Sustainable synthesis of bright green fluorescent carbon quantum dots from lignin for highly sensitive detection of Fe³⁺ ions

Biomass transformation into high-value carbon nanomaterials plays a dual role of easing the energy material crisis and reasonable disposal of waste. Here, we employed biomass lignin as carbon source to synthesize fluorescent carbon quantum dots (CQDs) through a facile two-step method. The preparation condition is optimized at 0.3 g of acid additive and 200 ℃, 16 h of hydrothermal treatment. The resultant CQDs with the average diameter of 4.86 nm and high quantum yield of 23.68% are composed of carbon cores and surface functional groups, exhibiting the maximum green emission wavelength of 476 nm. The formation mechanism involves acid dissociation of lignin in the first step, and then the aromatic refusion of lignin fragments. The CQDs show great advantages as fluorescent nanoprobe for metal ion detection, which present an apparent and selective fluorescence quenching effect on Fe³⁺. This CQD nanoprobe has a highly sensitive response to Fe³⁺ ions in the concentration of 0 ~ 300 μM with detection limit of 0.77 μM. The utilization of renewable biomass lignin in this study not only opens the avenue of the sustainable, cost-effective and mass production of CQDs, but also provides a novel alternative nanoprobe for sensing field.