Molecular tunneling in large tubes of 3D nitrogenated micropore materials

• Published in: Journal of applied physics Vol. 124; no. 19
• Main Authors: Pimachev, Artem, Dahnovsky, Yuri
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 21.11.2018
• Subjects: Acids; Ammonia; Applied physics; Channels; Chemical reactions; Crystal structure; Drug delivery systems; Energy gap; Energy harvesting; Energy storage; Fragments; Gas separation; Gas transport; Hydrogen storage; Organic chemistry; Tubes
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.5045194

We study new 3D materials, π-conjugated microporous polymers (aza-CMPs), where 2D layers are connected by methanoic and ethanoic acid groups. The crystal parameters and the band structures are calculated. The energy gaps for a 3D crystal with the ethanoic ( Eg3D=1.04eV) and methanoic ( Eg3D=1.26eV) acid connecting groups are smaller than those for a 2D material ( Eg2D=1.64eV). The symmetry of a 3D crystal becomes lower than for a 2D aza-CMP by changing selection rules and optical spectra. The upper hole bands become non-degenerate for an aza-CMP with ethanoic acid and are doubly degenerate for an aza-CMP with methanoic acid connecting groups. The upper bands in the valence zone become more flat implying heavier hole masses that lead to lower hole mobilities. We also investigate molecular transport through the channels. We find that a CH 4 molecule moves easily along the tube in a large pore material and is hindered in a small pore (with ethanoic acid connecting groups) crystal. The ammonia molecule is attached to the tube walls with a large activation energy (about 0.39eV). For the large molecules NR 4 (R=CH 3, C 2H 5), chemical reactions take place in the narrow tubes. In particular, an N(CH 3)4 molecule decays in the fragments. The two atoms, N and C, are attached to the tube walls, and the three molecular fragments, CH 4, C 2H 6, and H 2, can further tunnel along the channels. The low energy gaps and tunable transport properties of π-conjugated microporous polymeric structures can be used for electronics, energy harvesting, gas separation, selective gas transport, hydrogen storage, and biomedicine (drug delivery).