Enhanced activation of hydrogen peroxide using nitrogen doped graphene for effective removal of herbicide 2,4-D from water by iron-free electrochemical advanced oxidation

Degradation of the herbicide 2,4-dichlorophenoxiacetic acid (2,4-D) in aqueous solutions has been studied by electrochemical oxidation process using N-doped graphene modified graphite felt cathode with ammonium nitrate as nitrogen source. The graphene was obtained via electrochemically exfoliated method (EEGr). Different ratios of EEGr/ammonium nitrate (1:0, 1:1, 1:3, 1:7) modified cathodes (N0-EEGr-GF, N1-EEGr-GF, N3-EEGr-GF, N7-EEGr-GF) were explored with electrochemical characterizations, and it was verified that N1-EEGr had the most significant catalytic performance for accelerating the activation of in-situ generated H2O2 into hydroxyl radicals. The effects of operating parameters such as applied potential, solution pH and initial concentration of 2,4-D on the degradation efficiency with N1-EEGr-GF were investigated. A fairly high mineralization rate (88%) was attained at pH 7 after 480 min electrolysis of 20 mg L−12,4-D solution. The N-doped graphene as catalyst was found to be more efficient in degradation performance compared with the unmodified graphite felt cathode. The electrochemical advanced oxidation process using this modified cathode allows extension of the working pH range compared to electro-Fenton process which is optimal at pH 3. Finally, a plausible pathway for 2,4-D mineralization was proposed according to the identified intermediated products.