Photocatalytic Composite Sr2MgSi2O7:(Eu, Dy)/g-C3N4: A Z-Scheme Heterojunction Material Formed by Long-Afterglow Phosphors and Photocatalysts on Round-the-Clock Photocatalytic Degradation of Methylene Blue

The long-afterglow luminescent material Sr2MgSi2O7:(Eu, Dy) was combined with the photocatalytic material g-C3N4 to construct a type of Sr2MgSi2O7:(Eu, Dy)/g-C3N4 self-luminous photocatalytic composite. This overcomes the limitation that photocatalytic experiments can only be carried out under an external light source, and it provides a more flexible way to use photocatalytic technology in environmental purification. The morphology, structure, luminescence, and photocatalytic properties of the samples were investigated using a variety of advanced characterization techniques. The results show that the significant improvement in the photocatalytic performance is attributed to the formation of a Z-scheme heterojunction between the luminescent and photocatalytic materials and the promotion of the photocatalytic reaction by the properties of the long-afterglow luminescent material itself. A possible mechanism for the photocatalytic process of the composite is proposed, and it is speculated that the reason for the increased photocatalytic activity is internal electron transfer and electron–hole pair separation based on tests such as X-ray photoelectron spectroscopy and density functional theory calculations. This study provides a strategy for enhancing the photocatalytic activity of photocatalysts and achieving round-the-clock degradation of pollutants.