Effect of Mesoporosity on Structural, Textural, and Optical Characteristics of Fe(III) Ion-Exchanged ZSM-5 Zeolites

This study investigates the influence of mesoporosity, pre-created by alkali etching in ZSM-5 zeolite, on the characteristics of Fe³⁺ ion-exchange and subsequent changes in its textural and optical properties. It is shown that the formed hierarchical porosity facilitates the penetration of hydrated iron complexes into the internal channels. This not only increases the degree of exchange, but also leads to the formation of multinuclear Fe_xO_y clusters and, possibly, to the partial isomorphic replacement of Al³⁺ with Fe³⁺ in the framework. Comprehensive characterization of mesoporous samples (XRD, SEM, N₂ adsorption, UV-Vis) confirms the preservation of the microporous crystal structure of MFI on the one hand, and demonstrates a significant change in the distribution of iron-containing species in mesoporous matrices on the other. The introduction of Fe ions significantly reduces the bandgap energy, shifting the absorption edge into the visible range. The results obtained demonstrate that preliminary mesostructuring is an effective approach for creating hierarchically porous Fe zeolites with great potential for photocatalytic applications.