Enhanced electron transfer using NiCo2O4@C hollow nanocages with an electron-shuttle effect for efficient tetracycline degradation

Spinel oxides are recognized as promising Fenton-like catalysts for the degradation of antibiotics. However, the catalytic performance is restrained by the poor electron transfer rate (ETR). Herein, hollow NiCo2O4@C nanocages are rationally designed and prepared to accelerate ETR in peroxymonosulfate (PMS) activation for tetracycline (TC) degradation. Enhanced ETR of the NiCo2O4@C/PMS system is due to three aspects: (1) The hollow nanocage facilitates the diffusion and adsorption of TC, improving the ion transfer at a macroscopic level; (2) Electron reconfiguration in octahedral sites of NiCo2O4 increases the ratio of Co2+, resulting in highly efficient PMS activation; (3) In-situ generated carbon acts as "electron shuttles", improving the electrical conductivity of catalysts at a microscopic level. As a result, the NiCo2O4@C demonstrates rapid ETR, leading to a highefficiency activation of PMS. The NiCo2O4@C/PMS system exhibits exceptional TC degradation efficiency and reusability. Non-radical pathway, including 1O2 and direct electron transfer, dominates the system. This work offers a feasible strategy for enhancing electron transfer in the Fenton-like system.