Preparation of hierarchically porous diatomite/MFI-type zeolite composites and their performance for benzene adsorption: The effects of desilication

Abstract

Hierarchically porous diatomite/MFI-type zeolite composites were prepared by transforming the natural diatomaceous silica into MFI-type zeolite by a vapor-phase transport method, followed by a desilication treatment. The morphology and macroporosity of the diatomite were well preserved in the parent diatomite/MFI-type zeolite composite (Dt/Z). Treatment of Dt/Z by desilication in aqueous 0.2M NaOH solution at 60°C for 1h resulted in a mesopore size distribution centered at approximately 7nm, without significantly altering the macroporosity and microporosity of the resulting composite. Further desilication treatment (10h) broadened the mesopore size distribution, whereas the macropores sourced from the diatomite support were significantly damaged and a fraction of the micropores was narrowed to approximately 0.49nm. Under the optimal desilication condition (1h), the desilication-treated Dt/Z sample (Dt/Z-A1h) exhibited a higher adsorption capacity, better affinity, and faster adsorption kinetics toward benzene than the parent Dt/Z, as evaluated via a gravimetric method using an Intelligent Gravimetric Analyzer. The excellent benzene adsorption performance of Dt/Z-A1h was attributed both to the increase in porosity and the formation of terminal silanol groups on the surface of newly developed pores after the desilication treatment.