Template-directed synthesis and organization of shaped oxide/phosphate nanoparticles

Oxide nanoparticles (NPs) are typically synthesized from the assembly of atoms, ions or other species by bottom-up methods. Here we report an alternative, top-down approach as a general route to synthesize porous and nonporous oxide/phosphate nanocubes. The method is based on the construction of three-dimensionally ordered macroporous (3DOM) structures via colloidal crystal templating, followed by the spontaneous disassembly of these structures into particulate building blocks assisted by the introduction of amphiphilic surfactants. Syntheses and analyses of nanocubes composed of d-block transition metal (Cr, Mn, Fe, Co, Ni, Cu and Zn) oxides and several mixed oxides are presented to exemplify the generality of the method. Because the NP morphology is defined by the rigid colloidal crystal template, particle composition and characteristics can be readily tuned, leaving much freedom for the development of NP functionality. In addition, the shaped particles retained their geometric relation, namely the face-centered cubic arrangement dictated by the colloidal crystal template, but they could self-reassemble into ordered simple cubic arrays, which provides a unique approach for in situ particle organization. In this paper, the self-reassembly process is also discussed in detail.