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

Seeking porphyrin-based nanoporous organic polymers for adsorption and separation of simple molecular gases (e.g., CO₂, C₂H₆, CH₄, etc.) is still challenging. Herein, we report three-dimensional porphyrin-based nanoporous organic polymer (PNOP) networks based on tetrahedral-structured building blocks, which represent ideal materials for the adsorption/separation of carbon dioxide (CO₂). 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 m²/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 CO₂, ethane (C₂H₆), and methane (CH₄) gas adsorption performance. Interestingly, PNOP-1 with tetraphenylmethane units, featuring higher microporous volume and microporous specific surface areas compared to PNOP-2, displays CO₂, C₂H₆, and CH₄ gas uptake of up to 160.1, 80.2, and 16.8 mg/g at 273 K and 1 bar, respectively. The values of CO₂ 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 CO₂/N₂, CO₂/CH₄, and C₂H₆/CH₄ 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.