Synergetic Effect of Ti³⁺ and Oxygen Doping on Enhancing Photoelectrochemical and Photocatalytic Properties of TiO₂/g-C₃N₄ Heterojunctions

Abstract

To improve the utilization of visible light and reduce photogenerated electron/hole recombination, Ti³⁺ self-doped TiO₂/oxygen-doped graphitic carbon nitride (Ti³⁺-TiO₂/O-g-C₃N₄) heterojunctions were prepared via hydrothermal treatment of a mixture of g-C₃N₄ and titanium oxohydride sol obtained from the reaction of TiH₂ with H₂O₂. In this way, exfoliated O-g-C₃N₄ and Ti³⁺-TiO₂ nanoparticles were obtained. Simultaneously, strong bonding was formed between Ti³⁺-TiO₂ nanoparticles and exfoliated O-g-C₃N₄ during the hydrothermal process. Charge transfer and recombination processes were characterized by transient photocurrent responses, electrochemical impedance test, and photoluminescence spectroscopy. The photocatalytic performances were investigated through rhodamine B degradation test under an irradiation source based on 30 W cold visible-light-emitting diode. The highest visible-light photoelectrochemical and photocatalytic activities were observed from the heterojunction with 1:2 mass ratio of Ti³⁺-TiO₂ to O-g-C₃N₄. The photodegradation reaction rate constant based on this heterojuction is 0.0356 min^-1, which is 3.87 and 4.56 times higher than those of pristine Ti³⁺-TiO₂ and pure g-C₃N₄, respectively. The remarkably high photoelectrochemical and photocatalytic performances of the heterojunctions are mainly attributed to the synergetic effect of efficient photogenerated electron-hole separation, decreased electron transfer resistance from interfacial chemical hydroxy residue bonds, and oxidizing groups originating from Ti³⁺-TiO₂ and O-g-C₃N₄.