Synthesis of anisotropic silica nanoparticles by organic amine with diverse structures

Abstract Anisotropic silica nanoparticles (AISNPs) possess a greater effective surface area accompanied with more active sites, rendering them viable candidates for numerous potential applications. However, their preparation through sol-gel synthesis proves challenging due to the particles' inherent tendency to assume a spherical shape to minimize surface energy. Herein, we synthesized AISNPs with organic amines with different structures. Monoamines and diamines with distance between amine groups shorter than ca. 4 Å have been observed to facilitate the formation of isotropic silica nanoparticles (ISNPs). AISNPs were synthesized with diamines with distance between amine groups longer than ca. 4 Å and linear structures of triamines. Non-linear structures with amine groups positioned in a triangular configuration and the cage-like structure of tetra-amines directed the formation of ISNPs. It has been speculated that the formation of AISNPs would be due to the spherical primary particles connecting by organic amines with two or more amine groups with distances between them longer than ca. 4 Å. On the contrary, the formation of ISNPs would be atributed to the adsorption of two amine groups on the same primary particles, or to steric hindrance that prevent their connection.