A metal–organic framework functionalized with piperazine exhibiting enhanced CH4 storage†
NJU-Bai 19, the first cycloaliphatic ring (piperazine) functionalized MOF-505 analogue, exhibits a notably high methane storage capacity of 246.4 cm3 (STP) cm−3 (at room temperature and 65 bar); this is 93.6% of the new volumetric target of the US Department of Energy if the packing density loss is ignored. Compared with NOTT-101, when piperazine groups are inserted, the methane uptake capacity of NJU-Bai 19 at 65 bar and RT can be significantly enhanced with lower Qst. A relatively low increase was also observed in the uptake at 5 bar. Thus it has a much higher methane storage working capacity (deliverable amount of methane between 65 and 5 bar) of 185 cm3 (STP) cm−3 compared with NOTT-101 (174 cm3 (STP) cm−3). When the temperature was decreased from 298 to 273 K at working pressures between 65 bar and 5 bar, the volumetric CH4 working capacity of NJU-Bai 19 is almost unchanged (from 185 to 189 cm3 (STP) cm−3), while some of the famous MOFs with high Qst showed a decrease with a decrease in temperature. The combination of the balanced porosity and framework density and the lipophilic surface is considered to result in the increased methane storage and working capacities.