Low-temperature wet chemistry synthetic approaches towards ferrites

Ferrites are a broad class of iron-containing oxides that includes spinel ferrites MFe2O4, perovskites MFeO3, and hexagonal ferrites (hexaferrites) such as BaFe12O19. These materials have a wide array of applications owing to their diverse properties: notable instances include catalysis, piezoelectric components, magnetic components, biomedical applications, heterogeneous catalysis and photocatalysis. Given the growing importance of environmentally friendly, low-temperature methodologies to obtain functional materials, there is a growing interest in synthetic approaches which are compatible with the principles of "green chemistry". In this context, wet chemistry represents an attractive choice, and furthermore offers the possibility of scale-up for manufacture of materials in volumes for practical application. Though there is a sizeable amount of literature on the synthesis of ferrites, the most common approaches require treatments at temperatures above 200 degrees C, either as the main synthetic procedure itself (thermal decomposition), or as a post-synthetic step (for example, calcination after sol-gel autocombustion). This review aims at summarising, categorising, classifying and critically discussing the different low-temperature (<200 degrees C), wet chemistry approaches employed in recent years for the synthesis of ferrites. This will include hydrothermal, solvothermal, sonochemical, and microwave methods, with examples taken from literature making reference to the various sub-classes of ferrites.