Metal-free g-C₃N₅ photocatalyst coupling MXenes Ti₃C₂ for tetracycline degradation: Insight for electron transfer mechanism, degradation mechanism and photothermal effect

At present, nitrogen-rich graphitic carbon nitride (g-C₃N₅) has emerged as an alternative for traditional graphitic carbon nitride (g-C₃N₄), due to better visible-light utilization efficiency and abundant surface functional groups. In this paper, a g-C₃N₅/MXenes (Ti₃C₂) binary heterojunction was prepared and used as a photocatalyst in environmental remediation. In tetracycline (TC) degradation, g-C₃N₅/Ti₃C₂ displayed better performance than those of the reference photocatalysts, including g-C₃N₅, g-C₃N₄, Ti₃C₂ and g-C₃N₄/Ti₃C₂. The underlying electron (e^-) transfer mechanism was investigated in detail. Besides higher visible-light harvest, better separation efficiency of photo-induced charge carrier and lower surface resistance, an internal-electric-field was established at the interface between g-C₃N₅ and Ti₃C₂, and the driving force for e^- transfer was 93.9 mV. hole (h⁺), ¹O₂, ^•OH and ^•O₂^- were involved into TC degradation, where h⁺ played a dominating role due to the high e^- transfer efficiency. Benefiting from the good photothermal effect, g-C₃N₅/Ti₃C₂ could efficiently transfer solar energy to thermal energy, leading to the high temperature of catalyst surface and acceleration of the surface degradation reaction rate. This work provided a possibility to construct a g-C₃N₅-based visible-light photocatalyst to efficiently degrade the persistent organic contaminants.