Controllable synthesis of hierarchical mesoporous/microporous nitrogen-rich polymer networks for CO2 and Cr(vi) ion adsorption

Abstract

A facile and scalable one-pot approach has been developed for the preparation of hierarchical meso- and microporous nitrogen-rich polymer networks by sol–gel polymerization of melamine, resorcinol and terephthaldehyde. The obtained polymer networks have a hierarchical porous structure with moderate microporous surface area and high mesoporous volume. The micropores are within the networks of highly cross-linked polymer chains, while the mesopores result from a 3-D continuous polymeric gel network formed by the reaction-induced sol–gel phase separation. The addition of hexafunctional melamine to the polymer precursor could enhance the crosslinking degree at a molecular level, thus leading to more accessible micropores within the networks. It can also increase the size of polymer clusters, leading to the formation of larger mesopores. Moreover, the nitrogen functional groups inherited from melamine and the –OH functional groups from resorcinol can also be adjusted by changing the precursor composition. These rich surface functional groups could serve as irregular sites with chemical heterogeneity available for CO₂ and chromium Cr(VI) ion adsorption. High CO₂ uptake up to 2.4 mmol g⁻¹ and high chromium adsorption capacity of 126.3 mg g⁻¹ are obtained. The outstanding advantages of the MRT networks presented here include their low price, commercially available starting compounds and the easy method of synthesis. This kind of new porous polymer with tailored physical and chemical properties has promise for further applications.