# Synthesis and Magnetic and Optical Properties of Novel Fe@ZSM-5 Composites

## TL;DR

This paper explores how creating mesopores in ZSM-5 zeolite affects the properties of iron composites, showing potential for photocatalytic environmental applications.

## Contribution

The study introduces a novel method to control the mesoporosity of ZSM-5 and demonstrates its impact on the magnetic and optical properties of Fe@ZSM-5 composites.

## Key findings

- Mesoporosity in ZSM-5 significantly influences the size and dispersion of iron species.
- Fe@ZSM-5 composites exhibit strong visible-light absorption and magnetic separability.
- Higher mesoporosity leads to smaller iron clusters with reduced magnetization and lower blocking temperatures.

## Abstract

Alkaline treatment in 0.2 and 0.4 M NaOH solutions successfully generated controlled mesoporosity into ZSM-5 (Zeolite Socony Mobil-5) zeolite, resulting in average mesopore diameters of approximately 15 and 25 nm, respectively, while preserving the crystalline structure of the zeolite framework. Parent ZSM-5 and its mesoporous derivatives obtained by desilication were used to prepare (Fe species)@(zeolite matrix) composites. The synthesis was carried out by co-precipitating Fe2+/Fe3+ ions onto both parent and desilicated ZSM-5 matrices under oxygen-free conditions. Comprehensive characterization by X-ray diffraction, scanning electron microscopy, N2 adsorption, vibrating-sample magnetometry, 57Fe Mössbauer spectroscopy, and diffuse reflectance UV–Vis spectroscopy revealed that the degree of introduced mesoporosity dramatically influences the size, dispersion, phase composition, and oxidation state of the iron-containing nanospecies. On purely microporous ZSM-5, relatively large (~15 nm) partially oxidized magnetite nanoparticles are formed predominantly on the external surface, exhibiting superparamagnetism at room temperature (Mₛ = 11 emu/g) and a band gap of 2.12 eV. Increasing mesoporosity leads to progressively smaller and more highly dispersed iron(III) oxo/hydroxo clusters with significantly lower blocking temperatures and reduced magnetization (down to 0.7 emu/g for Fe@ZSM-5_0.4). All composites display strong visible-light absorption confirming their potential as magnetically separable visible-light-driven photocatalysts for environmental remediation.