▎ 摘　　要

NOVELTY - Removal of hardness calcium ion in water by nitrogen-modified graphene electrode involves ultrasonically dispersing an oxidized graphene in deionized water, ultrasonically treating, dispersing, adding urea, mechanically stirring, heating, freeze-drying, mixing with a pre-formulated polyvinyl alcohol solution to obtain a paste-like dispersion, uniformly coating on a hard paper, drying to obtain a nitrogen-doped graphene aerogel paper electrode, adding calcium ion solution to an electric absorption vessel, placing the paper electrode, and carrying out electroabsorption of heavy metal ions. USE - Removal of hardness calcium ion in water by nitrogen-modified graphene electrode (claimed). ADVANTAGE - The method enables simple, rapid, convenient and environmentally-friendly removal of hardness calcium ion in water using nitrogen-modified graphene electrode having high adsorption efficiency. The nitrogen-modified graphene electrode has excellent recycling performance. DETAILED DESCRIPTION - Removal of hardness calcium ion in water by nitrogen-modified graphene electrode involves ultrasonically dispersing an oxidized graphene in deionized water, ultrasonically treating for 10-30 minutes, dispersing uniformly, adding urea, mechanically stirring for 15 minutes, adding the mixed solution into a hydrothermal reactor, heating in a muffle furnace at 180 degrees C for 12 hours, soaking the reaction product in distilled water for 2-3 days and freeze-drying to obtain a nitrogen-doped graphene aerogel material, mixing the nitrogen-doped graphene aerogel material with a pre-formulated polyvinyl alcohol solution to obtain a paste-like dispersion, removing 0.1-0.4 mL dispersion liquid, uniformly coating on a hard paper, drying to obtain a nitrogen-doped graphene aerogel paper electrode, preparing calcium ion solution, adding to an electric absorption vessel, placing the nitrogen-doped graphene aerogel paper electrode into the vessel, carrying out electroabsorption of heavy metal ions using the three-electrode system, using conductivity meter to monitor the change of solution conductivity, removing the voltage on the electrode, restoring the conductivity of the solution to near the initial value and regenerating the electrode. The three-electrode system comprises the paper electrode as working electrode, a platinum sheet electrode as counter electrode and a calomel electrode as reference electrode. The adsorption of nitrogen-doped graphene aerogel paper electrode is in equilibrium, when the conductivity is kept constant.