Influence of Group Modification at the Edges of Carbon Quantum Dots on Fluorescent Emission

Abstract

We present a detailed investigation on the effect of functional group modulation at the edges of carbon quantum dots (CQDs) on the fluorescence from the CQDs. The CQDs attached by N, S, and P elements are synthesized via pyrolysis of a mixture of citric acid and NH 3 H 2 O, H 2 SO 4 , and H 3 PO 4 , respectively. Thus, part of –COOH at the edges of CQDs can be converted into –C=O and functional groups such as –NH 2 , –SO 2 , –HSO 3 , and –H 2 PO 4 can connect to the carbon bonds. We find that the formation of the N/S/P-CQDs can reduce the amount of –COOH that attaches to the edges of sp 2 -conjugated π -domains located at centers of these CQDs. This effect can result in the reduction of the non-radiative recombination for electronic transition in these CQDs. As a result, the quantum yield (QY) for fluorescence from the CQDs can be efficiently enhanced. We demonstrate experimentally that the QYs for N/S/P-CQDs can reach up to 18.7%, 29.7%, and 10.3%, respectively, in comparison to 9% for these without functional group modulation. This work can provide a practical experimental approach in improving the optical properties of fluorescent CQDs.

Synthesis and Characterization of Green Carbon Dots for Scavenging Radical Oxygen Species in Aqueous and Oil Samples

“…Begheri et al [ 42 ] have suggested that during the thermal treatment, along with CDs more carbonized carbon particles (MCCPs) may also be formed as a major by-product, which have quenching effects on the photoluminescence of the CDs. The full width at half maximum (FWHM) of the emission band was used to evaluate both the homogeneity of the CDs [ 43 ] and the synthesis reproducibility. So, the fluorescence emission band of GCDs with its maximum intensity at 418 nm presented a FWHM of (126 ± 4.5) nm.…”

Carbon Quantum Dots Derived from Different Carbon Sources for Antibacterial Applications

“…Poor size control [19,[37][38][39][40][41][42][43][44] Avoids use of strong acids or alkalis, cost effective, suitable for widely different carbon sources…”

Passivated graphene quantum dots for carbaryl determination in juices

“…(C) Emission curves for the as-synthesized GQDs in acid conditions zag perimeter after doping produced an increase in the absorbance accompanied of a red-shifting [31]. On the other hand, an increment in the number of carboxyl groups at the edges of GQDs produces an increase in the nonradiative recombination of the electronic transitions, thus, reducing the quantum yield efficiency [32]. Absorbance spectra of all GQD types (Figure 2B) showed a broad band in the range of 350-400 nm, being very intense for those with passivated surfaces.…”

“…Smaller sizes of the dots (a5-and o5-GQDs) after longer reaction time achieved blue-shifted emission bands [33]. Blue-shifting emission may be possibly due to -OH groups and free zigzag sites states as the major contribution while the greener emission may be attributed to the presence of mostly -COOH functional groups as occurred in o1-GQDs [32]. The trend regarding the PL intensity is as follows: a5-GQDs > a1-GQDs > o1-GQDs > o5-GQDs, which is related to the oxidation degree (more oxidation of the layers led to less intense PL intensity).…”