Mineralogy and thermal analysis of natural pozzolana opal shale with nano-pores

Thermodynamic stability, microvoid distribution and phases transformation of natural pozzolana opal shale (POS) were studied systematically in this work. XRD analysis showed that opal-CT, including microcrystal cristobalite and tridymite, is a major component of POS. DTA and FT-IR indicated that there were many hydroxyl groups and acid sites on the surface of amorphous SiO₂ materials. FE-SEM analysis exhibited amorphous SiO₂ particles (opal-A) covering over stacking sequences microcrystal cristobalite and tridymite. Meanwhile, MIP analysis demonstrated that porosity and pore size distribution of POS remained uniform below 600 °C. Because stable porous microstructure is a key factor in improving photocatalyst activity, POS is suited to preparing highly active supported.