Robust Removal of Ligands from Noble Metal Nanoparticles by Electrochemical Strategies

Ligand-stabilized metal nanoparticles (MNPs) have attracted much attention due to their promising catalytic applications. Fully/partially removing these ligands is critical to realize their proper functions. The traditional ligand-removing approaches (e.g., thermal annealing) focus on the ligand side. Herein, we demonstrate an electrochemical method that pays attention to the MNPs side. By rationally regulating the potential (oxidizing Pt and hydrogen evolution) to construct robust Pt-O or Pt-H covalent bond to displace Pt-ligand coordination bond, the approach could effectively remove almost all kinds of ligands from Pt NPs. For the oxidizing Pt method, up potential > 1.3 V and cycling number (n) > 20 are preferred to completely remove the ligands. The water-soluble ligands (such as poly(vinylpyrrolidone), cetyltrimethylammonium bromide, sodium acetate) can be removed by just one cycle after thoroughly being washed by water to remove the unattached ligands. However, the oil-soluble ligands (such as oleylamine, triphenylphosphine, dodecanethiol) need more cycles (n > 20), which may due to the strong coordination interaction between the ligands and Pt NPs. For the hydrogen evolution method, the generated Pt-H bond during hydrogen evolution reaction (HER, potential < -0.1 V) could break the interaction between the ligands and Pt NPs, resulting in the cleaned surface of Pt. The reverse adsorption of ligands and their further removal demonstrate the reliability of the above two methods. In addition, these methods can be extended to remove the ligands from other noble metals, such as Pd and Au NPs, without altering the particle size and morphology. This work verifies the effectiveness of using electrochemical strategies to remove the ligands. The successful removal of ligands is useful and important in getting the reliable data in many areas which are not limited to electrocatalysis, electrochemical sensing, and surface-enhanced Raman scattering.