奈米科技的發展逐漸影響到人類的生活型態，尤其奈米碳管的發現更是一大驚奇，亦對於污染物的去除開發了新的契機。一般在利用奈米碳管做一吸附材時，必須經過純化程序去除合成奈米碳管時所使用金屬觸媒顆粒，以及在高溫合成時產生碳的不純物質，以提高奈米碳管純度。 本研究藉由奈米碳管對於不同極性分子(對-二甲苯與鄰-二甲苯)的吸附能力，探討奈米碳管表面極性在酸純化前後的變化。研究結果發現，經硝酸純化處理後奈米碳管的金屬含量有明顯降低，相對增加了奈米碳管的純度，並伴隨著官能基的存在。此外，表面積與微孔體積亦有顯著的增加。由動力吸附實驗發現，奈米碳管吸附鄰-二甲苯達平衡的時間比活性碳短，並遵循一階動力模式。等溫吸附曲線實驗結果顯示，鄰-二甲苯與對-二甲苯由於甲基團位置之差異，將會造成苯環上π電子轉移程度不同之現象而直接影響吸附行為。再者，純化後之奈米碳管所增加之表面官能基會吸引水分子聚集現象，即而減低了奈米碳管吸附能力。不論純化前後的奈米碳管，對於二甲苯的吸附皆可以Langmuir與Freundlich吸附模式描述之。在競爭吸附實驗顯示，當奈米碳管同時吸附鄰-二甲苯與對-二甲苯時，表現出相同之親和力。若比較奈米碳管與活性碳的吸附能力，因為活性碳擁有巨大的表面積，因此表現出比奈米碳管為高的吸附量；但以單位表面積表現吸附量時，則顯示出純化前之奈米碳管擁有較高的吸附能力，表示有效吸附孔徑的重要性。此外，由純化前後之奈米碳管對於二甲苯之吸附量比較，純化程序是否真的有其必要性是有待思考的。 CNT is considered a good sorbent due to its high specific surface area and large micropore volume. Usually, raw CNTs contain large amount of impurities (e.g., amorphous carbon and catalytic metal) which come from synthetic process, therefore, purification of CNT is usually required. In this study, o-xylene and p-xylene were used to probe the alternation of surface properties of CNTs by acidic purification. It is found that purification of CNT by nitric acid significantly reduced the amount of metal catalyst, increased surface area as well as micropore volume of the CNTs, and introduced oxygen-containing group. Adsorption of o-xylene by purified-CNT attained adsorption equilibrium faster than that by activated carbon. The adsorption capacity of CNTs for o-xylene and p-xylene are mainly influenced by the positition of methyl groups and the presence of oxygen functional groups. Purified-CNTs have lower adsorption capability because water clusters compete with o-xylene and p-xylene for sorption sites. The competitive adsorption studies showed that there is no different affinity of o-xylene and p-xylene adsorbed by purified-CNT. Compared to both CNTs and purified-CNTs, activated carbons have larger adsorption capacity for its large specific surface area and no oxygen-containing functional group. However, when the adsorption capacity is calculated on the basis of unit surface area, CNTs have large adsorption capability than activated carbon for CNTs have more suitable pore size.
