Graphitic carbon nitride (g-C₃N₄) is a typical sp² π conjugated polymer semiconductor material with a variety of unique physical and chemical properties. However, g-C₃N₄ obtained by a conventional calcination method has some shortcomings such as small specific surface area, a few exposed active sites, and a poor dispersibility in aqueous solution, restricting its practical application. Compared with bulk g-C₃N₄, g-C₃N₄ nanosheets obtained by different exfoliation processes have attracted much attention in the fields of energy, catalysis and sensing due to their high specific surface area, short carrier path, abundant active sites and large band gap. g-C₃N₄ has some disadvantages of nanosheet agglomeration, high energy consumption, long time consumption and low yield in the exfoliation preparation process. It is thus necessary to develop a green and cost-effective method for the preparation of g-C₃N₄ nanosheets. This paper reviewed the exfoliation mechanisms of top-down liquid exfoliation, chemical exfoliation and thermal exfoliation. The structure, composition, lamellar thickness and specific surface area of g-C₃N₄ nanosheets obtained by three methods were compared. In addition, some applications in photocatalysis were introduced, and the future development of g-C₃N₄ nanosheets was also prospected.

To meet the growing demand for electrochemical performance of batteries in electronic devices and electric vehicles, high-performance lithium ion batteries and their electrode materials have attracted recent attention. Silicon oxide (SiO_x, 0<x<2) is considered as a promising anode material for lithium ion battery because of its high theoretical capacity, low voltage platform and abundant natural resources. However, SiO_x has some severe challenges, such as poor cycle performance, low Coulombic efficiency and low rate properties, seriously hindering its commercial development. In this review, the lithium storage mechanism of SiO_x was introduced from its structural characteristics. The research progress of SiO_x and its composite was represented in detail from three aspects, i.e., the selection of silicon source, the design of binder and electrolyte. Furthermore, the effects of organosilicon sources such as esters, silanes and biomass and inorganic silicon sources on the structure and electrochemical properties of SiO_x and its composites were summarized. Finally, some challenges in the process of commercialization of SiO_x and its composites were analyzed. It is indicated that the challenges can be solved by comprehensively adopting modification strategies and approaches such as the design of special structure, element doping, pre-lithiation and the introduction of good conductive carriers, which can effectively promote the commercialization of SiO_x anode materials.

The preparation of silicon anode materials via reduction of silicate minerals can improve the electrochemical properties and reduce the production cost. In this paper, silicon-carbon composites were prepared by a simple evaporation solvent method with natural halloysite aluminothermic reductive product as a raw material and asphalt as a carbon source. The results show that silicon exists in the form of nanotubes with a diameter of approximately 30 nm. The carbon layer is uniformly coated on the silicon nanotubes, which increases the diameter of the silicon carbon composite. The thickness of the carbon layer is approximately 7 nm. The carbon exists in an amorphous structure, and the carbon coating leads to the decrease of the specific surface area. According to the results of electrochemical tests, the optimum electrochemical performance of silicon-carbon composites can be obtained at a mass fraction of coated carbon of 15%, i.e., the first charge and discharge capacities of 1387.8 mA·h/g and 1615.7 mA·h/g, respectively, and the first coulomb efficiency of 85.9%. The silicon-carbon composites maintain the first charge discharge efficiency of silicon nanotubes, and greatly improve the cycle performance. Compared with the 200 cycles capacity retention rate of silicon nanotubes of 38%, the 200 cycles capacity retention rate of silicon-carbon composites coated with a carbon content of 15% is increased by 45.8%. The specific capacity of silicon-carbon composites coated with a carbon content of 15% is 1065.6 mA·h/g after 500 cycles. The capacity retention rate is 76.8%.