A rich gallery of carbon dots based photoluminescent suspensions and powders derived by citric acid/urea

Abstract

In this study we demonstrate simple guidelines to generate a diverse range of fluorescent materials in both liquid and solid state by focusing on the most popular C-dots precursors, i.e. the binary systems of citric acid and urea. The pyrolytic treatment of those precursors combined with standard size separation techniques (dialysis and filtration), leads to four distinct families of photoluminescent materials in which the emissive signal predominantly arises from C-dots with embedded fluorophores, cyanuric acid-rich C-dots, a blend of molecular fluorophores and a mixture of C-dots with unbound molecular fluorophores, respectively. Within each one of those families the chemical composition and the optical properties of their members can be fine-tuned by adjusting the molar ratio of the reactants. Apart from generating a variety of aqueous dispersions, our approach leads to highly fluorescent powders derived from precursors comprising excessive amounts of urea that is consumed for the build-up of the carbogenic cores, the molecular fluorophores and the solid diluent matrix that suppresses self-quenching effects.

Towards N–N-Doped Carbon Dots: A Combined Computational and Experimental Investigation

“…which let us imagine that the source of this emission could be the same in all samples. Instead, in the urea sample, the estimated lifetime is 5.6 ns, longer than in the other products, a value close to the one reported in literature [61][62][63]. Exciting the samples at higher wavelength, the average lifetime is the same in CA-Hy and CA-DM-Hy, but it definitely increases in CA-P-Hy with the presence of a longer time of 8.8 ns and reaching an average lifetime of 5.1 ns, close to that of CA-urea of 4.6 ns.…”

Carbon Dots/Iron Oxide Nanoparticles with Tuneable Composition and Properties

“…As summarized in Table 4, C/Fe-NPs demonstrate excellent antimicrobial activity after incubation with bacterial species for 24 h at 37 • C, causing 99.0-99.9% and 99.5-99.9% reduction in E. coli and S. aureus colonies, respectively. Very similar performance was observed for CNP230 as well as for a variety of C-dots-based materials [78], while Fe-NPs synthesized as a control sample via the same synthetic approach but without the carbogenic coating displayed 91.4% and 99.9% decrease in E. coli and S. aureus under identical conditions, respectively [37,79]. The photo-activated antimicrobial mechanism of C-dots has been largely associated with the formation of reactive oxygen species (ROS), while the occurrence of nanoparticle-bacterial membrane electrostatic attractions can damage the membrane leading to leakage of the cytoplasm [80].…”

Physicochemical Characterization and Antibacterial Properties of Carbon Dots from Two Mediterranean Olive Solid Waste Cultivars

“…The absorption spectrum of CDs_P ( Figure 2 a) exhibits broadband UV absorption, with a trend compatible with the light scattering operated by a small nanoparticle’s colloidal dispersion. The UV–Vis absorbance spectrum of CDs_P shows two detectable peaks as shoulders located around 270 nm and 300 nm, attributed respectively to the π–π* transition of CDs and n–π* transitions of the functional groups present on CDs [ 41 , 42 ]. These two absorption shoulders probably suggest the existence of conjugated structures as well as the presence of functional groups containing oxygen in the CDs [ 12 , 13 , 14 ].…”