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.