Ultra-high surface area nano-porous silica from expanded perlite: Formation and characterization

Abstract Ultra-high surface area silica, UHSAS (N2 BET surface area:>700 m2 g−1) was obtained from expanded perlite (EP) by a two-step process. In the first step, a hydrothermal process using aqueous sodium hydroxide (at 70 °C for 24 h) was employed to convert EP into an ordered intermediate zeolitic phase. The materials and the process dynamics were examined by various analytical techniques to elucidate the material transformation mechanism involved and to optimize the silica surface area. The structural details of conversion of EP to high surface silica has been identified by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Solid State Nuclear Magnetic Resonance (SSNMR). These analyses have confirmed that the conversion includes an intermediate zeolite phase, which is predominantly NaP1 type zeolite. In the next stage, this intermediate NaP1 type zeolite was converted to amorphous high surface-area silica by hydrochloric acid treatment. Amorphous high-surface area silica was also recovered from the supernatant solution obtained from hydrothermal process by hydrochloric acid treatment. The overall process of silica extraction from EP was optimized to achieve the UHSAS products.