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 (Cr) 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 Cr. 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 Cr, which exhibit highly sensitive and selective fluorescence quenching for Cr with good linearity (R ≤ 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 Cr through a multichannel sensing platform.