Unusual loading-dependent sintering-resistant properties of gold nanoparticles supported within extra-large mesopores

Unexpected, excellent antisintering property of highly loaded AuNPs is observed when extra-large mesoporous silica EP-FDU-12 (cage size >25 nm) is used as the supports. The average particle size of the entrapped AuNPs after 550 C calcination approaches 25.6 ± 5.2 nm at the gold loading amount of 5.0 wt %, but it greatly reduces into only 5.6 ± 1.2 nm as the metal loading reaches up to 26.1 wt %. It is demonstrated that the unique three-dimensional porous structure of EP-FDU-12 makes particle-migration difficult to occur and thus prevents direct particle-particle aggregation. This further allows two or more AuNPs to be encapsulated in every extra-large cage at high particle concentrations (10-35 wt %), which enables interparticle interactions via significant overlapping of the diffusion-spheres of AuNPs. As a result, atom-migration via vapor from cage to cage is largely shut off and local vapor-particle equilibrium within each cage is possible, leading to a successful stable AuNPs/mesoporous silica system.