Enhancing adsorption capacities of low-concentration VOCs under humid conditions using NaY@meso-SiO2 core-shell composite

Y zeolite with high specific surface area and peculiar microporous channels has been regarded as a promising adsorbent in volatile organic compounds (VOCs) control. However, a scalable strategy for improving the hydrophobicity and mass diffusion of Y zeolite to remove VOCs remains a challenge. In this study, we successfully synthesized two NaY@meso-SiO2 core-shell composites with different shell thicknesses by coating NaY zeolite with mesoporous SiO2 (NaY@meso-SiO2-0.8 and NaY@meso-SiO2-1.2), which significantly improved the hydrophobicity of NaY zeolite and diffusion of VOCs into NaY zeolite. The results of XRD, SEM, TEM, FTIR and BET confirmed the successful synthesis of core-shell composites. The adsorption equilibrium experiments showed that coating NaY zeolite with mesoporous SiO2 effectively enhanced the hydrophobicity of NaY zeolite. Under RH = 0, the adsorption capacity of pristine NaY zeolite was the highest; while under RH = 50%, NaY@meso-SiO2 1.2 exhibited stronger adsorption ability and excellent hydrophobicity. The adsorption diffusion indicated that coating NaY zeolite with mesoporous SiO2 remarkably promoted the diffusion of VOCs into composites. Compared with the pristine NaY, core-shell composites showed higher diffusion coefficients and lower diffusion activation energy under RH = 0, particularly NaY@meso-SiO2-1.2. In addition, linear solvation energy relationships (LSERs) revealed that pi-/n-electron pairs interaction became weak and dipolar interactions were enhanced when water was adsorbed on the surface of NaY@meso-SiO2-1.2. Hydrogen bonding decreased when RH level reached 50% and then increased with the increase of RH from 50% to 90%.