Comparison of adsorption selectivity for (-)-epigallocatechin gallate and caffeine by porous materials modified with different amino groups

- Comparison of different adsorption behaviors of porous materials with different amino groups.
- Adsorption selectivity for EGCG was greatly enhanced after modification.
- Specific surface area did not play an important role in the adsorption process.
- Geometrical matching and narrow pore diameter distribution were dominant.
- Ethylenediamine group introduced could greatly enhance adsorption selectivity.

Porous materials modified with different amino groups were prepared and characterized, and then applied to selectively separate (-)-epigallocatechin gallate (EGCG) and caffeine (CAF). After modification, surface area, pore volume decreased while average pore diameter increased to some extent. The range of pore diameter distribution turned to be narrow. It was shown that the porous materials modified with ethylenediamine exhibited higher adsorption efficiency and adsorption selectivity for EGCG with selectivity factor of 17.91. The porous materials modified with triethylenetetramine exhibited comparative higher adsorption efficiency and adsorption selectivity with original porous materials while that modified with melamine showed lower adsorption efficiency for EGCG. The phenomenon may be due to that the steric hindrance affected the adsorption process. The different adsorption behaviors of the porous materials with different amino groups indicated that functional groups on the porous materials played an important role in the adsorption process. The results showed that except for conventional hydrogen bonding, π-π, and sieving effect, geometrical matching and narrow pore diameter distribution range could make modified porous materials have highly selective adsorption properties for EGCG. This study provides new insight into the design and preparation of porous materials with different functional groups and adsorption selectivity for efficient isolation and purification of complex products.

Effects of contact time on adsorption for EGCG (A) and CAF (B).124