains challenging. Among the various synthetic routes, chemical vapour deposition (CVD) is preferred on the grounds of its potential to yield large BNNS with controllable atomic layers and minimal contamination. We thus devote this review to the CVD growth of BNNS, and its characterization and applications. The recent progresses in the CVD growth of BNNS is firstly summarized from the aspects of precursors, substrates, growth mechanisms, and transfer techniques. This review then moves on to the characterization of few-atomic-layered h-BN sheets, covering a variety of microscopic and spectroscopic techniques that have proved useful for assessing the quality of BNNS. The applications of the BNNS are also summarized. This review is expected to instigate new methods and improvements in relation to the CVD growth of BNNS, which has enabled exceptional performance as a key component of nanoscale electronics.
Outstanding protection of Cu by high‐quality boron nitride nanofilm (BNNF) 1–2 atomic layers thick in salt water is observed, while defective BNNF accelerates the reaction of Cu toward water. The ...chemical stability, insulating nature, and impermeability of ions through the BN hexagons render BNNF a great choice for atomic‐scale protection.
Hexagonal boron nitride nanosheets (h-BNNS) have been proposed as an ideal substrate for graphene-based electronic devices, but the synthesis of large and homogeneous h-BNNS is still challenging. In ...this contribution, we report a facile synthesis of few-layer h-BNNS on melted copper via an atmospheric pressure chemical vapor deposition process. Comparative studies confirm the advantage of using melted copper over solid copper as a catalyst substrate. The former leads to the formation of single crystalline h-BNNS that is several microns in size and mostly in mono- and bi-layer forms, in contrast to the polycrystalline and mixed multiple layers (1-10) yielded by the latter. This difference is likely to be due to the significantly reduced and uniformly distributed nucleation sites on the smooth melted surface, in contrast to the large amounts of unevenly distributed nucleation sites that are associated with grain boundaries and other defects on the solid surface. This synthesis is expected to contribute to the development of large-scale manufacturing of h-BNNS/graphene-based electronics.
Single-layer graphene films, crystallized by chemical vapor deposition, host a low density of vacancy defects that are attractive for the size-sieving of molecules. The size and the density of such ...defects are a function of the growth temperature and the carbon precursor. So far, the studies applying the intrinsic defects of graphene have only used CH4 as the precursor. Since there are reports claiming the synthesis of graphene from benzene at low temperature (up to 100 °C on Cu foil), we systematically studied the crystallization of benzene-derived graphene and the evolution of intrinsic defects. We demonstrate that graphene cannot grow from benzene below 700 °C on Cu. We attribute the reports on low-temperature growth of graphene to the practice of pre-annealing of the Cu foil at 1000 °C and to the unintentional benzene residues in the reactor if the reactor is not purged carefully. Finally, we report that high-quality single-layer-graphene can be synthesized using benzene above 825 °C. The majority of vacancy defects in benzene-derived graphene (900–1000 °C) are smaller than 0.38 nm, leading to an attractive H2 sieving (H2 permeance over 2000 gas permeation units; H2/C3H8 and H2/SF6 selectivities of 12 and 50, respectively).
Display omitted
Abstract
The icosahedral
closo
dodecaborate cluster B
12
H
12
2−
is gaining increasing interest due to its unique properties including the ease of functionalization, 3D aromaticity, and formation of ...metal salts with high ion conductivity. In this work, simple and effective preparation of silver
closo
dodecaborte (Ag
2
B
12
H
12
) films is reported by an electrochemical route. The size of the Ag
2
B
12
H
12
particles in the films can be tuned from nanometers to micrometers by varying the electrochemical parameters. Ag nanoclusters with controllable sizes are successfully generated via electrochemical reduction reactions or thermal anneal of the Ag
2
B
12
H
12
films. When tested for hydrogen evolution reaction (HER) in an acidic solution, the as‐prepared Ag nanoparticles deliver a current density of 10 mA cm
−2
at 376 mV overpotential. This research sheds light on a new synthesis of B
12
H
12
2−
based thin films, the generation of metal nano‐powders, and their application in HER or other applications.
The quality of hexagonal boron nitride nanosheets (h-BNNS) is often associated with the most visible aspects such as lateral size and thickness. Less obvious factors such as sheet stacking order ...could also have a dramatic impact on the properties of BNNS and therefore its applications. The stacking order can be affected by contamination, cracks, and growth temperatures. In view of the significance of chemical-vapour-decomposition (CVD) assisted growth of BNNS, this paper reports on strategies to grow carbon- and crack-free BNNS by CVD and describes the stacking order of the resultant BNNS. Pretreatment of the most commonly used precursor, ammonia borane, is necessary to remove carbon contamination caused by residual hydrocarbons. Flattening the Cu and W substrates prior to growth and slow cooling around the Cu melting point effectively facilitate the uniform growth of h-BNNS, as a result of a minimal temperature gradient across the Cu substrate. Confining the growth inside alumina boats effectively minimizes etching of the nanosheet by silica nanoparticles originating from the commonly used quartz reactor tube. h-BNNS grown on solid Cu surfaces using this method adopt AB, ABA, AC', and AC'B stacking orders, which are known to have higher energies than the most stable AA' configuration. These findings identify a pathway for the fabrication of high-quality h-BNNS via CVD and should spur studies on stacking order-dependent properties of h-BNNS.
The quality of hexagonal boron nitride nanosheets (
h
-BNNS) is often associated with the most visible aspects such as lateral size and thickness. Less obvious factors such as sheet stacking order ...could also have a dramatic impact on the properties of BNNS and therefore its applications. The stacking order can be affected by contamination, cracks, and growth temperatures. In view of the significance of chemical-vapour-decomposition (CVD) assisted growth of BNNS, this paper reports on strategies to grow carbon- and crack-free BNNS by CVD and describes the stacking order of the resultant BNNS. Pretreatment of the most commonly used precursor, ammonia borane, is necessary to remove carbon contamination caused by residual hydrocarbons. Flattening the Cu and W substrates prior to growth and slow cooling around the Cu melting point effectively facilitate the uniform growth of
h
-BNNS, as a result of a minimal temperature gradient across the Cu substrate. Confining the growth inside alumina boats effectively minimizes etching of the nanosheet by silica nanoparticles originating from the commonly used quartz reactor tube.
h
-BNNS grown on solid Cu surfaces using this method adopt AB, ABA, AC′, and AC′B stacking orders, which are known to have higher energies than the most stable AA′ configuration. These findings identify a pathway for the fabrication of high-quality
h
-BNNS
via
CVD and should spur studies on stacking order-dependent properties of
h
-BNNS.
Large crystalline hexagonal boron nitride nanosheets are grown
via
chemical vapor deposition. Unusual stacking orders have been observed. This could inspire studies on the control of stacking order and order-property correlation.
Spent zinc–carbon dry cell batteries were characterized in the process of recovery of metal values. Zinc, manganese and steel were the major metallic materials constituting 63 % of the weight of ...spent batteries. Different components of the spent batteries were separately processed to extract the metallic values. A maximum of 92 % of total amount of zinc contained in the anodes could be extracted with a purity of over 99.0 % from the anodes by heating at 600 °C for 10 min in presence of 12 % NH
4
Cl flux. Spent electrolyte paste containing manganese and zinc as major metallic elements, was leached in sulfuric acid solution in presence of hydrogen peroxide as a reducing agent. The optimum condition for leaching was found to be concentration of sulfuric acid: 2.5 M, concentration of hydrogen peroxide: 10 %, temperature: 60 °C, stirring speed: 600 rpm and solid/liquid ratio 1:12. A maximum of 88 % manganese contained in the paste could be dissolved within 27 min of leaching under the optimized conditions. Dissolution of zinc under the same conditions was 97 %. A maximum of 69.89 % of manganese and 83.29 % of zinc contained in the leach liquor could be precipitated in the form of manganese carbonate and zinc oxalate.
PDF
