Abstract
The commercially acquired aqueous solution of “carbon quantum dots” sample was evaluated by optical absorption and fluorescence emission methods; in reference to aqueous dispersed small carbon nanoparticles and representative carbon dots prepared from chemical functionalization of the carbon nanoparticles. The results suggest a very low content of carbon that is associated with nanoscale carbon particles/domains in the as-supplied sample; and likely significant contamination by dye-like species/mixtures. In the absence of any information on the synthesis and history of the commercial sample, the possible cause of the contamination was illustrated by an example on similar dye formation in the one-pot carbonization synthesis of “red carbon dots” from citric acid–formamide precursor mixtures under too mild processing conditions that were insufficient for the intended carbonization. The negative impacts to the carbon dots research field by the apparent proliferation and now commercial availability of carbon-deficient or even largely carbon-less “carbon quantum dots”, which are more susceptible to dye contamination or dominance, are discussed.
Highlights
Carbon dots (CDots) [1,2] which are generally defined as small carbon nanoparticles with various surface passivation schemes (Figure 1) [3] have attracted much attention, as reflected by the large and ever increasing number of relevant publications in the literature [4,5,6,7,8,9,10,11,12,13,14,15]
The optical absorption spectrum of the as-supplied solution was measured as-supplied dot sample from MilliporeSigma was an aqueous solution of a very light pink in a standard cmThe cuvette, the observed absorbances were ~0.12 at was 400 nm and ~0.054 color
The excitation wavelength dependence of fluorescence spectra reverted back to the characteristic pattern (Figure 6), and so did the dependence of fluorescence quantum yields (Figure 5) [35]. These findings suggest that in the one-pot thermal processing, significantly more robust conditions than those used in many of the reported studies are necessary in order to ensure sufficient carbonization of the organic precursors
Summary
Carbon dots (CDots) [1,2] which are generally defined as small carbon nanoparticles with various surface passivation schemes (Figure 1) [3] have attracted much attention, as reflected by the large and ever increasing number of relevant publications in the literature [4,5,6,7,8,9,10,11,12,13,14,15]. These processes were generally not under conditions that would carbonize the precursors into soot-like materials composed of solid carbon nanoparticles, rather more like mixtures of some nanoscale carbon domains created as a result of the carbonization and the remaining organic species that survived the processing conditions For such mixtures to be considered as dot samples,. C 2019, 5, 70 carbon nanoparticles, rather more like mixtures of some nanoscale carbon domains created as a result of the carbonization and the remaining organic species that survived the processing conditions. MilliporeSigma understandably with respect to contentchemical of nanoscale carbon domains andhas dot recently started to market the dot sample of red absorption and emission features from unspecified structures in such samples and the potentially substantial interference from dye-like species source(s) or production method. The dangers for the proliferation of carbon-deficient or even largely carbon-less “carbon quantum dots” ( more vulnerable to dye contamination or dominance) to cause serious damages to the relevant research fields are highlighted and discussed
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