| 摘要: | 本研究主要是利用奈米模鑄法及簡單一步合成法來合成具有相同結構 (二維六角柱狀 (p6mm) 及三維立方體/四面體 (Ia3 ?d/ I41/a) ) 的中孔洞碳材，希望比較這兩種方法所合出碳材的孔洞結構性質差異，藉此探討對不同染料分子吸附能力的影響，特別是二維及三維孔道結構對不同大小染料分子 (一維鏈狀結構的小分子亞甲基藍、三維結構的大分子維多利亞藍) 吸附能力的影響，並藉由另一種不帶電荷染料蘇丹紅 G，來探討碳材孔洞表面的電荷性質對其吸附能力的影響。
對於吸附一維小分子結構的亞甲基藍，發現碳材不管是二維或三維孔道結構，大致上隨著其孔洞表面積愈大，吸附量就愈大，且由 Langmuir 及 Freundlich 等溫吸附模型的分析，發現其比較符合 Langmuir 所假設的單層吸附模式，所以證明孔洞表面積為影響其吸附此小分子染料的主要因素。
而對於吸附三維大分子結構的維多利亞藍，實驗發現反而是孔洞體積及孔道結構才是影響碳材吸附能力的主要因素，且由 XRD 及 N2 等溫吸脫附結果，發現三維四面體 (I41/a) 的碳材都發生程度不等的結構相轉變，使其孔道結構比二維六角柱狀 (p6mm) 碳材還複雜許多，造成其吸附量甚至是吸附速率都大幅下降。另外，由於結構相轉變會產生孔徑更大的孔洞造成雙孔徑的分佈，所以亦發現雙孔徑分佈的程度愈高，其孔道結構愈複雜，愈不利於吸附大分子維多利亞藍。
至於對於吸附不帶電荷的染料蘇丹紅 G，發現碳材孔洞表面與染料分子之間的靜電吸引力為影響其對前述兩種帶正電荷染料吸附能力較優越的原因之一，顯示碳材孔洞表面的電荷性質也會大大影響其對染料的吸附能力。
另外，藉由 pseudo-first-order 及 pseudo-second-order 動力學模型的分析，發現所有碳材對這三種染料的吸附都比較適合用 pseudo-second-order 動力學模型來描述。
Mesoporous carbons with the same structure (2D hexagonal p6mm and 3D cubic/tetragonal (Ia3 ?d/ I41/a) ) were synthesized by the strategies of nanocasting and simple one-pot, and used for the adsorption of dyes. The goal was to compare the pore structure difference between the carbon materials synthesized by these two strategies, and investigate how these structure difference effect the adsorption of different dyes. Especially how the pore structure in two dimensions and three dimensions effected the adsorption of different molecule size dyes (such as small size methylene blue with 1D chain structure and large size victoria blue with 3D structure). In addition, we used another dye molecule with zero net charge, such as sudan red G, to investigate how the charge on the pore surface of mesoporous carbons effected the adsorption properties.
For the adsorption of methylene blue with 1D small molecule size, we found that no matter the pore structure of mesoporous carbons was in two dimensions or three dimensions, generally the bigger the pore surface area, the larger the adsorption capacity for the dye. After analyzing the adsorption isotherm data by the Langmuir and Freundlich models, we also found that they could be better described by the Langmuir model. The pore surface area of carbon materials was therefore the main factor for adsorption of small-size methylene blue.
In contrast, for the adsorption of victoria blue with 3D large molecule size, the adsorption capability was mainly dependent on the pore volume and the pore structure of the materials. The structure of 3D tetragonal (I41/a) mesoporous carbons all had different degree of phase transformation as revealed from XRD and N2 adsorption results, indicating that their pore structure were more complicated than the mesoporous carbons with 2D hexagonal (p6mm) symmetry. As a result, their adsoption capacities and adsorption velocities all dramatically decreased. On the other hand, due to phase transformation might produce more pores with much bigger size and result in bimodal porosity, our results also indicated that the higher the degree of bimodal porosity, the more complicated the pore structure, and therefore the less the adsorption capability for large-size victoria blue.
As for the adsorption of sudan red G with zero net charge on mesoporous carbons, it was found that the electrostatic attraction between the pore surface and dye molecules was the determinative factor for the better adsorption of last two dyes with positive charge, suggesting that the charge on the pore surface of carbon materials might greatly contribute to its adsorption capability for dyes.
In addition, after analyzing experimental data by the pseudo-first-order and pseudo-second-order kinetic models, we found that the adsorption of last three dyes on carbon materials all could be well depicted by the pseudo-second-order kinetic model. |
