Suzuki Yuka, Ishida Masaya, Hata Kenji, Ohba Tomonori
Graduate school of Science, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan.
AIST Tsukuba, Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.
Langmuir. 2023 Nov 7;39(44):15431-15440. doi: 10.1021/acs.langmuir.3c01415. Epub 2023 Oct 20.
The adsorption dynamics and mechanism of nitrogen molecules in 1-7 nm carbon nanotubes (CNTs) at 77 K were investigated by experiments and molecular dynamics simulations. The adsorbed nitrogen amount rapidly increased in 7 nm CNTs, while it gradually increased in 1 and 3 nm CNTs. The gradual increase in 3 nm CNTs was unexpected because of the presence of sufficient adsorption sites and the weak adsorption potential of nitrogen. The molecular dynamics simulations indicated that molecules were condensed in the entrance of nanopores after monolayer adsorption in 3 nm CNTs and monolayer and bilayer adsorption in 5 nm CNTs, called nanopore entrance filling. The proposed adsorption mechanism of nitrogen molecules in CNT nanopores is as follows: first, layer-by-layer adsorption occurs on monolayer sites, followed by preferential adsorption at the nanopore entrance. Consequently, preadsorbed molecules form a fluidic pore neck similar to an ink-bottle pore. Then, newly adsorbed molecules are condensed on the fluidic pore neck, and condensed molecules in the nanopore entrance finally move into the inner part of the nanopore. The proposed sequential adsorption mechanism via nanopore entrance filling without pore blocking starkly differs from micropore filling in micropores and layer-by-layer adsorption associated with capillary condensation in mesopores.
通过实验和分子动力学模拟研究了77 K下1 - 7纳米碳纳米管（CNT）中氮分子的吸附动力学和机理。在7纳米碳纳米管中吸附的氮量迅速增加，而在1纳米和3纳米碳纳米管中则逐渐增加。3纳米碳纳米管中吸附量的逐渐增加出乎意料，因为存在足够的吸附位点且氮的吸附势较弱。分子动力学模拟表明，在3纳米碳纳米管中单层吸附以及在5纳米碳纳米管中单层和双层吸附后，分子在纳米孔入口处凝聚，称为纳米孔入口填充。碳纳米管纳米孔中氮分子的吸附机理如下：首先，在单层位点上发生逐层吸附，随后在纳米孔入口处优先吸附。因此，预吸附的分子形成类似于墨水瓶孔的流体孔颈。然后，新吸附的分子在流体孔颈上凝聚，纳米孔入口处的凝聚分子最终进入纳米孔内部。所提出的通过纳米孔入口填充且无孔堵塞的顺序吸附机理与微孔中的微孔填充以及中孔中与毛细管凝聚相关的逐层吸附明显不同。
