Abstract
The introduction of N doping atoms in the carbon network of Carbon Dots is known to increase their quantum yield and broaden the emission spectrum, depending on the kind of N bonding introduced. N doping is usually achieved by exploiting amine molecules in the synthesis. In this work, we studied the possibility of introducing a N–N bonding in the carbon network by means of hydrothermal synthesis of citric acid and hydrazine molecules, including hydrated hydrazine, di-methylhydrazine and phenylhydrazine. The experimental optical features show the typical fingerprints of Carbon Dots formation, such as nanometric size, excitation dependent emission, non-single exponential decay of photoluminescence and G and D vibrational bands in the Raman spectra. To explain the reported data, we performed a detailed computational investigation of the possible products of the synthesis, comparing the simulated absorbance spectra with the experimental optical excitation pattern. The computed Raman spectra corroborate the hypothesis of the formation of pyridinone derivatives, among which the formation of small polymeric chains allowed the broad excitation spectra to be experimentally observed.
Highlights
In the research of luminescent materials free of toxic and dangerous elements such as heavy and rare earth metals, a new class of carbon nanoparticles has been widely studied for its outstanding properties, which range from high quantum yield (QY) to easy and lowcost synthetic methods [1,2,3,4]
The possible mechanism of reaction among the two precursors during hydrothermal synthesis is reported in the following scheme (Scheme 1), where citric acid and hydrazine react to produce a pyridinone molecule—by means of condensation and dehydration reactions—with different possible substituents depending on the starting hydrazine molecule precursor (Scheme 1, path a)
In the case of simple hydrazine, we can reaction might evolve through the dimerization as described in hypothesize that the reaction might evolve through the dimerization as described in the Scheme path b, once moreand by means of condensation and dehydration reactions, leading to di-pyridinone structures
Summary
In the research of luminescent materials free of toxic and dangerous elements such as heavy and rare earth metals, a new class of carbon nanoparticles has been widely studied for its outstanding properties, which range from high quantum yield (QY) to easy and lowcost synthetic methods [1,2,3,4]. Carbon Dots (CDs) are generically defined as quasi-spherical nanometric particles with a core-shell structure composed by a graphitic carbon core and a disordered surface domain with oxygen and nitrogen-containing functional groups and moieties [5,6]. Thanks to this peculiar structure, CDs present highly desirable properties such as water dispersibility, low toxicity and tunable and efficient photoluminescence (PL), which makes them greener counterparts of heavy metals and semiconductor quantum dots [7,8]. A range so vast of applications relies on synthetic conditions and choice of the right precursor in order to achieve the desired properties
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