Photo-modulated regeneration of hypercrosslinked polymer adsorbents for water treatment

Hypercrosslinked polymers (HCPs) are highly effective adsorbents for removing dyes from water. However, the regeneration of such adsorbents is typically achieved with energy-intensive thermal methods or with solvents that generate chemical waste. Here in this proof of concept study, we used HCPs loaded with azobenzene molecules (HCPs@Azo) that were developed in our previous work, and four types of dyes - Methyl Orange (MO), Methylene Blue (MB), Rhodamine B (RB), Uniblue A (UA), at concentrations ranging from 10 to 500 mg L-1, to demonstrate the feasibility of photo-modulated regeneration of HCP-based adsorbents. Azobenzene in HCP pores reduced dye adsorption by 4-31 %, but upon photo-isomerisation from trans to cis states, led to the desorption of 1.7-20 % dyes that were previously adsorbed. These desorption capacities were 71-209 % higher than using water for regeneration. Compared to the traditional method using organic solvents such as methanol to regenerate HCP-based adsorbents, our approach of photo-modulated regeneration led to the desorption of 50 % more MO and MB dyes. HCPs@Azo also demonstrated good reusability, showing comparable photo-modulated adsorption and desorption capacities after four cycles of UV-visible light irradiation. Results from this work can potentially pave the way for solvent-less regeneration of adsorbents, creating a waste-less adsorbent regeneration process.