CO₂ adsorption on zeolite 13X modified with hydrophobic octadecyltrimethoxysilane for indoor application

Hydrophobic-coated zeolite 13X (HZ) with octadecyltrimethoxysilane (ODTMS) exhibits a higher humidity resistance and CO₂-adsorption capacity than pristine zeolite 13X in indoor-simulating low–CO₂–concentration conditions. The hydrophobic coating modifies the surface characteristics and adsorption tendency of CO₂ and H₂O, and these changes affect the gas selectivity for adsorption. Characteristic analysis (BET, TGA, and DVS) confirmed the rationality behind the use of zeolite@20 wt%ODTMS (HZ-2) for optimal loading of the hydrophobic coating under other experimental conditions. CO₂ and moisture adsorption capacities of HZ-2 decreased by 15% (from 4.0 mmolCO₂/g to 3.4 mmolCO₂/g) to 44.1% (from 5.5 mmolH₂O/g to 3.3 mmolH₂O/g) under pure-gas conditions, respectively. The moisture resistance developed by the hydrophobic coating improves the CO₂ selectivity in ambient-air conditions; this was tested in an indoor-condition-simulating chamber. The CO₂-capture performance of HZ-2 increased by 33.3% (from 0.3 mmolCO₂/g to 0.4 mmolCO₂/g) and the moisture-adsorption capacity decreased by 41.6% (from 3.3 mmolH₂O/g to 1.9 mmolH₂O/g). Furthermore, the CO₂ gas selectivity of hydrophobic coated zeolite increased by 4.1 times. This modified synthesis provides a broader perspective on adsorbents for the utilization of CO₂-capture in indoor conditions.