<p>Based on the concept of resource utilization, this study successfully prepared a green and highly efficient nitrogen-doped biochar catalyst (N-BC-800) using agricultural waste cotton hulls as a raw material. This catalyst was then applied to the ozone-catalyzed degradation of N,N-diethyl-meta-toluamide (DEET), a typical insect repellent in water bodies. The apparent second-order rate constant reached 2358&#xa0;M⁻¹&#xa0;s⁻¹, representing a 106-fold increase compared to the O₃ system alone, and a 25-fold increase compared to the O₃/BC system. Experimental characterization and theoretical analysis indicate that C=O groups and pyridinic N structures on the material surface serve as primary catalytic active sites. These synergistically promote ozone decomposition and generate highly reactive intermediates which are further converted into reactive oxygen species (ROS), significantly enhancing DEET degradation performance. This catalyst exhibits excellent stability and applicability in real aquatic environments. It demonstrates broad-spectrum degradation effects on multiple pollutants while significantly reducing the ecotoxicity of reaction byproducts. This study provides theoretical support and practical pathways for developing highly efficient, green ozone-catalyzed materials.</p> Graphical Abstract <p></p>