▎ 摘　　要

NOVELTY - Preparing a cathode material involves cutting magnetic sponge material into a square with a side length of 1-5 cm as a skeleton material, ultrasonically treat the graphite oxide suspension to obtain a uniformly dispersed graphene oxide solution, immersing the trimmed skeleton material in step one in prepared graphene oxide solution, extruding the excess graphene oxide solution in obtained skeleton material, drying it, and repeating above step for 1-5 times. The obtained solution is placed in a ferrous chloride solution, heated in a water bath at 70-95 degrees C for 6 to 24 hours, and cooled to room temperature. The ammonia water is added dropwise to the obtained in step five, slowly stirred and adjusted to pH 9-12, and heat in a water bath at 60-95 degrees C for 0.5-6 hours under a sealed condition. The obtained cooled to room temperature, and washed with distilled water to obtain a graphite sponge nitrogen modified magnetic iron cathode material doped with ferric oxide. USE - Method for preparing cathode material. ADVANTAGE - The method enables to prepare a cathode material has strong catalytic oxidation ability and strong ability to remove difficult-to-degrade organic matter. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for following: (1) a cathode material, which is prepared by using the preparation method; (2) bioelectric Fenton system, which comprises cathode material; and (3) a method for constructing a bioelectric Fenton system, which involves taking the sludge with a thickness of 5-20cm as the anode deposit, and bury the anode material at 0.5-15cm above the bottom of the anode deposit, slowly adding 100-1000 mL of sewage on the anode deposit to form a sewage layer and place the cathode material in the sewage layer, setting aeration equipment 3-10 cm above the solid-liquid interface between the anode deposit and the sewage layer, connecting the cathode material and anode material through an external circuit, and connecting a 50-10000 ohm resistor in series as the external circuit.