Modified Activated carbon by in-situ co-precipitation process of tetra metal oxide magnetic nanocomposite for adsorption of Th(IV) from aqueous media

doi:10.21203/rs.3.rs-2576765/v1

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Modified Activated carbon by in-situ co-precipitation process of tetra metal oxide magnetic nanocomposite for adsorption of Th(IV) from aqueous media

https://doi.org/10.21203/rs.3.rs-2576765/v1

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Activated carbon was doped by tetra metal oxide magnetic nanoparticles (Fe_3n Co_n Cu_n Sr_n O_7n) by in-situ co-precipitation process to prepare a new efficient adsorbent (AC4MO) for thorium ions removal from aqueous media. Also, tetra metal oxide magnetic nanoparticles (4MO) used for removing thorium ions from aqueous media. The morphology and structural properties of the new magnetic nanocomposites 4MO and AC4MO have been described by SEM, EDX, TEM, XRD, and FTIR. Four operating conditions parameters have been studied in the adsorption process for new adsorbents, pH, contact time, initial concentration, and temperature. The adsorption kinetics has been well described by the pseudo-second order model, while the Langmuir model better fits the adsorption isotherms. 4MO and AC4MO adsorption capacities were 222.22 and 714.29 mg/g, respectively. Thermodynamic parameters have been calculated to indicate the spontaneous and endothermic nature of the adsorption process and show that AC4MO has little sensitivity to temperature. The results showed that 4MO and AC4MO have higher selectivity towards Th(IV) ions from radioactive wastewater. AC4MO is the more effective adsorbent and has a higher adsorption capacity for Th(IV) as discussed in the comparative study.

Tetra-metal oxide

Magnetic nanocomposite

Thorium ions

Adsorption

With the depletion of fossil energy, nuclear energy as a distinct new energy has received widespread attention (Wu et al. 2019; Gu et al. 2018). Thorium is a fissionable nuclide used widely in laboratory research and the nuclear industry to prepare fuel for nuclear reactors. Through the development and use of thorium resources, radioactive wastewater and waste residues are generated, which poses an extreme threat to the ecological environment and human health (Qi et al. 2018; Wang et al. 2021). Removing thorium from aqueous media is of great interest for radionuclide purification as radioactive waste disposal for environmental concerns (Deb et al. 2013). Thus, the removal of thorium from contaminated water is essential. Nowadays, various techniques are used to remove thorium from aqueous media, such as ion exchange (Radchenko et al., 2013), solvent extraction (Bayyari et al. 2010; Shaeri et al. 2015), membrane separation (Al Lafi et al. 2017), chemical precipitation (Rao et al., 2006), and adsorption (Xiu et ail, 2019; Zhou et al. 2016). Adsorption method has received much attention due to its ease of operation, no environmental hazards, and high stability (Nilchi et al. 2013; Sarafraz et al. 2017). There are many previous reports that give examples of the adsorption of thorium (IV) from aqueous media. Qi et al. investigated the adsorption of Th(IV) by using the new complex of sulfated β-cyclodextrin and α-naphthyl acetic acid. The maximum Th(IV) adsorption capacity was 12.75 mg/g at a pH of 2.5 (Qi et al. 2018). Ma et al. reported a highly crosslinked hybrid polymer poly(cyclotriphosphazene-co-melamine) microspheres eliminated Th(IV) from aqueous media, and the maximum experimental adsorption capacity was 98.6 mg/g at pH value 2 (Ma et al. 2020). Hu et al. modified silica gel with butanedioic anhydride for recovery of U(VI), Th(IV), and Eu(III) with maximum adsorption capacities of 5.10 × 10^− 5, 5.06 × 10^− 5, and 3.44 × 10^− 5 mol/L, respectively at pH from 1 to 5 (Hu et al. 2019). Therefore, improving effective eco-friendly adsorbent materials is a vital stage in the adsorption technique (Wang et al. 2013; Kim et al. 2013; Jiang et al. 2015). Carbonaceous material has become a sort of adsorption medium for eliminating thorium from aqueous media due to its suitable physical and chemical properties for the adsorption process as large surface area, thermal stability, excellent acid resistance, irradiation resistance, and environmental friendliness (Ren et al. 2013). Deb et al. reported that Multi-walled carbon nanotubes functionalized with diglycolamide for thorium treatment from aqueous media at pH 3.0–4.0. The adsorption capacity was estimated to be 10.58 mg/g at 298 K (Deb et al. 2013). Xiu et al. investigated that a functional graphene oxide nanoribbons/manganese dioxide composite material (MnO₂-GONRs) was synthesized by hydrothermal method using graphene oxide nanoribbons (GONRs) as raw material used for thorium adsorption with maximum monolayer coverage of 166.11 mg/g at pH 3 in aqueous media (Xiu et al. 2019). Milani and Karimi reported that 3-aminopropyltriethoxysilane-modified titano-silicate successfully adsorbs thorium with a maximum adsorption capacity of 83.4 mg/g [22](Milani and Karimi 2017). Activated carbon is a type of carbonaceous material, that has attracted much attention recently because it has high adsorption capacity and great application value (Saha et al. 2017). Yakout et al. use rice straw activated carbon for U(VI) and Th(IV) removal, where the adsorption reaches maximum adsorption of 45 mg/g at pH 4 for Th(IV) and 93 mg/g at pH 5.5 for U(VI) (Yakout et al. 2015). Kutahyal and Eral prepared activated carbon from olive stone for U(VI) and Th(IV) removal from aqueous media. The experimental results showed that the adsorption capacities are 40 and 13 mg/g, respectively (Kutahyal and Eral 2010). Mahmoud et al. reported that polyvinylpyrrolidone-modified magnetic activated carbon acts as adsorbent material for thorium adsorption from aquatic media in the batch adsorption process, and the adsorption capacity is 149.35 mg/L at pH 3.5, 30°C and 40 min (Mahmoud et al. 2019).

Metal oxide nanoparticles (MONPs) have favorable adsorption in radionuclides and heavy metal ions removal from wastewater due to their high adsorption capacities and excellent selectivity. MONPs have a significant role in radionuclide removal in environmental concerns and purification in safeguards application (Elhefnawy and Elabd 2022). Xiu et al. synthesize hydrated MnO₂ for Th(IV) and U(VI) adsorption. The maximum adsorption capacities were 218.34 and 55.19 mg/g for Th and U, respectively (Xiu et al. 2019). Abd El‑Magied et al. successfully synthesized Co_0.5Mn_0.5Fe₂O₄ nanoparticles for U(VI) removal with adsorption capacities of 104 mg/g at pH 6 (Abd El‑Magied1 et al. 2020). Liu et al. synthesized titanate nanotubes by a hydrothermal method for thorium removal with a maximum adsorption capacity of 232.56 mg/g at pH 4 (Liu et al. 2013). Besides traditional MONPs, magnetic metal oxide nanoparticles (MNPs) attract great attention due to the quick separation and ease of isolation from aqueous media in the adsorption and regeneration process using a magnetic field. Fe₃O₄ (MNPs) has been used widely in adsorption due to its low production cost, easy preparation, and large-scale production capabilities (Elhefnawy et al. 2013). Wu et al. investigated that magnetic graphene oxide nanoribbons are used effectively in Th(IV) adsorption. The experimental adsorption capacity was 31.4 mg/g at pH 3 (Wu et al. 2019). Therefore, the main target of this work is to examine the feasibility of thorium adsorption onto new magnetic nanocomposites. This study reports the synthesis of mixed tetra metal oxide magnetic nanoparticles (4MO) and their precipitation in activated carbon (AC4MO) in order to design novel Th(IV) adsorbents. Both new adsorbents 4MO and AC4MO were characterized by SEM, EDX, TEM, XRD, and FTIR. The adsorption performance of nanocomposite adsorbents on Th(IV) was investigated under various parameters such as pH, contact time, initial concentration, and temperature. The adsorption mechanism was discussed by kinetics and isothermal models. At the same time, the energy profile of the adsorption process was investigated by calculating thermodynamic parameters.

All solutions were prepared in deionized water. ferric nitrate, cobalt nitrate, cupper nitrate, strontium nitrate, 65% nitric acid, 68% ammonia media, the buffer media and methanol were purchased from Merck Company. 36% hydrochloric acid was manufactured from Fisher chemicals company. While EDTA disodium salt was manufactured from Across company. Th(IV) stock solution was prepared from thorium salt [Th(NO₃)₄.4H₂O], which supplied by Mallinckrodt company. Thorium solution was prepared in deionized water and measured with UV-Visible Spectrophotometer (Thermo-Evolution 300, England), at a wavelength of 665 nm with 0.2% arsenazo (III) reagent and ethanol were provided by Aldrich company and with Inductively coupled plasma optical emission spectrometer (ICP-OES) from Thermo Fisher Scientific iCAP 6500 – UK, with ITEVA operating software. The Transmission electron microscope (TEM) images were obtained using a JEOL JEM-2100 instrument using an accelerating voltage of 200 kV. Samples were ultra-sonicated in ethanol for 15 min and then dispersed on copper grids. The pH values were measured with a Jenway 3510 pH meter supplied with a combined glass electrode (Sentek). The structure and purity of the nanocomposites were verified by means of an X-ray powder diffraction technique on a PANalytical apparatus with X’pert PRO software. The surface morphology of the new adsorbents was investigated using scanning electron microscopy by (ZIESS, Gemini Sigma 300 VP), and Atomic force microscope by (nano-surf flexaxiom c3000). Elemental analysis of the new adsorbents was analyzed with an energy-dispersive X-ray detector by JEOL, 6510 LA. The chemical structures of the prepared hydrogels were analyzed by the FTIR system (Shimadzu 8001, Japan). Fourier transforms infrared (FTIR) spectra were measured at room temperature.

2.1. Preparation of tetra metal oxide magnetic nanoparticles (4MO)

The mixture of metal salts Cu(NO₃)₂, Co(NO₃)₂, Sr(NO₃)₂, and Fe(NO₃)₃ were dissolved separately with the molar ratio 3 M²⁺: 1 M³⁺, then mixed together with continuous stirring during dropwise addition of aqueous 1M NaOH for 1 hr. The black precipitate was formed at pH 10 and removed by magnetic separation, then washed many times using deionized water and dried in an oven at 120 ºC overnight. The product was burned in the oven at 600 ºC to produce tetra metal oxide magnetic nanoparticles (4MO).

2.2. Preparation of magnetic tetra metal oxide on activated carbon nanocomposite (AC4MO)

Activated carbon (AC) has been synthesized according to the previous report (Elhefnawy and Elabd, 2023), in which the magnetic tetra metal oxide nanoparticles were in situ preparation during the co-precipitation of nitrate salts of different metals as Co²⁺, Cu²⁺, Sr²⁺, and Fe³⁺ by NaOH media in the presence of 0.2 g of AC. The mixture of metal media was continuously stirred during the dropwise addition of 1M aqueous NaOH. Adjust the pH media to 10, and shake it for 1 hr. Separate the resulting ppt magnetically from the working media. Wash the ppt many times and dry it in an oven at 120 ºC overnight. The product burnt at 600 ºC to form tetra metal oxide magnetic nanocomposites on AC (AC4MO). Both prepared adsorbents were stored in the dry bottle for Th(IV) adsorption process.

2.3. Adsorption experiments

Th(IV) adsorption from the aqueous media was examined by batch experiments using the following procedure: 50 mg of the new adsorbent [4MO/ AC4MO] was equilibrated with 20 ml of thorium nitrate media in different concentrations under constant temperature and shaking rate of 150 rpm. After equilibrium, the magnetic nanocomposite adsorbent [4MO/ AC4MO] was magnetically separated from the working media. The initial and equilibrium thorium concentrations were determined spectrophotometrically. The adsorption capacity q_e (mg/g) was calculated according to the following equation (Atia et al. 2019):

$${q}=\frac{{({C}}_{0}-{{C}}_{{t}}) {V}}{{m}}$$

Where; C_o and C_e are the concentrations of thorium in the initial and equilibrium media, respectively, V is the volume of the aqueous media (L) and m is the mass of the adsorbent (g). The distribution coefficient K_d (L/g) is defined as the concentration of the species adsorbed per gram of the adsorbent divided by its concentration in the liquid phase. It was calculated by using the following equation (Elhefnawy and Elabd 2022).

$$\mathbf{K}\mathbf{d} = \frac{\left( \mathbf{C}\mathbf{o} - \mathbf{C}\mathbf{e} \right) \mathbf{V} }{\mathbf{C}\mathbf{e} \mathbf{m}} \left(2\right)$$

3.1. Characterization

Figure 1 shows the morphology of the new adsorbents [AC4MO and 4MO] verified by SEM analysis at different magnifications (5.00–50.00) KX. Figure 1(a, b) describes the new adsorbent (4MO) as irregular globular nanoparticles stacked on a large irregular mass. Figure 1(c) shows micrographs of the new magnetic nanocomposite AC4MO that looks like a polygonal lamella arranged horizontally on the AC surface. Figure 1(d) shows that those lamellae were coated with the irregular globular nanoparticles prove the uniform distribution of 4MO on the AC surface.

EDX is a semi-quantitative analysis that measures the ions fraction locate close to the matrix surface. Figure 2 shows the EDX analysis of the new magnetic nanocomposites 4MO and AC4MO confirming the presence of Co, Cu, Fe, Sr, and O in both adsorbents AC4MO and 4MO. In addition to the presence of carbon on the prepared magnetic nanocomposite AC4MO. The low percentage of carbon is due to the distribution of the tetra metal oxide on the surface of the AC and covering its surface to form the new nanocomposite AC4MO. TEM images show the microstructure of the new adsorbent 4MO in Fig. 3. Figure 3 shows the nanoparticles of 4MO, which appear as irregular sheets that pile up to form a single bulk. That proves the large irregular masses in the SEM images consist of various metal oxide nanoparticles aggregated into bulk masses.

XRD pattern in Fig. 4 shows the characteristic peaks of Fe₃O₄ at 30°, 35°, 44°, and 62.8° that match well with the characteristic diffraction peaks of Fe₃O₄ as reported in [ JCPDS PDF No. 89–0691) (Zhuang et al. 2015). The diffraction peaks observed at 2θ = 35°, 38.37°, and 48.5° in each of the new adsorbents are attributed to the characteristic peaks (002), (200), and (202) of CuO nanoparticles as reported in [JCPDS Pdf # 892531] (Suresh et al. 2016). In addition to the previous oxides, both new adsorbents have diffraction peaks associated with CoO which appeared at 36.9°, 45.2°, and 59°. These diffraction peaks are in good order with the standard diffraction peaks of cobalt oxide nanoparticles [JCPDS data card no. 80–1538] (Jadhav et al. 2021). Furthermore, sharp peaks related to SrO appear in the spectrum at 2θ = 26.46°, 32.36°, 33.25°, and 50.21. These peaks correspond to the SrO cubic nanoparticle structure’s reflection planes, which indicate the crystallinity of the strontium oxide nanoparticles. All those diffraction peaks agreed with the SrO literature (JCPDS, File No. 00-048-1477) (Koberg et al. 2011). Activated carbon hasn’t appeared in diffraction peaks, which proves the complete covering of the surface of the activated carbon by tetra metal oxides. Thus, the XRD spectrum of both prepared adsorbents (4MO and AC4MO) proved the successful preparation of the tetra metal oxides magnetic nanocomposites, with complete distribution on the surface of AC in AC4MO adsorbent.

FTIR technique was used to obtain information about the functional groups in the new adsorbents 4MO and AC4MO as shown in Fig. 4. In detail, the absorption bands at 3401 cm^− 1 and 3431 cm^− 1 for 4MO and AC4MO, respectively are related to stretching vibration peaks of O-H of water molecules (Feiqiang et al. 2018). While vibrational bands at 1617 cm^− 1 and 1632 cm^− 1 are related to the bending vibration of O-H of water molecules. Other bands in the range of (3000–2500) cm^− 1 agreed with the stretching vibration of the aromatic–CH₂– and -CH = bonds corresponding to AC in the new adsorbent AC4MO (Elhefnawy and Elabd 2016). The sharp absorption bands at 1381.92 cm^− 1 and 1390.69 cm^− 1 belong to CO₃²⁻ vibrations and can be explained by the adsorption of CO₂ on the surface of the new adsorbents (Elhefnawy and Elabd, 2022; Zhai et al. 2004). The bands at range (1205 − 991) cm^− 1 are corresponding to symmetrical and antisymmetric vibrational stretching modes of M-O-M, M-O-X, (where M, X = Fe, Co, Cu, or Sr) for each adsorbent. Also, it might be the vibrational bands at the range of (908 − 445) cm^− 1 are attributed to the stretching and bending vibration mode of M-O or O–M–O (where; M = Fe, Co, Cu, or Sr) (Karaduman et al. 2017; Abedi and Mehrpooya 2021). As shown in the two spectra, there are identical vibrational peaks with only slight shifts due to the chemical effects of the distribution of metal oxides on the AC surfaces. According to XRD and FTIR analyses, the new adsorbents have high crystallinity and confirm the successful preparation of the new adsorbents 4MO and AC4MO.

3.2. Effect of initial media pH

The effect of pH of the initial media on thorium adsorption was investigated under initial thorium concentration C₀ = 20 mg/L, sample volume = 20 ml, and in the range of 1 to 10. Figure 6 shows that the removal efficiency (%) of Th(IV) was increased until reaching maximum values 99% and 91% at pH 5 and 4 on 4MO and AC4MO, respectively. When the pH rises to 10.00, the removal efficiency (%) of Th(IV) decreases obviously to 78% and 88%. It was clear that the acidic condition is more favorable in Th(IV) adsorption process and the metal ions mainly existed as Th(OH)³⁺, Th(OH)₂²⁺, and Th(OH)³⁺ cations (Kaynar and Şabikoğlu 2018). The adsorption reaction occurred through the electrostatic attraction between the positive charge Th(OH)₂²⁺ and the negative charge on the deprotonated adsorbent’s surface. The adsorption reaction process was estimated as shown in Scheme 1. Thus, the adsorption reaction was carried out effectively with the adsorbent binding sites forming complexes as the following equations:

$${\mathbf{T}\mathbf{h}\left(\mathbf{O}\mathbf{H}\right)}_{2}^{2+}+\mathbf{H}\mathbf{O}-\left[4\mathbf{M}\mathbf{O}\right] \to {\mathbf{T}\mathbf{h}\left(\mathbf{O}\mathbf{H}\right)}_{2}^{+}-\mathbf{O}-\left[4\mathbf{M}\mathbf{O}\right] \left(3\right)$$

$${\mathbf{T}\mathbf{h}\left(\mathbf{O}\mathbf{H}\right)}_{2}^{+}-\mathbf{O}-\left[4\mathbf{M}\mathbf{O}\right] + \mathbf{H}\mathbf{O}-\left[4\mathbf{M}\mathbf{O}\right] \to \left[4\mathbf{M}\mathbf{O}\right] -\mathbf{O}-{\mathbf{T}\mathbf{h}\left(\mathbf{O}\mathbf{H}\right)}_{2}-\mathbf{O}-\left[4\mathbf{M}\mathbf{O}\right] \left(4\right)$$

The removal efficiency of the adsorption of Th(IV) onto AC4MO has a higher value than 4MO, which suggests that the prepared adsorbent AC4MO is more effective than 4MO, and that will be discussed in more detail in further adsorption studies.

3.3. Effect of contact time and kinetic studies

The effect of contact time on Th(IV)adsorption on different contact time ranges (5-150) min is shown in Fig. 7. The adsorption capacity of Th(IV) has a significant change in the first 40 min. After that, the amount of adsorbed Th(IV) changes slowly over time and achieves equilibrium at 60 min. The rapid removal of Th(IV) may be due to the metal ions chemically binding with hydroxyl groups of the prepared adsorbents 4MO and AC4MO to form strong surface complexation. On-time the adsorption progresses are reduced owing to the continuous diffusion of Th(IV) into the 4MO and AC4MO microspheres. And the adsorbent binding site is gradually saturated, which decreases the efficiency of the adsorption of Th(IV). Therefore, 60 min is considered the equilibrium contact time for further experiments. To study the kinetic models of the adsorption reaction of Th(IV) on both prepared adsorbents 4MO and AC4MO, the pseudo-first-order, pseudo-second-order, and intra-particle diffusion kinetics models were studied according to the following equations (Feng et al. 2018):

$${L}{n}\left({{q}}_{{e}}-{{q}}_{{t}}\right)={L}{n}{{q}}_{{e}- }{{K}}_{1}{t} \left(5\right)$$

$$\frac{{t}}{{{q}}_{{t}}} = \frac{1}{{{K}}_{2 }{{q}}_{{e}}^{2}} +\frac{{t}}{{{q}}_{{e}}} \left(6\right)$$

$${{q}}_{{t}}={{K}}_{{P}} {{t}}^{0.5}+{I} \left(7\right)$$

Where q_e and q_t are the adsorption capacities (mg/g) at equilibrium and contact time t, respectively. K₁ is the pseudo-first order rate constant in (1/min) and k₂ is the pseudo-second-order rate constant in (g/mg. min). k_p is the diffusion rate parameter in (mg/g. min^0.5), and I is the boundary layer thickness. The three kinetic models were employed to fit the adsorption experimental data obtained as described in Supplementary documents S.1, 2, and 3. All kinetic parameters for both new adsorbents are listed in Table 1. According to R², the pseudo-second order model fits better with the experimental results, explaining the adsorption mechanism as the chemisorption. Figure 8 represents the intraparticle diffusion model and shows that Th(IV) adsorption process happened in two steps. The first occurred at a fast rate and expressed as a film diffusion of the metal ions on the adsorbents’ surface. While the second was carried out at a slow rate and described as the metal ions diffusion on the boundary layer of the adsorbents. Also, it is clear that the two straight lines represent the two steps in both adsorbents that don’t pass through the origin (I > 0), showing the significant effect of the boundary layer thickness in the adsorption process (Côrtes LN et al. 2019).

3.4. Effect of initial concentration and adsorption isotherms

The effect of the initial concentration of Th(IV) adsorption has been investigated at a concentration ranging from 20 to 250 mg/L, at pH 4 and 5 on 4MO and AC4MO, respectively. Langmuir and Freundlich models were used to simulate the experimental adsorption data as the linear and nonlinear expressions (see supplementary document S.4, and 5) according to the following equations (Ganguly et al. 2020; Nnadozie and Ajibade 2020).

$$\frac{{{C}}_{{e}}}{{{q}}_{{e}}}=\frac{1}{{{K}}_{{L} }{{q}}_{{m}}}+\frac{{{C}}_{{e}}}{{{q}}_{{m}}} \left(8\right)$$

$${{q}}_{{e}}=\frac{{{q}}_{{m}} {{K}}_{{L}} {{C}}_{{e}} }{1+{{k}}_{{L}} {{C}}_{{e}}} \left(9\right)$$

$$\mathbf{l}\mathbf{o}\mathbf{g} {\mathbf{q}}_{\mathbf{e}} =\mathbf{l}\mathbf{o}\mathbf{g}\mathbf{l}\mathbf{o}\mathbf{g} {\mathbf{K}}_{\mathbf{F} } + \left(\frac{1}{\mathbf{n}}\right)\mathbf{L}\mathbf{o}\mathbf{g} {\mathbf{C}}_{\mathbf{e}} \left(10\right)$$

$${{q}}_{{e}}={{K}}_{{F}} {{C} }_{{e}}^{\frac{1}{{n}}} \left(11\right)$$

Where q_e and q_m are the adsorption capacity at equilibrium and the maximal adsorption capacity, respectively. K_L and K_f are the Langmuir and Freundlich constants, respectively, and n is the intensity of the adsorption. All isothermal parameters are listed in Table 3. The simulation of the experimental data with the nonlinear form of Langmuir and Freundlich isotherm models is shown in Fig. 9a, b. The results of isothermal calculations and simulation data indicated that the correlation coefficient R² of Langmuir adsorption isotherm models was higher than the Freundlich models. Thus, Langmuir adsorption isotherm models could better describe the adsorption process of Th(IV) on the adsorbents. That demonstrates that the adsorption sites on the adsorbent’s surface are uniform distribution and all the active sites on 4MO and AC4MO have equal affinities for Th(IV). Thus, the adsorption process can be described as a homogenous chemisorption. The new adsorbents value of 1/n indicates a favorable adsorption process that the value of 1/n is in the range of [0 < 1/n < 1] (Côrtes et al. 2019; Yildirimet al. 2020). That proves the adsorption process was relatively easy to carry out.

3.5. Adsorption thermodynamics

The effect of temperature on Th(IV) adsorption by 4MO and AC4MO has been studied to discuss the thermodynamic behaviour of the Th(IV) adsorption process. The experimental study was carried out under different temperatures 298, 308, 318, and 328 K, as shown in Fig. 10a. The results show that the adsorption capacity of 4MO increases with the temperature increased from 298 to 323 K, indicating the endothermic nature of its adsorption process. While there is an insignificant change in the adsorption capacity by AC4MO proves that the adsorption process by AC4MO is a little sensitive to temperature. Figure. 10(b) shows the linear plot of ln K_d versus 1/T at different temperatures and is used to calculate the thermodynamic parameters ΔH°, ΔG°, and ΔS° according to the equations given below (Abutaleb et al. 2020; Qu et al. 2021):

$$\mathbf{L}\mathbf{n} {\mathbf{K}}_{\mathbf{d}} = \frac{\varDelta {\mathbf{S}}^{^\circ }}{\mathbf{R}} - \frac{\varDelta {\mathbf{H}}^{^\circ }}{\mathbf{R}\mathbf{T}} \left(12\right)$$

Where K_d is the distribution coefficient (mL/g), T is the absolute temperature (K), and R is the gas constant 8.314 (J/mol. K). ΔS° is the standard change of entropy (J/mol. K), ΔH° is the enthalpy change (kJ/mol), and ΔG° is the change of Gibbs’ free energy (KJ/mol). The thermodynamic parameters and calculation results are illustrated in Table 3 and all details of the linear plot of ln K_d versus 1/T at different temperatures were shown in supplementary document S.6. The positive ΔH° value showed that Th(IV) adsorption was an endothermic process. The value of ΔG° was negative and decreased with the increasing temperature, indicating that adsorption was a spontaneous process (Nezhad et al. 2021).

3.6. Adsorption selectivity

To evaluate the selectivity of 4MO and AC4MO in Th(IV) removal. A simulated wastewater effluent containing some interference ions such as Na⁺, Zn²⁺, Mn²⁺, Ni²⁺, Ca²⁺, Cu²⁺, and Fe³⁺ was prepared and treated with both new adsorbents at optimal conditions. The initial metal ions concentration was 5 (mg/L) for all cations. Figure 11 shows that 4MO and AC4MO have better selectivity and high adsorption capacity for Th(IV) other than interfering metal ions. The selectivity coefficient S_Th/M for Th(IV) relative to interfering ions is calculated by the following equation: (Tan et al. 2018; Zhang et al. 2020)

$${\mathbf{S}}_{\frac{\mathbf{T}\mathbf{h}}{\mathbf{M}}}=\frac{{\mathbf{K}}_{\mathbf{d}}^{\mathbf{T}\mathbf{h}}}{{\mathbf{K}}_{\mathbf{d}}^{\mathbf{M}}} \left(13\right)$$

${S}_{\frac{Th}{M}}$ are distribution coefficients of metal ions where (M = Mg²⁺, Na⁺, Zn²⁺, Mn²⁺, Ni²⁺, Ca²⁺, and Fe³⁺). S_(Th/M) values show a higher selectivity of both 4MO and AC4MO towards Th(IV) ions, which confirms the high performance of 4MO and AC4MO in the interaction of the hydroxyl and carboxylic functional groups with Th(IV).

3.7. Comparison with other adsorbents

The maximum adsorption capacities for Th(IV) adsorption on the new adsorbents 4MO and AC4MO were 222.22 and 714.29 mg/g, respectively. Furthermore, the adsorption capacities of other adsorbents with different functional groups in previous literature have been compared with the new adsorbents 4MO and AC4MO and are listed in Table 4. The comparative list includes the adsorption capacity, temperature, contact time and optimum pH. The combative study illustrate that adsorption capacity of AC4MO is higher than other adsorbents, which indicates that AC4MO is more efficient adsorbent for Th(IV) removal from aqueous media in normal operating conditions.

In this study, 4MO and AC4MO were successfully fabricated and proved their chemical structure by SEM, EDS, TEM, AFM, XRD, and FTIR. The resultant materials were explored as the new adsorbents to remove Th(IV) from aqueous media under different pH, contact time, initial concentration, and temperature. The adsorption mechanism has described as the electrostatic attraction between thorium cations Th(OH)₂²⁺ and the hydroxyl ions on the surface of the adsorbents for complex formation. Theoretical models prove that the adsorption of Th(IV) onto 4MO and AC4MO followed the pseudo-second order kinetic model, indicating chemisorption. The higher coefficient of isothermal models indicates that Langmuir isotherms describe the adsorption better, which illustrates the thorium (IV) adsorption as a monolayer on the adsorbents surface. The selectivity of 4MO and AC4MO has been investigated on simulated wastewater effluent containing some interference ions showing higher selectivity of the new adsorbents towards Th(IV) ions. A comparison study was performed between 4MO and AC4MO and other adsorbents from previous reports to verify the performance of the new prepared adsorbents. Overall, AC4MO shows a higher adsorption capacity for Th(IV) and it can be used effectively for recover thorium from radioactive wastewater media.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Ethical Approval

The authors approve all the journal Ethical instruction and respect third parties’ rights such as copyright and/or moral rights.

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The authors approve to publish this work study in the journal “Environmental Science and Pollution Research”

Authors Contributions

O.A. Elhefnawy conceived of the presented idea. O.A. Elhefnawy and A. A. Elabd carried out the experiment and performed the analysis. O.A. Elhefnawy wrote the manuscript and designed the figures. A. A. Elabd supervised the work. Both O.A. Elhefnawy and A. A. Elabd authors contributed to the final version of the manuscript. All authors discussed the results and contributed to the final manuscript.

Funding

The authors did not receive support from any organization for the submitted work.

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The authors ensure that all data and materials support their published claims and comply with field standards.

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Table 1 Kinetic parameters of Th(IV) adsorption on the new magnetic nanocomposite adsorbents (4MO and AC4MO)

Model

Parameters

4MO

AC4MO

Pseudo first ordered

K₁(1/min)

q_e(mg/g)

R²

0.056

50.866

0.849

0.0669

105.583

0.914

Pseudo second ordered

K₂ (g/mg. min)

q_e (mg/g)

R²

0.002099

127.06

0.995

0.00486

205.760

0.994

Intra-particle diffusion

K_1d(g/mg. min^0.5)

I₁

R²

K_2d(g/mg. min ^0.5)

I₂

R²

5.153

79.89

0.976

2.737

100.485

0.999

11.22

109.925

0.930

4.748

156.117

0.987

First step

Second step

Table 2 Isothermal parameters of Th(IV) adsorption on the new magnetic nanocomposite adsorbents (4MO and AC4MO)

q_experimental (mg/g)	Langmuir Isotherm Model			Freundlich Isotherm Model
q_experimental (mg/g)	q_m(mg/g)	k_l(L/ mg)	R²	K_F(mg^1-1/n. L^1/n/g)	1/n	R²
4MO	222.222	0.0349	0.993	18.634	0.483	0.981
AC4MO	714.285	0.0894	0.999	61.007	0.72	0.983

Table 3 Thermodynamic parameters of Th(IV) adsorption on the new magnetic nanocomposite adsorbents (4MO and AC4MO) at different temperatures

Adsorbent	Temperature (K)	ln (K_d) (mL/g)	∆G^o (KJ/mol)	∆S^o (J/mol K)	∆H^o (kJ/mol)	Adj. R²
4MO	298	6.6549	-16.488	103.8751	14.5268	0.982
	308	6.78997	-17.387
	318	6.99145	-18.484
	328	7.1852	-19.5941
AC4MO	298	9.492	-23.5189	199.319	35.908	0.999
	308	9.9307	-25.4298
	318	10.399	-27.4929
	328	10.8097	-29.478

Table 4 Comparison study of the Th(IV) adsorption capacity on the new magnetic nanocomposite adsorbents (4MO and AC4MO) with other adsorbent

Adsorbent	q_max (mg/g)	Experimental conditions	Reference
Functionalized magnetic graphene oxide nanoribbons (MGONRs) composite	36.54	pH=3.0, T=298 K t = 6 hr	(Wu et al., 2019)
Sulfated β‑cyclodextrin inclusion complex	12.75	pH=2.5, T=293K t= 30 min	(Qi et al., 2018)
diglycolamide functionalized multi-walled carbon nanotubes	10.58	pH=4.0, T= 298 K t=40 min	(Deb et al., 2013)
Highly crosslinked organic–inorganic hybrid polymer poly(cyclotriphosphazene-co-melamine) microspheres (PZM)	142.86	pH=3.0, T=303K t=10 min	(Ma et al., 2020)
Modification of silica gel by butanedioic anhydride (SiO₂–BDAH)	0.0506 mmol/L	pH=2.1, T=298 K t = 3 hr	(Hu et al., 2019)
Graphene oxide nanoribbons/manganese dioxide composite (MnO₂-GONRs)	166.11	pH=3.0, T=298 K t=900 min	(Xiu et al., 2019)
Polyvinylpyrrolidone magnetic activated carbon	149.35	pH=3.5, T=303 K t=40 min	(Mahmoud et al. 2019)
Hydrated manganese dioxide (HMO)	218.34	pH=3.5, T=308 K t=7 hr	( Xiu et al., 20`9)
Titanate nanotubes	232.56	pH=3.0, T=298 K t=12 hr	( Liu et al., 2013)
ACPS	471 mmol/g	pH=4, T=293 K t=90 min	(Elhefnawy and Elabd, 2023)
Chitosan-formaldehyde aerogel (CFA) Chitosan-resorcinol-formaldehyde aerogel (CRFA) C₃N₄-chitosan-resorcinol-formaldehyde hydrogel (CN@CRFA)	223.1 379.4 526.2	pH=4, T= 298 K t= 20 min	(Chen et al., 2022)
Nano Ca₃Y₂B₄O₁₂(CYBO)	134.62	pH=2.38, T= 293 K ---	(Kaynar et al., 2023)
Graphene oxide nanoflakes (GONFs)	427.77	pH=2.38, T= 293 K t= 8 hr	(Gao et al., 2022)
Mesoporous graphite carbon nitride (MPG-C₃N₄)	108.18	pH= 4; T=298 K t= 20 min	(Huang et al., 2021)
Nano-ZnO Al-doped nano ZnO (nano-ZnO:Al)	49.05 192.3	pH= 5, T=298 K ---	(Kaynar et al., 2021)
Hydrochars and microporous carbons (oxygen-rich microporous carbon)	624.98	pH 4.9, T=298 K t=12 hr	(Gao et al., 2021)
Magnetic talc titanium oxide composite	54.5	pH 4, T=298 K t= 30 min	(Morsy, 2017)
Chitosan/TiO₂ nanocomposite	455	pH =6.5, T=318K t= 30 min	(Broujeni et al., 2021)
N,N,N′,N′-tetraoctyldiglycolamide impregnated graphene aerogel (GA-TODGA)	66.8	pH= 6.5, T=318 K, t= 64 min	(Chen et al., 2018)
Activated titanium hydroxide	42.55	pH=3.0, T=298 K, t=40 min	(Gado and Zaki, 2015)
Ti(OH)₄ (Ti–Na-bent)	56.30 231.37	pH=2.5, T=298 K t=2 hr	(Xiong et al., 2019)
4MO	222.22	pH=5, T=298 K t=60 min	This study
AC4MO	714.29	pH=4, T=298 K t= 60 min	This study

Scheme 1 is available in the Supplementary Files section.

AC4MOTH.pdf
Scheme 1 The mechanism of the adsorption process of Th(IV) on the new magnetic nanocomposite adsorbents (4MO and AC4MO)
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Modified Activated carbon by in-situ co-precipitation process of tetra metal oxide magnetic nanocomposite for adsorption of Th(IV) from aqueous media

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Abstract

Figures

1. Introduction

2. Materials And Equipment

2.1. Preparation of tetra metal oxide magnetic nanoparticles (4MO)

2.2. Preparation of magnetic tetra metal oxide on activated carbon nanocomposite (AC4MO)

2.3. Adsorption experiments

3. Results And Discussion

3.1. Characterization

3.2. Effect of initial media pH

3.3. Effect of contact time and kinetic studies

3.4. Effect of initial concentration and adsorption isotherms

3.5. Adsorption thermodynamics

3.6. Adsorption selectivity

3.7. Comparison with other adsorbents

4. Conclusions

Declarations

References

Tables

Scheme 1

Supplementary Files

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