Experimental and Statistical approach to understand the adsorption properties of hazardous Cr(VI) on Al₂O₃@TiFe₂O₄ nanocomposite: An efficient adsorbent for water treatment

2.1 Materials and Instrumentation

Analytical reagent-grade chemicals and double distilled water (DDW) were used for this experiment. AlCl₃·6H₂O (≥ 99.0 % Pure), TiCl₄ (Purity: ≥99.9 %) and FeCl₃ (Purity: ≥98 %) were of Sigma-Aldrich. Potassium dichromate (K₂Cr₂O₇), phthalic acid, and 1,5-diphenyl carbohydrazide (DPC) were also obtained from Sigma-Aldrich. DPC reagent was prepared by dissolving phthalic acid (12 g) and 0.75 g of 1,5-diphenyl carbohydrazide (0.75 g) in ethanol (300 mL). The adsorbent was characterized by the Equip-Tronics model EQ 610 Digital pH-meter, the Hitachi SU8010 Field FE-SEM, the Jeol Jem 2100 Plus High-Resolution TEM, EDX performed on the same instrument at 30 kev, the Bruker D8-Advance X-ray diffractometer, Bruker Alpha FTIR, and the Shimadzu UV mini-1240 spectrophotometer.

2.2 Preparation of Al₂O₃@TiFe₂O₄ nanocomposite

The synthesis of the Al₂O₃@TiFe₂O₄ nanocomposite involved a meticulous procedure to ensure the formation of a high-quality adsorbent material. Firstly, analytical reagent-grade chemicals including AlCl₃·6H₂O, TiCl₄, and FeCl₃ were carefully measured in appropriate ratios (4:61:35). These precursor salts were then mixed homogeneously in a 500 mL beaker under constant stirring to achieve a uniform distribution. The temperature of the mixture was gradually raised to 75 °C to facilitate the reaction while maintaining the stability of the solution. Subsequently, a controlled amount of 0.5 M NaOH solution was slowly added to the beaker, resulting in the precipitation of the desired nanocomposite material. The formed precipitate was then subjected to thorough washing to remove any impurities or by-products. After washing, the material was dried to remove excess moisture, followed by calcination at 400 °C for 3 h to stabilize its structure. The resulting nanocomposite material was carefully ground into a fine powder to ensure uniformity and maximize surface area, thus enhancing its adsorption properties.

2.3 Cr(VI) removal study

In a batch adsorption absorption process, Cr(VI) ion removal from aqueous solution were performed. This systematic approach helps to determine the optimal adsorption conditions for maximum efficiency. Initially, varying doses of the nanocomposite material (ranging from 0.20 to 2 g/L) were added to separate batches of chromium-containing solutions with 100 rotations per min for different contact times (ranging from 5 to 90 min). The kinetics of chromium adsorption were monitored closely to understand the rate at which the ions were being captured by the adsorbent material. Effect of solution pH on the adsorption process was also investigated by varying the pH of the solutions from 2.0 to 10 by keeping other parameters (adsorbent dose and time contact) constant. All experiment was repeated 3 times to ensure the reproducibility and reliability of the results. Finally, the Cr(VI) ions adsorption capacity of the nanocomposite was determined under all these variable parameters. These batch adsorption studies provided valuable insights into the adsorption behavior and mechanism of the synthesized nanocomposite material, thereby guiding its potential applications in environmental remediation and wastewater treatment processes.

2.4 Studying isotherm, kinetic and thermodynamic study

Thermodynamic and kinetic isotherm are important tools to understand the mechanism of adsorptions properties of an adsorbent (Dastgerdi et al., 2019; Crini et al., 2008; Jethave et al., 2022, Weber, et al., 1974). Necessary equations used for this study are given in the supplement file.

2.5 Statistical study

Statistical physics-based monolayer to multilayer adsorption models are used to study and determine the adsorption layers of the adsorbent. When it comes to mass transfer, measurement, and the interpretation of experimental data, the application of mathematical modeling and process simulation can be extremely helpful.

2.6 Adsorption studies by batch process

The batch adsorption studies were conducted to evaluate the efficacy of the synthesized nanocomposite material in removing Cr(VI) ions from aqueous solutions. A systematic approach was employed to determine the optimal adsorption conditions for maximum efficiency. Initially, varying doses of the nanocomposite material (ranging from 0.20 to 2 g/L) were added to separate batches of chromium-containing solutions. These solutions were then subjected to agitation at 100 rotations per min for different contact times, ranging from 5 to 90 min. The kinetics of chromium adsorption were monitored closely to understand the rate at which the ions were being captured by the adsorbent material. Additionally, the effect of solution pH on the adsorption process was investigated by adjusting the pH of the solutions within a range of 2.0 to 10, while keeping the adsorbent dose and contact time constant. Each experiment was conducted in triplicate to ensure the reproducibility and reliability of the results. The adsorption capacity of the nanocomposite material under various conditions was determined by analyzing the concentration of Cr(VI) ions remaining in the solution after adsorption using suitable analytical techniques. These batch adsorption studies provided valuable insights into the adsorption behavior and mechanism of the synthesized nanocomposite material, thereby guiding its potential applications in environmental remediation and wastewater treatment processes.

3.1 Characterization of Al₂O₃@TiFe₂O₄

The average size range of Al₂O₃@TiFe₂O₄ nanocomposite is 20.79 nm and a minor aggregation, the nanocomposite is shown to be arranged as circular particles, but the surface is not fully plane, as observed in SEM images (Fig. 1a). However, as seen in Fig. 1a the particle densities are regular. The adsorption process benefits from this uniform crystal structure. The TEM image of the synthesized Al₂O₃@TiFe₂O₄ nanocomposite is shown in Fig. 1b to confirm the size of the nanoparticles. In Fig. 1c, before and after adsorption of Cr(VI) the powder X-ray diffraction (XRD) patterns of Al₂O₃@TiFe₂O₄ are depicted, revealing characteristic peaks at specific angles. The alignment of XRD peaks for each metal can be accomplished by referencing the Joint Committee on Powder Diffraction Standards (JCPDS) files. This alignment aids in identifying the crystallographic phases present in the material. Before adsorption the observed peaks at angles 5.03° and 2.71° correspond to the characteristic peaks of aluminum oxide (Al₂O₃) according to the JCPDS-ICDD File No 46–1212 (Feret, 2000). These peaks signify the presence of the cubic lattice structure of Al₂O₃. The peaks at angles 24.35°, 27.65°, 36.65°, 48.95°, and 53.15° can be attributed to the titanium ferrite (TiFe₂O₄) phase. By referencing the JCPDS file number 04–008-6392 for TiFe₂O₄, these peaks align with the hexagonal lattice structure of TiFe₂O₄ (Nouh, 2019). Therefore, the XRD analysis confirms that the synthesized Al₂O₃@TiFe₂O₄ nanocomposite comprises both phases, as indicated by the alignment of peaks with the respective JCPDS files. After adsorption peak at 24.56° is close to the peak at 24.35° before adsorption, suggesting the retention of a similar phase, possibly indicating minimal structural change at this angle and the peak at 47.12° is not directly matching any of the original peaks but close to 48.95°, suggesting a shift in the peak position due to structural changes or interaction with Cr(VI). The peaks at 24.35° shifted to 24.56°, indicating a slight change in the lattice parameters. This could be due to the incorporation or adsorption of Cr(VI) ions into the lattice structure, causing minor distortions. The original peak at 48.95° shifted to 47.12°, indicating a significant change in the lattice structure, possibly due to Cr(VI) adsorption affecting the crystal lattice or forming a new phase. Peaks at 27.65°, 36.65°, and 53.15° disappeared after adsorption, suggesting possible phase transformations, dissolution of specific crystallographic planes, or masking by the adsorbed Cr(VI) layer. The shifts and disappearance of peaks indicate that the crystalline structure of the AlFeTi oxide nanoparticles is altered upon adsorption of Cr(VI). This can be attributed to the interaction of Cr(VI) with the nanoparticle surface, causing changes in the crystallographic planes. The absence of distinct crystal plane reflections may be due to nanocomposite amorphization, nanostructure effects, and strong interactions at the Al₂O₃/TiFe₂O₄ interface, which may obscure traditional crystalline features.

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Fig. 1

Morphological characterization results of Al₂O₃@TiFe₂O₄ adsorbent, (a) SEM image, (b) TEM images, (c) XRD spectra, (d) EDX spectra, (e) before and after FTIR spectrum.

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Fig. 1

Morphological characterization results of Al₂O₃@TiFe₂O₄ adsorbent, (a) SEM image, (b) TEM images, (c) XRD spectra, (d) EDX spectra, (e) before and after FTIR spectrum.

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Fig. 1

Morphological characterization results of Al₂O₃@TiFe₂O₄ adsorbent, (a) SEM image, (b) TEM images, (c) XRD spectra, (d) EDX spectra, (e) before and after FTIR spectrum.

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The EDX spectra of the Al₂O₃@TiFe₂O₄ in Fig. 1(d) show the sample composition via peaks for Al, Ti, Fe, and O are 0.83, 13.34, 9.10, and 15.19 respectively (Table S1). The results agree with the SAED analyses that were done (Venkatrajan et al., 2018).

Fig. 1e shows the FTIR data.

FTIR Data Before Adsorption

Observed Peaks:

3350 cm⁻¹: Typically associated with O–H stretching vibrations, indicating the presence of hydroxyl groups or adsorbed water.

1628 cm⁻¹: Corresponds to bending vibrations of adsorbed water or N–H bending in amines.

1522 cm⁻¹: Generally associated with C = C stretching in aromatic rings or N-O stretching in nitro compounds.

FTIR Data After Adsorption

Observed Peaks:

3334 cm⁻¹: Slightly shifted from 3350 cm⁻¹, still indicating O–H stretching vibrations, but possibly indicating changes in hydrogen bonding environment or interaction with Cr(VI).

1634 cm⁻¹: Slightly shifted from 1628 cm⁻¹, corresponding to bending vibrations of water or N–H bending, suggesting interaction or coordination with Cr(VI).

Shift from 3350 cm⁻¹ to 3334 cm⁻¹: The shift suggests a change in the hydrogen bonding environment, possibly due to the interaction of Cr(VI) with hydroxyl groups on the nanoparticle surface. The presence of Cr(VI) could alter the electron density around the O–H groups, leading to a shift in the stretching frequency.

The shift 1628 cm⁻¹ to 1634 cm⁻¹: The shift indicates a change in the bending vibrations, likely due to the interaction or complexation of Cr(VI) with functional groups on the nanoparticle surface. This shift could be due to changes in the bonding environment of adsorbed water or amine groups.

The disappearance of this peak 1522 cm⁻¹ after adsorption suggests that the functional group responsible for this vibration is either involved in the adsorption process or is altered due to the interaction with Cr(VI). This could indicate that the Cr(VI) ions interact with or disrupt the structure containing aromatic or nitro groups. (Qi et al., 2016).

3.2 Optimization of Al₂O₃@TiFe₂O₄ dose, contact time, pH, Cr(VI) concentration

Different parameters were varied to study adsorption property and to streamline the adsorbent mass. With a fixed Cr(VI) ion concentration of 100 ppm adsorbent property of the of the nanocomposite was investigated with various doses (200–2000 mg) at 25 °C. Fig. 2a shows the effect on the removal efficiency of Cr(VI) with adsorbent vs. mass loaded. The optimal productivity of 92.1 % for Cr(VI) evaluation is achieved by using 200 mg of the adsorbent.

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Fig. 2

Adsorption properties of the Al₂O₃@TiFe₂O₄. adsorbent, (a) Cr(VI) dose, (b) contact time and (c) solution pH optimization.

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Fig. 2b reveals that the nanocomposite is saturated around 60 min and therefore 60 min of contact time is selected as optimum (at 200 ppm and 200 mg). The availability of multiple adsorption sites led to faster adsorption and a Cr(VI) adsorption rate of 84.48 %. The adsorption of Cr(VI) is carried out by pH estimates onto the outer layer of Al₂O₃@TiFe₂O₄. Factors, for example, pores, practical hydrogen gatherings, electrostatic attraction, and pH are utilized to oversee the adsorption capability of Cr(VI) particles (Lesaoana, et al., 2019). Fig. 2c shows that the ideal pH value obtained for better adsorption is 3.0 and A progressive lowering of the adsorption of Cr(VI) is seen when the pH increases. The presence of hydroxyl groups on the surface of Al₂O₃@TiFe₂O₄ in an aqueous solution is responsible for this phenomenon, and the amount of hydroxyl groups changes depending on the pH level. An adsorbent's surface charge reaches neutrality at the point of zero charge (pHpzc). The isoelectric point (pHpzc) of Al₂O₃@TiFe₂O₄ is 5 (supplementary figure S1). Anions adhere to the positively charged adsorbent surface when the pH is below the point of zero charge (pHpzc), and the opposite occurs when the pH is above the pHpzc. Raising the pH results in a greater amount of OH⁻ ions, which then compete with Cr(VI) species (CrO₄²⁻) for the adsorption sites, leading to a reduction in the adsorption of Cr(VI). When the pH is higher than the point of zero charge (pHpzc), an increase in electrostatic repulsion causes the release of the adsorbed HCrO₄⁻ and CrO₄²⁻ into the solution (Ko, 2007, Barad, 2022). The chromium ion takes various forms depending on the pH of the solution. Chromate (CrO₄^-) is the most common form of dichromate (Cr₂O₇^2-) and chromate (CrO₄^-) is the primary type above pH 6.0 at pH 2.0–3.0 of hydrogen chromate (HCrO₄^-). In a chromium adsorption component, the numerous chromate particles appear to assume a huge part. Highest adsorption of chromium was achieved at pH 3.0 as displayed in Fig. 2c.

3.3 Kinetics, Isotherm, and Thermodynamic parameters of chromium adsorption

Different active models are utilized to find the adsorption interaction between the adsorbent (Al₂O₃@TiFe₂O₄) and the pollutant (Cr(VI)). The adsorption information was assessed on the basis of the pseudo-first, and pseudo-second order models to study the working states the synthesized nanocomposite of an adsorbent. Obtained data confirmed that the adsorption of Cr(VI) suited the pseudo-second-request dynamic model (R² = 0.999) (Table 1 and Fig. 3a). The best fitting in the experimental findings is tracked using the three standard isothermal models Langmuir, Freundlich, and Temkin. While monolayer adsorption occurs on a heterogeneous surface with varying strengths in Freundlich, it does so on a uniform surface with the same attraction and energy in Langmuir (Langmuir, 1918). The linearized isotherm and separation factor models for Cr(VI) adsorption onto Al₂O₃@TiFe₂O₄ are displayed in Fig. 3b-3e. Table 1 also provides a summary of the calculated isotherm parameters for Cr(VI) adsorption onto Al₂O₃@TiFe₂O₄ derived from linearized isotherm models. The adsorption behavior of the Al₂O₃@TiFe₂O₄ determined by Freundlich and Temkin are in concurrence with their linearized Langmuir isotherm model, as the R² values are approaching solidarity (Freundlich and Heller, 1939). For the Langmuir, Temkin and Freundlich isotherm models, the R² values are approximately 0.996, 0.9888, and 0.9674, respectively. Results propose that Cr(VI) is consistently circulated on the outer layer of Al₂O₃@TiFe₂O₄ during compound harmony. With the Langmuir isotherm model, all adsorption locales on the outer layer of the adsorbent are indistinguishable and just a single kind of communication happens between the Al₂O₃@TiFe₂O₄ and every adsorbate. The calculated maximum adsorption capacity of Al₂O₃@TiFe₂O₄ for Cr(VI) is about 312.52 mg/g.

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Fig. 3

A) pseudo second order kinetic (b) langmuir (c) freundlich (d) temkin isotherm, (e) separation factor of cr(vi) adsorption by al₂O₃@TiFe₂O₄ nanocomposite.

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Fig. 3

A) pseudo second order kinetic (b) langmuir (c) freundlich (d) temkin isotherm, (e) separation factor of cr(vi) adsorption by al₂O₃@TiFe₂O₄ nanocomposite.

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Fig. 3

A) pseudo second order kinetic (b) langmuir (c) freundlich (d) temkin isotherm, (e) separation factor of cr(vi) adsorption by al₂O₃@TiFe₂O₄ nanocomposite.

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Between 25 and 45 °C, researchers studied how temperature affected Cr(VI) adsorption onto Al₂O₃@TiFe₂O₄. Cr(VI)'s thermodynamic parameters are calculated (Pierott et al., 1974; Lei et al., 2020; Lotfi et al., 2019). At three different temperatures of 25, 35, and 45 °C, the Cr(VI) adsorption onto the surface of Al₂O₃@TiFe₂O₄ is examined under advanced conditions. The unrestricted course of Cr(VI) adsorption is advised by the negative value of ΔG°. The negative value of ΔH°, it can be inferred from Table 1 that the adsorption process is exothermic. Additionally, the observed positive value of ΔS° indicates an increase in entropy after the removal of Cr(VI) at the solid/solution interface.

3.4 Statistical analysis

Fig. 4. presents the application of physics models towards the adsorption isotherms of Cr(VI) on the nanocomposite in different temperature. The experimental data are also found to be well-fitted in this instance. Here the results of the Al₂O₃@TiFe₂O₄ nanocomposite (Model 2) to fit the Cr(VI) adsorption isotherms to the best possible fitting models. Table 2 demonstrates that the double layer model (Models 2) uses parameters such as n, NM, Q_sat, ε₁, ε₂ for Cr(VI) adsorption on Al₂O₃@TiFe₂O₄.

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Fig. 4

Fitting of double layer model at different temperatures.

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The mathematical orientation of the captured Cr(VI) particles on the Al₂O₃@TiFe₂O₄ composite surface (horizontal or vertical) and the system (multi-docking and multi-ionic) are not fixed it is depending the value of n. The horizontal orientation and multi-docking mechanism are associated with n = 1, while the vertical orientation and multi-molecular behavior are associated with n = 2. The n values 0.40, 0.42, and 0.43 were calculated at 25, 35, and 45 °C, respectively shown the horizontal orientation and multi-docking mechanism. When n < 1, a multimolecular bond may be explained by several active sites adsorbing a single molecule or ion, however when n > 1, a multimolecular bond can be explained by a single active site adsorbing many molecules or ions. Fig. 5a shows how the value of n changed with temperature, and Table 2 lists the results of mathematical comparisons (Lotfi and Franco et al., 2019, Jethave et al 2017).

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Fig. 5

Temperature dependence parameters are plotted as, (a) n, (b) Nm, (c) Q_esat, and (d) Energy of adsorption Vs T (K).

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Fig. 5

Temperature dependence parameters are plotted as, (a) n, (b) Nm, (c) Q_esat, and (d) Energy of adsorption Vs T (K).

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Cr(VI) adsorption follow horizontal orientation on the surface of nanoparticle. For Cr(VI)-Al₂O₃@TiFe₂O₄ adsorption, parameter n is determined and recorded as a temperature-dependent on thermal movement in a decrement order (0.364 to 0.358). It should be mentioned that the Cr(VI)-Al₂O₃@TiFe₂O₄ aggregates in the solution lose their bond around 318 K, which reduces the development of layers on the adsorbent's surface.

The effect of temperature on the density of receptor sites (Nm) is shown in Fig. 6b. This boundary uncovered the contrary example of the boundary n. Fundamentally, the accessible region on the Al₂O₃@TiFe₂O₄ surface might be expanded, and subsequently the quantities of fortified Cr(VI) particles on the dynamic locales are decreased because of the accessibility of extra dynamic destinations.

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Fig. 6

Schematic Representation of adsorption mechanism.

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Fig. 5b shows the barrier affects arrangement temperature in single-compound and double frameworks. Temperature increased Cr(VI) and Al₂O₃@TiFe₂O₄ adsorption receptor site density (N_M) in the two systems under study. N_M increased due to a temperature-dependent expansion effect in the Al₂O₃@TiFe₂O₄ structure that created new active sites (Elhadj et al. 2020, Jethave et al., 2022). The exothermic effect that was discovered through the analysis of the experimental data is in line with this outcome. As depicted in Fig. 5b, an increase in the adsorbed quantity was accompanied by an increase in the N_M value, mirroring the control of the new vacant Al₂O₃@TiFe₂O₄ dynamic destinations by the adsorbed particles. This confirmed that Cr(VI) adsorption is more specific to Al₂O₃@TiFe₂O₄ dynamic destinations.

The Langmuir model is used to study Cr(VI) adsorption from aqueous solutions onto Al₂O₃@TiFe₂O₄. No matter the adsorbent, this conventional model holds that the only way Cr(VI) can be adsorbed is through the formation of an adsorbed sheet. At long last, the last fascinating physicochemical boundary is the absolute number of soaked Al₂O₃@TiFe₂O₄ particles. Q_sat (for instance, Q_esat = N*Nm and the model with two-fold layer Q_sat = 2 N*Nm) observed to decrease as the experimental temperature increases (Fig. 5c), which is now confirmed in the explanation of trial data. Calculating the adsorption energy of two practical groupings helps explain the Cr(VI) expulsion procedure. The following formulas quantify half-saturation concentration adsorption energies at 298–328 K, where the energy of adsorption is determined by the following equations.

Adsorption energies (E) values are shown in Fig. 5d for all solution temperatures (25, 35, and 45 °C). At 25, 35, and 45 °C, the El displayed values of 20.05, 22.76, and 23.91 kJmol⁻¹. The values of the E2 at the same succession of solution temperatures were 10.91, 3.58, and 10.15 (Table 2). As a result, the Al₂O₃@TiFe₂O₄ adsorbent's active sites were better able to absorb hexavalent Cr ions due to the adsorption energy (i.e., the Qsat and had the same trend with temperature) (Ibrahim et al. 2019). Additionally, the Cr(VI) ion adsorption onto Al₂O₃@TiFe₂O₄ was related to uptake energies that were all 40 kJmol⁻¹, indicating a physical component to the adsorption phenomenon. It was evident that a larger adsorption energy indicates the second functional group's binding contact, proving their significant role in the elimination of Cr(VI) ions. The Al₂O₃@TiFe₂O₄ and Cr(VI) adsorbents previously described in the literature are compared in Table 2.

3.5 Mechanism

To provide a comprehensive understanding of the adsorption mechanism considering pH and other results, we need to consider various factors such as the surface chemistry of the adsorbent, the chemical properties of the adsorbate, and the influence of pH on the adsorption process. The Al₂O₃@TiFe₂O₄ nanocomposite possesses active surface sites due to its composition of aluminum oxide (Al₂O₃) and titanium ferrite (TiFe₂O₄). These surface sites play a crucial role in adsorbing chromium ions (Cr(VI)) from the solution. pH significantly affects the surface charge of both the adsorbent and the adsorbate species. At lower pH values, the surface of the Al₂O₃@TiFe₂O₄ nanocomposite is positively charged due to protonation of surface hydroxyl groups, while Cr(VI) ions are predominantly present as chromate ions (CrO₄^2-) and dichromate ions (Cr₂O₇^2-) depending on the pH. The positively charged surface of the adsorbent facilitates electrostatic attraction with the negatively charged Cr(VI) species, enhancing adsorption. Under acidic conditions (pH < 7), the predominant Cr(VI) species are dichromate ions (Cr₂O₇^2-) and chromate ions (CrO₄^2-). The positively charged surface of the Al₂O₃@TiFe₂O₄ nanocomposite interacts with the negatively charged Cr(VI) species via electrostatic attraction. Additionally, surface complexation reactions may occur between Cr(VI) ions and functional groups present on the adsorbent surface, such as hydroxyl groups and surface oxide species. The adsorption capacity of the nanocomposite for Cr(VI) ions is influenced by factors such as, contact time, adsorbent dosage, and temperature, as determined from batch adsorption studies.

The low ΔH° value indicates that the dominant mechanism is likely electrostatic attraction between the positively charged surface of the Al₂O₃@TiFe₂O₄ nanocomposite and the negatively charged Cr(VI) species (e.g., chromate and dichromate ions).

The small negative ΔH° also implies that the process is exothermic but not highly energy-intensive, characteristic of weak interactions typical in physical adsorption.

3.6 Regeneration and application to industrial wastewater

Reusability is one of the significant properties of a good absorbent. The initial objective of this study is to choose cost-effective adsorbents after disposal and to minimize the potential environmental impacts regarding sustainable solid waste management. The reusability studies are performed using the optimized experimental conditions for the adsorption of Cr(VI) on the surface of Al₂O₃@TiFe₂O₄. The used adsorbent is successfully gathered using a centrifuge machine and cleaned with HCl (0.1 M) after each adsorption process followed by neutralization with NaOH (0.1 M). A similar process is used after every adsorption cycle. The adsorbent is used for up to five cycles and it is observed that the adsorption efficiency decreases by less than 2 % (Fig. 7 and Table 3). The regeneration performance of the adsorbent is almost constant for up to five cycles. This confirms a substantial balance between its ecological effect and its affordability. The % regeneration efficiency is calculated at the end of each cycle, using the following Eq. (3):

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Fig. 7

Regeneration study (for 100 mg/L concentration of Cr(VI)).

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The synthesized Al₂O₃@TiFe₂O₄ is successfully adopted for the treatment of chemical, metal and textile industrial effluents containing Cr(VI) to achieve a clean environment and save water by recycling it. The % adsorption for Cr(VI) at 93 % with the RSD less than 2 %. Furthermore, experimental data from this study demonstrated the ability and efficiency of the Al₂O₃@TiFe₂O₄ and therefore, it has become an efficient candidate for the treatment of industrial effluents. And superior adsorption capacity as compared to previously reported various adsorbent (Table 4).

The novelty of this work lies in several key aspects that distinguish it from previous studies in the literature, highlighting the significance and necessity of this research:

This study presents the synthesis of a novel nanocomposite material, Al₂O₃@TiFe₂O₄, using the co-precipitation method. While previous studies have investigated various adsorbents for Cr(VI) removal, the synthesis of this specific nanocomposite material is novel and offers unique properties for efficient adsorption. Through a comparison with existing adsorbents reported in the literature, this study highlights the superior adsorption capacity and efficiency of the Al₂O₃@TiFe₂O₄nanocomposite for Cr(VI) removal. This comparative analysis underscores the significance of the synthesized nanocomposite as a promising candidate for industrial effluent treatment. The investigation of the nanocomposite's recyclability, with minimal decrease in adsorption efficiency over multiple cycles, underscores its potential for sustainable use in wastewater treatment applications. This aspect of the study addresses the need for environmentally friendly and cost-effective adsorbents. Overall, this study addresses the gaps in the existing literature by introducing a novel adsorbent material, elucidating its adsorption mechanism, and demonstrating its superior performance for Cr(VI) removal. By highlighting these aspects, the study underscores the importance and relevance of its findings in advancing the field of wastewater treatment and environmental remediation.