Effect of tetravalent ions dopants and CoO _x surface modification on hematite nanorod array for photoelectrochemical degradation of Orange-II dye

The surface modified tetravalent ions doped hematite nanorod photoanodes has been synthesized by successive hydrothermal and spin coating approaches. The effect of tetravalent ion (Sn, Ti, and Zr) doping and high temperature annealing on to the morphological, structural and photoelectrochemical properties has been investigated. Photoelectrochemical analyses indicate tetravalent doping (Sn, Ti, and Zr) and high-temperature annealing (800 °C) showed higher photocurrent and improved activity towards Orange-II dye degradation, compared to the pristine hematite film. Amongst tetravalent dopants, Zr ⁴⁺ doped hematite can significantly enhance the photocurrent density (1.37 mA cm ⁻² at 1.23 V vs. RHE) as well as the Orange-II dye degradation activity (93% under one sun illumination in 270 min). Kinetic parameters are also investigated by first-order rate equation. Further, Zr–Fe ₂ O ₃ photoanode modified with the appropriate composition of CoO _x and specific structural features demonstrated improvement in photocurrent from 1.6 to 1.78 mA cm ⁻² (at 1.4 V vs. RHE). The efficient charge carrier separation and generated hydroxyl radicals led to enhancements of the Orange-II dye degradation efficiency up to 97% within 270 min. The significant decrease in chemical oxygen demand values suggests the removal of Orange-II dye. This work demonstrates that enhancement in photoelectrochemical activity is due to the combined effect of passivation of surface states and the formation of CoO _x /Zr–Fe ₂ O ₃ heterojunction.