pH and solvent induced discoloration behavior of multicolor fluorescent carbon dots

Green, blue and pink fluorescent carbon dots (o/m/p-CDs) were prepared by one-step hydrothermal method with three isomers (o/m/p) of phenylenediamine as nitrogen and carbon sources and ethanol as solvent. The obtained carbon dots exhibited different luminescence behaviors, and the luminescence behaviors were affected by solvent and pH. More interestingly, m-CDs exhibited obvious discoloration behavior under different pH conditions and had excellent linear relationship under acidic and basic conditions, respectively. Furthermore, we combined mCDs with test paper, PVA film, and cotton fabric, respectively, to prepare composites for visual pH detection. The as-prepared composite material has excellent visual detection effect for a small amount of test sample (<5 mu L) in the fine pH range (0.5 unit), and could be applied to trace pH detection.