Dopamine inspired lignin-derived green emissive carbon dots for pH sensing and metal ions separation

Lignin is the most abundant, but underutilization polyphenolic material on the earth. In this paper, an integrated platform for pH sensing and ions separation was prepared from lignin to make use of this abundant bioresource. Demethylation of enzymatic hydrolysis lignin was first achieved to mimic the catechol structure of dopamine. The demethylated lignin was then converted into carbon dots by a facile hydrothermal treatment. The as-prepared carbon dots emit green fluorescence with enhanced quantum yield, and exhibited pH-responsive color changes from yellow-green to blue. When incorporated into a chitosan aerogel, the pH-responsive property of the carbon dots was intact, whereas the adsorption capacity of the aerogel for Cu2+ ions was noticeably improved, which was owed to the abundant oxygen containing functional groups and unique optical properties of the as-prepared carbon dots. This study provides a feasible approach to convert lignin into fluorescent nanomaterials for pH sensing and metal ions recovery from wastewater.