pH-switched luminescence and sensing properties of a carbon dot–polyaniline composite

Abstract

A novel carbon dot–polyaniline (CD–PANI) composite has been successfully synthesized through an efficient one-pot chemical-oxidation polymerization and subsequently applied as a pH responsive material. PANI has a role in effectively passivating the CDs, which greatly enhances the luminescence intensity of the CDs. The pH-switched luminescence and pH sensing properties of the CD–PANI composite were investigated via detecting the fluorescence response on changing the solution pH. The switching operation exhibited excellent reversibility, and the luminescence intensity of the CD–PANI composite showed linear relationships with the solution pH in the range of 3.50–5.50 and 6.00–12.00. The reasons for the presence of two linear regions on the plot were further discussed in detailed. A probable mechanism was speculated to involve both the conjugation between the CDs and PANI, as well as the transfer between different PANI forms (emeraldine base and emeraldine salt). Moreover, OH⁻ ions could serve as the fluorescence quencher of the CD–PANI composite. The luminescence intensity of the CD–PANI composite displayed a good linear relationship with OH⁻ ions in the concentration range of 5–800 mM.