(377h) Method for Precise Tuning of Shell Thickness on Silica-Encapsulated Gold Core-Shell Nanoparticles and Impact on Catalytic Performance

Precisely tunable silica-encapsulated gold core-shell nanoparticles (Au@SiO₂ CSNPs) were synthesized via an updated seeded encapsulation method. This updated method allows the synthesis of core-shell nanoparticles with different shell thicknesses without influencing core diameter. Reducing the solvent volume resulted in CSNPs with 75.1, 140.8, and 202.6 nm thick shells, following a clear linear relationship. By decoupling the gold core reduction and silica condensation phases, gold core diameters were unaffected by silica growth reaction conditions. This was achieved by reducing CTAB-stabilized gold nanoparticles (CTAB-Au NPs) in bulk, condensing silica shells via the Stöber method in a separate reaction.

When used to catalyze solvent-free benzyl alcohol oxidation, it was found that CSNPs with thicker shells demonstrated both higher catalytic activity and higher selectivity towards the desired aldehyde product. CSNPs with 75.1, 140.8, and 202.6 nm shells reached 11.4%, 13.9%, and 17.0% conversion and 81.4%, 84.2%, and 86.2% selectivity respectively. This surprising trend shows agreement with a growing bulk of research suggesting that mesopores can passively improve catalytic activity by promoting beneficial in-pore orientation of reactants.