Porphyrin-Based Nanoporous Organic Polymers for Adsorption of Carbon Dioxide, Ethane, and Methane

Abstract

Seeking porphyrin-based nanoporous organic polymers for adsorption and separation of simple molecular gases (e.g., CO 2 , C 2 H 6 , CH 4 , etc.) is still challenging. Herein, we report threedimensional porphyrin-based nanoporous organic polymer (PNOP) networks based on tetrahedral-structured building blocks, which represent ideal materials for the adsorption/separation of carbon dioxide (CO 2 ). Two PNOP networks, denoted as PNOP-1 and PNOP-2, have been prepared successfully by a facile one-pot method using pyrrole with the tetrahedral-structured building blocks tetrakis(4-aldehydephenyl)methane (TFPM) and 1,3,5,7-tetrakis(4′aldehydephenyl)adamantane (TFPAd), respectively. The resulting PNOPs are composed of rough spherical particles and exhibit specific surface areas of up to 830 m 2 /g as well as nanometer-scale pore size of <2 nm. The dense porphyrin structure and high and stable nanoporosity endow the PNOPs with excellent CO 2 , ethane (C 2 H 6 ), and methane (CH 4 ) gas adsorption performance. Interestingly, PNOP-1 with tetraphenylmethane units, featuring higher microporous volume and microporous specific surface areas compared to PNOP-2, displays CO 2 , C 2 H 6 , and CH 4 gas uptake of up to 160.1, 80.2, and 16.8 mg/g at 273 K and 1 bar, respectively. The values of CO 2 adsorption obtained herein exceed those obtained for previously reported PNOP materials. In addition, the developed PNOP-2 contained 1,3,5,7-tetraphenyladamantane units with smaller pore size than PNOP-1, exhibiting CO 2 /N 2 , CO 2 /CH 4 , and C 2 H 6 /CH 4 selectivities as high as 80.1, 11.0, and 25.7, respectively, at 273 K and 1 bar. The results are beneficial for designing and constructing better nanoporous organic polymers derived from tetrahedral-structured building blocks for simple molecular gas adsorption/separation in the future.

Friedel–Crafts Synthesis of Carbazole-Based Hierarchical Nanoporous Organic Polymers for Adsorption of Ethane, Carbon Dioxide, and Methane

“…Furthermore, we observed that CNOP-2 showed higher capacities and lower Q st for C 2 H 6 , CO 2 , and CH 4 than CNOP-1, which is ascribed to the higher BET surface area and larger pore sizes of CNOP-2. This phenomenon has also been reported in previously published works. ,,, …”

“…Additionally, the C 2 H 6 adsorption capacity of the CNOPs initially decreased with increasing temperature and then increased in going from 273 to 298 K, which indicates that the gases were adsorbed by physisorption. Nonetheless, under ambient conditions, CNOP-2 adsorbed C 2 H 6 at a capacity of 71.0 cm 3 /g, which is considerably more than those of reported porous materials, including PNOP-1 (47.1 cm 3 /g), MCOF-1 (44 cm 3 /g), PAN-T1 (49.8 cm 3 /g), and LIFM-W2 (28.5 cm 3 /g) . Furthermore, CNOPs that feature carbazole fragments exhibited high CO 2 uptakes of 84.2–90.2 cm 3 /g at 1 bar and 273 K that are inferior to those of the reported CNOPs, as shown in Table S1, such as CPOPs (39.7–67.2 cm 3 /g), Car-TPA COF (62.6 cm 3 /g), PCMOP-H1 (61.6 cm 3 /g), and SCHPP-2 (40.1 cm 3 /g) .…”

“…We note that CNOP-1 with larger TCPA building blocks displayed a lower BET surface area and smaller pore size than CNOP-2 due to the interpenetration effect. This phenomenon was also observed in the previously reported NOPs originating from TCPA and TCB , and NOPs derived from rigid tetrahedral building blocks …”

“…Field-emission scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy, solid-state 13 C cross-polarization/total suppression of spinning side bands (CP/TOSS) NMR spectroscopy, and gas (N 2 , CH 4 , C 2 H 6 , and CO 2 ) sorption isotherm measurements were performed using the same approach and apparatus as in our previously published works. ,, …”

“…Interest in nanoporous organic polymers (NOPs) has been driven by their extensive applications in gas adsorption and separation (e.g., CO 2 , C 2 H 6 , CH 4 , and N 2 ), − I 2 capture, − toxic pesticides detection, − detection of nitroaromatic explosives, water treatment, and heterogeneous catalysis. − A lot of research has been done over the past few years to find simple synthetic approaches that could create materials with excellent porosity and functionality. Many NOPs have been developed for a wide range of reactions, including metal-catalyzed C–C coupling, − electrochemical polymerization, − nitrile-based trimerization, − and the Friedel–Crafts (FC) reaction. ,, Compared with other methods, the FC reaction is a facile approach for synthesizing NOPs.…”