Phosphate modulated nitrogen-doped titanium dioxide/carbon nitride heterogeneous photocatalysts with efficient O2 activation for ametryn degradation†

Abstract

4P-5NT/CN nanocomposites with high O₂ activation and charge separation properties were synthesized via wet chemistry and calcination for photocatalytic degradation of ametryn (AME). With their wide visible light absorption range, the 4P-5NT/CN nanocomposites exhibited excellent charge transfer and separation properties, which significantly improved the photocatalytic degradation of AME by CN photocatalysts. The Z-type charge transfer mechanism between N-doped TiO₂ (NT) and g-C₃N₄ (CN) and the high oxygen adsorption oxygen activation function of surface-modified phosphoric acid were crucial to the improved photocatalytic performance. The improved oxygen activation performance further induced the generation of more active species and accelerated the interaction with AME to initiate degradation. Results showed that the photocatalytic degradation of AME by 4P-5NT/CN was 25.8 times greater than that by pure CN under optimal loading conditions. Oxygen temperature-programmed desorption (O₂-TPD) experiments showed that H₃PO₄ promoted the physical adsorption of O₂ on the surface of the material, effectively facilitating oxygen activation and inducing ·O₂⁻ generation. Reactive oxide species (ROS) were determined through ESR and free radical capture detection. The intermediate fragmentation products of AME degradation were detected using liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the synergistic degradation pathways of ·O₂⁻ and ·OH were obtained. The synergistic effect is reflected in the fact that ·O₂⁻ tends to attack the ethyl chain, triggering the degradation reaction, whereas ·OH tends to attack the sulfur methyl group, ultimately leading to better mineralisation. This work reveals the selection pattern of AME active sites by ROS during photocatalytic degradation and provides a new idea for the design of visible-light-driven high-oxygen-activity photocatalysts for the efficient treatment of environmental pollutants with effective mineralisation.