Synergistic experimental and computational investigation of azo-linked porphyrin-based porous organic polymers for CO capture.

We synthesized a series of azo-linked porphyrin-based porous organic polymers (APPs) with linear, bent, and trigonal linkers (APP-1 to APP-6) and with directly connected tetraphenylporphyrin units (APP-7a, APP-7b and APP-8). The synthesized APPs are amorphous solids demonstrating good thermal stability and diverse BET surface areas. APPs with linkers showed significantly higher surface areas (469 to 608 m g) compared to those with directly connected tetraphenylporphyrin units (0.3 to 23 m g). Higher surface areas correlated with enhanced CO adsorption, particularly for APP-1, APP-2, and APP-5 with experimental CO uptake values of 41 mg g, 38 mg g, and 38 mg g, respectively, at 306 K. The computational study supported the experimental findings and provided insights on how surface area and the local landscape affect the CO adsorption. Although the computational models were based on ideal structures, while the experiments revealed the materials were amorphous, the calculated CO adsorption capacities were roughly comparable to the experimental results, particularly for the 3D systems (APP-5 and APP-6) and the 2D systems with directly connected building units (APP-7 and APP-8). Porphyrin units in the framework serve as additional binding sites for CO, especially when unhindered and available on either side of the porphyrin plane. This work highlights the potential of 2D layered APPs and 3D topologies for efficient CO capture.