Eco-friendly synthesis of nano ferrites for effective dye degradation and enhanced antimicrobial protection

1 Introduction

Nanoparticles (NPs) have garnered significant attention in catalytic, energy, medicinal, and materials science research due to their unique chemical and physical properties.(Tiekink 2002, Nam et al., 2009). Their physiochemical, optical, and electronic attributes are profoundly influenced by dimensions, structure, and surface topology.Traditional metallic NP synthesis methods include sol–gel, ultra-sonication, electrochemical synthesis, hot spraying, physical vapor deposition (PVD), chemical reduction of metallic ions, and microwave-assisted synthesis. (Byun et al., 2000, Sarkar et al., 2017, Zou et al., 2017, Chung and Zhang 2021, Vorobyova et al., 2023, Pedone et al., 2005) However, these methods often employ ecologically hazardous chemicals and reagents. Recently, eco-friendly approaches utilizing microorganisms and plant-based extracts have emerged as viable alternatives for NP synthesis, offering a facile and environmentally sustainable solution.(Al-Farraj et al., 2018, Laghrib et al., 2019, Patil and Behera 2023, Masuku et al., 2024).

Nanomaterials based on 3D transition metal oxides (Fe₃O₄, α-Fe₂O₃, γ-Fe₂O₃, CoO, Co₃O₄, and NiO) and mixed metal oxides (CoFe₂O₄, NiFe₂O₄, and MnFe₂O₄) have demonstrated potential in catalytic, medical, and various research applications. Notably, plant extracts have emerged as effective biotemplates for synthesizing NPswith enhanced surface area and stability. Specifically, extracts from kobushi magnolia (Mokryeon), kaki persimmon (Japanese persimmon), and Ficus indica (banyan) have been shown to produce highly stable NPs(Prathna et al., 2011, Dhayalan et al., 2018, Shanmugam et al., 2022). This stability is attributed to the presence of bioactive compounds, including flavonoids, polyphenols, and alkaloids, which serve as reducing agents in plant extracts.

The synthesis and application of functional metal ferrites have garnered significant attention in recent years due to their exceptional magnetic properties. Notably, their superparamagnetic nature enables effortless separation from reaction mixtures, eliminating the need for tedious and prolonged separation steps (Ranjithkumar et al., 2014). Consequently, researchers have leveraged ferrite NPs to address various challenges, including water contamination treatment, sensor development, and antibacterial applications. Previous studies have demonstrated the versatility of cobalt ferrite NPs in oxidizing carbamazepine. (He et al., 2017) targeting human ferritin cancer cells.(Leonel et al., 2021) and detecting NO₂ gas (Bagade et al., 2017) Similarly, magnetically recoverable NiFe₂O₄ NPs have been synthesized for reducing nitroarenes(Zeynizadeh et al., 2017) and explored for magnetic resonance imaging (MRI), target drug delivery, and controlled drug release applications.(Wu et al., 2011, Koul et al., 2021)

The widespread use of synthetic dyes, such as methylene blue and rhodamine-B, in various industries poses significant environmental risks(Alfryyan et al., 2022). The discharge of untreated industrial wastewater containing these dyes into water bodies deteriorates water quality and potentially harms human health and aquatic ecosystems. Due to their mutagenic and carcinogenic properties, efficient treatment strategies are crucial to remove or degrade dye contaminants from industrial effluents. (McMullan et al., 2001, Wang et al., 2018,Jara et al., 2024) In response, governments in developed countries have implemented strict environmental regulations. Currently, industries are focusing on synthesizing efficient catalysts using cost-effective, eco-friendly materials to reduce dye concentrations. This effort aligns with the United Nations Sustainable Development Goal (SDG) 6.3, aiming to improve water quality by 2030 through reduced pollution, elimination of harmful chemicals, and increased wastewater treatment and safe reuse globally (Chirgwin et al., 2021).

A clean and green calcination method was developed to synthesize cobalt and nickel ferrite nanomaterials using Araucaria heterophylla resin as a sustainable biotemplate (Scheme 1).The synthesized ferrites were subjected to a thorough characterization, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-rayspectroscopy,and vibrating sample magnetometry, to elucidate their structural, morphological, chemical, elemental, and magnetic properties. Additionally, their photocatalytic efficiency and antibacterial efficacy were assessed through standardized assays.

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Scheme 1

Green synthesis of CoFe₂O₄ and NiFe₂O₄ Nanoparticles.

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2 Experimental

3 Results and discussion

Fourier Transform Infrared (FT-IR) spectroscopy was employed to investigate the surface composition of synthesized NPs. This analysis revealed specific functional groups involved in NPs formation, shedding light on interactions between metal ions (cobalt and nickel ferrite) and phytochemicals from plant extracts. (Chirgwin et al., 2021, McMullan et al., 2001) The FT-IR spectrum of AH gum extract displayed characteristic bands at 3360.35 cm⁻¹ (O–H stretching), 2913.26 cm⁻¹ (C–H/CH2 vibrations), 1644 cm⁻¹ (C=C stretching), 1375 cm⁻¹ (C-O stretching), and 1020 cm⁻¹ (C-O bonds) (Fig. 1a). Comparison of FT-IR spectra for AH-bound metal nitrates (Fig. 1a, c) and corresponding ferrite NPs (Fig. 1b, d) revealed distinct peak patterns. The AH-bound metal nitrates exhibited numerous peaks between 1000–3000 cm⁻¹, indicating various active functional groups from the AH biopolymer. Peaks at 555/462 cm⁻¹ (Fig. 1a) and 486/584 cm⁻¹ (Fig. 1c) arose from bond formation between AH biopolymer and metal nitrates. In contrast, ferrite NPs (Fig. 1b, d) showed no characteristic peaks in this region. Firm peaks at 458/540 cm⁻¹ (Fig. 1b) and 452/630 cm⁻¹ (Fig. 1d) indicated cobalt and nickel ferrite formation. FT-IR analysis confirmed complete decomposition of AH biopolymer extracts during calcination at 600°C.(Hajdu et al., 2022, Passero et al., 2024) The band shift in FT-IR spectra suggested interactions between extract compounds and metal ions during NP construction. Soluble extract components possibly acted as capping agents, preventing FeNP aggregation.(Ahmed et al., 2020, Hajdu et al., 2022).

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Fig. 1

FT-IR spectra of CoFe₂O₄ and NiFe₂O₄ precursors and NPs.

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XRD patterns are frequently used to study the phase structure of the various nanocatalysts. The powdered XRD (PXRD) patterns of cobalt ferrite and nickel ferrite are illustrated in (Fig. 2a1 and 2a2 respectively). The JCPDS card numbers 22–1086 nicely match the seven sharp peaks (111, 220, 311, 400, 511, 620, and 533) seen in (Fig. 2a1). Similarly, (Fig. 2a2) displays five distinct peaks that match the JCPDS card no. 03–0875 (220, 311, 400, 511, and 440). The production of cobalt and nickel ferrite NPs in their cubic spinel structure was confirmed by the JCPDS card results.(Ahmed et al., 2020, Alzoubi 2022) Using XRD data and the Scherrer equation, the typical crystallite structure was 7 nm for cobalt ferrite and 11nm for nickel ferrite, and these results were also in agreement with TEM results (Fig. 2b).

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Fig. 2

XRD patterns (a1, a2) and TEM images of CoFe₂O₄, NiFe₂O₄ (b1-6).

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The study utilized TEM to visualize the size and morphology of the cobalt and nickel ferrite NPs. TEM images displayed the broken pieces of rock of the NPs with higher aggregation, which were evenly distributed. The crystalline size of cobalt ferrite and nickel ferrite was found to be < 10 nm. The TEM images of cobalt and nickel ferrite NPs are presented in (Fig. 2b). The powdered XRD data's Full width at half maximum (FWHM) value agreed with the TEM findings. Moreover, the occurrence of diffraction rings and perky spots in the selected area electron diffraction (SAED) pattern indicated that the produced ferrite NPs were highly crystalline, as shown in (Fig. 2a). The nine diffraction peaks that were seen for Co and Ni ferrite NPs (220, 111, 400, 422, 311, 511, 620, 533, and 642 in (Fig. 2a1), and 220, 311, 400, 511, and 440 in (Fig. 2a2) match the JCPDS card numbers 22–1086 and 03–0875 quite well. The production of Co/Ni Fe₂O₄ NPs with a cubic spinel shape was confirmed by the JCPDS card results. Compared to the SAED pattern of the produced ferrite NPs, the PXRD pattern yielded the same results.(Londono-Calderon et al., 2017, Khoso et al., 2021).

Scanning electron microscopy (SEM) was employed to investigate the surface morphology of cobalt and nickel ferrite catalysts (Fig. 3). The micrographs revealed irregular, rock-like structures with significant agglomeration, attributed to steric effects and magnetic interactions between ferrite NPs. The magnetic dipole–dipole interactions likely caused NPs to attract and aggregate. Complementary energy-dispersive X-ray analysis (EDAX) spectra (Fig. 3) confirmed the atomic composition of cobalt and nickel ferrite catalysts, displaying a 1:2:4 ratio of Co/Ni:Fe:O. This ratio corroborates the successful synthesis of cobalt and nickel ferrite catalysts using AH biopolymer extract. The SEM and EDAX results provide valuable insights into the morphology and composition of the ferrite catalysts, informing the development of efficient and effective catalysts for various applications.

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Fig. 3

SEM images (a-d) and EDAX spectra of (e) CoFe₂O₄ and (f) NiFe₂O₄.

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The magnetic characteristics of cobalt and nickel ferrite NPs were investigated at room temperature using a vibrating sample magnetometer with a 10 kOe applied field (Supplementary Fig. 1). The hysteresis loops yielded saturation magnetization (Ms), remanence (Mr), and coercive force (Hc) values (Table 1). Compared to bare cobalt ferrite (Ms = 94 emu/g).(Sadeghi et al., 2020) and bare nickel ferrite (Ms = 19 emu/g)(Yelgaonkar et al., 2020) the magnetic parameters of cobalt and nickel ferrite NPs decreased, consistent with reduced NP size. The ferromagnetic behavior was confirmed by the Mr/Ms ratio (Supplementary Table 1), indicating that cobalt ferrite NPs exhibited ferromagnetism, while nickel ferrite NPs displayed superparamagnetic behavior at room temperature, with Mr/Ms ratios <25%.(Tandon et al., 2021, Sofronie et al., 2022, Dippong et al., 2023).

3.1

3.1 Optimization of the dye degradation process

The discharge of persistent industrial pollutants, including dyes, nitroarenes, pharmaceuticals, and cosmetics, deteriorates surface and subsurface water quality, posing significant risks to human and environmental health. Ferrite NPs have emerged as effective heterogeneous catalysts for removing water-borne dye pollution (Bagade et al., 2017, Jara et al., 2024). To mitigate these harmful effects, efficient removal of these pollutants is crucial. The degradation of dyes can be achieved through reduction using mild reducing agents. Sodium borohydride (NaBH₄) is a commonly employed reducing agent for this purpose. The reduction mechanism involves the transfer of hydride ions (H^-) from NaBH₄ to the dye solution, breaking down large dye molecules into smaller, less toxic fragments (Jara et al., 2024).

3.1.1

3.1.1 Optimization of NaBH₄ concentration

NaBH₄ was selected as the reducing agent due to its mild, selective, and eco-friendly properties. Its non-toxicity, non-flammability, and ease of handling make it an ideal choice for dye degradation. To optimize the degradation process, experiments were conducted using 5 mg of CoFe₂O₄ catalyst with varying NaBH₄ concentrations (1–14 mM). Results (Fig. 4a, b) showed maximum degradation of RhB and MB dyes at 10 mM and 12 mM NaBH₄, respectively. Similarly, using NiFe₂O₄ catalyst, optimal degradation was achieved at 9 mM (RhB) and 11.5 mM (MB) NaBH₄ concentrations.

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Fig. 4

Effect of NaBH₄ concentration (4a-b) and catalyst amount on MB/RhB degradation (4c).

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3.1.2

3.1.2 Optimization of catalyst amount

The effectiveness of a catalyst in dye degradation is dependent on the amount of catalyst used, as it directly impacts the surface area of the catalyst available for the reaction. A higher surface area of the catalyst can lead to more active sites for the reaction, resulting in more effective degradation of dyes. On the other hand, using too much catalyst can result in agglomeration, which reduces the surface area accessible for the reaction and, in turn, hinders the efficacy of the catalyst. Furthermore, the amount of catalyst used can also affect the reaction kinetics. For instance, too little catalyst may reduce the reaction rate, leading to incomplete dye degradation. At the same time, too much catalyst may cause the reaction to proceed too quickly, leading to incomplete degradation. Therefore, it is essential to optimize the amount of catalyst used for the reaction to achieve the desired degradation efficiency and minimize cost. Therefore, in the present work, the amount of ferrite NPs was varied from 2.5 to 20 mg, tested for 30 min using a 10 mM concentration of NaHB₄ for the degradation of MB and RhB. The results depicted in (Fig. 4 c) clearly showed that 10 mg of catalysts exhibited the maximum degradation of MB and RhB, and it remained constant at 15 mg of catalyst. When increasing the catalyst amount to more than 15 mg, dye degradation is lessened due to the accessibility of less energetic surface area on the catalyst surface due to agglomeration.

3.1.3

3.1.3 Optimization of contact time

During the experiment, a dye solution (2 mL) of 20 mg/L initial concentration was treated with 10 mg of ferrite catalyst and 10 mM NaBH₄ at varied contact time range (0 to 40 min). Results showed that the maximum degradation of MB by CoFe₂O₄ and NiFe₂O₄ NPs was observed at 25 min and 30 min contact times, respectively. While maximum RhB degradation by CoFe₂O₄ and NiFe₂O₄ NPs was observed at 20 min and 10 min, respectively, as illustrated in (Fig. 5) The absorbance bands presented in ( Fig. 6a and 6b) at varied contact times affirmed the results for dyes degradation. Comparative results our study show that nickel ferrite catalyst exhibited a 97% better degradation against RhB dye within 10 min under the studied experimental conditions (Fig. 7).

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Fig. 5

Time-dependent degradation of MB/RhB using CoFe₂O₄/NiFe₂O₄.

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Fig. 6

Electronic band structure during MB/RhB reduction.

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Fig. 7

Removal efficiency of MB/RhB using CoFe₂O₄/NiFe₂O₄.

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3.1.4

3.1.4 Kinetic modelling for dyes reduction

Pseudo-first-order and pseudo-second-order kinetic models in linearized forms were practical to MB and RhB degradation data by CoFe₂O₄ and NiFe₂O₄ NPs._. The best-fitted model was decided to be constructed on higher regression coefficient (R²) value.

The pseudo-first order and the pseudo-second-order kinetic models are given by expressions:

Pseudo-first order model:

(1)

$$\mathit{log}(q_e-q_t)=log{q}_e-\frac{k_{1}t}{2.303}\cdots$$ Pseudo-second order model:

(2)

$$\frac{t}{q_t}=\frac{1}{k_2{q_e}^2}+\frac{t}{q_e}\cdots \cdots \cdots$$ Where t is the reduction process's time (min), q_e and q_t are the amounts of MB and RhB condensed (mg/L) at any time t and at equilibrium, and k₁ (1/min) and k₂ (g/mg-min) are the pseudo-first and second-order rate constants, correspondingly. (Supplementary Table 2) lists the R² values, and (Supplementary Fig. 2) displays their plot. For CoFe₂O₄ and NiFe₂O₄ NPs, the data fitted well to pseudo-second-order kinetic model.

3.1.5

3.1.5 Mechanism of reduction process

The reduction of MB and RhB in the presence of NaBH₄ and the synthesized ferrite catalyst NPs at room temperature have been studied. After being treated with NaBH₄ and a catalyst, the colors of the MB and RhB solutions instantly turn colorless. It is understood that the catalytic reaction occurred in the existence of ferrite NPs by an electron transfer and by an electrochemical mechanism in which nucleophile BH₄⁻ ions donate electrons to electrophilic organic MB and RhB concluded ferrite NPs. After the chemisorption of dyes and BH₄⁻ on their surfaces, synthesized ferrite NPs were allowed for electron transport, which speeds up the reduction of dyes. Consequently, after being treated with NaBH₄, the dye solution, including NPs, was completely discolored. This result demonstrates how quickly and completely MB and RhB can be converted by ferrite NPs to their colorless leuco form.(Jara et al., 2024).

3.1.6

3.1.6 Stability and reuse of ferrite catalysts

The NPs’ recovery was evaluated using an external magnet by the exclusion of nanocatalysts from the reaction mixture (Supplementary Fig. 3). The catalyst was observed to be drawn to the magnet and adhered to the magnet’s surface, making the solution transparent and easily removed by decanting the colorless solution. It can be utilized as a magnetic catalyst to lessen the dye pollution in aqueous solutions. The findings in (Fig. 8) provide information about the catalytic behavior of recovered materials utilized for more cycles after being rinsed with ethanol, acetone, and water, dried, and reused even after up to four additional runs. These also confirm the catalytic behavior of synthesized catalysts without any loss of activity by reducing almost 90% of both dyes (MB and RhB).

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Fig. 8

Recycling capability of NiCoFe₂O₄ NPs for MB/RhB degradation.

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4 Conclusions

The current study has covered a straightforward, environmentally friendly process for creating stable magnetic ferrite NPs without hazardous chemicals. Other transition and rare earth metal oxides can be treated using this technique. Ferrite NPs have very small magnetic characteristics. In addition,there is a permanent magnet in aqueous media. The degradation of MB and RhB is appropriate aimed at the pseudo-second-order model. Our findings demonstrate that transition metal-substituted cobalt ferrite NPs possess enhanced antibacterial activity against E.coli, outperforming the other three compounds assessed. Given their unique properties, ferrite NPs have significant potential for exploitation in various biomedical and biotechnological contexts, including the development of targeted drug delivery platforms and efficient catalytic systems.

CRediT authorship contribution statement

Manikandan Dhayalan: Writing – review & editing, Writing – original draft, Validation, Supervision, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Rathika Govindasamy: Writing – review & editing, Writing – original draft, Supervision, Software, Resources, Project administration, Methodology, Investigation, Data curation, Conceptualization. Karthikeyan Prakasham: Writing – review & editing, Supervision, Investigation, Funding acquisition, Conceptualization. Moonis Ali Khan: Writing – review & editing, Supervision, Project administration, Funding acquisition, Formal analysis. Anuchit Phanumartwiwath: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.