Synthesis of Dual p–n Heterojunction of Ni/Mn-MOF-74/CdS@Co3O4 Photocatalyst as a Photoassisted Fenton-like Catalyst for Removal of Tetracycline Hydrochloride

In this study, a novel composite material, Ni/Mn-MOF-74/CdS@Co3O4 was synthesized. This material consisted of a dual p–n heterojunction, which enabled efficient separation and transfer of charge carriers. Compared to a single p–n heterojunction, the presence of this dual heterojunction significantly enhanced the overall efficiency. The improved efficiency could be attributed to the unique properties of the constituent semiconductors. Co3O4 exhibited p-type semiconductor properties, while Ni/Mn-MOF-74 and CdS exhibited n-type semiconductor properties. By a combination of these materials to form a composite photocatalyst, a Z-type heterojunction was created at the interface of the p–n junction. This design established an internal electric field at both ends, effectively separating the photogenerated electrons and holes in each individual photocatalyst. As a result, the respective photocatalytic activities of the materials were maximized. To demonstrate the practical application of this composite material, it was utilized for the activation of peroxymonosulfate under visible light irradiation, with the aim of enhancing the photocatalytic degradation efficiency of tetracycline hydrochloride. The photocatalytic mechanism of Ni/Mn-MOF-74/CdS@Co3O4 in activating peroxymonosulfate and degrading tetracycline hydrochloride was investigated in detail. Furthermore, the toxicity of tetracycline hydrochloride and its intermediates was evaluated by using toxicity evaluation software.