Design and Construction of an Azo-Functionalized POP for Reversibly Stimuli-Responsive CO₂ Adsorption

A porous azo-functionalized organic polymer (JJU-2) was designed and prepared via oxidative coupling polymerization promoted by FeCl₃. JJU-2 exhibited reversibly stimuli-responsive CO₂ adsorption properties as a result of the trans/cis isomerization of the polymer's azo-functionalized skeleton. Under UV irradiation and heat treatment, this porous material displayed various porous structures and CO₂ adsorption properties. The initial Brunauer-Emmett-Teller (BET) surface area of JJU-1 is 888 m² g^-1. After UV irradiation, the BET surface area decreases to 864 m² g^-1, along with the decrease of micropores around 0.50 nm and 1.27 nm during the trans-to-cis isomerization process. In addition, CO₂ sorption isotherms demonstrate an 8%t decrease, and the calculated Qst of CO₂ has decreased from 29.0 kJ mol^-1 to 26.5 kJ mol^-1 due to the trans to cis conversion of the azobenzene side group. It is noteworthy that JJU-2's CO₂ uptakes are nearly constant over three cycles of alternating external stimuli. Therefore, this azo-functionalized porous material was a potential carbon capture material that was responsive to stimuli.