Temperature controlled shape evolution of iron oxide nanostructures in HMTA media

Abstract

This work reported an improved approach to the synthesis of iron oxide nanostructures using iron(III) chloride as the precursor and hexamethylenetetramine (HMTA) as the key auxiliary. A range of iron oxide (alkoxide) nanostructures including nanosheets, hierarchical flowers (assembled by thin nanosheets), mesoporous hollow nanospheres and solid nanospheres were obtained only by altering the reaction temperature from 180 C to 240 C in a single synthetic protocol. Supplementary experiments driven by reaction time were designed in order to further clarify the morphological evolution behaviors of these nanostructures, which discovered that the spherical morphology with the size of about 150-200 nm formed from the inside of micro-scaled flower-like clusters gradually by the condensing and weaving of curled nanosheets, suggesting that the hollow nanospheres were obtained consequently by the further condensation of incompact nanospheres with the assistance of the rearrangement of surfactant micelles, followed by the oriented attachment assembly and Ostwald ripening.

A novel route to the formation of 3D nanoflower-like hierarchical iron oxide nanostructure

“…The formation of 3D nanoflower-like morphology using different synthesis routes other than anodization is reported mostly in EG medium as mentioned earlier. EG is coordinated with the iron precursors to form different hierarchical nanostructures of iron oxides [14,18,39,40]. Therefore, the role of EG in obtaining the 3D nanoflower-like morphology of iron alkoxide through anodization cannot be ignored and is of prime importance, which will be discussed later.…”

“…The nuclei of iron alkoxide start to form at the grain boundaries of the Fe sheet. These nuclei are unstable due to their high surface energy, so with the anodizing time they will tend to lower their surface energy by aggregation in the form of a nanosheet following the Ostwald ripening model [14,16,39]. These nanosheets from different sides meet each other to form an interconnected network structure.…”

“…Jin et al reported the formation of magnetite with 3D nanoflower-like morphology via a solvothermal method in EG medium [18]. Zhao and co-workers have prepared 3D flower-like morphology of iron alkoxide using an EG-mediated solvothermal method [39]. Similarly, Cao et al also demonstrated the formation of Fe 3 O 4 and γ-Fe 2 O 3 hierarchically nanostructured hollow spheres in EG medium via a microwave-assisted hydrothermal method [40].…”