Controlled synthesis, growth mechanism and optical properties of FeWO4 hierarchical microstructures

Abstract

Monoclinic ferrous tungstate (FeWO₄) microcrystals with hierarchical nano/microstructures have been selectively synthesized via a facile hydrothermal process in the presence of ethylenediamine tetraacetic acid disodium salt (Na₂EDTA) and hexamethylenetetramine (HMT). HMT played triple roles as the reducing agent, alkaline source, and crystal growth modifier, while Na₂EDTA served as the chelating reagent and structure-directing agent. The appropriate conditions for synthesis of multilayer flower-like FeWO₄ were 200 °C and 8 h with the concentrations of Na₂EDTA and HMT at 0.03 mol L⁻¹ and 0.025 mol L⁻¹, respectively. The morphology of FeWO₄ showed dramatic changes from a bulky amorphous crystal to multilayer hexangular microcrystals with increasing Na₂EDTA concentration, while increasing HMT concentration would transform the hexagonal structure to a sixfold symmetry architecture and the aspect ratio of symmetry axis decreased gradually. Ostwald ripening and the self-assembled process was proposed for the possible formation mechanism. The photoluminescence (PL) intensity of the multilayer FeWO₄ microcrystals was higher than that of other FeWO₄ structures. Magnetic measurement of hexangular FeWO₄ microcrystals showed a small ferromagnetic ordering at low temperature. Furthermore, this work may open novel routes to the chelating reagent-assisted synthesis of hierarchical architectures with various morphologies.