Physicochemical characterization to assess Ni and Zn incorporation into zeotype SAPO-34 nanoparticles synthesized with different mixing methods through ultrasound-promoted crystallization

Abstract

The synthesis of transition metal (Me = Ni and Zn) containing SAPO-34 nanoparticles was conducted by applying insonation as the precrystallization treatment. The effects of synthesis parameters on the properties of SAPO-34 products and their derivatives in terms of the crystallinity, size and morphology of particles, structure and hydroxyl functional groups, and stereochemistry of metal ions were investigated to elucidate how the isomorphous substitution or the mere presence of transition metal ions was influenced by the crystallization treatment, mixing method, or the amount and type of metal species. The physicochemical properties of the prepared samples were characterized by various techniques including XRD, SEM, TEM, EDX, UV-Vis DRS, FTIR, and TGA. The results indicated that sonochemically prepared SAPO-34 samples possessed higher crystallinity and uniform crystals with narrow particle size distribution. The nature of the metal species could affect the physicochemical properties of the synthesized samples and Zn-doped SAPO-34 samples showed a lower crystallinity, larger unit cell parameters, and more uniform crystals. Also, it was found that the significant variations in the morphology, size, and uniformity of the metal-doped SAPO-34 crystals were acquired based on the different mixing methods. Meanwhile, the mixing methods played a key role in the incorporation of metal ions into the SAPO-34 framework, and mixing method (II), in which the metal sources were added to the precursor gel prior to the addition of the phosphoric acid, had prominent capability to locate the metal ions, in particular nickel ions, in the SAPO-34 skeleton.