Fluoride-assisted galvanic replacement synthesis of Ag and Au dendrites on aluminum foil with enhanced SERS and catalytic activities

Although Al has a lower redox potential [Al3+/Al, -1.67 V vs. SHE] than most metallic ions, metal galvanic replacement reactions on pure aluminum foil can be hardly observed because of the existence of the thin layer of aluminum oxide, In this work, we develop a facile, economical and general approach to achieve large-scale production of silver and gold dendrites as well as other metal hierarchical micro/nanostructures (Cu, Pt, Pd, Ni, Co and Zn) on commercial aluminum foil in the presence of NaF or NH4F. Studies of the galvanic replacement reaction by open circuit potential-time (OCP-t) measurements demonstrate that fluoride plays an important role in etching the alumina layer and thus induces the continuous proceeding of the galvanic replacement reaction. The synthesis process is carried out at room temperature and without any templates, surfactants, or special reagents. The obtained silver and gold dendrites show significantly enhanced SERS signals of a self-assembled monolayer of 2-naphthalenethiol and 4-mercaptobenzoic acid, and also could effectively catalyze the reduction reaction of 4-nitrophenol and 2-nitrophenol at room temperature.