Triple-emission nitrogen and boron co-doped carbon quantum dots from lignin: Highly fluorescent sensing platform for detection of hexavalent chromium ions

Considering that hexavalent chromium ions (Cr⁶⁺) with high toxicity poses a huge threat to human health and the ecological environment, constructing a rapid and accurate sensing platform is of great significance in detecting the toxic substance. The novel nitrogen and boron co-doped carbon quantum dots (N, B-CQDs) from lignin are synthesized as fluorescent sensors for the detection of Cr⁶⁺. The synthetic processes involve the acid hydrolysis step followed by the hydrothermal treatment step. Lignin is firstly depolymerized by cleaving ether bonds in the acidolysis, and N, B-CQDs are consequently formed by the aromatic re-fusion of lignin nanoparticles in the hydrothermal process. The lignin-derived N, B-CQDs show triple emission of purple, blue and green fluorescence under the excitation of 300, 330, and 490 nm, respectively. The triple-emission N, B-CQDs are applied for the triple-channel detection of Cr⁶⁺, which exhibit highly sensitive and selective fluorescence quenching for Cr⁶⁺ with good linearity (R² ≤ 0.996) and very low limit of detection as 0.054, 0.049, and 0.077 μM under the excitation of 300, 330 and 490 nm, respectively. The utilization of renewable lignin as CQDs-based fluorescent sensors opens a new avenue for the rapid and accurate detection of Cr⁶⁺ through a multichannel sensing platform.