posted on 2019-09-30, 14:13authored byZhifang Wang, Nivedita Sikdar, Shi-Qiang Wang, Xia Li, Mei-Hui Yu, Xian-He Bu, Ze Chang, Xiaolong Zou, Yao Chen, Peng Cheng, Kuang Yu, Michael J. Zaworotko, Zhenjie Zhang
Soft porous crystals (SPCs) that exhibit stimuli-responsive dynamic sorption behavior are attracting interest
for gas storage/separation applications. However, design and synthesis of SPCs is challenging. Herein, we report a new type
of SPC based on a [2+3] imide-based organic cage (NKPOC-1) and find that it exhibits guest-induced breathing behavior.
Various gases were found to induce activated NKPOC-1 crystals to reversibly switch from a “closed” nonporous phase (α) to
two porous “open” phases (β and γ). The net effect is gate-opening behavior induced by CO2 and C3 hydrocarbons.
Interestingly, NKPOC-1-α selectively adsorbs propyne over propylene and propane at ambient conditions. Thus, NKPOC-1-
α has the potential to separate binary and ternary C3 hydrocarbon mixtures and performance was subsequently verified by
fixed bed column breakthrough experiments. In addition, molecular dynamics calculations and in situ X-ray diffraction
experiments indicate that the gate-opening effect is accompanied by reversible structural transformations. The adsorption
energies from molecular dynamics simulations aid are consistent with the experimentally observed selective adsorption
phenomena. The understanding gained from this study of NKPOC-1 supports the further development of SPCs for
applications in gas separation/storage since SPCs do not inherently suffer from the recyclability problems often
encountered with rigid materials.
Funding
Investigation of the triple mutual system Li, Ba // BO2, F and the growth of bulk crystals of b-BaB2O4