Activation of peroxymonosulfate and peroxydisulfate by nitrogen-doped carbon nanotubes for effective degradation of neonicotinoid insecticides

Abstract

Nitrogen-doped carbon nanotubes (N-CNTs) have been considered as an excellent metal-free activator for persulfate-based advanced oxidation processes. However, the critical role of N-doping in the activation of peroxymonosulfate (PMS) and peroxydisulfate (PDS) remains a significant difference even opposed in scientific understanding. Herein, the CNTs and N-CNTs were used to active PMS and PDS for degradation of neonicotinoid insecticides (NNIs), one of the emerging refractory organic pollutants. The N-CNTs achieve 92.6% of nitenpyram (Nit) degradation within only 10 min under PMS system, much higher than that of CNTs/PMS system (∼10%). Moreover, the N-CNTs can active PMS to conduct degradation through a combined 1O2 and electron transfer process with k of 4.94 × 10−2 L·mg−1·min−1, which was quite different from N-CNTs/PDS system (single electron transfer process, k = 1.84 × 10−3 L·mg−1·min−1). A positive correlation between degradation rates of five NNIs and their electron-donating ability is established, further verifying the importance of electron transfer in NNIs degradation. This study proves the superiority of N-CNTs/PMS over N-CNTs/PDS in Nit degradation and the underlying mechanisms, and reveals the importance of electron-donating ability of NNIs in their degradation by N-CNTs/PMS. These findings are of great significance for their removal from the environment.