Abstract
In this work, carbon dots were created from activated and non-activated pyrolytic carbon black obtained from waste tires, which were then chemically oxidized with HNO3. The effects caused to the carbon dot properties were analyzed in detail through characterization techniques such as ion chromatography; UV–visible, Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy; ζ potential; transmission electron microscopy (TEM); and spectrofluorometry. The presence of functional groups on the surface of all carbon dots was revealed by UV–visible, FTIR, XPS, and Raman spectra. The higher oxidation degrees of carbon dots from activated precursors compared to those from nonactivated precursors resulted in differences in photoluminescence (PL) properties such as bathochromic shift, lower intensity, and excitation-dependent behavior. The results demonstrate that the use of an activating agent in the recovery of pyrolytic carbon black resulted in carbon dots with different PL properties. In addition, a dialysis methodology is proposed to overcome purification obstacles, finding that 360 h were required to obtain pure carbon dots synthesized by a chemical oxidation method.
Highlights
The D band at approximately 1350 cm−1 is attributed to the functional groups on the carbon dots surface and indicates hydrocarbon or aliphatic moieties connected to the graphitic structure [11,57]
The Raman spectra (Figure 7) obtained from all of the carbon dots samples show a high degree of surface functionalization, which is consistent with the findings of Wu et al [58], who reported that defects on graphene quantum dots during chemical passivation cause an increase in the Carbon dots from activated precursors, except for Cd.H2 SO4 + KOH with an ID /IG of
The dialysis purification process was carefully analyzed by ion chromatography, concluding that 360 h were required to completely purify the carbon dots synthesized from pyrolytic carbon black from waste tires by a chemical oxidation method
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Carbon dots (CDs), a type of carbon nanomaterial with a size below 10 nm and a quasi-spherical shape, were discovered in 2004 by Xu et al [1] Their intriguing properties, such as biocompatibility and fluorescence, have made them important in a variety of fields [2,3,4,5,6,7]. In the case of top-down approaches, the precursors used for nanomaterial synthesis, which are waste carbon-rich materials, have an important role as an excellent option for the conversion of low-value materials into high-value products [10] In this manner, waste tires could be considered an ideal precursor to produce CDs because nearly 76% of their composition are carbon-based materials [11], and using a precursor with a low economic value reduces the cost of the process. The CDs dialysis purification process is examined to determine the time required for complete purification
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