Production of mesoporous and thermally stable silica powder from low grade kaolin based on eco-friendly template free route via acidification of appropriate zeolite compound for removal of cationic dye from wastewater

Abstract

The amorphous silica with the extended surface area was fabricated for the methylene blue (MB) adsorption. In the first step, the zeolite compounds were produced hydrothermally from the transformation of a low grade kaolin, containing quartz by changing NaOH concentration, temperature, and reaction time based on the central composite design method (CCD). In the second step, the mesoporous silica powders were fabricated by the acid treatment of obtained zeolite compounds at 80 °C. Although quartz was deleted in the alkali concentrated solutions, > 4 mol L−1, hydroxysodalite, and cancrinite mixtures were formed at the higher temperatures, and longer reaction times. The acidification of these mixtures led to the formation of silica powders with the unacceptable adsorption yield. The adsorptive performance of silica produced from the powder predominantly containing hydroxysodalite was comparable with those fabricated from the other zeolite compounds. The average pore size, and specific surface area of produced SiO2 were 4.3 nm, and 637 m2 g−1 respectively, which provided a large number of functional groups in the surface of particles, leading to the strong affinity towards MB in the neutral condition with a maximal adsorption capacity of 135 mg g−1. The used adsorbent can be thermally regenerated without significant losing the adsorption efficiency, which is of great importance from engineering view point. The convenient fabrication from an inexpensive resource according to a template-free route plus reusability facilitate the application of obtained silica in the treatment of wastewaters contaminated with the cationic dyes.