• Journal of the Mineralogical Society of Korea
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• v.30 no.2
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• pp.45-57
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• 2017

Two single crystals of fully dehydrated $Cd^{2+}$-exchanged zeolites Y were prepared by the exchange of ${\mid}Na_{75}{\mid}[Si_{117}Al_{75}O_{384}]-FAU$ ($Na_{75}-Y$, Si/Al = 1.56) with aqueous $0.05M\;Cd(NO_3)_2$ (pH = 3.65) at 294 K, followed by vacuum dehydration at 723 K (crystal 1) and a second crystal, similarly prepared, was exposed to zeolitically dried benzene for 72 hours at 294 K and evacuated (crystal 2). Their structures were determined crystallographically using synchrotron X-rays and were refined to the final error indices using $F_o$>$4{\sigma}(F_o)$ of $R_1/wR_2=0.040/0.121$ and 0.052/0.168, respectively. In crystal $1({\mid}Cd_{36}H_3{\mid}[Si_{117}Al_{75}O_{384}]-FAU)$, $Cd^{2+}$ ions primarily occupy sites I and II, with additional $Cd^{2+}$ ions at sites I', II', and a second site II. In crystal $2({\mid}Cd_{35}(C_6H_6)_{24}H_5{\mid}[Si_{117}Al_{75}O_{384}]-FAU)$, $Cd^{2+}$ ions occupy five crystallographic sites. The 24 benzene molecules are found at two distinct positions within the supercages. The 17 benzene molecules are found on the 3-fold axes in the supercages where each interacts facially with one of site IIa $Cd^{2+}$ ions. The remaining 7 benzene molecules lie on the planes of the 12-rings where each is stabilized by multiple weak electrostatic and van der Waals interactions with framework oxygens.

• Journal of the Korean Chemical Society
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• v.43 no.4
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• pp.384-385
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• 1999

Two anhydrous crystal structures of fully dehydrated, $Ca^{2+}$- and $Tl^+$-exchanged zeolite X, TEX>$Ca_{18}Tl_{56}Si_{100}Al_{92}O_{384}($Ca_{18}Tl_{56}$-X;\alpha=24.883(4)\AA)$ and TEX>$Ca_{32}Tl_{28}Si_{100}Al_{92}O_{384}($Ca_{32}Tl_{28}$-X;\alpha=24.973(4)\AA)$ per unit cell, have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3 at $21(1)^{\circ}C.$ $Ca_{18}Tl_{56}-X$ was prepared by ion exchange in a flowing stream of 0.045 M aqueous $Ca(NO_3)_2$ and 0.005 M $TlNO_3$. $Ca_{32}Tl_{28}-X$ was prepared similarly using a mixed solution of 0.0495 M $Ca(NO_3)_2$ and 0.0005M $TlNO_3$. Each crystal was then dehydrated at 360 $^{\circ}C$ and $2{\times}10^{-6}$ Torr for 2 days. Their structures were refined to the final error indices, $R_1=0.039\;and\;R_2=0.036$ with 382 reflections for $Ca_{18}Tl_{56}-X$ , and $R_1=0.046\;and\;R_2=0.045$ with 472 reflections for $Ca_{32}Tl_{28}$-X for which $/>3\sigma(I).$ In the structures of dehydrated $Ca_{18}Tl_{56^-}X\;and\;Ca_{32}Tl_{28}$-X, $Ca^{2+}\;and\;Tl^+$ ions are located at six crystallographic sites. Sixteen $Ca^{2+}$ ions fill the octahedral sites I at the centers of double six rings ($Ca_{18}Tl_{56}$-X:Ca-O=2.42(1) and O-Ca-O=93.06(4)$^{\circ}$; $Ca_{32}Tl_{28}$-X Ca-O=2.40(1) $\AA$ and O-Ca-O=93.08(3)$^{\circ}$). In the structure of $Ca_{18}Tl_{56}$-X, another two $Ca^{2+}$ ions occupy site II (Ca-O=2.35(2) $\AA$ and O-Ca-O=111.69(2)$^{\circ}$) and twenty six $Tl^+$ ions occupy site II opposite single six-rings in the supercage; each is 1.493 $\AA$ from the plane of three oxygens $(Tl-O=2.70(8)\AA$ and O-Tl-O=92.33(4)$^{\circ}$). About four $Tl^+$ ions are found at site II',1.695 $\AA$ into sodalite cavity from their three oxygen plane (Tl-O=2.81 (1) and O-Tl-O=87.48(3)). The remaining twenty six $Tl^+$ ions are distributed over site III'(Tl-O=2.82 (1) $\AA$ and Tl-O=2.88(3)$^{\circ}$). In the structure of $Ca_{32}Tl_{28}$-X, sixteen $Ca^{2+}$ ions and fifteen $Tl^+$ ions occupy site III' (Ca-O=2.26(1) $\AA$ and O-Ca-O=119.14(4)$^{\circ}$; Tl-O=2.70(1) $\AA$ and O-Tl-O=92.38$^{\circ}$) and one $Tl^+$ ion occupies site II'. The remaining twelve $Tl^+$ ions are distributed over site III'. It appears that $Ca^{2+}$ ions prefer sites I and II in that order and $Tl^+$ ions occupy the remaining sites.

• Journal of the Mineralogical Society of Korea
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• v.29 no.2
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• pp.59-71
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• 2016

To investigate the sorption characteristics of Cs, which is one of the major isotopes of nuclear waste, on natural zeolite chabazite, XRD, EPMA, EC, pH, and ICP analysis were performed to obtain the informations on chemical composition, cation exchange capacity, sorption kinetics and isotherm of chabazite as well as competitive adsorption with other cations ($Li^+$, $Na^+$, $K^+$, $Rb^+$, $Sr^{2+}$). The chabazite used in this experiment has chemical composition of $Ca_{1.15}Na_{0.99}K_{1.20}Mg_{0.01}Ba_{0.16}Al_{4.79}Si_{7.21}O_{24}$ and its Si/Al ratio and cation exchange capacity (CEC) were 1.50 and 238.1 meq/100 g, respectively. Using the adsorption data at different times and concentrations, pseudo-second order and Freundlich isotherm equation were the most adequate ones for kinetic and isotherm models, indicating that there are multi sorption layers with more than two layers, and the sorption capacity was estimated by the derived constant from those equations. We also observed that equivalent molar fractions of Cs exchanged in chabazite were different depending on the ionic species from competitive ion exchange experiment. The selectivity sequence of Cs in chabazite with other cations in solution was in the order of $Na^+$, $Li^+$, $Sr^{2+}$, $K^+$ and $Rb^+$ which seems to be related to the hydrated diameters of those caions. When the exchange equilibrium relationship of Cs with other cations were plotted by Kielland plot, $Sr^{2+}$ showed the highest selectivity followed by $Na^+$, $Li^+$, $K^+$, $Rb^+$ and Cs showed positive values with all cations. Equilibrium constants from Kielland plot, which can explain thermodynamics and reaction kinetics for ionic exchange condition, suggest that chabazite has a higher preference for Cs in pores when it exists with $Sr^{2+}$ in solution, which is supposed to be due to the different hydration diameters of cations. Our rsults show that the high selectivity of Cs on chabazite can be used for the selective exchange of Cs in the water contaminated by radioactive nuclei.

• Journal of the Korean Chemical Society
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• v.35 no.3
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• pp.189-195
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• 1991

Two crystal structures of dehydrated $Ag_{2.8}ZN_{4.6}-A$ and of its ethylene sorption complex have been determined by single-crystal X-ray diffraction techniques. The structures were solved and refined in the cubic space group Pm3m at 23(1)$^{\circ}$C. Dehydration of two crystals studied were achieved at 400$^{\circ}$C and $2{\times}10^{-6}$ Torr for 2 days and one crystal was treated with 250 Torr of ethylene at 25(1)$^{\circ}$C. The structures of dehydrated $Ag_{2.8}ZN_{4.6}-A$ (a = 12.137(2) ${\AA}$ and of its ethylene sorption complex (a = 12.106(2)${\AA}$) were refined to final error indices, R(weighted) = 0.044 with 237 reflections and R(weighted) = 0.050 with 301 reflections, respectively, for which I > 3${sigma}$(I). 2.8 $Ag^+$ ions are recessed 0.922(2) ${\AA}$ from (111) plane of three 6-ring oxygens into the large cavity where each forms a lateral ${\pi}$ complex with an ethylene molecule. These $Ag^+$ ions are in 2.240(5)${\AA}$ from three framework oxide ions and 2.290(5) ${\AA}$ from each carbon atom of an ethylene molecule. The $Zn^{2+}$ ions occupy two different threefold axis positions of the unit cell. 2.8 $Zn^{2+}$ ions are recessed 0.408(2) ${\AA}$ from (111) plane of the 6-ring oxygens and each $Zn^{2+}$ ion forms a $\pi$ complex with an $C_2H_4$ molecule. The distances between $Zn^{2+}$ ions and carbon atom of ethylene molecule, Zn(2)-C = 2.78(4) ${\AA}$ are long. This indicates that this bond is relatively weak.

• Korean Journal of Crystallography
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• v.8 no.1
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• pp.6-14
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• 1997

The crystal structures of $Sr_{31}K_{30}-X\;(Sr_{31}K_{30}Si_{100}A1_{92}O_{384};\;a=25.169(5) {\AA}$) and $Sr_{8.5}Tl_{75}-X (Sr_{8.5}Tl_{75}Si_{100}A1_{92}O_{384};\;a=25.041(5) {\AA}$) have been determined by single-crystal X-ray diffraction techniques in the cubic space group $\=F{d3}\;at\;21(1)^{\circ}C$. Each crystal was prepared by ion exchange in a flowing stream of aqueous $Sr(ClO_4)_2\;and\;(K\;or\;T1)NO_3$ whose mole ratio was 1 : 5 for five days. Vacuum dehydration was done at $360^{\circ}C$ for 2d. Their structures were refined to the final error indices $R_1=0.072\;and\;R_w=0.057$ with 293 reflections, and $R_1= 0.058\;and\;R_w=0.044$ with 351 reflections, for which $I>2{\sigma}(I)$, respectively. In dehydrated $Sr_{31}K_{30}-X,\;all\;Sr^{2+}$ ions and $K^+$ ions are located at five different crystallographic sites. Six-teen $Sr^{2+}$ ions per unit cell are at the centers of the double six-rings (site I), filling that position. The remaining 15 $Sr^{2+}$ ions and 17 $K^+$ ions fill site II in the supercage. These $Sr^{2+}$ and $K^+$ ions are recessed ca $0.45{\AA}\;and\;1.06{\AA}$ into the supercage, respectively, from the plane of three oxygens to which each is bound. ($Sr-O=2.45(1){\AA}\;and\;K-O=2.64(1){\AA}$) Eight $K^+$ ons occupy site III'($K-O=3.09(7){\AA}\;and\;3.11(10){\AA}$) and the remaining five $K^+$ ions occupy another site III'($K-O=2.88(7){\AA}\;and\;2.76(7){\AA}$). In $Sr_{8.5}Tl_{75}-X,\;Sr^{2+}\;and\;Tl^+$ ions also occupy five different crystallographic sites. About 8.5 $Sr^{2+}$ ions are at site I. Fifteen $Tl^+$ ions are at site I' in the sodalite cavities on threefold axes opposite double six-rings: each is $1.68{\AA}$ from the plane of its three oxygens ($T1-O=2.70(2){\AA}$). Together these fill the double six-rings. Another 32 $Tl^+$ ions fill site II opposite single six-rings in the supercage, each being $1.48{\AA}$ from the plane of three oxygens ($T1-O=2.70(1){\AA}$). About 18 $Tl^+$ ions occupy site III in the supercage ($T1-O=2.86(2){\AA}$), and the remaining 10 are found at site III' in the supercage ($T1-O=2.96(4){\AA}$).