# Recent Developments on Magnetically Separable Ferrite-Based Nanomaterials for Removal of Environmental Pollutants

Authors: Shreyas Pansambal; Arpita Roy; Hamza Elsayed Ahmed Mohamed; Rajeshwari Oza; Canh Minh Vu; Abdolrazagh Marzban; Ankush Chauhan; Suresh Ghotekar; H. C. Ananda Murthy
Journal: Journal of Nanomaterials
 (2022)

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## Abstract

The current water supply situation demonstrates the predominance of contamination caused by industrial effluent runoff. Polluted waters have contributed to significant health and environmental risks, calling for an acceptable alternative to address the effects. However, diverse chemical and treatment physical stages commonly used for dye effluent processing are more cost-intensive, less effective, and time-consuming. Instead, nanomaterials have developed as a good alternative for dye removal and degradation because of their special chemical reactivity and superior surface features/properties. In this regard, the ability of modified or hybrid ferrite-based magnetically recoverable nanomaterials in dye effluent treatment has been extensively explored. The present study especially emphasizes magnetic ferrite (Fe3O4 + X) or metal-doped ferrite (MFe2O4 + X) nanocomposite for dye degradation (where M consists of Co, Cu, Zn, Mg, Mn, Ni, etc., and X consists of reduced graphene oxide, graphene oxide, metal, or metal oxide). Several dye degradation efficiencies of various ferrite and metal ferrite nanomaterial were discussed. Degradation is carried out using direct sunlight, and various lamps (e.g., visible light/UV-C lamp/halogen lamp/Mercury-Xenon lamp/UV lamp with UV filter for visible light) are used as a source. This review article covers the degradation of various dyes from wastewater using ferrite-based nanomaterial as an efficient catalyst and making water pollution free.


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## 1. Introduction

The first commercially effective synthetic dye was explored in 1856, and till now, numerous dyes have been synthesized [1]. The reseals of synthetic dyes in natural water sources increase pollution, causing severe harm to humans [2]. According to Jin et al., textiles discharged 280,000 tons of industrial effluents worldwide [3]. The effluent encompasses a wide range of pollutants, including organic and inorganic salts, surfactants, heavy metals, enzymes, oxidizing, and reducing agents [2, 4]. The human being swallows such contaminated water persuades respiratory tract, gastrointestinal tract irritation, and skin and eye irritation. Furthermore, the reports also prove the developmental, chronical, and neurotoxicity effects of dyes on human beings [5]. A huge volume of freshwater is essential to carry out the daily process in the textile industry. Scrutiny of the literature reveals that for the treatment of 1 kg of textile materials, about 100 L of water is essential [2]. Therefore, to avoid such environmental degradation due to synthetic dyes, the degradation of dyes is essential.Diverse techniques are used for the effluent treatment [6–8], which are listed in Figure 1. Traditional techniques for the dye degradation used are adsorption utilizing activated carbon, reverse osmosis, ion exchange employing resins, etc. However, the technique mentioned earlier can only transform the phase creating secondary pollution, which needs additional treatment to regenerate the adsorbent [9]. Traditional technologies for the treatment of west water were unsuccessful by Forgacs et al. [10]. Furthermore, the report also states that these techniques are insufficient to degrade/treat certain azo dyes selected for the study. Recently, the advanced oxidation process (AOPs) has been used mostly to treat polluted water. Reactive oxygen species (ROS) produced using AOPs quickly oxidize dyes in the industrial effluent and make the water pollution free [11].Figure 1
Classification of methods of effluent treatments.Magnetic nanomaterials are of massive enthusiasm for scientists from a vast variety of domains, including catalysis [12–14], magnetic fluids [15], biomedicine [16], data storage [17], magnetic resonance imaging [18, 19], biosensors [20], and environmental remediation [21–25]. While several effective approaches for the fabrication of selective magnetic nanomaterials of diverse compositions have been developed, the efficient uses of certain magnetic nanomaterials in the fields mentioned above are strongly reliant on the stability of the nanomaterials under a variety of situations. The nanomaterial works perfectly in most planned applications when the size of the nanomaterials is around a particular value, which relies on the nanomaterial. Then, when the temperature is beyond the so-called blocking temperature, each nanomaterial becomes a unified magnetic field and exhibits superparamagnetic conduct. These nanomaterials have a broad stable magnetic moment and operate as a large paramagnetic atom with a quick reaction with negligible coercivity and remanence to applied magnetic fields. These features render superparamagnetic nanomaterials very appealing for such a large scope of bioengineering uses since the possibility of agglomerations at room temperature is negligible [26].Various strategies have been created, including adsorption, biological, electrochemical, ion exchange, membrane processes, and solvent extraction techniques. These methods have a variety of disadvantages, including as high operating costs, pollution transfer from one phase to another, and the challenge of eliminating biologically or chemically persistent contaminants. Advanced oxidation processes (AOPs) are the most effective way to remove pollutants from water because they can produce powerful oxidizing agents at ambient temperature and normal atmospheric pressure [27–30]. Heterogeneous photocatalysis has proven to be a more successful method for addressing energy and environmental concerns as an oxidation mechanism. Heterogeneous photocatalysts can remove persistent nonbiodegradable organic pollutants by supplying strong oxidizing agents and converting them into mineral salts, H2O, and CO2. Intriguing materials for CO2 photoreduction, microbial disinfection, N2 photofixation, and organic compound synthesis are also heterogeneous photocatalysts. An ideal heterogeneous photocatalyst will have a high quantum efficiency, be physiologically and chemically inert, have a considerable capacity to absorb solar energy, be nontoxic, be resistant to photocorrosion, and be inexpensive. Despite heterogeneous photocatalysts’ potential for addressing energy and environmental problems, removing and recycling these parts from the reaction solution is difficult. Centrifugation and filtration techniques are used to separate used photocatalysts from systems that have been treated. Meanwhile, these methods are time- and money-consuming, restricting the widespread application of heterogeneous photocatalysts [31–33]. The fixation of heterogeneous photocatalysts has addressed this issue with an inert substrate. Despite the fact that this method lessens particle aggregation and makes it simpler to separate heterogeneous photocatalysts, photocatalytic performance is anticipated to suffer as a result of the decreased photocatalyst active sites. In order to separate and recover heterogeneous photocatalysts on a large scale, this problem is solved by combining photocatalysts with magnetic materials. Magnetic materials are more desirable in photocatalytic applications because they may show considerable photocatalytic activity and separability [34, 35].Thus, this perspective review article intends to present reports on photocatalytic degradation of various dyes using ferrite-based nanocomposites.


## 2. Hazards of Dyes to Environment and Human Health

In addition to having adverse effects, the dye materials are often aesthetically undesirable in water. Several structure varieties are used in the textile industry, such as basic, acidic, disperse, reactive, azo, anthraquinone-based, diazo, and metal complex dyes [36]. Having more or less destructive consequences, it puts up. Increased heart rate, shock, vomiting, cyanosis, Heinz body formation, quadriplegia, human tissue necrosis, and jaundice are associated with extreme exposure to dyes [37]. Dyes such as metanil yellow seem to have a tumor-producing effect [38] and can generate human body enzyme disorders [39]. However, it is nonmutagenic, but it can change gene expression sequences [40]. It produces harmful methaemoglobinaemia [41] and cyanosis [42] in humans when taken orally, while skin interaction leads to allergic dermatitis [43]. Testicular lesions are caused by intratesticular and intraperitoneal administration or oral feeding of dyes in animals due to damage to seminiferous tubules and reduced spermatogenesis level [44, 45].


## 3. Magnetic Behavior of Ferrite-Based Magnetized Nanomaterials

The properties of magnetic nanomaterials are determined by the extrinsic magnetic field induced to materials. Descriptions of magnetic polarity in a nanomaterial help classify various types of magnetism found in nature. It is possible to define 5 main types of magnetism: antiferromagnetism, diamagnetism, ferrimagnetism, ferromagnetism, and paramagnetism [46]. Diamagnetism is a primary property of all atoms, and magnetization is quite low and opposite to the direction of the induced magnetic field. Lots of nanomaterials show paramagnetism property, whereas the orbit is raised from zero, a magnetization grows parallel to the induced magnetic field, but the magnetization efficiency is weak. Also, ferromagnetism is the property of such objects that are naturally magnetically arranged and which, even without using a field, develop spontaneous magnetization. Ferrimagnetism, where distinct atoms have various moment abilities, is different from ferromagnetism, but there is always an organized state under a specific critical temperature at that state. The magnetic substance, i.e., diamagnet, paramagnet, and ferromagnet, can be sorted according to its susceptibility. Many of the unique magnetic characteristics of nanomaterials are due to their strong surface-to-volume ratio [47, 48]. Saturation magnetism (Ms) changes through size before it reaches a threshold size above which magnetization is stable and near the bulk’s value. In diverse disciplines, the linear dependency of Ms on size underneath this threshold was seen. Research on the shape effect affects magnetic nanocomposites’ volume or associated size parameter properties. For spherical nanoparticles, the anisotropy value (magnetic anisotropy is the directional dependence of a material’s magnetic properties) is greater than for cubic nanoparticles of a similar volume [49–52]. Composition is perhaps the most widely cited factor accountable for assessing a material’s particular magnetic properties. These magnetic properties occur in the absence or presence of unpaired valence electrons deposited on metal ions or metal atoms present in magnetic nanomaterials [53, 54]. Magnetic behaviour is characterized by the direction of the magnetic moment (μ) connected with the electrons. We can measure the magnetic moment in magnetic nanomaterial [45, 55, 56] using the magnetic moment of only one electron, 1.73 Bohr magnetons (BM).


## 4. Diverse Approaches for the Fabrication of Magnetically Ferrite-Based Nanomaterials

There are multifarious approaches employed for the practical synthesis of using ferrite-based nanocomposite [57, 58], for instance, hydrothermal, sol-gel, sonochemical, solvothermal, precipitation, coprecipitation, solution combustion, probe sonication method, green synthesis, ultrasonication, and microwave-assisted methods [59–63]. Particle size distribution, crystal structure, particle size and shape control, and alignment are the crucial factors in the manufacturing of ferrite-based nanocomposite. Such approaches help produce magnetic ferrite-based composites, which are selectively stable at normal room temperature, regular shape, uniform size, nonaggregate, high monodispersity, etc. These methods are further categorised into three different approaches, physical, chemical, and biological, as shown in Figure 2.Figure 2
Diverse approaches for the efficient fabrication of ferrite-based nanomaterial.The aforementioned synthetic approaches require comparatively higher experimental duration and high pressure and energy and involve noxious compounds or solvents, and stability depends on capping agents. However, nanomaterial synthesized via these methods shows higher photocatalytic degradation efficiency.


## 5. General Procedure for the Dye Degradation

Magnetic metal Fe2O4/doped metal Fe2O4 composite is taken as a catalyst for the dye degradation of different dye (Figure 3) solution (any one among the following: MB, MO, MG, CV, CR, EY, RR 198, RR120, IC, DY, RB. etc.); dye under magnetic stirring/ultrasound irradiation/microwave irradiation with or without the addition of H2O2 in the presence of visible light/UV-C lamp/halogen lamp/Mercury-Xenon lamp/UV lamp with UV filter for visible light is used as the source (Table 1). At the start of the reaction, the catalyst is added to the dye solution and stirred the solution in the absence of light for 30 mins to attain the absorption equilibrium. Then, after 30 mins, the dye solution is exposed to the source. Then, the absorbances are measured, and from the reading, calculate the efficiency of the catalyst and the time required for the dye degradation. Figure 4 represents the graphical representation of the dye degradation using magnetic ferrite NPs.Figure 3
Various dye and their chemical structure.Table 1
Various dye degradation using ferrite and metal-doped ferrite nanoparticles with some additives.
Name of the catalystSynthetic methodSize (nm)ShapeLight sourceDegradation %Time (min)AdditiveDye degradedRef.CoFe2O4@ZnSHydrothermal18SpheresUltrasonic bath power of 100 W and frequency of 37 kHz10070H2O2Methylene blue dye[59]CuS/CoFe2O4Hydrothermal17SpherelikeUltrasonic bath power of 100 W and frequency of 37 kHz10030H2O2Methylene blue dye[60]CuS/CoFe2O4Hydrothermal17SpherelikeUltrasonic bath power of 100 W and frequency of 37 kHz7230H2O2Rhodamine B (RhB)[60]CoFe2O4 (MST-2)Solvothermal15SphericalVisible light80140H2O2Methylene blue dye[61]Ag3PO4-CoFe2O4Precipitation<30SphericalTungsten halogen lamp with 500 W10060—Methyl orange (MO)[62]Ag3PO4-CoFe2O4Precipitation<30SphericalTungsten halogen lamp with 500 W10060—Rhodamine B (RhB)[62]Co0.25Zn0.75Fe2O4@SiO2/ZnOCoprecipitation10.6SphericalUV irradiation100120—Red amaranth dye[63]Cu Fe2O4/RGOSolution combustion synthesis—Plate likeTwo100 W Xenon lamps with an UV cut-off filter (λ=420 nm)92180—Methylene blue (MB)[64]Cu Fe2O4@GO————93.330PMSMethylene blue (MB)[65]Cu Fe2O4/GOHydrothermal30-40—Visible light by 450 W Xe arc lamp——H2O2Rhodamine B (RhB)Acid orange II (AO7)[66]Cu Fe2O4Coprecipitation25.4——91.360H2O2Reactive red 2 (RR)[67]Cu Fe2O4–Fe2O3Pechini method——Solar radiation100180H2O2Methylene blue (MB)[68]Fe3O4-C-cuGreen synthesis25Spherical—100<1NaBH4Methyl orange (MO)[69]Fe3O4-C-cuGreen synthesis25Spherical—1003.20NaBH44-Nitrophenol[69]Fe3O4-C-cuGreen synthesis25Spherical—1002.40NaBH42,4-Dinitrophenylhydrazine[69]Ag-Fe3O4/graphene——SphericalTwo 40 W UV-C lamps94.78120H2O2Methyl orange (MO)[70]Ag-Fe3O4/graphene——SphericalTwo 40 W UV-C lamps99120H2O2Methylene blue (MB)[70]Ag-Fe3O4/graphene——SphericalTwo 40 W UV-C lamps81120H2O2Crystal violet (CV)[70]Ag-Fe3O4/graphene——SphericalTwo 40 W UV-C lamps89120H2O2Malachite green (MG)[70]Ag-Fe3O4/graphene——SphericalTwo 40 W UV-C lamps75120H2O2Congo red (CR)[70]Ag-Fe3O4/graphene——SphericalTwo 40 W UV-C lamps70120H2O2Eosin Y (EY)[70]S- Fe3O4Hydrothermal10-20Spherical—10030H2O2Rhodamine B (RhB)[71](RGO)/Fe3O4Green synthesis18Spherical—95.1812NaBH4Methylene blue dye[72]Ag3PO4@MgFe2O4Sol-gel15-20Irregular300 W Xenon short arc lamps9830H2O2Rhodamine B (RhB)[73]MgFe2O4Solid-state reaction12.31SphericalSunlight100<1H2O2Malachite green (MG)[74]MgFe2O4Autocombustion7-16Irregular————Methylene blue (MB)[75]MgFe2O4/TiO2Sol-gel20-30—500 W Xenon lamp———Rhodamine B (RhB)[76]Ni0.2CuxMn0.2Fe2O4Probe sonication19IrregularUV light98.1120—Methylene blue (MB)[77]Ni0.2CuxMn0.2Fe2O4Probe sonication23IrregularUV light43.3120—Drimarene yellow (DY)[77]MnFe2O4———UV–C lamp (200–280 nm, 9 W, Philips)>9090H2O2Reactive red 120 (RR120)[78]MnFe2O4———UV–C lamp (200–280 nm, 9 W, Philips)>9090H2O2Reactive red 198 (RR198)[78]MnFe2O4/TA/ZnOHydrothermal—SphericalVisible light84.290—Congo red (CR)[79]MnFe2O4/rGOCoprecipitation—SphericalUV irradiation9760—Methylene blue (MB)[80]MnFe2O4Solvothermal90-100SphericalSunlight98180H2O2Methyl orange (MO)[81]NiFe2O4Chemical precipitation——Microwave irradiation972—Brilliant green (BG)[82]NiFe2O4/T/GOxSolvothermal—ClusterUV98.690—Indigo carmine (IC)[83]NiFe2O4@TiO2Sol-gel18.85SphericalUV lamp 300 W Xenon lamp90.0690—Methyl orange (MO)[84]BCN/NiFe2O4Sol-gel100Sheet-likeMercury-Xenon lamp (350 W)9880—Methylene blue (MB)[85]NiFe2O4Sonochemical9-17Cube-likeUV light 400 W hg lamp89.4<80—Methylene blue (MB)[86]NiFe2O4Sonochemical9-17Cube-likeUV light 400 W hg lamp43120—Drimarene yellow (DY)[86]ZnO/CF/NGHydrothermal——10 W LED lamp98140—Malachite green (MG)[87]ZnO/ZF/NGHydrothermal——10 W LED lamp92140—Malachite green (MG)[87]ZnO/CF/NGHydrothermal——10 W LED lamp99140—Methyl orange (MO)[87]ZnO/ZF/NGHydrothermal——10 W LED lamp94140—Methyl orange (MO)[87]ZnFe2O4———UV-C lamp 200–280 nm 9 W——H2O2Reactive red 198 (RR198)Reactive red 120 (RR120)[88]ZnFe2O4@ZnOMicrowave17—Visible light 125 W hg lamp100540—Methyl orange (MO)[89]MIL-101(Cr)/RGO/ZnFe2O4Hydrothermal24SpherelikeUltrasonic frequency of 37 kHz9550H2O2Methylene blue (MB)[90]MIL-101(Cr)/RGO/ZnFe2O4Hydrothermal24SpherelikeUltrasonic frequency of 37 kHz1002H2O2Congo red (CR)[90]MIL-101(Cr)/RGO/ZnFe2O4Hydrothermal24SpherelikeUltrasonic frequency of 37 kHz9450H2O2Rhodamine B (RhB)[90]ZnFe2O4Combustion reaction—Spherical————Rhodamine B (RhB)[91]Ni0.4Zn0.6Fe1.8Al0.1Gd0.1O4Sol-gel———96180—Reactive blue (RB-21)[92]MnCe0.3Fe1.7O4Microwave combustion22-26Sphere-shapedVisible light (Xenon lamp 300 W;λ>400 nm)91.53120—Methylene blue (MB)[93]CuO/HAP/ferritePrecipitation<25—Visible irradiation>9060—Rhodamine B (RhB)[94]CoFe2O4/SnO2Sol-gel13SpherelikeHg lamp at 365 nm a UV-A lamp (15 W)<55120—Indigo carmine (IC)[95]MnFe2O4/B. claSolid-state8-38Spherical50 W tungsten halogenated lamp71.68H2O2Methylene blue (MB)[96]Co0.4Mg0.4Cu0.2Fe1.9Cr0.1O4Sol-gel20-60Spherical—84150—Congo red (CR)[97]CoFe2O4-SiO2-TiO2Coprecipitation—Spherical—93.46160—Methyl orange (MO)[98]Ca0.2Cu0.8Fe2O4Coprecipitation19-32Cubical and irregular—96180Fenton’s agentMethylene blue (MB)[99]Mn0.6Zn0.4Fe2O4Coprecipitation3-47Spherical—9815H2O2Synozol blue CA[100]NiFe2O4Solid state40-50—Visible light9535H2O2Malachite green (MG)[101]Figure 4
Dye degradation using magnetic ferrite and metal-doped ferrite nanocatalyst.


## 6. Dye Degradation Using Ferrite-Based Nanomaterials

Diverse dyes exist, which can be synthesized chemically in industry and occur in nature. The dyes we studied in this article are shown in Figure3 with their name and structure for better understanding.Farhadi et al. reported the ultrasound-assisted photocatalytic degradation of methylene blue (MB) dye (25 mg/L) within 70 min using CoFe2O4@ZnS composite and H2O2 (4 mM). The composite shows excellent reusability up to five cycles with significant property changes [59]. Siadatnasab et al. stated that the dye degradation efficiency of CuS/CoFe2O4 nanohybrid towards methylene blue (MB) dye (25 mg/L) and rhodamine B (RhB) dye (25 mg/L) along with H2O2 was accomplished within 30 minutes with 100% and 72% efficiency, respectively, via sonocatalytic process. However, the reusability study shows 5% drop in the catalytical activity after the 4th cycle [60]. Kalam et al. specified that photocatalytic degradation of methylene blue (MB) dye (1 mg/L) with H2O2 in visible light CoFe2O4 sample MST-2 shows 80% degradation of MB dye within 140 min than the MST-3 and MST-1 [61]. Gan et al. quantified the photocatalytic performance of Ag3PO4-CoFe2O4 nanocomposite in a tungsten halogen lamp with light 500 W output power towards methylene blue (MB) dye (10 mg/L) and rhodamine B (RhB) dye (10 mg/L) which completely degraded within 30 min. Increasing the dye concentration to 40 mg/L was degraded completely within 60 min. Ag3PO4-CoFe2O4 (7.5%) shows high degradation capacity that Ag3PO4-CoFe2O4 (10%) sample [62]. López et al. reported that the multifunctional Co0.25Zn0.75Fe2O4@SiO2 with and without ZnO coated nanomaterial was used for the dye degradation of red amaranth dye (25 mg/L). The Co0.25Zn0.75Fe2O4@SiO2/ZnO degrades red amaranth dye by about 90% after 90 min under UV irradiation [63].Moreover, Astaraki et al. specified the synthesis of CuFe2O4/RGO nanocomposite for dye degradation of methylene blue (MB) (15 mg/L) with a light source as two 100 W Xenon lamps with a UV cut-off filter. The catalyst shows a 3% decrease in catalytic activity after the 4th cycle [64]. Lei et al. show the synthesis and catalytic activity of CuFe2O4@GO hybrid for methylene blue (MB) dye degradation. The 200 mg/L catalysts and PMS dosage of 0.8 mmol/L are sufficient for 93.3% photocatalytic degradation of methylene blue (MB) dye (20 mg/L) in 30 min. Furthermore, an increase in the catalyst amount to 400 mg/L does not show a boost in the catalytic degradation rate of MB dye. In contrast, the rise in the PMS dosage to 1 mmol/L shows a small decline in MB degradation rate [65]. Chen et al. demonstrated the hydrothermal synthesis of magnetic CuFe2O4/GO and their dye degradation potential towards acid orange II (AO7) and rhodamine B (RhB) without H2O2 in the presence visible light. The photocatalytic application of CuFe2O4/GO (800 mg/L) for acid orange II (AO7) dye (0.05 mM) degradation at pH=7 shows 77% efficiency [66]. Yu et al. testified dye degradation C.I. Reactive red 2 (RR) (100 mg/L), with 10 mg of the nanoscale-confined precursor of CuFe2O4 and 4 mL of H2O2, displays 91.3% degradation in 60 min. Furthermore, the efficiency of the CuFe2O4 enhances to 94.3% by calcination at higher temperatures [67]. da Nóbrega Silva et al. revealed that the visible-light-driven photocatalytic performance of CuFe2O4–Fe2O3 (1 g/L) nanocatalyst for the methylene blue (MB) dye (50 mg/L) degradation in the presence of H2O2 (300 Mg/L) at neutral pH shows 64% efficiency with 0.6-FC-2. Furthermore, the recyclability study of the catalyst shows a 2.33% decrease in April and a 10.15% increase in May in the second cycle [68]. Kalantari et al. disclosed catalytic activity of Fe3O4-C-Cu nanocatalyst (30 mg) and aqua solution of methyl orange (MO) (3.0×10−5 M, 25 mL) with aqueous NaBH4 (5.3×10−3 M, 25 mL), and MO degradation takes place within 50 seconds. Moreover, there is no significant loss in the catalytical activity after 4th cycle [69].In addition, Saleh and Taufik explained the ultraviolet-light-assisted degradation of the MO and MB (20 mg/L). Ag-Fe3O4/graphene (0.4 gm) composites act as a catalyst with 4 mL 30% H2O2. Furthermore, Ag-Fe3O4/graphene composite (25 wt% Ag-Fe3O4/graphene and 10 wt% of graphene) shows efficient catalyst reusability [70]. Tang et al. exhibited that sulfidation-modified Fe3O4 nanoparticle (S-Fe3O4NP) (50 mg/L) catalyst for the photocatalytic degradation of rhodamine B (10 mg/L) in the presence of H2O2 (13 mg/L) shows 99% degradation within 10 min. Recyclability study shows the catalyst 84.3% efficiency for rhodamine B dye after 3rd cycle [71]. Vinothkannan et al. showed that the synthesis of RGO/Fe3O4 nanocomposites (10 mg) for methylene blue (MB) (9.37×10−5 M) dye degradation with the addition of using 5.8×10−2 M of NaBH4 under ultrasonicated shows 95.18% efficiency within 12 min. Moreover, the catalyst displays 89.4% efficiency after the 7th cycle [72]. Zhou et al. synthesised Ag3PO4@MgFe2O4 composites for the dye degradation of rhodamine B using visible irradiation. The dye degradation experiment of aqueous RhB (10 mg/L) was performed in the presence of 300 W Xenon short-arc lamps with a UV filter (≥400 nm), and the amount of Ag3PO4@MgFe2O4 (10%) catalyst (20 mg/100 mL) degrades 98% of dye in 20 min [73]. Das and Dhar publicized the photocatalytic degradation of malachite green (MG) by using MgFe2O4 nanocatalyst in the presence of H2O2. The 40 mg of catalyst in 70 mL of MG (10 mg/L) and 0.1 mL 10% H2O2 in absence of light gives 100% degradation in 50 seconds [74].Cabrera et al. manufacture nanostructured MgFe2O4 ferrites and check their methylene blue dye degradation efficiency. In 35 min, 60 and 75% of methylene blue (MB) dye degraded under light and dark conditions, respectively [75]. Zhang et al. testified the fabrication of MgFe2O4/TiO2 and checked the degradation efficiency of rhodamine B (RB) dye in the presence of UV and visible light 500 W Xenon lamps as a source. The 2 wt% MgFe2O4/TiO2 catalyst shows 100% efficiency in 40 min using UV light whereas 3 wt% MgFe2O4/TiO2 catalysts evince excellent efficiency in visible light [76]. Amulya et al. manufacture Cu-doped NiMnFe2O4 (60 mg) nanoparticles using the probe sonication method and study their photocatalytic dye degradation activity under UV light towards Drimarene yellow (DY) and methylene blue (MB) dyes. The degradation efficiency of DY is 43.3% when dopant 0.1, whereas MB is 98.1% when 0.4 is dopant [77]. Mahmoodi reported the synthesis of MnFe2O4 and dye degradation ability for reactive red 120 (RR120) and reactive red 198 (RR198), concentration (100 mg/L), in the presence of H2O2 (1.2 mM) [78]. Boutra et al. described the synthesis of MnFe2O4/TA/ZnO nanocomposites and studied their dye degradation performance for the Congo red (CR) using visible light radiations. Congo red (CR) (16 mg/L) dye degraded using 50 mg of the catalyst shows 84.2% efficiency in 90 min. Reusability study confirmations and degradation efficiency at the end of 5th cycle were 77.5% [79]. Mandal et al. investigated the methylene blue dye (MB) (10 mg/L) degradation utilizing MnFe2O4/rGO. The catalyst (0.03 g) shows 97% efficiency in 60 min in the presence of a UV lamp of 40 W [80]. Sahoo et al. described the synthesis of mesoporous silica encapsulated with magnetic MnFe2O4 nanoparticles for the dye degradation study. The methyl orange (MO) dye (0.6 mg mL/L) is degraded utilizing mesoporous silica encapsulated MnFe2O4 (20 mg) along with 2 mL H2O2, resulting in 98% degradation in the presence of sunlight in 180 min. Furthermore, the catalyst shows a negligible change in the efficiency after 5th cycle [81]. Zhang et al. showed NiFe2O4 powders as a nanocatalyst for the photocatalytic degradation of brilliant green (BG) dye (20 mg mL/L) under microwave irradiation (output power 500 W) for 2 min to degrade 97% dye [82]. Atacan et al. explained the decolorization of indigo carmine (IC) dye (10 mg/L) using NiFe2O4/T/GOx in 90 min. Decolorize 98.6% and 37.6% under a UV lamp and Fenton process, respectively [83]. Baig et al. explained that the synthesis of NiFe2O4@TiO2 for dye degradation of methyl orange (MO) dye using a UV lamp (300 W Xenon) with a cut-off filter shows 90.06% activity. Furthermore, increasing the percentage of TiO2 from 10% to 40% in the catalyst NiFe2O4 increases the photocatalytic activity from 72% to 90.06%, respectively [84].Furthermore, Kamal et al. stated that boron-doped C3N4/NiFe2O4 nanocomposite was fabricated and investigated their use for methylene blue (MB) dye degradation. The catalyst BCN/NiFe2O4 (100 mg) is mixed with methylene blue (MB) dye (5 ppm) in a Mercury-Xenon lamp (350 W) as a source of visible light and shows 98% degradation efficiency in 80 min. However, the reusability study shows a 1.69% decrease in the catalyst after 3rd cycle [85]. Amulya et al. reported the sonochemical fabrication of NiFe2O4 nanocatalyst and studied their dye degradation activity for the Drimarene yellow (DY) and methylene blue (MB) dyes. The 60 mg NiFe2O4 is added to MB and DY dyes separately; each with 20 ppm concentration and irradiated with a 400 W Hg lamp shows 89.4% for MB and 43.3% for DY degradation. In addition, the catalyst shows a 10% decrease in efficiency after 5th consecutive cycle [86]. Chandel et al. elucidate the fabrication of ZnO/ZnFe2O4/NG and ZnO/CoFe2O4/NG nanocatalyst for the efficient degradation of malachite green (MG) and methyl orange (MO) dyes in the presence of halogen lamp. The ZnO/ZnFe2O4/NG shows 92% and 98%, and with ZnO/CoFe2O4/NG shows 98% and 99% for MG and MO dyes, respectively. A recyclability study shows an insignificant change in the catalytic activity after the 10th cycle [87]. Mahmoodi explained the synthesis of ZnFe2O4 and dye degradation capacity for reactive red 120 (RR120) and reactive red 198 (RR198) concentrations (100 mg/L) and the amount of nanocatalyst (0.20 g) and H2O2 (1.2 mM) at 25°C in the presence of UV-C lamp (200–280 nm, 9 W, Philips) [88]. Kulkarni et al. enlighten that the synthesis of core-shell ZnFe2O4@ZnO nanocatalyst for degradation of methyl orange (MO) dye in visible light using 125 W Hg lamp 100% degradation takes place in 9 h. Reusability study shows a 5% decrease in the efficiency after 2nd reuse [89]. Nirumand et al. convey that the synthesis of MIL-101(Cr)/RGO/ZnFe2O4 nanocatalyst (0.5 g/L) for the degradation of rhodamine B (RB) (25 mg/L) dye using ultrasound irradiation in the appearance of H2O2 is 95% in 50 min. The methylene blue (MB) and Congo red (CR) dyes degraded 100% and 95%, and the time required were 2 min and 50 min, respectively, under similar conditions. The catalyst study shows excellent recyclability after the 4th cycle [90]. Oliveira et al. explain the fabrication of ZnFe2O4 and examine the dye degradation performance using visible light degradation of rhodamine B (RB) and malachite green (MG) dye degradation using visible irradiation of 3 lamps from Taschibra® full spiral of 25 W as source [91].


## 7. Mechanistic Study of Dye Degradation Using Ferrite-Based Nanomaterials

The mechanistic study, which shows how the magnetic ferrite is responsible for the dye degradation and the graphical representation, was discussed in this section.Nirumand et al. [90] reported the sonocatalytic dye degradation, which involves a sonoluminescence phenomenon capable of generating a relatively wide wavelength range that is used to excite the electron in both ZnFe2O4 and MIL-101(Cr), leading to the formation of holes. The transfer of an electron from CB of ZnFe2O4 to CB of MIL-101(Cr) and the holes from VB of MIL-101(Cr) to VB of ZnFe2O4 and how it is utilized for the degradation is shown in Figure 5(a) graphically, and Figure 5(b) shows how the step-wise reaction takes place in the dye degradation.Figure 5
(a) A plausible mechanism for sonocatalytic degradation of dyes over MIL-101(Cr)/RGO/ZnFe2O4 nanocomposite using ultrasound irradiation. (b) Schematic representation of mechanism takes place during dye degradation (reproduce from [81]).
(a)(b)Amulya et al. [77] specified the catalytic role of Cu-doped NiMnFe2O4 in dye degradation. The catalyst is subjected to light irradiation that excites the electron in CB, which leads to holes in the VB. Furthermore, the created holes react with water to generate OH• radicals which disintegrate dye molecules, and super oxide is generated using oxygen and excited electron in CB. The detailed reaction progress and schematic representation of dye degradation are shown in Figures 6(a) and 6(b), respectively.Figure 6
(a) A proposed mechanism for degradation of dyes using Cu-doped NiMnFe2O4 nano-photocatalyst under UV light. (b) Schematic representation of mechanism takes place during dye degradation (reproduce from [68]).
(a)(b)Furthermore, Chandel et al. [87] elucidated how the ZnO/CoFe2O4/NG and ZnO/ZnFe2O4/NG magnetic nanocomposites degrade dye solution. When exposed to a visible-light source, the catalyst creates electrons and holes in CB and VB, respectively. The redox scale shows strong interfacial contact, and the positioning of CB facilitates the movement of an electron from CB of ZF to ZnO and avoids the hole-electron recombination by forming heterojunction-type II. The detailed schematic representations of dye degradation using ZnO/ZnFe2O4/NG and ZnO/CoFe2O4/NG catalyst are shown in Figures 7(a) and 7(b), respectively.Figure 7
(a, b) Schematic representation of dye degradation using ZnO/ZnFe2O4/NG and ZnO/CoFe2O4/NG catalysts, respectively (reproduce from [78]).
(a)(b)Similarly, various reports on catalytic dye degradation using ferrites and metal ferrites are tabulated in Table1.


## 8. Future Scope

This article compiled and reviewed the degradation of different dyes using ferrite-based nanomaterials. According to the literature, dye degradation using ferrite-based nanomaterials is supposed to have improved efficiency. However, the distinction between both the magnetic and ferrite-based composites is just a guideline. From this reconsideration, we also like to point out that it is necessary to choose a minimum manufacturing cost with strong dye degradation performance and also a multipurpose catalyst viable for various types of contaminants because the selection of the catalyst is an important event in the decision to introduce a suitable large-scale magnetic catalyst. This article shows that the ferrite-based nanomaterial used for dye degradation contains a simple preparation method and cheap chemical reagents. However, by analyzing the efficacy of magnetic nanocomposite regeneration, economic viability should be improved, as regeneration studies can assess the reusability of magnetic nanocomposites. On the other hand, a lot of new, powerful software is built to resolve mathematical models and complex data that are supposed to be represented more adequately and help understand the mechanism’s insight. In addition, the use of energy-dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), electron spin resonance (ESR), scanning tunneling microscopy (STM), dynamic light scattering (DLS), X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), superconducting quantum interference device (SQUID), vibrating sample magnetometer (VSM), magnetic force microscopy (MFM), atomic force microscopy (AFM), X-ray absorption spectroscopy (XAS), zeta potential, and thermogravimetric analysis (TGA) is strongly recommended for characterization assessments.Moreover, from an environmental point of view, developing a safer and more effective approach to dye degradation is necessary. Keeping this in mind, the study was carried out to find magnetic nanoparticles for dye degradation.


## 9. Conclusion

The article highlights the implications of the successful production of nanomaterials based on magnetic ferrite and its applications for the treatment of dye effluents. Special note should be made of the important mechanisms of action of magnetic nanomaterials in the treatment of dye effluents, like photocatalytic degradation and adsorption, concerning just the mitigation of dyes typically used throughout the textile sector. The use of renewable or environmentally friendly reductants to fabricate ferrite-based nanomaterials has been shown to demonstrate the effective elimination of different dyes from wastewater. However, with recent research data, the possibility of ferrite-based nanomaterials discharged into the ecosystem and their exposure to terrestrial and marine biological systems at trace concentrations is known. In addition, the application of ferrite-based nanomaterials to dye effluent treatment procedures involves extensive obstacle evaluations, as well as there are also restricted environmental protection assessment studies. Furthermore, no legislation relating to the maximum allowable concentrations of ferrite-based nanomaterials in wastewater is in place to ensure the environment’s safety and human health. Therefore, it is essential to evaluate ferrite-based nanomaterial harmful effects and hazards associated with the implementation of ferrite-based nanomaterials in the treatment of dye effluent. The sulphidation process has recently become one of the natural solutions for mitigating the toxicity of ferrite-based nanomaterials and their effects on sewage processing plants. The study on in vivo immunotoxicity, the effect of ferrite-based nanomaterials form on toxic effect, and the thorough advancement of ferrite-based nanomaterial adsorption kinetics on various biological macromolecules occur during infancy. The overall understanding of ferrite-based nanomaterial absorption, distribution, and effective dye degradation is demonstrated in this study.



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