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. 2025 Aug 24;15:31077. doi: 10.1038/s41598-025-16962-x

Co3O4@mSiO2 nanocomposite supported Pd/ionic liquid as an efficient and magnetically recoverable nanocatalyst

Hakimeh Ardeshirfard 1, Dawood Elhamifar 1,✉, Masoumeh Shaker 1
PMCID: PMC12375050  PMID: 40849580

Abstract

In this work, a novel core–shell structured magnetic Co3O4@mSiO2 nanocomposite supported ionic liquid/palladium (Co3O4@mSiO2/IL-Pd) is synthesized and its structure is characterized by using PXRD, EDX, FT-IR, SEM, TEM, TGA and VSM. This magnetic material was prepared through coating of mesoporous silica shell on magnetic cobalt oxide nanoparticles followed by chemical immobilization of ionic liquid/Pd complex. The Co3O4@mSiO2/IL-Pd nanocomposite was used as an efficient and powerful catalyst for the reduction of nitrobenzenes. The excellent yield of the products, short reaction time and easy catalyst recoverability with no significant decrease in activity showed the high efficiency and stability of the designed nanocomposite under applied conditions.

Keywords: Magnetic nanocatalyst, Core–shell structured nanocomposite, Ionic liquid, Palladium, Reduction of nitrobenzenes

Subject terms: Catalysis, Green chemistry

Introduction

Ionic liquids (ILs) are compounds consisting of cations and anions, which their special properties and applications can be enhanced by altering the composition of cations and anions1,2. These have attracted much attention due to their unique properties such as high thermal stability, excellent electrical conductivity, high solubility and miscibility, and non-flammability. They are also known as green solvents due to their environmental compatibility3–11. Due to possible hydrogen bonding and coulomb interactions between their ions and different surfaces, ionic liquids are widely used in various fields such as pharmaceuticals12–14, solar energy15–17, supercapacitors18–21, waste recycling22, catalysts23–26, etc. ILs also have suitable structures for linking with metals to perform complexes with high catalytic activity. Some reports in this matter are TiO2/IL‐Pd27, GR-IL-Pt28, Mag@mSiO2/IL-Cu29, BPMO-Ph-IL/Mn30 and SBA-15-IL/Pd31. Among the different metals, palladium (Pd) is widely used in pharmaceutical industries, fuel cells, photography, dentistry, etc.32–42. Due to the stability against moisture and air, high catalytic activity, and other amazing properties, the palladium metal can also be selectively used as an effective catalyst in many organic processes such as coupling43–47, oxidation and reduction reactions48–53. Therefore, the Pd-ionic liquid complex will be a high-performance catalyst, however, its non-recyclability is a big drawback. The immobilization of these complexes on solid supports such as magnetic core–shell structured nanomaterials, is an important strategy to solve this restriction. Some reports in this matter are Pd/ILNH2/SiO2/Fe3O454, Fe3O4@PEG–AIm–NH2–IL–Pd55, Mag-IL-Pd56, Fe3O4@MePMO-IL/Pd57 and SGCN/Fe3O4/PVIs/Pd58.

On the other hand, the core–shell structured nanomaterials containing Co3O4 nanoparticles have attracted the attention of many researchers due to their high thermal and chemical stability, easy magnetic separation, high surface area, and special electrical and optical properties59–61. These materials have garnered significant scientific interest and technological relevance due to their potential applications in various fields. These materials exhibit unique properties that make them suitable candidates for use in biomedical applications, catalysis, chemical sensing, adsorbent, energy storage, and electrochromism62–66. Some recent reports in this regard are Co3O4@SiO2/OS-SO3H63, Co3O4@NC67, Co3O4–C68, RuO2–Co3O469, Co3O4@NiMoO470, Co3O4/ZnCo2O471 and Co3O4/ZnO72.

The reduction of toxic and harmful nitrobenzenes, is one of the important methods for the production of aromatic amines which are widely used to prepare many fine chemicals such as dyes, pesticides, antioxidants, spices, etc.73–78. To date, many catalytic systems have been applied for the reduction of nitrobenzenes to aniline derivatives. Some reports in this matter are Fe3O4@CPd79, C-Fe3O4-Pd80, Pd@CQD@Fe3O481, Fe3O4@SiO2/ Schiff base/Pd(II)82 and Pd-Fe3O4-ES83. However, the use of toxic organic solvents, high reaction temperature and high loading of catalyst are the limitations of these systems. Therefore, preparation of novel recoverable catalytic systems with high efficiency and recoverability is an important challenge in this matter.

In view of the above, herein, a novel magnetic Co3O4@mSiO2 nanocomposite supported ionic liquid/palladium complex (Co3O4@mSiO2/IL-Pd) with core–shell structure is prepared, characterized and its catalytic performance is developed in the reduction of nitrobenzenes.

Experimental

Preparation of 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium chloride

For this aim, in a well-dried 250 mL two-necked Schlenk flask, 1-methylimidazole (10.12 g) was dissolved in 120 mL of anhydrous toluene. To this solution, (3-chloropropyl)trimethoxysilane (24.23 g) was added. The system was then evacuated and backfilled with argon three times to ensure an inert atmosphere, followed by refluxing the mixture under argon for 24 h. Upon completion, the biphasic reaction mixture was allowed to cool to room temperature. The organic (toluene) layer was carefully separated from the ionic liquid (IL) phase. The pale-yellow IL layer was subsequently washed with dry diethyl ether (5 × 20 mL) to remove any unreacted materials and organic residues. Finally, the purified IL was dried under vacuum at room temperature for 12 h84.

Preparation of Co3O4 nanoparticels

Magnetic cobalt oxide (Co3O4) nanoparticles were synthesized via a chemical reduction method. In a typical procedure, CoCl2·6H2O (1.85 mmol, 0.440 g) was dissolved in 15 mL of absolute EtOH under magnetic stirring at room temperature. Subsequently, a solution of pluronic P123 (0.2 g dissolved in 5 mL of EtOH) was added dropwise to the mixture. After thorough mixing, NaBH4 (12.9 mmol, 0.487 g) was added as a reducing agent, and the reaction mixture was stirred for 10 min at ambient temperature. The resulting nanoparticles were magnetically separated and washed several times with warm EtOH and deionized water to remove excess pluronic P123 and other residual impurities. Finally, the purified product was dried at 65 °C for 5 h to obtain the Co3O4 nanoparticles63.

Preparation of Co3O4@SiO2

For preparation of Co3O4@SiO2, magnetic cobalt oxide NPs (1g) were dispersed in EtOH (30 mL), while aqueous ammonia (5.3 mL, 60% wt) was added drop-wise. Then, tetraethylorthosilicate (TEOS, 1 mL) was slowly added and the obtained mixture was stirred at RT for 16 h. Finally, the magnetic product was collected by using a magnet, washed with water and EtOH, dried at 70 °C for 6 h and called Co3O4@SiO2 nanocomposite.

Preparation of Co3O4@mSiO2

For this aim, the Co3O4@SiO2 (1 g) was dispersed in a mixture of distilled water (70 mL) and EtOH (50 mL) under ultrasonic condition at RT for 30 min. Subsequently, aqueous ammonia (3.5 mL, 25% wt) and cetyltrimethylammonium bromide (CTAB, 1 g) were introduced into the reaction vessel. The resulting mixture was mechanically agitated at ambient temperature for 15 min. Thereafter, TEOS (1 mL) was gradually added, and the reaction mixture was stirred at RT for 2 h. The obtained mixture was then aged at 100 °C for 48 h. Following this step, the magnetic product was isolated using a magnet, rinsed with water and EtOH, and subsequently dried at 70 °C for 6 h. The CTAB template was finally eliminated through calcination at 500 °C for a duration of 5 h, yielding the final material designated as Co3O4@mSiO2.

Preparation of Co3O4@mSiO2/IL

For this, Co3O4@mSiO2 (1 g) was completely dispersed in toluene (40 mL) at RT for 30 min. Then, 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium chloride (1.3 mmol) was added and the obtained mixture was refluxed and stirred for 24 h under argon atmosphere. After cooling to RT, the product was separated by using a magnet, washed with water and EtOH, dried at 70 °C for 6 h and denoted as Co3O4@mSiO2/IL.

Preparation of Co3O4@mSiO2/IL-Pd

For the preparation of Co3O4@mSiO2/IL-Pd nanocatalyst, Co3O4@mSiO2/IL (1 g) was completely dispersed in DMSO (40 mL). Then, Pd(OAc)2 (3 mmol) was added to the reaction flask and the resulting mixture was stirred at RT for 24 h. Finally, the nanocatalyst product was magnetically separated, washed completely with EtOH, dried at 70 °C for 6 h and denoted as Co3O4@mSiO2/IL-Pd.

General procedure for the reduction of nitrobenzenes

For this, nitrobenzene derivative (1 mmol), sodium borohydride (2 mmol) and Co3O4@mSiO2/IL-Pd nanocatalyst (0.01 g) were added in water (8 mL). The obtained mixture was stirred at RT and the progress of the reaction was monitored by TLC. After completing of the reaction, the catalyst was separated by using a magnet. The water-soluble impurities of residue were removed through decantation process by using a mixture of water and ethyl acetate. The pure products were obtained after evaporation of organic phase or via recrystallization of impure mixture in EtOH (Fig. 1).

Fig. 1.

Fig. 1

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The schematic representation of the reduction of nitrobenzenes in the presence of the Co3O4@mSiO2/IL-Pd catalyst.

IR and NMR data of aniline products

Benzene-1,4-diamine

IR (KBr, cm−1): 3420, 3400 (N–H, stretching vibration), 3024 (C-H, stretching vibration sp2), 1627, 1450 (C = C, Ar stretching sp2). 1H NMR (400 MHz, CDCl3): δ (ppm) 3.30 (broad peak, 4H, NH2), 6.55 (s, 4H, ArH).

4-Chloroaniline

IR (KBr, cm−1): 3483, 3400 (N–H, stretching vibration), 3042 (C-H, stretching vibration sp2), 1621, 1496 (C = C, Ar stretching sp2). 1H-NMR (400 MHz, CDCl3): δ (ppm) 5.31 (s, 2H, NH2), 6.48 (d, 2H, J = 8.7), 7.15 (d, 2H, J = 8.7).

Results and discussion

Figure 2 shows the synthesis procedure for the Co3O4@mSiO2/IL-Pd nanocatalyst. Firstly, Co3O4@SiO2 was prepared according to our previous report63. Following this step, a secondary shell was generated through the alkaline hydrolysis and condensation of TEOS in the presence of the CTAB surfactant. Upon the successful elimination of the surfactant template, the resultant material, denoted as Co3O4@mSiO2, was obtained. Then, Co3O4@mSiO2 was modified with 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium chloride to give the Co3O4@mSiO2/IL nanocomposite. Finally, Co3O4@mSiO2/IL was treated with Pd(OAc)2 to deliver the desired Co3O4@mSiO2/IL-Pd nanocatalyst.

Fig. 2.

Fig. 2

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Preparation of the Co3O4@mSiO2/IL-Pd nanocatalyst.

The FT-IR spectra of Co3O4, Co3O4@SiO2 and Co3O4@mSiO2/IL-Pd are shown in Fig. 3. For all materials, the band at 618 cm−1 is assigned to the Co–O stretching vibration. Moreover, the bending and stretching vibrations of O–H bonds are, respectively, observed at 1635 and 3417 cm−185. For Co3O4@SiO2 and Co3O4@mSiO2/IL-Pd, the peaks appeared at 928 and 1080 cm−1 are attributed to symmetric and asymmetric vibrations of the Si–O–Si bonds (Figs. 3b and c)63. For Co3O4@mSiO2/IL-Pd, the new peaks at 2920, 1420 and 1638 cm−1 are, respectively, assigned to aliphatic C–H, C = C57 and C = N30 bonds of immobilized IL moieties (Fig. 3c) . These results confirm the successful synthesis of the Co3O4@mSiO2/IL-Pd nanocatalyst.

Fig. 3.

Fig. 3

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FT-IR spectra of (a) Co3O4, (b) Co3O4@SiO2 and (c) Co3O4@mSiO2/IL-Pd.

The structural feature of Co3O4@mSiO2/IL-Pd was studied by using powder X-ray diffraction (PXRD) analysis. This showed nine peaks at 2 theta of 24, 32, 34, 36, 45, 55, 59, 66 and 68° proving the high stability of crystalline structure of Co3O4 nanoparticles during catalyst preparation63,85 (Fig. 4).

Fig. 4.

Fig. 4

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PXRD pattern of the Co3O4@mSiO2/IL-Pd nanocatalyst.

The surface morphology and particle size of the designed nanomaterial was investigated by using scanning electron microscopy (SEM). This showed a spherical morphology for Co3O4@mSiO2/IL-Pd nanocatalyst (Fig. 5).

Fig. 5.

Fig. 5

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SEM image of the Co3O4@mSiO2/IL-Pd nanocatalyst.

The TEM images of the Co3O4@mSiO2/IL-Pd nanomaterial also showed a core–shell structure with black cores (Co3O4 NPs) and mesoporous silica shell (Fig. 6). The highly ordered mesoporous structure of the designed nanomaterial indicates the key role of CTAB-structuring directing agent during material preparation. Interestingly, these type materials are very good candidates for adsorption and catalysis processes.

Fig. 6.

Fig. 6

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TEM images of the Co3O4@mSiO2/IL-Pd nanocatalyst.

The energy dispersive X-ray (EDX) analysis of Co3O4@mSiO2/IL-Pd is demonstrated in Fig. 7. The presence of Co, Si, O, C, N, Pd and Cl elements in this analysis proves the successful immobilization of IL-Pd complex on the Co3O4@SiO2 nanoparticles.

Fig. 7.

Fig. 7

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EDX spectrum of the Co3O4@mSiO2/IL-Pd nanocatalyst.

In the next study, the thermal gravimetric analysis (TGA) of Co3O4@mSiO2/IL-Pd nanocatalyst was investigated at temperature range from 25 to 900 °C. TG curve shows three weight losses. As illustrated in Fig. 8, the initial weight loss of approximately 2.5% below 180 ºC can be attributed to the evaporation of residual water and organic solvents involved in the catalyst synthesis process. The second weight loss of circa 2.5%, observed between 180 and 240 °C, is associated with the removal of residual CTAB surfactant. Lastly, the most significant weight loss of approximately 30%, occurring in the temperature range of 240–510 °C, corresponds to the thermal decomposition and subsequent elimination of the ionic liquid groups immobilized on the Co3O4@mSiO2 nanocomposite.

Fig. 8.

Fig. 8

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TGA curve of the Co3O4@mSiO2/IL-Pd nanocatalyst.

The magnetic behavior of the synthesized Co3O4 and Co3O4@mSiO2/IL-Pd nanostructures was examined using vibrating sample magnetometry (VSM). The saturation magnetization (Ms) values were determined to be approximately 55 emu/g for Co3O4 and 30 emu/g for Co3O4@mSiO2/IL-Pd. The observed reduction in magnetic saturation clearly indicates the successful surface functionalization of Co3O4 nanoparticles with silica precursors and ionic liquid–palladium complexes. Despite this decline, the materials retained sufficient magnetic response, ensuring efficient magnetic separation, which is a crucial feature for practical applications in catalytic and recovery processes (Fig. 9).

Fig. 9.

Fig. 9

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VSM curve of the (a) Co3O4 and (b) Co3O4@mSiO2/IL-Pd nanomaterials.

After characterization, the Co3O4@mSiO2/IL-Pd nanomaterial was employed as a powerful catalyst in the reduction of nitrobenzenes. To optimize the reaction conditions, the effect of solvent and the amount of catalyst were investigated. For this, the reduction of 4-nitroaniline in the presence of sodium borohydride at RT was chosen as a reaction model. Firstly, the effect of catalyst amount was studied. In the absence of catalyst, no product was observed (Table 1, entry 1). While, with increasing the amount of catalyst, the yield of the desired product was increased, in which the best result was obtained in the presence of 0.01 g of Co3O4@mSiO2/IL-Pd (Table 1, entries 2–4). In the next step, the effect of different solvents was investigated. Among the different solvents of H2O, MeOH, THF and EtOH, the highest yield of product was obtained in water as an environmentally friendly solvent (Table 1, entry 3 vs entries 5–7). Accordingly, the use of 0.01 g of catalyst, water solvent and RT were selected as optimum conditions (Table 1, entry 3).

Table 1.

The effect of different parameters in the reduction of 4-nitroaniline at RT.

graphic file with name 41598_2025_16962_Figa_HTML.gif
Entry Catalyst (g) Solvent Yield (%) a
1 – H2O NR
2 0.005 H2O 75
3 0.01 H2O 95
4 0.015 H2O 95
5 0.01 MeOH 62
6 0.01 EtOH 50
7 0.01 THF 35
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a Isolated yields.

After optimization, to explore the substrate scope and also to study the activity and efficiency of the designed nanocatalyst, the reduction of various nitrobenzenes was investigated under optimized conditions. As shown in Table 2, both electron-donating containing nitro-compounds such as –NH2, -OH and -CH2OH (Table 2, entries 1–4) and electron‐withdrawing substituted nitrobenzenes such as 4-nitrobenzaldehyde (Table 2, entry 5) were used as substrate and gave the high yield of the desired products. It is noteworthy that, where 4-nitrobenzaldehyde was used as substrate, 0.015 g of catalyst was used and the aldehyde functional group also reduced to the corresponding alcohol during applied reaction86,87. These results prove the high catalytic activity of the Co3O4@mSiO2/IL-Pd nanocatalyst for the reduction of a wide range of nitrobenzenes.

Table 2.

Reduction of nitrobenzenes in the presence of Co3O4@mSiO2/IL-Pd.

graphic file with name 41598_2025_16962_Figb_HTML.gif
Entry Substrate Time (min) Yield (%)a [g] Product M. P. (°C)
Found Reported
1 graphic file with name 41598_2025_16962_Figc_HTML.gif 15 95 [0.103] graphic file with name 41598_2025_16962_Figi_HTML.gif 144–145 143–14488
2 graphic file with name 41598_2025_16962_Figd_HTML.gif 20 94 [0.102] graphic file with name 41598_2025_16962_Figj_HTML.gif 62–64 63–6688
3 graphic file with name 41598_2025_16962_Fige_HTML.gif 25 91 [0.100] graphic file with name 41598_2025_16962_Figk_HTML.gif 184–185 185–18688
4 graphic file with name 41598_2025_16962_Figf_HTML.gif 20 90 [0.111] graphic file with name 41598_2025_16962_Figl_HTML.gif 60–62 61–6386
5 graphic file with name 41598_2025_16962_Figg_HTML.gif 25 89 [0.108] graphic file with name 41598_2025_16962_Figm_HTML.gif 60–62 61–6386
6 graphic file with name 41598_2025_16962_Figh_HTML.gif 20 94 [0.120] graphic file with name 41598_2025_16962_Fign_HTML.gif 69–71 70–7286
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The reusability and durability of the designed catalyst were also studied. For this, the reduction of 4-nitroaniline was selected as a test model. According to the results, the catalyst was stable under the applied conditions and easily was recovered and reused for seven times without considerable decrease in its activity (Fig. 10).

Fig. 10.

Fig. 10

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Recoverability and reusability of the Co3O4@mSiO2/IL-Pd nanocatalyst.

In Fig. 11, a plausible mechanism for the reduction of nitrobenzene derivatives in the presence of the Co3O4@mSiO2/IL-Pd catalyst and NaBH4 in aqueous medium is proposed89. As shown, the reduction likely proceeds through intermediates I–IV. These intermediates represent distinct stages in the stepwise conversion of the nitro group to the corresponding amine, emphasizing the role of the catalyst in facilitating electron transfer and stabilizing reaction intermediates throughout the process.

Fig. 11.

Fig. 11

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Proposed mechanism for reduction of nitrobenzenes in the presence of Co3O4@mSiO2/IL-Pd catalyst.

In the next, a comparative study of Co3O4@mSiO2/IL-Pd with former catalysts in the reduction of nitrobenzenes was performed (Table 3). The result showed the better efficiency of the present catalyst in terms of reaction conditions and recovery times. These observations are attributed to magnetic nature and high stability of the Co3O4@mSiO2/IL-Pd nanocatalyst. In fact, the immobilized IL moieties play a key role in the successful immobilization and stability of catalytically active palladium sites.

Table 3.

The comparative study of Co3O4@mSiO2/IL-Pd with former catalysts in the reduction of nitrobenzenes.

Entry Catalyst Conditions Recovery times References
1 MMT@Fe3O4@Cu H2O, 60 °C 5 90
2 Pd NPs/C@ Fe3O4 H2O, EtOH, 70 °C 5 91
3 Fe3O4@SiO2/EP.EN.EG@Cu H2O, 60 °C 4 92
4 Fe3O4‐Glu‐Ag H2O, 60 °C 4 93
5 Fe3O4@C@Ag-Au H2O, RT 5 94
6 Co3O4@mSiO2/IL-Pd H2O, RT 7 This work
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a Isolated yields.

Conclusion

In conclusion, an ionic liquid-palladium complex was immobilized on the magnetic core–shell structured Co3O4@mSiO2 nanoparticles to prepare a novel nanocatalyst named Co3O4@mSiO2/IL-Pd. The FT-IR and EDX analyses confirmed the successful immobilization of IL-Pd on the magnetic Co3O4@mSiO2 NPs. The VSM analysis also showed very good magnetic properties for the designed catalyst. The PXRD pattern illustrated high stability of the crystalline structure of Co3O4 NPs during catalyst preparation. The SEM and TG analyses showed, respectively, a spherical morphology and a high thermal stability for the nanocatalyst. The Co3O4@mSiO2/IL-Pd nanomaterial was effectively used as an efficient catalyst in the reduction of nitrobenzenes and gave the desired aniline products in high to excellent yields. Furthermore, the Co3O4@mSiO2/IL-Pd nanocatalyst was easily separated by using a magnet and recovered several times with no significant decrease in its activity.

Acknowledgements

The authors thank Yasouj University and the Iran National Science Foundation (INSF) for supporting this work.

Author contributions

H.A.: Investigation, Writing—original draft, Formal analysis, Resources. D.E.: Conceptualization, Writing—review and editing, Visualization, Supervision. M.S.: Writing—original draft, Resources, Formal analysis.

Funding

There is no funding to declare.

Data availability

All data and materials are included in the manuscript.

Declarations

Competing interests

The authors declare no competing interests.

Ethical approval

This declaration is not applicable.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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