Conductivity of Mono- and Divalent Cations in the Microporous Zincosilicate VPI-9

Abstract

Impedance spectroscopy is used to investigate the long-range ionic conductivity of the microporous, zincosilicate VPI-9 (Si/Zn ) 4.0) (International Zeolite Association framework type VNI) containing the alkali cations Li + , Na + , K + , Rb + , and Cs + , and the alkaline earth cations Mg 2+ , Ca 2+ , and Sr 2+ . Monovalent cation-exchanged samples Li-and Na-VPI-9 lose X-ray crystallinity upon vacuum dehydration at 450 °C, whereas K-, Rb-, and Cs-VPI-9 remain crystalline and exhibit conductivities of 1.7 × 10 -4 , 3.5 × 10 -4 , and 4.9 × 10 -4 S/cm, respectively, at 450 °C and activation energies of 0.72, 0.64, and 0.69 eV, respectively, in the temperature range 150-450 °C. Divalent cation-exchanged sample Mg-VPI-9 also loses X-ray crystallinity, but Ca-and Sr-VPI-9 remain crystalline and exhibit conductivities of 2.3 × 10 -6 S/cm and 7.7 × 10 -7 S/cm, respectively, at 450 °C, and activation energies of 0.88 and 0.91 eV, respectively, over the temperature range 150-450 °C. When compared to aluminosilicate zeolite X (Si/Al ) 1.25) exchanged with the same cations, all crystalline M-VPI-9 materials have greater conductivities than M-X, with the exception of K-X (1.6 × 10 -3 S/cm at 450 °C), with the greatest differences arising between the divalent exchanged materials. Dense, crystalline zincosilicate samples with the compositions K 2 ZnSi x O 2(x+1) (x ) 2-5), Rb 2 ZnSi 5 O 12 , and Cs 2 ZnSi 5 O 12 are also prepared and characterized for comparison with the microporous materials and exhibit much lower conductivities than their microporous counterparts at the same composition.

Effect of Transition Metals on the Electrical Conductivity Response of dPPV/Zeolite Y Composites toward Ketone Vapors

“…27,[30][31][32][33] In addition, the electron orbitals of the cation in the zeolite framework are other factors affecting the electrical conductivity. 80CuNaY shows a higher value of the electrical conductivity than 80NiNaY and 80FeNaY, respectively, because of the charge-balanced ion size.…”

“…27,[30][31][32][33] The cation radii of Fe 2+ , Ni 2+ , and Cu 2+ are 0.75, 0.83, and 0.87Å, respectively. The electrical conductivity sensitivities are 2.38 × 10 −01 ± 1.66 × 10 −02 , 2.64 × 10 −01 ± 2.05 × 10 −02 , 3.53 × 10 −01 ± 1.93 × 10 −02 , and 5.00×10 −01 ± 2.20 × 10 −02 , respectively.…”

“…The electrical conductivity response in-creases with increasing cationic radii. [22][23][24][30][31][32][33] In this work, 80CuNaY is used to further investigate the effects of dPPV and the ketone vapor concentration and will be discussed next. 27,[30][31][32][33] The cation radii of Fe 2+ , Ni 2+ , and Cu 2+ are 0.75, 0.83, and 0.87Å, respectively.…”

“…The large cation size leads to a reduction in the electrostatic force of the zeolite framework and the increase in the proton mobility along the zeolite structure. 27,[30][31][32][33] In addition, the electron orbitals of the cation in the zeolite framework are other factors affecting the electrical conductivity. Figure 2 shows the electron orbitals of Cu 2+ , Ni 2+ , and Fe 2+ .…”

Electrical conductivity response and sensitivity of ZSM-5, Y, and mordenite zeolites towards ethanol vapor

“…For the effect of zeolite framework type, the Z80 exhibits a higher electrical conductivity than the Y80 because of the charge balancing cation size; the ionic radius of NH 4 + (1.47Å) is larger than H + (0.37Å) [15], which leads to a reduced electrostatic interaction with the anionic framework sites and to the ease in which a cation can move from one site to another [16]. In addition, the electrical conductivity of the Y30 is the same as the M30 because their charge balancing cations, H + , are the same.…”