Hydrophobic micro/mesoporous silica spheres assembled from zeolite precursors in acidic media for aromatics adsorption

The micro/mesoscopic silicas (MMS) were successfully synthesized with a self-assembly approach by employing silicalite-1 zeolite seeds as precursors in acid media. The resulting MMS samples were characterized by X-ray diffraction (XRD), nitrogen adsorption/desorption, n-nonane pre-adsorption and transmission electron microscopy (TEM). After aging for 18 h, the obtained materials exhibit both well-defined low- and high-angle XRD peaks. The XRD results combined with other characterizations confirm that the zeolite precursors, after aging for 18 h, were assembled to hierarchical porous composites, featuring both zeolite-like microporous and mesoporous structures rather than a physical mixture of bulk zeolite and mesoporous solid. It was found that the MMS samples exhibit spherical morphology, with high surface area and large total pore volume. Even with the aging time increasing up to 24 h, the obtained biporous composite MMS-24 still presents high surface area of 536 m² g^-1 and large total pore volume of 0.66 cm³ g^-1. The adsorption of benzene by the hierarchical materials under static and dynamic conditions was also investigated. The results of the adsorption isotherms and isosteric adsorption heat reveal that MMS-24 represents super hydrophobicity and high affinity towards aromatics. The adsorption capacity of benzene on MMS-24 is approximately three times higher than that on silicalite-1 zeolite. As indicated by the adsorption dynamic study, MMS-24 has high tendency towards benzene in the presence of water vapor, retaining high benzene removal efficiency (85%) comparing with that under dry condition.