Building a Z-scheme heterojunction with Keggin-type heteropolymer modified two-dimensional g-C3N4 for significant photocatalytic performance

Abstract

Building Z-scheme heterojunction systems is a high-efficiency pathway to improve the utilization of visible light. Herein, Cs_xPW₁₁M/g-C₃N₄ (M = Co, Fe) was successfully prepared by the simple grinding and calcination technology with a Z-scheme heterojunction structure. This Z-scheme heterojunction structure could significantly improve the separation and utilization efficiency of photogenerated carriers while enhancing the redox capacity and photocatalytic activity. The energy band structure of Keggin-type polymers was optimized by modulating the coordination metal. The prepared composites have specific high photocatalytic properties and good reusability. The photocatalytic degradation activity of the prepared Cs_xPW₁₁M (M = Co, Fe) modified 2D g-C₃N₄ materials was investigated using two different types of pollutants. Currently, when the loading capacity of Cs_xPW₁₁M in the Cs_xPW₁₁M/g-C₃N₄ sample reached 3 wt%, the photocatalyst of this composite material showed the best photocatalytic degradation performance. Meanwhile, the active species of the response were explored through free radical trapping experiments and ESR characterization, indicating that h⁺,˙O₂ and ˙¹O₂ played a key role. The suitable band structure and the correct charge analysis, as well as the investigation of the transfer mechanism, provided new ideas for the construction of a Z-scheme heterojunction structure using Keggin-type transition metal-substituted heteropolymers and 2D g-C₃N₄. It improves the performance of conventional catalysts.