The High Performance of Multi-Metal Layered Double Hydroxides (LDHs) in the Removal of Organic Dyes ^†

Abstract

In this work, both MgNiAl-LDH and MgNiFe-LDH hydrotalcites were utilized to remove the anionic dye Congo red (CR) from an aqueous solution. Samples characterization was carried out by X-ray diffraction (XRD), infrared spectroscopy (IR) and Thermogravimetric/Differential Scanning Calorimetry (TG/DSC). Various parameters were investigated, including the initial dye concentration, adsorbent mass, contact time, solution pH, and temperature. Using classical pseudo-first-order, pseudo-second-order, and intraparticle diffusion models, adsorption kinetics were investigated. The dynamical data fit well with the pseudo-second order kinetic model. The equilibrium adsorption data were analyzed using three linear adsorption models: Langmuir, Freundlich, and Temkin. The findings showed that the Langmuir isotherm adequately predicts experimental results with an ideal correlation coefficient. The isothermal Langmuir model revealed a maximum adsorption capacity of q_max of 5548 mg/g for the MgNiFe-LDH and of 4043 mg/g for MgNiAl-LDH. This result is very useful when selecting sorbents to improve removal technology in the aquatic environment.

1. Introduction

The presence of organic pollutants in natural bodies of water is frequently identified, generating concerns about preserving both the environment and public health. Dyes are a complex class of organic compounds with a vast range of applications in industry and in the pharmaceutical field [1]. Large quantities of colorants are wasted, which is detrimental to natural resources [2]. Congo red (CR) is an organic dye, in particular an anionic diazo dye, with two azo bonds. It is produced by linking bis-diazotized benzidine to two molecules of naphthenic acid [3]. CR can alter the biochemical characteristics of freshwater systems, which could have a detrimental effect on aquatic life due to its persistent chemical structure, lack of biodegradability, and toxicity [4]. Furthermore, the presence of these organic pollutants can both raise chemical oxygen demand and decrease biological oxygen demand [5,6]. The development of highly effective, economical, and ecologically friendly wastewater treatment technology is therefore urgently needed. Currently, a number of physical and chemical techniques have been explored to treat contaminated water, including biodegradation [7], photocatalytic degradation [8], flocculation [9,10], and adsorption [11,12,13]. Pollutants are frequently separated from effluents using the adsorption technique. In particular, it is an efficient method that is inexpensive, straightforward, simple to use, and insensitive to harmful materials [14]. The adsorption process has evaluated a wide variety of active materials, mostly to increase their adsorption capacity, lower the cost of preparation, or make them easier to use.

Due to their high anion capacity and higher surface area, layered double hydroxides (LDH) are the subject of extensive research on their; reusability, porosity, and basic properties. Regarding low cost, high adsorption capacity, and non-toxicity, they are more efficient than commercially available adsorbents [15]. LDH, also known as anionic clays, are represented by the general formula [${\mathrm{M}}_{1-\mathrm{x}}^{\mathrm{I}\mathrm{I}}{\mathrm{M}}_{\mathrm{x}}^{\mathrm{I}\mathrm{I}\mathrm{I}}{\left(\mathrm{O}\mathrm{H}\right)}_2]$ (Aⁿ⁻)_x/n.mH₂O, where ${\mathrm{M}}^{2+}$(${\mathrm{N}\mathrm{i}}^{2+}$, ${\mathrm{M}\mathrm{g}}^{2+}$, ${\mathrm{Z}\mathrm{n}}^{2+}$, ${\mathrm{M}\mathrm{n}}^{2+}$) and ${\mathrm{M}}^{3+}$(${\mathrm{A}\mathrm{l}}^{3+}$, ${\mathrm{F}\mathrm{e}}^{3+}$, ${\mathrm{C}\mathrm{r}}^{3+}$, ${\mathrm{C}\mathrm{o}}^{3+}$) represent the divalent and trivalent cations, respectively, and Aⁿ⁻ (OH⁻, CO₃²⁻, NO₃⁻, Cl⁻) the interlayer anions. The electroneutrality of the structure is guaranteed by the Columbian force of attraction between the intercalary anions and the positively charged metals on the LDH layer [16]. Layered double hydroxide is a particularly interesting substance due to the wide range of applications it has, including medication delivery, adsorbents [17], and catalysis [18]. Therefore, it would be fascinating to learn more about how LDH can be used to assess problems brought on by azo-dye pollutants. Among the many LDH species, a hydrotalcite-like substance composed of MgAl-, MgFe-, NiAl-, NiFe-LDH using carbonates as the interlayer anions, is frequently employed for a number of applications [19,20,21]. In this work, three precursor cations were employed to prepare the LDHs. The redox and acid base qualities of LDHs are improved by the isomorphic replacement of another metal. These characteristics play a crucial role in catalysis and adsorption. Hydrotalcites MgNiAl-LDH and MgNiFe-LDH were prepared, characterized by X-ray diffraction powder (XRD), and infrared spectroscopy (IR), Thermogravimetric/Differential Scanning Calorimetry (TG/DSC), then used for adsorption of Congo red (CR).

2. Materials and Methods

Magnesium nitrate hexahydrate Mg(NO₃)₂·6H₂O (≥99.9%), nickel nitrate hexahydrate Ni(NO₃)₂·6H₂0 (≥98.5%), aluminum nitrate nonahydrate Al(NO₃)₃·9H₂O (≥99.99%), ferric nitrate nonahydrate Fe(NO₃)₃·9H₂O (≥99.95%), and Congo red (C₃₂H₂₂N₆Na₂O₆S₂) (>99%) were purchased from the Sigma-Aldrich company. All products were used without further purification.

2.1. Preparation of MgNiAl and MgNiFe-LDH

MgNiAl-LDH with (Mg²⁺ + Ni²⁺)/Al³⁺ molar ratios of 2 was prepared by the co- precipitation method at a constant pH. An aqueous solution containing 0.33 M of Mg(NO₃)₂·6H₂O, 0.33 M of Ni(NO₃)₂·6H₂0, and 0.33 M of Al(NO₃)_3·9H₂O was dissolved in 75 mL distilled water. A mixed base solution, (1 M NaOH and 0.5 M Na₂CO₃) dissolved in 75 mL distilled water, was added dropwise to the stirred mixture at 25 °C until the pH reached 10. The resulting solution was carried out under reflux at 75 °C for 24 h. Afterward, the solution was washed several times with distilled water, filtered, and dried overnight at 60 °C. Finally, LDH powder was obtained [22]. Similarly, pristine MgNiFe-LDH was prepared via the identical co-precipitation method.

2.2. Characterizations

The XRD patterns of the prepared samples at room temperature were collected in the range of 0 ˂ 2θ ˂ 80° using an X-Ray diffractometer (Bruker, D8-Advance) with Cu k_α (λ = 0.15406 nm) radiation operating with 40 mA and 40 KV. The FTIR spectra were recorded from 4000 to 400 cm⁻¹ using the JASCO 4600 FT/IR Spectrometer. TG–DSC curves of the prepared samples were performed using a Thermo-gravimetric analyzer (LABSYS evo SETARAM) under air atmosphere with a heating rate of 10 °C/min from room temperature to 900 °C.

The surface charge of the samples was determined by measuring the pH of zero point charge (pH_ZPC). An amount of 20 mg of the adsorbent was added to 20 mL of a NaCl solution (0.1 M) by using HCl (0.1 M) and/or NaOH (0.1 M) solutions. The initial pH value was adjusted between 2 and 12, and conical flasks with the prepared solutions were agitated on a shaker at 150 rpm for 24 h. The final pH (pH_f) values of the solutions were then measured using a pH meter (pHenomenal^® pH lab set pH 1000 L).

2.3. Kinetic Studies

In this experiment, a solution with a concentration of 1 g/L was prepared by dissolving the appropriate amount of CR in distilled water. After that, the solution was diluted to the required strength (50 and 100 mg/L).

Adsorption kinetics were achieved at room temperature with a contact period varying from 2 to 120 min by adding 20 mg of adsorbent in varied dye concentrations (50 and 100 mg/L).

The following equations was used to compute the amount of CR adsorbed onto LDH:

$$Q_t=\frac{C_0-C_t}{m}·V$$

(1)

where q_t is the amount of adsorbed CR at time t (mg/g); C₀ and C_t are the starting and at time t CR concentrations, respectively (mg/L); V (L) is the volume of the solution and m is the mass of adsorbent (g).

2.4. Adsorption Isotherms

Adsorption isotherm studies of CR were performed by adding 20 mg of adsorbent to a 25 mL batch of CR (20–350 mg/L) prepared from stock solution (500 mg/L) at differential temperatures (298–317 K). The solution was stirred for 30 min and then analyzed by a UV-vis spectrophotometer (JASCO V-730 Double Beam Spectrophotometer) at 498 nm.

The CR amount q_e and its corresponding removal efficiency R (%) at the adsorption time t (min) were respectively calculated by the following equation:

$$Q_e=\frac{C_0-C_e}{m}·V$$

(2)

$$R(\%)=\frac{C_0-C_e}{C_0}·100$$

(3)

where q_e is adsorption capacity at equilibrium; C₀ and C_e (mg/L) are initial and equilibrium CR concentrations respectively; m (g) is the adsorbent mass and V (L) is the volume of the solution.

3. Results and Discussion

3.1. Characterization of Prepared Samples

3.1.1. XRD Analysis

Figure 1 displays the XRD patterns of MgNiAl-LDH (Figure 1a) and MgNiFe-LDH (Figure 1b), where both samples exhibit numerous distinct reflections, such as double-layered hydroxide reflections, at 11.83°, 23.44°, 34.89°, 38.94°, 46.9°, and 62.5°, which correspond to (003), (006), (009), (015), (018), and (110), respectively. The distinctive diffraction peaks of both samples are sharp, fine, and symmetrical, indicating the single crystal phase and the high degree of crystallinity of the sample’s crystal structure [23,24,25].

In accordance with the unit cell parameters of synthesized samples shown in

Table 1. Characteristic parameters of MgNiAl-LDH and MgNiFe-LDH.

Sample	a (Å)	c (Å)	basal Spacing d003 (Å)	Interlayer Distance d (Å)
MgNiAl-LDH	3.031	22.438	7.479	2.679
MgNiFe-LDH	3.093	23.225	7.741	2.941

, MgNiAl-LDH and MgNiFe-LDH represented 7.48 and 7.74, respectively, in the basal spacing (d003), showing that carbonate anions are located in the interlayer space.

3.1.2. IR Spectroscopy Analysis

The IR-spectra of the two samples (MgNiAl-LDH and MgNiFe-LDH) studied are presented in Figure 2, which shows that the IR spectrum of the MgNiAl-LDH sample (Figure 2a), has a band located around ~1626 ${\mathrm{c}\mathrm{m}}^{-1}$ and at around 1630 ${\mathrm{c}\mathrm{m}}^{-1}$ for MgNiFe-LDH (Figure 2b). The stretching vibration of the hydrogen bonding groups v(O-H) in the brucite layer and the interlayer water is represented by the very broad one at approximately 3375 cm⁻¹ (around 3369 cm⁻¹ for MgNiFe-LDH). The corresponding bands for intercalated carbonate anions v(CO₃²⁻) are at 1360 and 771 cm⁻¹ (1356 cm⁻¹ and 711 cm⁻¹ for MgNiFe-LDH). Additional adsorption bands at 616 and 558 cm⁻¹ have been attributed to metal-oxygen vibrations in the layers of brucite [26].

3.1.3. TG-DSC

The thermal decomposition of the generated materials was studied using TG-DSC. The results are shown in Figure 3, which illustrate that the thermal degradation of the MgNiAl-LDH sample occurs, in accordance with the dTG curves, in three main steps: dehydration, dehydroxylation, and departure of the carbonate anion. Between ambient temperature and 194 °C, dehydration occurs; this step can be explained by the detachment of interlayer water and adsorbed water. The second loss occurs in the 194–293 °C temperature range, when hydroxyl ions are removed from the brucite sheet. The interlayer carbonate thermally decomposes in the final step, which is completed at 640 °C. The total mass loss is 40.64% (Figure 3a). On the other hand, the thermal decomposition of the MgNiFe-LDH sample is similar to that of MgNiAl-LDH with a total mass loss of 33.04% (Figure 3b); a first mass loss occurred between ambient temperature and 215 °C, the second mass loss was; observed between 215 and 260 °C, and a last loss that ended at 600 °C.

3.2. Kinetic Studies

3.2.1. pH_pzc

The point of zero charge (pH_PZC) is the parameter that corresponds to the pH at which the solid surface has zero charge (the positive charges are equal to the negative charges) [27]. Theoretically, the surface becomes positively charged at pH < pH_PZC, which facilitates the adsorption of negatively charged dye anions by electrostatic attraction forces. The surface of LDH particles becomes negatively charged when pH > pH_PZC, favoring adsorption of the cationic dye [28].

Figure 4 displays the pH_PZC of the two samples; MgNiAl-LDH has a pH_PZC of 9 (Figure 4a), whereas MgNiFe-LDH has a pH_PZC of 10 (Figure 4b). Below the pH_PZC zero charge point, the adsorbed amount of CR in LDH increases as a result of the electrostatic attraction between the positively charged adsorbent and the negative dye molecules [29]. At pH > pH_PZC, the adsorption capacity of LDH decreases due to the electrostatic repulsion between the adsorbent surface and the dye molecules [30]. As a result, pH = 3 was selected for both materials MgNiAl- and MgNiFe-LDH for the remainder of the study.

3.2.2. The Effect of Adsorbent Mass

To 25 mL of 100 mg/L CR at pH = 3, several quantities (10–50 mg) of MgNiAl-LDH or MgNiFe-LDH were added. The solution was then agitated for 24 h at room temperature before being UV-vis analyzed (Figure 5).

Figure 5 displays that the mass of LDH significantly influences the removal of CR. For the MgNiAl-LDH samples, the percentage of CR removal increases from 76.31 to 99.59% (Figure 5a) and from 84.99 to 99.83% for the MgNiFe-LDH samples (Figure 5b) when the mass of adsorbent increases from 10 to 50 mg. It is remarkable that a mass of 10 mg of the LDH is able to remove a maximum of CR dye in the order of 99% for the both LDH samples, which indicates the speed and efficiency of LDH as a potential adsorbent for CR removal. Furthermore, this effect may be due to the low mass of the adsorbent, which causes the LDH granules to disperse in the aqueous solution, exposing all of the different types of surface sites and making them accessible to CR molecules at different sites. In this case, the surface adsorption is rapidly saturated, with a high adsorption capacity of up to 381.6 mg/g for MgNiAl-LDH and 424.95 mg/g for MgNiFe-LDH. Additionally, a large adsorbent quantity increases the probability of collision between solid particles and thus creates particle aggregation, leading to a decrease in total surface area and an increase in diffusion path length [31].

3.2.3. Effect of Contact Time on CR Adsorption

The adsorption times ranged from 0 to 120 min in a demonstration of the impact of the contact time on CR adsorption by the LDH samples (Figure 6). From the results obtained, we can see that the process of retention of CR by LDH is influenced by the initial concentration of dye as well as by the contact time. Figure 6 shows that the amounts of CR adsorbed increase rapidly during the first 5 min for both samples, after this time, the adsorption of dyes is almost at its maximum value corresponding to the equilibrium time (60 min) [32]. Furthermore, the exterior carbonate ions are relatively weakly attached to the particle surface and are easily replaced by CR anions, which is why the adsorption of CR anions on LDH occurs exclusively on the external surfaces of LDH particles. Moreover, adsorption capacity increases from 62.3 to 123.65 mg/g for MgNiAl-LDH (Figure 6a) and from 62.2 to 121.33 mg/g for MgNiFe-LDH (Figure 6b) when the initial CR dye concentration increases from 50 to 100 mg/L.

3.2.4. Kinetic Models Applied to the Adsorption of CR onto LDHs

In order to better understand the phenomenon of dye adsorption on LDH, three kinetic models were used to evaluate the experimental results in kinetics: pseudo-first order expressed by (Equation (4)) [33], pseudo-second order expressed by (Equation (5)) [34] and the intra-particle diffusion model expressed by (Equation (6)) [35].

$$\mathrm{Pseudo}-\mathrm{first}-\mathrm{order} \mathrm{kinetic} \mathrm{model} Ln(Q_e-Q_t)=Ln(Q_e)-\frac{K_{1}t}{2.303}$$

(4)

$$\mathrm{Pseudo}-\sec \mathrm{ond}-\mathrm{order} \mathrm{kinetic} \mathrm{model} \frac{t}{Q_t}=\frac{1}{K_2{Q_e}^2}+\frac{t}{Q_e}$$

(5)

$$\mathrm{Intraparticle} \mathrm{diffusion} \mathrm{model} Q_t=K_{ip}{t}^{1/2}+C$$

(6)

where k₁ (min⁻¹), k₂ (mg⁻¹·min⁻¹) and K_ip (mg/g. min^1/2) represents the rate constants of the pseudo-first order, pseudo-second order, and intra-particle diffusion kinetic models, respectively, and C represents the thickness of the boundary layer.

Figure 7 displays the linearized plots of the pseudo-first order, pseudo-second order, and intra-particle diffusion kinetic models of CR adsorption on MgNiAl-LDH and MgNiFe-LDH. In addition, the kinetic parameters for these models are shown in

Table 2. The parameters of the CR adsorption kinetic model on MgNiAl-LDH and MgNiFe-LDH pseudo-first-order, pseudo-second-order and intra-particle diffusion.

C0	qe,exp	Pseudo-First Order			Pseudo-Second Order			Intra-particle Diffusion
		qe,cal	k1	R2	qe,cal	k2	R2	Kip	C	R2
MgNiAl-LDH
50	62.287	60.890	1.158	0.993	61.791	0.059	0.997	3.179	39.069	0.340
100	123.650	113.477	1.508	0.998	115.477	0.035	0.978	6.522	70.254	0.400
MgNiFe-LDH
50	62.220	60.168	1.139	0.990	61.129	0.056	0.995	3.225	38.159	0.357
100	121.330	111.526	1.225	0.967	111.798	0.027	0.978	6.342	69.029	0.393

, Comparing the correlation coefficient R² of these three models for the two samples, the pseudo-second-order model is more consistent with the results of this adsorption experiment than the pseudo-first-order model and the intra-particle diffusion model. The higher rate constant k² of MgNiAl-LDH (Figure 7a) obtained by the pseudo-second-order model indicates that the adsorption rate of MgNiAl-LDH is higher than that of MgNiFe-LDH (Figure 7b), which is consistent with the analysis of the adsorption kinetics. In addition, the equilibrium adsorption amount (qe,_cal: 115.47 mg/g for MgNiAl-LDH; 113.79 mg/g for MgNiFe-LDH) calculated by the pseudo-second order model is closer to the experimental value (qe,_exp: 123.65 mg/g for MgNiAl-LDH; 121.33 mg/g for MgNiFe-LDH). Therefore, utilizing pseudo-second order kinetics to describe the adsorption of CR on the surface of both samples is more accurate.

Furthermore, the intra-particle diffusion kinetic model plot for both MgNiAl-LDH (Figure 7a) and MgNiFe-LDH Figure 7b) materials clearly reveals the existence of several steps during the adsorption process. In accord with this model, if the linear plot passes through the origin, intraparticle diffusion controls the rate of adsorption kinetics. However, Figure 7 clearly shows that the plot does not pass through the origin, indicating that the adsorption process involves intraparticle diffusion, which is not the only rate-limiting step [36]. The first step is the adsorption on a readily available outside adsorption site, the middle step is the diffusion of dye molecules within the pores, and the last step is the equilibrium process, where complete adsorption on the unoccupied sites has been achieved [37]. Surface adsorption and intraparticle diffusion are both confirmed by the plot. Furthermore, the thickness of the boundary layer C increases with increasing CR dye concentration (50 and 100 mg/L), which can be accounted for by an increase in the boundary layer effect brought on by the instantaneous adsorption of accessible sites [16].

3.3. Adsorption Isotherms

Adsorption isotherms, for solid-liquid systems, are among the important physico-chemical aspects as; they show the adsorbent-adsorbate affinity, allow understanding of some mechanisms related to adsorption, and determine the maximum quantity that an adsorbent can retain on its surface [38]. In this study, three well-known isotherm models are assessed; Langmuir, Freundlich, and Temkin. The parameters collected from the various models offer crucial details on the sorption mechanisms as well as the sorbent’s surface characteristics and affinities.

Langmuir’s adsorption model is based on the principle that a saturated monolayer of solute molecules on the adsorbent surface is equivalent to maximum adsorption. As a result, the Langmuir isotherm model was chosen to calculate the maximal adsorption capacity q_m, which equates to complete monolayer coverage on the sorbent surface. The following is the supplied equation [39,40]:

$$\frac{C_e}{Q_e}=\frac{1}{Q_m}{C}_e+\frac{1}{Q_{m}K}$$

(7)

K_L is Langmuir’s constant and relates to the adsorption energy. The value of K_L indicates whether the isotherm is unfavorable (K_L > 1), linear (K_L = 1), favorable (0 < K_L < 1), or irreversible (K_L = 0).

Freundlich’s theory suggests multilayer adsorption, which takes place on a heterogeneous surface containing sites with different adsorption energies. The maximum adsorption occurs when the surface is covered with a monolayer of adsorbent ions [41]. The Freundlich equation can be described as shown below [42]:

$$Ln(Q_e)=Ln(K_F)+\frac{1}{n}Ln(C_e)$$

(8)

In terms of adsorption capacity, K_F is the Freundlich isotherm constant (L/g); and 1/n is the heterogeneity factor.

The Temkin isotherm model [43] describes the adsorbate-adsorbent interaction on an adsorption isotherm. The Temkin isotherm model can be stated as follows:

$$Q_e=\frac{RT}{b_T}Ln(K_T)+\frac{RT}{b_T}Ln(C_e)$$

(9)

where K_T is the Temkin isotherm constant (L/g), R is the gas constant (8.314 J/mol.K), T is the absolute temperature (K), and B = RT/b, where b is the Temkin constant related to the heat of adsorption (J/mol).

The isotherm data obtained at 298 K were fitted according to the Langmuir, Freundlich, and Temkin models for MgNiAl-LDH and MgNiFe-LDH, as shown in Figure 8. The isothermal parameters of all models are summarized in

Table 3. Parameter values for Langmuir, Freundlich and Temkin adsorption isotherm models for CR adsorption onto MgNiAl-LDH and MgNiFe-LDH (Adsorbent = 20 mg, CR= 25 mL of 20–350 mg/L, T = 298 K).

Temperature (K)	Langmuir			Freundlich			Temkin
	qm	kL	R2	KF	1/n	R2	KT	B	R2
MgNiAl-LDH
298	4043.90	3.34035 × 10−4	0.991	1.638	1.053	0.988	0.038	133.436	0.899
MgNiFe-LDH
298	5584.740	2.29685 × 10−4	0.969	1.471	1.036	0.999	0.041	120.778	0.919

. From the results obtained, the values of 1/n calculated at 298 K for both samples are between 0 and 1, which indicates that the CR adsorption is favorable according to what was mentioned above. However, the acceptability of the isothermal model that best fits the experimental data is determined on the basis of the correlation coefficient R² value closest to unity. The Langmuir isotherm is based on the adsorption of a homogenous monolayer adsorbent material with uniform energy at all active adsorption sites. The Freundlich isotherm involves multilayer and heterogenous adsorption of adsorbent molecules on the sorbent surface, in contrast to the Langmuir model. When adsorption isotherms were analyzed for MgNiAl-LDH and MgNiFe-LDH, it indicated that for both samples, the R² value of the Langmuir isotherm was better than that of the Freundlich and Temkin isotherms. As a result, the adsorption of CR occurred in the monolayer on the surface of both LDH and its maximum adsorption capacity was found to be 5584 mg/g for MgNiFe-LDH (Figure 8a) and 4043 mg/g for MgNiAl-LDH (Figure 8b).

Table 4. CR adsorption capacity of MgNiAl-LDH and MgNiFe-LDH samples and other reported adsorbents.

ADSORBENT	ADSORPTION CAPACITY (MG/G)	REFERENCE
MgNiFe-LDH	5584	This work
MgNiAl-LDH	4043	This work
MgNiCo-LDH	1194	[43]
ZnAl-LDH/Al(OH)3	2348	[44]
Histidine/MgAl-LDH	1112	[45]
ZnFe2O4/MgAl-LDH	294	[46]
ZnAl-550	166	[47]
NiCo-LDH	909	[48]
ZrO2/MgAl-LDH	169	[49]
NIFE-LDH	484	[20]

compares the maximal adsorption capabilities of CR adsorbents with those of other adsorbents. MgNiFe-LDH and MgNiAl-LDH have significantly higher CR adsorption capacity than the other adsorbents [43,44,45,46,47,48,49,50]. As a result, due to their high adsorption capacity and simplicity of synthesis, the adsorbents created here are regarded as attractive options for the disposal of dye-containing effluents.

4. Conclusions

According to the study’s findings, the produced LDHs are excellent anionic dye sorbents, particularly effective for removing CR dye at quite high concentrations. The pseudo-second-order kinetic model successfully fit the adsorption kinetic data, while the Langmuir model perfectly modeled the isothermal data. Using the produced LDHs, the anionic dye CR was successfully removed with an adsorption equilibrium time of 60 min and the highest adsorption capacities for MgNiAl-LDH and MgNiFe-LDH, are 4043 mg/g and 5584 mg/g, respectively. When compared to other adsorbents, we believe that the prepared materials are incredibly competitive and show great promise for the removal of anionic dyes in industrial wastewater treatment.