Development of a waste-derived lignin-porphyrin bio-polymer with enhanced photoluminescence at high water fraction with wide pH range and heavy metal sensitivity investigations

Lignin is a common by-product of pulping industries. Diverse functional groups in the polymeric matrix make lignin a superior alternative for carbon-based materials. Meanwhile, porphyrin family is well known in multiple applications; however, aggregation-caused quenching (AQC) due to the strong π-π interaction in poor-solvent environments will limit the photoluminescence intensity of porphyrin. In this study, a new lignin-porphyrin (AL-CTPP) polymer was developed, which combined and promoted the functionalities of the two chemicals. In photoluminescence investigations, the emission intensity of AL-CTPP in the 600 to 780 nm region was 30-fold stronger than that of porphyrin alone when the water fraction (f_w) > 0.9. Lignin served as a stable backbone immobilizing porphyrin and prevented unwanted aggregation of porphyrin and the related aggregation-caused quenching in high f_w solution at various pH. Furthermore, linear correlations were established between absorption properties of AL-CTPP with concentrations of five metal ions (i.e., Mn²⁺, Ni²⁺, Co²⁺, Cu²⁺, and Zn²⁺). With these unique features, AL-CTPP showed enhanced performance for potential bio-imaging and environmental applications. Lignin-porphyrin polymers may represent a significant potential product of biorefineries and the effective utilization of lignin to fabricate a new functional material which offers significant benefits to support waste valorization.