Templated Synthesis of Porous Capsules with a Controllable Surface Morphology and their Application as Gas Sensors

Porous capsules composed of hematite, silica, and hematite–silica composites are prepared by a templated synthesis method. Polyelectrolyte multilayer‐coated particles (PEMPs) are used to synthesize goethite nanocrystals and the resulting goethite‐nanocrystal‐embedded PEMPs (PEMP–goethite) are then used as templates to form porous capsules. The surface morphology and surface area of the porous capsules can be controlled by the size of the PEMP–goethite template, which is determined by the extent of growth of the goethite nanocrystals. By controlling the surface morphology and area, it is also possible to tune the sensitivity of the hematite capsules for use as gas‐sensing materials. This surfactant‐free approach is also used to synthesize silica and silica‐based composite capsules with a controllable porous shell thickness. This straightforward approach can also be extended to the synthesis of other porous capsules or particles with a controllable surface morphology.