Surface amino group modulation of carbon dots with blue, green and red emission as Cu2+ ion reversible detector

Clarifying the effects of surface amino groups on the luminescence and electronic structure for CDs. • CDs with blue, green and red emission were synthesized by electrochemical method. • The effects of surface amino groups on optical properties were investigated. • Surface states modulation mechanism of CDs is illustrated by an energy level diagram. • The B-CDs can serve as a fluorescent reversible turn-off–on detector for Cu 2+ ions. The surface functional groups of carbon dots (CDs) play a significant role in the luminescence performances, but it is still unclear about the effects of special groups on the luminescence mechanism since there are different groups on the surface of prepared CDs. Here, electrochemical method was adopted to synthesize initial CDs and graphite rods served as raw materials, and initial CDs were only modified with amino groups to regulate their surface states, which lead to the blue, green and red luminescence for the modified CDs. The amino groups with different contents are only introduced on the surface of CDs without affecting carbon core. With the increased contents of amino groups, the luminescence spectra of CDs can be successfully modulated from blue to red emission. In addition, the blue emitting carbon dots (B-CDs) have a specific response to Cu 2+ ions and can be applied as a fluorescent probe to detect Cu 2+ ions in the solution. Moreover, the addition of DL-serine can restore the blue emission of B-CDs quenched by Cu 2+ ions. Therefore, the B-CDs have great potential application as a fluorescent reversible ion detector.