Optimal synthesis of zeolite materials for humidity control from recycled industrial waste: central composite design

Abstract

This article examines the process of optimizing the parameters used in the alkali fusion/hydrothermal synthesis of zeolite materials from solar panel waste glass (SPWG) and sandblasting waste (SW). Central composite design (CCD) was used to assess the influence of SiO₂/Al₂O₃ molar ratio (X1), synthesis temperature (X2) and synthesis duration (X3) on the crystallinity (%) and moisture maximum adsorption capacity. The resulting zeolite materials were also characterized using X-ray diffraction, fourier-transform infrared spectroscopy, Scanning electron microscope, and Brunauer-Emmett-Teller method. Analysis of variance (ANOVA) revealed that all three process variables had a significant effect on the crystallinity and moisture maximum adsorption capacity, and that X3 had the most surprising effects. The optimal parameter set (X 1 = 2.0, X 2 = 120 °C, and X 3 = 48 h) resulted in the highest crystallinity (91.98%) and largest surface area (372.75 m2/g) due to a well-ordered structure with an average pore diameter of 2.11 nm and an overall pore volume of 0.197 cm3/g. As expected, these samples presented the highest 24-h moisture maximum adsorption capacity (66.75 g/m2). These results provide insight into the synthesis of low-cost environmentally-friendly zeolite materials from industrial waste.