Abstract
In our previous work, a citric acid assisted sol–gel method was developed for preparing monolithic metal oxide aerogels. Such method adopted citric acid as the gelator, which replaced the well-studied proton scavenger propylene oxide. In this work, we have further extended this “organic acid assisted” sol–gel method and investigated the gelation mechanism. Four different organic acids (butanedioic acid, l-malic acid, l-aspartic acid and mercaptosuccinic acid) with an identical main chain but different side groups were used as the gelators for preparing monolithic zirconia aerogels. It was found that complex interactions including covalent bond and coordination bond interactions between organic acids and zirconium ions were vital to give a rigid gel network. After supercritical drying, crystalline zirconia aerogels can be obtained with high surface areas over 330 m2 g−1 and large pore volumes over 3.574 cm3 g−1.
Highlights
The ZrO2 aerogel has attracted lots of interest due to its potential applications as catalyst supports,[1,2] absorbents,[3,4,5] light-weight thermal insulators[6,7] etc
It can be seen that the monolithic appearance of the wet gel can be well reserved in the aerogel
This is due to the fact that the supercritical drying process prevented the pores collapse in the wet gel during the drying
Summary
The ZrO2 aerogel has attracted lots of interest due to its potential applications as catalyst supports,[1,2] absorbents,[3,4,5] light-weight thermal insulators[6,7] etc. The same mechanism worked in the case of LMA and MSA series samples, as the Zr4+ ions would coordinate to –OH and –SH in the side groups (as shown in reaction (5) and (7)), when such –OH and –SH would form hydrogen bond (in reaction (6) and (8)) to extend the network.
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