Preparation Of Novel Nitrogen Doped Porous Carbon Nanosheet And Its Functionalization

In recent years,graphene has received great attention due to its unique structure and excellent optical,electrical,thermal,mechanical and chemical properties.Based on these features,graphene has been widely used in many fields including new display,composite materials,hydrogen storage,energy storage,water treatment,and so on.As the research moves along,regular graphene has been unable to meet the needs of people on the performance of graphene materials.On this point,novel structured graphene materials with controllable defects and heteroatoms doping have recently received intensive interest.This kind of graphene-like materials still own excellent physicochemical properties similar to regular graphene such as large surface area and good conductivity.And their performance can be adjusted intentionally.In this research,a kind of graphene-like materials?nitrogen doped porous carbon nanosheets,N-PCNs?were reported,and its functionalization and application were studied systematically.The main results are as follows:?1?The nitrogen-doped porous carbon nanosheets were successfully prepared by a two-step method?solvothermal reaction and high-temperature carbonization?,using monohydrated lactose and zinc nitrate hexahydrate as raw materials.Then we studied the selective adsorption behavior of N-PCNs towards organic dyes,using the neutral red?NR?as model dye.The results show that the nitrogen-doped porous carbon nanosheets own high adsorption capacity of up to 439.6 mg/g,and the adsorption mechanism was related to the acid-base interactions and?-?stacking interactions between N-PCNs and NR.While N-PCNs adsorption capacities towards methylene blue?MB?and eosin Y?EY?are very low,thus achieving the purpose of separating mixed dyes?MB/NR or EY/NR?in aqueous solution.In addition,due to the good desorption capability?97.9%?towards NR,the N-PCNs have great potential to be used as an excellent cyclable adsorbent.?2?The nitrogen and phosphorus co-doped porous carbon nanosheets?NP-PCNs?were successfully prepared through polyphosphazene loading on the surface of N-PCNs,followed by carbonization at high temperature.Based on the structure feature of NP-PCNs,the electrochemical performance of NP-PCNs was fully characterized when used as the active electrode materials for supercapacitors.The results are as follows:the NP-PCNs have a high specific capacitance of up to 322.9 F g^-11 at the current density of 1 A g^-1,a good rate performance((retention of 64.4%from1 to 20 A g^-1),and an excellent cycling stability(98%retention of the initial specific capacitance after 10000 consecutive charge-discharge cycles at 20 A g^-1).In addition,we used the NP-PCNs as the electrode materials to assemble the symmetric supercapacitors and performed its characterization.The symmetric supercapacitors own a wide voltage window of 1.6 V,a specific capacitance of up to 47.9 F g^-11 at 0.5A g^-1,and a rate performance as high as 65%retention from 0.5 to 20 A g^-1.And the symmetric supercapacitors also have a very good cycle performance(90%capacitance retention after 10000th cycle under a high current density of 10 A g^-1).Meanwhile,the symmetric supercapacitors exhibit an energy density of 17.04 Wh/kg when the power density is 400 W/kg,which is higher than that of most carbon materials reported before.?3?The NiMn-LDH/N-PCNs composites?nickel manganese layered double hydroxide loaded onto N-PCNs?were successfully prepared through an in situ growth route.The morphology and structure of the Ni Mn-LDH/N-PCNs composites were characterized and its electrochemical performance was tested.The results are as follows:the NiMn-LDH/N-PCNs composites exhibit specific capacitance of up to2010.7 F g^-11 at 1 A g^-11 and capacitance retention of 55.1%from 1 to 20 A g^-1.The NiMn-LDH/N-PCNs composites also present a good cycle stability and the capacitance retention was as high as 80.35%of the initial specific capacitance after4000th cycle under high current density of 20 A g^-1.Then we used the NiMn-LDH/N-PCNs as the positive electrode material and NP-PCNs as negative electrode material to assemble the asymmetric supercapacitors.Characterization results show that the asymmetric supercapacitors have a wide voltage window of 1.8V,a high specific capacitance of up to 89.69 F g^-11 at 0.5 A g^-1,a good rate performance(59.2%capacitance retention from 0.5 to 20 A g^-1),and an excellent cycle performance(79.73%retention of the initial specific capacitance after 4000th cycle under a high current density of 20 A g^-1).In addition,the asymmetric supercapacitors exhibit an energy density of 40.36 Wh/kg when the power density is460 W/kg,which is higher than that of most reported carbon materials before.In conclusion,we have developed a facile method to prepare porous nitrogen doping carbon nanosheets with large quantity and low cost,and a series of functionalization was also carried out.The as-prepared materials are expected to be used widely in the field of water treatment and energy storage.