The type-II n-n inorganic/organic nano-heterojunction of Ti3+ self-doped TiO2 nanorods and conjugated co-polymers for photoelectrochemical water splitting and photocatalytic dye degradation

In this article, we have reported the synthesis of two organic semiconductors which are anthraquinone and benzothia/selenadiazole-based pi-conjugated D-A1-D-A2 (D-donor, A-acceptor) type co-polymers. We have coupled these organic semiconductors with the Ti3+ self-doped TiO2 nanorods (Ti3+/TiO2 NRs)-grown on the fluorine-doped fin oxide-coated glass substrate-to get type-II n-n inorganic/organic nano-heterostructures (NHs). Ti3+ self-doping effectively produces oxygen vacancies which, in turn, incorporates many sub-bandgap states in TiO2-making them visible-light active. The NHs electrodes acting as the photo-anodes initiate water oxidation under the visible-light illumination. The NHs not only boost the visible-light absorbance but also owing to the advantageous type-II band alignments, expedite better delocalization and faster transportation of the photogenerated carriers. The NHs comprising of benzothiadiazole (TP1) have been found exhibiting better photoelectrochemical performances than the Ti3+/TiO2 NRs as well as the NHs comprising of benzoselenadiazole (TP2). The saturated photocurrent densities offered by the TP1 and TP2 NHs electrodes at 1 V vs Ag/AgCl are 0.50 mA/cm(2) and 0.30 mA/cm(2), respectively, signifying almost 466.7% and 233.3% increments over the photo-current density shown by the Ti3+/TiO2 NRs electrode at 1 V vs Ag/AgCl. As far as the overall photocatalytic activities are concerned, the TP1 NHs thin film has shown the best performance. The photocatalytic efficiency for both of the NHs thin films substantially augmented in the presence of 1 mM H2SO4. This phenomenon is attributable to the photochemical formation of H2O2 because of the structural uniqueness of the polymers. Besides, experiments with the electron and hole scavengers admit the photocatalytic reactions are mostly dominated by electron mediated routes for both of the NHs. The photogenerated electrons produce (OH)-O-center dot radicals which govern the holistic degradation mechanism.