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Carbon materials are usually used as the sulfur host in rechargeable lithiumsulfur (Li-S) batteries that are considered as promising electrochemical energy storage systems. However, the "shuttling" caused by the soluble lithium polysulfides (LiPSs) formed by the reaction of Li and sulfur causes rapid capacity fade and low sulfur utilization, greatly hindering their practical use. The carbon materials can also be tailored to prevent LiPS shuttling because of their abundant porosity and controllable surface chemical properties, which are divided into four specific functions: confining, trapping, blocking, and breaking up. Confinement means physically confining the LiPSs in pores in the carbon while trapping refers to chemical adsorption on the carbon surface to restrict their diffusion and promote their transformation to insoluble Li 2 S 2 /Li 2 S. Blocking means placing a barrier in the cells to inhibit LiPS diffusion to the anode, while breaking up means decreasing the size of the sulfur moiety to increase its affinity with carbons. The advantages and disadvantages of functional carbons in relation to these four functions are summarized and the specific ways to achieve them are highlighted. The design of advanced carbons with synergistic functions is discussed and some perspectives on the future development of carbons in Li-S batteries are given.

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In this paper, polydopamine/graphitic carbon nitride (PDA/g-C 3 N 4 ) has been synthesized by the dopamine (DA) polymerization modification of the surface of g-C 3 N 4 . For a study of the morphology and optical property of catalysts, the obtained PDA/g-C 3 N 4 composites were characterized by FTIR, XRD, SEM, TEM, BET, XPS, TGA, DRS (diffuse reflectance spectroscopy), photoluminescence, and photocurrent generation. Polydopamine (PDA) plays multiple roles as a light absorption substance, an electron transfer acceptor, and an adhesive interface in the design of PDA/g-C 3 N 4 photosynthetic systems. The optical results demonstrate that PDA has an effect on the PDA/g-C 3 N 4 composite light-harvesting capacity. With an increasing PDA ratio, the photocatalyst's light-harvesting ability was gradually improved. In addition, the 10%PDA/g-C 3 N 4 composite has been shown to be highly efficient for the degradation of the organic dyes methylene blue (MB), Rhodamine B (RhB), and phenol under visible-light irradiation. The degradation efficiency of MB is about 98% in 3 h, and the catalysts can have a degradation efficiency higher than 90% after four cycles. Polydopamine (PDA), as a surface-modified additive with abundant semiquinone and quinone functional ligands, was introduced for an improvement of the transfer ability of photoinduced electrons and accepts them from a semiconductor-based photocatalysis material (g-C 3 N 4 ), which can reduce electron−hole recombination of g-C 3 N 4 and enhance the photocatalytic activity.