Structure, magnetism and heating ability of pyrrole-functionalized magnetic biochar (PFMB) for magnetic hyperthermia

Abstract

This work reports the synthesis, characterization, and magnetic hyperthermia performance of pyrrole-functionalized magnetic biochar (PFMB) nanocomposites prepared via a hydrothermal method. The PFMB system comprises Fe₃O₄ nanoparticles embedded in a biochar matrix and coated with pyrrole to improve colloidal stability and heating efficiency. Structural and morphological analyses (XRD, FTIR, SEM/EDAX) confirmed the formation of a magnetite phase and successful surface functionalization. Magnetic measurements reveal a transition from ferrimagnetic behavior in bare MB to superparamagnetism in PFMB, with saturation magnetization reduced significantly from 58.8 to 20.8 emu g⁻¹. Magnetic hyperthermia experiments under alternating magnetic fields (AMF) manifest enhanced heating efficiency for PFMB, with sample absorption rate (SAR) values varying considerably from 24.27 to 53.77 W g⁻¹, compared to 12.34–31.80 W g⁻¹ for MB. The results indicate that at higher frequencies (332 kHz and 469 kHz), both MNPs reach the therapeutic hyperthermia threshold of 42 °C in a relatively short time. The heating performance correlates well with both frequency and field amplitude. Intrinsic loss power (ILP) values for PFMB reach 0.70 nH m² kg⁻¹, aligning with the values reported for established polymer-coated MNPs. These results demonstrate the potential of PFMB nanocomposites as efficient and stable candidates for in vitro magnetic hyperthermia applications.

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1. Introduction

Pyrrole-functionalized magnetic biochar (PFMB) is a hybrid nanocomposite consisting of iron oxide magnetic nanoparticles (MNPs) embedded within a biochar matrix and subsequently coated with pyrrole. This configuration has attracted growing interest for biomedical applications, particularly in magnetic hyperthermia (MH) therapy for cancer, owing to its enhanced thermal efficiency and biocompatibility.^1,2 Under an AMF, the magnetic core acts as a nano-heater, converting electromagnetic energy into heat via magnetic relaxation processes.

Pyrrole coating plays a pivotal role in maintaining colloidal stability by mitigating MNP agglomeration, which is a requirement for enhanced heating efficiency of MNPs and for an efficient MH.³ Furthermore, the functionalization of magnetic biochar (MB) with naturally derived caffeic acid introduces surface hydroxyl and carboxyl groups, thus enhancing aqueous dispersibility and biocompatibility while offering potential sites for drug loading or molecular targeting.^4,5

The heat generation capability of MNPs under AMF is governed primarily by two relaxation mechanisms: Néel relaxation, involving the reorientation of magnetic moments within the crystal lattice, and Brownian relaxation, in which the entire particle rotates in suspension to follow the magnetic field.⁶ The efficiency of each mechanism depends on several factors such as particle size, magnetic anisotropy, and matrix confinement. In the PFMB system, both the pyrrole shell and biochar scaffold influence these mechanisms by controlling particle mobility and interparticle interactions. Notably, the pyrrole coating prevents aggregation and maintains interparticle separation, which is crucial to sustaining efficient magnetic relaxation.⁷ Numerous studies have highlighted the multifunctional advantages of pyrrole-coated MNPs, including improved heating efficiency, enhanced dispersion in aqueous media, and increased thermal stability.^2,8,9 For instance, Mol et al.² demonstrated that Fe₃O₄ MNPs coated with pyrrole exhibit enhanced biocompatibility and tunable heating capacity. Bao et al.⁸ reported SAR of 1648 W g⁻¹ for pyrrole-coated magnetite nanorings subjected to simultaneous AMF and near-infrared (NIR) irradiation, along with negligible cytotoxicity. Similarly, Sethulakshimi et al.⁹ found that plasma polymerization of polyaniline on iron oxide nanoparticles led to increased saturation magnetization and improved biocompatibility.

While substantial advances have been achieved in the development of polymer-coated magnetic nanoparticles (MNPs) for magnetic hyperthermia—particularly with coatings such as poly(acrylic acid) (PAA), polyethylene glycol (PEG), dextran, hyaluronic acid, chitosan, and polyvinylpyrrolidone (PVP)^10–13—there remains a notable gap in systematic investigations focused on the magnetothermal performance of pyrrole-coated MNPs. Despite the promising conductive and stabilizing properties of pyrrole, its potential as a surface functionalization agent for enhancing heat dissipation efficiency in magnetic hyperthermia is still underexplored.

Motivated by recent work in which MB and PFMB MNPs were successfully synthesized via a hydrothermal approach for sensing applications,¹⁴ we extended our investigation to evaluate their magnetothermal properties. In this study, MB and PFMB were fully characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy with energy-dispersive X-ray analysis (SEM/EDAX), and superconducting quantum interference device (SQUID) magnetometry.

To assess their performance in magnetic hyperthermia, the specific absorption rate (SAR) was measured under varying alternating magnetic field (AMF) frequencies and field strengths. This study provides new insights into the role of pyrrole surface modification in optimizing the heating efficiency of MNPs for theranostic applications.

2. Experimental

2.1. Synthesis of PFMB nanocomposite

The synthesis procedure of the nanocomposite has been previously detailed in previous work, as illustrated in Fig. 1.¹⁴ Briefly, the shells were cut into small fragments and thoroughly washed with distilled water to remove impurities and residual contaminants. After cleansing, the biomass was dehydrated in a hot-air oven at 80 °C for 24 h. The dried material was then finely ground using an electric grinder to yield a homogeneous powder.

Fig. 1 Synthesis of Pyrrole Functionalized Magnetic Biochar (PFMB) nanocomposite (reproduced from our early work¹⁴).

To synthesize PFMB, the carbon precursor was mixed with iron(III) chloride hexahydrate (FeCl₃·6H₂O), polyethylene glycol (PEG), and pyrrole (Py). The mixture was subjected to ultrasonic dispersion for 1 h to ensure uniform mixing with a Py/Fe molar ratio of 1.5. The resulting suspension was transferred into a 150 mL Teflon-lined autoclave and subjected to hydrothermal treatment at 180 °C for 17 h in a hot-air oven. The final product was collected as a dry powder.

2.2. Characterization

X-ray diffraction (XRD) patterns were recorded on a PROTO Benchtop powder diffraction system equipped with Cu Kα radiation source (λ = 1.5418 Å) and under the operating conditions: voltage of 30 V, current of 20 A, and power of 0.6 kW. The patterns were recorded in the 2θ range 20–80° using a scan rate of 0.015° and a counting time of 2 s. FTIR spectra were recorded using INFRALUM FT-08 ALUMEX in the wavenumber range 40–4000 cm⁻¹. Morphological observation and chemical composition were performed using SEM-SERON TECHNOLOGIES (Model, AIS 1800C). A Superconducting Quantum Interference Device (SQUID) magnetometer (San Diego, CA, USA) was used for the magnetic characterizations. A magnetic field of 100 Oe was applied to record zero-field-cooled and field-cooled (ZFC-FC) curves.

The heating efficiency of the samples was performed using a commercial system “Nanotherics Magnetherm”. The SAR values are calculated by the following equation:

where C_w is the specific heat capacity of water (4.185 J g⁻¹ K), ρ is the density of the colloid, Mass_MNP is the concentration of the magnetic nanoparticles in the suspension and represents the heating rate. By performing a linear fit of temperature increase versus time at the initial time interval (1 to ∼30 s), the slope ΔT/Δt is obtained.

3. Results and discussion

3.1. Structural, morphological and chemical composition characterizations

3.1.1. X-ray diffraction analysis. Fig. 2a depicts XRD patterns refined using the Rietveld method of magnetic biochar powders before and after pyrrole coating. It can be observed the presence of several broad peaks with a relatively low intensity, indicating the formation of nanocrystalline phase(s). These peaks are characteristic reflections (220), (311), (400), (422), (511), (440), and (533) of the magnetite phase Fe₃O₄ with an inverse spinel cubic structure (space group of Fd3̄m, no. 225), in good agreement with JCPDS card no. 01-088-0315.

Fig. 2 (a) XRD diffraction of magnetic biochar powder before and after pyrrole coating, Rietveld refinements of (b) magnetic biochar and (c) biochar coated with pyrrole.

To further compute both structural and microstructural parameters, Rietveld refinements of the XRD patterns have been performed, see Fig. 2b and c. It is evident that the theoretical pattern based on the standard phase JCPDS card no. 01-088-0315 (blue curve) fits very well the experimental pattern (red curve), since the difference between the two curves (orange curve) gives almost a straight line. The goodness of fit parameter (S) is around 0.17. This indicates that the as prepared powdered samples are pure phases.

Table 1 summarizes the computed structural and microstructural parameters as obtained from the Rietveld refinements. It can be observed that the lattice parameter a is found to be 8.389 Å for magnetic biochar which decrease slight up to 8.379 Å for pyrrole coated magnetic biochar. This slight variation in the lattice parameter is usually associated with the local atomic arrangement (sites occupancy, vacancies), a typical behavior occurring within the inverse spinel cubic structure, where (Fe²⁺ with an ionic radius of 0.077 nm) occupies octahedral sites and (Fe³⁺ with an ionic radius of 0.063 nm) occupy tetrahedral sites. This effect has been widely reported in the literature and was found to have a direct effect on the magnetic properties,¹⁶ since both ions have different magnetic moments, i.e. 4.89 μ_B for Fe²⁺ and 5.92 μ_B for Fe³⁺.

Table 1 Structural and microstructural and fitting parameters computed from the Rietveld refinements of XRD patterns^a

Sample	Phase composition (%)	Crystallite size D (nm)	Microstrain ε (%)	Lattice parameters (Å)	Fitting parameters
a Rwp: weighted profile R-factor; Re: expected R-factor; Rp: profile R-factor; S: goodness of fit (S = Rwp/Re); χ^2 = S^2.
MB	Fe3O4 (magnetite)	11.1(1)	0.078(13)	a = b = c = 8.389(1)	Rwp = 2.10%; Re = 12.37%; Rp = 1.64%; S = 0.1695; χ^2 = 0.0287
				α = β = γ = 90°
PFMB	Fe3O4 (magnetite)	13.5(1)	0.711(8)	a = b = c = 8.379(2)	Rwp = 2.26%; Re = 14.17%; Rp = 1.80%; S = 0.1591; χ^2 = 0.0253
				α = β = γ = 90°

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For microstructural parameters, it can be observed that the crystallite D size increases after coating, from 11.1 nm to 13.5 nm, due to the growth of a thin layer of pyrrole. Similarly, the microstrain ε increases significantly from 0.078% up to 0.711%. This is most probably originating from the coating of magnetic biochar with a polymeric layer of pyrrole compound.

3.1.2. FTIR analysis. The FTIR spectrum of Fe₃O₄/biochar exhibits a strong absorption band at approximately 587 cm⁻¹ which correspond to the stretching vibrations of the Fe–O bond, confirming the presence of magnetite (Fig. 3). A broad absorption band centered around 3400 cm⁻¹ is attributed to O–H stretching vibrations from hydroxyl groups and adsorbed water. The bands observed at 2920 and 2850 cm⁻¹ could be assigned to C–H stretching vibrations of aliphatic groups. A band at 1630 cm⁻¹ corresponds to the bending mode of adsorbed water molecules, while the peak at 1557 cm⁻¹ is attributed to C=C stretching, indicating the presence of aromatic structures in the biochar. The spectrum of the pyrrole-coated Fe₃O₄/biochar nanocomposite contains all characteristic peaks of Fe₃O₄ and biochar, along with additional bands attributed to the presence of polypyrrole. Notably, the Fe–O stretching vibration shifts slightly to 592 cm⁻¹, and an additional peak appears at ∼628 cm⁻¹, suggesting modifications in the Fe₃O₄ environment due to coating. The band at 1542 cm⁻¹, associated with the C=C stretching in the pyrrole ring, shows increased intensity, indicating successful incorporation of polypyrrole. Additional pyrrole-specific vibrations include bands at 1458 cm⁻¹ (symmetric stretching of the pyrrole ring and conjugated C–N bonds), 1376 and 1165 cm⁻¹ (in-plane deformation and bending of C–H), and 1041 cm⁻¹ (N–H in-plane deformation).

Fig. 3 FTIR spectra of (a) MB and (b) PFMB nanocomposites.

3.1.3. Morphological observations and chemical composition. The surface morphology and microstructure of the synthesized materials were examined via scanning electron microscopy (SEM), as shown in Fig. 4a–g. In Fig. 4a and 1b, bare Fe₃O₄ particles are observed with irregular, angular structures in the micron scale, indicating aggregated crystalline clusters. Upon compositing with biochar, the Fe₃O₄ particles appear to be embedded on the porous carbon matrix (Fig. 4c), suggesting improved dispersion and potential enhancement in surface area and stability. After coating with pyrrole, a substantial morphological transformation is observed (Fig. 4d and e), where Fe₃O₄ particles are uniformly encapsulated within a rough, interconnected polymeric network, forming spherical agglomerates with decreased particle definition. This indicates successful coating of Fe₃O₄ with pyrrole, which is further confirmed by higher magnification in (Fig. 4e). The particle size distribution histogram (Fig. 4f) derived from SEM analysis shows that the coated composite particles exhibit an average diameter of approximately 0.63 μm, indicating a relatively narrow and controlled size distribution. Furthermore, it is important to notice the values particle size estimated by SEM are different from the values of the crystallite size computed from the Rietveld analysis of XRD patterns. This indicates that each particle is in fact composed of several crystallites.

Fig. 4 SEM and compositional analysis of the synthesized composite materials: (a and b) low and higher magnification SEM images of pristine Fe₃O₄ particles showing angular and aggregated morphology. (c) Fe₃O₄ dispersed on biochar, indicating improved distribution. (d and e) pyrrole-coated Fe₃O₄ particles with spherical agglomerates and rough surface morphology. (f) Particle size distribution with an average diameter of ∼0.63 μm. (g) SEM image showing core–shell structure of Fe₃O₄@PPy. (h) EDAX spectrum confirming the presence of Fe, Co, C, and Cl elements in the composite.

The high-magnification SEM image (Fig. 4g) further validates the coating of pyrrole on Fe₃O₄ within the pyrrole matrix, showing a core–shell-like structure with visible contrast differences. Adding this, the energy-dispersive X-ray spectroscopy (EDAX) elemental profile (Fig. 4h) confirms the presence of key elements including Fe, O, C thereby verifying the elemental composition of the composite. The strong Fe and O peaks indicate the magnetic core, while the presence of Cl and C supports pyrrole shell and possible doping elements. The detection of Na and minor atomic (At) peaks ascribed to residuals from the precursor or synthesis process. These morphological and compositional analyses collectively confirm the successful synthesis of a Fe₃O₄/biochar@pyrrole composite.

3.2. Magnetic properties

The magnetic behaviour of the MB and PFMB nanocomposites was comprehensively assessed through M–H hysteresis loops at 300 K and ZFC/FC magnetization measurements under a field of 100 Oe. As depicted in Fig. 4a, the MB sample exhibits a ferrimagnetic response, characterized by a noticeable coercivity and remanent magnetization, while the PFMB nanocomposite displays superparamagnetic behavior, evidenced by negligible coercivity and remanence (see inset of Fig. 5a). As shown in Fig. 5a, the MB MNPs do not reach magnetic saturation even at an applied field of 20 kOe. Therefore, the saturation magnetization (M_s) was estimated by applying the law of approach to saturation using the linear extrapolation of the M versus H⁻¹ plot, resulting in an M_s of 58.8 emu g⁻¹ (Fig. 5b). PFMB MNPs exhibit M_s of 20.8 emu g⁻¹, corresponding to a reduction of approximately 63% compared to the MB MNPs.

Fig. 5 (a) Room temperature M–H curves for the MB and PFMB MNPs. (bottom inset) Enlarged view of the M–H curves for the low field region and (b) extrapolated saturation magnetization for MB.

This significant decrease in M_s upon pyrrole coating is attributed to several factors, including.^{12,13,15–17} (i) Interfacial disruptions caused by the non-magnetic polymer shell, which weaken dipolar interactions and reduce the collective magnetic response; (ii) the coating process may also influence the cation distribution within the spinel lattice. The magnetic properties of spinel ferrites are strongly governed by the occupancy of Fe ions in tetrahedral and octahedral sites. Interaction of the polymer matrix with the particle surface during the coating procedure can induce local alterations in cation arrangement, affecting the superexchange interactions responsible for ferrimagnetic ordering. This interpretation is corroborated by XRD analysis, which confirmed an inverse spinel structure for the PFMB nanocomposite; and (iii) possible surface oxidation effects promoted by the functional groups of pyrrole, subtly impacting the Fe²⁺/Fe³⁺ ratio and the overall magnetization.

These observations from M–H measurements are further supported by the ZFC/FC magnetization curves presented in Fig. 6a and b. The MB MNPs display a broad, gradual increase in the ZFC curve with no distinct blocking temperature (T_B), indicating a strong dipolar interaction, characteristic of clustered or multi-domain systems. In contrast, the PFMB exhibits a T_B around 290–300 K, reflecting a more uniform size distribution and effective magnetic decoupling provided by the pyrrole coating. This thermal behavior aligns well with the superparamagnetic nature of PFMB observed in the M–H curves at room temperature, confirming the stabilizing effect of the coating on the magnetic core and its role in reducing interparticle interactions.

Fig. 6 The ZFC-FC magnetization measured under the field of 100 Oe for (a) MB and (b) PFMB MNPs.

To further verify the superparamagnetic behavior of the PFMB nanocomposite, the experimental M(H) data were analyzed using the Langevin model of paramagnetism, described by the equation:

where M_s stands for saturation magnetization, m_np for magnetic moment, μ₀ for free-space permeability, K_B for the Boltzmann constant, T for temperature, and H for the applied magnetic field.

The experimental data showed an excellent agreement with the Langevin model, as evidenced by a coefficient of determination R² = 0.998, as illustrated in Fig. 7. This high correlation further confirms that the PFMB nanocomposite exhibits a superparamagnetic response at room temperature, dominated by the thermal fluctuation of non-interacting magnetic moments, and consistent with M–H loop characteristics.

Fig. 7 Langevin fitting of magnetization of PFMB at 300 K

It can be concluded from the detailed magnetic study that while the pyrrole coating substantially reduces the saturation magnetization, it effectively enhances the superparamagnetic response and thermal stability of the nanocomposite, properties that are crucial for magnetic hyperthermia application.

3.3. Magnetic hyperthermia study

Fig. 8a–c depicts the temperature rise of aqueous dispersions of MB and PFMB with a fixed alternating magnetic field (AMF) amplitude of 170 Oe under different frequencies. The dispersions, with the concentration of 10 mg mL⁻¹, exhibit a significant temperature rise, achieving the therapeutic hyperthermia threshold of 42 °C at higher frequencies of 332 kHz and 469 kHz for both MNPs, which is essential for effective cancer treatment. In contrast, at lower frequencies (113 kHz and 170 kHz), neither MNPs system attains the hyperthermia threshold within the experimental timeframe, indicating their limited heating efficiency under such conditions. Quantitative analysis of the heating performance through specific absorption rate (SAR) (Table 2) revealed a clear enhancement following surface functionalization.

Fig. 8 (a–c) Temperature rise at different frequency for MB and PFMB and (d) corresponding SARs values for both MNPs.

Table 2 SAR and ILP for MB and PFMB MNPs

Samples	Frequency (kHz)	Field (mT)	SAR (W g^−1)	ILP (nH m^2 kg^−1)
MB	169	17	12.34	0.39
	332	17	16.11	0.26
	469	16	31.8	0.41
PFMB	169	17	24.27	0.78
	332	17	28.24	0.46
	469	16	53.77	0.70

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For MB MNPs, SAR values ranged from 12.34 W g⁻¹ to 31.80 W g⁻¹, while the PFMB exhibited notably higher SAR values, in the range 24.27 W g⁻¹ to 53.77 W g⁻¹ across the studied frequencies. The enhanced SAR values observed for PFMB can be attributed to several factors. (i) The pyrrole surface functionalization likely improves colloidal stability by mitigating agglomeration, thereby facilitating more efficient heat dissipation. Furthermore, the superparamagnetic behavior of PFMB, as confirmed by magnetic characterization, reduces interparticle magnetic interactions that typically hinder heating performance. It is well known that heat dissipation under an AMF for superparamagnetic MNPs arises from Néel and Brownian relaxations. (ii) The presence of pyrrole reduces magnetic interactions between nanoparticles, which in turn affects the Néel relaxation time—potentially enhancing the heating efficiency. Brownian relaxation may also become faster due to improved dispersion and reduced aggregation. While these factors contribute positively to the heating performance, it is important to note that the overall magnetization tends to decrease due to the pyrrole coating, which can partially offset the heat generation. (iii) The mesoporous and carbonaceous framework of biochar improve heat dissipation by providing a thermally conductive scaffold that improves the overall magnetothermal conversion efficiency. This conductive network also helps dissipate localized heat from individual nanoparticles across a broader volume, minimizing thermal hotspots and supporting a more homogeneous temperature rise during hyperthermia treatment. These effects synergistically contribute to the superior heating capability of PFMB compared to uncoated MB nanoparticles. Earlier studies have demonstrated that chitosan, dextran, PEG, PVP, and PAA coatings enhance heating properties of MNPs by improving dispersion and reducing interparticle magnetic interactions.^19–23

To assess the effect of magnetic field strength on the heating ability of PFMB MNPs, experiments were conducted at a fixed frequency of 469 kHz and concentration of 10 mg mL⁻¹, while varying the AMF amplitude (H = 10, 12, 14, and 16 mT). The corresponding temperature rises are illustrated in Fig. 9a. The results clearly demonstrate that the temperature rise is highly dependent on the field amplitude. At lower field strengths (10 mT and 12 mT), the PFMB dispersions fail to reach the therapeutic hyperthermia threshold (42 °C) within the experimental duration, indicating insufficient heat generation under sub-threshold field amplitudes. In contrast, at higher amplitudes (14 mT and 16 mT), the temperature surpasses 42 °C, confirming that high heating ability under these fields. This trend is further supported by the calculated SAR values (Fig. 9b), which exhibit a positive correlation with increasing field amplitude.

Fig. 9 (a)Temperature rise at different field amplitude and frequency of 469 kHz for PFMB and (b) SAR values.

The maximum SAR observed for the PFMB nanocomposites in this study, 53.77 W g⁻¹, is within the upper range of SAR values reported for conventional polymer-coated iron oxide nanoparticles and is comparable to previously published values for similarly synthesized MNP systems (see Table 3). However, this value remains substantially lower than the exceptionally high SAR of 1648 W g⁻¹ reported for pyrrole-coated magnetite nanorings subjected to simultaneous AMF and near-infrared (NIR) irradiation, a dual-stimulus strategy known to enhance hyperthermic performance through combined magnetothermal and photothermal effects.⁸

Table 3 Comparison of SAR values for different polymeric MNPs

Synthesis method	Composition	Field (kA m^−1)	Frequency (kHz)	SAR (W g^−1)	ILP (nH m^2 kg^−1)	Reference
Hydrothermal	Pyrole-Fe3O4	17	469	53.77	0.46	This work
Hydrothermal	Fe3O4-PVP	17	332	160	0.6	19
Co-precipitation	Fe3O4-NH4HCO3	17.1	386.5	69.6	0.613	20
Emulsion polymerization	Fe3O4-PDMAEMA	20.25	260	∼25	∼0.4	21
Co-precipitation	Fe3O4-Chitosan	10–20	100	∼20	∼0.3	22
Hydrothermal	Fe3O4-PAA	17	332	36	0.59	23
Hydrothermal	Fe3O4-PEG	332	17	70	∼0.55	19

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It is essential to emphasize that direct comparisons of SAR values across different studies must be approached with caution, as SAR is not an intrinsic material property but rather a function of numerous experimental and physical variables. Critical parameters influencing SAR include nanoparticle size and morphology, coating nature, magnetic anisotropy, and saturation magnetization, as well as external field parameters such as field amplitude (H), frequency (f). Additionally, calorimetric methods, sample holders, and data processing protocols vary across laboratories, contributing to systematic discrepancies in reported values.

For a more reliable comparison of heating efficiencies reported across different magnetic hyperthermia studies, the concept of Intrinsic Loss Power (ILP) has been introduced. Unlike the specific absorption rate (SAR), which is strongly influenced by experimental parameters such as field amplitude and frequency, ILP offers a normalized metric that facilitates objective evaluation of the intrinsic heating efficiency of magnetic nanoparticles.

It can be determined using the following expression:

ILP = SAR/fH² (3)

where SAR is the specific absorption rate (W g⁻¹), H represents the applied field amplitude (A m⁻¹), and f denotes the applied frequency (Hz).

The resulting ILP is expressed in nH m² kg⁻¹ and reflects the intrinsic ability of MNPs to convert electromagnetic energy into heat, independent of the applied field conditions.

As shown in Table 3, the ILP values obtained for PFMB MNPs fall within the range reported for similar polymer-coated MNP systems^21–25 and are comparable to those of commercial ferrofluids, which typically exhibit ILP values between 0.2 and 3.1 nH m² kg⁻¹.²⁶ These values reflect the relatively high intrinsic heating efficiency of PFMB under alternating magnetic field conditions, supporting their promising potential for in vitro magnetic hyperthermia applications.¹⁸

4. Conclusion

In this study, PFMB nanocomposites were successfully synthesized and characterized using a hydrothermal approach. The incorporation of Fe₃O₄ nanoparticles into a biochar matrix, followed by pyrrole surface coating, yielded a hybrid system with enhanced stability and less agglomeration. Comprehensive characterization confirmed the formation of an inverse spinel magnetite phase and effective polymer encapsulation. Magnetic measurements at room temperature demonstrated a transition from ferrimagnetism in bare MB to superparamagnetic behavior in PFMB, accompanied by a notable reduction in saturation magnetization due to the surface coating. Magnetic hyperthermia experiments revealed substantially improved heating performance in PFMB, with SAR values reaching up to 53.77 W g⁻¹, significantly exceeding those of uncoated MB. Both MNNPs reached the therapeutic hyperthermia threshold of 42 °C at higher AMF frequencies (332 kHz and 469 kHz). Furthermore, the calculated intrinsic loss power (ILP) values, as high as 0.70 nH m² kg⁻¹, fall within the performance range of polymer-coated iron oxide nanoparticles reported in the literature. These results highlight the critical role of pyrrole functionalization in enhancing magnetothermal efficiency by improving dispersion and reducing magnetic interaction. The PFMB nanocomposite emerges as a promising candidate for in vitro magnetic hyperthermia, with potential further development in theranostic applications.

Conflicts of interest

There are no conflicts to declare.

Data availability

All authors declare that all data of the paper are available on request.

Acknowledgements

This work was supported and funded by the Deanship of Scientific Research at Imam Mohammad Ibn Saud Islamic University (IMSIU) (grant number IMSIU-DDRSP2501).

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