Juan Du,Xiang Wan,Caixiong Song,Kangsheng Wu,Wenbing Yang,Beiye Liu,Qi Yang,Jingjing Fang,Ayesha Razzaq
Crystal twinning, a common growth phenomenon, can substantially affect material performance in fields such as semiconductors, nonlinear optics, and drug development, yet its elimination during crystallization is challenging. This study presents a method for the controlled synthesis of ZSM-5 zeolite as either single crystals or twinned crystals using kaolin as the primary raw material. The method leverages the etching effect of ammonium fluoride (NH4F) on the aluminosilicate structure derived from pre-treated kaolin. By adjusting the concentrations of NH4F and the structure-directing agent tetrapropylammonium bromide (TPABr), pure ZSM-5 single crystals and twinned crystals were selectively synthesized. Conventionally, NH4F is employed to introduce defects into zeolite structures. In contrast, this work demonstrates its utility in controlling crystal habit. The synthesis utilizes kaolin, an abundant and low-cost aluminosilicate mineral, to provide the entire aluminum source and a portion of the silicon source, offering an economical alternative to expensive precursors like aluminum isopropoxide. The resulting single and twinned crystals exhibited high crystallinity, demonstrating the viability of using natural minerals to produce high-quality zeolites. The physical and chemical properties of the kaolin-derived ZSM-5 were characterized and compared to those of ZSM-5 synthesized from conventional chemical reagents. A growth mechanism for the formation of single and twinned crystals is also proposed.
Hu Luo,Yingming Wang,Gongwei Wang,Li Xiao,Juntao Lu,Lin Zhuang
Redox electrochemical capacitors , using soluble redox couples to utilize the “dead weight” of the electrolyte to add faradaic charge, are considered as an effective strategy to increase the energy storage capacity of the electro-chemical double-layer capacitors. In this work, we report a new aqueous dual-redox electrochemical capacitor, using Zn 2+ /Zn as the anolyte and Br 3 ˉ/Brˉ as the catholyte. The electrolyte contains 1 M ZnBr 2 , 0.1 M TPABr and 2 M Zn(OTf) 2 . The theoretical voltage gap of the two redox couples is larger than 1.7 V, which is expected to be an advantage for higher specific energy. Tetrapropyl ammonium cation (TPA + ) has been used as a complex agent to solve the Br 3 ˉ cross diffusion issue. To avoid the generation of [TPA] 2 [ZnBr 4 ] precipitation, an appropriate amount of Zn(OTf) 2 has been added to the electrolyte to adjust the Zn/Br ratio. After adding these two additives, the coulombic efficiency of the dual-redox EC has been increased from 90% to 99%, and the open-circuit voltage loss (24 h) has been dropped from 31% to 5%. The newly configured Zn/OTf/TPA/Br redox EC exhibits a specific energy of 110 W h/kg at 1 A/g, a high power density (7 kW/kg) and stable cycling over 6000 cycles.
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