Subcritical Water Treatment: A Simple Method to Prepare Porous Glass with a Core–Shell Structure

This paper presents a subcritical water treatment method for preparing porous glass with a core–shell structure from ordinary soda-lime glass beads in one step. In this method, reactive subcritical water rather than any other chemical additive was utilized to selectively corrode the glass and mainly leach the alkali ions from the glass. The core–shell structure has been characterized by scanning electron microscope observation. The mesoporous structure of the porous glass beads has been confirmed by a nitrogen adsorption–desorption measurement. The treated alkali–lime–silicate glass beads have mesopores with a narrow distribution ranging around 4 nm, and a uniform nanoflake array on the surface. The shell structure can be easily tailored by changing the treatment temperature and water flow rate. A possible mechanism of a corrosion-ion immigrating-recondensation pattern was hypothesized to explain the formation of the core–shell porous structure.