Effect of residual Na+ on the properties of aerogel prepared with sodium silicate via APD

•Na+ reduces the pore volume by alkaline dissolution and blocking mesopores.•The properties of aerogel drop sharply as Na+ content is more than 1.5 wt.%.•Na+ affects the hydrophobicity of aerogel by hindering surface modification.•Na+ does not change the skeleton composition of the silica aerogel. The removal of Na+ in the process of preparing silica aerogel with sodium silicate as the precursor is a very important and costly step. In this study, effects of residual Na+ content (0∼3.0 wt.%) in the precursor on the properties of silica aerogel were investigated. The thermal conductivity, bulk density, porosity and hydrophobic of the aerogel were tested. And the action mechanism of Na+ was discussed, based on the test results of pore structure, microscopic morphology, and chemical structure composition characterized by N2 adsorption-desorption, SEM and FT-IR. The results showed that as the content of residual Na+ increased, the thermal conductivity and density of the aerogel increased, and the porosity and hydrophobicity decreased. It may be the alkaline dissolution effect of Na+ and the agglomerations of Na+ block part of mesopores, but did not change the skeleton composition of the silica aerogels.