TD-DFTB Investigation and Deposition of Au onto Ag Nanocubes for Enhanced Stability and Sensing

Silver nanocubes are appealing to scientists and significant in technology due to their optical, electric, and chemical properties. However, there are limitations to chemically modifying silver nanocubes and they are susceptible to oxidation leading to the loss of their shape, stability, and quality. A solution is to deposit a metal like gold on silver nanocubes that is resistant to oxidation and chemically modifiable. This prevents silver nanocube deterioration, ensuring their stability and modification potential. Unfortunately controlling the synthetic parameters that shape gold-coated silver nanocubes is difficult. The galvanic replacement reaction between gold and silver can erode, hollow, or disintegrate silver nanocubes. We conducted several tests to create a viable and reproducible gold-coated silver nanocube synthesis process. This research employed both thermodynamic and kinetic control to prevent galvanic replacement reaction by decreasing the gold precursor's reduction potential with potassium iodide and adjusting the pH to regulate the reduction power of the reducing agent. We also evaluated various experimental settings and parameters vital to the synthesis. The refractive index sensing potential of gold-coated silver nanocubes was assessed and chemically treated with MUTAB ((11-Mercaptoundecyl)-N, N, N-trimethylammonium bromide). The Time dependent density theory functional (TD-DFTB) computational methodology was used to better understand the synthetic process and the atomic system, focusing on gold and silver electronic interactions and the effects of Iodide (I^-), Chlorine (Cl^-), and Sulphite ions (SO₃^2-) on the galvanic replacement reaction, nanostructure geometry and stability. Overall, this study expands on gold-coated silver nanocube research. It gives more insights on how gold-coated silver nanocubes are synthesized, maintains their shape, improves stability, and functionality.