Mercury Ion Sensing Using Mercaptosuccinic Acid-Derived Carbon Quantum Dots

Carbon quantum dots, prepared from mercaptosuccinic acid (MSA), were used to sense metal ions in aqueous solutions. Two fractions of nanoparticles were obtained after several purification steps, designated blue and green based on their color under UV illumination. We monitored the photoluminescence of the carbon nanoparticles upon the addition of metal ions. Stern-Volmer plots were made to determine whether photoluminescence quenching of the nanoparticles in solution occurred. Photoluminescence quenching was observed with adding Hg²⁺, Fe³⁺, Cr³⁺, Co²⁺, Ag⁺, Fe²⁺, Cu²⁺, and Ni²⁺. Most of these metal ions have partially filled d orbitals, contributing to the transfer of electrons from the photoexcited nanoparticles to the available empty orbitals of the metal ions. The detection limits for sensing the metal ions were calculated. The lowest detection limits observed were for Hg²⁺, with values of 4.1 and 1.4 ppm using the blue and green MSA-CQDs, respectively. Changes in the excitation wavelength and pH had a moderate impact on the spectral properties of the nanoparticles.