Bioinspired Synthesis of Monolithic and Layered Aerogels

Abstract

Aerogels are the least dense and most porous materials known to man, with potential applications from lightweight superinsulators to smart energy materials. To date their use has been seriously hampered by their synthesis methods, which are laborious and expensive. Taking inspiration from the life cycle of the damselfly, a novel ambient pressure-drying approach is demonstrated in which instead of employing low-surface-tension organic solvents to prevent pore collapse during drying, sodium bicarbonate solution is used to generate pore-supporting carbon dioxide in situ, significantly reducing energy, time, and cost in aerogel production. The generic applicability of this readily scalable new approach is demonstrated through the production of granules, monoliths, and layered solids with a number of precursor materials.

Morphology control of nickel nanoparticles prepared in situ within silica aerogels produced by novel ambient pressure drying

“…As stated above, FT-IR spectra show the presence of both NH 4 + and HCO 3 − ions in the wet gel, but they disappear upon drying. The absence of any signal from bicarbonate in the dried aerogel indicates that the drying process leads to decomposition and elimination of this species, supporting the hypothesis for an aerogel drying mechanism analogous to that proposed by Han et al 9 SEM micrographs showing the microstructure of silica aerogels synthesized at different ammonium bicarbonate concentrations are shown in Fig. 4.…”

“…An almost identical variation in average pore size from 2.7 to 6.1 nm is also observed. Based on the mechanism of aerogel formation through the generation of pore-supporting gases within the wet gel, proposed by Han et al 9 , these results indicate that increasing the volume of pore-supporting gas www.nature.com/scientificreports/ within the wet gel leads directly to a larger pore size in the resultant aerogel and a resultant increase in specific surface area. The linear relationship between the concentration of ammonium bicarbonate and average pore size/ specific surface area above 10 wt.% concentration indicates that it is straightforward to tailor the aerogel pores for specific applications through an appropriate choice of precursor concentration.…”

“…Silica aerogels with specific surface areas of up to 530 m 2 g −1 have been produced by a novel ambient pressure drying technique modified from that reported by Han et al 9 in which a bicarbonate solution is fully decomposed with the application of heat, producing pore supporting gas within the body of the wet gel and preventing collapse during the drying process without leaving any residue. This has significant advantage over the original technique which leaves salt within the aerogel requiring washing for removal to avoid degradation of desirable properties such as ultra-low density.…”

“…Practical application of aerogels has, however, been limited by high materials costs and laborious methods for drying. These issues have been solved only recently by the development of a low-cost ambient pressure drying (APD) approach 9 for aerogel production by Han and co-workers. In this method the reaction of sodium bicarbonate with HCl, generated from tetramethylchlorosilane (TMCS), was used to generate pore-supporting carbon dioxide within the wet gel during the drying process, so avoiding the need for low surface tension solvents.…”

“…In addition, in this work, we have modified the APD approach of Han et al 9 by employing the thermal decomposition of ammonium bicarbonate to generate pore-supporting gases (NH 3 and CO 2 ) within the wet gel. This approach has significant advantages over the previous method since it eliminates the initial "pre-drying" stage and no salts are produced, removing the need for a washing step to produce a pure silica aerogel.…”