The preparation of hollow inorganic capsules of defined shape, composition and with tailored properties is of immense scientific and technological interest. This article mainly features recent research progress towards various methods for preparing porous inorganic capsules. By choosing some typical inorganic porous capsules as examples, we present a comprehensive overview of synthetic strategies for inorganic capsules, and some typical organic capsules are also included. The available strategies are broadly categorized into three themes, i.e., hard-templating, soft-templating, and template-free routes, and each includes several well-established methods. The current methods show great success in controlling the size, composition, thickness, permeability and function of the finally achieved porous capsules. Applications of porous capsules in biomedicine, energy resources, environment protection and catalysis are also discussed. It is the intention of this contribution to provide a brief account of these research activities.

The formation of tubular nanostructures normally requires layered, anisotropic, or pseudo-layered crystal structures, while inorganic compounds typically do not possess such structures, inorganic nanotubes thus have been a hot topic in the past decade. In this article, we review recent research activities on nanotubes fabrication and focus on three novel synthetic strategies for generating nanotubes from inorganic materials that do not have a layered structure. Specifically, thermal oxidation method based on gas–solid reaction to porous CuO nanotubes has been successfully established, semiconductor ZnS and Nb₂O₅nanotubes have been prepared by employing sacrificial template strategy based on liquid–solid reaction, and an in situ template method has been developed for the preparation of ZnO taper tubes through a chemical etching reaction. We have described the nanotube formation processes and illustrated the detailed key factors during their growth. The proposed mechanisms are presented for nanotube fabrication and the important pioneering studies are discussed on the rational design and fabrication of functional materials with tubular structures. It is the intention of this contribution to provide a brief account of these research activities.

Hierarchical WO₃ hydrates have been synthesized via an ion exchange method using Na₂WO₄·2H₂O as a precursor. The morphologies and phase structures of WO₃ hydrates can be controlled by tuning the concentration of Na₂WO₄·2H₂O solution. The as-synthesized urchin-like WO₃·0.33H₂O and flower-like WO₃·H₂O possess high specific surface area and numerous adsorption functional groups, such as WO and O–H bonds, on the surface. These characteristics result in excellent adsorption performance for both organic dyes and heavy metal ions from wastewater. The maximum uptake capacities of the urchin-like WO₃·0.33H₂O for methylene blue and Pb²⁺ are 247.3 and 248.9 mg g⁻¹, respectively and those of the flower-like WO₃·H₂O are 117.8 and 315.0 mg g⁻¹, respectively. The formation mechanism of such hierarchical mesoporous urchin-like WO₃·0.33H₂O and adsorption mechanism are studied in this paper.