Ligand-Assisted Phase Engineering of Nanomaterials

Conspectus The synthesis of monodisperse colloidal nanomaterialswith well-definedstructures is important for both fundamental research and practicalapplication. To achieve it, wet-chemical methods with the usage ofvarious ligands have been extensively explored to finely control thestructure of nanomaterials. During the synthesis, ligands cap thesurface and thus modulate the size, shape, and stability of nanomaterialsin solvents. Besides these widely investigated roles of ligands, ithas been recently discovered that ligands can affect the phase ofnanomaterials, i.e., their atomic arrangement, providing an effectivestrategy to realize the phase engineering of nanomaterials (PEN) byselecting appropriate ligands. Nanomaterials normally exist in thephases that are thermodynamically stable in their bulk states. Previousstudies have shown that under high temperature or high pressure, nanomaterialscan exist in unconventional phases which are unattainable in the bulks.Importantly, nanomaterials with unconventional phases exhibit uniqueproperties and functions different from conventional-phase ones. Consequently,it is feasible to utilize the PEN to tune the physicochemical propertiesand application performance of nanomaterials. During wet-chemicalsynthesis, ligands binding to the surface of nanomaterials can modifytheir surface energy, which could significantly affect the Gibbs freeenergy of nanomaterials and thus determine the stability of differentphases, making it possible to obtain nanomaterials with unconventionalphases at mild reaction conditions. For instance, a series of Au nanomaterialswith unconventional hexagonal phases have been prepared with the assistanceof oleylamine. Therefore, the rational design and selection of differentligands and deep understanding of their effect on the phase of nanomaterialswould significantly accelerate the development of PEN and the discoveryof novel functional nanomaterials for diverse applications. In this Account, we briefly summarize the recent progress in ligand-assistedPEN, elaborating the important roles of different ligands in the directsynthesis of nanomaterials with unconventional crystal phases andamorphous phase as well as the phase transformation of nanomaterials.We first introduce the background of this research topic, highlightingthe concept of PEN and why ligands can modulate the phase of nanomaterials.Then we discuss the usage of four kinds of ligands, i.e., amines,fatty acids, sulfur-containing ligands, and phosphorus-containingligands, in phase engineering of different nanomaterials, especiallymetal, metal chalcogenide, and metal oxide nanomaterials. Finally,we provide our personal views of the challenges and future promisingresearch directions in this exciting field.

Automated summary

The rational design and selection of ligands can modulate the phase of nanomaterials, leading to the development of phase engineering of nanomaterials (PEN). Ligands can affect the stability of different phases by modifying the surface energy of nanomaterials during wet-chemical synthesis. The use of appropriate ligands enables the synthesis of nanomaterials with unconventional phases under mild reaction conditions.