Characterization of Chemically Activated Pyrolytic Carbon Black Derived from Waste Tires as a Candidate for Nanomaterial Precursor

Abstract

Pyrolysis is a feasible solution for environmental problems related to the inadequate disposal of waste tires, as it leads to the recovery of pyrolytic products such as carbon black, liquid fuels and gases. The characteristics of pyrolytic carbon black can be enhanced through chemical activation in order to produce the required properties for its application. In the search to make the waste tire pyrolysis process profitable, new applications of the pyrolytic solid products have been explored, such as for the fabrication of energy-storage devices and precursor in the synthesis of nanomaterials. In this study, waste tires powder was chemically activated using acid (H₂SO₄) and/or alkali (KOH) to recover pyrolytic carbon black with different characteristics. H₂SO₄ removed surface impurities more thoroughly, improving the carbon black's surface area, while KOH increased its oxygen content, which improved the carbon black's stability in water suspension. Pyrolytic carbon black was fully characterized by elemental analysis, inductively coupled plasma-optical emission spectrometry (ICP-OES), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), N₂ adsorption/desorption, scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), dynamic light scattering (DLS), and ζ potential measurement. In addition, the pyrolytic carbon black was used to explore its feasibility as a precursor for the synthesis of carbon dots; synthesized carbon dots were analyzed preliminarily by SEM and with a fluorescence microplate reader, revealing differences in their morphology and fluorescence intensity. The results presented in this study demonstrate the effect of the activating agent on pyrolytic carbon black from waste tires and provide evidence of the feasibility of using waste tires for the synthesis of nanomaterials such as carbon dots.

Keywords: carbon dots; chemical activation; particle characterization; pyrolysis; valorization.

Figure 1

Methodology followed for the recovery of pyrolytic carbon black from waste tires and the synthesis of carbon dots.

Figure 2

Scanning electron microscopy (SEM) images from (a) CB, (b) CB.H₂SO₄, (c) CB.KOH and (d) CB.H₂SO₄ + KOH. The right column shows the energy-dispersive X-ray spectroscopy (EDS) results from each carbon black sample.

Figure 3

(a) N₂ adsorption/desorption isotherm and (b) pore size distribution of carbon black samples.

Figure 4

Fourier transform infrared (FTIR) spectra of carbon black samples.

Figure 5

Fitted Raman spectra (black straight line) of (a) CB, (b) CB.H₂SO₄ (c) CB.KOH and (d) CB.H₂SO₄ + KOH. The D and G bands are plotted in a gray dash line (a–d). (e) XRD patterns of CB.H₂SO₄ + KOH inset: X-ray diffraction (XRD) pattern of the identified K₂CO₃ · 1.5H₂O, International Centre for Diffraction Data (ICDD) Reference code 98-007-8315).

Figure 6

Interaction plot showing the KOH activation effect increasing the effective diameter when H₂SO₄ activation is also involved.

Figure 7

Results of ζ potential analysis. (a) Interaction plot showing the KOH activation effect increasing the ζ potential and (b) oxygen content effect on the ζ potential of carbon black samples.

Figure 8

Transmission electron microscopy (TEM) images from (a) carbon dots from CB, (b) carbon dots from CB.H₂SO₄, (c) carbon dots from CB.KOH, and (d) carbon dots from CB.H₂SO₄ + KOH. The bar plots show the mean relative fluorescence units (RFU) at different emission ranges of carbon dots from fraction 0 to 10 kDa and 10 to 30 kDa. Note: Water was used as a control for fluorescence measurements; the maximum difference between the replicas was 101 RFU.