One of the primary sources of water pollution is the wastewater released from textile industry. In the current research, green magnetized ferrite biochar nanocomposites for the purification of basic dye Blue-XGRRL were prepared and characterized. The optimal pH values to attain maximum adsorption for orange peels/MnFe2O4, peanut shells/CuFe2O4, tree twigs/Ni Fe2O4, and wood/CoFe2O4 were noticed in the basic range of 11 (43.5 mg/g), 10 (37.8 mg/g), 10 (31.9 mg/g), and 10 (14.9 mg/g) at 0.05 g/0.05 L at optimal adsorbent dosage correspondingly. The equilibrium observed within 60 min in order of 45.7, 39.9, 33.9, and 18.9 mg/g for adsorbents. The optimal initial dye concentration 100 mg/L was determined for 46.8, 41.4, 37, and 25 mg/g of dye removal utilizing their corresponding adsorbing material at optimal temperature of 30 °C. The data adhered to Langmuir equilibrium and pseudo-second-order kinetic models. Positive Gibbs free energy values led to the conclusion that the process lacks spontaneity. For Blue-XGRRL dye, the maximum desorption (45.4, 41.9, 36.3, and 23.9%) was achieved. For the first two cycles, the removal efficiencies were constant and then marginally declined in third cycle. These green nanocomposites hold promise for effective adsorption in water treatment, signifying their potential as impactful and sustainable solutions.

  • The maximum adsorption capacity was 46.90, 41.89, 35.33, and 25.09 mg/g, for orange peels/MnFe2O4, peanut shells/CuFe2O4, tree twigs/Ni Fe2O4, and wood/CoFe2O4, respectively.

  • Green ferrite biochar nanocomposites have advantages of easy separation, low cost, and high sorption capacity.

  • Thermodynamic research unveiled a negative enthalpy and entropy, reflecting an exothermic and disorderly nature.

Water is the most plentiful natural resource, responsible for the existence of life on Earth, but only a small percentage (almost 1%) of this reserve is accessible to man for usage (Anjum et al. 2019). Wastewater from industries is a chief cause of pollution (Almasian et al. 2015a). Dye is a contaminant that has been used in a number of industries, involving food, paper, plastics, pharmaceuticals, cosmetics, paper processing, and textiles, as well as petroleum additives (Zaman et al. 2023). Dye types generally fall into three categories: cationic, anionic, and non-ionic. Blue-XGRRL dye is a cationic dye that is used widely in textile industry. According to several studies, cationic dyes which are more readily able to attach to the cytoplasm of cells are more hazardous than other colors used in industry (Safarzadeh et al. 2022). The robustness and resistance of many dyes to microbiological and optical degradation pose a significant challenge for their efficient removal through conventional methods. Hence, the imperative need to eliminate color molecules from wastewater (Khan et al. 2023a).

Many techniques comprising biodegradation, oxidation, and adsorption have been established. The most supreme strategies are sedimentation, screening, precipitation, crystallization, flotation, flocculation, reverse osmosis, electrolysis, and biological treatments, etc. These methods have certain drawbacks, including reduced efficiency, intricate operational environments, an inability to fully eliminate pollutants, a requirement for high energy input, increased costs and complexity, as well as the generation of noxious sludge that leads to secondary pollution (Munir et al. 2023). In the present era, there is a significant demand for a cost-effective, environmentally friendly, and sustainable technology to treat wastewater. This is crucial for expanding water resources and addressing the issue of water pollution (Asefi et al. 2009; Khan et al. 2023d).

Among these options, adsorption has emerged as an economical, environmentally friendly, effective, selective, and highly convenient approach. This is attributed to its low cost, superior efficiency, higher adsorption limit, ease of operation, and the ability to regenerate sorbents. These advantages make adsorption not only suitable for water treatment but also for analytical purposes (Almasian et al. 2015b). Green technology is economical, effective, and ecologically benign when combined with other methods, and it may complement other water management systems (Arami et al. 2007; Yang et al. 2021; Khan et al. 2022b). There are several studies available that show spinel ferrite-based composites are superior adsorbents than many other traditional adsorbents (Das et al. 2020, 2022; Deb et al. 2021; Das & Debnath 2022). Ferrites and biochars (BCs) have been commonly used for electro-deposition. To give BC materials magnetic properties, a variety of magnetic particles were used. Because of its variable iron valence, the spinel ferrite general formula is AFe2O4 (A = Mn, Zn, Ni, Co, etc.), has efficient magnetic properties and structural stability. When these ferrites are combined with BC, the resulting composite should have good magnetic properties as well as efficiency (Beiyuan et al. 2023).

The application of ferrites BC composites for the adsorption of basic dyes has been studied because of the interaction between its negatively charged backbone and positively charged dye ions, which has a larger capacity to adsorb all basic dyes because of its intrinsic cationic character. But there isn't much study on using this ferrite BC combination to get rid of simple dyes. In order to create ferrite BC composite material by incorporating BC, the current research was focused on this issue. In comparison to previous methods, the suggested process is now being considered as a promising solution for the eradication of basic dyes from waste water. Some ferrite-BC composite is presented in Table S1, Supplementary material.

The peculiarity of this process in this instance was that all the biomass-based BC was made in an extremely fine environment, the finished product has a sizable surface area and is repeatable in terms of degree of activation (Khan et al. 2023d). As biomass-based BCs along with ferrite don't generate any additional or toxic material, using them to prepare adsorbent is a very eco-friendly and practical procedure. Orange peels (OP) BC, peanut shells (PS) BC, tree twigs (TT) BC, and wood (W or wood) BC were utilized in the study for BC composites because of their distinctive and alluring behavior in this field, while many biomasses are used for this purpose that were not synthesized before in studies for adsorption of dye, to the best of our knowledge.

In the current experiment, composites of manganese ferrite and orange peels (OP-MnFe2O4 or Mn FBC), copper ferrite and peanut shells (PS-CuFe2O4 or Cu FBC), nickel ferrite and tree branches (TT-NiFe2O4 or Ni FBC), and cobalt ferrite and wood (W-CoFe2O4 or Co FBC) were all bio-synthesized and characterized that was not done before. For the Blue-XGRRL dye's adsorption, nanoferrites were used due to limited study on these. It was thoroughly investigated how dye removal regulating factors, such as pH, timings, adsorbent dosage, and initial dye concentrations, affected the process. Through kinetic and isotherm modeling studies, the adsorption experimental data were also used to investigate the nature of adsorption and its process. The main benefits of this approach were that all the products produced in this study were cost-effective because of the availability of biomass and, most critically, had excellent sorption capacity relative to their mass. The sole challenge in this research was separating the adsorbent from the dye. All of this creates a fantastic adsorbent that can be used for other green technologies, such as microbial fuel cells, to get even better outcomes.

Chemicals and reagents

The chemical store at the University of Agriculture, Faisalabad provided all the analytical-grade chemicals and reagents that were utilized. All chemicals were brought from Sigma-Aldrich. Distilled water, sodium hydroxide (NaOH pellets, 99.99%), ethanol (CH3CH2OH, ≥ 99.5%), iron(II) sulfate heptahydrate (FeSO4·7H2O, ≥ 99%), anhydrous copper chloride (CuCl2, ≥ 99.995%), nickel(II) chloride hexahydrate (NiCl2·6H2O, ≥ 99.9%), potassium permanganate (KMnO4, ≥ 99%), cobalt(II) chloride hexahydrate (CoCl2·6H2O, 98%), cetrimonium bromide (C19H42BrN (CTAB), 99.9%), sodium dodecyl sulfate (C12H25NaO4S (SDS), ≥99.0%).

Preparation of dye solution

Basic dye was acquired from local markets in Faisalabad, Pakistan, and employed without undergoing any additional purification processes. 1 g of dye was added in 1,000 mL of distilled water to make dye stock solutions. Dilution from stock solution prepared dye solutions ranged in concentration from 10 to 50 mg/L (Figure 1).
Figure 1

Structure of Blue-XGRRL (Basic Blue 41).

Figure 1

Structure of Blue-XGRRL (Basic Blue 41).

Close modal

Choice and selection of BC

Collection of different BC materials (OP, PS, TT, and W dust) was carried out through different regions of Punjab in Pakistan. For the purpose of removing debris and other impurities, BC materials were repeatedly washed with distilled water. BCs that had been cleaned were dried in the sunshine followed by oven drying at a temperature of 60 °C overnight. The dried-up BC materials were crushed to powdered form with the help of a flour mill/grinder.

Synthesis of ferrite BC composites

Different types of ferrite BC composites such as manganese ferrite/OP BC composites, copper ferrite/PS BC composites, nickel ferrite/TT BC composites, and cobalt ferrite/W BC composites were synthesized to remove selected dyes up to the maximum extent.

Synthesis of OP/MnFe2O4, PS/CuFe2O4, TT/Ni Fe2O4, and W/CoFe2O4

The process of creating MnFe2O4 BC composites involves a carefully executed two-stage procedure. In the initial phase, the BC is meticulously prepared using OP sourced from the local market in Faisalabad. This raw material is chosen for its abundance and suitability for BC production. To ensure the purity of the BC, the OP undergoes a thorough cleaning process involving rinsing with distilled water to remove any contaminants, including dirt and sand particles. Following the cleaning, the peels are left to sun-dry for a period of 3 days. This extended drying duration not only eliminates moisture but also contributes to the stabilization of the peels. Once adequately dried, the OP are divided and crushed to achieve an average particle size of about 0.5 mm. The next crucial step involves subjecting these processed peels to pyrolysis in a furnace set at 800 °C for a duration of 3 h. During this thermal treatment, the organic components of the OP decompose, leaving behind a stable carbonaceous material known as BC. In the second stage of the process, the BC undergoes further enhancement through the incorporation of manganese ferrite (MnFe2O4). This compound is selected for its unique magnetic and catalytic properties, which can impart specific functionalities to the resulting BC composites. The synthesis of the MnFe2O4 BC composites involves a meticulous mixing process to ensure the uniform distribution of manganese ferrite throughout the BC matrix. This careful amalgamation promotes homogeneity and synergistic effects in the final composites (Amin et al. 2019). After pyrolysis, the powdered BCs were sieved to 300-μm mesh size and stored in an air tight bag for the further experiment. In the second stage, the manganese ferrite BC composites were prepared through the co-precipitation method. For this, 100 mL of 0.3 M solution of FeSO4·7H2O was prepared and marked as suspension A. Then, 100 mL of 0.1 M solution of potassium permanganate were also prepared and added into suspension A. After that the stirring of the resulting mixture was done for 5 h at 200 rpm. To keep the solution's pH at about 10, 1 M solution of NaOH was applied drop by drop to the mixture. It makes use of it to enhance their crystallinity, controllable nanoscale, and magnetic characteristics. This is a prerequisite for the nanoparticles to precipitate. The solution exhibited a dark brown color initially. Subsequently, the precipitate was washed using distilled water until a colorless solution was achieved. This process aimed to eliminate side products and any additional BC material associated with the precipitate. The material obtained at the end was nominated as MnFe2O3-BC composites.

The PS/copper ferrite BC composites were prepared in a manner similar to that described above for OP/MnFe2O4 BC composites, with a slight modification involving the use of anhydrous CuCl2. Consequently, a blackish-colored composite was obtained, which was then subjected to centrifugation and rinsed with distilled water until a colorless filtrate was achieved. Similarly, the BC composites of TT/nickel ferrite and W/cobalt ferrite were prepared using a method analogous to the one outlined for OP/MnFe2O4 BC composites, with a slight modification involving the use of NiCl2·6H2O and CoCl2·6H2O chemicals. The resulting composite exhibited a dark brown color (Figure 2).
Figure 2

Synthesis of ferrite BC composites.

Figure 2

Synthesis of ferrite BC composites.

Close modal

Batch experimental program

Batch adsorption studies were employed to assess the effectiveness of OP/MnFe2O4, PS/CuFe2O4, TT/Ni Fe2O4, and W/CoFe2O4. The necessary parameters, including solution pH, adsorbent dose, dye contact duration, temperature, and initial dye concentration, were optimized for the removal of Blue-XGRRL dye using conventional techniques. Erlenmeyer flasks, each containing 50 mL of dye solution with a defined pH and a specific quantity of adsorbent, were placed in an orbital shaker (PA250/25H) at a shaking rate of 120 rpm. The pH was adjusted using 0.1 M HCl and NaOH solutions within the range of 2–12. The sorbent dose varied from 0.05 to 0.4 g, the contact period ranged from 3 to 90 min, the initial dye concentration spanned from 10 to 400 mg/L, and the temperature was maintained between 30 and 65 °C.

Samples were withdrawn at predetermined intervals, followed by centrifugation for 20 min at 5,000 rpm to assess the remaining amount of dye in the solution. Absorbance at 608.5 nm (λmax) was measured using a UV–Vis spectrophotometer from Schimadzu Company of Japan. The adsorption capacity () in mg/g was determined using the following equation:
formula
(1)
formula
(2)

In this context, represents the initial dye concentration in mg/L, while denotes the equilibrium dye concentration in mg/L. The volume of the solution in liters is represented by V, and W signifies the amount of adsorbent in grams.

Techniques of characterization

The specific surface area was determined using a Micromeritics ASAP-2010C automated analyzer and the Brunauer–Emmett–Teller (BET) method at 77 K. Nano adsorbents were observed through scanning electron microscopy (SEM) analysis using an S-3400N HITACHI Japan instrument. X-ray diffraction (XRD) experiments were carried out on a D/max-3B diffractometer with Cu K irradiation and a scan rate of 0.02° 2θs−1 to identify existing phases and determine crystallite sizes. Thermo Nicolet's Fourier Transform Infrared (FTIR) Spectroscopy was utilized to identify functional groups. Energy-dispersive X-ray (EDX) was employed for elemental identification.

Characterization

FTIR analysis can be utilized to identify active binding functional groups capable of absorbing contaminants. In the study of several hybrid materials, FTIR spectra were examined before and after the adsorption of dyes with wavelengths ranging from 400 to 4,000 cm−1. Figure 3 and 4 display the FTIR spectra of OP/MnFe2O4, PS/CuFe2O4, TT/Ni Fe2O4, and W/CoFe2O4 before and after the adsorption of Blue-XGRRL dye. The FTIR spectra of unloaded materials revealed various peaks, indicating the complexity of the materials. Peaks in the range of 3,217–3,427 cm−1 indicated the presence of –NH and bound –OH functional groups, while peaks at 2,829–2,930 cm−1 confirmed the existence of methyl and methylene groups stretching the C–H bond. Peaks observed at 1,603–1,794 cm−1 signified carbonyl group stretching due to a unionized carboxylate functional group and carbonyl stretching due to a carboxylic acid with a hydrogen bond. Peaks from 1,405 to 1,461 cm−1 denoted symmetric bending of the CH3 group, and those at 1,501–1,575 cm−1 indicated the presence of secondary amines.
Figure 3

FTIR spectrum of untreated (a) OP/MnFe2O4; (b) PS/CuFe2O4; (c) TT/Ni Fe2O4; and (d) W/CoFe2O4.

Figure 3

FTIR spectrum of untreated (a) OP/MnFe2O4; (b) PS/CuFe2O4; (c) TT/Ni Fe2O4; and (d) W/CoFe2O4.

Close modal
Figure 4

FTIR spectrum of treated (a) OP/MnFe2O4; (b) PS/CuFe2O4; (c) TT/Ni Fe2O4; and (d) W/CoFe2O4.

Figure 4

FTIR spectrum of treated (a) OP/MnFe2O4; (b) PS/CuFe2O4; (c) TT/Ni Fe2O4; and (d) W/CoFe2O4.

Close modal

The peaks at 1,392–1,121 cm−1 showed that stretching vibrations of the –NH and –SO3 as well as the –CO contributed. Peaks due to C–O–C vibrations arise between 1,000 and 1,091 cm−1. Bands that form in the finger print zone, which is lower than 1,000 cm−1, are challenging to identify owing to the intricacy of vibrations. Spectra bands at 3,112–3,427 cm−1 emerged with much increased intensity in dye and effluent-loaded samples, indicating active engagement of hydroxyl and amine groups when associating with the sorbent surface. Bands between 2,829 and 2,930 cm−1 that appeared in loaded spectra were slightly shifted, indicating the participation of functional groups involved in dye binding. The insertion of secondary amines and the C = O group responsible for the binding of dye cations caused the bands at 1,501–1,575 cm−1 and 1,603–1,794 cm−1 to shift. In this approach, FTIR spectra aided the identification of functional groups that were active and caused dye cations to adsorb (Bai et al. 2015; Chen et al. 2019).

Figure 5(a) illustrates the patterns of OP/MnFe2O4, PS/CuFe2O4, TT/Ni Fe2O4, and W/CoFe2O4 before and after adsorption. In the figure, the diffraction pattern displays an amorphous broadband with maximum intensity at 2θ = 25.00°, attributed to the BC. The ferrite exhibits a well-defined crystalline structure, with peaks at 29.91°, 35.40°, 38.90°, 43.13°, 57.28°, and 62.28°, corresponding to the (220), (311), (222), (400), (511), and (440) spinel planes of magnetized ferrite BC composites (Zhao et al. 2020).
Figure 5

(a) XRD patterns before the adsorption and (b) BET studies of magnetized ferrite BC composites.

Figure 5

(a) XRD patterns before the adsorption and (b) BET studies of magnetized ferrite BC composites.

Close modal

N2 physisorption measurement is shown in Figure 5(b); the N2 physisorption isotherm can be classified as type IV. It was done on the composite to find out about the surface area, typical pore size, and pore volume of the adsorption pores that had formed on the adsorbent surface. The graph representing the composite's N2 adsorption-desorption isotherm was constructed in Figure 5(b) and tested under ambient circumstances. In terms of surface area, total pore size, and pore volume, the W/CoFe2O4 composite was found to have values of 45.93 m2/g, 4.22 nm, and 0.3683 cm3/g, respectively. Tree TT/NiFe2O4 has surface area, total pore size, and pore volume of 70 m2/g, 2.65 nm, and 0.125 cm3/g, respectively, while PS/CuFe2O4, has 75.0 m2/g, 2.44 nm, and 0.182 cm3/g, respectively. The composite clearly exhibits a high surface area, larger pore size, and high pore volumes based on the aforementioned observations. Composites made of OP/ MnFe2O4 have BET surface areas and total pore volumes of 181.2 m2/g and 0.2957 cm3/g, respectively. The average pore size of OP/ MnFe2O4 composites was proven to be 6.21 nm, which is a part of the mesoporous structure (2–50 nm), as measured by the desorption branch (Chen et al. 2021).

SEM methods were used to analyze the morphological and structural data of the as-synthesized composite before and after adsorption. The distribution of BC was uniform, with ferrite composite build-up on the surface and irregular border sites for the magnetized ferrite BC composite, as shown in Figure 6. It was a completely distinct surface alteration compared to the magnetized ferrite BC composite's bare surface after dye adsorption, which was explained by the fact that dye ions were adsorbed on the surface of the composite (Yin et al. 2021).
Figure 6

SEM images before and after adsorption of (a) OP/MnFe2O4; (b) PS/CuFe2O4; (c) TT/NiFe2O4; and (d) W/CoFe2O4.

Figure 6

SEM images before and after adsorption of (a) OP/MnFe2O4; (b) PS/CuFe2O4; (c) TT/NiFe2O4; and (d) W/CoFe2O4.

Close modal
EDX spectra illustrated in Figure 7, OP/ MnFe2O4, PS/ CuFe2O4, TT/ NiFe2O4, and W/CoFe2O4 composite are represented in Figure 7. The structure of magnetized ferrite BC composite wherein BC (carbon and oxygen) while iron, manganese, copper, nickel, cobalt, and oxygen characteristic peaks are presented in the spectra. The occurrence of components like Mn, C, N, O, Cu, Cl, Co, Fe, Ni, and P were represented by different spots onto the surface of adsorbents (Leichtweis et al. 2021).
Figure 7

EDX spectrum of OP/MnFe2O4, PS/CuFe2O4, TT/Ni Fe2O4, and W/CoFe2O4.

Figure 7

EDX spectrum of OP/MnFe2O4, PS/CuFe2O4, TT/Ni Fe2O4, and W/CoFe2O4.

Close modal

Adsorption selectivity

A series of batch adsorption experiments were conducted for (a) reactive red 195 (RR 195) and (b) basic blue 41 (Blue-XGRRL) with an initial concentration of 100 mg/L, and the adsorption capacity at various contact times was displayed in Figure 8 to investigate the selectivity of the magnetized ferrite BC composites. Figure 8 shows that the OP-MnFe2O4, PS-CuFe2O4, TT-NiFe2O4, and W-CoFe2O4 had high (b) Blue-XGRRL adsorption capacities (38, 35, 32, and 22 mg/g) but very low adsorption capacities for (a) RR 195, demonstrating that these materials were effectively selective adsorbents for basic dyes. Based on their chemical character, the magnetized ferrite BC composites' selectivity for fundamental dyes may be explained. According to the explanation above, the crosslinked shell of the magnetized ferrite BC composites as they were made included an unusually high density of negatively charged hydroxyl and amine groups. Due to strong electrostatic contact, the magnetized ferrite BC composites had great adsorption capacity for the positively charged (b) Blue-XGRRL, whereas extremely poor adsorption capacity was noted for the negatively charged a RR 195 as a result of electrostatic repulsion (Wang et al. 2016).
Figure 8

Selective adsorption of various adsorbents.

Figure 8

Selective adsorption of various adsorbents.

Close modal

Point of zero charge

The point of zero charge (pHpzc) serves as a crucial metric for evaluating the adsorption capacity of a surface and determining the nature of surface binding centers. It represents the pH level at which the charge on the adsorbent surface reaches zero. This point is instrumental in elucidating the electrokinetic characteristics of surfaces. It's important to note that the pHpzc value specifically pertains to media where the determination of potential is influenced by H+ and OH– ions (Yagub et al. 2014). The adsorption of cationic species is more favorable at pH values higher than the pHpzc, while the adsorption of anionic species is favored at pH values lower than the pHpzc. The pHpzc values for the composite materials composed of OP, PS, TT, and W were determined using the solid addition technique (Mall et al. 2006).

The obtained results are presented in Figure 9(a), indicating pHpzc values of 6, 8, 9, and 7 for OP-MnFe2O4, PS-CuFe2O4, TT-NiFe2O4 and W-CoFe2O4, respectively. These findings demonstrate that above these pH levels, the adsorbent material carries a negative charge due to the deprotonation of functional groups on the surface, resulting in electrostatic attraction for dye cations. Conversely, below these pH levels, a positive charge is generated on the adsorbent's surface, repelling cationic dyes. Consequently, the formation of a negative charge on the adsorbent surface renders the adsorption of basic dyes advantageous at pH levels greater than pHpzc.
Figure 9

Effect of (a) point of zero charge; (b) pH (conditions: dose of adsorbent: 0.05 g/50 mL, shaker speed: 120 rpm, temperature: 30 °C, time); (c) adsorbent dosage (conditions: optimal pH, 30 °C temperature, 120 rpm shaking speed, 60 min); (d) contact time (conditions: optimized pH, adsorbent amount: 0.05 g, dye concentration: 50 mgL−1, shaking speed: 120 rpm, temperature: 30 °C); (e) initial concentration of dye (conditions: Optimal pH, adsorbent amount: 0.05 g, shaking speed: 120 rpm, equilibrium time, temperature: 30 °C); (f) temperature (conditions: optimized pH, 0.05 g adsorbent amount, 120 rpm shaking speed, equilibrium time, 50 mgL−1 initial dye concentration) of OP/MnFe2O4, PS/CuFe2O4, TT/Ni Fe2O4, and W/CoFe2O4.

Figure 9

Effect of (a) point of zero charge; (b) pH (conditions: dose of adsorbent: 0.05 g/50 mL, shaker speed: 120 rpm, temperature: 30 °C, time); (c) adsorbent dosage (conditions: optimal pH, 30 °C temperature, 120 rpm shaking speed, 60 min); (d) contact time (conditions: optimized pH, adsorbent amount: 0.05 g, dye concentration: 50 mgL−1, shaking speed: 120 rpm, temperature: 30 °C); (e) initial concentration of dye (conditions: Optimal pH, adsorbent amount: 0.05 g, shaking speed: 120 rpm, equilibrium time, temperature: 30 °C); (f) temperature (conditions: optimized pH, 0.05 g adsorbent amount, 120 rpm shaking speed, equilibrium time, 50 mgL−1 initial dye concentration) of OP/MnFe2O4, PS/CuFe2O4, TT/Ni Fe2O4, and W/CoFe2O4.

Close modal

Furthermore, it was observed that the adsorption of basic dyes is favorable at pH values greater than pHpzc. The adsorption behavior of basic dye was explained based on the pHpzc of the adsorbent. For PANI-TGSd, the pHpzc value was determined to be 5. Consequently, at pH values less than 5, the adsorbent surface becomes cationic due to protonation. Conversely, at pH greater than 5, the surface turns negatively charged due to deprotonation, resulting from a higher concentration of OH̄ ions. Therefore, the favorable medium for the adsorption of Crystal Violet (CV) dye on the material surface is at pH greater than 5, as the material surface acquires a negative charge that facilitates the adsorption of basic dye (CV) (Mashkoor & Nasar 2019).

Parameter optimization

Effect of pH

The pH value provides information about the amount of electrostatic charges on the surfaces of both adsorbing materials and dyes (Salleh et al. 2011). Besides affecting charge on the surface of the sorbent, the pH of the solution also influences the solubility of dyes (Subbaiah & Kim 2016). As a result, the rate of adsorption exhibits variability with changes in the pH of the dye solution. The impact of pH on the adsorption process of a basic dye, utilizing different ferrite BC composites, was investigated over a pH range from 2 to 12, while keeping other conditions constant (0.05 g/50 mL, shaker speed 120 rpm, temperature 30 °C, and time 60 min). The findings indicated that a basic pH was more favorable for the removal of Blue-XGRRL dye. The optimized values of pH for achieving the maximum adsorption capacity of OP-MnFe2O4, PS-CuFe2O4, TT-NiFe2O4 and W-CoFe2O4 for the removal of Blue-XGRRL dye were determined to be 11 (43.5 mg/g), 10 (37.8 mg/g), 10 (31.9 mg/g), and 10 (14.9 mg/g), respectively (Figure 9(b)).

As shown in Figure 9(b), dye absorption rose as the pH of the solution climbed and reached its maximum at pH 11 10, then reduced when the solution's pH level increased to a higher level. The pH points zero charger (pHpzc) can be used to explain this phenomenon. The pHpzc values of OP/MnFe2O4, PS/CuFe2O4, TT/NiFe2O4, W/CoFe2O4 are determined to be 6, 8, and 7, respectively, as stated above. Once the solution's pH exceeds pHpzc, deprotonation of functional groups on the surface that are exhibiting electrostatic attraction for dye cations causes the net surface charge on the solid surface for the adsorbent to turn negative. Due to the presence of negatively charged sites on the adsorbent surface, a proper removal of dye above pHpzc may be seen. Furthermore, even if the surface has a negative charge, it is still possible to produce a dye absorption in the alkaline values. This behavior is explained by the severe rivalry between the dye and hydrogen ions for binding to active sites.

From the aforementioned results, it is evident that the pH of the dye solution plays a crucial role in influencing the adsorptive removal efficiency of basic dyes when using different ferrite BC composite materials. The optimized values of pH for achieving the maximum removal efficiency of basic dye were found to be in a basic environment. This observation aligns with the findings of Rajabi and colleagues, who similarly reported a higher pH value for the adsorption of basic dye and a lower pH value for the adsorptive removal of anionic dye (Rajabi et al. 2015, 2016). The elimination degree of methylene blue by BiFeO3/BC magnetic beads that are connected was influenced by pH. Adsorption amount and the rate of removal both improved significantly when the pH of the mixture was raised from 6.0 to 3.0. With such a pH of 3.0 and a large concentration of H+ cations, the mixture is highly corrosive. As a result, the BiFeO3/BC using the linked magnetic materials is efficient in obtaining methylene blue in basic and moderate conditions (Cai et al. 2020).

Effect of adsorbent dosage

The quantity of adsorbent is crucial for the removal of adsorptive dye as it reflects the adsorbent's capacity for a specific concentration of adsorbate in a stable reaction environment (Mahmoodi et al. 2010; Sadaf & Bhatti 2014). The impact of adsorbent dose (0.050.40 g) on the adsorption of basic dye was investigated for various ferrite BC composites, while maintaining constant reaction conditions (optimized pH, shaker speed 120 rpm, temperature 30 °C, and duration 60 min). The results revealed a decrease in the adsorption capacity of the adsorbent materials (OP-MnFe2O4, PS-CuFe2O4, TT-NiFe2O4 and W-CoFe2O4) from 44.2 to 5.6 mg/g, 38.9 to 4.1 mg/g, 32.6 to 3.1 mg/g, and 16 to 1.6 mg/g, respectively, with an increase in dosage from 0.05 to 0.40 g/50 mL at their optimum pH levels (11, 10, 10, and 10). The optimal dosage for achieving the highest removal of Blue-XGRRL dye for all ferrite composite materials was identified as 0.05 g/50 mL (Figure 9(c)).

According to all of the data above, adding more adsorbent doses caused a decrease in the adsorption of basic dyes. All ferrite BC composite materials were used in the least amount necessary to achieve the highest adsorption of basic dyes (0.05 g/50 mL dosage). The decline in adsorption potential at higher doses can be attributed to the overlapping of binding active sites. This overlap reduces the total surface area available for binding with dye cations and extends the diffusion path, causing a lack of dye molecules to adequately cover all the binding functional active sites on the exterior of the adsorbent. Consequently, this leads to lower solute uptake. Another contributing factor to the reduced adsorption potential of adsorbents at greater material dosages is the incomplete coverage of binding functional active sites by dye molecules (Sadaf et al. 2014; Foroutan et al. 2018). Furthermore, it was noted that an elevated quantity of adsorbent in the dye solution reduces the spacing between adsorbent particles, resulting in numerous active sites becoming vacant. A higher dose also induces aggregation, leading to a reduction in the available surface area for adsorption (Mashkoor & Nasar 2019).

Effect of contact time

The impact of dye contact time between the adsorbing material and adsorbate on the adsorptive removal of Blue-XGRRL dye using various adsorbents was investigated through a batch adsorption experiment with variable times ranging from 3 to 90 min. The results are presented in Figure 9(d), revealing a swift removal of Blue-XGRRL dye within the initial 40 min, reaching equilibrium by the 60th minute. The maximal adsorption capacity (45.7, 39.9, 33.9, and 18.9 mg/g) using various adsorbents (OP-MnFe2O4, PS-CuFe2O4, TT-NiFe2O4, and W-CoFe2O4) were obtained at 60 min of contact time. After that, adsorption capacity did not change considerably with increasing contact period. Hence, the optimum contact times for the blue-XGRRL dye were 60 and 45 min.

The graphs obtained depict that the adsorption process exhibited a rapid initial increase, followed by a gradual slowdown, and eventually reached a constant level after establishing equilibrium. After that, adsorption capacity did not change considerably with increasing contact period. Such adsorption behavior occurs because there are initially more active functional binding locations outside of the adsorbent that subsequently get engaged with adsorbate molecules. Subsequently, when dye molecules start to diffuse into the adsorbent bulk, the adsorption rate decreases. Electrostatic attraction between positively charged dye molecules that have been adsorbed or other positively charged sorbate molecules that are still present in the reaction medium may also contribute to a lower adsorption potential with an increase in reaction time.

Effect of initial concentration of dye

A batch study was conducted to assess the impact of varying initial dye concentration (50 − 400 mg L−1) on the adsorption potential of various BC materials for specific basic dyes at their respective optimal pH, with a dosage of 0.05 g/50 mL adsorbent, temperature set at 30 °C, equilibrium time, and shaking speed of 120 rpm. The highest adsorption capacities of OP-MnFe2O4, PS-CuFe2O4, TT-NiFe2O4, and W-CoFe2O4 for Blue-XGRRL at initial dye concentrations of 100, 200, and 75 mg/L were determined to be 46.8, 41.4, 37, and 21.1 mg/g, respectively (Figure 9(e)).

All findings indicate a significant increase in the adsorption efficiency of all ferrite BC composites with an increase in the initial concentration of the dye, possibly due to reaching the saturation point of the adsorbing material. This trend may be attributed to the presence of a substantial driving force resulting from the initial concentration of the dye, which enhances the diffusion rate of the dye toward the adsorbing material. Additionally, the results reveal a similar trend indicating incomplete adsorption of dye at higher concentrations, suggesting the existence of a saturation limit for each hybrid material beyond which it does not adsorb any more dye. At higher dye concentrations, lower adsorption capacity is observed because the adsorption sites become saturated. In contrast, at lower dye concentrations, all dye molecules already present in the aqueous media are adsorbed on all available binding sites on the adsorbent surface, resulting in a larger capacity for adsorption (Almasian et al. 2015a).

Effect of temperature

Temperature plays a significant role in the adsorptive behavior of dyes, making it a crucial parameter to consider when designing an adsorption system applicable to actual effluents. Under constant reaction conditions, the impact of temperature variations between 30 and 65 °C on the capacity of various adsorbents to remove Blue-XGRRL dye was examined. The adsorption potential of all types of adsorbent materials (OP-MnFe2O4, PS-CuFe2O4, TT-NiFe2O4 and W-CoFe2O4) for removing Blue-XGRRL dye from aqueous solutions considerably decreased from 46 to 28.1, 40.8 to 21.8, 35.3 to 17.2, and 24.8 to 8.8 mg/g, respectively, with an increase in temperature in the range of 30 − 65 °C. All the results indicated a significant decrease in the adsorption potential of all adsorbents for removing Blue-XGRRL dye, suggesting the exothermic nature of the adsorption processes. The maximum adsorption capacity for all adsorbent materials was achieved at 30 °C for the removal of the basic dye (Figure 9(f)).

All the data pointed toward a significant reduction in the capability of all adsorbents to remove basic dyes, indicating the exothermic nature of all adsorption pathways. The maximum adsorption capacity for removing all basic dyes using all adsorbent materials was observed at 30 °C. The decline in the adsorption of basic dyes at higher temperatures may be attributed to the weakening of the sorption forces responsible for attaching the dye ions to the adsorbent surface. It also investigated a substantial impact of rising temperature on basic dye elimination utilizing chitosan aniline composite. A higher dye adsorption was achieved at lower temperatures, and the dye removal decreased as the temperature was increased.

Effect of detergents or surfactants on adsorption of Blue-XGRRL

The study examined the impact of 1% solutions of two detergents (Arial and Bonus) and three surfactants (CTAB, Triton X-100, and SDS) on the efficacy of various adsorbents in removing Blue-XGRRL dye from a water medium. The results are presented in Figure 10(a)–10(d). Additionally, with the addition of the cationic surfactant (CTAB), the findings indicated a relatively greater decrease in the adsorption potential of all adsorbent materials for the corresponding basic dye compared to the impact observed with other adsorbing materials.
Figure 10

Impact of detergents/surfactants on adsorption of basic dyes by (a) Co FBC composites, (b) Ni FBC composites, (c) Cu FBC composites, (d) Mn FBC composites, (e) effect of NaCl electrolytes, and (f) effect of AlCl3·6H2O electrolytes.

Figure 10

Impact of detergents/surfactants on adsorption of basic dyes by (a) Co FBC composites, (b) Ni FBC composites, (c) Cu FBC composites, (d) Mn FBC composites, (e) effect of NaCl electrolytes, and (f) effect of AlCl3·6H2O electrolytes.

Close modal

The observed decrease in adsorption potential when adding the cationic surfactant (CTAB) may be attributed to the development of greater electrostatic repulsive forces between CTAB molecules and dye cations. Similar investigations on the influence of surfactants on the adsorption of dyes (MB and ARG) have shown that an increase in the concentration of CTAB or SDBS leads to a reduction in the adsorption of dyes. This reduction in adsorption can be explained by the competitive adsorption of surfactant molecules with dyes, where surfactants may occupy and deplete active sites on the adsorbent surface. Furthermore, the formation of micelles by dye molecules with the aid of surfactants can lead to an enlargement of dye molecules, making them less adsorbent. The combination of these factors contributes to the overall decrease in adsorption capacity (Hosseini et al. 2016; Abid et al. 2023). Similarly, studies have described a similar impact of the presence of surfactants on the adsorption of a reactive dye using sugarcane bagasse as the adsorbent. The introduction of SDS in the dye solution led to a significant decrease in the adsorption potential of the adsorbents for the reactive dye. This observation further supports the notion that certain surfactants can adversely affect the adsorption capacity of adsorbents for various dyes.

Effect of electrolytes on adsorption of used Blue-XGRRL dye

In the textile industry, a considerable amount of salts is employed during the dyeing of fibers. The quantity of electrolyte in textile effluents plays a crucial role in regulating both electrostatic and non-electrostatic interactions between dye molecules and the surface of the adsorbent. The study investigated the impact of various electrolyte levels ranging from 0 to 0.5 M, including AlCl3·6H2O, on the adsorption capacity of various adsorbent materials for the removal of their corresponding basic dye, Blue-XGRRL, under standard operational conditions. The outcomes are presented in Figure 10(e) and 10(f). The findings from the current study suggest that the adsorption capacity of all the utilized adsorbents for removing their specific basic dyes decreased with an increase in electrolyte concentration. This decrease is attributed to the screening of electrostatic attractive forces between the adsorbent and dye molecules caused by the presence of electrolyte ions (Gong et al. 2005).

Similarly, studies have explored the influence of the ionic concentration of sodium sulfate (Na2SO4) on the adsorption capacity of ferrites. The findings indicated that an increase in ionic concentration decreases the electrostatic repulsive forces among adsorbate molecules, thereby enhancing the adsorption amount. Furthermore, in the study of the impact of increasing amounts of Na2SO4 on Polypyrrole (PPy)/TiO2, it was observed that the rise in salt concentration led to the contraction of the adsorbent and a reduction in pore size, causing a decrease in electrostatic attractive forces between the adsorbent and adsorbate. These factors collectively contributed to a decrease in adsorption capacity. Similarly, the adsorption of a basic dye onto a starch composite of polyacrylonitrile (PAN) was found to decrease in the presence of NaCl, CaCl2, KNO3 and MgSO4. Additionally, the presence of NaNO3 salt (0.04 − 0.2) decreased the adsorption ability of Pyracantha coccinea for the removal of acid red 44 dye by 15%. This behavior was attributed to nitrate anions competing with sulfonate groups belonging to the dye for binding sites on the adsorbent surface (Akar et al. 2010).

Desorption/ stability, and ion leaching studies

Through desorption experiments, it may be possible to recover both adsorbent and adsorbate. The degree of reusability of an adsorbent can guarantee its suitability for use on a wider industrial scale (Almasian et al. 2015b). Desorption of basic dye Blue-XGRRL from most effective adsorbents (OP-MnFe2O4, PS-CuFe2O4, TT-NiFe2O4 and W-CoFe2O4) was conducted utilizing 0.05 N concentration of several eluents (HCl, CH3COOH, Ethanol, NH4OH, and NaOH) correspondingly. The findings are shown in Figure 11(a), which shows that utilizing various eluents and the most efficient adsorbents resulted in varying percentages of desorption for basic dyes. Using 0.05 N HCl, the maximum percentage desorption of basic dyes was attained (39.8, 35.3, 30.3, and 20.2%). Additional research was done to examine the effects of different HCl concentrations from 0.05 to 1 Normal on elution efficiency. The results are displayed in Figure 11(b). According to the results, elution performance improved when HCl concentration increased to 0.5 N. For the adsorbed Blue-XGRRL dye, the maximum desorption (45.4, 41.9, 36.3, and 23.9%) was achieved using 0.5 N HCl. After then, every further rise in HCl content caused the dye to desorb to a lesser extent.
Figure 11

Desorption behavior of basic dye utilizing (a) different agents, (b) variable concentrations (N) of HCl, (c) regeneration cycle, and (d) ion leaching.

Figure 11

Desorption behavior of basic dye utilizing (a) different agents, (b) variable concentrations (N) of HCl, (c) regeneration cycle, and (d) ion leaching.

Close modal

The adsorbent's regeneration ability (Figure 11(c)) was examined. The nano adsorbent was repeatedly cleaned with distilled water after adsorption, and it was then briefly dried at 25 ± 2 °C before being used again for adsorption. For the first two cycles, the removal efficiencies were constant and then marginally declined. The elimination efficiency was further decreased to 40.01–19% after the second cycles. The decline in adsorbent absorption efficiency may be caused by the nanocomposite's loss of surface shape after repeated washings (Ajibade & Nnadozie 2022). Magnetized ferrite BC composites' potential for leaching was investigated. However, as can be seen from the Figure 11(d), the concentrations of magnetized ferrite BC composites in the leachate were determined to be extremely low. This could be because the behavior of magnetized ferrite BC composites during their dissolution and precipitation varies depending on the pH of the solution (Devi & Saroha 2015). The highest % desorption of dye was achieved with 0.5 M concentration that was due to greater electrostatic repulsive force among dye ions as well as adsorbent functional groups causing detachment of dye molecules from adsorbent surface.

Kinetic studies

The kinetic parameters were determined using pseudo-first-order kinetics, pseudo-second-order kinetics, intraparticle diffusion kinetics, and Elovich model. Detailed information is available in Supplementary data (Text S1). The results suggest that both pseudo-first-order and pseudo-second-order kinetics are applicable to the kinetic data obtained from batch adsorption experiments for all adsorbents. The selection of the pseudo-second-order model as a better fit was based on higher R2 values (0.99) and the closer agreement between theoretical and experimental qe values. The lower R2 values (0.90–0.92) compared to the other two models indicated a lesser fit of the intraparticle diffusion model to the adsorption data of all adsorbents for the removal of Blue-XGRRL. The pseudo-second-order kinetic model, assuming chemical sorption or chemisorption as the rate-limiting phase, is deemed predictive across the entire adsorption range (Table 1).

Table 1

Kinetic study parameters for the removal of Blue-XGRRL utilizing ferrite composites

Kinetic modelsBlue-XGRRL dye
OP-MnFe2O4PS-CuFe2O4TT-NiFe2O4W-CoFe2O4
Pseudo-first-order     
k1 (Lmin−10.06 0.05 0.05 0.04 
qe exp (mg/g) 45.57 39.88 33.68 18.99 
qe cal (mg/g) 41.39 44.55 45.08 19.93 
R2 0.92 0.93 0.92 0.90 
Pseudo-second-order     
k2 (gm/g min) 0.005 0.003 0.005 0.004 
qe exp (mg/g) 45.76 39.94 33.97 18.93 
qe cal (mg/g) 47.16 42.55 36.76 21.97 
R2 0.99 0.99 0.99 0.99 
Intraparticle diffusion     
Kpi (mg/g. min1/21.67 2.99 3.09 2.89 
Ci 30.9 19.8 18.5 6.23 
R2 0.92 0.95 0.96 0.94 
Elovich kinetic model     
α (mg/mg min−19,112.532 85.40 125.33 8.215 
β (g/mg) 0.275 0.179 0.224 0.259 
R2 0.8268 0.9706 0.975 0.9812 
Kinetic modelsBlue-XGRRL dye
OP-MnFe2O4PS-CuFe2O4TT-NiFe2O4W-CoFe2O4
Pseudo-first-order     
k1 (Lmin−10.06 0.05 0.05 0.04 
qe exp (mg/g) 45.57 39.88 33.68 18.99 
qe cal (mg/g) 41.39 44.55 45.08 19.93 
R2 0.92 0.93 0.92 0.90 
Pseudo-second-order     
k2 (gm/g min) 0.005 0.003 0.005 0.004 
qe exp (mg/g) 45.76 39.94 33.97 18.93 
qe cal (mg/g) 47.16 42.55 36.76 21.97 
R2 0.99 0.99 0.99 0.99 
Intraparticle diffusion     
Kpi (mg/g. min1/21.67 2.99 3.09 2.89 
Ci 30.9 19.8 18.5 6.23 
R2 0.92 0.95 0.96 0.94 
Elovich kinetic model     
α (mg/mg min−19,112.532 85.40 125.33 8.215 
β (g/mg) 0.275 0.179 0.224 0.259 
R2 0.8268 0.9706 0.975 0.9812 

Adsorption isotherms

Important parameters related to Langmuir, Freundlich, Temkin, Harkins-jura and D-R biosorption isotherms such as R2, theoretical and practical qe values for used basic dye Blue-XGRRL, are recorded in Table 2. Detailed text is present in Supplementary data (Text S2). The applicability of mentioned sorption isothermal models on sorption mechanism of chosen basic dyes utilizing their corresponding adsorbents was analyzed. Better fitness to sorption isotherms was decided on behalf of higher value of correlation coefficient (R2) and closeness among qm calculated and qm experimental.

Table 2

Equilibrium study parameters for the removal of Blue-XGRRL dye

Isotherm modelsBlue-XGRRL dye
OP-MnFe2O4PS-CuFe2O4TT-NiFe2O4W-CoFe2O4
Langmuir     
qmcal (mg/g) 48.5 45.0 41.3 26.5 
qmexp (mg/g) 46.86 41.23 37.53 24.46 
b 0.11 0.05 0.03 0.33 
RL 0.22 0.02 0.25 0.03 
R2 0.99 0.98 0.95 0.94 
Freundlich     
qmcal (mg/g) 50.27 40.38 32.16 20.92 
KF 13.24 6.47 3.47 2.36 
n 3.92 2.70 2.14 2.19 
R2 0.74 0.66 0.63 0.57 
Temkin     
qmcal (mg/g) 38.41 32.22 27.57 19.0 
A 2.30 0.53 0.28 0.32 
B 8.00 9.34 9.59 6.00 
R2 0.78 0.73 0.70 0.64 
Harkins-Jura     
qmcal (mg/g) 2.63 4.91 6.89 10.26 
A −27.32 −91.74 −172.41 −370.37 
B −2.09 −2.06 −1.98 −2 
R2 0.53 0.46 0.47 0.32 
Doubinin-Radushkevich     
qmcal (mg/g) 25.83 39.67 48.48 61.68 
β (mol2/kJ22 × 10−5 7 × 10−6 3 × 10−6 6 × 10−7 
E (kJ/mol) 158 267 408.25 912.87 
R2 0.85 0.93 0.84 0.61 
Isotherm modelsBlue-XGRRL dye
OP-MnFe2O4PS-CuFe2O4TT-NiFe2O4W-CoFe2O4
Langmuir     
qmcal (mg/g) 48.5 45.0 41.3 26.5 
qmexp (mg/g) 46.86 41.23 37.53 24.46 
b 0.11 0.05 0.03 0.33 
RL 0.22 0.02 0.25 0.03 
R2 0.99 0.98 0.95 0.94 
Freundlich     
qmcal (mg/g) 50.27 40.38 32.16 20.92 
KF 13.24 6.47 3.47 2.36 
n 3.92 2.70 2.14 2.19 
R2 0.74 0.66 0.63 0.57 
Temkin     
qmcal (mg/g) 38.41 32.22 27.57 19.0 
A 2.30 0.53 0.28 0.32 
B 8.00 9.34 9.59 6.00 
R2 0.78 0.73 0.70 0.64 
Harkins-Jura     
qmcal (mg/g) 2.63 4.91 6.89 10.26 
A −27.32 −91.74 −172.41 −370.37 
B −2.09 −2.06 −1.98 −2 
R2 0.53 0.46 0.47 0.32 
Doubinin-Radushkevich     
qmcal (mg/g) 25.83 39.67 48.48 61.68 
β (mol2/kJ22 × 10−5 7 × 10−6 3 × 10−6 6 × 10−7 
E (kJ/mol) 158 267 408.25 912.87 
R2 0.85 0.93 0.84 0.61 

The Langmuir sorption isotherm was found to fit the equilibrium sorption data of Blue-XGRRL dye better for the respective adsorbents OP-MnFe2O4, PS-CuFe2O4, TT-NiFe2O4, W-CoFe2O4, yielding high values of R2 (0.94 − 0.99) and a close agreement between theoretical and experimentally determined values of qm. In contrast, the Temkin and Harkins-Jura sorption isotherms showed poor fits to the equilibrium sorption data, while the D − R sorption isotherm demonstrated good fitness only for PS-Cu Fe2O4 in the removal of Blue-XGRRL. The results indicate that the Langmuir isotherm model has a greater potential to describe the isotherm behavior of the adsorption process, as the correlation coefficient (R2) calculated using the Langmuir isotherm model is closer to 1 compared to the Freundlich model (0.57–0.74, respectively). Additionally, the value of n is greater than 1, indicating that the adsorption process is physical in nature (Abshirini et al. 2019).

Thermodynamic studies

Thermodynamic analysis is crucial for comprehending the nature of the adsorption process (Mahmoodi et al. 2011). Adsorption thermal data for the removal of Blue-XGRRL dye using their respective adsorbent materials was utilized to determine various thermodynamic parameters, such as the change in Gibbs free energy (ΔG), entropy (ΔS), and enthalpy (ΔH) (refer to Supplementary data (Text S3)). Numerical values for each thermodynamically significant criterion are documented in Table 3. The negative values obtained for ΔH in relation to basic dye indicate that all sorption processes for removing basic dyes are exothermic in nature. Simultaneously, the negative values of ΔS suggest a reduction in disorder at the solid and liquid interface for all sorption processes involved in removing basic dyes using their corresponding adsorbent materials. The positive values of ΔG imply a non-spontaneous nature of the sorption process.

Table 3

Thermodynamic study parameters for removal of Blue-XGRRL dye

Thermodynamic parametersBlue-XGRRL
303308314321327333339
OP-MnFe2O4 
ΔG (kJmol−10.07 1.52 2.82 4.17 5.59 6.93 7.55 
ΔH (kJmol−1−51762.9       
ΔS(J/mol K) −152.02       
PS-CuFe2O4 
ΔG (kJmol−12.20 −0.59 0.89 1.85 2.72 3.61 4.39 
ΔH (kJmol−1−41402.8       
ΔS(J/mol K) −125.60       
TT-NiFe2O4 
ΔG (kJmol−1−3.75 −2.06 −0.77 0.59 1.59 2.54 3.25 
ΔH (kJmol−1−61.29       
ΔS (J/mol K) −116.09       
W-CoFe2O4 
ΔG (kJmol−1−6.57 −3.71 −2.32 −0.70 0.59 1.61 2.24 
ΔH (kJmol−1−76.86       
ΔS(J/mol K) −235.70       
Thermodynamic parametersBlue-XGRRL
303308314321327333339
OP-MnFe2O4 
ΔG (kJmol−10.07 1.52 2.82 4.17 5.59 6.93 7.55 
ΔH (kJmol−1−51762.9       
ΔS(J/mol K) −152.02       
PS-CuFe2O4 
ΔG (kJmol−12.20 −0.59 0.89 1.85 2.72 3.61 4.39 
ΔH (kJmol−1−41402.8       
ΔS(J/mol K) −125.60       
TT-NiFe2O4 
ΔG (kJmol−1−3.75 −2.06 −0.77 0.59 1.59 2.54 3.25 
ΔH (kJmol−1−61.29       
ΔS (J/mol K) −116.09       
W-CoFe2O4 
ΔG (kJmol−1−6.57 −3.71 −2.32 −0.70 0.59 1.61 2.24 
ΔH (kJmol−1−76.86       
ΔS(J/mol K) −235.70       

Proposed mechanism of adsorption

The ferrite-BC composite possesses a substantial surface area for adsorption and exhibits high porosity. Various mechanisms, including metal complexation, hydrogen bonding, and electrostatic interaction through ion-exchange and surface complexation, contribute to the adsorption of dyes onto BC-mediated nanocomposites. The presence of functional groups, such as hydroxyl and carboxyl groups, on the negatively charged surface of the adsorbents enhances the adsorption of dye pollutants through electrostatic contact, representing a crucial process. The affinity of the dye particles and their sorption on the adsorbent's surface are facilitated by functional groups like carbonyl, amine, carboxyl, and hydroxyl. Due to electrostatic contact, the M-O stretching vibration of the ferrite composite has somewhat displaced from its initial location (Karthikeyan et al. 2020). The ionic strength and pH of the solution determine whether it will attract or repel impurities. Through a pore-filling process, the porous design of BC (BC) surfaces reduces the adsorption of dye pollutants. The deposition of modifying agents on BC during the modification mechanism increases BC's surface area, increasing the quantity of adsorbates that may be adsorbed on the surface. The adsorption process of dye onto the activated carbon adsorbent is governed by various intricate mechanisms, with one noteworthy factor being the hydrogen bonding interactions that occur between the functional groups present in activated carbon (specifically, CO and –OH) and the positive ions of the dye. This intermolecular bonding not only plays a crucial role in facilitating the adsorption phenomenon but also contributes to the overall efficacy of the adsorbent. In addition to hydrogen bonding, another significant aspect influencing the adsorption procedure is the occurrence of π–π electron donor-acceptor interactions. These interactions specifically take place between the aromatic rings of the dye and the surface of the adsorbent. The π–π interactions add a layer of complexity to the adsorption dynamics, as they contribute to the overall affinity and binding forces between the dye molecules and the activated carbon surface. In essence, the multifaceted interplay of hydrogen bonding and π–π electron donor-acceptor interactions underscores the intricate nature of the dye adsorption process onto the activated carbon adsorbent (Khan et al. 2022a, 2023b, 2023c; Asghar et al. 2023). Additionally, the ferrite nanoparticles in the ferrite-BC composite have magnetic characteristics, which may potentially aid in the adsorption process (Allahkarami et al. 2022; Murtaza et al. 2022). The ferrite-BC composite's magnetic characteristics make it simple to separate the adsorbent substance from the solution after adsorption. Due to its high adsorption capacity, cheap cost, and ease of separation, the adsorption of basic dyes using ferrite-BC composite is a successful approach for the removal of colors from wastewater (Figure 12).
Figure 12

Possible mechanisms between magnetized ferrite BC composites and dye.

Figure 12

Possible mechanisms between magnetized ferrite BC composites and dye.

Close modal

Comparison of green adsorbents

Table 4 outlines a comparison of the dye removal efficiency between golden marble and its nanocomposites in relation to other adsorbents. The results indicate that the composite materials exhibited a greater capacity for dye removal compared to the previously documented adsorbent.

Table 4

Comparison of green adsorbents

AdsorbentGreen sourceThe maximum adsorption capacityAdsorbateReference
OP/MnFe2O4, PS/CuFe2O4, TT/Ni Fe2O4, and W/CoFe2O4 OP, PS, TT, and W 46.90, 41.89, 35.33, and 25.09 mg/g Basic Blue-XGRRL Dye This study 
Magnetite iron oxide nanoparticles Azolla and fig leaves 30.21 Crystal Violet Alizadeh et al. (2017)  
Azola filiculoides biomass Azola filiculoides aquatic fern 41.73 Reactive Black 5 Balarak et al. (2020)  
Hydrochars Golden shower pod (GSH), coconut shell (CCH), and orange peel (OPH) GSH (59.6 mg/g) > CCH (32.7 mg/g) > OPH (15.6 mg/g) Methylene Green Tran et al. (2017)  
Lignin Lignin 31.2 mg/g Malachite Green Lee et al. (2019)  
Calcium ferrite (CaFe2O4Citric acid (lemon juice) 42.42 mg/g Evans blue Adarsha et al. (2022)  
Activated carbon Khat (Catha edulis) Stem 5.62 mg/g Malachite Green Abate et al. (2020)  
AdsorbentGreen sourceThe maximum adsorption capacityAdsorbateReference
OP/MnFe2O4, PS/CuFe2O4, TT/Ni Fe2O4, and W/CoFe2O4 OP, PS, TT, and W 46.90, 41.89, 35.33, and 25.09 mg/g Basic Blue-XGRRL Dye This study 
Magnetite iron oxide nanoparticles Azolla and fig leaves 30.21 Crystal Violet Alizadeh et al. (2017)  
Azola filiculoides biomass Azola filiculoides aquatic fern 41.73 Reactive Black 5 Balarak et al. (2020)  
Hydrochars Golden shower pod (GSH), coconut shell (CCH), and orange peel (OPH) GSH (59.6 mg/g) > CCH (32.7 mg/g) > OPH (15.6 mg/g) Methylene Green Tran et al. (2017)  
Lignin Lignin 31.2 mg/g Malachite Green Lee et al. (2019)  
Calcium ferrite (CaFe2O4Citric acid (lemon juice) 42.42 mg/g Evans blue Adarsha et al. (2022)  
Activated carbon Khat (Catha edulis) Stem 5.62 mg/g Malachite Green Abate et al. (2020)  

OP/MnFe2O4, PS/CuFe2O4, TT/Ni Fe2O4, and W/CoFe2O4 were used for the adsorption of Blue-XGRRL dye in batch studies. It was characterized by XRD, SEM, EDX, FTIR spectroscopy, and BET analysis. The optimum pH for OP/MnFe2O4, PS/CuFe2O4, TT/Ni Fe2O4, and W/CoFe2O4 were found to be at 11, 10, 10 and 10 respectively, contact time of 60 min, the temperature of 30 °C, the initial chromium ion concentration of 100 mg/L and the adsorbent dose of 0.05 g/mL, and under these conditions, the removal efficiency of dye by the adsorbent with maximum adsorption of 46.90, 41.89, 35.33, and 25.09 mg/g. The pseudo-second-order and Langmuir sorption isotherm were fitted well to the dye sorption data with maximum sorption capacities. All sorption processes to remove basic dyes are exothermic in nature. Furthermore, the use of green adsorbents, such as OP, PS, TT, and W, highlights the environmentally friendly nature of our approach. These readily available and sustainable materials not only demonstrate effective dye removal but also contribute to the promotion of green and eco-friendly solutions for wastewater treatment. The incorporation of BC composites as green adsorbents opens avenues for developing innovative, cost-effective, and environmentally conscious strategies for addressing water pollution challenges. The primary challenge encountered in this research pertained to the separation of the adsorbent from the dye. Future perspectives include exploring wider applications of these adsorbents and further research on their long-term efficacy in diverse environmental conditions, emphasizing their potential significance in sustainable wastewater treatment strategies.

The authors would like to extend their sincere appreciation to the acknowledgment and research supporting project (RSP-2024/95, King Saud University, Riyadh, Saudi Arabia).

All authors have read and approved this manuscript.

H.A. was involved in methodology, conceptualization, writing – original draft, collected resources, S.N. was involved in supervision, conceptualization, formal analysis, writing – reviewing and editing, R.M. was involved in Conceptualization, formal analysis, writing – reviewing and editing, G.A. was involved in resource collection, writing-review and editing, A.M. was involved in statistical analysis, writing-review and editing, M.S. was involved in execution, writing-review and editing, F.Y. was involved in conceptualization, interpretation, A.M. was involved in execution, writing-review and editing.

Research does not involve human participants or/and animals.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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Supplementary data