Ultrasensitive detection of Ag+ and Ce3+ ions using highly fluorescent carboxyl-functionalized carbon nitride nanoparticles.

The fluorescence quenching of carboxyl-rich g-C3N4 nanoparticles was found to be selective to Ag+ and Ce3+ with a limit of detection as low as 30 pM for Ag+ ions. A solid-state thermal polycondensation reaction was used to produce g-C3N4 nanoparticles with distinct green fluorescence and high water solubility. Dynamic light scattering indicated an average nanoparticle size of 95 nm. The photoluminescence absorption and emission maxima were centered at 405 nm and 540 nm respectively which resulted in a large Stokes shift. Among different metal ion species, the carboxyl-rich g-C3N4 nanoparticles were selective to Ag+ and Ce3+ ions, as indicated by strong fluorescence quenching. The PL sensing of mixtures of Ag+/Ce3+ and Ce3+ followed static Stern-Volmer kinetics with the Stern-Volmer constants determined to be 74.18 ×10^3 M-1 and 27.2 ×10^3 M-1 respectively. The PL sensing of Ag+ followed modified Stern-Volmer kinetics. Sensing was also demonstrated using commercial filter paper functionalized with g-C3N4 nanoparticles, enabling practical on-site applications.&#xD.