It is widely accepted that templated methods produce nanostructures whose morphologies are defined by preformed templates. Inspired by mutualism in biological systems, here we challenge this general impression by developing a mutual-template concept based on the simultaneous growth of template and target materials. This mutual-template strategy is not limited by preformed templates and enables the preparation of nanostructures with unusual morphologies. As a proof-of-concept, this strategy is demonstrated in the controlled growth of unusual silica nanocapsules with abundant morphologies, structures, and functionalities. We further demonstrate the postencapsulation of functional nanoparticles within the inner cavity of open-mouthed nanocapsules, providing a new model system of nanomotors for the fundamental understanding of motion mechanisms. This study paves the way for the preparation of nanostructures with unusual morphologies that are usually difficult to obtain, bringing new opportunities for applications in self-assembly, nanoreactors, nanomotors, and drug delivery.

The etching of colloidal silica by hot water provides a green chemistry method for the preparation of mesoporous silica. Nevertheless, the reaction mechanism of this etching process has not been elucidated and its reproducibility is often questionable, which has hindered its widespread application in the preparation of mesoporous silica materials. Herein, we present a systematic study on the hot-water etching of sol-gel derived silica shells coated on α-FeO particles. Transmission electron microscopy and infrared spectroscopy studies provide substantial evidence that colloidal silica with low hydrolysis and condensation degrees (or aging degrees) is preferentially etched by hot water. More importantly, we show that the aging degree of silica shells, which determines the etching rate, can be precisely tuned by controlling the sol-gel preparation time and the storage time in room-temperature water prior to hot-water etching. These results provide novel insights into the physicochemical properties of sol-gel derived colloidal silica and the mechanistic understanding of the reaction kinetics of silica etching by hot water.

Interest in the preparation of colloidal heterostructures with complex shapes, structures, and spatial compositions is driven by their unique optical, electrical, magnetic, or rheological properties. Despite recent advances, it is highly desired but challenging to further extend the library of heterostructured particles with increased degrees of complexity.Here we report a general step-by-step strategy for controlled preparations of complex heterostructured colloids with various structures and compositions. A local-curvature-controlled emulsion polymerization method is first employed for siteselective growth of secondary polystyrene nanostructures on different nonspherical colloidal seeds. The following functionalization and selective removal steps further increase the degree of particle complexity. We also demonstrate a new type of chemically powered nanomotors based on heterostructured α-Fe 2 O 3 @SiO 2 /Pt particles. This growth strategy is a versatile, general method suitable for the preparation of complex heterostructured particles with tailored structures, compositions, and functionalities, paving the way for their applications for various purposes.