氨气改性活性炭表面含氮官能团的形成与演变

Formation and Evolution of Surface Nitrogen Functionalities on Activated Carbons by Ammonia Modification

为研究活性炭表面含氮官能团的形成与演变规律,以硝酸氧化预处理后的水蒸气活化椰壳活性炭(ACO)为原料,在300~1 000℃范围内采用了3种模式进行氨气改性,制得含有各类含氮官能团的改性活性炭。采用元素分析法、Boehm滴定法和X射线光电子能谱(XPS)技术分析了活性炭的元素含量、酸碱性和表面含氮官能团种类。结果表明:在改性温度700℃之前的氨气改性过程中,活性炭表面含氮官能团主要来源于表面含氧官能团与氨气的结合所形成酰胺、酰亚胺和内酰胺等氮氧型(N-X),以及部分氨气与碳原子直接结合形成的吡啶型(N-6)和吡咯型(N-5)等含氮官能团;当氨气处理温度达到800℃时,炭表面的含氮基团主要来源于氨气与炭表面的碳原子直接结合形成的N-6、N-5和季氮型(N-Q)含氮官能团。在热处理温度升高过程中,N-X逐渐转变为N-6、N-5和N-Q含氮官能团;当温度大于800℃时,N-6、N-5含氮基团能逐渐转化为N-Q含氮官能团。氨气改性温度达到800℃之前,活性炭表面没有形成N-Q官能团。

Three types of ammonia modification was carried out in 300 - 1 000 ℃ using nitric acid oxidized activated carbon obtained commercially from steam activation using coconut shell as raw materials. The formation and evolution of surface nitrogen functional groups of the activated carbon were investigated. Element analysis, Boehm titration and X-ray photoelectric spectroscopy （XPS） were employed to determine the element contents, acid and basic functional groups contents and the types of nitrogencontaining functional groups of activated carbons. The results showed that when the activated carbon were treated at the temperature below 700 ℃, nitrogen functional groups were mostly nitrogen oxides（ N-X, such as amides, imides and lactams） generated mainly by combining ammonia and surface oxygen-containing functional groups, and some pyridinic（N-6） and pyrrolic（N-5） groups by the reaction of ammonia and carbon atoms in the carbon matrix, when the temperature increased to 800 ℃, the formation of nitrogen functional groups were contributed to the combination of ammonia and carbon atoms and pyridinic, pyrrolic and quaternary（N-Q） groups were predominantly generated. With the temperature increasing, amides, lactams and imides were progressively converted into pyridinic, pyrrolic groups and eventually into quaternary groups. Besides, there was no quaternary surface group below 800 ℃.