Preparation And Application Of Nitrogen-Doped Carbon Spheres And Its Composite Electrode Material For Copper Removal Using Capacitive Deionization Technology

Due to the low-concentration copper ions（<50 ppm）and the competitive adsorption of other ions in electroplating rinse wastewater,conventional techniques like electrodialysis and evaporation concentration cannot remove copper ions with low energy consumption and high efficeiency.Capacitive deionization（CDI）technology is a new type of technology for water treatment,which can realize the adsorption of low-concentration ions with its electric field and electrode materials.The key to this technology lies in the preparation of highly efficient electrode materials.Therefore,in this paper,nitrogen-doped carbon spheres（NCS）and few-layer molybdenum disulfide/nitrogen-doped carbon spheres（FL-MoS₂/NCS）electrode materials were prepared,and the performance of these two materials in copper removal by capacitance deionization was investigated.Firstly,in this paper,polydopamine spheres（PDAS）were prepared by one-step chemical oxidation polymerization method.The properties of nitrogen-doped carbon spheres（NCS）prepared at different calcination temperatures（600℃,800℃and1000℃）were studied.On this basis,NCS-800 was used as the electrode material to study the copper removal by electrosorption.The results indicated that NCS-800electrode has the best electrochemical performance with a specific capacitance of 56.9F/g,which is 1.6 and 2.1 times that of NCS-600 and NCS-1000 electrodes,respectively.In the solution of 50 ppm CuCl₂(Cu²⁺:23.63 ppm),500 ppm NaCl and 80 ppm FeCl₃,the adsorption capacity of NCS-800 electrode for Cu²⁺was 67.48 mg/g at 0.8 V.Compared with the adsorption capacity（82.38 mg/g）in CuCl₂ solution,its capacity retention rate was 81.9%.This proves that the NCS-800 electrode still has a good adsorption capacity for Cu²⁺in the competitive environment.The XPS test further proved that the adsorption of Cu²⁺by the NCS-800 electrode was achieved by the synergistic effect of electrical double layer（EDL）and complexation between Cu²⁺and active sites of Pyrrolic N.Secondly,in order to improve the adsorption capacity and selectivity of the electrode to low-concentration Cu²⁺,the FL-MoS₂/NCS composite was prepared by one-pot method using PDAS as carbon precursor and prepared into CDI electrodes for adsorption of low-concentration Cu²⁺by electrosorption.The results suggested that the FL-MoS₂/NCS electrode possesses excellent electrochemical performance with a specific capacitance of 472.2 F/g,2.7 times that of MoS₂ electrode（176.1 F/g）.Meanwhile,the FL-MoS₂/NCS electrode has a low equivalent series resistance（0.25Ω）.In the solution of 50 ppm CuCl₂,500 ppm NaCl and 80 ppm FeCl₃,the adsorption capacity of FL-MoS₂/NCS electrode at 0.8 V for Cu²⁺was 1071.6 mg/g,which is much higher than that for Na⁺（199.2 mg/g）and Fe³⁺（262.8 mg/g）.Meanwhile,compared with the adsorption capacity（1199.63 mg/g）in CuCl₂ solution,its capacity retention rate was 89.3%.These results indicate that the electrode has good adsorption selectivity for low-concentration Cu²⁺.The XPS test further proved that the high efficiency and selectivity of the FL-MoS₂/NCS electrode for the adsorption of Cu²⁺was achieved by the synergistic effect of EDL and complexation between Cu²⁺and the active sites of S and Pyrrolic N.