Synthesis of blue emissive carbon quantum dots from Hibiscus Sabdariffa flower: Surface functionalization analysis by FT-IR spectroscopy

Carbon Quantum Dots (CQDs) were obtained, for first time, from the Hibiscus Sabdariffa flower (Roselle flower) by an easy, economical, and eco-friendly single-step carbonization method in air atmosphere at different times and carbonization temperatures. All the obtained samples presented luminescent properties with blue color emission. The obtained CQDs at different temperatures and times of calcination were characterized by Dynamic Light Scattering (DLS) technique to determine the average hydrodynamic diameter, it was found that at 400°C the smallest particle size was 34 nm, which are considered as agglomerates. The obtained CQDs were characterized by Fourier Transform Infrared Spectroscopy (FTIR) and compared with the Hibiscus Sabdariffa´s spectra to identify the functional groups that performed the surface passivation, and they allow the obtaining of luminescent properties; the identified groups were OCH and C-OH from xylose and glucose, which are part of the sambubioside group of anthocyanins (responsible the red coloration of the flower); -COOH, ortho-CO-C6H4-OH and =C-O-C. HRTEM technique showed monodisperse particles with approximate diameter of 10 nm and XRD demonstrate the samples composition of Carbon, with different crystalline system for samples synthesized at distinct conditions. The obtained CQDs at 200°C-1h (lower conditions), 300°C-3hrs (middle conditions) and 400°C-4hrs (higher conditions) were embedded into a thin PMMA film with a decrease in emissive intensity from CQDs with respect to embedded ones.