A pH-Induced Size Controlled Deposition of Colloidal Ag Nanoparticles on Alumina Support for Catalytic Application

A rational synthetic method of supported metal catalysts has been proposed. Highly dispersed Ag nanoparticles (NPs) with a mean diameter of ca. 10 nm and a narrow size distribution have been prepared in the presence of 3-mercaptopropionic acid (3-MPA) as a protective reagent. The zeta electric potential of the Ag NPs was negatively charged in the region of pH higher than 5 due to the presence of dissociated carboxylate ion (−COO−), which led to the electric repulsion between Ag NPs. On the other hand, the electric charge gradually increased in the region of pH less than 5 owing to the formation of a protonated carboxyl group (−COOH), which induced the hydrogen bonding between Ag NPs. Such pH-triggered assembly dispersion control enables a strong protocol to deposit Ag NPs with different diameters on the positively charged Al2O3 support by electrostatic attraction. The obtained Ag/Al2O3 materials were characterized by means of UV−vis spectra and transmission electron microscopy (TEM), and the catalytic act...