Removal and Utilization of Capping Agents in Nanocatalysis

Capping agents are frequently used in colloidal synthesis to inhibit nanoparticle overgrowth and aggregation as well as to control the structural characteristics of the resulted nanoparticles in a precise manner. Study of the effect of the residual capping agents on particle surface has unveiled various adverse and favorable behaviors in catalytic applications. In essence, while the capping agents usually act as a physical barrier to restrict the free access of reactants to catalytic nanoparticles, they can also be utilized to promote catalytic performance of nanocrystals. Due to the complexity of these effects, a general survey of capping agents in nanocatalysis is therefore necessary. This short review starts from a brief introduction of common capping agents in nanoparticle synthesis and their adverse impact on heterogeneous catalysis. Next, representative progresses in capping agent removal and surfactant-free synthesis for obtaining surface-clean nanocatalysts are summarized. Lastly, we discuss the recent advance in utilizing the capping agent effect including chiral modification, molecular recognition, adsorption regulation, surface crowding, and charge transfer at the metal–organic interface and so on to improve the catalytic performance of nanocatalysts.