Water Compatible Conjugated Polymer Photocatalysts By Side Chain Engineering

Conjugated polymers have emerged as a new class of heterogeneous photocatalysts for utilizing visible light as an environmentally friendly energy source. By virtue of structural designability, the conjugated polymers can be tuned to show better hydrophilicity by side chain engineering particularly for targeting the photocatalytic reactions in an aqueous medium, i.e. photocatalytic degradation of contaminants. We have designed a linear chain conjugated polymer to have different terminal functionalities such as diethylamine (DEA) and vinylimidazole (Vim) for initiating a reversible wettability change in water by the introduction of external stimuli. The DEA-based conjugated polymer exhibited the reversible hydrophilicity in the presence of CO₂ gas as the tertiary amine captured CO₂ molecules with water to form ammonium-bicarbonate salt, making the whole polymers hydrophilic for improving photocatalytic activity in water. Once the CO₂ was desorbed, the polymer could be easily separated from water for recycling. In the case of Vim-terminated conjugated polymer, the polymer chain could form a polyelectrolyte complex with hydrophilic polymer by ionic complexation, giving a hydrogel photocatalyst to show great volume expansion in water. With the structural expansion, the photoactive sites in hydrogel were also expanded, enhancing the overall photocatalytic activities in aqueous solution. The utility of the water-compatible conjugated polymer photocatalysts was demonstrated under visible light illumination, namely, photodegradation of organic dyes and micropollutants in water.