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Article

Co-Polymerized P(AN-co-IA)-Derived Electrospun Nanofibers with Improved Graphitization via Dual-Metallocene Integration at Low Temperature

by
Taewoo Kim
1,2,
Tae Hoon Ko
1,2,
Byoung-Suhk Kim
2,
Yong-Sik Chung
2,* and
Hak Yong Kim
1,2,*
1
Department of Nano Convergence Engineering, Jeonbuk National University, Jeonju 561756, Republic of Korea
2
Department of Organic Materials and Textile Engineering, Jeonbuk National University, Jeonju 561756, Republic of Korea
*
Authors to whom correspondence should be addressed.
Inorganics 2025, 13(10), 318; https://doi.org/10.3390/inorganics13100318
Submission received: 25 August 2025 / Revised: 17 September 2025 / Accepted: 22 September 2025 / Published: 26 September 2025
(This article belongs to the Special Issue Carbon-Based Hybrid Materials for Environmental and Energy Applications)
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Abstract

In this study, COOH-functionalized co-polymer of acrylonitrile and itaconic acid (P(AN-co-IA)) is synthesized via free radical copolymerization using DMSO as solvent. The continuous non-aligned carbon nanofibers (CNFs) with different amounts of metallocene (zirconocene and ferrocene) are fabricated through electrospinning, followed by a series of heat treatments under an inert atmosphere. The influence of metallocenes on electrospun carbon nanofiber diameter, alignment, and structural ordering was systematically investigated using FESEM, XRD, Raman spectroscopy, and TEM. Incorporation of dual metallocenes significantly alters the fiber diameter, improves orientation, and promotes graphitic domain formation at 1100 °C, a much lower temperature than conventional graphitization. The optimized sample (Zr-Fe)1-P(AN-co-IA)-eGNF) exhibited the lowest ID/IG ratio compared to pristine and all prepared samples, indicating an improved degree of graphitization due to the uniform distribution of metallocene nanofiber matrix. Furthermore, the electrical conductivity of optimized (Zr-Fe)1-P(AN-co-IA)-eGNF reached the highest value (1654.5 S/m) due to the high degree of graphitization of carbon nanofibers. These results show that integrating dual metallocene is an efficient pathway for tailoring nanofiber morphology and achieving conductive, structurally ordered electrospun eGNFs at reduced temperatures, with potential applications in various fields.

Graphical Abstract

1. Introduction

Carbon has long been considered a major component of technological development due to its versatile and outstanding material properties [1,2]. Among the different forms of carbon, graphitic carbons hold a significant position for their use in high-tech advancements owing to their light weight, environmental friendliness, cost effectiveness, sustainability, and high thermal and electrical conductivity [3,4,5]. Graphitic carbons can be achieved via adopting different sources, such as biomass-derived activated carbons, metal–organic frameworks, and coordination polymers-derived porous carbon, thermal annealing of polymeric precursors, and electrospun nanofibers [4,6,7]. These various methods produce graphitic carbon in various forms, such as 0D, 1D, 2D, and 3D [8,9]. The highly graphitic carbon nanostructure in 1D form with a high aspect ratio and maximum carbon percentage can be prepared using the electrospinning technique [10]. Electrospinning is a fiber-producing technique that involves applying a high-voltage electric field to a polymer solution [11,12]. Various polymers such as polyacrylonitrile (PAN), polycaprolactone (PCL), polystyrene (PS), polyamic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), phenolic resins, and cellulose and its derivatives have been employed as a carbon source during the electrospinning process [13,14]. Among these, PAN is regarded as an identical polymer for electrospinning owing to its excellent spinnability, favorable stabilization and carbonization, high carbon yield, high mechanical strength, and ease of modification and compositing [15,16].
To obtain high-quality graphitic carbons, synthesizing PAN in the laboratory starting from its monomer, acrylonitrile, is considered the original and highly effective approach [17]. Another advantage of this PAN polymerization is that the chemical and functional composition of the synthesized PAN can also be in situ modulated by adopting a copolymerization process [18,19]. For instance, acrylonitrile and itaconic acid can be copolymerized to obtain the carboxylic acid-enriched PAN polymer, as itaconic acid provides its carboxylic acid functionalities to PAN during copolymerization and itself converts into poly(itaconic acid) polymer [20]. These groups promote cyclization and intermolecular crosslinking, leading to a thermally stable ladder-like polymer structure. As a result, the fibers exhibit enhanced thermal stability and oxidative resistance, while maintaining uniform morphology during electrospinning. This combination of improved stabilization and processability makes P(AN-co-IA) an effective precursor for producing high-quality graphitized carbon nanofibers [21,22]. Furthermore, the intrinsic properties of such P(AN-co-IA) copolymer can be easily modified by adding catalyst additives during electrospinning, which will ultimately produce high-quality graphitized carbons [17,19,23]. Such modification of the electrospinning solution of the laboratory-synthesized copolymer by adding some catalyst additives to enhance the degree of graphitization is regarded as catalytic graphitization [24,25]. Metallocenes, such as zirconocene and ferrocene, can be used as a catalytic agent to obtain graphitic carbon in a low-temperature graphitization process. Bimetallic or synergistic catalysis offers multiple active sites and cooperative electronic effects, lowering the barrier for converting amorphous carbon into graphitic structures. Zirconocene was chosen as a co-catalyst because it produces Zr-based intermediates (ZrC, ZrO2) that act as nucleation centers for the growth of graphitic domains. Combined with ferrocene, zirconocene enhances overall catalytic efficiency through a dual-metal synergistic effect, consistent with previous reports [17,26]. Zirconocene and ferrocene decompose into Zr and Fe nanoparticles, respectively, or their respective metal carbide nanoparticles at high temperature and catalyze the graphitization process during thermal annealing. Such metallic active sites act as nucleation sites for the rearrangement of the disordered carbon to the more ordered graphitic layers [27,28,29]. By comparison, conventional graphitization protocols that reach up to 3000 °C would require nearly three-fold higher energy input, in addition to more sophisticated equipment and a higher cost of operation. This striking reduction in energy demand demonstrates the energy-efficient nature of our approach and strengthens the case for its scalability [30]. Furthermore, these metallocenes catalyze the formation of other forms of carbon, such as carbon nanotubes (CNTs), having highly ordered graphitic carbon networks [31].
In a previous study (Kim et al. (2025)), boron and iron at an optimized concentration were used as co-catalysts to obtain highly graphitized PAN-derived carbon starting from the polymerization of acrylonitrile [19]. Kim et al. (2025) synthesized a composite of iron and carbon by grafting ferrocene on electrospun carbon nanofibers and tested it for energy storage applications [32]. Gumrukcu et al. (2021) synthesized ferrocene derivative-catalyzed electrospun PAN nanofibers [33]. Hunter et al. (2022) investigated the current understanding of the mechanistic aspects and limitations of the iron-catalyzed graphitization for the synthesis of highly graphitic carbons [34]. To the best of our knowledge, studies on the effect of the dual metallocene (ferrocene and zirconocene) on the catalytic graphitization of laboratory-synthesized P(AN-co-IA)-derived electrospun carbon nanofibers have not been conducted yet, despite their versatile applications. Therefore, synthesizing modified P(AN-co-IA) in the laboratory and electrospinning it with metallocene catalysts in optimized concentrations to obtain highly graphitic carbon is a crucial task.
Herein, we have synthesized carboxylic group functionalized P(AN-co-IA) in the laboratory starting from acrylonitrile and itaconic, adopting free radical copolymerization using DMSO as the solvent. The as-synthesized carboxylic group-enriched P(AN-co-IA) was used as a polymer source for electrospinning to obtain graphitic carbon nanofibers. To catalyze the degree of graphitization of the electrospun P(AN-co-IA) fiber, two metallocene additives, zirconocene and ferrocene, were added during electrospinning and subjected to low-temperature graphitization. The concentration of the zirconocene and ferrocene was varied in order to optimize the concentration for achieving a high degree of graphitization. The results showed that the sample containing 1 wt% of zirconocene and 1 wt% of ferrocene (Zr-Fe)1-P(AN-co-IA)-eGNF had the highest degree of graphitization. This work not only established the novel approach of copolymerization, electrospinning, and low-temperature graphitization as a viable approach for obtaining highly graphitized carbon but also demonstrated zirconocene and ferrocene as promising catalytic additives for the enhancement of the degree of graphitization.

2. Results and Discussion

The electrospun P(AN-co-IA) nanofiber-derived graphitized carbon nanofiber (P(AN-co-IA)-eGNF) was synthesized as illustrated in Figure 1 via various step processes. First, P(AN-co-IA) polymer was synthesized through a free radical polymerization reaction between acrylonitrile and itaconic acid in DMSO as the solvent, in which 1-dodecanethiol and AIBN were added as a chain transfer agent and as the initiator, respectively, under deoxygenated conditions. In this process, AIBN decomposes thermally at 60–70 °C to give cyno-isopropyl radicals and N2 gas, initiating polymerization by attacking the C=C double bond of acrylonitrile or itaconic acid monomers, propagating the chain. In the chain transfer step, the chain transfer agent (CTA; 1-dodecanethiol) donates a hydrogen atom to growing radical chains, forming a terminated polymer and regenerating a new radical, also ensuring processability by controlling the molecular weight of the polymer. Termination of polymer chains occurred via radical coupling or disproportionation mechanisms. The viscous copolymer solution was dried at 60 °C using a vacuum oven to remove DMSO solvent and again dissolved in DMF prior to electrospinning [35,36,37,38].
The successful synthesis of P(AN-co-IA) is confirmed by comparative 1H-NMR analysis of P(AN-co-IA) dissolved in DMSO-d6 and DMF (Figure 2a,b). The peak observed at 1.98–2.16 ppm (*) is assigned to the methylene protons (-CH2-) of the polyacrylonitrile units, while the signals at 3.07–3.2 ppm (#) correspond to the methine proton (-CH-) along the polymer backbone. The intense peaks at 3.3 ppm and 2.5 ppm are attributed to residual water (H2O) and the residual solvent (DMSO-d6), respectively [39,40]. Notably, the 1H-NMR spectra of P(AN-co-IA) in DMSO and DMF show similar patterns; however, the -CH2- and -CH- peaks in DMF are slightly shifted to a lower value and of reduced intensity, likely due to the solvent effect. FTIR spectra of P(AN-co-IA) in DMSO and DMF are shown in Figure 2c,d. The strongest peak in the spectrum of P(AN-co-IA) in DMSO appears at ~2243.60 cm−1 and corresponds to the stretching vibration (ν) of the nitrile group (C≡N); this peak is slightly shifted in P(AN-co-IA) dissolved in DMF (~2242.68 cm−1), indicating that the acrylonitrile units remain uninterrupted in long sequences in both conditions [41]. The polymer backbone also shows a characteristic C-H stretching and bending vibration (νC–H) at ~2936.28–2938.28 cm−1 and 1458.24 cm−1 [42]. The peak at 1625.9–1645.09 cm−1 is attributed to the hydrolysis of AN units during polymerization. The strong shoulder peaks at ~1360 cm−1 and 1060.64–1070.19 cm−1 are attributed to symmetric bending vibration of -CH3 groups and the bending vibrations of -CN groups [43]. Evidence of itaconic acid incorporation is provided by oxygen-containing vibrations: a broad O-H stretching band at ~3608.39 cm−1 (associated with hydrogen-bonded carboxylic acid groups) and a pronounced band in the carbonyl region at ~1625–1645 cm−1 corresponding to C=O stretching of carboxyl/acidic groups (or carboxylate-related modes) [44]. Additional supporting bands for COOH functionality appear in the 1440–1200 cm−1 region, specifically at ~1360.22 cm−1 and ~1240.2–1247.03 cm−1, which match the expected C–O stretching and –OH bending vibrations of carboxylic acids and related ester/acid structures in PAN copolymers. The weaker peaks at the fingerprint region (~1050–414 cm−1) correspond to C-C skeletal and deformation modes of the polymer backbone and side groups. The presence of small peaks around ~952–1022 cm−1 is also consistent with the literature and can be attributed to C-H out-of-plane bending and skeletal vibrations from itaconic acid-modified PAN fibers [20,45,46]. This spectrum confirms the successful formation of COOH-functionalized P(AN-co-IA) copolymer, showing strong PAN features (nitrile and CH modes) together with clear carboxyl-related bands (carbonyl, hydroxyl, and C-O) from IA. The electrospun P(AN-co-IA) carbon nanofiber stabilized at 250 °C for 1 h at a heating rate of 2 °C min−1 in a furnace (Figure S1a) and carbonized at 700 °C for 1 h at a heating rate of 2 °C min−1 in a tube furnace. The carbonized nanofiber mats (Figure S1b) were then graphitized at 1100 °C for 1 h under a nitrogen atmosphere at the same heating rate (Figure S1c).
Upon increasing the dual-metallocene by double, as shown in Figure 3e and Figure 4a–d, the (Zr–Fe)1-P(AN-co-IA)-eGNF nanofibers became more homogeneous, exhibiting unique alignment, with a few roughness and diameters ranging from 300 to 400 nm (average diameter = 322 ± 61.44). This composition showed excellent electrospinning performance, likely due to the synergistic action between zirconocene and ferrocene, which improved both conductivity and rheological properties of the solution. The EDX elemental maps in Figure 4e–e4 reveal a homogenous dispersion of Zr, Fe, O, and N throughout the carbon matrix after graphitization, confirming the effective incorporation of both metallocenes into the nanofiber network. However, further increasing both metallocene concentrations by four times, as shown in Figure 3f and Figure S7, the obtained nanofibers have a slightly larger diameter (average diameter = 357 ± 131.30) with some rough surface. This may be attributed to metallocene aggregation within the polymer matrix at higher concentrations, disrupting fiber uniformity and morphology. These results confirm that both the type and ratio of metallocene additives significantly influence nanofiber diameter, alignment and surface structure. An intermediate concentration of dual metallocene-tuned morphology for further improvements.
The X-ray diffraction (XRD, Cu Kα radiation (λ = 0.154 nm)) was used to study the amorphous and crystalline carbon by observing the presence or absence of sharp diffraction peaks in the XRD pattern. Figure S8 and Figure 5a show the XRD patterns of P(AN-co-IA)-eGNF, Zr1-P(AN-co-IA)-eGNF, Fe1-P(AN-co-IA)-eGNF, and (Zr-Fe)1-P(AN-co-IA)-eGNF, respectively. The characteristic peaks at around ~24.38° and ~44.1° observed in (Zr-Fe)1-P(AN-co-IA)-eGNF sample correspond to the (002) and (100) planes of graphitized carbon derived from P(AN-co-IA) polymer, reflecting enhanced structural order due to the catalytic effects of metallocene [17,47]. In Zr1-P(AN-co-IA)-eGNF, an additional peak at 30.27° is attributed to the ZrO2 (PDF#50-1089), which was formed during the stabilization of the sample in an oxygen atmosphere. The effect of integrated metallocene on the degree of graphitization in carbon nanofiber was analyzed via Raman spectroscopy (Figure 5b–f). The G-band (at around ~1580 cm−1) corresponds to the in-plane vibration of sp2-hybridized carbon atoms and is a key parameter for assessing graphitic, ordered carbon structures. However, the disordered carbon, such as structural defects, edges, or amorphous regions, is indicated by the D-band near 1350 cm−1 [48]. The intensity ratio of D-band and G-band (ID/IG) is a widely accepted metric for evaluating the crystallinity and quality of graphitic materials: a higher intensity ratio indicates more defects, whereas a lower intensity ratio indicates more graphitic [49]. Additionally, the 2D band (at around 2650–2750 cm−1) provides information about the number of layers and stacking in graphitic materials: an intense 2D band means few but well-ordered graphitic domains, while a less intense 2D band reflects multi-layers or more structural disorders [17,50,51]. The typical spectrum measured for all prepared samples exhibits three peaks that are characteristic of P(AN-co-IA)-based CFs at 1330, 1585, and 2750 cm−1, which correspond to the D, G, and 2D bands, respectively, and they indicate the successful carbonization of electrospun P(AN-co-IA) and metallocene-integrated carbon nanofiber. Although Raman spectra have a similar pattern, metallocene-integrated P(AN-co-IA)-based eGNF displays higher and intense G-band peaks than the pattern of pure P(AN-co-IA)-eGNF, indicating a more graphitic nature than a defective nature. As shown in (Figure 5b,c), the zirconocene- and ferrocene-integrated eGNF have a low ID/IG ratio compared to pure P(AN-co-IA)-eGNF, demonstrating the potential of metallocene in enhancing graphitization. Among the various amounts of dual-metallocene-integrated electrospun and in comparison to some reported catalytic graphitization of carbon-based materials, (Zr-Fe)1-P(AN-co-IA)-eGNF demonstrates a low ID/IG ratio, corresponding to a higher degree of graphitization (as presented in Figure 5f, and Table S1) [52,53,54,55,56]. This enhancement is attributed to the catalytic activity of the metallocene, which facilitates the rearrangement of disordered carbon into more ordered graphitic structures during the carbonization process. Furthermore, a broad 2D peak is observed in the metallocene-integrated electrospun fibers, which is attributed to the formation of turbostratic graphite stacked or misoriented multi-layer graphene with smaller crystalline domains or the presence of residual defects within the carbon structure [57,58]. These results suggest that metallocene integration not only catalyzes graphitic domain formation but also promotes structural ordering within the carbon nanofiber matrix. In contrast, both lower (Zr-Fe)0.5 and higher (Zr-Fe)2 metallocene contents result in a diminished graphitic structure (Figure 5d,e). The insufficient catalytic effect at a low amount of metallocene fails to initiate efficient graphitic domain formation, leading to a higher degree of disorder. On the other hand, an excessive amount of metallocene induces aggregation within the polymer matrix, which can disrupt the homogeneity and electrospinning process and hinder the formation of continuous carbon domains (introducing more structural defects) during pyrolysis [19]. This suggests that an optimal concentration of metallocenes is essential to balance catalytic graphitization and to produce highly graphitized electrospun carbon nanofibers. The conductivity of carbon nanofiber is directly related to the degree of graphitization. The conductivity of carbon nanofibers is directly related to the degree of graphitization [59]. Higher electrical conductivity is attributed to a high degree of graphitization, where the formation of well-ordered sp2 carbon domains facilitates π-electron delocalization and creates continuous conduction pathways for charge transport [60,61]. As shown in Table S2, the optimum amount of dual-metallocene-integrated (Zr-Fe)1-P(AN-co-IA)-eGNF also demonstrates high electrical conductivity, which was measured by a four-probe machine, and is attributed to a higher degree of graphitization than pristine P(AN-co-IA)-eGNF and all other prepared samples.
The integrated metallocene (zirconocene and ferrocene) enhanced graphitization owing to their catalytic activity. During the high-temperature carbonization process, the integrated metallocenes ferrocene (FeCP2) and zirconocene (ZrCP2) thermally decompose to generate metallic Fe0 and Zr0 nanoparticles, along with the release of volatile organic byproducts and decomposed cyclopentadienyl (Cp) ligands [62,63,64,65]. These in situ-formed metal species act as effective catalysts for graphitization. Specifically, Fe0 facilitates the carbon dissolution–precipitation mechanism, where amorphous carbon dissolves into the Fe matrix at elevated temperatures and subsequently precipitates out as well-aligned graphitic layers upon cooling [34]. Concurrently, Zr0 may undergo carbothermal reactions to form ZrC nanocrystals, which locally promote the ordering of surrounding carbon atoms into graphitic domains [66,67]. The combination of zirconocene and ferrocene introduces a synergistic effect that enhances catalytic activity through improved metal dispersion, stabilization on the carbon matrix, and cooperative bimetallic interactions that lower the graphitization temperature and increase crystallinity [68]. Furthermore, the cyclopentadienyl (Cp) ligands from the metallocenes may contribute structurally by forming intermediate aromatic species that facilitate early-stage ring fusion, aiding in the nucleation of graphitic structures during the initial phase of carbonization [69]. This multifaceted catalytic and templating behavior significantly enhances the formation of highly graphitized carbon nanofiber structures.
XPS was performed to confirm the elemental state of (Zr-Fe)1-P(AN-co-IA)-eGNF. The low-resolution spectra (Figure S9a) covering the binding energy range of 0–800 eV confirm the incorporation of C, N, O, Zr, and Fe elements, indicating the successful formation of a metal–carbon composite during graphitization. High-resolution XPS spectra of C 1s (Figure S9b) show multiple deconvoluted peaks including C-C, C-N, C-O, C=O, and carbide carbon at binding energies of ~284.7, ~285.6, ~286.2, ~287.9, and ~282.3 eV, respectively, indicating various carbon bonding environments, with a dominant sp2-hybridized C–C peak [70,71]. The N 1s spectrum (Figure S9c) depicts distinct contributions from pyridinic-N (~398.4 eV), pyrrolic-N (~400.1 eV), graphitic-N (~401.3 eV), and oxidized-N species (~403.2 eV), confirming the incorporation of nitrogen into the carbon lattice [72]. The O 1s spectrum (Figure S9d) shows peaks related to C-O (~532.3 eV), C=O, and metal-O at ~532.4, ~531.1, and ~529.6 eV, indicating the oxidized carbon and metal structures [73]. The Zr 3d spectrum (Figure S9d) exhibits well-defined peaks corresponding to Zr 3d5/2 and Zr 3d3/2 of Zr4+ species, along with additional peaks for Zr-O (~182.5 eV), Zr-C (~180.1 eV), and Zr-O-C (~181.3 eV), indicating mixed oxidation states and bonding environments. The Fe 2p spectrum (Figure S9f) presents complex multiple splitting with major peaks at Fe 2p3/2 (~711.3 eV) and Fe 2p1/2 (~724.6 eV), as well as satellite features, denoting the presence of Fe3+/Fe2+ species and metallic Fe0 (~707.6 eV) [72,74]. These results demonstrate a partial reduction of iron and its involvement in the evolution of graphitic structure. The coexistence of oxide and carbide forms of Zr and Fe indicates active sites for catalytic graphitization [17].
The direct observation of the integrated metallocene-derived nanoparticles and the formation of graphitic layers or fringes of zirconocene- and ferrocene-integrated P(AN-co-IA)-based carbon nanofibers was analyzed by transmission electron microscopy (TEM). From Figure 6a–c, it can be observed that the graphitized (Zr-Fe)1-P(AN-co-IA)-eGNF nanofiber exhibits a continuous tubular morphology with a dense structure, consistent with FESEM images. The observation of black spots throughout the nanofiber matrix suggests the well integration of metallocene-derived nanoparticles during synthesis. These embedded nanoparticles enhanced graphitization during the thermal treatment process. The observed well-developed ordered or graphitic fringes, which correspond to the (100) plane Ref. pattern carbon, #41-1487) of graphitized carbon at high-resolution image (shown in Figure 6d and Figure S10), suggest effective carbonization and graphitization [75,76,77]. Furthermore, the homogeneous integration of metallocene is also confirmed via elemental mapping. As shown in Figure 6e–e5, (Zr-Fe)1-P(AN-co-IA)-eGNF demonstrates a homogeneous distribution of C, Zr, and Fe elements across the nanofiber. These findings confirm that the embedded metallocenes catalyze the transformation of amorphous carbon into highly ordered graphitic domains upon thermal treatment, highlighting the effectiveness of Zr- and Fe-based metallocenes in promoting carbon crystallinity.

3. Materials and Methods

Materials and details of characterization techniques are presented in Sections S1.1 and S1.2 of the electronic Supplementary Information file, respectively.

3.1. Synthesis of P(AN-co-IA) Co-Polymer via Radical Polymerization

The P(AN-co-IA) polymer was synthesized via free radical polymerization using DMSO as the solvent. In a typical procedure, a mixture of acrylonitrile (9.0 g, 0.17 mol, MW = 53.06) and itaconic acid (1.0 g, 7.7 mmol, MW = 130.10) was dissolved in 50 mL of DMSO in a 100 mL three-neck round-bottom flask equipped with a stirrer, a condenser, and a nitrogen inlet. To this monomer solution, 1-dodecanethiol (0.1 mL, MW = 202.40) was added as a chain transfer agent. The solution was then deoxygenated by bubbling nitrogen gas through it for 30 min under constant stirring to remove any dissolved oxygen. After deoxygenation, 2,2′-azobisisobutyronitrile (AIBN, 0.1 g, MW = 164.21) was added as a radical initiator, and the flask was sealed. The polymerization reaction was carried out at 65 °C for 8 h under a continuous nitrogen atmosphere. Upon completion of the reaction, the resulting viscous polymer solution (viscosity: 52000 centipoise) was poured into a mold to allow partial evaporation of the DMSO solvent. The solidified product was then washed thoroughly with methanol to remove any residual solvent and unreacted monomers and subsequently dried under vacuum at 60 °C for 24 h.

3.2. Electrospinning and Graphitization of Metallocene-Integrated P(AN-co-IA) Nanofiber Mats

The obtained solid P(AN-co-IA) polymer is dissolved in DMF to make an electrospinable viscous solution. A 20 wt% P(AN-co-IA) solution was prepared, and electrospinning was carried out using a 21-gauge metal needle, a voltage of 17 kV, and a feed rate of 0.05 mL min−1 at room temperature (25 ± 2 °C) and humidity (50 ± 5%) conditions. The resulting nanofiber mat, collected in a rotating steel collector fixed at a 15 cm distance from a 21-gauge metal needle, was designated as P(AN-co-IA)-eNFs. To incorporate metallocene additives, 1 wt% (relative to the weight of the polymer solution) of zirconocene, ferrocene, or their mixtures was physically blended into the P(AN-co-IA) solution prior to electrospinning. Specifically, P(AN-co-IA) solutions were prepared with 1 wt% zirconocene (Zr-P(AN-co-IA)-eNF), 1 wt% ferrocene (Fe-P(AN-co-IA)-eNF), and wt% of both metallocenes decreased and increased by two-fold to optimize the amount of metallocene, designated as (Zr–Fe)0.5-P(AN-co-IA)-eNF, (Zr–Fe)1-P(AN-co-IA)-eNF, and (Zr–Fe)2-P(AN-co-IA)-eNF, respectively, and electrospinning was performed as the above-mentioned condition. All electrospun nanofiber mats were stabilized in a muffle furnace and then carbonized at 700 °C for 1 h at a heating rate of 2 °C min−1 in a tube furnace. The carbonized mats were then graphitized at 1100 °C for 1 h under a nitrogen atmosphere at the same heating rate. The final graphitized carbon nanofiber mats were designated as P(AN-co-IA)-eGNF, Zr1-P(AN-co-IA)-eGNF, Fe1-P(AN-co-IA)-eGNF, (Zr-Fe)0.5-P(AN-co-IA)-eGNF, (Zr-Fe)1-P(AN-co-IA)-eGNF, and (Zr-Fe)2-P(AN-co-IA)-eGNF, respectively.

4. Conclusions

In summary, we successfully developed COOH-functionalized P(AN-co-IA) copolymer from acrylonitrile and itaconic acid by co-polymerization process and developed a low-temperature (1100 °C) catalytic graphitization strategy for electrospun P(AN-co-IA) nanofibers by integrating zirconocene and ferrocene as dual metallocene catalysts. The integration of dual metallocene additives into the co-polymer solution effectively altered fiber diameter, improved alignment, and promoted graphitic domain formation during carbonization, followed by graphitization. The improved electrical conductivity of (Zr-Fe)1-P(AN-co-IA)-eGNF further confirmed the improved graphitization effect of metallocene. These results highlight that metallocene-integrated P(AN-co-IA)-derived CNFs provide an effective approach to design highly conductive and structurally ordered carbon nanofibers, offering great promise for various applications such as EMI shielding, heat dispersion, energy storage and conversion, sensor, etc.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/inorganics13100318/s1, Figure S1: photographic image of (a) electrospun P(AN-co-IA)-eCNF mat, (b) stabilized P(AN-co-IA)-eCNF mat, and (c) graphitized P(AN-co-IA)-eGNF mat. Figure S2: Histogram of fiber diameter distribution of: (a) P(AN-co-IA)-eGNF, (b) Zr1-P(AN-co-IA)-eGNF, (c) Fe1-P(AN-co-IA)-eGNF, (d) (Zr-Fe)0.5-P(AN-co-IA)-eGNF, (e) (Zr-Fe)1-P(AN-co-IA)-eGNF, and (f) (Zr-Fe)2-P(AN-co-IA)-eGNF. Figure S3: (a,b) FESEM images of graphitized P(AN-co-IA)-eGNF mat, and (c–e) elemental mapping of graphitized P(AN-co-IA)-eGNF. Figure S4: (a,b) FESEM images of graphitized Zr1-P(AN-co-IA)-eGNF, and (c–f) elemental mapping of graphitized Zr1-P(AN-co-IA)-eGNF. Figure S5: (a,b) FESEM images of graphitized Fe1-P(AN-co-IA)-eGNF, and (c–f) elemental mapping of graphitized Fe1-P(AN-co-IA)-eGNF. Figure S6: (a,b) FESEM images of graphitized (Zr-Fe)0.5-P(AN-co-IA)-eGNF, and (c–g) elemental mapping of graphitized (Zr-Fe)0.5-P(AN-co-IA)-eGNF. Figure S7: (a,b) FESEM images of graphitized (Zr-Fe)2-P(AN-co-IA)-eGNF, and (c–g) elemental mapping of graphitized (Zr-Fe)2-P(AN-co-IA)-eGNF. Figure S8: XRD pattern of P(AN-co-IA)-eGNF,(Zr1-P(AN-co-IA)-eGNF, and  Fe1-P(AN-co-IA)-eGNF. Figure S9: XPS analysis of (Zr-Fe)1-P(AN-co-IA)-eGNF, (a) low-resolution XPS spectra, (b) high-resolution XPS spectra of C 1s, (c) high-resolution XPS spectra of N 1s, (d) high-resolution XPS spectra of O 1s, (e) high-resolution XPS spectra of Zr 3d, and  (f) high-resolution XPS spectra of Fe 2p. Figure S10: HR-TEM image showing lattice fringes with a d-spacing of 0.201 nm of (100) plane. Table S1: A comparison table of all prepared materials, including terms of temperature, and catalytic graphitization (ID/IG) of carbon-based electrospinning materials with some reported materials. Table S2: Conductivity measurement of all prepared samples by the 4-probe machine.

Author Contributions

T.K.: methodology, formal analysis, investigation, writing—original draft preparation, and data curation; T.H.K.: visualization, data curation, software, and writing—review and editing; B.-S.K.: writing—review editing and validation; Y.-S.C. and H.Y.K.: writing—review and editing, methodology, supervision, resources, project administration, funding acquisition, and supervision. All authors have read and agreed to the published version of the manuscript.

Funding

The Korean Research Institute for Defense Technology Planning and Advancement (KRIT), funded by the Korean government (DAPA-Defense Acquisition Program Administration) (Grant No. KRIT-CT-22-025, Ultra-High Modulus Carbon Fiber Research Laboratory), supported this work.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author due to legal or ethical reasons.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this research.

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Inorganics 13 00318 g001
Figure 1. Schematic representation for the synthesis of graphitized nanofiber materials.
Figure 1. Schematic representation for the synthesis of graphitized nanofiber materials.
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Figure 2. 1H-NMR analysis of (a) P(AN-co-IA)@DMSO and (b) (P(AN-co-IA)@DMF; FTIR analysis of (c) P(AN-co-IA)@DMSO and (d) (P(AN-co-IA)@DMF.
Figure 2. 1H-NMR analysis of (a) P(AN-co-IA)@DMSO and (b) (P(AN-co-IA)@DMF; FTIR analysis of (c) P(AN-co-IA)@DMSO and (d) (P(AN-co-IA)@DMF.
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Figure 3. FESEM images of (a) P(AN-co-IA)-eGNF, (b) Zr1-P(AN-co-IA)-eGNF, (c) Fe1-P(AN-co-IA)-eGNF, (d) (Zr-Fe)0.5-P(AN-co-IA)-eGNF, (e) (Zr-Fe)1-P(AN-co-IA)-eGNF, and (f) (Zr-Fe)2-P(AN-co-IA)-eGNF.
Figure 3. FESEM images of (a) P(AN-co-IA)-eGNF, (b) Zr1-P(AN-co-IA)-eGNF, (c) Fe1-P(AN-co-IA)-eGNF, (d) (Zr-Fe)0.5-P(AN-co-IA)-eGNF, (e) (Zr-Fe)1-P(AN-co-IA)-eGNF, and (f) (Zr-Fe)2-P(AN-co-IA)-eGNF.
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Figure 4. (a–d) FESEM images and (e–e4) elemental color mapping image of (Zr-Fe)1-P(AN-co-IA)-eGNF.
Figure 4. (a–d) FESEM images and (e–e4) elemental color mapping image of (Zr-Fe)1-P(AN-co-IA)-eGNF.
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Figure 5. (a) XRD patterns, and (b–f) Raman spectra of P(AN-co-IA)-eGNF-based samples.
Figure 5. (a) XRD patterns, and (b–f) Raman spectra of P(AN-co-IA)-eGNF-based samples.
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Figure 6. (a–d) TEM images and (e–e5) elemental color mapping images of (Zr-Fe)1-P(AN-co-IA)-eGNF.
Figure 6. (a–d) TEM images and (e–e5) elemental color mapping images of (Zr-Fe)1-P(AN-co-IA)-eGNF.
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Kim, T.; Ko, T.H.; Kim, B.-S.; Chung, Y.-S.; Kim, H.Y. Co-Polymerized P(AN-co-IA)-Derived Electrospun Nanofibers with Improved Graphitization via Dual-Metallocene Integration at Low Temperature. Inorganics 2025, 13, 318. https://doi.org/10.3390/inorganics13100318

AMA Style

Kim T, Ko TH, Kim B-S, Chung Y-S, Kim HY. Co-Polymerized P(AN-co-IA)-Derived Electrospun Nanofibers with Improved Graphitization via Dual-Metallocene Integration at Low Temperature. Inorganics. 2025; 13(10):318. https://doi.org/10.3390/inorganics13100318

Chicago/Turabian Style

Kim, Taewoo, Tae Hoon Ko, Byoung-Suhk Kim, Yong-Sik Chung, and Hak Yong Kim. 2025. "Co-Polymerized P(AN-co-IA)-Derived Electrospun Nanofibers with Improved Graphitization via Dual-Metallocene Integration at Low Temperature" Inorganics 13, no. 10: 318. https://doi.org/10.3390/inorganics13100318

APA Style

Kim, T., Ko, T. H., Kim, B.-S., Chung, Y.-S., & Kim, H. Y. (2025). Co-Polymerized P(AN-co-IA)-Derived Electrospun Nanofibers with Improved Graphitization via Dual-Metallocene Integration at Low Temperature. Inorganics, 13(10), 318. https://doi.org/10.3390/inorganics13100318

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