Alkali metal ion induced cube shaped mesoporous hematite particles for improved magnetic properties and efficient degradation of water pollutants

Abstract

Mesoporous cube shaped hematite (α-Fe₂O₃) particles were prepared using FeCl₃ as an Fe³⁺ precursor and 1-butyl-3-methylimidazolium bromide (ionic liquid) as a soft template in the presence of different alkali metal (lithium, sodium and potassium) acetates, under hydrothermal conditions at 150 °C/4 h followed by calcination at 350 °C. The formation of the α-Fe₂O₃ phase in the synthesized samples was confirmed by XRD, FTIR and Raman spectroscopy. Unlike K⁺ ions, intercalation of Li⁺ and Na⁺ ions occurred in α-Fe₂O₃ crystal layers as evidenced by XRD and Raman spectroscopy. Electron microscopy (FESEM and TEM) images showed the formation of cube-like particles of different sizes in the presence of Li⁺, Na⁺ and K⁺ ions. The mesoporosity of the products was confirmed by N₂ adsorption–desorption studies, while their optical properties were analyzed by UV-DRS. Na⁺ ion intercalated α-Fe₂O₃ microcubes showed improved coercivity (5.7 kOe) due to increased strain in crystals, and shape and magnetocrystalline anisotropy. Temperature dependent magnetization of the samples confirmed the existence of Morin temperature in the range of 199–260 K. Catalytic degradation of methylene blue (MB), a toxic water pollutant, was studied using the synthesized products via a heterogeneous photo-Fenton process. The degradation products were traced by electrospray ionization-mass spectrometry (ESI-MS). The α-Fe₂O₃ microcubes obtained in the presence of Na⁺ ions exhibited a more efficient degradation of MB to non-toxic open chain products.