Lignin derived multicolor carbon dots for visual detection of formaldehyde

Formaldehyde (FA) is a common toxic pollutant in air and water, which is harmful to human's health. Although the fluorescent probes based on carbon dots (CDs) for FA detection have been reported, most of them only work under UV excitation conditions. It is a challenge to develop a CDs probe which can detect the FA more directly without UV excitation. In this work, a series of lignin derived multicolor carbon dots (M-CDs) from blue to cyan and to green emission were synthesized by hydrothermal method. Polychromatism of CDs was successfully achieved by adjusting the amount of hydrochloric acid (HCL) in the hydrothermal process. The blue emitting carbon dots (B-CDs) exhibited good selectivity and sensitivity towards FA in dual modes. Without the UV excitation, the B-CDs probe was able to detect the FA by observing with naked eyes, and the LOD in sunlight was 0.4 mg/L. Moreover, the fluorescent intensity of B-CDs can be quenched by FA, and it correlated linearly with FA concentration from 0.02 mg/L to 1 mg/L with LOD of 7.40 μg/L. This work is in favor of developing the lignin derived CDs with multi fluorescent color and simplifies the method of formaldehyde detection based on CDs.