Synthesis of Triangular Silver Nanoprisms by Stepwise Reduction of Sodium Borohydride and Trisodium Citrate

Triangular silver nanoprisms were synthesized by stepwise reduction of silver nitrate with sodium borohydride (NaBH4) and trisodium citrate. In this approach, first small spherical silver nanoparticles were prepared by the rapid reduction of the precursor with NaBH4 at ice-bath temperature. After being heated to 70 degrees C, further reduction of the precursor contributed to the formation of additional small spherical silver nanoparticles attributed to the catalysis effect of the silver particles formed at the low temperature. The residual precursor after the formation of the small spherical silver nanoparticles is necessary to promote the dissolution of the small nanoparticles and their transformation into the triangular nanoprisms. After consumption of most of the precursor, the nanoprisms became more uniform in shape and size driven by the Ostwald ripening. The triangular nanoprisms prepared by such an approach are expected to be potentially useful in biolabeling since the citrate ligand on the nanoprism surface is ready to be replaced by biomolecules.