Skip to Content
You are currently on the new version of our website. Access the old version .
MDPIMDPI

Advanced

Applied NanoApplied Nano
PDF
  • Article
  • Open Access

1 October 2026

22 Pages

Lime-Juice-Assisted Synthesis of Magnetically Recoverable CoFe2O4/Chitosan Nanocomposites for Visible-Light Removal of Methylene Blue

,
and
College of Education, Vinh University, Truong Vinh Ward, Nghe An 43131, Vietnam
*
Author to whom correspondence should be addressed.
Appl. Nano2026, 7(4), 33;https://doi.org/10.3390/applnano7040033
This article belongs to the Topic Nanocomposites: Properties and Applications in Health and Environmental Care
Version Notes
Order Reprints

Abstract

A lime-juice-assisted route was used to synthesize CoFe2O4 nanoparticles, which were subsequently immobilized in a chitosan matrix to obtain a magnetically recoverable CoFe2O4/chitosan (CoFe2O4/CS) nanocomposite for methylene blue (MB) removal under visible light. X-ray diffraction confirmed the cubic spinel phase and its retention after composite formation, while FTIR and XPS supported interfacial interactions between CoFe2O4 and the amino/hydroxyl functionalities of chitosan. Electron microscopy showed predominantly spherical-to-quasi-spherical ferrite nanoparticles (approximately 10–20 nm) distributed on the polymer matrix with reduced agglomeration. Chitosan incorporation decreased the BET surface area from 81.9 to 51.3 m2 g−1 and the saturation magnetization from 51.5 to 31.4 emu g−1, but the nanocomposite remained readily separable with an external magnet. The optical band gap increased from 2.17 to 2.61 eV, whereas photoluminescence quenching was consistent with altered radiative charge-carrier behavior. At pH 9, an initial MB concentration of 20 mg L−1, and a catalyst dosage of 0.7 g L−1, the composite achieved 98.5% MB removal within 120 min under a 30 W visible-light LED, with a pseudo-first-order rate constant of 0.035 min−1. Removal remained at 90.3% after five cycles. Scavenger tests indicated major contributions from pathways involving h+ and •OH. These findings support further evaluation of bio-assisted CoFe2O4/CS nanocomposites as magnetically recoverable photocatalysts for MB-containing wastewater treatment.

1. Introduction

Synthetic dyes released by the textile, leather, pharmaceutical, and related industries remain a persistent challenge for aquatic environments because many dye molecules are chemically stable, intensely colored, and poorly biodegradable [1,2,3]. Methylene blue (MB), a cationic phenothiazine dye, is frequently used as a model contaminant in photocatalytic studies owing to its strong visible absorption and resistance to conventional biological treatment [1,3]. Even at relatively low concentrations, dye-containing effluents can impede light penetration and oxygen transfer, disrupt aquatic photosynthesis, and create potential human-health concerns [1,2,3,4,5]. Accordingly, treatment technologies must combine high removal efficiency with low chemical demand, operational simplicity, and catalyst reusability.
Semiconductor photocatalysis is an attractive advanced oxidation process because absorbed photons generate electron–hole pairs that can initiate the formation of reactive oxygen species, including hydroxyl radicals (•OH) and superoxide species (•O2−), under comparatively mild conditions [2,5,6,7,8,9]. Practical performance, however, is often limited by rapid charge recombination, insufficient visible-light utilization, nanoparticle aggregation, and difficult post-treatment separation. Material design must therefore balance optical activity, interfacial charge transfer, accessible adsorption sites, and recoverability rather than optimize any single property in isolation.
Spinel ferrites (MFe2O4; M = Co, Zn, Ni, Mn, Mg, or Cu) are promising photocatalytic platforms because their electronic structures support visible-light response and their magnetic properties enable separation from treated water [10,11]. CoFe2O4 is particularly attractive because of its chemical stability, high magnetocrystalline anisotropy, coercivity, and saturation magnetization [12,13,14,15]. Nevertheless, bare CoFe2O4 nanoparticles tend to aggregate through magnetic and high-surface-energy interactions, reducing the number of accessible sites and complicating reproducible photocatalytic operation.
CoFe2O4 has been prepared by co-precipitation, sol–gel, hydrothermal, vapor-phase, laser-ablation, and mechanochemical methods [16,17,18,19,20,21]. Several of these routes require synthetic complexing agents, hazardous solvents, strong reducing agents, or energy-intensive processing [22]. Bio-assisted synthesis partially addresses these limitations by using plant-derived metabolites as complexing, capping, and stabilizing species [14,22,23,24,25,26,27,28]. Citrus juices contain citric and ascorbic acids, reducing sugars, flavonoids, polyphenols, and other oxygen-containing compounds, which have been reported to exhibit complexing, capping, and stabilizing functions in nanoparticle synthesis [29,30,31,32]. Their successful application to ZnO, CuO, MgO, TiO2, and related nanomaterials supports the use of lime juice as a bio-derived synthesis medium [29,30,33,34].
CoFe2O4-based materials have previously been applied to MB photocatalytic removal, although their performance strongly depends on composition and operating conditions. For example, bare CoFe2O4 achieved approximately 80% MB degradation within 140 min under visible light in the presence of H2O2 [35,36], while Al-doped CoFe2O4 reached approximately 93% removal after 120 min at pH 11 [37]. Coupling CoFe2O4 with additional inorganic photoactive phases has also been explored to improve MB degradation. A CoFe2O4@ZnO core–shell photocatalyst achieved a maximum MB degradation of 78.3% after 180 min under UV irradiation [8], whereas a g-C3N4/CoFe2O4 composite reached approximately 97.4% degradation after 180 min under sunlight/visible-light irradiation [38]. These results demonstrate the photocatalytic potential of CoFe2O4-based materials but also indicate that high removal efficiencies are often obtained through the use of additional semiconductor phases, external oxidants, strongly alkaline conditions, or relatively long irradiation times. Chitosan (CS), a natural polysaccharide derived from chitin, is attractive as a supporting matrix because of its biodegradability, biocompatibility, and abundance of amino and hydroxyl functional groups. These functional groups provide interaction and adsorption sites, while the polymer matrix can improve the dispersion of inorganic nanoparticles and suppress their agglomeration [36,39]. Therefore, incorporation of CoFe2O4 into chitosan can combine the magnetic recoverability of the ferrite with the adsorptive and dispersing characteristics of chitosan, providing a suitable composite architecture for pollutant removal [40,41]. CoFe2O4/chitosan systems have also been reported for the removal of acidic yellow, indigotine blue, Congo red, and methyl orange, mainly through adsorption [40,41,42], while a modified chitosan–CoFe2O4 material has been investigated for the photocatalytic degradation of Rhodamine B [43]. To the best of our knowledge, however, the application of CoFe2O4/chitosan composites to visible-light photocatalytic removal of MB has not yet been reported.
In the present study, a magnetically recoverable CoFe2O4/CS system was developed by combining lime-juice-assisted CoFe2O4 synthesis, chitosan immobilization, and irradiation with a 30 W visible-light LED. The resulting composite was systematically examined in terms of its structural, morphological, optical, textural, and magnetic characteristics, together with its visible-light MB-removal performance, reusability, and magnetic recoverability.

2. Materials and Methods

2.1. Materials

All reagents were of analytical grade and were used without further purification. Cobalt(II) nitrate hexahydrate [Co(NO3)2·6H2O, 99%], iron(III) nitrate nonahydrate [Fe(NO3)3·9H2O, 99%], medium-molecular-weight chitosan (degree of deacetylation, 75–85%), and methylene blue (97%) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Sodium hydroxide (NaOH, 98%), acetic acid (CH3COOH, 99%), and hydrochloric acid (HCl, 37%; density, 1.19 g mL−1) were obtained from Aladdin Reagent Co., Ltd. (Shanghai, China). Deionized water was used throughout.

2.2. Preparation of Lime-Juice Extract

Fresh limes obtained in Nghe An Province, Vietnam, were washed thoroughly with deionized water and mechanically pressed. The juice was centrifuged at 13,000 rpm for 10 min and filtered, and the clear supernatant was stored at 4 °C until use.

2.3. Synthesis of CoFe2O4 Nanoparticles and CoFe2O4/CS Nanocomposite

CoFe2O4 nanoparticles were synthesized by dissolving 0.005 mol Co(NO3)2·6H2O and 0.010 mol Fe(NO3)3·9H2O in 50 mL of deionized water under stirring, thereby maintaining the stoichiometric Co:Fe ratio of 1:2. Lime-juice extract (20 mL) was added at room temperature, and the mixture was stirred at 80 °C until a gel formed. The gel was dried at 80 °C for 4 h, heated to the selected calcination temperature at 5 °C min−1, held for 2 h, and cooled naturally. Samples calcined at 300, 400, 500, and 700 °C were used to evaluate phase development; the material calcined at 500 °C was used for composite preparation and subsequent photocatalytic tests.
For nanocomposite fabrication, 1.0 g of chitosan was dissolved in 100 mL of 1% (v/v) aqueous acetic acid. CoFe2O4 nanoparticles (0.30 g) were dispersed in the chitosan solution by magnetic stirring followed by sonication for 30 min. The pH was adjusted gradually to approximately 11 with 2 M NaOH, and the dispersion was sonicated for another 30 min and heated at 80 °C for 3 h. The solid was collected by filtration, washed repeatedly with deionized water to neutral pH, and dried at 60 °C for 5 h.

2.4. Characterization

Crystalline phases were analyzed by X-ray diffraction (XRD) using a D8 Advance diffractometer (Bruker, Karlsruhe, Germany) with Cu Kα radiation (λ = 0.15406 nm) over 2θ = 10–70°. Crystallite size was estimated from the (311) reflection using the Scherrer equation, and lattice parameters, unit-cell volume, and X-ray density were calculated from the diffraction data.
Surface functional groups and ferrite–polymer interactions were examined by Fourier-transform infrared spectroscopy (FTIR; Thermo-Nicolet Nexus 670, Thermo Fisher Scientific, Madison, WI, USA). Morphology and particle distribution were observed by field-emission scanning electron microscopy (FESEM; Hitachi S-4800, Hitachi High-Tech Corporation, Tokyo, Japan) and transmission electron microscopy (TEM; JEOL JEM-1400, JEOL Ltd., Tokyo, Japan). Elemental composition was assessed by energy-dispersive X-ray spectroscopy (EDX; HORIBA 7593-H, HORIBA, Ltd., Kyoto, Japan) coupled to the SEM.
Surface elemental composition and oxidation states were investigated by X-ray photoelectron spectroscopy (XPS; ESCALab 250, Thermo VG, East Grinstead, UK). Nitrogen adsorption–desorption measurements were performed on a Tristar-3000 analyzer (Micromeritics, Norcross, GA, USA), and the specific surface area and pore-size distribution were determined using the BET and BJH methods, respectively.
Diffuse-reflectance spectra were recorded with a Cary 5000 UV–Vis–NIR spectrometer (Agilent Technologies, Santa Clara, CA, USA). Reflectance data were transformed using the Kubelka–Munk function, and optical band gaps were estimated from Tauc plots assuming a direct allowed transition. Photoluminescence spectra were measured with a Fluorolog-3 spectrofluorometer (FL3C-22, HORIBA Scientific, Edison, NJ, USA) to compare the relative radiative recombination behavior of CoFe2O4 and CoFe2O4/CS.
Magnetic hysteresis loops were recorded at room temperature using a Lake Shore 7404 vibrating sample magnetometer (VSM; Lake Shore Cryotronics, Inc., Westerville, OH, USA). Saturation magnetization (Ms), remanent magnetization (Mr), and coercivity (Hc) were extracted from the hysteresis curves. Magnetic separation from water was assessed qualitatively using an external permanent magnet.

2.5. Photocatalytic Experiments

Photocatalytic tests were performed in a glass reactor containing 50 mL of MB solution and the required amount of catalyst. A 30 W visible-light LED (Philips, Eindhoven, The Netherlands, 6500 K) was positioned 20 cm above the liquid surface. Before irradiation, each suspension was stirred in the dark for 60 min to establish adsorption–desorption equilibrium. Aliquots were withdrawn at 30 min intervals, the catalyst was separated, and the residual MB concentration was determined by UV–Vis spectrophotometry. Control experiments included direct photolysis and dark adsorption by CS, CoFe2O4, and CoFe2O4/CS. The MB removal efficiency (RE) was calculated as follows:
R E % = C 0 − C t C 0 × 100 %
where C0 and Ct (mg L−1) are the MB concentrations at the beginning of the test and at irradiation time t, respectively.
The apparent photocatalytic kinetics were evaluated using the pseudo-first-order expression:
L n C 0 C t = k t
where k is the pseudo-first-order rate constant (min−1), and t is the irradiation time (min). The value of k was obtained from the slope of the linear plot of ln(C0/Ct) versus t.
Operational parameters were examined over the following ranges: initial pH, 3–11; initial MB concentration, 10–40 mg L−1; and CoFe2O4/CS dosage, 0.2–1.0 g L−1. Unless a parameter was being varied, the remaining conditions were held constant. The point of zero charge (pHPZC) of the nanocomposite was determined using the pH-drift method.
Reactive-species tests were performed by adding p-benzoquinone (BQ), isopropanol (IPA), ethylenediaminetetraacetic acid disodium salt dihydrate (Na2EDTA·2H2O, abbreviated as EDTA), or AgNO3 as scavengers for •O2−, •OH, h+, and e−, respectively. The resulting removal efficiencies were compared with a scavenger-free control under otherwise identical irradiation conditions.
Reusability was evaluated for five consecutive cycles under the optimized conditions (pH 9, 20 mg L−1 MB, 0.7 g L−1 catalyst, and 120 min irradiation). After each cycle, the nanocomposite was recovered with an external magnet, washed with ethanol and deionized water, vacuum-dried at 80 °C for 5 h, and reused in a freshly prepared MB solution. Phase stability was additionally assessed by comparing the XRD patterns of fresh material and a separately recovered specimen after five irradiation–recovery cycles.
All photocatalytic experiments were conducted in triplicate. Results are reported as mean ± standard deviation (SD), and error bars represent three independent measurements (n = 3).

3. Results and Discussion

3.1. Calcination-Dependent Formation of CoFe2O4

Figure 1a shows the XRD patterns of the ferrite precursors calcined at 300–700 °C. The sample treated at 300 °C exhibited only weak, broad features, indicating limited crystallization. At 400 °C, reflections appeared at 2θ = 30.3°, 35.6°, 43.3°, 53.7°, 57.3°, and 62.9°, corresponding to the (220), (311), (400), (422), (511), and (440) planes of cubic spinel CoFe2O4 (JCPDS 22-1086). Increasing the calcination temperature sharpened and intensified these reflections, consistent with progressive crystallite growth and improved long-range order.
Figure 1. (a) XRD patterns of CoFe2O4 nanoparticles calcined at 300, 400, 500, and 700 °C. (b) Enlarged (220)/(311) region showing the shift toward lower 2θ values with increasing calcination temperature.
The mean crystallite size D was estimated from the (311) reflection using the Scherrer equation [44]:
D = K λ β cos θ
where K = 0.9 is the shape factor, λ = 1.5406 Å is the Cu Kα wavelength, β is the full width at half maximum of the (311) peak (in radians), and θ is the corresponding Bragg angle.
The cubic lattice parameter (a), unit-cell volume (V), and theoretical X-ray density (ρ) were calculated using the following relationships:
a = d h k l ( h 2 + k 2 + l 2 )
V = a 3
ρ = 8 M N V
where dhkl is the interplanar spacing, h, k, and l are the Miller indices, M is the molar mass of CoFe2O4, N is Avogadro’s constant (6.022 × 1023 mol−1), and the factor 8 is the number of formula units per spinel unit cell.
The calculated crystallographic parameters are summarized in Table 1.
Table 1. Crystallite size, lattice parameter, unit-cell volume, and X-ray density of CoFe2O4 nanoparticles calcined at different temperatures.
The crystallite size increased from 8.1 nm at 400 °C to 10.0 nm at 500 °C and 18.9 nm at 700 °C, reflecting thermally activated domain growth and coalescence [14,15]. Concurrently, a increased from 8.3304 to 8.3530 Å and V from 578.09 to 582.81 Å3, while ρ decreased slightly from 5.39 to 5.35 g cm−3. The shift in the (220) and (311) reflections toward lower 2θ values (Figure 1b) is consistent with this small lattice expansion [45,46,47].
A calcination temperature of 500 °C was selected for subsequent work because it produced well-defined spinel CoFe2O4 while retaining a comparatively small crystallite size (10.0 nm). The 700 °C treatment increased crystallinity but nearly doubled the crystallite size, a change expected to reduce external surface area and potentially diminish photocatalytic accessibility. The selected temperature therefore represents a compromise between phase purity and nanoscale dimensions.

3.2. Crystal Structure of the CoFe2O4/CS Nanocomposite

The XRD patterns of CS, CoFe2O4, and CoFe2O4/CS are compared in Figure 2. Chitosan displayed a broad maximum near 2θ = 20°, characteristic of its semi-crystalline polysaccharide structure [48,49].
Figure 2. XRD patterns of CS, CoFe2O4, and the CoFe2O4/CS nanocomposite.
The nanocomposite retained the characteristic spinel reflections of CoFe2O4 together with the broad chitosan contribution. The reduced ferrite peak intensities primarily reflect dilution by the polymer matrix and partial attenuation of the diffracted signal; interfacial disorder may provide an additional contribution. No new crystalline impurity phase or substantial peak displacement was observed, demonstrating that composite formation preserved the CoFe2O4 spinel framework [50,51].

3.3. FTIR Analysis

Figure 3 compares the FTIR spectra of CS, CoFe2O4, and CoFe2O4/CS.
Figure 3. FTIR spectra of CS, CoFe2O4, and the CoFe2O4/CS nanocomposite.
Chitosan exhibited a broad band at 3462.6 cm−1 assigned to overlapping O–H and N–H stretching vibrations. The bands at 2933.5 and 2877.6 cm−1 arose from asymmetric and symmetric C–H stretching, respectively [52,53,54,55].
The band at 1660.5 cm−1 was associated with residual amide C=O stretching, whereas the features at 1592.1 and 1394.1 cm−1 were assigned to amino-group bending (amide II region) and C–H deformation, respectively [56,57,58,59,60]. Bands at 1171.9 and 1073.4 cm−1 corresponded to C–O–C stretching and coupled C–O/C–N vibrations of the glucosamine framework [56,57,58].
CoFe2O4 displayed broad O–H stretching and adsorbed-water bending bands at 3451.2 and 1635.3 cm−1, respectively [15,40,61]. The feature at 1383.7 cm−1 was attributed to residual surface-bound organic species from the bio-assisted synthesis [62]. The bands at 586.2 and 416.7 cm−1 are characteristic of metal–oxygen vibrations at tetrahedral and octahedral sites of the spinel lattice, respectively [63].
Both polymer and ferrite vibrations were present in CoFe2O4/CS. The metal–oxygen bands shifted from 586.2 and 416.7 cm−1 to 575.6 and 408.8 cm−1, and the broad O–H/N–H band shifted from 3462.6 to 3441.7 cm−1. These coordinated shifts, together with intensity changes, support hydrogen-bonding and/or coordination interactions between surface metal/oxygen sites and the –NH2/–OH groups of chitosan [39,42].

3.4. Morphology and Elemental Composition

FESEM, TEM, and EDX results for CoFe2O4 and CoFe2O4/CS are presented in Figure 4.
Figure 4. (a) FESEM image and (b) EDX spectrum of CoFe2O4 nanoparticles; (c) FESEM image and (d) EDX spectrum of the CoFe2O4/CS nanocomposite. Insets show the corresponding TEM images.
Pristine CoFe2O4 consisted of predominantly spherical-to-quasi-spherical particles with an approximate size range of 10–20 nm (Figure 4a and inset). The particles formed aggregates, as expected from their high surface energy and magnetic interactions [64]. After incorporation into chitosan, ferrite domains were distributed across the polymer matrix and appeared more spatially separated (Figure 4c). TEM likewise indicated a lower degree of compact agglomeration in the composite. These observations support the role of chitosan as a steric and interfacial stabilizer that restricts direct ferrite–ferrite contact [36,39].
EDX detected Co, Fe, and O in the ferrite sample and additionally C and N in CoFe2O4/CS, confirming the presence of the chitosan phase (Figure 4b,d). The lower relative Co and Fe signals in the composite are consistent with polymer dilution and surface coverage of the ferrite particles.

3.5. Optical Absorption and Photoluminescence

Figure 5a shows the diffuse-reflectance response of CS, CoFe2O4, and CoFe2O4/CS. Chitosan absorbed mainly in the ultraviolet region, whereas CoFe2O4 exhibited broad visible-light absorption. Although both direct and indirect electronic transitions have been reported for CoFe2O4, the direct-allowed transition was adopted in the present study because this transition has been considered suitable for optical band-gap estimation of CoFe2O4-based ferrites in previous studies [43,62,65]. Accordingly, the Kubelka–Munk-transformed reflectance data were analyzed using the Tauc method for a direct allowed transition by plotting (F(R)hν)2 versus hν (Figure 5b), yielding optical band gaps of 2.17 eV for CoFe2O4 and 2.61 eV for CoFe2O4/CS [62,65]. The observed blue shift after chitosan incorporation may be associated with changes in electronic transitions induced by interactions between the ferrite phase and the chitosan matrix [43,66]. A similar increase in band-gap energy has been reported for a chitosan Schiff base-modified cobalt ferrite system, from 2.35 to 2.52 eV [43]. Likewise, the band gap of MnFe2O4/GO increased from 3.0 to 3.5 eV after chitosan incorporation, which was associated with modification of the electronic transitions in the resulting nanocomposite [66].
Figure 5. (a) UV–Vis diffuse-reflectance spectra of CS, CoFe2O4, and CoFe2O4/CS; (b) Tauc plots used to estimate the optical band gaps of CoFe2O4 and CoFe2O4/CS.
PL emission provides a comparative indication of radiative electron–hole recombination [6,67,68,69]. CoFe2O4 showed a broad emission centered near 430 nm, whereas CoFe2O4/CS exhibited substantially lower intensity without a pronounced shift in the emission maximum (Figure 6). The quenching is consistent with changes in the radiative recombination behavior of photogenerated carriers and may also reflect carrier trapping or interfacial interactions. Because the composite contains a lower fraction of emissive ferrite, dilution may also contribute to the absolute intensity decrease. Therefore, the PL results are regarded as indirect evidence of altered charge-carrier behavior in CoFe2O4/CS.
Figure 6. Photoluminescence spectra of CoFe2O4 and CoFe2O4/CS.

3.6. XPS Analysis

The XPS survey spectrum of CoFe2O4/CS confirmed the presence of C, N, O, Co, and Fe (Figure 7a). The comparatively weak Co and Fe intensities are consistent with partial coverage of the ferrite domains by the chitosan-rich surface layer rather than an absence of the inorganic phase.
Figure 7. XPS spectra of CoFe2O4/CS: (a) survey spectrum and high-resolution (b) Fe 2p, (c) Co 2p, (d) O 1s, (e) C 1s, and (f) N 1s spectra.
The high-resolution Fe 2p spectrum contained satellite features at 718.1 and 732.4 eV and components assigned to Fe3+ in octahedral and tetrahedral coordination (Figure 7b) [70,71,72]. The Co 2p spectrum (Figure 7c) showed Co2+ spin–orbit components at 779.1/794.5 eV and 781.3/795.8 eV, assigned to Co2+ species at octahedral and tetrahedral sites, respectively, together with satellites at 785.1 and 801.1 eV [70,71,73]. No distinct Co3+ contribution was resolved [74]. These assignments are consistent with the expected mixed-site cation distribution of spinel CoFe2O4.
The O 1s envelope was resolved into components at 530.0, 531.4, and 532.9 eV, attributable to lattice oxygen, carbonyl/defect-associated oxygen, and hydroxyl/ether oxygen from chitosan, respectively (Figure 7d) [71,75]. The C 1s spectrum (Figure 7e) contained contributions from C–C/C–H (284.5 eV), C–N/C–O (286.1 eV), and O–C–O/C=O (287.6 eV), whereas the N 1s spectrum (Figure 7f) showed amino and protonated-amino environments at 399.5 and 400.3 eV [76,77]. The coexistence of ferrite lattice oxygen and chitosan-derived C/N/O environments corroborates the composite structure indicated by XRD and FTIR.
Because XPS measurements of the individual CoFe2O4 and chitosan components were not performed, the present XPS data are used primarily to identify the chemical states and composition of the nanocomposite rather than to quantitatively evaluate interfacial binding-energy shifts.

3.7. BET Analysis and Magnetic Properties

Both materials exhibited type-IV nitrogen adsorption–desorption isotherms with H3 hysteresis, indicating mesoporous structures (Figure 8). CoFe2O4 had a BET surface area of 81.9 m2 g−1 and a pore volume of 0.149 cm3 g−1, whereas CoFe2O4/CS showed corresponding values of 51.3 m2 g−1 and 0.122 cm3 g−1 (Table 2). The decrease is attributable to polymer coverage of ferrite surfaces and partial occupation or shielding of pore space. The mean pore diameter changed only slightly, from 6.8 to 7.4 nm, indicating that mesoporosity was broadly retained [40].
Figure 8. Nitrogen adsorption–desorption isotherms and BJH pore-size distributions of (a) CoFe2O4 and (b) CoFe2O4/CS.
Table 2. The BET surface area, pore volumes, and pore sizes of CoFe2O4 and CoFe2O4/CS.
Room-temperature magnetic hysteresis loops are shown in Figure 9. CoFe2O4 exhibited Ms = 51.5 emu g−1, Mr = 3.8 emu g−1, and Hc = 70.3 Oe. For CoFe2O4/CS, Ms decreased to 31.4 emu g−1, while Mr and Hc increased to 7.46 emu g−1 and 679.8 Oe, respectively. The non-magnetic chitosan fraction may contribute to the lower mass-normalized Ms; however, other effects associated with composite formation cannot be excluded based on the present data. The marked increase in coercivity indicates a change in the magnetic behavior after incorporation into the chitosan matrix.
Figure 9. Room-temperature magnetic hysteresis loops of CoFe2O4 and CoFe2O4/CS. The inset shows the response of CoFe2O4/CS in water to an external magnet.
Despite the lower saturation magnetization, CoFe2O4/CS was rapidly collected from water with an external magnet (Figure 9 inset). This recoverability is operationally important because it enables catalyst removal without filtration and supports repeated use. The textural and magnetic results therefore reveal a deliberate trade-off: chitosan decreases accessible ferrite surface area and magnetization but provides a dispersing, adsorptive, and recoverable composite architecture.

3.8. Photocatalytic Performance and Mechanistic Analysis

3.8.1. Time-Dependent MB Removal and Kinetics

Figure 10 compares dark adsorption, direct photolysis, and light-assisted MB removal. After the dark-equilibration period, CS, CoFe2O4, and CoFe2O4/CS removed 35.1%, 30.5%, and 43.4% of MB, respectively, indicating greater dark MB uptake by the CoFe2O4/CS nanocomposite. Direct photolysis under visible light was weak (12.4% after 120 min). Under illumination, removal increased to 84.6% for CoFe2O4 and 98.5% for CoFe2O4/CS.
Figure 10. (a) Time-dependent MB removal under dark and visible-light conditions and (b) pseudo-first-order kinetic plots for CoFe2O4 and CoFe2O4/CS.
The rate constant increased from 0.016 min−1 for CoFe2O4 to 0.035 min−1 for CoFe2O4/CS (Figure 10b), corresponding to an approximately 2.2-fold enhancement. This enhancement occurred despite the lower BET surface area and wider apparent optical band gap of the composite. This improvement may be associated with the greater dark MB uptake observed for CoFe2O4/CS, reduced ferrite aggregation, and altered charge-carrier behavior at the nanocomposite interface. The reduced ferrite aggregation is consistent with the FESEM/TEM observations showing more spatially separated ferrite domains in the chitosan matrix. XPS indicates the coexistence of ferrite- and chitosan-derived surface chemical environments, including an O 1s component assigned to carbonyl/defect-associated oxygen. The lower PL intensity may be associated with altered radiative recombination behavior, carrier trapping, and/or interfacial interactions. Taken together, these observations may help contextualize the improved photocatalytic performance.

3.8.2. Effect of Initial pH

MB removal increased from 72.6% at pH 3 to 84.7%, 90.9%, and 98.5% at pH 5, 7, and 9, respectively, before decreasing slightly to 96.7% at pH 11 (Figure 11a). The corresponding rate constants were 0.011, 0.016, 0.020, 0.035, and 0.028 min−1 (Figure 11b). Thus, pH 9 provided the highest efficiency and kinetic rate under the investigated conditions.
Figure 11. (a) Effect of initial pH on MB removal and (b) pseudo-first-order kinetic plots at different pH values.
The pH dependence can be discussed in relation to the measured pHPZC of 6.7 (Figure S1) [78,79,80]. In acidic media, protonation of chitosan amino groups has been reported to influence pollutant adsorption in chitosan-based photocatalytic systems [81]. Below pHPZC, the composite surface is on average positively charged, and protonated amino groups may make interactions with cationic MB less favorable. Above pHPZC, the more negative net surface charge may favor interactions between MB and the composite surface. The modest decline at pH 11 may be associated with changes in ionic speciation, surface interactions, and reactive-species chemistry under strongly alkaline conditions [82].
The correspondence between removal efficiency and k indicates that the overall MB removal behavior varied with pH. However, because dark adsorption was not evaluated separately at each pH, the respective contributions of adsorption and photocatalysis cannot be quantitatively distinguished. The optimum near pH 9 may reflect the combined effects of pH-dependent surface interactions and photochemical oxidation at the composite–solution interface.

3.8.3. Effect of MB Concentration

At initial MB concentrations of 10, 20, 30, and 40 mg L−1, removal efficiencies after 120 min were 99.3%, 98.5%, 90.5%, and 84.1%, respectively (Figure 12a). The decline at higher concentrations reflects saturation of a finite number of adsorption/photocatalytic sites and stronger attenuation of incident light by the intensely colored solution [1,2,4]. These effects reduce the ratio of reactive species to dye molecules and slow removal.
Figure 12. (a) Effect of initial MB concentration on removal efficiency and (b) pseudo-first-order kinetic plots at different initial concentrations.
The rate constants decreased from 0.044 to 0.035, 0.019, and 0.015 min−1 as the MB concentration increased from 10 to 40 mg L−1 (Figure 12b). An initial concentration of 20 mg L−1 was selected for subsequent optimization because it retained near-complete removal and a relatively high rate constant while representing a more demanding dye loading than 10 mg L−1.

3.8.4. Effect of Catalyst Dosage

Catalyst dosage controls the number of accessible reaction sites and the fraction of incident light that reaches the suspended particles [83]. CoFe2O4/CS loadings from 0.2 to 1.0 g L−1 were therefore examined (Figure 13).
Figure 13. (a) Effect of CoFe2O4/CS dosage on MB removal and (b) pseudo-first-order kinetic plots at different catalyst dosages.
Increasing the dosage from 0.2 to 0.7 g L−1 raised MB removal from 65.3% to 84.5% and then to 98.5%. The rate constant increased in parallel from 0.009 to 0.015 and 0.035 min−1. The improvement is attributed to the larger number of adsorption and photocatalytic sites and the resulting increase in productive photon absorption [1,4].
At 1.0 g L−1, removal decreased slightly to 96.7% and k to 0.027 min−1. Excess catalyst can increase turbidity, light scattering, and particle shielding and may promote aggregation, thereby lowering the effectively illuminated surface area [2,82]. A dosage of 0.7 g L−1 was therefore selected as the optimum.

3.8.5. Reusability, Reactive Species, and Proposed Mechanism

Under the optimized conditions, MB removal decreased from 98.5% in the first cycle to 96.2%, 95.7%, 92.6%, and 90.3% in cycles 2–5, respectively (Figure 14a). The loss after five cycles was 8.2 percentage points, indicating that most of the initial performance was retained. The gradual decline may result from incomplete desorption of MB/intermediates, partial blockage of pores and active sites, small handling losses during recovery, or progressive surface modification [1,5,83]. Magnetic collection simplified catalyst recovery and is a practical advantage of the composite architecture.
Figure 14. (a) Reusability of CoFe2O4/CS for MB removal over five cycles and (b) effect of EDTA, IPA, BQ, and AgNO3 scavengers on MB removal.
Scavenger tests provided qualitative evidence for the dominant reactive pathways (Figure 14b). In the absence of scavengers, removal was 98.5%. BQ and AgNO3 reduced removal to 83.6% and 87.4%, respectively, suggesting secondary contributions from •O2−- and electron-mediated reactions. EDTA and IPA caused much larger decreases, to 54.8% and 60.7%, indicating that pathways involving photogenerated holes and •OH radicals made major contributions to MB removal [83]. Because EPR/ESR measurements were not performed, these scavenger results should be regarded as indirect evidence of reactive-species involvement rather than direct confirmation of their formation.
The XRD pattern of a separately recovered sample after five irradiation–recovery cycles retained the characteristic spinel reflections with no evident new crystalline phase (Figure 15), indicating good phase-level structural stability after repeated use. To assess metal-ion leaching during repeated photocatalytic use, the concentrations of dissolved Fe and Co in the reaction solution were determined by ICP-OES following the fifth cycle, after separation of the recovered catalyst. Low concentrations of Fe (0.21 mg L−1) and Co (0.06 mg L−1) were detected, indicating limited metal release under the investigated experimental conditions.
Figure 15. XRD patterns of the CoFe2O4/CS catalyst before and after five photocatalytic cycles.
To evaluate the thermodynamic feasibility of the proposed reactive pathways, the conduction-band (ECB) and valence-band (EVB) edge potentials were estimated using Mulliken electronegativity theory [84]:
E V B = χ − E e + 0.5 E g
E C B = E V B − E g
Here, χ is the absolute electronegativity of the semiconductor (5.8 eV for CoFe2O4), Ee is the free-electron energy on the hydrogen scale (4.5 eV vs. NHE), and Eg is the measured optical band gap. Using Eg = 2.61 eV for CoFe2O4/CS gave ECB ≈ −0.005 eV and EVB ≈ +2.605 eV versus NHE. The strongly positive valence-band potential is sufficient for direct hole oxidation and for oxidation of H2O/OH− to •OH, consistent with the strong inhibition caused by EDTA and IPA [85]. By contrast, ECB is less negative than the standard O2/•O2− potential, indicating that direct superoxide generation is not the dominant thermodynamic pathway. The moderate BQ effect may therefore arise from secondary oxygen-reduction routes associated with defects/interfacial states or from non-ideal scavenger selectivity.
The proposed photocatalytic degradation pathway is summarized in Figure 16. Visible-light excitation generates conduction-band electrons and valence-band holes. Interfacial interactions with chitosan and altered charge-carrier behavior may facilitate the participation of photogenerated holes in surface oxidation, where they can oxidize adsorbed MB directly or react with H2O/OH− to form •OH. The greater dark MB uptake observed for CoFe2O4/CS may increase MB availability near the reactive interface. Electrons and oxygen-derived species make a smaller contribution, in agreement with the scavenger results.
Figure 16. Proposed photocatalytic degradation pathway of MB removal over CoFe2O4/CS. In the schematic, e− and h+ denote photogenerated electrons and holes, respectively; Eg represents the band-gap energy, and •OH denotes hydroxyl radicals. Colors are used only for visual distinction.
The dominant reactions can be represented schematically as follows:
CoFe2O4/CS + hν → CoFe2O4/CS (e−(CB) + h+(VB))
H2O + h+(VB) → •OH + H+
OH− + h+(VB) → •OH
MB + •OH/h+(VB) → CO2 + H2O + other products
These reactions describe a proposed degradation pathway rather than demonstrated complete mineralization. The CO2, H2O, and other products presented in Equation (12) and Figure 16 represent possible products of the proposed oxidation pathway. Because total organic carbon/chemical oxygen demand, degradation intermediates, and real-wastewater matrix effects were not evaluated, the present results should be interpreted primarily as evidence of efficient MB removal and decolorization under controlled laboratory conditions.
As summarized in Table 3, the CoFe2O4/CS nanocomposite developed in this work exhibited competitive MB-removal performance compared with previously reported photocatalysts. Under a 30 W visible-light LED, CoFe2O4/CS achieved 98.5% MB removal at an initial concentration of 20 mg L−1 and a catalyst dosage of 0.7 g L−1 within 120 min. In comparison, several reported systems required longer irradiation times of 180–240 min, higher-power light sources, or lower initial MB concentrations to achieve comparable removal efficiencies. For example, CeO2/CoFe2O4 achieved 88.7% removal after 180 min, while g-C3N4/CoFe2O4 reached 97.4% after 180 min. Although direct comparison should be made cautiously because of differences in light sources, catalyst dosages, initial MB concentrations, and other experimental conditions, the present CoFe2O4/CS system demonstrates competitive photocatalytic performance under relatively low-power visible-light LED irradiation. These characteristics suggest its potential for practical dye-removal applications.
Table 3. Comparison of the MB removal performance of CoFe2O4/CS with previously reported photocatalysts.

4. Conclusions

A magnetically recoverable CoFe2O4/CS nanocomposite was prepared by combining lime-juice-assisted CoFe2O4 synthesis with chitosan immobilization. XRD confirmed preservation of the cubic spinel phase, whereas FTIR and XPS supported interfacial interactions between ferrite surface sites and chitosan amino/hydroxyl groups. Chitosan reduced ferrite aggregation and improved dark MB uptake, although it decreased the BET surface area from 81.9 to 51.3 m2 g−1, increased the apparent optical band gap from 2.17 to 2.61 eV, and lowered Ms from 51.5 to 31.4 emu g−1. The composite nevertheless remained magnetically separable and exhibited a lower PL intensity and superior light-assisted removal. Under the optimized conditions (pH 9, 20 mg L−1 MB, 0.7 g L−1 catalyst, 30 W visible-light LED), 98.5% removal was achieved within 120 min with k = 0.035 min−1, approximately 2.2 times the value for pristine CoFe2O4. Removal remained at 90.3% after five cycles, while scavenger experiments indicated major contributions from pathways involving h+ and •OH. This improvement may be associated with the combined effects of greater dark MB uptake, reduced ferrite aggregation, and altered charge-carrier behavior in the CoFe2O4/CS nanocomposite. Overall, these findings support further evaluation of lime-juice-assisted CoFe2O4/CS nanocomposites as magnetically recoverable photocatalysts for MB-containing wastewater.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/applnano7040033/s1, Figure S1: The point of zero charge (pHPZC) of CoFe2O4/CS.

Author Contributions

Conceptualization, N.X.D.; methodology, L.T.H., P.T.M.H. and N.X.D.; investigation and data curation, L.T.H. and P.T.M.H.; validation and supervision, N.X.D.; writing—original draft preparation, L.T.H. and P.T.M.H.; writing—review and editing, L.T.H., P.T.M.H. and N.X.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Vietnam Ministry of Education and Training under grant number B2024-TDV-10.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data supporting the findings of this study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Tran, D.T.; Nguyen, K.-H.; Nghiem, L.D.; Van, H. High-Performance and Easily Recoverable Bismuth Vanadate Based Photocatalyst for Boosting Degradation of Organic Dyes by Visible Light. Ceram. Int. 2026, 52, 24010–24022. [Google Scholar] [CrossRef] [Scilit]
  2. Geldasa, F.T.; Kebede, M.A.; Shura, M.W.; Hone, F.G. Experimental and Computational Study of Metal Oxide Nanoparticles for the Photocatalytic Degradation of Organic Pollutants: A Review. RSC Adv. 2023, 13, 18404–18442. [Google Scholar] [CrossRef] [Scilit]
  3. Ahmadi, B.; Fallah, A.; Ghamarpoor, R.; Jamshidi, M. Methylene Blue beyond the Dye: A Critical Review on Its Role as a Benchmark Pollutant in Photocatalyst Design. Results Chem. 2025, 18, 102910. [Google Scholar] [CrossRef] [Scilit]
  4. Kouser, H.A.; Kumar, E.V.; Kamat, V.; Naik, H.S.B. Photocatalytic Degradation Phenomena of Methylene Blue Dye by ZnFe2O4 Decorated with RGO Nanocomposites under Visible Light Irradiation. Next Nanotechnol. 2026, 9, 100342. [Google Scholar] [CrossRef] [Scilit]
  5. Kumar, H.; Nike, T.; Kaushal, D.; Sheel, V.; Chauhan, V.; Shandilya, P.; Kumar, M. Fabrication of Synergistic CuBi2O4/CaTiO3 Heterojunction towards Methylene Blue Dye Degradation under Sunlight. Nano Trends 2026, 14, 100207. [Google Scholar] [CrossRef] [Scilit]
  6. Rana, M.S.; Putul, R.A.; Salsabil, N.; Kabir, M.T.; Hossain, M.S.; Masum, S.M.; Molla, M.A. Solar-Driven Photodegradation of Methylene Blue Dye Using Al-Doped ZnO Nanoparticles. Appl. Nano 2026, 7, 3. [Google Scholar] [CrossRef] [Scilit]
  7. Stiadi, Y.; Wendari, T.P.; Zilfa; Zulhadjri; Rahmayeni. Tuning the Structural, Magnetic, and Optical Properties of ZnO/NiFe2O4Heterojunction Photocatalyst for Simultaneous Photodegradation of Rhodamine B and Methylene Blue under Natural Sunlight. Environ. Eng. Res. 2022, 28, 220074. [Google Scholar] [CrossRef] [Scilit]
  8. Suharyadi, E.; Muzakki, A.; Nofrianti, A.; Istiqomah, N.I.; Kato, T.; Iwata, S. Photocatalytic Activity of Magnetic Core-Shell CoFe2O4@ZnO Nanoparticles for Purification of Methylene Blue. Mater. Res. Express 2020, 7, 085013. [Google Scholar] [CrossRef] [Scilit]
  9. Malakootian, M.; Asadzadeh, S.N.; Mehdipoor, M.; Kalantar-Neyestanaki, D. A New Approach in Photocatalytic Degradation of Tetracycline Using Biogenic Zinc Oxide Nanoparticles and Peroxymonosulfate under UVC Irradiation. Desalin. Water Treat. 2021, 222, 302–312. [Google Scholar] [CrossRef] [Scilit]
  10. Patnaik, S.; Das, K.K.; Mohanty, A.; Parida, K. Enhanced Photo Catalytic Reduction of Cr (VI) over Polymer-Sensitized g-C3N4/ZnFe2O4 and Its Synergism with Phenol Oxidation under Visible Light Irradiation. Catal. Today 2018, 315, 52–66. [Google Scholar] [CrossRef] [Scilit]
  11. Kumar Das, K.; Sahoo, D.P.; Mansingh, S.; Parida, K. ZnFe2O4@WO3–X/Polypyrrole: An Efficient Ternary Photocatalytic System for Energy and Environmental Application. ACS Omega 2021, 6, 30401–30418. [Google Scholar] [CrossRef] [Scilit]
  12. Ramadan, R.; Uskoković, V.; El-Masry, M.M. Triphasic CoFe2O4/ZnFe2O4/CuFe2O4 Nanocomposite for Water Treatment Applications. J. Alloys Compd. 2023, 954, 170040. [Google Scholar] [CrossRef] [Scilit]
  13. El-Masry, M.M.; El-Shahat, M.; Ramadan, R.; Abdelhameed, R.M. Selective Photocatalytic Reduction of Nitroarenes into Amines Based on Cobalt/Copper Ferrite and Cobalt-Doped Copper Ferrite Nano-Photocatalyst. J. Mater. Sci. 2021, 32, 18408–18424. [Google Scholar] [CrossRef] [Scilit]
  14. Banifatemi, S.S.; Davar, F.; Aghabarari, B.; Segura, J.A.; Alonso, F.J.; Ghoreishi, S.M. Green Synthesis of CoFe2O4 Nanoparticles Using Olive Leaf Extract and Characterization of Their Magnetic Properties. Ceram. Int. 2021, 47, 19198–19204. [Google Scholar] [CrossRef] [Scilit]
  15. Purnama, B.; Suwandi, A.D.; Hartono, R.; Alim, S.; Bawono, T.; Utari, U.; Aldila, H.; Rahwanto, A.; Kusumandari, K. Annealing Temperature Dependence on Magnetic Properties, Crystalline Structure and Photocatalyst Activity of Coprecipitated Cobalt Ferrite (CoFe2O4). J. Phys. Sci. 2023, 34, 75–89. [Google Scholar] [CrossRef] [Scilit]
  16. Yu, W.; Li, Y.; Shu, M.; Liu, C.; Liang, Y.; Mao, Y.; Tan, J.; Liu, Y.; Ai, T. CS/CoFe2O4 Nanocomposite as a High-Effective and Steady Chainmail Catalyst for Tetracycline Degradation with Peroxymonosulfate Activation: Performance and Mechanism. Environ. Geochem. Health 2024, 46, 40. [Google Scholar] [CrossRef] [Scilit]
  17. Zhang, J.; Zhang, S.; Bian, X.; Yin, Y.; Huang, W.; Liu, C.; Liang, X.; Li, F. High Efficiency Removal Performance of Tetracycline by Magnetic CoFe2O4/NaBiO3 Photocatalytic Synergistic Persulfate Technology. Molecules 2024, 29, 4055. [Google Scholar] [CrossRef] [Scilit]
  18. Ibrahim, I.; Belessiotis, G.V.; Elseman, A.M.; Mohamed, M.M.; Ren, Y.; Salama, T.M.; Mohamed, M.B.I. Magnetic TiO2/CoFe2O4 Photocatalysts for Degradation of Organic Dyes and Pharmaceuticals without Oxidants. Nanomaterials 2022, 12, 3290. [Google Scholar] [CrossRef] [Scilit]
  19. Dong, S.; Dai, J.; Yang, Y.; Zada, A.; Qi, K. Extended Interfacial Charge Transference in CoFe2O4/WO3 Nanocomposites for the Photocatalytic Degradation of Tetracycline Antibiotics. Molecules 2024, 29, 4561. [Google Scholar] [CrossRef] [Scilit]
  20. Aspe, B.; Malyeyev, A.; Vakilinejad, A.; Menguelti, K.; Michels, A.; Bahlawane, N. Chemical Vapor Deposition of CoFe2O4 Micropillar Arrays with Enhanced Magnetic Properties. J. Alloys Compd. 2022, 890, 161758. [Google Scholar] [CrossRef] [Scilit]
  21. Cedeño-Mattei, Y.; Perales-Pérez, O.; Uwakweh, O.N.C. Effect of High-Energy Ball Milling Time on Structural and Magnetic Properties of Nanocrystalline Cobalt Ferrite Powders. J. Magn. Magn. Mater. 2013, 341, 17–24. [Google Scholar] [CrossRef] [Scilit]
  22. Ahmed, R.; Manik, K.H.; Islam, M.S.; Rhine, A.; Mim, J.J.; Hossain, N. Green Synthesis Methods for Nanoparticles: Principles, Biological Routes, and Physicochemical Approaches toward Sustainable Nanotechnology. Next Mater. 2026, 11, 101929. [Google Scholar] [CrossRef] [Scilit]
  23. Saxena, R.; Kotnala, S.; Bhatt, S.C.; Uniyal, M.; Rawat, B.S.; Negi, P.; Riyal, M.K. A Review on Green Synthesis of Nanoparticles toward Sustainable Environment. Sustain. Chem. Clim. Action 2025, 6, 100071. [Google Scholar] [CrossRef] [Scilit]
  24. Refat, N.M.; Nassar, M.Y.; Sadeek, S.A. A Controllable One-Pot Hydrothermal Synthesis of Spherical Cobalt Ferrite Nanoparticles: Synthesis, Characterization, and Optical Properties. RSC Adv. 2022, 12, 25081–25095. [Google Scholar] [CrossRef] [Scilit]
  25. Alotaibi, A.M.; Alansi, A.M.; Alade, I.; Qahtan, T.F. Green Nanochemistry Approaches for the Sustainable Synthesis of Biomedical Nanomaterials and Their Emerging Applications. Adv. Powder Technol. 2026, 37, 105226. [Google Scholar] [CrossRef] [Scilit]
  26. Kumar, R.; Yadav, V.; Gagnish; Rishu; Bhardwaj, V.K. Green Synthesis of Fe2O3 Nanoparticles Using Sunflower Seed Extract for Enhanced Photodegradation of Rhodamine B. Mater. Chem. Phys. 2026, 360, 132662. [Google Scholar] [CrossRef] [Scilit]
  27. Ger, T.-Y.; Arokia Vijaya Anand, M.; Yang, C.-J.; Yao, C.-H.; Lai, J.-Y. Recent Progress in Green Synthesis of Bioinspired Nanoceria for Therapeutic Applications. Mater. Des. 2026, 267, 116334. [Google Scholar] [CrossRef] [Scilit]
  28. El Ouardy, K.; Akhrouf, A.; Faik, A.; Mir, Y. Green Synthesis of Metal and Metal Oxide Nanoparticles: A Pathway to Sustainable Energy and Sensing Applications. Nanotechnol. Rev. 2026, 15, 20250207. [Google Scholar] [CrossRef] [Scilit]
  29. Alvarado, J.A.; Conzalez, G.S.A.; Arce-Plaza, A.; Reyes-Carmona, S. New Approach in Effective and Reproducible Green Synthesis of Pure ZnO Nanoparticles Using Lemon Juice with Less Solvent and without Strong Base Chemical. Ceram. Int. 2025, 51, 18348–18355. [Google Scholar] [CrossRef] [Scilit]
  30. Jebali, M.; Gómez-Merino, A.I.; Colangelo, G. Influence of the Lemon (Citrus Limon L.) Juice Amount on the Green Synthesis of CuO Nanoparticles: Characterization, Stability and Thermal Conductivity. Ceram. Int. 2025, 51, 72–84. [Google Scholar] [CrossRef] [Scilit]
  31. Mahiuddin, M.; Ochiai, B. Comprehensive Study on Lemon Juice-Based Green Synthesis and Catalytic Activity of Bismuth Nanoparticles. ACS Omega 2022, 7, 35626–35634. [Google Scholar] [CrossRef] [Scilit]
  32. Borowska, M.; Pszczoła, J.; Pawlak, K.; Ruzik, L.; Ombugadu, J.N.; Trzaskowski, M.; Jankowski, K. Microwave-Assisted Green Synthesis of Selenium Nanoparticles Using Citrus Extracts: Insights into Size-Controlled Formation and Surface Characteristics. Colloids Surf. A Physicochem. Eng. Asp. 2025, 725, 137516. [Google Scholar] [CrossRef] [Scilit]
  33. Alam, M.K.; Hossain, M.S.; Tabassum, S.; Bahadur, N.M.; Ahmed, S. Green Synthesis of Nano-MgO Using Lemon Juice for Amplified Photocatalytic Degradation of Organic Pollutants. Open Ceram. 2024, 19, 100625. [Google Scholar] [CrossRef] [Scilit]
  34. Rahman, A.; Akter, S.; Prapti, B.B.R.; Rafsan, A.; Hossain, M.I.; Chouhan, C.S.; Hossain, K.A.; Rahman, M.B.; Siddique, M.P. Green Synthesis of Antibacterial TiO2 Nanoparticles Using Citrus Lemon Extract to Combat MDR Clostridium Perfringens. Environ. Technol. Innov. 2025, 39, 104347. [Google Scholar] [CrossRef] [Scilit]
  35. Kalam, A.; Al-Sehemi, A.G.; Assiri, M.; Du, G.; Ahmad, T.; Ahmad, I.; Pannipara, M. Modified Solvothermal Synthesis of Cobalt Ferrite (CoFe2O4) Magnetic Nanoparticles Photocatalysts for Degradation of Methylene Blue with H2O2/Visible Light. Results Phys. 2018, 8, 1046–1053. [Google Scholar] [CrossRef] [Scilit]
  36. Preethi, S.; Abarna, K.; Nithyasri, M.; Kishore, P.; Deepika, K.; Ranjithkumar, R.; Bhuvaneshwari, V.; Bharathi, D. Synthesis and Characterization of Chitosan/Zinc Oxide Nanocomposite for Antibacterial Activity onto Cotton Fabrics and Dye Degradation Applications. Int. J. Biol. Macromol. 2020, 164, 2779–2787. [Google Scholar] [CrossRef] [Scilit]
  37. Abbas, N.; Rubab, N.; Sadiq, N.; Manzoor, S.; Khan, M.I.; Fernandez Garcia, J.; Barbosa Aragao, I.; Tariq, M.; Akhtar, Z.; Yasmin, G. Aluminum-Doped Cobalt Ferrite as an Efficient Photocatalyst for the Abatement of Methylene Blue. Water 2020, 12, 2285. [Google Scholar] [CrossRef] [Scilit]
  38. Weldekirstos, H.D.; Mengist, T.; Belachew, N.; Mekonnen, M.L. Enhanced Photocatalytic Degradation of Methylene Blue Dye Using Fascily Synthesized G-C3N4/CoFe2O4 Composite under Sun Light Irradiation. Results Chem. 2024, 7, 101306. [Google Scholar] [CrossRef] [Scilit]
  39. Alhokbany, N.; Alshehri, S.M. Highly Porous Chitosan Based Magnetic Polymeric Nanocomposite (PNC) for the Removal of Radioactive, Cs(I) and Sr(II) Ions from Aqueous Solution. J. King Saud Univ. Sci. 2022, 34, 102036. [Google Scholar] [CrossRef] [Scilit]
  40. dos Santos, J.M.N.; Pereira, C.R.; Pinto, L.A.A.; Frantz, T.; Lima, É.C.; Foletto, E.L.; Dotto, G.L. Synthesis of a Novel CoFe2O4/Chitosan Magnetic Composite for Fast Adsorption of Indigotine Blue Dye. Carbohydr. Polym. 2019, 217, 6–14. [Google Scholar] [CrossRef] [Scilit]
  41. Simonescu, C.M.; Tătăruş, A.; Culiţă, D.C.; Stănică, N.; Ionescu, I.A.; Butoi, B.; Banici, A.-M. Comparative Study of CoFe2O4 Nanoparticles and CoFe2O4-Chitosan Composite for Congo Red and Methyl Orange Removal by Adsorption. Nanomaterials 2021, 11, 711. [Google Scholar] [CrossRef] [Scilit]
  42. Ansari, H.; Miralinaghi, M.; Azizinezhad, F. CoFe2O4/Chitosan Magnetic Nanocomposite: Synthesis, Characterization and Application for Adsorption of Acidic Yellow Dye from Aqueous Solutions. Cellul. Chem. Technol. 2019, 53, 191–204. [Google Scholar] [CrossRef] [Scilit]
  43. Ahmad, S.; Shah, S.A.; Ahmed, S. A New Chitosan Schiff Base-Modified Cobalt Ferrite: Mechanistic Insights and Performance Enhancement in Photocatalysis of Rhodamine B Dye and Antibacterial Applications. Int. J. Biol. Macromol. 2024, 283, 136841. [Google Scholar] [CrossRef] [Scilit]
  44. Patterson, A.L. The Scherrer Formula for X-Ray Particle Size Determination. Phys. Rev. 1939, 56, 978–982. [Google Scholar] [CrossRef] [Scilit]
  45. Vichery, C.; Poggi, M.; Bonville, P.; Gacoin, T.; Maurin, I. Post-Synthesis Annealing of Coprecipitated CoFe2O4 Nanoparticles in Silica Matrix. J. Magn. Magn. Mater. 2018, 465, 186–192. [Google Scholar] [CrossRef] [Scilit]
  46. Kumar, P.; Pathak, S.; Singh, A.; Khanduri, H.; Basheed, G.A.; Wang, L.; Pant, R.P. Microwave Spin Resonance Investigation on the Effect of the Post-Processing Annealing of CoFe2O4 Nanoparticles. Nanoscale Adv. 2020, 2, 1939. [Google Scholar] [CrossRef] [Scilit]
  47. Monalisa; Sharma, S.; Satyapal, H.K.; Singh, R.K. Correlation between Lattice Strain and Magnetic Properties Enhancement of Nanocrystalline Cobalt Ferrite with Controlled Annealing. J. Mater. Sci. Mater. Electron. 2021, 32, 23843–23853. [Google Scholar] [CrossRef] [Scilit]
  48. Ali, M.E.A.; Aboelfadl, M.M.S.; Selim, A.M.; Khalil, H.F.; Elkady, G.M. Chitosan Nanoparticles Extracted from Shrimp Shells, Application for Removal of Fe(II) and Mn(II) from Aqueous Phases. Sep. Sci. Technol. 2018, 53, 2870–2881. [Google Scholar] [CrossRef] [Scilit]
  49. Hu, X.; Jia, X.; Zhi, C.; Jin, Z.; Miao, M. Improving the Properties of Starch-Based Antimicrobial Composite Films Using ZnO-Chitosan Nanoparticles. Carbohydr. Polym. 2019, 210, 204–209. [Google Scholar] [CrossRef] [Scilit]
  50. Dananjaya, S.H.S.; Kumar, R.S.; Yang, M.; Nikapitiya, C.; Lee, J.; De Zoysa, M. Synthesis, Characterization of ZnO-Chitosan Nanocomposites and Evaluation of Its Antifungal Activity against Pathogenic. Int. J. Biol. Macromol. 2018, 108, 1281–1288. [Google Scholar] [CrossRef] [Scilit]
  51. Saad, A.; Halim, A.; Azzam, A.M.; El-Wakeel, S.T.; Mostafa, B.B.; Abd El-latif, M.B. Removal of Toxic Metal Ions from Wastewater Using ZnO@Chitosan Core-Shell Nanocomposite. Environ. Nanotechnol. Monit. Manag. 2018, 9, 67–75. [Google Scholar] [CrossRef] [Scilit]
  52. Lazăr, A.I.; Șelaru, A.; Croitoru, A.M.; Motelica, L.; Oprea, O.C.; Trușcă, R.D.; Ficai, D.; Văireanu, D.I.; Ficai, A.; Dinescu, S. Conductive Chitosan–Graphene Oxide Scaffold with Applications in Peripheral Nerve Tissue Engineering. Polymers 2025, 17, 2398. [Google Scholar] [CrossRef] [Scilit]
  53. Fahmy, T.; Sarhan, A. Characterization and Molecular Dynamic Studies of Chitosan–Iron Complexes. Bull. Mater. Sci. 2021, 44, 142. [Google Scholar] [CrossRef] [Scilit]
  54. Tiama, T.M.; Ismail, A.M.; Elhaes, H.; Ibrahim, M.A. Structural and Spectroscopic Studies for Chitosan/Fe3O4 Nanocomposites as Glycine Biosensors. Biointerface Res. Appl. Chem. 2023, 13, 547. [Google Scholar] [CrossRef] [Scilit]
  55. Habtoor, S.S.; Basri, H.B.; Zaini, M.; Rahmawati, A.; Shah, T. Ex Situ Synthesis and Characterization of Chitosan-ZnO Nanocomposites Using ZnO Nanoparticles Prepared by the Precipitation Method. AIMS Mater. Sci. 2025, 12, 686–702. [Google Scholar] [CrossRef] [Scilit]
  56. Milosavljević, N.B.; Ristić, M.Đ.; Perić-Grujić, A.A.; Filipović, J.M.; Štrbac, S.B.; Rakočević, Z.L.; Krušić, M.T.K. Removal of Cu2+ Ions Using Hydrogels of Chitosan, Itaconic and Methacrylic Acid: FTIR, SEM/EDX, AFM, Kinetic and Equilibrium Study. Colloids Surf. A Physicochem. Eng. Asp. 2011, 388, 59–69. [Google Scholar] [CrossRef] [Scilit]
  57. Nordin, N.; Zaini Ambia, N.F.A.; Majid, S.R.; Abu Bakar, N. Efficient Encapsulation of a Model Drug in Chitosan Cathodic Electrodeposition: Preliminary Analysis Using FTIR, UV–Vis, and NMR Spectroscopy. Carbohydr. Polym. 2025, 348, 122830. [Google Scholar] [CrossRef] [Scilit]
  58. Butwong, N.; Thatujirangkul, T.; Kunthadong, P.; Mukdasai, S.; Luong, J.H.T. Molecularly Imprinted Film Based on Chitosan-GQDs Using Citric Acid as a Crosslinker for Creatinine Adsorption and Detection by FTIR-ATR. Results Chem. 2026, 20, 103045. [Google Scholar] [CrossRef] [Scilit]
  59. Kumar, N.S.; Krishnakumar, B.B.; Sobral, A. Bio-Based (Chitosan/PVA/ZnO) Nanocomposites Film: Thermally Stable and Photoluminescence Material for Removal of Organic Dye. Carbohydr. Polym. 2019, 205, 559–564. [Google Scholar] [CrossRef] [Scilit]
  60. Saral Sarojini, K.; Indumathi, M.P.; Rajarajeswari, G.R. Mahua Oil-Based Polyurethane/Chitosan/Nano ZnO Composite Films for Biodegradable Food Packaging Applications. Int. J. Biol. Macromol. 2019, 124, 163–174. [Google Scholar] [CrossRef] [Scilit]
  61. Sharifi, E.; Reisi, F.; Yousefiasl, S.; Elahian, F.; Barjui, S.P.; Sartorius, R.; Fattahi, N.; Zare, E.N.; Rabiee, N.; Gazi, E.P.; et al. Chitosan Decorated Cobalt Zinc Ferrite Nanoferrofluid Composites for Potential Cancer Hyperthermia Therapy: Anti-Cancer Activity, Genotoxicity, and Immunotoxicity. Adv. Compos. Hybrid Mater. 2023, 6, 191. [Google Scholar] [CrossRef] [Scilit]
  62. Suharyadi, E.; Muzakki, A.; Istiqomah, N.I.; Puspitarum, D.L.; Purnama, B.; Djuhana, D. Reusability of Photocatalytic CoFe2O4@ZnO Core-Shell Nanoparticles for Dye Degradation. ECS J. Solid State Sci. Technol. 2022, 11, 023004. [Google Scholar] [CrossRef] [Scilit]
  63. Zhang, J.; Zhao, Y.; Zhang, K.; Zada, A.; Qi, K. Sonocatalytic Degradation of Tetracycline Hydrochloride with CoFe2O4/g-C3N4 Composite. Ultrason. Sonochem. 2023, 94, 106325. [Google Scholar] [CrossRef] [Scilit]
  64. Ashraf, M.A.; Peng, W.; Zare, Y.; Rhee, K.Y. Effects of Size and Aggregation/Agglomeration of Nanoparticles on the Interfacial/Interphase Properties and Tensile Strength of Polymer Nanocomposites. Nanoscale Res. Lett. 2018, 13, 214. [Google Scholar] [CrossRef] [Scilit]
  65. Popa, A.; Toloman, D.; Stefan, M.; Leostean, C.; Silipas, T.D.; Stefan Vasile, B.; Pana, O. High-Efficient Separation of Photoinduced Charge Carriers in CoFe2O4-ZnO Magnetic Heterostructures Mediated by Oxygen Vacancies. Appl. Surf. Sci. 2024, 677, 161059. [Google Scholar] [CrossRef] [Scilit]
  66. Mohammad Hosseini, N.; Sheshmani, S.; Shahvelayati, A.S. Manganese Ferrite-Graphite Oxide-Chitosan Nanocomposite for Efficient Dye Removal from Aqueous and Textile Wastewater under UV and Sunlight Irradiation. Sci. Rep. 2025, 15, 866. [Google Scholar] [CrossRef] [Scilit]
  67. Pawariya, V.; De, S.; Dutta, J. Synthesis and Characterization of a New Developed Modified-Chitosan Schiff Base with Improved Antibacterial Properties for the Removal of Bismarck Brown R. Carbohydr. Polym. Technol. Appl. 2023, 6, 100352. [Google Scholar] [CrossRef] [Scilit]
  68. Sahoo, D.P.; Das, K.K.; Patnaik, S.; Parida, K. Double Charge Carrier Mechanism through 2D/2D Interface-Assisted Ultrafast Water Reduction and Antibiotic Degradation over Architectural S,P Co-Doped g-C3N4/ZnCr LDH Photocatalyst. Inorg. Chem. Front. 2020, 7, 3695–3717. [Google Scholar] [CrossRef] [Scilit]
  69. Das, K.K.; Mohanty, U.A.; Mohanty, R.; Sarangi, P.P.; Sahoo, D.P.; Parida, K. Improving Charge Carrier Separation through S-Scheme-Based 2D–2D WS2/Sulfur-Doped g-C3N4 Heterojunctions for a Superior Photocatalytic O2 Reduction Reaction. ACS Appl. Energy Mater. 2024, 7, 6360–6375. [Google Scholar] [CrossRef] [Scilit]
  70. Arman, M.M.; El-Dek, S.I. Structural, Surface, Magnetic Study and Application of Nanoparticles CoFe2O4, ZnO and Its Nanocomposite. J. Supercond. Nov. Magn. 2023, 36, 1913–1925. [Google Scholar] [CrossRef] [Scilit]
  71. Reyes-Vallejo, O.; Cano, F.J.; Sánchez-Albores, R.; Luévano-Hipólito, E.; Escorcia-García, J.; Torres-Martínez, L.M.; Joseph Sebastian, P. Orange Peel—Derived CoFe2O4 Spinel: A Sustainable Nanocatalyst for Dye Removal, Water Splitting, and CO2 Reduction. Sustain. Mater. Technol. 2026, 47, e01869. [Google Scholar] [CrossRef] [Scilit]
  72. Chen, X.; Wu, C.; Guo, Z. Synthesis of Efficient Cu/CoFe2O4 Catalysts for Low Temperature CO Oxidation. Catal. Lett. 2019, 149, 399–409. [Google Scholar] [CrossRef] [Scilit]
  73. Li, R.; Sun, C.; Liu, J.; Zhen, Q. Sulfur-Doped CoFe2O4 Nanopowders for Enhanced Visible-Light Photocatalytic Activity and Magnetic Properties. RSC Adv. 2017, 7, 50546–50554. [Google Scholar] [CrossRef] [Scilit]
  74. Magno De Lima Alves, T.; Amorim, B.F.; Morales Torres, M.A.; Bezerra, C.G.; Nóbrega De Medeiros, S.; Gastelois, P.L.; Fernandez Outon, L.E.; Augusto De Almeida Macedo, W. Wasp-Waisted Behavior in Magnetic Hysteresis Curves of CoFe2O4 Nanopowder at a Low Temperature: Experimental Evidence and Theoretical Approach. RSC Adv. 2017, 7, 22187–22196. [Google Scholar] [CrossRef] [Scilit]
  75. Aadnan, I.; Zegaoui, O.; Daou, I.; Esteves da Silva, J.C.G. Synthesis and Physicochemical Characterization of a ZnO-Chitosan Hybrid-Biocomposite Used as an Environmentally Friendly Photocatalyst under UV-A and Visible Light Irradiations. J. Environ. Chem. Eng. 2020, 8, 104260. [Google Scholar] [CrossRef] [Scilit]
  76. Zhang, W.; Li, X.; Zou, R.; Wu, H.; Shi, H.; Yu, S.; Liu, Y. Multifunctional Glucose Biosensors from Fe3O4 Chitosan/Graphene Nanocomposites. Sci. Rep. 2015, 5, 11129. [Google Scholar] [CrossRef] [Scilit]
  77. Bashal, A.H.; Riyadh, S.M.; Alharbi, W.; Alharbi, K.H.; Farghaly, T.A.; Khalil, K.D. Bio-Based (Chitosan-ZnO) Nanocomposite: Synthesis, Characterization, and Its Use as Recyclable, Ecofriendly Biocatalyst for Synthesis of Thiazoles Tethered Azo. Polymers 2022, 14, 386. [Google Scholar] [CrossRef] [Scilit]
  78. Chaudhari, R.; Adhale, M.; Bhapkar, A.; Desai, M.; Bhame, S.; Sartale, S.; Kasabe, S.; Bhongale, C. ZnO Nanoparticles Synthesis by Sacrificial Composite Monolith Method and Enhanced Photocatalytic Degradation of Methylene Blue Dye. Sustain. Chem. Environ. 2025, 12, 100295. [Google Scholar] [CrossRef] [Scilit]
  79. Huyen, P.T.M.; Hung, L.T.; Tuyet, P.T.H.; Dan, N.H.; Ha, L.T.V.; Quynh, T.T.N.; Dung, N.X. Synthesis and Characterization of ZnO/Chitosan Nanocomposites for Photocatalytic Degradation of Tetracycline in Water Media. Polymers 2026, 18, 1114. [Google Scholar] [CrossRef] [Scilit]
  80. Gao, X.; Yin, H.; Guo, C.; Yan, B.; Li, M.; Xin, L.; Wu, Z. Comprehensive Removal of Various Dyes by Thiourea Modified Chitosan/Nano ZnS Composite via Enhanced Photocatalysis: Performance and Mechanism. Int. J. Biol. Macromol. 2023, 247, 125677. [Google Scholar] [CrossRef] [Scilit]
  81. Malekkiani, M.; Magham, A.H.J.; Ravari, F.; Dadmehr, M. Facile Fabrication of Ternary MWCNTs/ZnO/Chitosan Nanocomposite for Enhanced Photocatalytic Degradation of Methylene Blue and Antibacterial Activity. Sci. Rep. 2022, 12, 5927. [Google Scholar] [CrossRef] [Scilit]
  82. Saint, U.K.; Chandra Baral, S.; Sasmal, D.; Maneesha, P.; Datta, S.; Naushin, F.; Sen, S. Effect of PH on Photocatalytic Degradation of Methylene Blue in Water by Facile Hydrothermally Grown TiO2 Nanoparticles under Natural Sunlight. JCIS Open 2025, 19, 100150. [Google Scholar] [CrossRef] [Scilit]
  83. Ashouri, F.; Khoobi, M.; Ganjali, M.R.; Karimi, M.S. Construction, Characterization, and Photocatalytic Study of La2Ti2O7/C3N4+xHy and La2Ti2O7/GO Nanocomposites as Efficient Catalysts toward Photodegradation of Harmful Organic Dyes. J. Photochem. Photobiol. A Chem. 2023, 435, 114279. [Google Scholar] [CrossRef] [Scilit]
  84. Varghese, D.; Niranjana, S.R.; Joselene Suzan Jennifer, P.; Muthupandi, S.; Madhavan, J.; Victor Antony Raj, M. Synergistic Design of CuO/CoFe2O4/MWCNTs Ternary Nanocomposite for Enhanced Photocatalytic Degradation of Tetracycline under Visible Light. Sci. Rep. 2025, 15, 320. [Google Scholar] [CrossRef] [Scilit]
  85. Varghese, D.; Joe, M.; Ruban, R.; Joselene, P.; Jennifer, S.; Anniecanisius, D.; Chakko, S.; Muthupandi, S.; Madhavan, J.; Victor, M.; et al. Comprehensive Analysis of NiFe2O4/MWCNTs Nanocomposite to Degrade a Healthcare Waste—Tetracycline. RSC Adv. 2023, 13, 28339–28361. [Google Scholar] [CrossRef] [Scilit]
  86. Seeharaj, P.; Pasupong, P.; Choojun, K. Magnetically Separable CeO2/CoFe2O4 Heterojunction Photocatalysts for Dye Degradation: Characterization and Mechanism. J. Asian Ceram. Soc. 2024, 12, 44–58. [Google Scholar] [CrossRef] [Scilit]
  87. Sudarmono; Istiqomah, N.I.; Budianti, S.I.; Cuana, R.; Puspitarum, D.L.; Mahardhika, L.J.; Chotimah; Suhar-yadi, E. Magnetically Separable and Reusable Fe3O4/Chitosan Nanocomposites Green Synthesized Utilizing Moringa Oleifera Extract for Rapid Photocatalytic Degradation of Methylene Blue. Results Chem. 2024, 7, 101245. [Google Scholar] [CrossRef] [Scilit]
  88. Ichipi, E.O.; Mapossa, A.B.; Costa, A.C.F.M.; Chirwa, E.M.N.; Tichapondwa, S.M. Fabrication and Characterization of Recyclable, Magnetic (CoFe2O4)x/Ag2S-ZnO Composites for Visible-Light-Induced Photocatalytic Degradation of Methylene Blue Dye. J. Water Process Eng. 2023, 54, 104040. [Google Scholar] [CrossRef] [Scilit]
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Article Metrics

Citations

Article Access Statistics

Journal Statistics
Multiple requests from the same IP address are counted as one view.
Hybrid Nanocatalysts Coupled with Advanced Oxidation and Reduction Processes for Emerging Organic Pollutants, Focusing on Design Evidence, Reactor Configurations, and Sustainability Metrics
Previous
Synthetic Receptors for Specific Cell Imaging and Signal Transduction
Next