Silver nanoparticles with an average size ofw15 nm obtained by
reduction by NaBH4 are adsorbed onto the APTMS-functionalized
silica surface by electrostatic interaction to form a thin silver
shell. It is known that alkylamines exist predominantly as positively
charged ReNH3
þ groups at values of pH < 10 [21], and reduction of
Agþ with excess NaBH4 was helpful to forming small silver nanoparticles
with a net negative interfacial charge [22]. Fig. 4 shows the
AFM image of the obtained silver nanoparticles, it can be seen that
the silver nanoparticles are uniform and the approximately diameter
is 15 nm.