Sodium-doped carbon nitride nanotubes （Nax-CNNTs） were prepared by a green and simple two-step method and applied in photocatalytic water splitting for the first time. Transmission electron microscopy （TEM） elemen...Sodium-doped carbon nitride nanotubes （Nax-CNNTs） were prepared by a green and simple two-step method and applied in photocatalytic water splitting for the first time. Transmission electron microscopy （TEM） element mapping and X-ray photoelectron spectroscopy （XPS） measurements confirm that sodium was successfully introduced in the carbon nitride nanotubes （CNNTs）, and the intrinsic structure of graphitic carbon nitride （g-C3N4） was also maintained in the products. Moreover, the porous structure of the CNNTs leads to relatively large specific surface areas. Photocatalytic tests indicate that the porous tubular structure and Na＋ doping can synergistically enhance the hydrogen evolution rate under visible light （λ 〉 420 nm） irradiation in the presence of sacrificial agents, leading to a hydrogen evolution rate as high as 143 μmol·h-1 （20 mg catalyst）. Moreover, other alkali metal-doped CNNTs, such as Lix-CNNTs and Kx-CNNTs, were tested; both materials were found to enhance the hydrogen evolution rate, but to a lower extent compared with the Nax-CNNTs. This highlights the general applicability of the present method to prepare alkali metal-doped CNNTs; a preliminary mechanism for the photocatalytic hydrogen evolution reaction in the Nax-CNNTs is also proposed.展开更多
Sulfur/graphene composites with different sulfur contents were prepared by two-step synthesis, where graphene was regarded as a carrier of sulfur active substance. The surface structure and crystal form of the composi...Sulfur/graphene composites with different sulfur contents were prepared by two-step synthesis, where graphene was regarded as a carrier of sulfur active substance. The surface structure and crystal form of the composites obtained were characterized and compared by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. It was found that sulfur was partially coated by graphene. The graphene folds provided more nano-pores and electron transport channels for sulfur. From TGA results, the sulfur contents of the sulfur/graphene compositcs measured were about 42.32 wt%, 54.94 wt%, and 65.23 wt%. Electrochemical tests demonstrated that sulfur/graphene composite （x=54.94 wt%） cathode exhibited better capacity retention （40.13%） compared with the pure cathode （20.46%）, where an initial discharge capacity was up to 1 500 mAh.g-t and it remained about 600 mAh·g-1 after 30 cycles. Furthermore, the electrochemical reaction mechanism and the state of reaction interface for Li/S battery were analyzed by cyclic voltammogram and AC-impedance spectra. The results indicated that the sulfur/graphene composite with a sulfur content of 54.94 wt%, based on a two-step synthesis, contributed to improving electrochemical properties of lithium/sulfur battery展开更多
基金The authors would like to thank the financial support from Sakura Science Program （Japan Science and Technology Agency）, National Natural Science Foundation of China （Nos. 51627803, 51402348, 11474333, 91433205, 51421002, and 51372270） and the Knowledge Innovation Program of the Chinese Academy of Sciences.
文摘Sodium-doped carbon nitride nanotubes （Nax-CNNTs） were prepared by a green and simple two-step method and applied in photocatalytic water splitting for the first time. Transmission electron microscopy （TEM） element mapping and X-ray photoelectron spectroscopy （XPS） measurements confirm that sodium was successfully introduced in the carbon nitride nanotubes （CNNTs）, and the intrinsic structure of graphitic carbon nitride （g-C3N4） was also maintained in the products. Moreover, the porous structure of the CNNTs leads to relatively large specific surface areas. Photocatalytic tests indicate that the porous tubular structure and Na＋ doping can synergistically enhance the hydrogen evolution rate under visible light （λ 〉 420 nm） irradiation in the presence of sacrificial agents, leading to a hydrogen evolution rate as high as 143 μmol·h-1 （20 mg catalyst）. Moreover, other alkali metal-doped CNNTs, such as Lix-CNNTs and Kx-CNNTs, were tested; both materials were found to enhance the hydrogen evolution rate, but to a lower extent compared with the Nax-CNNTs. This highlights the general applicability of the present method to prepare alkali metal-doped CNNTs; a preliminary mechanism for the photocatalytic hydrogen evolution reaction in the Nax-CNNTs is also proposed.
基金Funded partly by the Science and Technology Support Program of Hebei(No.11215114D)
文摘Sulfur/graphene composites with different sulfur contents were prepared by two-step synthesis, where graphene was regarded as a carrier of sulfur active substance. The surface structure and crystal form of the composites obtained were characterized and compared by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. It was found that sulfur was partially coated by graphene. The graphene folds provided more nano-pores and electron transport channels for sulfur. From TGA results, the sulfur contents of the sulfur/graphene compositcs measured were about 42.32 wt%, 54.94 wt%, and 65.23 wt%. Electrochemical tests demonstrated that sulfur/graphene composite （x=54.94 wt%） cathode exhibited better capacity retention （40.13%） compared with the pure cathode （20.46%）, where an initial discharge capacity was up to 1 500 mAh.g-t and it remained about 600 mAh·g-1 after 30 cycles. Furthermore, the electrochemical reaction mechanism and the state of reaction interface for Li/S battery were analyzed by cyclic voltammogram and AC-impedance spectra. The results indicated that the sulfur/graphene composite with a sulfur content of 54.94 wt%, based on a two-step synthesis, contributed to improving electrochemical properties of lithium/sulfur battery
