Enhanced accessibility of active sites in hierarchical ZSM-5 zeolite for removal of pharmaceutically active substances: Adsorption and microcalorimetric study

Abstract

The possibility of removal of pharmaceutically active substances, atenolol, diclofenac sodium and salicylic acid, from water solutions using hierarchical form of zeolite ZSM-5 is investigated in this paper. Mesopore formation in ZSM-5 was achieved using alkaline treatment. Zeolitic samples were characterized by X-ray diffraction, low temperature nitrogen adsorption, solid-state 27A1 MAS NMR, point of zero charge determination and microcalorimetry - volumetry of ammonia adsorption. Adsorption isotherms of pharmaceutically active substances were obtained and liquid calorimetric experiments were used to evaluate the strength of interactions. The capacity for salicylic acid adsorption measured for the mesoporous sample did not significantly differ from the results obtained for the parent ZSM-5. However, in the case of atenolol and diclofenac sodium, mesoporous ZSM-5 exhibited increased adsorption capacities. Calorimetric data revealed higher heats of atenolol adsorption on mesoporous ZSM-5, compared to the parent. Based on similar acidity and surface charge determined for the two samples, our results show that geometry and dimensions of both zeolite pores and adsorbing molecules play a crucial role in the studied adsorption processes and that tailoring ZSM-5 porosity by desilication can be used to expand its applicability in depollution processes.