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Control of Pore Size of High Purity Nanoporous Silica Formed from Volcanic Ash Deposit Shirasu

High purity nanoporous silica was fabricated using Shirasu volcanic ash as a starting material. The starting materials were placed into a platinum crucible and were melted at 1400°C. A mother glass was formed by quenching the melt in pure water. Leaching was performed by immersing the mother glass into an HCl solution. Nonsilica phases formed by phase separation in the mother glass were leached out with acid solution. The obtained porous silica was more than 99% pure and had pore size smaller than 2 nm. In order to control the pore size, post heat treatment was performed. The pore size could be controlled from 3.1 to 21.7 nm by changing the post treatment temperature.