(A) study on the structural transformation of $AlPO_4-8$ by photoacoustic technique and encapsulation of Co(Ⅱ)saloph complexes into $AlPO_4-8$ by the structural transformation of VPI-5 into $AlPO_4-8$

Abstract

Temperature-dependent photoacoustic technique was used to elucidate the structural transformation of aluminophosphate molecular sieves, the structural transformation of $AlPO_4-21$ into $AlPO_4-25$, and $AlPO_4-H_3$ into $AlPO_4-C$ and subsequent transformation into $AlPO_4-D$. Photoacoustic signal intensity was decreased drastically due to the endothermic process leading to the structural transformation. The definite transformation temperature of $AlPO_4-21$ into $AlPO_4-25$ was obtained at 537 K. The organic template n-propylamine, encapsulated during the synthesis of $AlPO_4-21$, had no effect on the variations of photoacoustic signal intensity caused by the structural transformation and dehydration processes. The organic template was removed around 573 K after the complete structural transition into $AlPO_4-25$. In the parallel photoacoustic study on the structural transformation of $AlPO_4-H_3$ into $AlPO_4-C$ and subsequent transformation into $AlPO_4-D$, the photoacoustic results suggested that the structural transition of $AlPO_4-H_3$ into $AlPO_4-C$ occurs around 378 K, and the topotactic transformation of $AlPO_4-C$ into $AlPO_4-D$ takes place around 497 K. The observation of different X-ray diffraction crystalline phases before and after the PA signal decrease, suggested that the sharp decrease in the PA signal intensity can be attributed to the structural transition process. The aluminophosphate-hosted cobalt Schiff base complexes were studied to examine the influence of a structural transformation on the encapsulated guest molecules. The Cobalt Shiff base complexes, Co(II)saloph (N,N- bis(salicylidene)-1,2-phenylenediamino-cobalt (II)), were encapsulated into VPI-5 and $AlPO_4-8$. Aluminophosphate-hosted cobalt complexes were obtained by impregnating VPI-5 with Co(saloph). Co(saloph) which did not diffuse easily into the channels of $AlPO_4-8$ could be encapsulated effectively into $AlPO_4-8$ utilizing the structural transformation of VPI-5 occlud...