Direct thermal decomposition of FeCl3.6H2O in oleic acid forms hematite cube and nano octahedron structure with quasicrystalline and supercell symmetries for enhanced photoelectrochemical functionality

Abstract

The direct formation of hematite nanostructures by the thermal decomposition of precursor salt in the oleic acid is discussed here. The obtained nanostructures show interesting structural properties with the unique presence of quasicrystalline and supercell symmetries. The quasicrystalline symmetry obtained is of 2- fold and 3-fold icosahedral symmetries. HRTEM study of the single nano octahedron each faces reveals different axis of symmetry along with the presence of 2-fold icosahedral quasicrystal. The synthesis route results well distributed hematite nano octahedron, where urea plays a role in controlling its distribution as confirmed by FESEM studies. Next, a mechanism is proposed for how 24 h aged Hematite nano octahedron decays with increased acidity of the reaction medium in the presence of urea? It is found that the Urea deprotonated first and keep the nano octahedron morphology stable depending on the salt to urea molar ratio. Finally, the photoelectrochemical properties of the hematite nano octahedron film is studied, and a photocurrent density of 200 μA/cm2 is obtained for non -Urea mediated one (24 O. A.). From the XRD comparison of both films (24 h and 24 O.A.), it is found that (110) Bragg plane diffracted intensity increases without Urea, which helps in the enhancement of the photocurrent density due to a well-established electronic conductivity of Hematite along (001) Basal plane.