Lignin-based carbon quantum dots as an efficient fluorescent sensor for aqueous MnO4− detection

Systematically clarifies how lignin molecular weight and sulfonation regulate CQDs fluorescence properties. • Develops green NSCDs from renewable sulfonated lignin, reducing the cost and environmental impact of CQDs. • Prepared NSCDs show high performance with 21.54% QY, 0.11 μM MnO₄⁻ LOD, and <1 min response time. • Confirms MnO₄ − fluorescence quenching is static quenching via chelation, excluding redox and energy transfer. • NSCDs sensor enables trace MnO₄ − detection in real water and promotes high-value utilization of lignin waste. Exploring a sensitive and accurate method for environmental permanganate detection is significant because of its great biotoxicity. Herein, various carbon quantum dots (CQDs) and the optimized N,S co-doped carbon quantum dots ( NSCDs ) fabricated from the hydrothermal treatment of sulfonated lignin could be used as fluorescent sensors for aqueous MnO 4 − detection. During the synthetic optimization process, compared with the positive effects of sulfonation degree increase of the sulfonated lignin and the proportion of 5-C sulfonation sites on the fluorescence intensity of CQDs, it was found that the increase of lignin molecular weight had the most significant effect on fluorescence intensity. The optimized NSCDs ( NSCDs , N from ethylenediamine, S from sulfonated lignin), with a 1.88 ± 0.37 nm particle size and Stokes shift as large as 245 nm, could emit green fluorescence under UV irradiation with a 21.54 ± 1.93% quantum yield and provide a low detection (LOD) limit of 0.11 μM for the MnO 4 − in an aqueous media with a rapid response within 1 min and good recoveries, showing good agreement with the indirect iodometric method in real water samples. Mechanistic studies suggested that the fluorescence quenching of NSCDs by MnO 4 − is predominantly a static process, likely associated with ground-state interaction between MnO 4 − and the surface functional groups of NSCDs . This work highlights precursor-structure regulation of sulfonated lignin as a distinct route for designing lignin-derived CQD sensors. Download: Download high-res image (117KB) Download: Download full-size image