Formation Mechanism of Carbogenic Nanoparticles with Dual Photoluminescence Emission

Abstract

We present a systematic investigation of the formation mechanism of carbogenic nanoparticles (CNPs), otherwise referred to as C-dots, by following the pyrolysis of citric acid (CA)-ethanolamine (EA) precursor at different temperatures. Pyrolysis at 180 °C leads to a CNP molecular precursor with a strongly intense photoluminescence (PL) spectrum and high quantum yield formed by dehydration of CA-EA. At higher temperatures (230 °C) a carbogenic core starts forming and the PL is due to the presence of both molecular fluorophores and the carbogenic core. CNPs that exhibit mostly or exclusively PL arising from carbogenic cores are obtained at even higher temperatures (300 and 400 °C, respectively). Since the molecular fluorophores predominate at low pyrolysis temperatures while the carbogenic core starts forming at higher temperatures, the PL behavior of CNPs strongly depends on the conditions used for their synthesis.

Hydrothermal Synthesis of Photoluminescent Nanocarbon from Hydroxylic Acids and Amines

“…The CDs at the reaction time of 1 h shows strong blue emission centered at ~450 nm under UV excitation at ~350 nm. For the CDs at longer reaction times, the blue emission becomes weaker, and the range of the emission and excitation wavelengths spread toward longer wavelength, resulting in wavelength dependent PL emission as reported in the previous works [15,16,21,23]. The red shifts of the emission and excitation spectra are in accordance with the increase of the absorption tail in Figure 3.…”

“…The decrease of the size of the CDs might lead to narrower distribution, because the experimental lower limit of the size distribution is close to the pore size of the dialyzing membrane (slightly smaller than 1 nm). According to the proposed mechanism of CDs formation [17,18,21], polymerization of CA and EDA is considered to be followed by the formation of CDs accompanied by various changes of the chemical structures.…”

“…The red shifts of the emission and excitation spectra are in accordance with the increase of the absorption tail in Figure 3. The spectral changes of the PL emission suggests that the formation 6 of carbogenic core which is considered to give emission at longer wavelengths [21]. Because careful fractionation of the CDs by their different surface polarities gives several distinct absorption bands in visible light region [24], the red shift may be caused by the surface modification of the CDs.…”

From highly graphitic to amorphous carbon dots: A critical review

“…In another approach, the thermal treatment of a mixture of citric acid and ethanolamine results in the evolution of a series of photoactive materials. 57 At the initial steps of pyrolysis, a crosslinked, highly viscous polymer network is formed due to intermolecular condensation and the subsequent formation of a precursor material that exhibits strong excitation-independent PL due to the presence of amide-containing fl uorophores (blue groups in Fig. 7 ).…”

Production of yellow-emitting carbon quantum dots from fullerene carbon soot

“…These methodologies can be mainly classified into two categories, namely, the "top-down" and "bottom-up" methods. The former includes laser ablation [12][13][14], plasma treatment [15], electrochemical oxidation [16][17][18][19], and acid-refluxing [20][21][22][23][24][25][26][27][28][29][30][31], while the latter is mainly focused on pyrolysis using simple heating and hydrothermal or microwave treatment [32][33][34][35]. Among these methods, the acid-refluxing of raw carbon materials offers a large-scale production of CQDs as it only needs simple instruments and can be easily scaled-up using standard industrial equipment.…”