Fluorescent Nanocomposites of Cadmium Sulfide Quantum Dots and Polymer Matrices: Synthesis, Characterization, and Sensing Application

Abstract

Fluorescent materials for sensing have gained attention for the visual detection of different substances as metals and pesticides for environmental monitoring. This work presents fluorescent nanocomposites in solution, film, and paper obtained without capping and stabilizing agents, coming from quantum dots of cadmium sulfide (CdS QDs) and anionic–cationic polymer matrices. Fluorescent films were formed by casting and fluorescent paper by impregnation from the solutions. The optical properties of CdS QDs in solution showed absorption between 418 and 430 nm and a maximum emission at 460 nm. TEM analysis evidenced particle size between 3 and 6 nm and diffraction patterns characteristic of CdS nanocrystals. Infrared spectra evidenced changes in the wavenumber in the fluorescent films. The band gap values (2.95–2.82 eV) suggested an application for visible transmitting film. Fluorescent solutions by UV-vis and fluorescence evidenced a chemical interaction with glyphosate standard between 1 and 100 µg/mL concentrations. The analysis of red, green, and blue color codes (RGB) evidenced a color response of the fluorescent paper at 10 and 100 µg/mL, but the fluorescent films did not show change. Nanocomposites of chitosan and pectin, in solution and on paper, exhibited a behavior “turn-on” sensor, while carboxymethylcellulose had a “turn-off” sensor. This methodology presents three fluorescent materials with potential applications in visual sensing.