TiO₂ Nanorods Synthesized by Hydrothermal Method for Biophotovoltaic Cells

Titanium dioxide (TiO₂) is one of the most important electron acceptor materials in the photoanode of biophotovoltaics devices due to its wide bandgap, good alignment of its conduction band with the lowest unoccupied molecular orbital of the biomolecules studied so far, and its diverse morphology. In this research, TiO₂ nanorods were synthesized by hydrothermal method for their application in a biophotovoltaic device that uses natural protein-chromophore complexes like photosystem-I or bacteriorhodopsin as light absorbers. The nanorod morphology is selected to increase the contact surface between the biomolecules and the photoanode material, in comparison to nanoparticles where the large protein size hinders its penetration inside the nanoporous film. The nanorods were grown on a fluorine doped tin oxide (FTO) substrate reactants using TiCl₄, H₂O, and HCl as the titanium precursor, oxygen source, and inhibitor, respectively. The incubation time, reactants concentration and substrate pre-treatment methods where studied to optimize the material for its application in the biophotovoltaic cells. The synthesized nanorods were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), ultraviolet-visible spectroscopy and fluorescence spectroscopy. The optoelectronic properties and morphology of the nanorods were optimized to use them in the biophotovoltaic devices using poly(3,4-ethylenedioxythiophene)/carbon nanotubes (PEDOT-CNT) cathodes and novel redox mediators.