Why Carbonized Polyacrylonitrile Fibers Could Replace Mined Graphite in GO Production

By Dr Silpaja Chandrasekar, PhDReviewed by Laura ThomsonMar 18 2025

A recent article in Nano-Micro Small demonstrated a scalable method for synthesizing graphene oxide (GO) nanosheets from carbonized polyacrylonitrile (PAN)-based carbon fibers, thus reducing dependence on mined graphite. Traditional GO nanosheets were obtained using a nitric acid exfoliation route, exhibiting a distinct shape compared to commercial GO.

The proposed method achieved monolayer GO exfoliation using a 5% nitric acid solution, yielding 200 mg per gram of fiber. Eliminating mined graphite lowers environmental impact and improves sustainability. The study findings highlight a viable alternative for large-scale GO production.

Related Work

Past work primarily synthesized GO from natural graphite using methods like Hummers' oxidation, which required strong acids and oxidizers. Variability in graphite purity, with impurities like quartz and feldspar, complicated extraction and exfoliation necessitating additional purification steps. Alternative approaches, such as electrochemical oxidation, showed promise but required pre-treatment of graphite.

Researchers also explored greener methods, including oxidation at room temperature and reducing acid usage, but challenges remained in achieving a simple, scalable process.

Electrochemical GO Exfoliation

The study involves processing carbon fibers purchased from Mitsubishi Chemical Group, with graphene oxide acquired as an aqueous suspension from Angstron Materials.

The protective polymer coating on the fibers is removed using either a high-voltage electric field or heat treatment at 600 °C.

Electrochemical oxidation is performed in nitric acid solutions of varying concentrations, with carbon fibers as the working electrode and platinum as the cathode. The oxidation process was evaluated under different voltages, and alternative electrolytes such as sulfuric, phosphoric, and lactic acids were tested. The exfoliated graphene oxide solutions display various colors, indicating different oxidation levels.

Post-processing includes drying the exfoliated graphene oxide using natural evaporation, heated surface deposition, and freeze-drying, which is useful for refining extracted graphite.

Morphological characterization involves field emission scanning electron microscopy and transmission electron microscopy, with selected area electron diffraction used to determine crystal structures.

Thickness measurements are conducted using atomic force microscopy in Quantitative Nano-Mechanics mode. Functional groups are analyzed via Fourier-transform infrared spectroscopy, while Raman spectroscopy is performed to study vibrational modes. Tensile strength is measured using a universal testing machine, and electrical properties are examined through chronoamperometry and I–V curve analysis.

X-ray photoelectron spectroscopy is employed to analyze surface atomic composition and carbon functionalities, with deconvolution performed for precise peak identification.

Statistical analysis ensures repeatability, with triplicate experiments conducted per sample. Researchers measured particle sizes using scanning electron microscopy images, and thickness values were determined from atomic force microscopy data.

Raman spectra are smoothed using polynomial regression, and tensile strength values are averaged using multiple measurements. These characterization techniques also help compare GO derived from mineral-derived graphite with sustainable alternatives, ensuring high-quality production while reducing dependence on traditional mining processes.

GO Exfoliation

The morphology of GO nanosheets is analyzed by comparing commercial GO with GO exfoliated from carbon fibers.

Monolayer nanosheets are observed at an optimized 5 wt.% nitric acid electrolyte and a potential 3V for carbon fibers treated at 600 °C.

The commercial GO has a narrower size range of 0.2 to 0.8 µm, while exfoliated GO varies from 0.1 to 1 µm, though both have similar average lateral sizes.

The thickness of exfoliated GO was 0.9 (± 0.2) nm, consistent with literature values. Unlike the polygonal shapes of commercial GO, exfoliated GO shows circular or elliptical structures due to oxidation patterns, demonstrating a sustainable alternative that reduces reliance on graphite sourced from mining and mitigates the environmental impact of traditional extraction methods.

Chemical analysis using energy dispersive spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) reveals compositional differences between the samples.

Commercial GO contains 53.5 wt.% carbon and 46.5 wt.% oxygen, whereas exfoliated GO has 26.9 wt.% carbon, 53.0 wt.% oxygen, and 20.1 wt.% nitrogen due to nitrate residues.

Raman spectra confirm greater oxidation in exfoliated GO, with a red shift in D1, G, and D2 bands.

XPS data shows that exfoliated GO has a higher oxidation state with 23.7% oxygen and 8.8% nitrogen, compared to 10.4% oxygen in commercial GO. High-resolution C1s XPS spectra indicate that the higher oxygen content in exfoliated GO is mainly due to surface-bonded nitrogen rather than direct oxygen functionalization.

The conductive behavior of carbon fibers is examined during exfoliation using nitric acid, revealing distinct outcomes for different heat treatments.

Fibers treated uniformly at 600 °C exhibit a controlled and gradual exfoliation process, leading to better monolayer formation than those subjected to a 3-second high-voltage treatment at 1200 °C, which results in excessive fragmentation. The effective exfoliation phase lasts approximately 75 minutes, coinciding with efficient electron transfer within the crystalline regions.

Higher nitric acid concentrations hinder exfoliation, causing bulk detachment rather than controlled layer separation.

Structural analysis confirms that exfoliated fibers retain their integrity initially but lose electrical conductivity as sp²-hybridized nanosheets are removed. The study examines the drying behavior of exfoliated graphene oxide, noting challenges in preventing agglomeration. Modeling reveals that smaller counterions like nitrate enable rapid exfoliation, emphasizing the need for controlled conditions to produce high-quality nanosheets and providing a sustainable alternative to mined graphite, which requires extensive purification to remove mineral impurities.

Conclusion

This study demonstrated a scalable electrochemical exfoliation method for producing high-quality graphene oxide nanosheets from carbonized polyacrylonitrile fibers. The process achieved a high yield with precise control over morphology, offering potential for applications in energy storage, catalysis, and water purification. Nitrogen doping enhanced functionalization possibilities, while the method aligned with sustainability efforts by reducing reliance on mined graphite. Future work aims to explore renewable carbon sources for environmentally conscious graphene oxide production.

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