Probing the surface reactivity of nanocrystals by the catalytic degradation of organic dyes: the effect of size, surface chemistry and composition

We herein present a comprehensive study on how the catalytic performance and reusability of Au nanocrystals (NCs) are affected by systematic variations of crystal size, surface coating and composition. The reductions of different organic dyes (4-nitrophenol, rhodamine B and methylene blue) by borohydride ions were used as model catalytic reactions. The catalytic performance of the Au NCs ranged between 3.6 to 110 nm was found to be dependent on crystal size, indicating that Au surface atoms have a distinct size-dependent reactivity in this reaction. Similarly, the catalytic performance was found to be strongly dependent on the nature of the coating molecule, obtaining lower catalytic activities for molecules strongly bound to the Au surface. Finally, the catalytic performance was found to be dependent on the chemical composition of the NC (Au, Ag, Pt) and the model dye used as a testing system, with the highest degradation rate found for methylene blue, followed by 4-nitrophenol and rhodamine B. We believe that this study provides a better understanding of the catalytic performance of Au NCs upon controlled modifications of the structural and morphological parameters, and a working environment that can be used to facilitate the selection of the optimum NC size, coating molecule and evaluation system for a particular study of interest.