A recyclable hydroxyl functionalized polyindole hydrogel for sodium hydroxide extraction via the synergistic effect of cation-π interactions and hydrogen bonding.

We have successfully constructed a new type of recyclable indole-based hydrogel, which exhibited highly effective extraction behavior for hydroxide via the synergistic effect of cation-π interactions and hydrogen bonds. More interestingly, the absorption performance could be visually detected by taking advantage of the color altering effect of the host-guest interactions.