Black phosphorus (BP) has received much attention as a two-dimensional layered solid lubricant in reducing friction and protecting against wear. Violet phosphorus (VP) is another stable allotrope of phosphorus with unique layered structures. However, the friction properties of VP have not been explored. Herein, we present a comprehensive study of the atomic-scale friction of BP and VP by friction force microscopy. The friction properties of VP were characterized for the first time. Atomic-scale stick−slip friction measurements along the lattice orientations of BP and VP clearly revealed the correlation between friction anisotropy and crystallographic structures. Relative to the nitrogen atmosphere, the friction behavior of BP and VP in water was also investigated. It was found that the friction coefficient was significantly increased in water, indicating that water was not a good medium for phosphorus achieving superlubricity. The results in this study not only provide indepth insights into the fundamental friction properties of phosphorus but also pave the crucial pathways toward such applications as lubricants in micro/nanoelectromechanical systems and a phosphorus-based superlubric generator with high efficiency and ultralong life.
Despite extensive studies have been conducted in exploring the friction in aqueous environment, the mechanism of hydration friction remains not well understood. Herein, we directly probed the hydration friction on...
Based on its unique features including 2D planar geometry, high specific surface area and electron conductivity, graphene has been intensively studied as oxygen reduction reaction (ORR) electrocatalyst and supercapacitor material. On the one hand, graphene possesses standalone electrocatalytic activity. It can also provide a good support for combining with other materials to generate graphene-based electrocatalysts, where the catalyst-support structure improves the stability and performance of electrocatalysts for ORR. On the other hand, graphene itself and its derivatives demonstrate a promising electrochemical capability as supercapacitors including electric double-layer capacitors (EDLCs) and pseudosupercapacitors. A hybrid supercapacitor (HS) is underlined and the advantages are elaborated. Graphene endows many materials that are capable of faradaic redox reactions with an outstanding pseudocapacitance behavior. In addition, the characteristics of graphene-based composite are also utilized in many respects to provide a porous 3D structure, formulate a novel supercapacitor with innovative design, and construct a flexible and tailorable device. In this review, we will present an overview of the use of graphene-based composites for sustainable energy conversion and storage.
The integration of graphene-based material and TiO 2 can greatly enhance the photodegradation efficiency toward contaminants in the environment. As the morphology of TiO 2 varies from a 0D nanoparticle (NP) and a 1D Nanotube (NT)/Nanowire (NW) to a 2D nanosheet, the contact between TiO 2 and graphene-based material would increasingly intensify and the distribution of TiO 2 on the graphene sheets becomes more uniform. Both factors lead to better photocatalytic performance. The graphene commonly possesses the intrinsic properties of higher surface area, more efficient charge transfer, inhibited electron-hole pairs (EHPs)' recombination and extended light absorption range. With the assistance of some functional surfactants, the photodegradation performance can be further improved according to more specific requirements such as the photodegradation selectivity. This paper provides an overview of recent progress regarding the method and mechanism of graphene in various TiO 2 /Graphene composites.
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