Influence of aging on textural properties and symmetry of K-zeolites synthesized via a green route from waste pumice

Abstract

This study not only explores the fabrication of rare zeolites from waste pumice and examines the impact of aging on their porosity and adsorbate uptake but also provides practical insights for waste management and agricultural applications. The use of organic templates was avoided in the synthesis due to their high cost and pollution associated with their calcination. Potassium-exchanged gonnardite (K-Gon) and perlialite were hydrothermally synthesized using KOH. Interestingly, we found that increasing the magnetic stirring duration during synthesis had a significant impact on the products’ surface area and pore volume, leading to an increase from 39 m²/g to 182 m²/g and from 0.11 cm³/g to 0.30 cm³/g, respectively. This improvement resulted in an increased adsorbate uptake at higher pressures. At shorter stirring times, potassium-exchanged gonnardite zeolite with tetragonal symmetry was the most prevalent phase, which differs from the orthorhombic symmetry of Na-rich gonnardites. Additionally, we observed that the product content of perlialite (hexagonal symmetry) increased with longer stirring durations while K⁺ ions decreased. This suggests that increased stirring time can increase the disorderliness of extra framework particles, as seen in perlialite, as opposed to K-Gon. Longer stirring time produces other zeolites with slightly less K but improved textural properties, which can potentially accommodate more water. It is also useful for agricultural purposes, such as keeping soils moist and decontaminated, and as adsorbents for greenhouses’ air conditioning.