Modification of sodium aluminum silicate hydrate by thioglycolic acid as a new composite capable of removing and preconcentrating Pb(II), Cu(II), and Zn(II) ions from food and water samples

2.1 Chemicals

Sodium hydroxide (NaOH), (3-aminopropyl)trimethoxysilane (C₆H₁₇NO₃Si), thioglycolic acid (C₂H₄O₂S), hydrochloric acid (HCl), toluene (C₇H₈), ethanol (C₂H₆O), lead(II) nitrate (Pb(NO₃)₂), zinc(II) chloride heptahydrate (ZnCl₂·6H₂O), copper(II) chloride dihydrate (CuCl₂·6H₂O), potassium chloride (KCl), ethylenediaminetetraacetic acid disodium salt dihydrate (C₁₀H₁₆N₂Na₄O₁₀), nitric acid (HNO₃), and thiourea (CH₄N₂S) were obtained from Sigma Aldrich Company (Purity = 99.99 %) and consumed as received without any additional purification. The rice husk was collected from a rice mill located near the Egyptian city of Menia Alqamh. Besides, aluminum cans were collected from a local market in Benha city, Egypt.

2.2 Synthesis of composite

Firstly, the sodium aluminum silicate hydrate sample was prepared according to our previous work by Ehab et al. exploiting rice husk as a silicon source and waste aluminum cans as an aluminum source (Abdelrahman et al., 2021; Al-wasidi et al., 2022; Al-Wasidi et al., 2022a). For obtaining rice husk ash, the rice husk was burnt at 700 °C for 7.00 hrs. Also, 2.50 g of rice husk ash was refluxed for 2.00 hrs using a 100.00 mL of 1.50 M sodium hydroxide solution for obtaining the silicon solution. Besides, 1.00 g of the outer part of aluminum cans was refluxed for 30 min using a 55.00 mL of 2.10 M sodium hydroxide solution for obtaining the aluminum solution. Moreover, the aluminum solution was added drop by drop to the silicon solution with continual stirring for 1.50 hrs. Furthermore, the mixture was heated until 75 mL remained then the remaining volume was hydrothermally treated for 12.00 hrs at 150.00 °C using a 100.00 mL Teflon-lined autoclave. The white precipitate formed was filtered using a centrifuge, washed carefully with hot distilled water and ethanol, and dried for 24 hrs at 60 °C. The novel composite of sodium aluminum silicate hydrate with (3-aminopropyl)trimethoxysilane was prepared according to our previous work by Khalifa et al. with some changes (Khalifa et al., 2020). 2.00 g of the sodium aluminum silicate hydrate and 2.20 mL of (3-aminopropyl)trimethoxysilane were mixed then refluxed for 24 hrs at 120 °C using a 50.00 mL toluene. The obtained composite was filtered using a centrifuge, washed carefully with hot distilled water and ethanol, and dried for 24 hrs at 60 °C. Additionally, 1.00 g of sodium aluminum silicate hydrate/(3-aminopropyl)trimethoxysilane composite, 1.00 mL of thioglycolic acid, and 60.00 mL of toluene were mixed then transferred into a 100.00 mL Teflon-lined autoclave to hydrothermally treated for 3.00 hrs at 120.00 °C using a domestic microwave oven (Abdelrahman et al., 2021; Al-wasidi et al., 2022; Al-Wasidi et al., 2022a). The formed product was filtered using a centrifuge, washed carefully with hot distilled water and ethanol, and dried for 24 hrs at 60 °C. The processes involved in the synthesis of sodium aluminum silicate hydrate/(3-aminopropyl)trimethoxysilane/thioglycolic acid composite are summarized in Scheme 1 (Abdelrahman et al., 2021; Al-wasidi et al., 2022; Al-Wasidi et al., 2022a).

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Scheme 1

The synthetic steps of the sodium aluminum silicate hydrate/thioglycolic acid composite.

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2.3 Instruments

X-ray diffraction patterns of the synthesized samples were obtained utilizing D₈ Advance X-ray diffractometer adopting copper target with K_α line have a wavelength equal to 0.15 nm. Infrared spectra of the synthesized samples were obtained using KBr disc in the range from 4000 to 400 cm⁻¹ utilizing a Nicolet FT-IR spectrometer. A Quantachrome NOVA touch LX₂ nitrogen gas sorption analyzer was employed for the measurement of the average pore radius, BET surface area, and total pore volume of the synthesized samples. The surface morphology and EDX spectra of the synthesized samples were obtained utilizing a JEOL 2000 Scanning electron microscope. The morphologies of the synthesized samples were obtained utilizing an EM-2100 high-resolution transmission electron microscope. A PerkinElmer CHN Elemental Analyzer was utilized for the measurement of the CHN percent of the synthesized composite. The concentration of studied metal ions was determined utilizing a 210 Buck Scientific atomic absorption spectrometer equipped with an acetylene–air flame. The wavelengths for lead, zinc, and copper were 283.30, 213.90, and 324.80 nm, respectively whereas a spectral bandwidth equals 7 Å.

2.4 Extraction of Cu(II), Pb(II), and Zn(II) ions from aqueous solutions

The effect of pH was studied as the following; 50 mg of the synthesized composite were mixed with 80 mL of 120 mg/L of the studied metal ion at adapted pH (2.00–8.00). After 180 min of stirring, the mixture was filtered. An atomic absorption spectrometer was used to determine the remaining concentration of the examined metal ion in the filtrate. The pH of the metal ion solution was adjusted using 0.1 M NaOH or HCl. A value higher than pH = 8 has not been studied for the occurrence of precipitation, which makes the % removal as a result of adsorption unreal. The effect of time was studied as the following; 50 mg of the synthesized composite were mixed with 80 mL of 120 mg/L of the studied metal ion at pH = 6 for varied times (5–120 min). After stirring at specified times, the mixture was filtered. An atomic absorption spectrometer was used to determine the remaining concentration of the examined metal ion in the filtrate. The effect of temperature was studied as the following; 50 mg of the synthesized composite were mixed with 80 mL of 120 mg/L of the studied metal ion at pH = 6 for varied temperatures (298–323 K). After stirring for 80 min, the mixture was filtered. An atomic absorption spectrometer was used to determine the remaining concentration of the examined metal ion in the filtrate. The effect of concentration was studied as the following; 50 mg of the synthesized composite were mixed with 80 mL of varied concentrations (5–180 mg/L) of the studied metal ion at pH equals 6. After stirring for 80 min, the mixture was filtered. An atomic absorption spectrometer was used to determine the remaining concentration of the examined metal ion in the filtrate. Eq. (1) was utilized to determine the quantity of extracted Pb(II), Zn(II), or Cu(II) ions per gram of the synthesized composite (Q, mg/g).

Eq. (2) was utilized to determine the % removal (% R) of Zn(II), Pb(II), or Cu(II) ions.

C_i (mg/L) denotes the starting concentration of Zn(II), Pb(II), or Cu(II) ions. Besides, C_e (mg/L) denotes the equilibrium concentration of Zn(II), Pb(II), or Cu(II) ions in the filtrate. Moreover, V (L) denotes the volume of Zn(II), Pb(II), or Cu(II) solution. Additionally, M (g) denotes the mass of the synthesized composite. To investigate the effect of desorption, 50 mg of the synthesized composite were mixed with 80 mL of 5 mg/L of the studied metal ion at pH = 6 for 80 min. Then, filtration was used to separate the solid phase from the liquid phase, which was then washed many times with distilled water to remove unloaded ions. Besides, adsorbed ions on the synthesized composite were desorbed by shaking for 10 min with 5 mL of 0.5 M of desorbing agents, for example, thiourea, EDTA disodium salt, and HNO₃. Eq. (3) was utilized to determine the % desorption (% D).

C_d (mg/L) denotes the concentration of Zn(II), Pb(II), or Cu(II) in the eluate. Besides, V_d (L) denotes the volume of the eluent. Four successive adsorption/desorption runs were accomplished to determine the reusability of the synthesized composite. Following each run, the adsorbent was repeatedly washed carefully with distilled water to prepare it for the following adsorption run. After each run, the percent removal (% R) was calculated using Eq. (1). Khalifa et al. method was used to calculate the point of zero charge (pH_PZC) of the synthesized composite (Khalifa et al., 2020) as the following: the initial pH value of 50 mL of 0.025 M KCl solutions was modified to accommodate a range of pH values ranging from 2.00 to 12.00 utilizing 0.1 M HCl or NaOH. Besides, 0.15 g of the synthesized composite was mixed with each KCl solution then the mixture was stirred for 8 hrs. After that, filtration was used to separate the solid phase from the liquid phase then the final pH value (pH_final) of the filtrate was determined. The pH_final values were plotted versus the pH_initial values. The pH_pzc value represents the pH_final value at which a typical plateau is reached (Khalifa et al., 2020).

2.5 Actual real sample collection and pretreatment

Water samples were gathered from several places in polypropylene flasks which were prewashed using nitric acid (10 % V/V). Before keeping the collected samples in the refrigerator, they were filtered using pore-size membranes (0.45-μm) and acidified to a pH of 2.0 using HNO₃. Food samples (spinach, chicken, and fish) were obtained from the local markets at Benha city, Egypt. Each sample's edible portion was separated and carefully washed using distilled water before being cut into little pieces. Following 12 hrs of drying at 65 °C, the samples were ground until homogeneity was achieved then kept in polyethylene grabs. The samples were digested using a microwave-assisted acid digestion technique for attaining a short-term process. 0.5 g of dry sample was collected in Teflon digesting tubes separately then 2 mL of 30 % H₂O₂ and 4 mL of HNO₃ were added. After 15 min at room temperature, the tubes were hermetically sealed then heated accordance to the one-step procedure outlined below (power: 1650 W; temperature: 200 °C; ramp time: 16 min; cooling time: 16 min; hold time: 16 min). After rewarming the tubes to room temperature, the solutions were almost totally evaporated and then diluted with distilled water to 50 mL.

2.6 Preconcentration process

In a conical flask, 50 mL of digested solution or water sample was combined with 0.05 g of the synthesized composite. The pH of the solution was changed to 6.0 with NaOH and/or HCl solutions, and the volume of solution was increased to 80 mL using distilled water. Also, the contents were stirred for 80 min then the adsorbent substance was separated and poured into a 25 mL beaker. After adding 5 mL of 0.5 M HNO₃, the mixture was stirred for 10 min to allow the metal ions to desorb. The filtrate was then analyzed for determining the concentration of studied metal ions using atomic absorption spectrometer.

3.1 Characterization of the synthesized composite

Fig. 1A–B illustrate the X-ray diffraction patterns of sodium aluminum silicate hydrate and sodium aluminum silicate hydrate/(3-aminopropyl)trimethoxysilane/thioglycolic acid composite, respectively (Abdelrahman et al., 2021). The distinct peaks of sodium aluminum silicate hydrate at 2θ = 13.9°, 24.3°, 31.6°, 34.7°, 37.4°, 42.8°, 52.0°, 58.2°, 62.0°, and 63.9° correspond to the lattice plans (1 1 0), (2 1 1), (3 1 0), (2 2 2), (3 2 1), (4 1 1), (5 1 0), (4 4 0), (6 0 0), and (6 1 1), respectively (Abdelrahman et al., 2021). The XRD pattern of the synthesized composite shows that there is a halo at 2θ = 25.0, which means that there is a crystalline structure that is combined with an amorphous background (Khalifa et al., 2020). Fig. 2 illustrates the FT-IR spectrum of sodium aluminum silicate hydrate/(3-aminopropyl)trimethoxysilane/thioglycolic acid composite. The peaks, which were observed at 3590 and 1645 cm⁻¹, are attributed to the stretching and bending vibration of adsorbed H₂O and/or C⚌N, respectively. The peaks, which were observed at 2600 and 2810 cm⁻¹, are attributed to the stretching vibration of SH and CH, respectively. Moreover, the peaks, which were observed at 1475 and 992 cm⁻¹, are attributed to external and internal asymmetric stretching of X-O-X (X = Si and/or Al), respectively. Also, the peaks, which were observed at 710 and 626 cm⁻¹, are attributed to external and internal symmetric stretching of X-O-X ((X = Si and/or Al), respectively. Besides, the peaks, which were observed at 563 and 460 cm⁻¹, are attributed to double ring vibration and bending vibration of X-O-X (X = Si and/or Al), respectively (Abdelrahman et al., 2021; Abdelrahman and Hegazey, 2019a, 2019b; Al-Wasidi et al., 2022b; Khalifa et al., 2020). The elemental analysis of the sodium aluminum silicate hydrate/(3-aminopropyl)trimethoxysilane/thioglycolic acid composite shows carbon, hydrogen, nitrogen, and sulfur content of 15.12, 2.50, 1.41, and 8.50 %, respectively. The SEM and TEM studies indicate that the synthesized composite has a structure similar to that of cotton. Hence, this indicates that the crystalline phase is combined with an amorphous background as shown in Figs. 3 and 4, respectively. The BET study exhibits that the synthesized composite is mesoporous (average pore radius = 4.20 nm) with an average surface area and total pore volume of 3.05 m²/g and 3.92 × 10^3- cc/g, respectively (Abdelrahman and Hegazey, 2019a, 2019b). The anticipated decline in the surface area following functionalization is owing to the presence of organic functional groups on the sodium aluminum silicate hydrate backbone, which prevent nitrogen gas from entering the sodium aluminum silicate hydrate pores during the BET method (Abdelrahman et al., 2021; Abdelrahman and Hegazey, 2019a, 2019b).

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Fig. 1

The X-ray diffraction patterns of the sodium aluminum silicate hydrate (A) and their thioglycolic acid composite (B).

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Fig. 2

The FT-IR spectra of the sodium aluminum silicate hydrate/thioglycolic acid composite.

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Fig. 3

The FE-SEM image of the sodium aluminum silicate hydrate/thioglycolic acid composite.

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Fig. 4

The HR-TEM image of the sodium aluminum silicate hydrate /thioglycolic acid composite.

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3.2 Extraction of Cu(II), Pb(II), and Zn(II) ions from aqueous solutions

3.2.1

3.2.1 Effect of pH

Fig. 5A-B represents the effect of pH on % R of Pb(II), Cu(II), or Zn(II) ions and adsorption capacity of the synthesized composite, respectively. It was found that when the pH is raised from 2 to 6, both the removal percentage and the adsorption capacity go up a lot. Also, it was found that there is a slight increase when the pH changes from 6 to 8 due to the saturation of active sites. As a result, pH = 6 was chosen as the optimal pH for the subsequent studies. % Removal of Pb(II), Cu(II), and Zn(II) ions at pH = 6 is 94.10, 81.62, and 62.08 %, respectively. At pH = 6, the produced composite has an adsorption capacity of 180.67, 156.70, and 119.20 mg/g for Pb(II), Cu(II), and Zn(II) ions, respectively. The pH_final vs pH_initial curve for several KCl solutions is given in Fig. 5C. Besides, the results indicated that the composite point of zero charge is 3.51. It was found that when the pH of the Cu(II), Pb(II), or Zn(II) solution is not greater than 3.51, the synthesized composite has a positive charge due to the presence of positive hydrogen ions which repelled the investigated ions, resulting in a reduction in the removal percentage and the adsorption capacity. Also, when the pH of the Cu(II), Pb(II), or Zn(II) solution is greater than 3.51, the synthesized composite has a negative charge due to the presence of negative hydroxide ions which are attracted to the investigated ions and therefore increase the removal percentage and the adsorption capacity (Abdelrahman and Hegazey, 2019a, 2019b; Al-Wasidi et al., 2022b; Khalifa et al., 2020).

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Fig. 5

The influence of pH of the examined metal ion solution on % removal (A) and adsorption capacity (B). Determination of point of zero charge via the plot of pH_final versus pH_initial for several KCl solutions (C).

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3.2.2

3.2.2 Effect of time

Fig. 6A-B represents the effect of time on % R of Pb(II), Cu(II), or Zn(II) ions and adsorption capacity of the synthesized composite, respectively. It was found that when the time is raised from 5 to 80 min, both the removal percentage and the adsorption capacity go up a lot. Also, it was found that there is a slight increase when the time changes from 80 to 120 min owing to the saturation of the active sites. As a result, time = 80 min was chosen as the optimal time for the subsequent studies. % Removal of Pb(II), Cu(II), and Zn(II) ions at time = 80 min is 94.17, 82.50, and 63.33 %, respectively. At time = 80 min, the produced composite has an adsorption capacity of 180.80, 158.40, and 121.60 mg/g toward Pb(II), Cu(II), and Zn(II) ions, respectively. Two kinetic models were employed to investigate the influence of contact time: pseudo-second-order (Eq. (4)) and pseudo-first-order (Eq. (5) (Abdelrahman and Hegazey, 2019a, 2019b; Al-Wasidi et al., 2022b; Khalifa et al., 2020).

(4)

$$\frac{t}{Q_t}=\frac{1}{K_2{Q}_e^2}+\frac{1}{Q_e}t$$

(5)

$$\log \left(Q_e-Q_t\right)=log{Q}_e-\frac{K_1}{2.303}t$$

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Fig. 6

The influence of contact time of the examined metal ion solution on % removal (A) and adsorption capacity (B).

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Q_e (mg/g) is the equilibrium adsorption capacity of the synthesized composite toward the examined metal ions. Q_t (mg/g) denotes the adsorption capacity of the synthesized composite toward the metal ions under investigation at the contact time t. The pseudo-first-order model's rate constant is denoted by K₁ (1/min), whereas the pseudo-second-order model's rate constant is denoted by K₂ (g/mg.min). Fig. 7A-B illustrate the pseudo-first-order and pseudo-second-order models, respectively. The correlation coefficients (R²) of the pseudo-first-order model are smaller than those of the pseudo-second-order model, as shown in Table 1. Additionally, the pseudo-second-order adsorption capacity is more consistent with experimental adsorption capacity than that of the pseudo-first-order. Consequently, the pseudo-second-order model explained the kinetic data more accurately than the pseudo-first-order model. Thus, the chemical reaction appears to be involved in the rate-controlling step.

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Fig. 7

The pseudo-first-order (A) and pseudo-second-order (B) kinetic models.

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Table 1 Kinetic constants for the removal of Pb(II), Cu(II), and Zn(II) ions using the sodium aluminum silicate hydrate /thioglycolic acid composite.

Metal ion	Pseudo first order				Pseudo second order
	Qe (mg/g)		K1 (1/min)	R2	Qe (mg/g)		K2 (g/mg.min)	R2
	Calculated	Experimental			Calculated	Experimental
Pb(II)	137.10	180.80	0.0283	0.9723	191.94	180.80	0.00035	0.9999
Cu(II)	97.95	156.70	0.0266	0.9363	155.28	156.70	0.00074	0.9994
Zn(II)	85.63	119.20	0.0278	0.9749	123.15	119.20	0.00071	0.9958

3.2.3

3.2.3 Effect of temperature

Fig. 8A-B represents the effect of temperature on % R of Pb(II), Cu(II), or Zn(II) ions and adsorption capacity of the synthesized composite, respectively. It was found that when the temperature is raised from 298 to 328 K, both the removal percentage and the adsorption capacity decrease. As a result, temperature = 298 K was chosen as the optimal temperature for the subsequent studies. % Removal of Pb(II), Cu(II), and Zn(II) ions at temperature = 328 K is 64.90, 49.94, and 21.70 %, respectively. At 328 K, the produced composite has an adsorption capacity of 124.61, 95.89, and 41.66 mg/g toward Pb(II), Cu(II), and Zn(II) ions, respectively. The thermodynamic parameters: change in enthalpy (ΔH^o), change in entropy (ΔS^o), and change in free energy (ΔG^o) were calculated using Eqs. (6) & (7) (Abdelrahman and Hegazey, 2019a, 2019b; Al-Wasidi et al., 2022b; Khalifa et al., 2020).

(6)

$$\mathit{ln}{K}_d=\frac{\mathrm{\Delta }S°}{R}-\frac{\mathrm{\Delta }H°}{\mathit{RT}}$$

(7)

$$\mathrm{\Delta }G°=\mathrm{\Delta }H°-T\mathrm{\Delta }S°$$

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Fig. 8

The influence of temperature of the examined metal ion solution on % removal (A) and adsorption capacity (B).

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T (Kelvin) is the adsorption temperature while K_d (L/g) denotes the distribution constant. Additionally, R (kJ/mol kelvin) is a gas constant. The distribution constant was determined using Eq. (8) (Abdelrahman and Hegazey, 2019a, 2019b; Al-Wasidi et al., 2022b; Khalifa et al., 2020).

(8)

$$K_d=\frac{Q_e}{C_e}$$

Fig. 9 depicts the lnK_d versus temperature graph. The thermodynamic parameters are listed in Table 2. Due to the fact that the enthalpy value exceeds 40 kJ/mol, the data established that the adsorption of Cu(II), Pb(II), or Zn(II) ions via the synthesized composite is chemical (Abdelrahman and Hegazey, 2019a, 2019b; Al-Wasidi et al., 2022b; Khalifa et al., 2020). Additionally, due to the negative sign of ΔH^o, the adsorption of Cu(II), Pb(II), or Zn(II) ions is exothermic when the synthesized composite is used (Abdelrahman and Hegazey, 2019a, 2019b; Al-Wasidi et al., 2022b; Khalifa et al., 2020). Moreover, due to the negative sign of the ΔG^o, the adsorption of Cu(II), Pb(II), or Zn(II) ions is spontaneous when using the synthesized composite. Due to the positive sign of ΔS^o, the adsorption of Cu(II), Pb(II), or Zn(II) ions occurs in a disorderly manner at the solution boundary/composite (Abdelrahman and Hegazey, 2019a, 2019b; Al-Wasidi et al., 2022b; Khalifa et al., 2020).

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Fig. 9

The plot of lnK_d versus temperature.

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Table 2 Thermodynamic parameters for the removal of Pb(II), Cu(II), and Zn(II) ions using the sodium aluminum silicate hydrate/thioglycolic acid composite.

Metal ion	ΔGo (KJ/mol)				ΔSo (KJ/molK)	ΔHo (KJ/mol)
	Temperature (kelvin)
	298	308	318	328
Pb(II)	−107.55	−109.22	−110.89	−112.57	0.1674	−57.66
Cu(II)	−81.50	−82.79	−84.07	−85.36	0.1284	−43.23
Zn(II)	−96.94	−98.52	−100.11	−101.69	0.1582	−49.79

3.2.4

3.2.4 Effect of concentration

Fig. 10A–B represents the effect of concentration on % R of Pb(II), Cu(II), or Zn(II) ions and adsorption capacity of the synthesized composite, respectively. It was found that when the concentration is raised from 5 to 180 mg/L, the removal percentage decreases while the adsorption capacity increases (Abdelrahman and Hegazey, 2019a, 2019b; Al-Wasidi et al., 2022b; Khalifa et al., 2020). Freundlich (Eq. (9)) and Langmuir (Eq. (10)) equilibrium isotherms were utilized for analyzing the concentration data (Abdelrahman and Hegazey, 2019a, 2019b; Al-Wasidi et al., 2022b; Khalifa et al., 2020).

(9)

$$\mathit{ln}{Q}_e=ln{K}_3+\frac{1}{n}ln{C}_e$$

(10)

$$\frac{C_e}{Q_e}=\frac{1}{K_4{Q}_m}+\frac{C_e}{Q_m}$$

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Fig. 10

The influence of concentration of the examined metal ion solution on % removal (A) and adsorption capacity (B).

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Q_m (mg/g) is the maximal adsorption capacity of the synthesized composite. K₄ (L/mg) is the Langmuir constant, while K₃ (mg/g)(L/mg)^1/n is the Freundlich constant. 1/n denotes the heterogeneity constant. The Freundlich isotherm can be used to determine the Q_m using Eq. (11) (Abdelrahman and Hegazey, 2019a, 2019b; Al-Wasidi et al., 2022b; Khalifa et al., 2020).

(11)

$$Q_m=K_3\left(C_i^{1/n}\right)$$

Fig. 11A–B illustrate the Langmuir and Freundlich isotherms, respectively. As indicated in Table 3, the Freundlich isotherm correlation coefficients (R²) are less than those of Langmuir. Accordingly, the Langmuir isotherm performed better than the Freundlich isotherm in representing equilibrium data. The synthesized composite has a maximum absorption capacity of 185.53, 168.92, and 125.94 mg/g for Pb(II), Cu(II), and Zn(II) ions, respectively. Besides, as illustrated in Table 4, the synthetic composite's adsorption capability was compared to that of various adsorbents such as xanthate modified magnetic chitosan, cross-linked chitosan with epichlorohydrin, iron oxide/activated carbon composite, zeolite, amidoxime-functionalized polypropylene fiber, maghemite nanotubes, carbon gel, and guanyl-modified cellulose (Chen et al., 2008; Jain et al., 2018; Joseph et al., 2020; Kenawy et al., 2018; Osińska, 2017; Roy and Bhattacharya, 2012; Zhao et al., 2020; Zhu et al., 2012). The synthesized composite outperformed the majority of adsorbents due to its high adsorption capacity.

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Fig. 11

The Langmuir (A) and Freundlich (B) isotherms.

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Table 3 Equilibrium constants for the removal of Pb(II), Cu(II), and Zn(II) ions using the sodium aluminum silicate hydrate /thioglycolic acid composite.

Metal ion	Langmuir			Freundlich
	Qm (mg/g)	K3 (L/mg)	R2	Qm (mg/g)	K4 (mg/g)(L/mg)1/n	R2
Pb(II)	185.53	1.8148	0.9996	407.81	69.7139	0.8581
Cu(II)	168.92	0.4134	0.9962	297.02	39.5679	0.9196
Zn(II)	125.94	0.8429	0.9997	173.99	41.0762	0.9228

Table 4 Comparison of adsorption capacity of various adsorbents toward Pb(II), Cu(II), and Zn(II) ions.

Adsorbent	Q (mg/g) toward Pb(II) ions	Q (mg/g) toward Cu(II) ions	Q (mg/g) toward Zn(II) ions	Ref
Xanthate modified magnetic chitosan	76.90	34.50	20.80	Zhu et al., 2012
Cross-linked chitosan with epichlorohydrin	34.13	35.46	10.21	Chen et al., 2008
Iron oxide/activated carbon composite	–	8.06	–	Jain et al., 2018
Zeolite	109.89	57.80	36.77	Joseph et al., 2020
Amidoxime-functionalized polypropylene fiber	45.64	47.23	37.78	Zhao et al., 2020
Maghemite nanotubes	71.42	111.11	84.95	Roy and Bhattacharya, 2012
Carbon gel	16.95	6.64	–	Osińska, 2017
Guanyl-modified cellulose	52.00	83.00	78.00	Kenawy et al., 2018
Sodium aluminum silicate hydrate/(3-aminopropyl)trimethoxysilane/thioglycolic acid composite	185.53	168.92	125.94	This study

3.2.5

3.2.5 Effect of desorption and reusability

The plot of % desorption versus some desorbing agents is presented in Fig. 12. Desorbing agents included 0.5 M EDTA disodium salt, nitric acid, and thiourea. The results indicate that 0.5 M of nitric acid is the optimal desorbing agent for retrieving the maximum amount of studied ions from the synthesized composite. Moreover, the plot of % removal versus the cycle number is presented in Fig. 13. The slight drop in percent removal indicates that the produced composite can be efficiently regenerated and reutilized for the adsorption of Cu(II), Pb(II), and Zn(II) ions from aqueous media.

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Fig. 12

The plot of % desorption versus several desorbing solutions.

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Fig. 13

The plot of % removal versus the cycle number.

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3.3 Application

The proposed separation procedure was used to preconcentrate Cu(II), Pb(II), and Zn(II) in real samples (Sea water, river water, fish muscles, chicken muscles, and spinach leaves) prior to atomic absorption spectrometer analysis. Tables 6, 7, and 8 summarizes the results of preconcentration of Cu(II), Pb(II), and Zn(II) ions along with the recoveries for the spiked samples, respectively. The recovery findings demonstrate that the process is accurate, adaptable, and resulted in quantitative separation (greater than95 percent). Furthermore, the % RSD was less than 3.5 percent, indicating good reproducibility.