Hydrothermal Treatment of a Hematite Film Leads to Highly Oriented Faceted Nanostructures with Enhanced Photocurrents

A simple one-pot hydrothermal method is described for converting a dip-coated hematite nanoparticulate film into an array of nanorods with superimposed flowerlike structures suitable for water splitting in photoelectrochemical cells. The hydrothermal treatment of the dip-coated hematite film with FeCl 3 ·6H 2 O and l -arginine enhances the photocurrent by a factor of 2. It has been found that hydrothermal treatment changes the optical properties of the pristine hematite film, but the energy band gap ( E g ) does not change significantly to show some electronic effect. X-ray diffractograms of pristine and hydrothermally modified films reveal evolution of preferential orientations and textures. Electron micrographs show that the particles are more prismatic after modification, with a size of around 40 nm × 200 nm. The X-ray photoelectron spectroscopy valence-band spectra point at a depletion of the spectral intensity near the Fermi energy upon hydrothermal modification. The photocurrent density of the pristine film reached 218 μA/cm 2 after 48 h of hydrothermal treatment, and this increase was found to be due to the higher specific surface area of the modified film and changes in the optical properties of the pristine film after hydrothermal treatment.