Tuning the Adsorption Capacities of Nanoporous Polyaminal Networks through Substituent Groups

Investigating the relationship between the substituent groups of nanoporous organic polymers and the adsorption capacities of the polymers for SO2, NH3, CO2, and I2 is a significant challenge. In this study, four nanoporous polyaminal networks (NPANs) with methyl or phenyl substituent groups were prepared, and they demonstrated high adsorption capacities for SO2, NH3, CO2, and I2. The four NPANs, which were referred to as NPAN-1, NPAN-2, NPAN-3, and NPAN-4, were fabricated via a one-pot polycondensation method by using inexpensive p-phthalaldehyde (p-PDA) or m-phthalaldehyde (m-PDA) and 6-methyl-1,3,5-triazine-2,4-diamine (MTDA) or 2,4-diamino-6-phenyl-1,3,5-triazine (DAPT). The NPANs had a dense aminal-rich structure and stable nanoporosity, which contributed to their high adsorption capacities for SO2, NH3, CO2, and I2 and their high SO2/CO2 selectivities. Notably, the SO2 adsorption capacities, NH3 adsorption capacities, CO2 adsorption capacities, and I2 adsorption capacities of NPAN-1 and NPAN-3, which were NPANs with electron-donating methyl groups, were higher than those of NPAN-2 and NPAN-4, which were NPANs with electron-withdrawing phenyl groups. This result indicated that the introduction of electron-donating groups into an NPAN enhanced the electron density of the nitrogen atoms in the polyaminal network, leading to increases in the adsorption capacities of the NPAN for SO2, NH3, CO2, and I2. This study offers important insights into the design and synthesis of NPANs with adjustable properties to tackle environmental and industrial challenges.