Advances in the green synthesis of magnetite nanoparticles for environmental remediation: A systematic review

2.1. Inclusion criteria (IC)

• IC1: Studies employing ecological synthesis methods, such as plant extracts, microorganisms, or natural reducing agents, as alternatives to conventional chemical synthesis.

• IC2: Research focused on specific applications of magnetite NPs synthesized through green methods, particularly in environmental remediation and water treatment.

• IC3: Studies describing the physicochemical characteristics and performance of magnetite NPs synthesized from different biological sources.

• IC4: Research evaluating contaminant adsorption effectiveness, process efficiency, or the reduction of toxic byproducts.

2.2. Exclusion criteria (EC):

• EC1: Publications that were not original research articles, such as reviews, theses, books, and conference papers. Grey literature was also excluded.

• EC2: Studies published before 2020.

• EC3: Articles written in languages other than English.

• EC4: Research focusing on carbon-based nanomaterials, such as graphene oxide, biochar, activated carbon, and carbon nanotubes.

The search yielded 1,061 articles (Scopus: 699; WoS: 326; Scilit: 36). Exclusions by EC-–EC3 removed 480 articles. After removing 109 duplicates, 472 remained. Screening by title/abstract removed 305 more. EC4 eliminated another 85, and nine reviews were discarded under EC1. After full-text evaluation, 15 more articles were excluded, resulting in 58 studies analyzed in this review (see Figure 1).

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Figure 1.

PRISMA flow diagram for study selection. Flowchart summarizing the systematic review process based on the PRISMA methodology. The diagram outlines the identification, screening, eligibility, and inclusion stages, along with the number of studies excluded at each step based on predefined eligibility and exclusion criteria.

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3.1. Current status and research trends in the green synthesis of magnetite NPs

This systematic review analyzed 58 studies focused on the synthesis of magnetite NPs through green chemistry methods. Figure 2 illustrates the publication frequency between 2020 and 2024, showing a progressive increase in studies, peaking in 2023 with 17 publications. This rise may be attributed to the growing interest of researchers in the synthesis and application of sustainable methods to leverage the advantages of these NPs, particularly in environmental applications. In 2022, 15 publications were recorded, while in 2020 and 2021, the numbers were lower, with five and 10 articles, respectively.

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Figure 2.

Annual distribution of selected publications (2020-2024). Bar chart depicting the number of articles published each year in the systematic review. The data indicate a progressive increase in studies on the green synthesis of magnetite NPs, peaking in 2023 with 17 publications.

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However, in 2024, the number of studies declined, possibly due to a shift towards more advanced or interdisciplinary approaches, such as the integration of magnetite into biomaterials, multifunctional systems, or novel hybrid nanomaterials like magnetite hydrogel nanocomposites [16], which may have redirected research efforts towards new directions. Additionally, the economic feasibility of large-scale synthesis and the lack of specific regulations for its production and application may have limited the continuation of research [17].

Figure 3 illustrates the geographical distribution of the articles examined in this review, with India standing out as the leading contributor with 15 publications. Iran, Iraq, and Turkey follow with nine, five, and five studies, respectively. Egypt, Ethiopia, and Pakistan each contributed three studies, while the United States, Ukraine, and China had two publications each. Additionally, Algeria, Brazil, Ecuador, Mexico, and Indonesia, among others, contributed one publication each. This analysis highlights the strong predominance of Asian countries in research on this topic, possibly due to their emphasis on developing sustainable technologies and the availability of biological resources in the region.

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Figure 3.

Geographical distribution of selected publications. World map showing the number of studies per country, with a color gradient indicating publication density.

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On the other hand, Latin America has a remarkably low representation, with only three countries included (Brazil, Ecuador, and Mexico). This limited presence may result from factors such as insufficient infrastructure, limited research funding, and the absence of public policies that support the adoption of green technologies for environmental remediation. These findings underscore the need to strengthen research efforts in underrepresented countries to advance the development of sustainable solutions.

In this context, the adoption of green synthesis of magnetite NPs in high Andean regions emerges as a promising alternative due to the availability of diverse local biological resources and the need to develop cost-effective and environmentally sustainable technologies. However, external factors such as low temperatures, water pH, and the chemical composition of high Andean soils must be considered, as they may influence the removal efficiency of these NPs. Therefore, further studies are required to assess their performance under extreme climatic conditions.

In addition, the use of industrial waste in these regions could promote a circular economy approach to environmental remediation. García et al. [18], for example, conducted a study in Ecuador in which orange peel, a common regional waste, served as a precursor for the synthesis of magnetite NPs. The study demonstrated their antibacterial capacity, which reinforces the feasibility of employing local materials for the sustainable treatment of contaminated water.

Figure 4 presents the diversity of sources in which the included studies were published. Chemosphere has the highest number of publications (4 articles), followed by Nanomaterials with 3 articles. Other journals, such as the International Journal of Biological Macromolecules, Analytical Chemistry Letters, Biomass Conversion and Biorefinery, Journal of Environmental Management, Scientific Reports, and Journal of Nanomaterials, each published two articles. The remaining journals contributed one article each.

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Figure 4.

Distribution of publications by Journal. Bar chart illustrating the distribution of the reviewed articles across different scientific journals. Chemosphere is the journal with the highest number of publications, followed by Nanomaterials. Other journals, such as Scientific Reports, Journal of Environmental Management, and Biomass Conversion and Biorefinery, contributed two publications each. Most studies were published in journals that had only one article on the topic.

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This distribution reflects the interest of multiple scientific journals in this topic, particularly in areas such as nanotechnology, chemistry, materials science, and environmental management. The variety of publication sources underlines the interdisciplinary nature of the topic and its relevance across different fields of knowledge.

Similarly, the presence of articles in journals with different focuses suggests that this field encompasses both fundamental research, which focuses on material characterization and optimization, and applied studies, which evaluate their performance in environmental and technological processes. This diversity of approaches reflects the multidisciplinary nature of the topic and the need to continue exploring its applications in various scientific and industrial contexts.

To identify the main research trends in the green synthesis of magnetite NPs, a network of key terms was constructed based on the 58 selected articles, considering only words that appeared at least twice. The bibliometric network (Figure 5) was generated and visualized using VOSviewer software. The core term green synthesis confirms that this approach predominates in the selected studies for obtaining magnetite NPs. It is directly linked to Fe₃O₄ NP, iron oxide NP, and magnetite NP, which reflects a strong interest in their sustainable production. The relationship between adsorption, wastewater, and biopolymer indicates that pollutant adsorption in wastewater is one of the most extensively studied applications. Additionally, the presence of biomass suggests the use of biological sources for extract-based synthesis. The connections with terms such as nanocomposite, TiO₂, and chitosan demonstrate ongoing research into hybrid nanomaterials with enhanced properties. Moreover, the inclusion of kinetics and response surface methodology suggests a focus on evaluating kinetic parameters and optimizing adsorption efficiency. This analysis confirms that research in this field is primarily directed toward understanding adsorption mechanisms and applying magnetite NPs for wastewater treatment.

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Figure 5.

Bibliometric network of key terms related to the green synthesis of magnetite NPs. Visualization of key terms from 58 studies using VOSviewer, highlighting research trends in synthesis, adsorption, and material hybridization.

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3.2. Biological sources used in the green synthesis of magnetite NPs

The synthesis of magnetite NPs through green chemistry methods utilizes various biological sources. In this review, 84.48% of the investigations used plant extracts, demonstrating their predominance as raw materials for NP synthesis.

Table 2 presents the adsorption capacities of magnetite NPs synthesized from these extracts and their efficiency in removing heavy metals and organic compounds, such as dyes. All the reviewed studies employed the coprecipitation method under basic conditions at either ambient or high temperatures.

The analysis of the studies confirms that the biological source used in the synthesis significantly influences the physicochemical properties and removal capacity of the NPs. Das et al. [19] reported an adsorption capacity of 294.1 mg/g for methylene blue using magnetite NPs synthesized from Terminalia arjuna extract, while with Cordia myxa, the efficiency was significantly lower (17.79 mg/g) [20]. These differences may be partly attributed to the presence of specific functional groups in each extract, which enhance interactions with certain contaminants. Ahmouda et al. [21] demonstrated that the acidity of the plant extract affects the density of acid sites on the surface of magnetite NPs, influencing the adsorption of azo dyes. FTIR spectra revealed that the intensity and position of hydroxyl groups varied depending on the extract used, indicating that the natural functionalization of magnetite depends on the chemical composition of the plant material. Similarly, Yew et al. [22] synthesized magnetite NPs using an extract of Kappaphycus alvarezii seaweed and confirmed the adsorption of hydroxyl and carbonyl groups on their surface.

On the other hand, the functionalization of the NPs improves their adsorption capacity by reducing the agglomeration on their surface and introducing new active sites available for further interaction with the contaminants. Mousavi et al. [23] functionalized magnetite NPs with cyanuric acid, which introduced hydroxyl (-OH) and cyano (-CN) groups on their surface. These groups acted as binding sites for heavy metal adsorption, which increased removal efficiency. Likewise, Yadav et al. [24] demonstrated this effect in a chitosan-modified nanocomposite, where Cd(II) adsorption increased from 290 mg/g (Fe₃O₄) to 426 mg/g after functionalization. These findings highlight the importance of surface modification in optimizing NP performance for environmental remediation.

In the green synthesis of magnetite NPs, the most employed method involves the simultaneous precipitation of Fe(II) and Fe(III) ions in a basic medium. This approach demonstrates robustness and adaptability, regardless of the plant extract used. For Cd(II) adsorption, Bakhtiari et al. [25] reported an adsorption capacity of 19.63 mg/g for NPs synthesized with green tea extracts, while Kobylinska et al. [26] achieved 33.5 mg/g using Artemisia annua extracts. These differences can be attributed to the phytochemical composition of each extract, as well as to synthesis parameters such as pH, temperature, and the type of iron precursor, all of which directly influence the formation and stability of the NPs. In alkaline media, the complete precipitation of iron species favors the formation of larger and more stable nuclei and improves the crystallinity and adsorption capacity of NPs [31]. In addition, pH adjustment modifies the surface charges of magnetite, which promotes electrostatic stabilization, reduces agglomeration, and improves dispersion in aqueous solutions [32].

Synthesis temperature plays a key role in determining NP morphology and size. While temperatures above 90°C favor the formation of pure magnetite and may increase surface area [32], excessive temperature increases can cause NP sintering, resulting in growth rather than size reduction [33]. This phenomenon is due to particle coalescence and migration of surface species, which leads to a decrease in specific surface area and a potential reduction in adsorption efficiency.

Moreover, the choice of the ferric precursor influences the quality and structure of the final material. Soluble salts such as FeCl₃ or Fe(NO₃)₃ allow more uniform nucleation, which enables the formation of homogeneous NPs. In contrast, alternative sources such as iron-rich sludge or industrial waste introduce variations in NP morphology and size, which may impact their performance in environmental applications [34].

Natural plant extracts are the main source for green synthesis, as they contain secondary metabolites such as polyphenols, flavonoids, and other antioxidant compounds, which contribute to the reduction and stabilization of NPs during synthesis [27]. As shown in Figure 6, leaves are the most used part, probably due to their high content of these compounds. For example, Medina-Zazueta et al. [29] used Vitex negundo leaf extract, which contains alkaloids, saponins, and cardiac glycosides in its phytochemical profile. Additionally, leaves are abundant and often discarded, making them an accessible and sustainable feedstock for green synthesis [5].

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Figure 6.

Distribution of plant parts used for the green synthesis of magnetite NPs. Proportion of different plant parts employed as biological precursors in the reviewed studies. Leaves represent the most used material (48.98%), followed by other plant-derived components (18.37%). Peels and seeds each account for 6.12%, while fruits, flowers, and roots contribute smaller percentages.

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Ghoohestani et al. [20] proposed that the mechanism for green synthesis of magnetite NPs from natural extracts is an oxide-reduction reaction. Bioactive compounds reduce Fe(III) to Fe(II) while undergoing oxidation. These iron ions then react with hydroxyl groups present in the medium to form magnetite NPs. Throughout this process, bioactive compounds coat the NP surface, and this organic layer prevents agglomeration, enhancing colloidal stability [28]. NPs synthesized from plant extracts exhibit greater stability, form more rapidly, and generate a wider range of shapes and sizes compared to those derived from other biological sources [35].

In addition to leaves, other parts of the plant, such as aerial parts, tubers, flower buds, or even the whole plant, have also been used for extract preparation. Natural tree secretions, such as resins and latex, can also serve as raw materials. Das et al. [36] used crude latex of Jatropha curcas to synthesize magnetite NPs, which exhibited high efficiency in dye and heavy metal adsorption, as well as antibacterial activity in wastewater treatment.

The use of non-edible parts and agro-industrial wastes, such as peels, promotes their reuse and revaluation within the circular economy model. Lingamdinne et al. [37] used tangerine peel as a reducing agent in the synthesis of magnetite NPs and obtained a mesoporous nanocomposite (T-Fe₃O₄) with a hexagonal morphology and a size below 100 nm, which exhibited high efficiency in lead adsorption. These strategies contribute to waste reduction and could reduce large-scale production costs.

However, the use of plants as biological sources introduces challenges in reproducibility and consistency in NP properties due to variations in species, growing regions, and processing conditions. These differences can affect their performance, so it is essential to control the synthesis parameters to ensure their efficacy in practical applications.

Alternative sources for the green synthesis of magnetite NPs include bacteria, fungi, algae, and natural by-products. Detailed information on the size, morphology, and specific applications of these NPs has been provided in Table 3. These studies confirm the effectiveness of green-synthesized magnetite NPs in removing heavy metals such as Cr(VI) and As(V), as well as organic dyes like methylene blue and methyl orange. The high removal efficiencies reported underscore their potential for environmental remediation applications.

Bacteria and algae have proven to be effective sources for the synthesis of NPs due to their ability to produce bioactive compounds that stabilize and functionalize nanomaterials. Microbial exopolysaccharides have enabled the formation of NPs with cytotoxic activity and high heavy metal adsorption capacity [38]. Meanwhile, marine algae contain pigments, enzymes, and other metabolites that facilitate the reduction of metal ions and enhance the colloidal stability of NPs. Their capacity to accumulate heavy metals and their rapid growth make them a sustainable source for developing nanomaterials applicable to contaminant removal and water purification [39].

Natural by-products such as red mud and pumice have been employed as precursors and offer a sustainable alternative to produce NPs without synthetic chemical reagents. Red mud, an iron-rich waste, has proven to be an effective precursor in synthesizing magnetite NPs with high drug adsorption rates, suggesting its potential for remediating waters contaminated with emerging compounds [34,40]. Similarly, Taqui et al. [41] synthesized magnetite NPs from scrap iron and pomegranate peel extract, achieving 98% removal of Pb(II), which reinforces the potential of using waste materials as sustainable precursors.

Furthermore, Ecer et al. [42] synthesized and characterized magnetite NPs functionalized with sporopollenin (Fe₃O₄@SP) and coated with polydopamine (PDA), on which silver NPs (Ag NPs) were deposited to modify the surface. Sporopollenin (a biopolymer), which is present in the walls of spores and pollen grains and used in the green synthesis, improved the stability and catalytic activity of the magnetite NPs. The results demonstrated an efficient degradation of rhodamine B in the presence of NaBH₄; thereby, these NPs could be applied in the treatment of contaminated water and the remediation of persistent organic compounds.

Figure 7 illustrates the green synthesis process of magnetite NPs from various biological sources, highlighting the key stages from extract preparation to NP formation and their application in contaminant removal. This schematic reinforces the synthesis strategies described in this section.

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Figure 7.

Green synthesis of magnetite NPs for environmental remediation. This schematic illustrates the green synthesis of Fe₃O₄ NPs using plant extracts, bacteria, fungi, and algae as reducing agents. Bioactive compounds facilitate NP formation, enabling efficient removal of heavy metals, organic dyes, and emerging contaminants from water. The magnetic properties of Fe₃O₄ NPs allow easy recovery with an external magnet, making them a sustainable solution for water treatment.

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3.3. Characterization of magnetite NPs synthesized by green methods

Characterization techniques allow the analysis of the physicochemical properties of biosynthesized magnetite NPs. Factors such as morphology, size, surface area, porosity, colloidal stability, and crystallinity directly influence their adsorption functionality [48]. Table 4 shows the main techniques used in characterization such as UV-Vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray energy dispersive spectroscopy (EDX), dynamic light scattering (DLS), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and vibrating sample magnetometry (VSM). These techniques provide essential information on the synthesized NPs’ structure, chemical composition, thermal stability, magnetic behavior, and surface properties. The reviewed literature reveals a variety of morphologies, with a predominance of spherical shapes and variations in NP size depending on the type of plant extract used.

The physicochemical properties of synthesized NPs, largely influenced by the biological sources used, play a central role in determining their stability and efficiency in contaminant removal [49]. The shape and size of metal oxide NPs have a greater impact on their adsorption sensitivity than their chemical composition [50]. SEM allowed for the characterization of NP morphology and aggregation. Lagashetty et al. [51] identified spherical particles with compact aggregates using an extract from Ficus benghalensis leaves, which may explain their lower efficiency in removing Pb(II) and Hg(II) compared to other NPs evaluated in their study. On the other hand, TEM analysis revealed that Fe₃O₄ NPs synthesized with Moringa oleifera extract ranged in size from 4 to 18 nm for Fe₃O₄ and 4-15 nm for Fe₃O₄/TiO₂. These results suggest that smaller, more uniform particles increase surface area, which could enhance catalytic activity in methylene blue removal [52].

However, López and Antuch [7] indicate that the morphology of NPs obtained through green synthesis is not entirely controllable, as the chemical composition of the plant extract directly influences particle shape. In contrast, Sun and Zeng [64] successfully synthesized monodispersed NPs with sizes between 3 and 20 nm through an organic-phase chemical method with iron acetylacetonate. This approach resulted in a homogeneous distribution without additional selection. They also adjusted the size of NPs in a controlled manner, which highlights the importance of optimizing synthesis conditions to enhance stability and performance in environmental applications.

As for the chemical composition, FTIR spectroscopy confirmed the presence of functional groups in magnetite NPs synthesized with calendula extract [54]. Fe-O bonds (570 cm^-1) were identified, confirming the formation of iron oxides, along with adsorption bands between 3400 and 3600 cm⁻¹, associated with hydroxyl groups from polyphenolic compounds in the extract. These hydroxyl groups could generate free radicals under UV radiation, which promotes the degradation of dyes such as methylene blue and rhodamine B [52,61]. UV-Vis spectroscopy was also employed in several studies to evaluate the optical properties and confirm the synthesis of magnetite NPs. Characteristic absorption bands were observed in the range of 300-400 nm, which is attributed to Fe–O charge transfer transitions [51,65,66]. Shifts in wavelength values, such as from 390 nm for Fe₃O₄ to 396 nm for Fe₃O₄/chitosan (CS) nanocomposites, indicated changes in the electronic environment due to surface modifications [67]. Additionally, reported bandgap energy values calculated via Tauc plots ranging from 1.81 to 3.74 eV reflect the influence of synthesis conditions and bioactive compounds on the NPs’ optical behavior [67-70]. These parameters are particularly relevant for the evaluation of the photocatalytic potential of the synthesized materials.

By applying BET, Mohammadpour et al. [57] determined a specific surface area of 206.75 m²/g and pore size of 6.1 nm for magnetite NPs synthesized from Prosopis farcta extract, while Chakraborty et al. [58] reported a value lower than 142.19 m²/g for NPs obtained with Delonix regia extract. Despite this difference, the NPs obtained with Delonix regia exhibited greater efficiency in methylene blue degradation, suggesting that, in addition to the specific surface, other factors such as the chemical composition of the extract and the presence of functional groups on the NP surface could influence their ability to adsorb and degrade contaminants.

The characterization of magnetic properties by VSM revealed that NPs synthesized with Boerhavia procumbens extract exhibited a saturation magnetization (Ms) of 55.3 emu/g, which suggests a magnetic response suitable for potential applications in contaminant separation from water under a magnetic field [56]. However, through an experimental design based on the Taguchi method, Azadi et al. [31] determined that the magnetic properties of magnetite NPs are not significantly influenced by the concentration of the plant extract used in the synthesis. Instead, factors such as the concentration of iron salts, pH, and process temperature have a more significant impact.

The colloidal stability and surface charge of NPs in aqueous solutions are evaluated through zeta potential analysis [71]. Rhus coriaria leaf extract was used to synthesize magnetite NPs, which exhibited a negative surface charge of -26.1 mV at pH 7, compared to -9.2 mV at pH 7 in chemically synthesized NPs [55]. The higher negative charge would enhance electrostatic repulsion, reduce agglomeration, and promote dispersion stability, optimizing performance in contaminant adsorption.

Klekotka et al. [72] demonstrated that magnetite NPs have high structural and magnetic stability in different aqueous media. This property supports their use in long-term environmental applications. However, this stability could lead to their accumulation in the environment, a concern that stresses the need to assess their ecological impacts. Since these studies were conducted with chemically obtained magnetite, further research is required to determine whether green-synthesized magnetite exhibits similar persistence.

3.4. Efficiency of contaminant removal using magnetite NPs

In addition to the biological source, factors such as pH, contact time, contaminant concentration, and magnetite NP dose directly affect removal efficiency. Table 5 presents studies on contaminant removal using magnetite NPs synthesized from different plant extracts. Most research has focused on the elimination of heavy metals such as Pb(II), Cd(II), Hg(II), and Cr(VI), as well as the adsorption of organic dyes, with reported efficiencies of up to 99% for compounds such as methylene blue and o-toluidine [66,67]. These results demonstrate the versatility of magnetite NPs in environmental decontamination applications.

The adsorption process on nanomaterials occurs in four stages: (1) external diffusion, (2) initial internal diffusion, (3) intraparticular diffusion, and (4) molecular attachment to active sites of the adsorbent [67]. As adsorption depends on these factors, their optimization is essential for enhancing removal efficiency.

The pH of the medium is a critical factor as it affects the surface charge of magnetite NPs and the solubility of contaminants. Studies indicate that Cr(VI) achieves maximum removal at pH 5 due to enhanced interactions with the NP surface, while a near-neutral pH favors Hg(II) adsorption [73]. Therefore, it appears safe to state that pH adjustment optimizes the interaction between magnetite NPs and metal ions.

Contact time and contaminant concentration are key factors in determining adsorption efficiency. For Hg(II), magnetite NPs synthesized using Aloe vera leaves and wheat straw achieved maximum removal within 45 min, with no significant improvements at longer durations due to the saturation of the adsorbent’s active sites [50]. Similarly, an increase in contaminant concentration from 20 to 100 mg/L reduced removal efficiency as the number of available surface sites on magnetite NPs became limited [78].

NP dosage is another critical factor, as it determines the amount of available adsorbent. However, excessive doses may cause agglomeration, reducing the effective adsorption surface. For tartrazine removal, optimal doses of magnetite NPs ranged between 300 and 800 mg/L [75], whereas for methylene blue, the most effective doses were below 5 mg/L [66,67]. These differences can be attributed to variations in the molecular structure and chemical properties of organic pollutants.

The removal of contaminants with green-synthesized magnetite NPs occurs through physicochemical interactions or catalytic processes. These mechanisms vary depending on the type of pollutant involved.

For organic pollutants such as heavy metals, the predominant mechanism is electrostatic adsorption, driven by the negatively charged surface of the NPs. This process is further enhanced by chemical interactions with functional groups such as hydroxyl (-OH) and carboxyl (-COOH), which form bonds with metal ions and facilitate their removal [73].

In contrast, photocatalysis serves as a key mechanism for the degradation of organic pollutants like dyes. In this process, magnetite acts as a semiconductor, facilitating electron transfer when exposed to sunlight or UV radiation. This reaction induces the formation of hydroxyl and superoxide radicals from water and oxygen, which then break the aromatic bonds of dyes, converting them into CO₂ and H₂O [77].

3.5. Multifunctional applications of magnetite NPs

Green-synthesized magnetite NPs have additional applications (Table 6). Studies have demonstrated that these NPs exhibit antimicrobial [79-81] and antifungal activity [68,82]. This effect is attributed to the generation of reactive oxygen species (ROS) on the NP surface, a mechanism that induces cell damage and microbial death [18]. Additionally, Abduljabar et al. [83] synthesized functionalized nanocompounds from Hypericum sabrum, which exhibited a scolicidal effect against Echinococcus granulosus cysts. Such an effect may be linked to the high surface-to-volume ratio and small size of the NPs, facilitating their penetration into the parasite. Due to these properties, magnetite NPs present a promising approach for water and surface disinfection, as well as for agricultural applications, such as crop protection in tomato cultivation [82].

Some studies have explored the application of green-synthesized magnetite NPs in cancer treatment through magnetic hyperthermia [84,85]. This technique induces thermal stress in tumor cells, leading to their destruction while minimizing damage to healthy tissues. Furthermore, the incorporation of natural extracts in the synthesis process enhances the biocompatibility and stability of the NPs [85]. Although this approach shows promise for less toxic anticancer therapies, further research is needed to optimize its efficacy and achieve clinical validation.

Magnetite NPs have proven effective in removing antibiotics from wastewater. For instance, NPs synthesized with Monsonia burkeana and Cucumis sativus extracts achieved removal rates of 60% for sulfisoxazole [68] and 94% for moxifloxacin [76], respectively. Moreover, a recent study has explored their potential for nanoplastic removal. Matar et al. [86] synthesized magnetite NPs functionalized with pine resin extract and achieved removal efficiencies between 95.45% and 99.13% for polystyrene nanoplastics (PSNPs) in aqueous solutions. These findings emphasize the versatility of green-synthesized magnetite NPs in the elimination of chemical pollutants, microbiological contaminants, and emerging pollutants, while expanding their potential applications in wastewater treatment systems.

Field tests have confirmed the effectiveness of magnetite NPs for treating contaminated water. Samejo et al. [90] evaluated magnetite NPs synthesized with Duranta erecta extract in drinking water collected from municipal fountains and hand pumps in the districts of Hyderabad and Jamshoro, Pakistan. The NPs achieved an adsorption efficiency above 93% for Cd(II), Cr(VI), and Pb(II), which underscores the importance of evaluating these nanomaterials under real environmental conditions to determine their suitability for large-scale applications.

3.6. Scaling up magnetite NPs

This section presents key findings on the scaling of magnetite NPs. Among the 58 studies that were analyzed in this systematic review, 25 included regeneration tests to assess NP durability in repeated applications through adsorption-desorption cycles. Figure 8 describes the frequency of studies based on the most common number of regeneration cycles, indicating that most report up to five cycles without a significant loss in efficiency. This level of reusability suggests adequate durability for various environmental remediation applications. However, for industrial-scale applications, improving long-term stability remains essential. Strategies such as biopolymer functionalization or the use of natural coatings may improve the resistance and performance of magnetite NPs over multiple reuse cycles [24].

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Figure 8.

Regeneration cycles of green-synthesized magnetite NPs. Frequency of studies based on the number of regeneration cycles reported in the reviewed literature. Most studies indicate that magnetite NPs maintain their adsorption efficiency for up to five cycles.

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Regarding economic viability, only two studies in this review examined production costs. Das et al. [19] estimated a cost of 19.48 USD/kg using Terminalia arjuna extract, while Roy et al. [62] calculated an approximate cost of 102.12 USD/kg for a ZnO@Fe₃O₄ nanocomposite encapsulated in an alginate-chitosan matrix. These cost differences highlight the substantial influence of raw materials and synthesis conditions on final production expenses. Large-scale manufacturing remains a challenge due to the limited number of studies addressing economic feasibility. Comprehensive techno-economic analyses that consider reagent costs, material inputs, and production scales are essential for evaluating the feasibility of industrial and environmental applications.

In terms of yield, Roy et al. [62] reported that approximately 5.35% of the total materials were converted into 250 g (wet weight) of a nanocomposite synthesized with Camellia sinensis extract. Similarly, García et al. [18] produced magnetite NPs from orange peel residues using 50% v/v ammonium hydroxide, which led to the production of 88 mg of synthesized material. However, the limited number of studies on yield and productivity restricts the extrapolation of laboratory-scale results to industrial applications.

Ecological adsorbents, such as green-synthesized magnetite NPs, represent a viable option for contaminant removal in Latin America. Liu et al. [2] emphasize that the use of waste materials and natural sources in the synthesis of green adsorbents reduces costs and minimizes environmental impact, which are particularly relevant in regions with infrastructure constraints. Additionally, factors such as raw material availability and the regeneration capacity of these adsorbents determine their feasibility for large-scale applications.

The use of green-synthesized magnetite NPs supports multiple Sustainable Development Goals (SDGs). Their application in water remediation aligns with SDG 6 (Clean water and sanitation) as it enhances water quality through the removal of heavy metals and emerging pollutants. The sustainable production of these NPs, based on agro-industrial residues and plant extracts, contributes to SDG 12 (Responsible consumption and production) by reducing dependence on harmful chemical reagents. Their potential biomedical applications advance SDG 3 (good health and well-being), offering non-toxic alternatives for medical treatments. Lastly, their development promotes SDG 9 (Industry, innovation, and infrastructure) and enables environmentally friendly technological advancements.

3.7. Future perspectives

Despite progress in the green synthesis of magnetite NPs, several challenges remain before large-scale implementation becomes viable. One critical issue is the variability of plant extract composition, which directly affects NP properties and synthesis reproducibility. To address this limitation, future research should prioritize the development of standardized protocols that use pre-characterized extracts and ensure consistent phytochemical composition and reaction conditions.

The adoption of high-volume continuous flow reactors also offers an opportunity to improve production scalability by ensuring consistent synthesis parameters. Although preliminary results from column experiments, such as the removal of cadmium and moxifloxacin in continuous flow systems [76], demonstrate potential, additional pilot-scale studies conducted under real environmental conditions are necessary to validate long-term performance and stability.

Given the persistent deficiencies in wastewater treatment in Latin America, where a significant proportion of wastewater is discharged untreated due to economic and technological limitations [91], the development of green-synthesized magnetite NPs may provide a viable solution. Their application has the potential to enhance water quality and support sustainability goals. However, effective implementation requires compatibility with existing treatment systems and may depend upon incorporating complementary technologies such as membranes or hybrid configurations.

Pilot-scale testing under actual operating conditions remains essential for evaluating long-term efficiency, economic feasibility, and environmental safety, thereby facilitating successful integration into regional water management strategies. Despite this potential, few studies have analyzed production costs, and even fewer have explored the ecological implications of long-term NP accumulation. Future efforts must include detailed techno-economic assessments and ecotoxicological evaluations to establish safe and sustainable operational frameworks.

Finally, incorporating advanced computational tools such as density functional theory (DFT) and machine learning can accelerate the rational design of nanomaterials by providing predictive insight into synthesis-property-function relationships. These strategies would enable a shift from empirical methods to more precise and scalable production models, strengthening the role of green nanotechnology in sustainable environmental remediation.