Porous polyelectrolyte frameworks: synthesis, post-ionization and advanced applications.

Porous organic polymers (POPs), which feature high surface areas, robust skeletons, tunable pores, adjustable functionality and versatile applicability, have constituted a designable platform to develop advanced organic materials. Endowing polyelectrolytes with the distinct characteristics of POPs will attract mounting interest as the structural diversity of polyelectrolytes will bring the new hope of intriguing applications and potential benefits. In this review, the striking progress in ionized POPs (i-POPs) has been systematically summarized with regard to their synthetic strategies and applications. In the synthesis of i-POPs, we illustrate the representative ionic building blocks and charged functional groups capable of constructing the polyelectrolyte frameworks. The synthetic methods, including direct synthesis and post-modification, are detailed for the i-POPs with amorphous or crystalline structures, respectively. Subsequently, we outline the distinctive performances of i-POPs in adsorption, separation, catalysis, sensing, ion conduction and biomedical applications. The survey concerns the interplay between the surface chemistry, ionic interaction and pore confinement that cooperatively promote the performance of i-POPs. Finally, we conclude with the remaining challenges and promising opportunities for the on-going development of i-POPs.

PEG-stabilized coaxial stacking of two-dimensional covalent organic frameworks for enhanced photocatalytic hydrogen evolution.

Two-dimensional covalent organic frameworks (2D COFs) featuring periodic frameworks, extended π-conjugation and layered stacking structures, have emerged as a promising class of materials for photocatalytic hydrogen evolution. Nevertheless, the layer-by-layer assembly in 2D COFs is not stable during the photocatalytic cycling in water, causing disordered stacking and declined activity. Here, we report an innovative strategy to stabilize the ordered arrangement of layered structures in 2D COFs for hydrogen evolution. Polyethylene glycol is filled up in the mesopore channels of a ß-ketoenamine-linked COF containing benzothiadiazole moiety. This unique feature suppresses the dislocation of neighbouring layers and retains the columnar π-orbital arrays to facilitate free charge transport. The hydrogen evolution rate is therefore remarkably promoted under visible irradiation compared with that of the pristine COF. This study provides a general post-functionalization strategy for 2D COFs to enhance photocatalytic performances.