High Surface Area And N-doped Activated Carbons Prepared From Chitosan And Their Adsorption Properties

N-heteroatoms doped on the carbon networks of activated carbon changed the surface properties and surface groups.As a result,the electrochemical performance and the adsorption properties of the N-doped activated carbon were improved.Presently,the preparation of N-doped activated carbon is still in the laboratory scale,and there is an urgent demand to develop a simple process to prepare N-doped activated carbon at low cost.Chitosan is abundant in nature,and is rich with amino groups,which can be used as both a nitrogen source and a carbon source.Therefore,N-doped activated carbons prepared from chitosan and their adsorption properties will be presented.First,carbonized chitosan（CN）,used as both a nitrogen source and a carbon source,is respectively reacted with NaOH and KOH to prepare N-doped activated carbon,and the effect of operationg conditions is investigated.It was shown that activated carbon prepared by NaOH activation has a larger pore volume than the activated carbon prepared by KOH activation.CNN2 was prepared by NaOH activation at 750 ^oC with a mass ratio of activating agent to CN R_w=3.The specific surface area and the pore volume of CNN2 reached as high as 3315 m²/g and 2.13 cm³/g respectively.The nitrogen content was 2.91%,and the nitrogen atoms mainly existed in the form of N-H and C-N.The effect of urea on the properties of N-doped activated carbon has been investigated.The results showed that urea restrained the development of the pores,as NaOH is used as an activation agent.Both the specific surface area and pore volume of activated carbon was decreased obviously,and the highest specific surface area was3015 m²/g.However,during the K₂CO₃ activation process,urea could improve the development of pores.CNKCU2.3 was prepared by K₂CO₃ activation at 800 ^oC and R_w=2,and the amount of urea added was 5 g.The specific surface area and the pore volume of CNKCU2.3 were 2407 m²/g and 1.21 cm³/g respectively.Comparing withhe sample CNKCU2.1 without adding urea,the specific surface area and pore volume were increased by 71%and 20%respectively.The nitrogen content of CNKCU2.3 was1.72%,which meant that urea failed to increase the nitrogen content of activated carbon.Adsorption isotherms of CO₂,CH₄ and N₂ on CNN2 and CNKCU3.3 at 268-308K and 0-1 MPa,were collected respectively.It was shown that the Langmiur-Freundlich（L-F）equation agreed with the experimental data better than the Langmiur equation.The adsorptive isosteric heats of each gas on both adsorbents decreased in the following order:CO₂>CH₄>N₂.The separation factors calculated from the ideal solution adsorption theory（IAST）for CO₂/CH₄ and CO₂/N₂ on CNN2 are 2.91 and 12.53respectively.The separation factors for CO₂/CH₄ and CO₂/N₂ on CNKCU3.3 were 3.19and 9.78,respectively.The separation factor for CO₂/CH₄ on CNKCU3.3 was slightly higher than that for CNN2;while for CO₂/N₂,CNN2 is better than CNKCU3.3.