Interaction of acetone with single wall carbon nanotubes at cryogenic temperatures: a combined temperature programmed desorption and theoretical study.
Interaction of acetone with single wall carbon nanotubes at cryogenic temperatures: a combined temperature programmed desorption and theoretical study.
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DOI：
10.1021/la800030y
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发表时间：
2008-07
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通讯作者：
Dmitry V. Kazachkin;Y. Nishimura;S. Irle;K. Morokuma;R. Vidic;E. Borguet
中科院分区：
文献类型：
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作者：
Dmitry V. Kazachkin;Y. Nishimura;S. Irle;K. Morokuma;R. Vidic;E. Borguet
通过结合程序升温解吸（TPD）和色散增强密度泛函紧密结合（DFTB-D）理论模拟，研究了丙酮与单壁碳纳米管（SWCNT）在低温下的相互作用。根据TPD研究和理论模拟的结果，丙酮的解吸峰可以归属于以下吸附位点：（i）能量约为75 kJ mol（-1）（T des 约300 K）的小直径纳米管内嵌位点（约7.7 A）； (ii) 能量为 40-68 kJ mol (-1)（T des 约 240 K）的位点丙酮吸附在较大纳米管（约 14 A）的可及间隙、凹槽位点和内嵌位点上； (iii) SWCNT外壁上能量为25-42 kJ mol (-1) (T des 约140 K)的位点丙酮吸附和多层吸附。由于氧官能团的存在，氧化纯化的单壁碳纳米管对内嵌位点的访问受到限制。通过退火至高温 (900 K) 可以去除氧官能团，从而打开纳米管内嵌位点的通道。未经纯化的原始单壁碳纳米管的特点是，即使在退火至高温（900 K）后，丙酮进入内嵌位点的机会也有限。将纯化的和生产出来的单壁碳纳米管退火到高温（1400 K）会导致丙酮分子进入小纳米管的内嵌位点的机会减少，这可能是由于单壁碳纳米管末端的缺陷自愈和帽形成。低温吸附实验中未检测到丙酮和单壁碳纳米管之间的化学相互作用。丙酮在不同直径的有限原始单壁碳纳米管上吸附的理论模拟表明，吸附能与管侧壁曲率之间存在明显的关系。丙酮的吸附是由于分散力的作用，其 C-O 键要么平行于表面，要么 O 指向远离表面的方向。没有发现明显的电荷转移或极化。炭黑用于模拟生产的单壁碳纳米管中存在的无定形碳质杂质。丙酮从炭黑中的解吸显示出在大约 140 K 和大约 180-230 K 处的两个峰，类似于 SWCNT 中的两个丙酮解吸峰。 SWCNT 中丙酮解吸的特征是在约 300 K 时达到峰值，而炭黑中未观察到这一点。为从碳纳米管解吸的分子分配 TPD 峰时应小心，因为无定形碳会干扰。
The interaction of acetone with single wall carbon nanotubes (SWCNTs) at low temperatures was studied by a combination of temperature programmed desorption (TPD) and dispersion-augmented density-functional-based tight binding (DFTB-D) theoretical simulations. On the basis of the results of the TPD study and theoretical simulations, the desorption peaks of acetone can be assigned to the following adsorption sites: (i) sites with energy of approximately 75 kJ mol (-1) ( T des approximately 300 K)endohedral sites of small diameter nanotubes ( approximately 7.7 A); (ii) sites with energy 40-68 kJ mol (-1) ( T des approximately 240 K)acetone adsorption on accessible interstitial, groove sites, and endohedral sites of larger nanotubes ( approximately 14 A); (iii) sites with energy 25-42 kJ mol (-1) ( T des approximately 140 K)acetone adsorption on external walls of SWCNTs and multilayer adsorption. Oxidatively purified SWCNTs have limited access to endohedral sites due to the presence of oxygen functionalities. Oxygen functionalities can be removed by annealing to elevated temperature (900 K) opening access to endohedral sites of nanotubes. Nonpurified, as-received SWCNTs are characterized by limited access for acetone to endohedral sites even after annealing to elevated temperatures (900 K). Annealing of both purified and as-produced SWCNTs to high temperatures (1400 K) leads to reduction of access for acetone molecules to endohedral sites of small nanotubes, probably due to defect self-healing and cap formation at the ends of SWCNTs. No chemical interaction between acetone and SWCNTs was detected for low temperature adsorption experiments. Theoretical simulations of acetone adsorption on finite pristine SWCNTs of different diameters suggest a clear relationship of the adsorption energy with tube sidewall curvature. Adsorption of acetone is due to dispersion forces, with its C-O bond either parallel to the surface or O pointing away from it. No significant charge transfer or polarization was found. Carbon black was used to model amorphous carbonaceous impurities present in as-produced SWCNTs. Desorption of acetone from carbon black revealed two peaks at approximately 140 and approximately 180-230 K, similar to two acetone desorption peaks from SWCNTs. The characteristic feature of acetone desorption from SWCNTs was peak at approximately 300 K that was not observed for carbon black. Care should be taken when assigning TPD peaks for molecules desorbing from carbon nanotubes as amorphous carbon can interfere.