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.
Highlights
A distinct advantage of carbogenic nanoparticles is their scalable and low cost synthesis by means of pyrolytic treatment of virtually any type of carbon-rich material, including abundant and renewable resources[1] such as biomass2, grass3, leaves4, fruits5, eggs[6] or even bacteria[7]
It has been well-established that molecular fluorophores are often coproduced during the synthesis of C-dots[28,29,30] and their presence has a profound impact on the optical properties of the resulting material
In this work we focus on the pyrolytic treatment of citric acid (CA)/urea mixtures that remain the most popular precursor systems for the synthesis of C-dots, an approach that unavoidably
Summary
A distinct advantage of carbogenic nanoparticles (refereed hereafter as C-dots) is their scalable and low cost synthesis by means of pyrolytic treatment of virtually any type of carbon-rich material, including abundant and renewable resources[1] such as biomass2, grass3, leaves4, fruits5, eggs[6] or even bacteria[7]. The radius of pyrolytically derived C-dots falls within 2–20 nm, nanospheres with size in excess of 50 nm have been demonstrated[12,13] In addition to their preparation ease, C-dots exhibit supreme photoluminescent (PL) properties and show low toxicity for humans and the environment[14]. The QY can be substantially improved via heteroatom doping, surface functionalization and p assivation[8,9,10], while application of a voltammetric field might have a profound impact to the PL intensity[27] It has been well-established that molecular fluorophores are often coproduced during the synthesis of C-dots[28,29,30] and their presence has a profound impact on the optical properties of the resulting material. The carbonaceous pyrolysis products were subjected to filtration to generate a family of hybrid materials comprising both nanoparticles and unbound molecular fluorophores (F-series), while the solid residues (preF1-series) were oxidised via H NO3 resulting in yet another photoactive type of materials (F1-series)
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