A Z-scheme defect-rich and dimensionally confined double functionalized g-C3N4 homojunction pectin hydrogels for the photocatalysis-self-Fenton-peroxymonosulfate system: Unraveling synergistic catalysis and reaction mechanism

Abstract

A highly efficient, defect-rich, and dimensionally engineered carbon nitride homojunction hydrogel (NTCN hydrogel) was developed for the in-situ generation of H₂O₂ under the illumination of visible light. The photocatalytic-self-Fenton (PSF) system was integrated with peroxymonosulfate (PMS), enhancing the production of reactive oxygen species, which aided the tetracycline degradation to 99.5 % in 8 min. The NTCN hydrogels also displayed a maximal reusability of 20 cycles with a slight decline in the degradation efficiency. The superior catalytic performance is indicated by the establishment of a Z-scheme junction in the NTCN hydrogel, which is attributed to the higher separation efficiency, rapid H₂O₂ generation, and synergistic interaction between the PMS and PSF in the hybrid oxidation system. The mechanistic pathways revealed the synergistic interaction between the PMS and H₂O₂ in the PSF-PMS hybrid oxidation system, enhancing the performance of NTCN hydrogels in a wider range of pH. Under basic pH conditions, the PMS and H₂O₂ are produced on the surface of NTCN hydrogels to mutually generate OH and ¹O₂, which led to enhance the lower degradation efficacy in the PSF system. At acidic pH, the O₂⁻ emerges as a predominant Reactive Oxygen Species (ROS), and the synergistic action of H₂O₂ and PMS completely avoided the dependency on protons by the PSF-PMS system. This study describes a highly efficient and sustainable hybrid multifunctional oxidation system for the purification of tetracycline from synthetic wastewater.