Synthesis of BEA zeolite from coal fly ash nano-silica extract: application in CO2 adsorption

Abstract

This study demonstrates a circular economy approach to carbon dioxide sorption by re-purposing coal fly ash (CFA) into BEA zeolite using CFA-derived nano-silica and aluminum precursors via hydrothermal synthesis. The XRD patterns, with characteristic peaks at 15° and 37° 2θ, and SEM images both confirmed the complete transformation of the spherical-shaped CFA particles into amorphous nano-silica materials with particle sizes less than 100 nm. The absence of amorphous phases and the formation of high-intensity peaks at 7.8° and 22.8° 2θ further indicated the production of a highly crystalline BEA zeolite, obtained after hydrothermal synthesis durations between 10 and 72 h. The conversion of amorphous nano-silica into BEA zeolites significantly enhanced the surface area from 54 m2/g to 547 m2/g. The as-synthesized BEA zeolites exhibit a spheroidal shape with crystal dimensions ranging from 190 to 450 nm, solely controlled by the molar ratio of H2O/Si during hydrothermal synthesis. CO2 sorption capacity upon the transformation of nano-silica into BEA zeolites rose from 0.91 to 3.24 mmol/g for low-temperature evaluation (≈0 °C, 1.2 bar). The BEA zeolite adsorbent retained structural integrity with only ∼9% performance loss after ten adsorption–desorption cycles. These outcomes highlight CFA-derived BEA zeolite as a robust, scalable, and resource-efficient adsorbent for CO2 capture.