Preparation & Properties Of Molecular Sieve Single Crystals And Magnetic Nano-oxides

I Molecular Sieve Single CrystalsThe synthesis of a variety of template-directed aluminophosphates with structuresof chains (1-D), layers (2-D) and frameworks (3-D) by hydrothermal and solvothermalmethods has been stimulated by the discovery of the aluminophosphate molecularsieves (AlPO4-n). In recent years, AlPO4-based large single crystals containingheteroelements (such as Si, Mg) in the framework have received great attention andefforts including 'two silicon source'technique and addition of F-ions have been madeto explore synthetic routes for perfect large single crystals, In this thesis, we report thesynthesis of the single crystals-AlPO4-5, SAPO-44 and AlPO4-11 (MAPO-11).AlPO4-11 is one of the crystalline microporous aluminophosphates first reported in1982. It is built of alternating AlO4 and PO4 tetrahedra linked together via oxygen atomsto form a three-dimensional framework with a 1-D channel system of 4.4×6.7 ?. Mostof the AlPO4-11 products synthesized previously were powders and nanocrystals ofAlPO4-11 have also been reported. Although MAPO-11 molecular sieve was preparedusing magnesium acetate as the magnesium source, the effect of magnesium source onthe crystallization process was not investigated. In our work, MgO was introduced intothe reaction system of AlPO4-11 and large single crystals of MAPO-11 were obtained.The crystal size and the crystallinity of MAPO-11 were both increased while thecrystallization time was shortened greatly in comparison with those for AlPO4-11.Solid-state NMR is an effective technique to investigate the crystalline mechanism ofmolecular sieve single crystals. On the basis of NMR, XRD and IR characterizations, itis believed that magnesium oxide not only decreases the supersaturation degree but alsoacts as a nucleation suppressor in the crystallization process. Both factors favor theformation of large MAPO-11 single crystals.