The Synthesis Of Nitrogen-doped Carbon Nanomaterials For Capacitive Deionization

Capacitive deionization (CDI), aslo known as elecrtosorption, has received world-wide attention since the 1960th. With the rapid expansion of population, industrial and agricultural production, global freshwater consumption has increased rapidly. In 20th Century, global water consumption has increased by 7 times, while the industrial water consumption increased by 20 times. The situation become even worse since the beginning of 21 st Century, which leads to a sever imbalance between water supply and demand. However, more than 98% of the global water resources are undrinkable seawater or brackish water, which has made desalination the most promising route to solve the water scarcity. Conventional water desalination techniques, including flash distillation, reverse osmosis, electrodialysis and ion exchange method, have suffered from problems like high energy consumption, secondary pollution, membrane fouling and low water use rate, which limit their pratical application. CDI has become one of the most promising desalination techniques for its highly efficient, energy-efficient, environment-friendly and high water use rate. As the key factor for CDI technique, electrode material has drawn world-wide attention. Therefore, further exploration on CDI electrode materials not only has important scientific value, but also exhibits broad application prospects and practical significance in the development of human society.In this work, we explored the systhesis and modification of several novel carbon materials. As electrode material, the effect of the structure, mophology and element doping on their CDI performance were studied. By optimizing the preparation processes, the most promising electrode materials are obtained. The main contents of this thesis are summarized as followed:1. Porous carbon spheres (PCSs) were prepared from sucrose via microwave-assisted method. The effect of carbonization temperature on their electrochemical and elecrosorption performance were investigated. The result shows that, the specific surface area of PCSs increases with the carbonization temperature. The PCSs treated at 1000℃ exhibit excellent elecrosorption performance with a elecrosorption capacity of 5.81 mg g"1 in 500 mg 1-1 NaCl solution. The PCSs were further subject to ammonia treatment and nitrogen doped PCSs (NPCSs) were obtained. The effect of ammonia treatment temperature on the nitrogen doping type, specific surface area, electrochemical and elecrosorption performance were investigated. The result shows that the nitrogen content increases with the ammonia treatment temperature, which will lead to higher specific surface area and easier charge transfer. The NPCSs treated at 1000℃ exhibit improved CDI performance with an electrosorption capacity of 14.91 mg g-1, which shows great improvement compared with that of PCSs.2. Carbon nanorods (CNRs) were synthesized through freezed-drying and subsequent thermal treatment from nano-crystalline cellulose. The effect of carbonization temperature on their morphology, specific surface area, electrochemical and CDI performance were investigated. The increased carbonization temperature improves the specific surface area and charge transfer. The CNRs treated at 1200℃ exhibits excellent elecrosorption performance with a elecrosorption capacity of 15.12 mg g-1. The CNRs were further subject to ammonia treatment and nitrogen doped CNRs (NCNRs) were obtained. The result shows that the nitrogen content increases with the ammonia treatment temperature, which will lead to higher specific surface area and easier charge transfer. The NCNRs treated at 1000℃ exhibit improved CD1 performance with an electrosorption capacity of 17.62 mg g-1.3. Carbon nanofiber (bc-CNFs) were synthesized from bacterial cellulose through freezed-drying and subsequent thermal treatment. The effect of carbonization temperature on their morphology, specific surface area, electrochemical and CDI performance were investigated. The results suggest that higher specific surface area and easier charge transfer were obtained with the increase of carbonization temperature. The bc-CNFs treated at 800℃ exhibit excellent elecrosorption performance with an elecrosorption capacity of 12.81 mg g-1. The bc-CNFs were further subject to ammonia treatment and nitrogen doped bc-CNFs (bc-NCNFs) were obtained. The result shows that after ammonia treatment the fibril morphology of bc-CNFs was well maintained, and the elecrosorption capacity of bc-NCNFs reaches 17.30 mg g-1, which shows obvious improvement compared with that of bc-CNFs.4. Nitrogen doped porous carbon polyhedra (PCPs) were synthesized using ZIF-8 as the template. The effect of carbonization temperature on their morphology, specific surface area, electrochemical and CDI performance were investigated. The results suggest that the polyhedron morphology of the ZIF-8 were well maintained after the carbonization process. With the increase of carbonization temperature, higher specific surface area and easier charge transfer were obtained. The PCPs treated at 1200℃ exhibit excellent elecrosorption performance with an elecrosorption capacity of 13.86 mg g-1.