Hollow-structured materials show promise in thermal insulation because the shells encapsulating gaseous voids can interrupt heat transport pathways. Here, we present two low-cost routes to fabricate hollow silica nanoshells, via gas-phase and liquid-phase methods. The gas-phase synthesis method generates hollow shells by a droplet surface precipitation mechanism in a flame aerosol reactor. The liquid-phase synthesis route forms hollow shells by removal of a carbon template, which is produced by hydrothermal reaction of glucose. Both approaches (gas- and liquid-phase) provide hollow silica with amorphous structure, low thermal conductivity (0.023 and 0.026 W m−1 K−1), small particle size (442 and 383 nm), thin shell (35 and 36 nm), and low density (0.015 and 0.033 g cm−3). We employed high shear mechanical mixing to fabricate hollow silica-fiberglass composite ceramics. The resulting three-dimensional network provides the ceramics with robust mechanical elasticity and fire-retardancy while maintaining low thermal conductivity, dramatically outperforming an analogous material using commercial silica gel in place of the hollow nanoshells. Our findings provide two practical routes to synthesize hollow silica, either of which can be used to manufacture a class of hollow shell-fiber nanocomposite soft ceramics for energy-saving applications.

Mesoporous silica is a versatile material for energy, environmental, and medical applications. Here, for the first time, we report a flame aerosol synthesis method for a class of mesoporous silica with hollow structure and specific surface area exceeding 1000 m²  g^-1 . We show its superior performance in water purification, as a drug carrier, and in thermal insulation. Moreover, we propose a general route to produce mesoporous nanoshell-supported nanocatalysts by in situ decoration with active nanoclusters, including noble metal (Pt/SiO₂ ), transition metal (Ni/SiO₂ ), metal oxide (CrO₃ /SiO₂ ), and alumina support (Co/Al₂ O₃ ). As a prototypical application, we perform dry reforming of methane using Ni/SiO₂ , achieving constant 97 % CH₄ and CO₂ conversions for more than 200 hours, dramatically outperforming an MCM-41 supported Ni catalyst. This work provides a scalable strategy to produce mesoporous nanoshells and proposes an in situ functionalization mechanism to design and produce flexible catalysts for many reactions.