Dielectric spectra of 4A zeolite particles bulked in deionized water（4A/W） or cyclohexane（4A/C） were measured respectively under different temperatures, and two dielectric relaxations were found in both of 4A/W an...Dielectric spectra of 4A zeolite particles bulked in deionized water（4A/W） or cyclohexane（4A/C） were measured respectively under different temperatures, and two dielectric relaxations were found in both of 4A/W and 4A/C. Because of existence of water molecules in pores, both low and high frequency relaxation times（t LFR and t HFR） of 4A/W decreased more sharply than 4A/C with increasing temperature.According to the temperature dependence of t LFR and t HFR, the activation energies of Na＋interacting with framework under hydrated and dehydrated environments were calculated respectively, and the original properties of Na＋in dehydrated zeolite were obtained by analyzing the dielectric properties of 4A/C.Furthermore, a transient state of Na＋motion with temperature was found in 4A/C system.展开更多
Zeolites are typically synthesized in alkaline or fluoride-containing near-neutral media.Sophisticated organic structure-directing agents have been investigated for such systems with the aim of discovering materials w...Zeolites are typically synthesized in alkaline or fluoride-containing near-neutral media.Sophisticated organic structure-directing agents have been investigated for such systems with the aim of discovering materials with unprecedented structures and properties for novel technical applications.In contrast,zeolite crystallization in strongly acidic media has yet to be explored.This study demonstrates that a zeolitic silicate phase crystallizes from acidic gels using trimethylamine as an organic additive with the composition 1 SiO_(2):0.3 TMA:0.3 HCl:0.15 HF:55 H_(2)O:(0.1-0.4)GeO_(2).This phase has an interrupted four-connected framework analog to the octahedron/tetrahedron-mixed framework of the mineral family pharmacosiderite.In comparison to the pharmacosiderite-type HK_(3)(Ge_(7)O_(16))(H_(2)O)_(4),the four GeO_(6)-octahedra forming the central[HGe_(4)O_(4)O_(12)]-cluster are replaced by four SiO_(4)-tetrahedra in a[Si_(4)O_(6)(OH)2.89]-unit in the new phase.However,the structure is distorted and may contain connectivity and point defects;thus,healing by the occasional incorporation of GeO_(6)-units is necessary.The refined unit cell has a cubic symmetry,space group P-43m(#215),with a=7.7005(1)Å.Acidic-medium synthesis is a useful way to find new zeolites that move in a fundamentally different direction from sophisticated organic structure-directing agents.展开更多
基金supported by Beijing Natural Science Foundation (Nos. 2143040, 2144047)the Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions (No. CIT&TCD201504009)National Natural Science Foundation of China (No. 21301012)
文摘Dielectric spectra of 4A zeolite particles bulked in deionized water（4A/W） or cyclohexane（4A/C） were measured respectively under different temperatures, and two dielectric relaxations were found in both of 4A/W and 4A/C. Because of existence of water molecules in pores, both low and high frequency relaxation times（t LFR and t HFR） of 4A/W decreased more sharply than 4A/C with increasing temperature.According to the temperature dependence of t LFR and t HFR, the activation energies of Na＋interacting with framework under hydrated and dehydrated environments were calculated respectively, and the original properties of Na＋in dehydrated zeolite were obtained by analyzing the dielectric properties of 4A/C.Furthermore, a transient state of Na＋motion with temperature was found in 4A/C system.
基金support provided by the Shandong Energy Institute(SEI S202107)Nature Science Foundation of Shandong Province(ZR2022MB053 and ZR2022QB216).
文摘Zeolites are typically synthesized in alkaline or fluoride-containing near-neutral media.Sophisticated organic structure-directing agents have been investigated for such systems with the aim of discovering materials with unprecedented structures and properties for novel technical applications.In contrast,zeolite crystallization in strongly acidic media has yet to be explored.This study demonstrates that a zeolitic silicate phase crystallizes from acidic gels using trimethylamine as an organic additive with the composition 1 SiO_(2):0.3 TMA:0.3 HCl:0.15 HF:55 H_(2)O:(0.1-0.4)GeO_(2).This phase has an interrupted four-connected framework analog to the octahedron/tetrahedron-mixed framework of the mineral family pharmacosiderite.In comparison to the pharmacosiderite-type HK_(3)(Ge_(7)O_(16))(H_(2)O)_(4),the four GeO_(6)-octahedra forming the central[HGe_(4)O_(4)O_(12)]-cluster are replaced by four SiO_(4)-tetrahedra in a[Si_(4)O_(6)(OH)2.89]-unit in the new phase.However,the structure is distorted and may contain connectivity and point defects;thus,healing by the occasional incorporation of GeO_(6)-units is necessary.The refined unit cell has a cubic symmetry,space group P-43m(#215),with a=7.7005(1)Å.Acidic-medium synthesis is a useful way to find new zeolites that move in a fundamentally different direction from sophisticated organic structure-directing agents.
