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. 2025 May 22;30(11):2275.
doi: 10.3390/molecules30112275.

Dependency of Catalytic Reactivity on the Characteristics of Expanded Graphites as Representatives of Carbonaceous Materials

Do Gun Kim  1 , Seong Won Im  1 , Kyung Hwan Ryu  2 , Seoung Ho Jo  1 , Min Gyeong Choe  1 , Seok Oh Ko  3
Affiliations

Dependency of Catalytic Reactivity on the Characteristics of Expanded Graphites as Representatives of Carbonaceous Materials

Do Gun Kim et al. Molecules. .

Abstract

Carbonaceous materials (CMs) have gained great attention as heterogeneous catalysts in water treatment because of their high efficiency and potential contribution to achieving carbon neutrality. Expanded graphite (EG) is ideal for studying CMs because the reactivity in CMs largely depends on graphitic structures, and most surface of EG is exposed, minimizing mass transfer resistance. However, EG is poor in adsorption and catalysis. In this study, EG was modified by simple thermal treatment to investigate the effects of characteristics of graphitic structures on reactivity. Tetracycline (TC) removal rate via activating peroxydisulfate (PDS) by the EG treated at 550 °C (EG550) was more than 10 times that of EG. The thermal modification did not significantly increase surfaces but led to increases in damaged, rough surfaces, graphitization degree, C content, defects, and C=O. Radical and non-radical pathways, such as SO4•-, O2•-, 1O2, and electron transfer, were involved in TC removal in EG550+PDS. TC degradation in EG550+PDS was initiated by hydroxylation, followed by demethylation, dehydroxylation, decarbonylation, and ring-opening. The ions ubiquitous in water systems did not significantly affect the performance of EG550+PDS, except for H2PO4- and HCO3-, suggesting the high potential of practical applications. This study demonstrated that graphitic structure itself and surface area are not detrimental in the catalytic reactivity of CMs, which is different from previous studies. Rather, the reactivity is governed by the characteristics, i.e., defects and functional groups of the graphitic structure. It is thought that this study provides valuable insights into the development of highly reactive CMs and the catalytic systems using them.

Keywords: antibiotics; catalytic degradation; expanded graphite; peroxydisulfate; thermal treatment.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
TC removal (A) by various EGs (EGs 0.1 g/L, PDS 0.1 mM), (B) at different EG550 doses in EG550+PDS (PDS 0.1 mM), and (C) at different PDS doses (EG550 0.1 g) in EG550+PDS (TC 20 mg/L).
Figure 2
Figure 2
Effects of temperature on TC removal in (A) EG350+PDS and (B) EG550+PDS (EGs 0.1 g, PDS 0.1 mM, TC 20 mg/L), as well as (C) Arrhenius relationships.
Figure 3
Figure 3
(A) N2 adsorption/desorption isotherm, (B) pore size distribution, and (C) FTIR spectra of EG, EG350, and EG550.
Figure 4
Figure 4
The Raman spectra of (A) EG, (B) EG350, and (C) EG550 (Grey symbols indicate raw data. Colored lines indicate deconvoluted bands).
Figure 5
Figure 5
The C1s XPS spectra of (A) EG, (B) EG350, and (C) EG550, and the O1s XPS spectra of (D) EG, (E) EG350, and (F) EG550 (Grey symbols indicate raw data. Colored lines indicate deconvoluted peaks).
Figure 6
Figure 6
(A) TC removal in the presence of scavengers; ESR spectra using (B) DMPO (10 mM) and (C) TEMP (10 mM) (EG550 0.5 g/L, PDS 0.5 mM, TC 20 mg/L); (D) reactive species generation by probe chemical conversion; (E) LSV (inset is I-t curve) and (F) EIS of EG550+PDS and EG550+PDS+TC.
Figure 7
Figure 7
Proposed TC degradation pathways in EG550+PDS.
Figure 8
Figure 8
TC removal in the presence of (A) cations and (B) anions, as well as (C) at different initial pH (EG550 0.1 g, PDS 0.1 mM, cations, and anions 10 mM).
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