Fig. 4 A schematic diagram of phase transition observed in zeolite X in a presence of (a) water and (b) HCO₃^- solution. Zeolite X, gmelinite, natrolite and smectite viewed along (111), (001), (001) and (100), respectively. Blue tetrahedra, sky blue tetrahedra, yellow balls and blue balls represent Si framework, Al framework, Na+ and water molecules, respectively.

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