Vol.
16 No.
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Comparative Study of Solvent-Assisted Exfoliation of Low Rank Coal for Few-Layer Graphene Production via Multi-Stage Ultrasonication Gimelliya Saragih1.
Vivi Purwandari2.
Zukhruf Akbari 3.
Nelson Silitonga4.
Abdillah5 145Department of Chemical Engineering.
Politeknik Teknologi Kimia Industri.
Medan.
Indonesia 23Faculty of Science.
Technology and Informatic.
Universitas Sari Mutiara.
Medan Indonesia
A R T IC L E I N F O
Article history:
Received September 29 , 2025 Received in revised form October 15.
Accepted Novemeber 20, 2025 Available online Novemeber 29, 2025 Keywords:
Graphene Low Rank Coal Exfoliation Ultrasonication ABSTRACT Low rank coal (LRC), due to its abundance and carbon richness, represents a promising and sustainable precursor for graphene synthesis.
This study compares the effects of different solvents CTAB .
%).
NaOH .
N).
HCCSOCE .
N), and isopropyl alcohol (IPA)Aion the exfoliation efficiency of LRC using a multi-stage ultrasonication approach.
The resulting materials were characterized by FTIR.
SEM.
TEM, and XRD to evaluate their structural, morphological, and chemical properties.
The findings reveal that IPA provides the most effective exfoliation, yielding few-layer graphene (FLG) with minimal oxidation and structural FTIR spectra showed reduced hydroxyl and carbonyl peaks in IPA-treated samples, while SEM and TEM confirmed more open and less-stacked layers.
XRD analysis indicated decreased crystallinity and larger interlayer spacing.
These results demonstrate that solvent selection plays a critical role in determining exfoliation performance, with IPA emerging as the most efficient and environmentally friendly medium for graphene production from LRC.
INTRODUCTION
Graphene is a two-dimensional nanocarbon material that exhibits extraordinary electrical conductivity (Gonyalves, 2025.
Zheng et al.
, 2.
high thermal stability (Gonyalves, 2.
, and superior mechanical strength.
Despite its immense potential in electronics (Menaa et al.
, 2021.
Rustamaji et al.
, 2.
energy storage, and catalysis (Fan et al.
, 2.
, the commercial-scale production of graphene remains limited due to the reliance on expensive precursors and energy-intensive synthesis routes (Tamuly et al.
, 2.
Among emerging alternatives, low rank coal (LRC) a carbon-rich, low-cost, and abundantly available material in Indonesia, offers a promising and underutilized source for graphene synthesis (Purwandari et al.
, 2.
Unlike highly crystalline graphite.
LRC possesses an amorphous structure enriched with oxygen-containing functional groups (Chen et al.
, making it chemically reactive and amenable to structural modifications (Das et al.
, 2.
This study explores the solvent-assisted exfoliation of LRC into graphene using a multi-stage ultrasonication method.
Four solventsAiCTAB.
NaOH.
HCCSOCE, and isopropyl alcohol (IPA)Aiwere evaluated based on their chemical interaction with LRC and their efficiency in layer separation and stabilization.
The resulting materials were analyzed by FTIR.
SEM.
TEM, and XRD to assess structural, morphological, and chemical Most previous studies have focused on graphite as the starting material and used expensive or toxic solvents for graphene exfoliation.
Only a few have explored low rank coal (LRC) as a viable carbon precursor, particularly in a comparative solvent conditions (Gao et al.
, 2.
Furthermore, the *Correspondence author.
E-mail: gimelliya@ptki.
id (Gimelliya Saragi.
doi: https://10.
21771/jrtppi.
2503-5010/2087-0965A 2024 Jurnal Riset Teknologi Pencegahan Pencemaran Industri-BBSPJPPI (JRTPPI-BBSPJPPI).
This is an open acces article under the CC BY-NC-SA license .
ttps://creativecommons.
org/licenses/by-nc-sa/4.
0/).
Accreditation number: (Ristekdikt.
158/E/KPT/2021 Saragih et.
/ Jurnal Riset Teknologi Pencegahan Pencemaran Industri Vol 16 No 2 .
168-175 combined influence of solvent types and multi-stage ultrasonication on the exfoliation efficiency and material quality remains largely unexamined.
address this gap, the present investigates the effect of four different solventsAiCTAB.
NaOH.
HCCSOCE, and isopropyl alcohol (IPA)Aion the exfoliation behavior of LRC through multi-stage ultrasonication.
The central objective of this study is to determine the solvent that produces the highest-quality few-layer METHODS Materials The main material utilized in this research was low rank coal (LRC) sourced from Musi Banyuasin.
Indonesia.
The coal was initially processed by crushing and screening it to achieve a particle size of less than 44 m with a 200-mesh sieve.
The solvents employed for exfoliation included 2% Cetyltrimethylammonium Bromide (CTAB) (Bu et al.
, 2.
, 1N Sodium Hydroxide (NaOH), 1N Sulfuric Acid (HCCSOCE), and Isopropyl Alcohol (IPA) (Dai et al.
, 2023.
Das et al.
, all of which were of analytical grade.
Deionized water was utilized in all the processes.
Sample Preparation The raw coal was subjected to pyrolysis at 400Ae 500AC for 3 hours to reduce volatile matter content.
Following thermal treatment, the sample was allowed to cool and stored in airtight containers prior to solvent Exfoliation Procedure graphene (FLG) with minimal oxidation and structural In this context, the term optimization refers to the comparative identification of solvent conditions that provide the best structural integrity and exfoliation efficiency, as verified through spectroscopic and microscopic analyses.
Around 2 grams of pretreated LRC was mixed into 100 mL of each solvent and stirred with a magnetic stirrer for 15 minutes to achieve homogenization ultrasonication setup.
Exfoliation was performed using a probe-type ultrasonic processor .
odel: MH-020S).
The operating frequency was 24 kHz, with amplitude set to 60% .
orresponding to an actual power of P = 120 W, measured at the generator Sonication was applied in a multi-stage regimen to limit overheating: n = 10 stages, each t_stage = 10 min, with cooling intervals = 15 min between stages .
otal effective sonication time t_total = 10 y 10 = 100 mi.
The suspension temperature was maintained below O 40 AC using an ice/water bath.
After sonication, the dispersion was centrifuged at 4000 rpm for 10 minutes to separate the graphene layers that were suspended.
The supernatant was gathered and Dehydrated in an oven at 105AC for a duration of 6 hours.
The residue was re-sonicated and centrifuged multiple times until all carbon particles were no longer visible.
Yulianto et.
/ Jurnal Riset Teknologi Pencegahan Pencemaran Industri Vol 15 No 1 .
10-14 Figure 1.
Sub-bituminous coal exfoliation Methods for Characterization The structural and chemical characteristics of the exfoliated samples were analyzed using various Fourier Transform Infrared Spectroscopy (FTIR.
Shimadz.
was employed to detect surface functional groups within the wavenumber range of 4000 to 400 cmAA.
The morphology and particle size distribution were examined using Scanning Electron Microscopy (SEM.
JEOL JSM-6.
High-resolution imaging for assessing layer thickness was achieved using Transmission Electron Microscopy (TEM.
JEOL JEM-2.
X-ray Diffraction (XRD.
PANalytical Empyrea.
was performed utilizing Cu K radiation ( = 1.
5406 yI) to assess the crystallinity and interlayer spacing.
LRC
In.
Moist (%, ad.
(%, ad.
The proximate analysis of the low rank coal (LRC) sample indicates it has promise as a suitable starting material for synthesizing graphene.
The sample contains a high percentage of volatile matter (VM) at 44.
40%, which suggests strong reactivity and ease of thermal decompositionAibeneficial traits for carbon exfoliation (Sun, 2.
The fixed carbon (FC) content of 40.
93% reflects a significant proportion of combustible carbon, crucial for forming graphitic structures (Sun, 2.
Meanwhile, the inherent moisture (In.
Mois.
is relatively moderate at 13.
which, although it may lower thermal efficiency, can enhance solvent interaction during liquid-phase Importantly, the ash content is low at 09%, minimizing the presence of inorganic residues RESULT AND DISCUSSION and thereby supporting the production of purer Proximate analysis graphene materials (Bu et al.
, 2.
Overall, this Table 1.
Proximate Analysis of low rank coal (LRC) proximate composition confirms that LRC possesses obtained from Musi Banyuasin.
Indonesia the fundamental characteristics necessary for Sample Proximateconversion into few-layer graphene via physical and chemical exfoliation methods.
Saragih et.
/ Jurnal Riset Teknologi Pencegahan Pencemaran Industri Vol 16 No 2 .
168-175 with C=O stretching (Nandiyanto et al.
, 2.
appeared in HCCSOCE-treated samples due to partial In contrast.
IPA-treated samples exhibited minimal oxygen-containing groups, preserving the C=C cmAA(Bouramdane et al.
, 2.
thereby indicating less disruption to the graphene basal planes.
These results confirm that IPA is a milder solvent, favoring structural integrity during exfoliation.
FTIR Spectral Analysis The FTIR spectra .
revealed distinct functional group variations between raw LRC and exfoliated samples.
A wide absorption band around 3400 cmAA was associated with OAeH stretching vibrations, which suggests the presence of hydroxyl (Dai et al.
, 2.
This peak was prominent in NaOH-treated samples, suggesting hydroxylation during exfoliation.
The band at 1700 cmAA, associated Figure 2.
FTIR Spectra of Low Rank Coal and Exfoliated Products Figure 2.
FTIR spectrum of raw low rank coal (ASD) showing characteristic peaks of hydroxyl group (-OH) 3493 cm-1, aliphatic carbon-hydrogen (CAeH) 2987 cm-1, carbonyl group (C=O) 1700cm-1, aromatic carbon-carbon double bond (C=C)1648 cm-1, and outof-plane bending of carbon-hydrogen (CAeH) bonds.
FTIR spectra of exfoliated coal using different solvents: NaOH.
IPA.
HCCSOCE, and CTAB.
Based on the FTIR results, the IPA-treated sample exhibited the most favorable spectral characteristics among all solvents.
The dominant aromatic C=C peak at 1595 cmAA was retained with the highest relative area, indicating that IPA effectively exfoliated the carbon layers while preserving the spA-hybridized graphene framework.
In contrast, the HCCSOCE-treated sample showed the smallest peak area and additional features near 998 cmAA, reflecting stronger oxidation and structural disruption.
The consistent yet minor shifts around 1411 cmAA observed in all treated samples suggest mild chemical modification, but in the case of IPA, these changes were minimal.
Overall, the broader aromatic intensity and absence of significant oxygenated bands confirm that IPA serves as the most efficient and least aggressive solvent for exfoliating low-rank coal into few-layer graphene.
SEM Morphological Observations SEM imaging .
revealed significant morphological differences before and after exfoliation.
The untreated LRC exhibited compact and agglomerated particles with rough surfaces.
Postexfoliation with IPA showed more porous structures and partially delaminated layers, suggesting effective CTAB and HCCSOCE-treated samples displayed moderate surface roughening and partial separation, while NaOH treatment resulted in irregular Yulianto et.
/ Jurnal Riset Teknologi Pencegahan Pencemaran Industri Vol 15 No 1 .
10-14 The open-layered morphology in IPA samples correlates with effective solvent penetration and cavitation-induced separation.
displayed diminished peak intensity and broadened diffraction signals, indicating reduced crystallinity and increased interlayer spacing.
Figure 3.
SEM Coal LRC and LRC-IPA TEM Imaging TEM analysis provided high-resolution images of exfoliated structures, confirming the presence of few-layer graphene (FLG) in IPA-treated samples.
The images exhibited transparent, thin sheets with moderate stacking, while CTAB and HCCSOCE treatments led to denser flake regions.
The hexagonal lattice fringes were visible in some regions, indicating the preservation of spA bonding networks.
NaOHtreated samples showed disordered carbon layers with limited transparency, suggesting partial degradation of the graphene structure.
Figure 4.
TEM image of LRC in IPA XRD Analysis XRD patterns revealed a broad peak at 2 OO 16A in raw LRC, characteristic of amorphous carbon (Moseenkov et al.
, 2.
Post-exfoliation.
IPA-treated samples Figure 5.
XRD analysis of LRC and LRC-NaOH.
LRC-IPA.
LRC-H2SO4.
LRC-CTAB samples The disappearance of the sharp peak at 26.
in IPA samples suggests successful delamination into few-layer graphene.
Meanwhile.
NaOH and HCCSOCE samples retained partial crystallinity, whereas CTAB-treated samples exhibited intermediate behavior.
These results substantiate that IPA enables better exfoliation with minimal disruption to the spA domains.
The XRD profiles (Figure .
show a broad diffraction band centered at 16A in raw LRC, corresponding to the amorphous .
plane of carbon.
Upon solventassisted exfoliation, all treated samples exhibit diminished peak intensity and increased broadness, reflecting disrupted graphitic stacking.
Among the tested solvents, the IPA-treated sample displays the most diffuse pattern and lowest .
intensity, confirming the effective delamination of LRC into few-layer graphene.
Conversely, the CTAB and HCCSOCE samples show partial retention of the .
reflection, indicating limited exfoliation.
Table 2.
XRD Parameters of Raw and SolventTreated LRC Samples Saragih et.
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168-175 Sample Main Diffraction Peak .
,A) .
Relative Intensity FWHM (Qualitativ.
Crystallinity / Structural Interpretation LRC 16.
Moderate Narrow Amorphous carbon with LRCAe NaOH 15.
Low Broad Partial oxidation and hydroxylation increases interlayer spacing.
LRCAe
IPA
Very low Very broad Highly indicates fewlayer graphene with minimal restacking.
LRCAe
HCCSOCE
Moderate Moderate Partial exfoliation and ordering or restacking LRCAe
CTAB
High Narrow Retained domains, possibly due to limited exfoliation.
Table 2 presents the XRD-derived parameters of raw and solvent-treated LRC samples.
The untreated coal (LRC) shows a broad amorphous .
peak at 16A, corresponding to a d-spacing of 0.
55 nm.
Following solvent-assisted exfoliation, all treated samples exhibit broadened and weakened diffraction peaks, confirming disruption of long-range stacking.
The IPA-treated sample, in particular, displays the lowest intensity and broadest profile, implying the formation of few-layer graphene.
In contrast.
NaOH and HCCSOCE cause partial oxidation and layer distortion, while CTAB retains partial graphitic order due to surfactant These findings confirm that IPA achieves the most efficient exfoliation with minimal structural CONCLUSION This study demonstrates that low-rank coal (LRC) can be effectively transformed into few-layer graphene (FLG) through solvent-assisted exfoliation using a multi-stage ultrasonication process.
Among the tested solvents, isopropyl alcohol (IPA) proved to be the most efficient and environmentally friendly medium, enabling the formation of thin, well-dispersed graphene layers while maintaining the structural integrity of the carbon framework.
Beyond laboratory findings, this work highlights a sustainable pathway for graphene production that utilizes an abundant, low-cost, and underexploited carbon source.
The process reduces reliance on high-purity graphite and toxic reagents.
Yulianto et.
/ Jurnal Riset Teknologi Pencegahan Pencemaran Industri Vol 15 No 1 .
10-14 offering compatibility with scalable, green manufacturing approaches.
These insights contribute to the growing field of sustainable nanocarbon synthesis and suggest that LRC-based graphene could complement existing industrial routes for energy storage, catalysis, and composite materials.
ACKNOWLEDGMENT
The author sincerely thanks everyone who has contributed to the execution of this research.
Special appreciation goes to the Badan Pengembangan Sumber Daya Manusia Industri (BPSDMI) under the Ministry of Industry, as well as to Politeknik Teknologi Kimia Industri Medan and Universitas Sari Mutiara Indonesia for their support in providing research facilities and technical assistance.
He also expresses his gratitude for the constructive collaboration and discussions with colleagues, which significantly contributed to improving the quality of this research.
Furthermore, he extends his gratitude to all members of the research team and laboratory staff for their assistance and dedication throughout the research
REFERENCE