Robust Removal of Ligands from Noble Metal Nanoparticles by Electrochemical Strategies

Abstract

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.

Electrooxidation, Size Stability, and Electrocatalytic Activity of 0.9 nm Diameter Gold Nanoclusters Coated with a Weak Stabilizer

“…Whether the ligands are strongly‐attached or weakly‐attached, researchers have developed various treatments to remove stabilizers in order to render the metal surface more active for the application of interest. These treatments include ozone cleaning, thermal treatment, or chemical and electrochemical treatments . Unfortunately, the treatment may change the size of the NCs in addition to removing the stabilizer .…”

“…These treatments include ozone cleaning, [31] thermal treatment, [32] or chemical [33] and electrochemical treatments. [34] Unfortunately, the treatment may change the size of the NCs in addition to removing the stabilizer. [16] NCs may also change their size during the application of interest.…”

Understanding Surface Modulation to Improve the Photo/Electrocatalysts for Water Oxidation/Reduction

“…However, the passivation layer also covers the catalytically active sites where the reactants adsorb and react to generate the fuels at the solid-liquid interface. Thus, the passivation layer degrades the efficiency of photo energy conversion into chemical energy [151][152][153]. Therefore, the introduction of stable catalysts or surface modulation of the passivation layer by incorporation of substitution of elements, doping, and functionalization is needed.…”

Co‐doped Pt Nanowire Networks with Clean Surfaces for Enhanced Oxygen Reduction Reactions

“…[11] Furthermore, the ultrafine nanowires (NWs) have attracted increasing attention due to their inherently efficient transport and diffusion pathways for electroactive species compared with nanoparticles. [12] The synthesis commonly involves the usage of ligands, [13] such as oleylamine (OAm) [14] and polyvinylpyrrolidone (PVP) [15] which can stabilize the reduced nanowires in oil phase. These ligands can strongly bind onto the metal surface, which inhibits the growth kinetics and contributes to the formation of the shape controlled Pt NWs.…”