Heterogeneous advanced oxidation processes (AOPs) based on non-radical reactive species are considered as a powerful technology for wastewater purification due to their long half-lives and high adaptation in a wide pH range. Herein, we fabricate surface Co defect-rich spinel ZnCo₂O₄ porous nanosheets, which can generate ≡Co^IV=O and ¹O₂ over a wide pH range of 3.81–10.96 by the formation of amphoteric ≡Zn(OH)₂ in peroxymonosulfate (PMS) activation process. Density functional theory (DFT) calculations show Co defect-rich ZnCo₂O₄ possesses much stronger adsorption ability and more electron transfer to PMS. Moreover, the adsorption mode changes from terminal oxygen Co–O–Co to Co–O, accelerating the polarization of adjacent oxygen, which is beneficial to the generation of ≡Co^IV=O and ¹O₂. Co defect-rich ZnCo₂O₄ porous nanosheets exhibit highly active PMS activation activity and stability in p-nitrophenol (PNP) degradation, whose toxicity of degradation intermediates is significant reduction. The Co defect-rich ZnCo₂O₄ nanosheet catalyst sponge/PMS system achieved stable and efficient removal of PNP with a removal efficiency higher than 93% over 10 h. This work highlights the development of functional catalyst and provides an atomic-level understanding into non-radical PMS activation process in wastewater treatment.

Two-dimensional (2D) semiconductor heterojunctions are considered as an effective strategy to achieve fast separation of photoinduced carriers. Herein, a novel CoWO₄/g-C₃N₄ (CWO/CN) p–n junction was synthesized using an electrostatic self-assembly method. The constructed 2D/2D p–n heterostructure had a rich hetero-interface, increased charge density, and fast separation efficiency of photoinduced carriers. The in-situ Kelvin probe force microscopy confirmed that the separation pathway of photoinduced carriers through the interface obeyed an II-scheme charge transfer mechanism. Experimental results and density functional theory calculations indicated the differences of work function between CWO and CN induced the generation of built-in electric field, ensuring an efficient separation and transfer process of photoinduced carriers. Under the optimized conditions, the CWO/CN heterojunction displayed enhanced photocatalytic H₂ generation activity under full spectrum and visible lights irradiation, respectively. Our study provides a novel approach to design 2D/2D hetero-structured photocatalysts based on p–n type semiconductor for photocatalytic H₂ generation.