Rational design of a g-C3N4/CdS/MIL-125 (Ti)-derived TiO2 ternary heterojunction as a highly efficient photocatalyst for wastewater treatment under visible-light irradiation†

The development of visible-light-active photocatalysts with high performance has been regarded as a promising way to address environmental wastewater issues. In this work, a highly efficient g-C₃N₄/CdS/TiO₂ ternary Z-type heterojunction photocatalyst with a hollow structure has been fabricated using a step-by-step self-assembly strategy, which demonstrates excellent photocatalytic performance under visible light and removes various water-soluble organic pollutants effectively. The photocatalytic degradation efficiency of 20-g-C₃N₄/CdS/TiO₂-10 against rhodamine B (RhB) is found to be 29.8 times higher than that of the pristine g-C₃N₄ within 90 minutes of visible light irradiation attributed to the active species of ˙O²⁻ and h⁺. Liquid chromatography mass spectrometry results suggest that the degradation pathway of RhB involves main steps such as N-de-ethylation, chromophore cleavage, ring opening, and mineralization. A series of characterization analyses, combined with the observed enhanced photocatalytic performance, indicate that the g-C₃N₄/CdS/TiO₂ ternary heterojunction benefits from the rapid transport and separation of photogenerated carriers facilitated by the formation of a heterointerface. Furthermore, the g-C₃N₄/CdS/TiO₂ ternary heterojunction exhibits favorable stability, with 88.1% degradation efficiency after five cycles of degradation experiments. This work provides novel insights into the preparation and application of ternary heterojunctions with superior photocatalytic performance for eliminating organic pollutants from wastewater.