Mechanistic Study of Shape Evolution of Silver Nanoprisms in The Presence of KSCN

Silver nanoprisms can be etched and transformed into silver nanodiscs in the presence of SCN- ions. However, the blue-shifts of SPR bands of silver colloids abnormally depend on the concentrations of SCN- ions; for example, the values of blue-shifts in this study were 40, 250, and 100 nm in the presence of 10(-4), 3 x 10(-4), and 3 x 10(-3) M SCN-, respectively. Blue-shifts of SPR bands reached the maxima, and two isosbestic points were found in the time-course spectra in the presence of KSCN within the so-called critical concentration range, at approximately 3 x 10-4 to 5 x 10(-4) M. These two isosbestic points indicate that silver nanoprisms were not etched gradually in the presence of a critical concentration range of KSCN, but transformed into nanodiscs directly and immediately without forming blunt intermediates. Time-course TEM images of silver nanostructures, which were protected by the modification of a thin layer of HS(CH2)(15)CO2H (MBA) on the surface of the nanoparticles, were recorded to verify the mechanisms. The time-course TEM images show that not all of the silver nanoprisms converted into nanodiscs immediately after the addition of the critical concentration range of KSCN; some of them remained unchanged for different periods and transformed into nanodiscs directly after those periods. The percentages of silver nanoprisms decreased with increasing time after the addition of KSCN within the critical concentration range. The percentage decrease with time fits a single exponential decay function. The decay time of silver nanoprisms in the presence of KSCN within the critical concentration range is approximately 3.2 +/- 0.5 min, which is consistent with the decay time of the peak intensities, approximately 3.6 +/- 0.8 min, of a dipolar SPR band at 668 nm in the time-course UV-vis spectra.