N/Ti3+-codoped triphasic TiO2/g-C3N4 heterojunctions as visible-light photocatalysts for the degradation of organic contaminants

Abstract

Herein, a series of N/Ti³⁺-codoped triphasic TiO₂/g-C₃N₄ heterojunctions were constructed by a simple hydrothermal treatment of TiN and g-C₃N₄ and systematically investigated by a number of characterization techniques. During the hydrothermal reaction, TiN is completely converted to a N/Ti³⁺-codoped triphasic heterophase junction, TiO₂, and the activated g-C₃N₄ can form heterojunctions with TiO₂. Importantly, a red-shift of the absorption edge, enhanced absorption intensity, and improved photocatalytic activity were observed for the N/Ti³⁺-codoped triphasic TiO₂/g-C₃N₄ heterojunctions as compared to the case of N/Ti³⁺-codoped triphasic TiO₂ and pure TiO₂. Especially, the N/Ti³⁺-codoped triphasic TiO₂/g-C₃N₄ heterojunctions with an optimal molar ratio of 1 : 0.025 exhibited highest visible-light photocatalytic activity for the degradation of methylene blue, rhodamine B, phenol, and levofloxacin. Furthermore, the photoelectrochemical and electrochemical impedance spectra measurements revealed that the prepared heterojunctions displayed more efficient electron–hole separation. The enhanced photoactivity is attributed to the synergistic effect of integrated factors, including N/Ti³⁺ doping levels, triphasic heterophase junctions, and TiO₂/g-C₃N₄ heterojunctions, which account for the improved charge separation efficiency and extended light absorption range and intensity. In this study, a novel structure of TiO₂-based heterojunction photocatalysts was developed by a simple one-step hydrothermal approach, and an efficient route to improve the photocatalytic activity of TiO₂ was revealed.