Effect of pore structure on the adsorption capacities to different sizes of adsorbates by ferrocene-based conjugated microporous polymers

Conjugated microporous polymers (CMPs) are potential materials for gas uptake, pollutant adsorption and photocatalysis. However, their relatively wide pore size distribution (PSD) makes it hard to establish the relationship between adsorption capacities and pore structure. Here, we synthesized two CMPs with similar chemical structure based on carbazole and ferrocene units. Poly[1,1'-di(9-carbazolyl)ferrocene] (PDCF) showed hierarchical pore structure with pore sizes distributed in three regions: 0.7-0.85 nm, 1-3 nm and 10-100 nm, while the pore sizes of poly{1,1'-di[4-(9-carbazolyl))phenyl]ferrocene} (PDCPF) were mostly less than 3 nm. The results of gas uptake and dye adsorption capacities show that the extra mesopores of PDCF exhibit better adsorption capacities to adsorbates with larger sizes. Besides, dye molecules adsorbed in the micropores are harder to desorption than that in the mesopores. The intermolecular forces between porous polymers and adsorbates were used to explain these results successfully. Our findings indicate that designing the right pore sizes for porous polymers when adsorbing gases or dyes with a specific molecules size is very important in the future.