Morphology changes of transition-metal-substituted aluminophosphate molecular sieve AlPO₄-5 crystals

In this work, poly ethylene glycol (pEG) was used as a cosolvent to control the morphology of transition metal substituted aluminophosphate molecular sieve AlPO₄-5 (AFI) crystals in the solvothermal reaction system of Al(OPrⁱ)₃-H₃PO₄-TEA-Me-H ₂O-pEG (Me = Cr, Ti, Fe, V). In the presence of pEG molecules, the growth rate of the Me-AFI crystals along c-direction was significantly inhibited. With the increase of the volume ratio of pEG/H₂O, the aspect ratio of hexagonal prismlike Cr-AFI crystals was gradually decreased and the tabletlike crystals were obtained. Further increasing the volume ratio of pEG/H₂O resulted in the novel flowerlike morphology for Cr ³⁺- and Fe³⁺-substituted AFI crystals and kiwi-fruit-like morphology for Ti⁴⁺ and V⁵⁺ substituted AFI crystals. Our studies revealed that the existence of pEG molecules and the isomorphic substitution of Al or P are important for the formation of these specific morphologies.