Tannic acid reinforced electro-Fenton system based on GO-Fe3O4/NF cathode for the efficient catalytic degradation of PNP

Abstract

In order to overcome the sluggish kinetics of the redox conversion between Fe³⁺ and Fe²⁺ in Fenton process, we established a novel electro-Fenton system based on GO-Fe₃O₄ cathode and tannic acid (TA) for the efficient degradation of p-nitrophenol (PNP). Under the optimal degradation parameters (including the initial PNP concentration of 20 mg L^-1, pH = 5, current density of 30 mA cm^-2 and feeding ratio of PNP: TA = 1:2), the TA reinforced GO-Fe₃O₄ electro-Fenton system exhibited the removal rate of PNP over 90.1 ± 0.2%, the COD removal rate of 69.5 ± 0.84% and satisfactory reusability (with the removal rate of ∼80% after 5 recycles). The excellent degradation performance of the proposed TA reinforced GO-Fe₃O₄ electro-Fenton system was partly attributed to the optimized morphology (with the particle size of Fe₃O₄ reduced to tens of nanometers, pore size decreased by ∼80% and pore volume increased by 24.3 times) and larger specific surface area (increased by 72.7 times) after compositing GO with Fe₃O₄, which exposed more active sites. In return, the electron transfer process, the two-electron oxygen reduction reaction (ORR) and the degradation efficiency were promoted in the cooperation of GO and Fe₃O₄. Moreover, the incorporated TA would form a TA-Fe(III) complex to promote the reduction reaction from Fe³⁺ to Fe²⁺, which strengthened the self-circulation of Fe²⁺ and Fe³⁺ and indirectly enhanced the conversion of H₂O₂ to ROS to decompose PNP into smaller organic fragments or mineralize into CO₂, H₂O, NO₂^- or NO₃^-, etc. Obviously, the incorporation of TA provided a promising strategy to improve the electro-Fenton efficiency and realize the efficient removal of PNP in wastewater.

Keywords: Electro-Fenton; GO-Fe(3)O(4) cathode; P-nitrophenol; Tannic acid.