Preparing Colour-Tunable Tannic Acid-Based Carbon Dots by Changing the pH Value of the Reaction System

Biomass carbon dots (CDs) have the characteristics of being green, nontoxic, inexpensive, and simple to prepare, and they can be used in luminescence-related fields. In this study, red, green, and blue luminescent CDs were synthesised by a simple hydrothermal method under alkaline, neutral, and acidic conditions using TA as carbon source and o-phthalaldehyde as blend. The unique optical properties of these CDs are due to the differences in their degrees of conjugation, which can be controlled by the pH value of the reaction system. These three kinds of biomass CDs have good applications in light-emitting diodes (LEDs). By mixing biomass CDs with epoxy resin, warm, and cold white LEDs with Commission Internationale de l’Elcairage (CIE) coordinates (0.35, 0.36) were successfully constructed on extremely stable multicolour CDs. This study shows that these biomass CDs are a promising material for white LED lighting.