Photo-tunable ultrafast removal of organic dyes by azobenzene and phosphonium functionalized porous organic polymers

Adsorption has been recognized as a highly economical and feasible technique for the removal of organic pollutants from water. Thus, the search for novel and efficient porous adsorbents for water purification is a crucial and pressing task. Here, a new family of azobenzene- and phosphonium-functionalized porous organic polymers (Azo-POPs) were fabricated via a post-synthesis approach. By taking advantage of the photo-tunable transformation of Azo units, the adsorption behaviors of two isomers of Azo-POP, trans-Azo-POP and cis-Azo-POP, were examined. The results demonstrated that both of Azo-POPs exhibited extraordinary adsorption capacity and adsorption rate towards anionic dyes due to their porous structure, cation-charged and hydrophilic skeleton. However cis-Azo-POP afforded much more efficient adsorption performances. The removal efficiency of Congo red (CR) could reach 100 % in 30 s, and the maximum adsorption capacity was as high as 1376.8 mg g−1, surpassing most previously reported adsorbents. The pseudo-second-order rate constant of cis-Azo-POP was 16.9153 g mg−1min−1. Additionally, Azo-POP adsorbents could be easily regenerated and reused over five cycles without any loss of adsorption capability. Therefore, the study suggests a universal platform for the fabrication of functional POP materials, which will find great potential in the fields of industrial wastewater treatment and catalysis.