Confined Nucleation and Growth of PdO Nanocrystals in a Seed-Free Solution inside Hollow Nanoreactor

This paper reports a novel and adaptable hollow nanoreactor system containing a solution of cucurbituril (CB) inside a silica nanoparticle (CB@<i>h</i>-SiO<sub>2</sub>) which enables the nucleation and formation of nanocrystals (NCs) to be confined at the seed-free interior solution inside the cavity. The above nanospace confinement strategy restricted the volume of medium available for NC formation to the solution inside the cavity to a few tens of nanometers in size and allowed homogeneous NC nucleation to be examined. Harboring of CB@<i>h</i>-SiO<sub>2</sub> in a Pd<sup>2+</sup> complex solution confined the nucleation and formation of PdO NCs to the well-isolated nanosized cavity protected by the silica nanoshell, allowing the convoluted formation of clustered PdO NCs to be thoroughly examined. The corresponding temporal investigation indicated that PdO NC clusters evolved via a distinct pathway combining dendritic growth on early nucleated seed NCs and attachment of small intermediate clusters. In addition, the explored strategy was used to fabricate a recyclable nanocatalyst system for selective catalytic oxidation of cinammyl alcohols, featuring a cavity-included Fe<sub>3</sub>O<sub>4</sub>/PdO nanocomposite.