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Low-temperature synthesis of hydrated zinco(beryllo)-phosphate and arsenate molecular sieves

Abstract

ALUMINOSILICATE (zeolite) molecular sieves, both natural and synthetic, have been studied extensively because of their utility in commercial processes such as petroleum cracking, water treatment and gas absorption 1–3. Although aluminium and silicon may be replaced by a variety of other tetrahedrally coordinated elements, there are few examples of molecular sieves that contain neither aluminium nor silicon: several gallophosphates are known4,5, and cacoxenite, a basic ferric oxyphosphate, occurs naturally6. Recently, two new beryllophosphate minerals have been identified7,8: tiptopite, isotypic with cancrinite, and pahasapaite (Li, Ca beryllophosphate), which has the structure of zeolite RHO. Harvey and Meier9 have prepared five new beryllophosphates, with structures analogous to RHO (Li), gismondine (Na), edingtonite (K), pollucite (Cs), and a new structure, BPH, that has no aluminosilicate analogue. Here we describe the preparation of new families of hydrated zincophosphates/arsenates and beryllo-phosphates/arsenates with structures that are also related to zeolitic aluminosilicates. These materials may be prepared from gels over a much wider range of pH and at much lower temperatures than are possible for aluminophosphates, perhaps because of the greater solubility of the framework elements: analogues of hydro-sodalite and zeolites RHO, Li-A(BW) and X are easily prepared at pH values ranging from 2 to 12 and between 4 and 100 °C. Growth of crystals adequate for X-ray structural analyses seems to be easier than is the case for aluminosilicate/phosphate materials.

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