Analyzing the reaction conditions for the different sized silver nanoparticles, NaBH4 demonstrated its predominant role
for the synthesis of AgNPs having the size range 5–20 nm (ESI, Fig. S2†). On the other hand, TSC was the predominant
reducing agent for synthesis of AgNPs of range 60–100 nm. For nanoparticles in the size range 25–60 nm, both NaBH4 and TSC may work concurrently to reduce Ag+ and form nanoparticles. By varying the temperature, we controlled the reducing ability of sodium borohydride and TSC and produced the most stable “initial” and “final” sols at 60 C and 90 C, respectively (ESI, Fig. S3†). The co-reduction approach gave a better balance between nucleation and growth of AgNPs and therefore, synthesis of size controlled silver nanoparticles could be achieved.7 Moreover, the size and morphology could be precisely tuned by controlling the reduction rate during the second stage with an optimal pH of 10.5 (ESI, Fig. S4†). Thus, this pH was maintained throughout for synthesis of silver nanoparticles of various sizes.