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DOI: 10.1039/D4CC03743J (Communication) Chem. Commun., 2024, 60, 10136-10139

Structure-dependent magnetoelectric and magnetothermal effects of MOF-derived zero-valence cobalt and iron oxide nanoparticles on a carbonaceous matrix†

Jing-Guan Liang‡ ab, Wei-Xiang Gao‡ ac, Chieh-Wei Chung a, Loise Ann Dayao a, Ho-Hsiu Chou c, Zong-Hong Lin d, Dehui Wan a, Jen-Huang Huang c, Ying-Chieh Chen *b and Tsai-Te Lu *aef
aInstitute of Biomedical Engineering, National Tsing Hua University, Hsinchu, 30013, Taiwan
bDepartment of Materials Science and Engineering, National Tsing Hua University, Hsinchu, 30013, Taiwan. E-mail: yisschen@mx.nthu.edu.tw
cDepartment of Chemical Engineering, National Tsing Hua University, Hsinchu, 30013, Taiwan
dDepartment of Biomedical Engineering, National Taiwan University, Taipei, 106319, Taiwan
eDepartment of Chemistry, National Tsing Hua University, Hsinchu, 30013, Taiwan. E-mail: ttlu@mx.nthu.edu.tw
fDepartment of Chemistry, Chung Yuan Christian University, Taoyuan 32023, Taiwan

Received 25th July 2024 , Accepted 15th August 2024

First published on 16th August 2024

Abstract

For the first time, the dominant magnetoelectric activity of ZIF-67-derived carbonaceous microparticles embedded with Co nanoparticles and distinctive magnetothermal effect of MIL-88B-derived Fe3O4 nanocubes decorated on carbonaceous microrods, respectively, were explored to be controlled by the structure of the MOF-derived electrically conductive carbonaceous matrix and metal nanoparticles.

Since the first publication in 1995,1 metal–organic frameworks (MOFs) have been explored as novel porous materials consisting of metal ions as the nodes and ligands as the organic linkers.2–5 Upon high-temperature pyrolysis of MOFs under inert gas (i.e. N2(g) or Ar(g)), carbonization/graphitization of the organic linkers into a carbonaceous matrix and transformation of isolated metal ions intometal nanoparticles occur to assemble MOF-derived metal–carbon hybrid materials.6–10 Relying on the hybrid nature, MOF-derived metal–carbon hybrid materials were explored for applications in electro-/photocatalysis,8–13 energy storage,6–9,14,15 anti-cancer/anti-bacteria biomedicine, and biosensors/bioimaging.16–18

Upon application of an alternating magnetic field (AMF) to MOF-derived Fe3O4:C microrods, rotation of the whole microrods via Brownian relaxation or rotation of the magnetic moments via Néel relaxation are reported mechanisms for induction of magnetic hyperthermia.18–20 Moreover, Brownian relaxation is retarded upon increase of the viscosity in the environmental matrix, while Néel relaxation features no viscosity-dependent nature.21–23 This AMF-induced magnetic hyperthermia further enabled the development of magnetic-responsive drug delivery and magnetic hyperthermia therapy against cancer,19,23–25 bacterial infection,18 thrombosis,20 and Alzheimer's disease.26 Besides the AMF-induced magnetothermal effects, exposure of other electrically conductive materials (i.e. cobalt,27 iron and steel,28 graphene,29 and MoS230) to AMF resulted in the generation of an electric potential and eddy current based on Lenz's law. Despite the well-documented generation of eddy currents in electrically conductive materials, the magnetoelectric activity of MOF-derived metal–carbon hybrid materials remains elusive. Consequently, in this study, MIL-88B-derived Fe3O4:C microrods and ZIF-67-derived Co@C microparticles were chosen to investigate the structure-dependent magnetoelectric and magnetothermal effects under AMF (Scheme 1).

Based on a previous study, ZIF-67-derived Co@C microparticles were synthesized through reaction of Co(NO3)2·6H2O with 2-methylimidazole followed by calcination of ZIF-67 at 600 °C for 2 h, whereas MIL-88B-derived Fe3O4:C microrods were prepared via reaction of Fe(NO3)3·9H2O with 1,4-benzenedicarboxylic acid followed by calcination of MIL-88B at 500 °C for 3 h.18,31 As shown in Fig. S1a (ESI†), scanning electron microscopy (SEM) analysis displayed the dodecahedral morphology of the ZIF-67-derived Co@C microparticles. Within the Co@C microparticles, well-dispersive and face-center-cubic (fcc) Co nanoparticles, featuring a lattice spacing of Co(111) as 0.204 nm, were encapsulated in the carbonaceous matrix based on (high-resolution) transmission electron microscopy ((HR)TEM) together with the energy-dispersive X-ray spectroscopy (EDS) elemental mapping analyses (Fig. S1b and c, ESI†). Using powder X-ray diffraction (PXRD) and synchrotron X-ray powder diffraction (SXRPD), moreover, the crystalline nature of fcc-Co nanoparticles was also evidenced according to the characteristic peaks at 2θ = 44.0°, 51.3°, and 75.8° corresponding to the (111), (200), and (220) planes (Fig. S1d, ESI†). Regarding the hybrid nature of ZIF-67-derived Co@C microparticles, its magnetic and electric properties were further investigated using a superconducting quantum interference device (SQUID) and four-point probe. As shown in Fig. S3a (ESI†), the saturation magnetization (MS) of Co@C microparticles, normalized to the weight of the whole material, was determined as 53.9 emu g−1. In addition, the electrical conductivity of Co@C microparticles as 0.512 S cm−1 was ascribed to the graphitic carbonaceous matrix, whereas the graphite exhibited an electrical conductivity of 457 S cm−1.32 On the basis of characterizations discussed above, ZIF-67-derived Co@C microparticles were best described as an electrically conductive hybrid material consisting of ferrimagnetic fcc-Co nanoparticles embedded within the dodecahedral carbonaceous matrix (Scheme 1). Under a series of similar characterizations of MIL-88B-derived Fe3O4:C microrods, its insulating nature (7.67 × 10−6 S cm−1) could be ascribed to the decoration of insulating and ferrimagnetic Fe3O4 nanocubes on the carbonaceous microrod (Fig. S2 and S3b, ESI†).33


image file: d4cc03743j-s1.tif
Scheme 1

Inspired by Lenz's law, potential generations of electric current and voltage from graphite, Co@C microparticles, and Fe3O4:C microrods under AMF were explored using a digital multimeter and oscilloscope (Fig. S4b, ESI†). Upon application of AMF (0.96 kW) to electrically conductive Co@C microparticles (or graphite), distinctive illumination of a light-emitting diode (LED) revealed the formation of electric current (Fig. S4a, ESI†), while no illumination was observed during application of AMF to Fe3O4:C microrods. Moreover, quantitative measurements on the induced electric currents from graphite/Co@C microparticles/Fe3O4:C microrods under different powers of AMF are collected in Fig. 1a–c and Table 1. In contrast to the negligible electric currents derived from insulating Fe3O4:C microrods, intermittent generations of electric currents from Co@C microparticles (or graphite) synchronized with the ON/OFF-switching of AMF suggested the instantaneous nature for the magnetoelectric effect. Moreover, an increase of eddy current from 68.0 ± 2.6 μA to 229.1 ± 8.5 μA and 399.4 ± 22.8 μA for Co@C microparticles (or from 67.5 ± 1.8 μA to 227.1 ± 6.3 μA and 400.2 ± 24.6 μA for graphite) when the power of AMF was elevated from 0.32 kW to 0.96 kW and 1.60 kW unraveled the critical role of external AMF power for control of the intensity of the magnetoelectric effect.


image file: d4cc03743j-f1.tif
Fig. 1 I–t curves for (a) graphite, (b) ZIF-67-derived Co@C microparticles, and (c) MIL-88B-derived Fe3O4:C microrods under intermittent application of AMF at 0.32 kW (black), 0.96 kW (red), and 1.60 kW (blue). Processed (dot) and simulated V–t curves (line) for (d) graphite, (e) ZIF-67-derived Co@C microparticles, and (f) MIL-88B-derived Fe3O4:C microrods under application of AMF at 0.64 kW (black), 1.60 kW (red), and 2.24 kW (blue).
Table 1 Magneto-driven current/voltage and magnetic hyperthermia upon application of different power of AMF to graphite, Co@C microparticles, and Fe3O4:C microrods
Magneto-driven current (μA)
Material AMF power
0.32 kW 0.96 kW 1.60 kW
a The viscosity of the aqueous solution of 2-wt%, 4-wt%, 8-wt%, and 10-wt% sodium alginate was measured as 17.3, 123.2, 1423.9, and 3211.9 mPa s, respectively, using a rheometer.
Graphite 67.5 ± 1.8 227.1 ± 6.3 400.2 ± 24.6
Co@C 68.0 ± 2.6 229.1 ± 8.5 399.4 ± 22.8
Fe3O4:C — — —
Magneto-driven voltage (V)
Material AMF power
0.32 kW 0.96 kW 1.60 kW
Graphite 0.19 ± 0.02 0.41 ± 0.02 0.70 ± 0.06
Co@C 0.27 ± 0.05 0.40 ± 0.02 0.47 ± 0.04
Fe3O4:C — — —
Magnetic hyperthermia (ΔTmax, °C)
Material Viscositya (mPa s) AMF Power
0.32 kW 0.96 kW 1.60 kW
Graphite 17.3 06.3 ± 1.4 12.1 ± 1.2 20.1 ± 1.6
123.2 05.3 ± 0.7 11.7 ± 1.7 17.0 ± 2.0
1423.9 05.8 ± 0.5 12.1 ± 1.1 18.4 ± 2.2
3211.9 06.2 ± 1.1 12.8 ± 1.9 20.1 ± 3.6
Co@C 17.3 06.1 ± 0.8 18.5 ± 3.0 26.0 ± 1.8
123.2 06.2 ± 1.2 14.6 ± 0.6 23.4 ± 2.0
1423.9 06.6 ± 1.5 12.9 ± 0.3 22.1 ± 1.6
3211.9 05.5 ± 1.5 13.3 ± 0.2 21.5 ± 1.7
Fe3O4:C 17.3 10.5 ± 0.3 32.2 ± 0.3 43.6 ± 3.1
123.2 07.1 ± 0.3 17.6 ± 0.4 30.1 ± 0.8
1423.9 06.7 ± 1.9 20.5 ± 1.4 31.6 ± 6.0
3211.9 07.2 ± 1.6 17.6 ± 2.2 29.2 ± 5.3

As measured using an oscilloscope, application of AMF to electrically conductive Co@C microparticles (or graphite) resulted in the formation of an overlapped sine wave feature across a wide frequency range (Fig. S5a, ESI†), which was opposed to the inert response displayed by insulating Fe3O4:C microrods. Through application of a Fast Fourier Transform (FFT) process to these original V–t curves, the frequency peaks at ∼0.94 MHz, within the range of 0.75–1.15 MHz for the AMF generator were further utilized to extract the AMF-induced V–t curves out from the noisy background signals via a reverse FFT process (Fig. 1d–f and Fig. S5b, ESI†). After fitting these processed V–t curves with a sine wave, the induced electric voltages from Co@C microparticles (or graphite) under different power of AMF are collected in Table 1. In comparison with the elevation of induced electrical voltage from 0.27 ± 0.05 V to 0.47 ± 0.04 V upon increase of the AMF power applied to Co@C microparticles, of interest, the graphite displayed a more significant dependence of generated electrical voltage on the power of AMF.

In addition to the distinctive magnetoelectric effects of ZIF-67-derived Co@C microparticles and MIL-88B-derived Fe3O4:C microrods, respectively, the magnetothermal activity of these MOF-derived materials under AMF was further investigated. Considering the hybrid nature of these MOF-derived materials, the potential mechanisms for the AMF-induced magnetic hyperthermia effect included (a) eddy current within the graphitic carbonaceous matrix, (b) Néel relaxation of the embedded Co nanoparticles/decorated Fe3O4 nanoparticles, and (c) Brownian relaxation of the whole Co@C microparticle/Fe3O4:C microrod, which is dependent on the viscosity of the environmental matrix.21–23 In an attempt to dissect these mechanisms, time-dependent changes of local temperature upon application of AMF to graphite, ZIF-67-derived Co@C microparticles, and MIL-88B-derived Fe3O4:C microrods, respectively, in aqueous solutions with different concentrations of sodium alginate were monitored using an IR thermal imaging camera. As shown in Fig. S6–S8 (ESI†), application of AMF to these materials induced an increase of temperature reaching a plateau at 400–600 seconds. Moreover, the ΔTmax of different materials under different powers of AMF and the viscosity of the aqueous solution with different concentrations of sodium alginate measured using a rheometer are collected in Table 1. Upon application of AMF to graphite, elevation of the AMF power from 0.32 kW to 0.96 kW and 1.60 kW resulted in the increase of ΔTmax from 5.3–6.3 °C to 11.7–12.8 °C and 17.0–20.1 °C (Fig. 2a and Table 1). That is, as opposed to the dependence of ΔTmax on the AMF power, limited effect of viscosity of the aqueous solution of sodium alginate on the ΔTmax was observed. Regarding the diamagnetic and electrically conductive nature of graphite, this AMF-induced magnetothermal activity of graphite was ascribed to the eddy current. Similarly, ZIF-67-derived Co@C microparticles displayed a viscosity-independent ΔTmax, as 5.3–6.3 °C, under exposure to AMF at 0.32 kW (Fig. 2b). When the power of AMF was strengthened to 0.96 kW (or 1.60 kW), of interest, the ΔTmax = 18.5 ± 3.0 °C (or 26.0 ± 1.8 °C) exhibited by Co@C microparticles at a viscosity of 17.3 mPa s was decreased to ΔTmax= 12.9–14.6 °C (or 21.5–23.4 °C) at higher viscosity. At higher power of AMF, this viscosity-dependent ΔTmax implied that magnetic hyperthermia of Co@C microparticles at lower viscosity occurred through the Brownian relaxation,21–23 while Néel relaxation of the embedded Co nanoparticles was the dominant mechanism for magnetothermal activity of Co@C microparticles at higher viscosity. As shown in Fig. 2c and Table 1, the ΔTmax of the MIL-88B-derived Fe3O4:C microrods exhibited a more significant dependence on the viscosity of the environmental matrix under different AMF power. Accordingly, Brownian relaxation of the Fe3O4:C microrods was proposed as the dominant mechanism for magnetic hyperthermia at the viscosity of 17.3 mPa s.21–23


image file: d4cc03743j-f2.tif
Fig. 2 Maximum change of temperature upon application of AMF (0.32 kW, black; 0.96 kW, red; 1.60 kW, blue) to (a) graphite, (b) ZIF-67-derived Co@C microparticles, and (c) MIL-88B-derived Fe3O4:C microrods in the aqueous solution of sodium alginate with different viscosity.

In summary, relying on the hybrid nature of MOF-derived Fe3O4:C microrods and Co@C microparticles, dual magnetothermal and magnetoelectric effects triggered by AMF were explored, for the first time, to be controlled by the structure of ferrimagnetic Fe3O4/Co nanoparticles and the electrically conductive carbonaceous matrix. Despite the electrically conductive carbonaceous microrods in MIL-88B-derived Fe3O4:C, the insulating and superparamagnetic Fe3O4 nanoparticles decorated on the surface dictated the dominant magnetothermal effect and hindered the magnetoelectric activity under AMF. In contrast, the electrically conductive carbonaceous dodecahedron in ZIF-67-derived Co:C microparticles served as a magneto-sensitizer to trigger the generation of AMF-power-dependent electric current and voltage, while the encapsulated ferrimagnetic Co nanoparticles featured minimal magnetothermal activity.

Data availability

The data supporting this article have been included as part of the ESI.†

Conflicts of interest

There are no conflicts to declare.

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Footnotes

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4cc03743j
‡ These authors contributed equally: Mr Jing-Guan Liang and Mr Wei-Xiang Gao.
This journal is © The Royal Society of Chemistry 2024