The extinction spectra and TEM images show that the silver nanoprisms would undergo shape transformation in the presence of 5 × 10 -6 M bromide ions. In this study, HS(CH 2 ) 15 CO 2 H (MHA) were introduced to modify the surface of silver nanoprisms. The MHA-modified silver nanoprisms can prevent the shape transformation in the presence of bromide ions with a concentration as high as 0.1 M. Furthermore, it was found that the etching process on the unmodified silver nanoprisms caused by the bromide ions can be stopped immediately by adding MHA into the colloid solution. However, the rate of the etching process in the initial stage was too fast to be stopped by adding MHA to control the silver colloid with the desired SPR wavelength. PVP-modified silver nanoprisms cannot prevent the shape evolution in high concentration bromide ions, such as 10 -3 M, but can slow down the etching rate. The silver nanostructures with the desired SPR wavelength can be obtained by the following simple method: KBr was added into the PVP-modified silver nanoprism colloid to initiate the shape evolution, and after a period of time, MHA was added to terminate the etching reaction. The PVP-KBr-MHA treated silver nanostructures with various colors produced by this simple method not only have long-term stability stored at room temperature but also can prevent shape transformation in highly concentrated chloride solutions.

Herein, we find that the surface plasmon resonance (SPR) spectra of silver nanoprisms in the presence of halide ions change gradually with reaction time. The changes in the spectra correspond to the shape transformation of silver nanoprisms. There are threshold concentrations of halide ions that initiate the shape-transformation reaction. The threshold concentrations for Cl(-), Br(-), and I(-) are about 3x10(-4) M, 1x10(-6) M, and 1.5x10(-6) M, respectively. Any concentrations of the added halide ions above these thresholds can eventually etch the silver nanoprisms into nanodisks if the reaction time is long enough. The higher the concentration of the halide ions, the higher the etching rate will be. The kinetics of the shape transformation of the silver nanoprisms can be studied by recording their time-dependent surface plasmon resonance (SPR) spectra on a commercial UV/Vis-NIR spectrometer. The peak positions of in-plane dipole SPR bands of silver colloids in the presence of chloride and bromide ions can be fitted very well with the biexponential functions. We propose that the fast components of the biexponential behaviors should correlate to the truncating effect on the corners of silver nanoprisms, and the slow component should correlate to the redeposition of the truncated residues onto the basal plane of the nanoplates.