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Abstract
Solid-state 29Si and 71Ga NMR was used to study the synthetic gallosilicate Na16Ga16Si24O80 ·16H2O (Ga–natrolite). It has been shown that Ga–natrolite contains mainly Si(GaO4)3(SiO4) and Si(GaO4)2(SiO4)2-structural units and has sufficiently ordered structure. Temperature dependence of the spin–lattice relaxation time T1 of 71Ga nuclei has also been studied using solid-state NMR. Spin–lattice relaxation of the 71Ga was determined to be governed by the electric quadrupole interaction with the crystal electric field gradients modulated by translational motion of H2O molecules in the Ga–natrolite pores.
Highlights
Nowadays, there has been considerable interest in the isomorphous replacement of Al atoms by other trivalent cations due to the increased interest in zeolites
The number of resonance NMR lines of the nuclei 29Si and 71Ga determined by the degree of ordered of the natrolite structure [6, 14, 17]. It has been demonstrated at first by Lipmaa et al [17] that chemical shifts of 29Si MAS NMR spectra of zeolite and other aluminoosilicates are sensitive to the number of AlO4 tetrahedra linked to the SiO4 tetrahedron, described as the second coordination sphere of silicon
The number of aluminium tetrahedra sharing oxygens with the SiO4 tetrahedron defines five different structural units in the alumosilicate framework, namely, Si(nAl), where index n = 0, 1, 2, 3, 4 specify the number of aluminium tetrahedra connected with S iO4 tetrahedron. 29Si chemical shift ranges by about 5 ppm lowfield shifts for each additional connected substituent [17]
Summary
There has been considerable interest in the isomorphous replacement of Al atoms by other trivalent cations due to the increased interest in zeolites. These micro-porous species possess different physical and chemical properties from their aluminium analogues and offer possibilities for new applications of molecular sieves [1,2,3,4,5]. Gallium is directly below aluminium in the periodic table; it forms chemically similar, analogous tetrahedra to A lO4. Isomorphous substitution of Ga for Al in alumosilicate natrolite (Na16Al16Si24O80·16H2O) gives gallosilicate natrolite (Ga–natrolite) [1].
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