Core-shell deAlY@SiO2 composite: A superior adsorbent for toluene capture under humidity condition

Abstract

Y zeolite has been regarded as an effective adsorbent in removal of volatile organic compounds (VOCs). However, the low Si/Al ratio causes Y zeolite to preferentially adsorb water when dealing with wet VOCs, which limits its practical application. In present work, Y zeolite was first dealuminated treated by steaming and acid etching, and then the obtained deAlY was used as cores to prepare deAlY@nSiO2 core–shell composites. The shell layer thickness in the as-prepared core–shell composites was adjusted by controlling the hydrolysis of tetraethoxysilane (TEOS). The Si-species yielded from the hydrolysis of TEOS not only fabricated the mesopore shell directed by CTA+, but also entered the zeolite framework by polycondensation with the adjacent hydroxyl (silicon hydroxyl of (SiO)3Si(OH) species or aluminum hydroxyl of penta-coordinated aluminum caused by steaming and acid etching) in the defect sites of the core deAlY. During the adsorption of dry toluene, the as-synthesized composite displayed an adsorption capacity superior to mesopore SiO2 while inferior to deAlY. When toluene and water molecules competed for the adsorption sites, the core–shell composite preferred to adsorb the former because of the greatly reduced sensitivity to the presence of water vapor. Under 55 % and 83 % relative humidity, the core–shell deAlY@nSiO2 (n < 1.5) respectively had 4.2 and 9.0 times higher toluene adsorption than the deAlY. The mesopores in the SiO2 shell was conducive to a fast mass transfer, the high hydrophobic surfaces (internal and external) resulted from reduced hydroxyl content, elevated framework Si/Al ratio and constructed SiO2 shell, contributed to shielding water, which promoted toluene in the wet VOCs to be adsorbed efficiently by the deAlY zeolite core.