Lignin fractionation-inspired carbon dots to enable trimodule fluorescent sensing of pH, silver ion and cysteine

Abstract

Photoluminescent carbon dots (CDs) inspire an emerging subclass of nanocarbons that is the topic of worldwide interest to smart materials with versatile functions. Despite an ideally sustainable biopolymer of industrial lignin with congenital phenylpropanoid skeleton, interior linkages and functional groups (e.g., –OCH3, –OH and –COOH), efficient lignin valorization is controversial by its heterogeneous structure. Herein, a “library” of CDs from technical lignin with gradient structure and narrow molecular dispersity is fabricated initiating by stepwise solvent fractionation, and lignin-derived CDs that function as the nanoprobe are thoroughly characterized with the interplay between fluorescence responses and sensing properties. Benefitting from the direction of molecular weights, β-aryl ether, hydroxyl/carboxyl groups and particle size by refined lignin, their bimodal emissive CDs radiate the switchable and controllable blue-green color under a wide excitation span, which can be modulated to trimodule detect pH, silver ion and cysteine with an acceptable selectivity and sensitivity in a broad concentration scale. It thus is believed that this work not only delivers a facile strategy to overcome the lignin heterogeneity, but also paves the avenue to rationally nanoscale-design multifunctional lignin valorization with a perspective of broadening the biorefinery frontiers.