Investigating the Multiple Roles of Polyvinylpyrrolidone for a General Methodology of Oxide Encapsulation

Growing oxide shells on seed nanoparticles requires the control of several processes: (a) the nucleation and growth of the shell material; (b) the “wetting” of the shell material on the seeds; and (c) the aggregation of the nanoparticles. These processes are influenced by a number of factors, many of which are related. Without understanding the interdependence of these contributing factors, it is difficult to circumvent problems and achieve rational synthesis. We first did a case study on encapsulating Au nanoparticles with ZnO to understand the multiple roles of polyvinylpyrrolidone (PVP) and their dependence on other factors. We developed a general method for coating ZnO on a variety of seeds, including metals, oxides, polymer nanoparticles, graphene oxide, and carbon nanotube. This method can be further extended to include Fe₃O₄, MnO, Co₂O₃, TiO₂, Eu₂O₃, Tb₂O₃, Gd₂O₃, β-Ni­(OH)₂, ZnS, and CdS as the shell materials. The understanding obtained in this systematic study will aid rational design and synthesis of other core–shell nanostructures.