Preparation of Multicolor Biomass Carbon Dots Based on Solvent Control and Their Application in Cr(VI) Detection and Advanced Anti-Counterfeiting

[Image: see text] Multicolor fluorescent carbon dots (CDs) have received widespread attention due to their excellent fluorescence performance and promising prospects in anti-counterfeiting and sensing detection. To date, most of the multicolor CDs synthesized are derived from chemical reagents; however, the overuse of chemical reagents during the synthesis process will pollute the environment and limit their application. Herein, multicolor fluorescent biomass CDs (BCDs) were prepared by a one-pot ecofriendly solvothermal method, with spinach as the raw material based on solvent control. The as-obtained BCDs can emit blue, crimson, grayish white, and red luminescence, and their quantum yields (QYs) are 8.9, 12.3, 10.8, and 14.4%, respectively. The results of the characterization of BCDs reveal that the regulating mechanism for multicolor luminescence is mainly ascribed to the change of the boiling point and polarity of solvents, which changes the carbonization process of polysaccharides and chlorophyll in spinach, resulting in the altered particle size, surface functional groups, and porphyrin luminescence properties. Further research reveals that blue BCDs (BCD1) show an excellent sensitive and selective response to Cr(VI) in a concentration scale of 0–220 μM with a detection limit (LOD) of 0.242 μM. More importantly, the intraday and interday relative standard deviation (RSD) values were less than 2.99%. The recovery rate of the Cr(VI) sensor for tap water and river water is 101.52–107.51%, which indicates that the sensor has the advantages of high sensitivity, selectivity, rapidity, and reproducibility. Consequently, different multicolor patterns are obtained by using the obtained four BCDs as fluorescent inks, which exhibit beautiful landscape and advanced anti-counterfeiting effects. This study provides a low-cost and facile green synthesis strategy for multicolor luminescent BCDs and proves that BCDs have broad application prospects in ion detection and advanced anti-counterfeiting.