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

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.