Syntheses, X-ray Powder Structures, and Preliminary Ion-Exchange Properties of Germanium-Substituted Titanosilicate Pharmacosiderites: HM3(AO)4(BO4)3·4
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- 作者：Elizabeth A. Behrens ; Damodara M. Poojary ; and Abraham Clearfield
- 刊名：Chemistry of Materials
- 出版年：1998
- 出版时间：April 1998
- 年：1998
- 卷：10
- 期：4
- 页码：959 - 967
- 全文大小：134K
- 年卷期：v.10,no.4(April 1998)
- ISSN：1520-5002
文摘
This paper describes a continuing research effort that involvessynthesizing new tunnel-type materials while attempting to understand their fundamentalion-exchange selectivitiesthrough the process of structural elucidation. For this study, wehydrothermally synthesizedand characterized two germanium-substituted titanosilicates in thecesium phase andprepared their potassium forms by ion exchange. A mixed Si//Ti/Gephase, HCs3(TiO)3.5(GeO)0.5(GeO4)2.5(SiO4)0.5·4H2O,crystallizes in the cubic space group P
3mwith a = 7.9376(1) Å, while the cesium titanogermanate,HCs3(TiO)4(GeO4)3·4H2O,possesses a body-centeredsupercell belonging to space group I23, a =15.9604(3) Å. Differences in symmetry betweenthe two cesium compounds can be explained in terms of entropy and sitemixing in the Si/Ti/Ge compound. Upon ion exchange with potassium, the resultingphases, HK3(TiO)3.5(GeO)0.5(GeO4)2.5(SiO4)0.5·4H2OandHK3(TiO)4(GeO4)3·4H2O,distorted to the tetragonal spacegroup Pb2, with a =b = 11.1571(2), c = 7.9165(2) Å,and a = b = 11.215(1), c =7.9705(2)Å, respectively. For the first time, we have observed tetragonaldistortions with alkali cationforms of the pharmacosiderite analogues. As compared toHK3(TiO)4(SiO4)3·4H2O,thesepotassium germanium-substituted phases show remarkable increases instrontium andcesium selectivity, which proves very beneficial for nuclear wasteremediation applications.An increase in selectivity can be explained in terms of theirinherent structures and bondstrengths associated with the charge-neutralizing cations and frameworkoxygens.
3mwith a = 7.9376(1) Å, while the cesium titanogermanate,HCs3(TiO)4(GeO4)3·4H2O,possesses a body-centeredsupercell belonging to space group I23, a =15.9604(3) Å. Differences in symmetry betweenthe two cesium compounds can be explained in terms of entropy and sitemixing in the Si/Ti/Ge compound. Upon ion exchange with potassium, the resultingphases, HK3(TiO)3.5(GeO)0.5(GeO4)2.5(SiO4)0.5·4H2OandHK3(TiO)4(GeO4)3·4H2O,distorted to the tetragonal spacegroup Pb2, with a =b = 11.1571(2), c = 7.9165(2) Å,and a = b = 11.215(1), c =7.9705(2)Å, respectively. For the first time, we have observed tetragonaldistortions with alkali cationforms of the pharmacosiderite analogues. As compared toHK3(TiO)4(SiO4)3·4H2O,thesepotassium germanium-substituted phases show remarkable increases instrontium andcesium selectivity, which proves very beneficial for nuclear wasteremediation applications.An increase in selectivity can be explained in terms of theirinherent structures and bondstrengths associated with the charge-neutralizing cations and frameworkoxygens.