Synthesis and pore formation study of amorphous mesoporous aluminophosphates in the presence of citric acid.

Amorphous mesoporous aluminophosphates (AlPO) with high thermal stability were synthesized from Al(NO3)3 and H3PO4 in the presence of citric acid (CA). The effects of different synthetic conditions, such as pH value, citric acid content, and calcined temperature, on the formation of the mesoporous structure of AlPO materials were investigated. The results of N2 adsorption/desorption and other characterization means demonstrate that the presence of a certain amount of citric acid in the synthetic mixture can result in the formation of uniform mesoporous AlPO materials in a wide pH range from 3.5 to 10. Thermal gravimetry and differential thermal analysis suggest that the existence of a moderate interaction between citric acid and the AlPO network might be a critical factor in obtaining uniform mesostructure. Therefore, as an organic additive, citric acid can be regarded as a template for the mesopore formation of AlPO materials.