Yan Zhao,Meng Zhang,Hong Yan,Yu Feng,Xinyu Zhang,Ruijie Guo
Since the original discovery, MXene can be synthesized by wet-chemical etching from the MAX phase. To avoid the shortcomings of the previous etchant, NaHF2 aqueous solution was used for the selective removal of Al from Ti3AlC2, while intercalating Na+ between layers. The d-spacing of the resulting accordion-like Ti3C2Tx is up to 12.35 Å; the by-product Na3AlF6 can be removed by H2SO4, and the product yield can reach about 85%. After a short time of centrifugation and sonication, few-layer (10–20 layers) Ti3C2Tx sheets in a large lateral size (3–4 μm) can be prepared, with high conductivity up to 2.3 × 105 S m−1. Ti3C2Tx can be stably dispersed in water and organic solvents for at least 96 h, and has excellent anti-thermal-oxidation ability. As the anode for sodium ion batteries, the Ti3C2Tx electrode delivers a high reversible capacity of 70 mA h g−1 after 900 cycles at a current density of 1 A g−1 with an extremely low-capacity decay rate. From 900 to 1000 cycles, the capacity can even be increased to 130 mA h g−1, and the Coulomb efficiency is close to 100%, showing that MXene can provide a stable structure for the Na+ cycle.
Luqing Xi,Yuexiao Pan,Mengmeng Zhu,Hongzhou Lian,Jun Lin
A novel red phosphor, NaHF2:Mn4+ (NHF:Mn), was obtained via substituting Na+ located at the center of the octahedron coordinated with six F− ions with Mn4+ in the host lattice of NHF. The phase purity and the exact composition of the obtained NHF:Mn were confirmed by X-ray powder diffraction (XRD), Rietveld refinement, energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and infrared (IR) spectroscopy, respectively. The luminescence intensity of NHF:Mn was enhanced by optimizing the synthetic conditions. A series of warm white light-emitting diodes (WLEDs) with a color rendering index (CRI) higher than 88.0 and correlated color temperatures (CCT) between 3146 and 5172 K were obtained by encapsulating the as-prepared red phosphor NHF:Mn with the yellow one Y3Al5O12:Ce3+ (YAG:Ce) on blue chips. The advantage of the synthetic strategy to obtain NHF:Mn can be extended to develop novel Mn4+ doped red phosphors via substituting for central ions with unequal electric charge in the centers of octahedra.
危险品化学品经营许可证（带存储）