Removal of Radioactive Iodine Using Silver/Iron Oxide Composite Nanoadsorbents

Efficient and cost-effective removal of radioactive iodine (radioiodine) from radioactive contaminated water has become a crucial task, following nuclear power plant disasters. Several materials for removing radioiodine have been reported in the literature. However, most of these materials exhibit some limitations, such as high production cost, slow adsorption kinetics, and poor adsorption capacity. Herein, we present silver/iron oxide nanocomposites (Ag/Fe3O4) for the efficient and specific removal of iodine anions from contaminated water. The Ag/Fe3O4 were synthesized using a modified method and characterized via scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analyses. This adsorbent showed a high adsorption capacity for iodine anions (847 mg/g of the adsorbent) in pure water. Next, Ag/Fe3O4 was applied to the removal of radioiodine, and high removal efficiencies were observed in water. In addition, its desalination capacity was retained in the presence of competitive ions and varied pH. After the adsorption process, Ag/Fe3O4 was easily removed from the water by applying an external magnetic field. Moreover, the same operation can be repeated several times without a significant decrease in the performance of Ag/Fe3O4. Therefore, it is expected that the findings presented in this study will offer a new method for desalinating radioiodine in various aqueous media.


Introduction
The safe and reliable treatment of radioactive waste is inevitably linked to the safe production of nuclear energy [1,2]. Environmental damage caused by radioactive waste has attracted global attention. Radioisotopes, such as radioactive iodine (radioiodine), which exhibit a high degree of dispersion in water and air, are produced by nuclear fission. These can exert long-term adverse effects on human lives [3][4][5]. Notably, the global concern regarding nuclear waste leakage was kindled by the Fukushima accident in 2011 [6]. Further, the Chernobyl disaster in Ukraine occurred in 1986 wherein iodine radioisotopes were a major component of the radioactive contamination [7]. Moreover, the continuous operation of nuclear power plants can produce and introduce trace amounts of radioiodine into the environment [8]. Radioiodine has also been extensively used in the diagnosis of diseases and treatment of thyroid cancer on the basis of the selective uptake of iodine into the thyroid [9,10]. Consequently, the introduction of trace amounts of radioiodine from nuclear medicine research institutes also needs to be considered. For example, the Nanomaterials 2021, 11, 588 2 of 11 medical applications of iodine-131 ( 131 I; half-life: 8 days) and iodine-129 ( 129 I; half-life: 15.7 × 10 6 years) are considered to be the main generators of radioiodine waste [11][12][13]. The short-lived as well as long-lived radioisotopes of iodine can accumulate and cause serious damage to the human body. Therefore, the efficient treatment of radioactive iodine in nuclear wastes and contaminated water is an essential area of research. In past decades, various adsorbents such as graphene-based sorbents [14,15], deep eutectic solvents [16,17], hydrogelators [18], nanoporous carbons [19,20], polyacrylonitrile-chalcogel [21], microporous polymers [22][23][24], metal-organic frameworks (MOFs) [25,26], and functionalized zeolites [27,28] were employed to remove radioiodine that was dissolved in solutions and/or gaseous radioiodine. However, these materials exhibited several drawbacks, including low removal efficiency, slow adsorption kinetics, and high production cost. Furthermore, layered bismuth-iodine-oxide [29], titanate nanolamina [30], Mg-Al(NO 3 ) layered double hydroxide (LDH) [31], and magnetite composites [32,33] have been employed to remove iodine. However, setbacks ranging from their poor reusability to their low adsorption capacities have limited the application of these methods. In previous studies, we reported that gold nanoparticles (AuNPs) immobilized adsorbents for the removal of radioiodine anions in aqueous media [34][35][36][37]. The method exhibited efficient and ion-selective desalination; however, the high cost of AuNPs-based systems hampered their large-scale syntheses and remediation applications.
Silver-based materials have also demonstrated a great potential for removing iodine owing to the high affinity of iodine toward silver [3,38,39]. In a typical procedure in the previous studies, silver nanoparticles or silver-based composite materials were immersed in the contaminated water to remove radioiodine. Thereafter, radioiodine containing solid waste was separated from the water via filtration or centrifugation. However, most of these methods require further steps to separate solid radioactive wastes from water after the desalination procedure. Moreover, the separation of nanosized adsorbents via these methods is time-consuming and non-applicable at an industrial scale. Thus, the development of additional cost-effective, efficient remediation procedures for radioactive wastes is still desired. Here, we designed a stable and efficient silver/iron oxide (Ag/Fe 3 O 4 ) nanocomposite-based desalination system for the efficient removal of radioiodine from water. Compared with nonmagnetic silver composites, the magnetic nature of the Ag/Fe 3 O 4 adsorbent is advantageous as it can be harvested by an external magnetic field. Therefore, the desalination procedure and recovery of radioisotope-containing adsorbents from treated water can be easy, rapid, and cost-effective ( Figure 1). of iodine into the thyroid [9,10]. Consequently, the introduction of trace amounts of radioiodine from nuclear medicine research institutes also needs to be considered. For example, the medical applications of iodine-131 ( 131 I; half-life: 8 days) and iodine-129 ( 129 I; halflife: 15.7 × 10 6 years) are considered to be the main generators of radioiodine waste [11][12][13]. The short-lived as well as long-lived radioisotopes of iodine can accumulate and cause serious damage to the human body. Therefore, the efficient treatment of radioactive iodine in nuclear wastes and contaminated water is an essential area of research. In past decades, various adsorbents such as graphene-based sorbents [14,15], deep eutectic solvents [16,17], hydrogelators [18], nanoporous carbons [19,20], polyacrylonitrile-chalcogel [21], microporous polymers [22][23][24], metal-organic frameworks (MOFs) [25,26], and functionalized zeolites [27,28] were employed to remove radioiodine that was dissolved in solutions and/or gaseous radioiodine. However, these materials exhibited several drawbacks, including low removal efficiency, slow adsorption kinetics, and high production cost. Furthermore, layered bismuth-iodine-oxide [29], titanate nanolamina [30], Mg-Al(NO3) layered double hydroxide (LDH) [31], and magnetite composites [32,33] have been employed to remove iodine. However, setbacks ranging from their poor reusability to their low adsorption capacities have limited the application of these methods. In previous studies, we reported that gold nanoparticles (AuNPs) immobilized adsorbents for the removal of radioiodine anions in aqueous media [34][35][36][37]. The method exhibited efficient and ion-selective desalination; however, the high cost of AuNPs-based systems hampered their large-scale syntheses and remediation applications. Silver-based materials have also demonstrated a great potential for removing iodine owing to the high affinity of iodine toward silver [3,38,39]. In a typical procedure in the previous studies, silver nanoparticles or silver-based composite materials were immersed in the contaminated water to remove radioiodine. Thereafter, radioiodine containing solid waste was separated from the water via filtration or centrifugation. However, most of these methods require further steps to separate solid radioactive wastes from water after the desalination procedure. Moreover, the separation of nanosized adsorbents via these methods is time-consuming and non-applicable at an industrial scale. Thus, the development of additional cost-effective, efficient remediation procedures for radioactive wastes is still desired. Here, we designed a stable and efficient silver/iron oxide (Ag/Fe3O4) nanocomposite-based desalination system for the efficient removal of radioiodine from water. Compared with nonmagnetic silver composites, the magnetic nature of the Ag/Fe3O4 adsorbent is advantageous as it can be harvested by an external magnetic field. Therefore, the desalination procedure and recovery of radioisotope-containing adsorbents from treated water can be easy, rapid, and cost-effective ( Figure 1).

Synthesis of the Fe 3 O 4 Nanoparticles
The Fe 3 O 4 nanoparticles were prepared using a slightly modified, coprecipitation method [38]. Briefly, FeCl 2 ·4H 2 O (1.99 g, 0.01 mol) and FeCl 3 ·6H 2 O (5.41 g, 0.02 mol) were dissolved in water and sonicated for 30 min. The FeCl 2 ·4H 2 O and FeCl 3 ·6H 2 O solutions were mixed and placed in a three-neck bottle. The resulting solution was heated at 90 • C in a nitrogen stream, after which it was vigorously mixed in a deoxygenated atmosphere. Next, the aqueous NaOH solution was added dropwise, and the Fe 3 O 4 nanoparticles were obtained as dark-brown precipitates. The precipitated mixture was stirred for an additional 6 h to achieve complete conversion. The Fe 3 O 4 nanoparticles were extracted from the solution by applying an external magnetic field, washed several times with water and ethanol, and vacuum-dried for 2 h at 80 • C.

Synthesis of the Ag/Fe 3 O 4 Composite Nanoadsorbents
The Ag/Fe 3 O 4 composite materials were prepared via APTMS [40]. Briefly, the Fe 3 O 4 nanoparticles (0.30 g) were dispersed in 150 mL of ethanol and sonicated for 45 min. Next, APTMS (1 mL) was injected into the reaction mixture and stirred for 10 h. The APTMSfunctionalized Fe 3 O 4 nanoparticles were extracted by applying an external magnetic field, washed several times with ethanol, and vacuum-dried for 2 h at 80 • C. Further, the APTMSfunctionalized Fe 3 O 4 nanoparticles (0.25 g) were dispersed in 100 mL of water, after which AgNO 3 (0.30 wt.%) was added to the reaction mixture, followed by sonication for 1 h. For the preparation of the silver nanoparticles, NaOH (50 mL, 0.1 M) and hydroxylamine hydrochloride (45 mL, 0.05 M) were added to the reaction mixture and stirred for an additional 2 h. Finally, the Ag/Fe 3 O 4 composites were extracted by applying a magnetic field, washed several times with water and ethanol, and vacuum-dried at 80 • C.

Adsorption of Nonradioactive Iodine( 127 I − ) Using Ag/Fe 3 O 4 Composite Nanoadsorbents
Adsorption efficiency of the Ag/Fe 3 O 4 nanocomposites was determined by measuring the absorbance variation of nonradioactive NaI/KI via UV-Vis spectroscopy at a maximum wavelength, λ max = 225 nm. Briefly, 100 ppm stock solution was prepared by dissolving KI in water, and the pH was maintained at 7. Further, the desired low concentrations were prepared by diluting the stock solution. In the adsorption experiment, the adsorbent, the Ag/Fe 3 O 4 composites, were shaken with an aqueous KI solution of a given concentration at a different time interval. After the experiment, the adsorbent was removed by an external magnet. The iodine concentration of the treated solution was measured via UV-Vis spectroscopy.
The percentage removal efficiency of Ag/Fe 3 O 4 nanocomposites was measured using Equation (1): Equilibrium adsorption capacity of Ag/Fe 3 O 4 nanocomposites, Q e (mg/g), was determined using Equation (2): where Q e (mg/g) is the quantity of I − that was adsorbed on the adsorbent at equilibrium time, C 0 (mg/L) is the initial concentration of I − in the aqueous solution, C e (mg/L) is the final concentration of I − in the aqueous solution at time t, V (L) is the volume of the solution, and M (g) represents the mass of the adsorbents (Ag/Fe 3 O 4 ).

Determination of Removal Efficiency in the Presence of Competitive Ions
The removal efficiency of Ag/Fe 3 O 4 nanocomposites was investigated in the presence of competitive ions. Radioiodine, [ 125 I]NaI (150 µCi), was diluted in an aqueous solution of NaCl, NaBr, NaF, NaClO 3 , NaBrCO 3 , or nonradioactive NaI (10 mL, 1.0 M). The Ag/Fe 3 O 4 nanoparticles were stirred with the [ 125 I]NaI solution of given radioactivity for 60 min. Next, the adsorbent was removed by an external magnet. The radioactivities of the supernatant and adsorbent material were measured using the radio-TLC system or dose calibrator.

Removal Efficiency in Different Aqueous Media
To investigate the removal efficiency of the adsorbents, [ 125 I]NaI (150 µCi) was diluted in 10 mL of different aqueous media (pure water, 1× PBS, water at 80 • C, river water, 0.1 M NaOH, 0.1 M HCl, or 1.0 M NaI). Ag/Fe 3 O 4 nanocomposites were stirred with the [ 125 I]NaI solution of given radioactivity for 60 min. Subsequently, the adsorbent was removed by an external magnet. The radioactivities of the supernatant and adsorbent materials were measured using the radio-TLC system or dose calibrator.

Reusability of the Composite Nanoadsorbents
To investigate the reusability of Ag/Fe 3 O 4 nanocomposites, [ 125 I]NaI (150 µCi) was diluted in 10 mL of pure water. Ag/Fe 3 O 4 (10 mg) was shaken with the [ 125 I]NaI solution of given radioactivity for 60 min. Subsequently, the adsorbent was removed by an external magnet. The radioactivity in the supernatant and adsorbent materials was measured using a gamma counter. The experiment was repeated for up to seven cycles.

Adsorption Isotherm Studies
The adsorption isotherm was measured using the KI solution at an ambient temperature and neutral pH. Briefly, 5 mg of the Ag/Fe 3 O 4 nanoparticles was treated with 100 mL of KI at different initial concentrations (100-200 ppm) with a constant increment of 10 ppm. The final concentration of iodine after adsorption procedure was determined via UV-Vis spectroscopy at different intervals. The adsorption of I − (Q e ) was calculated using Equation (2). The Langmuir and Freundlich isotherm models were applied to describe the equilibrium adsorption: Freundlich equation : lnQ e = lnK F + 1 n lnC e where C e (mg/L) are concentrations of I − at the initial and equilibrium times, respectively. Q e (mg/g) is the quantity of I − that was adsorbed on the adsorbing medium at the equilibrium time, and Q max (mg/g) is the maximum adsorption capacity of the adsorbent. K L and K F are the Langmuir and Freundlich adsorption constants, respectively.

Adsorption Kinetics of I − on the Adsorbents
The adsorption kinetics of I − on Ag/Fe 3 O 4 nanoparticles was determined using 100 ppm KI at pH 7 and room temperature. Briefly, 100 mL of KI (100 ppm) solution was shaken with 5 mg of Ag/Fe 3 O 4 nanocomposites. At different times, the absorbent was separated from the solution by applying an external magnet and the concentration of I − was determined via UV-Vis spectroscopy by measuring the absorbance variation at the maximum wavelength, λ max = 225 nm. The adsorption capacity was fitted into the pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetics equations with respect to time, as expressed in Equations (3) and (4), respectively. PFO kinetic model : ln(Q e − Q t ) = lnQ e − k 1 t 2.303 (5) PSO kinetic model : where Q e and Q t are the quantities of I − (mg/g) at equilibrium and time t, respectively. The Fe 3 O 4 nanoparticles were used in the control experiment under similar conditions. k 1 (min −1 ) and k 2 (g mg −1 min −1 ) are the PFO and PSO adsorption rate constants, respectively.

Results and Discussion
The adsorbent, Ag/Fe 3 O 4 nanoparticles, were synthesized in two steps using a modified procedure, as shown in Figure S1a. To prepare Fe 3 O 4 nanoparticles, a mixture of FeCl 2 ·4H 2 O and FeCl 3 ·6H 2 O was treated with NaOH at 90 • C, and the product was washed several times with water and ethanol, after which it was dried at a high temperature. In the next step, APTMS was coated on the surface of the Fe 3 O 4 nanoparticles. Further, the silver layer was formed using AgNO 3 in the presence of hydroxylamine hydrochloride and a base.
The particle morphology and size of the prepared nanoparticles were observed via SEM and TEM, respectively. SEM images of the bare Fe 3 O 4 exhibited the nearly spherical shapes of the particles ( Figure S2a,b), and a significant uniform particle-size distribution was observed. The observed average size of the Fe 3 O 4 particle was~27 nm ( Figure S2c-e). The crystal structure and phase of the prepared nanoparticles were determined via X-ray diffraction (XRD). The strong Bragg peaks of (220), (311), (400), (422), (511), and (440) corresponded to the diffractions from the inverse spinel structure of Fe 3 O 4 ( Figure S2f). The energy-dispersive X-ray spectroscopy (EDS) analysis of the Fe 3 O 4 nanoparticles revealed a set of peaks, which corresponded to iron as well as oxygen ( Figure S3). The characterization data of Ag/Fe 3 O 4 are shown in Figure 2. The TEM and SEM images of Ag/Fe 3 O 4 nanocomposites showed the nearly spherical-shaped agglomerates, respectively (Figure 2a,b). The additional TEM data are shown in Figure S4. The elemental mapping patterns revealed the presence of the main elements, including O, Fe, Si, and Ag (Figure 2c-f). A new peak, which corresponded to silver, is evident compared with the Fe 3 O 4 nanoparticles, thus confirming the presence of the silver coating on the Fe 3 O 4 nanoparticles. In addition, the EDS data of the Ag/Fe 3 O 4 nanoparticles revealed the presence of Fe, O, C, Si, and Ag atoms (Figure 3a). The presence of Si was observed after the surface modification of the Fe 3 O 4 particles via APTMS. The observed particle size was 35.9 nm with a standard deviation of 2.2 nm (Figure 3b). The size of nanomaterials was further analyzed by the Scherrer equation (Tables S1 and S2). The XRD peaks revealed the crystalline nature of the nanoparticles. The peaks indicated the ultrafine nature and small crystallite size of the nanoparticles. The strong Bragg peaks of (111), (200), (220), and (311) corresponded to the diffractions from the FCC (Face-centered Cubic) structure of silver nanoparticles. The absence of spurious diffractions indicated the absence of significant impurities in the sample (Figure 3c). The magnetic properties of the nanoadsorbent were assessed by applying a magnetic field in the range of −30,000 to 30,000 Oe via vibrational sample magnetometry. The bare Fe 3 O 4 nanoparticles exhibited the highest saturation magnetization (M s ) value (67.84 emu/g). However, the value decreased to 49.48 and 40.34 emu/g because of the APTMS coating and combination of silver with the APTMS coating, respectively (Figure 3d). The surface modification and formation of the silver nanoparticles on the surface of the magnetite nanoparticles caused a decrease in the M s value. This result can be attributed to the presence of more diamagnetic material per gram of the material. Zero remanence and coercivity of the magnetization curve suggested that the nanoadsorbents possessed superparamagnetic properties. As shown in Figure S1c-e, Ag/Fe 3 O 4 responded immediately to the external magnetic field, and the collected particles could be dispersed Nanomaterials 2021, 11, 588 6 of 11 again by gentle shaking after removing the magnet. This result indicates that the adsorbents can be easily removed from wastewater via a simple separation procedure. be easily removed from wastewater via a simple separation procedure.
To perform the iodine adsorption experiments, nonradioactive iodide anion (I − ) or radioiodine ( 125 I − ) were used. The calibration curve was plotted to determine the concentrations of I − (λmax = 225 nm) in aqueous media ( Figure S5) via UV-Vis spectroscopy. First, the adsorbent was added to a 100 ppm KI solution in pure water or a NaCl solution, after which the amount of I − absorbed on Ag/Fe3O4 was determined by comparing the UV absorbance at 225 nm for 1 h. Figure 4a reveals that I − in aqueous media could not be captured by the unmodified Fe3O4. Conversely, silver-coated adsorbents efficiently removed I − with a removal efficiency of ~100% in 1 h (Figure 4b). Interestingly, the excellent removal efficiency was also observed using 1.0 M NaCl solution with a Cl − to I − anion ratio ([Cl − ]:[I − ]) exceeding 10 3 :1, thereby indicating the ion-selective adsorption performance of the silver layer.   To perform the iodine adsorption experiments, nonradioactive iodide anion (I − ) or radioiodine ( 125 I − ) were used. The calibration curve was plotted to determine the concentrations of I − (λ max = 225 nm) in aqueous media ( Figure S5) via UV-Vis spectroscopy. First, the adsorbent was added to a 100 ppm KI solution in pure water or a NaCl solution, after which the amount of I − absorbed on Ag/Fe 3 O 4 was determined by comparing the UV absorbance at 225 nm for 1 h. Figure 4a reveals that I − in aqueous media could not be captured by the unmodified Fe 3 O 4 . Conversely, silver-coated adsorbents efficiently removed I − with a removal efficiency of~100% in 1 h (Figure 4b). Interestingly, the excellent removal efficiency was also observed using 1.0 M NaCl solution with a Cl − to I − anion ratio ([Cl − ]:[I − ]) exceeding 10 3 :1, thereby indicating the ion-selective adsorption performance of the silver layer.    Linear fitting of the observed data according to the Langmuir (3) and Freundlich isotherm models (4) revealed that the adsorption mechanism of Ag/Fe 3 O 4 was better described by the Langmuir equation with a correlation factor (R 2 ) of 0.995 (Figure 5a). This result also indicated the monolayer adsorption mechanism, and the observed maximum adsorption capacity (Q max ) obtained using Equation (3) was 847 mg/g. The corresponding parameters for these models are summarized in Table 1. The kinetic parameters of the adsorption are also pivotal to the practical application of the nanoadsorbent. The removal efficiency of I − was measured as a function of time (5-180 min) to determine the optimum time for the desalination experiments (Figure 5b). The adsorption of I − was rapid in the first 60 min, after which it became slower, before finally reaching a plateau after 180 min. The fitting results of the PFO and PSO kinetic models are shown in Figure S6a,b and Table 2. Based on the calculated kinetic parameters, it is clear that the PSO kinetic model fitted better with the kinetic results.

Type of Chemical Kinetics
Parameters R 2 First-order Q e = 613 mg/g 0.976 k 1 = 9.0 × 10 −3 min −1 Second-order Q e = 897 mg/g 0.996 k 2 = 6.03 × 10 −8 gmg −1 min −1 Using these results, we investigated the desalination of radioiodine by Ag/Fe 3 O 4 . For this study, the same adsorbents were immerged into aqueous solutions containing 150 µCi of [ 125 I]NaI. Afterward, the adsorbents were collected by an external magnet. The removal efficiency was determined by measuring the residual radioactivities in the solution and Ag/Fe 3 O 4 nanocomposite. As shown in Figure 6a, high removal efficiencies were observed in the presence of other competing anions as well (e.g., Cl − , Br − , and phosphate). By contrast, the adsorption of radioiodine was completely inhibited in an aqueous solution of nonradioactive NaI, which might be due to the surface area of the adsorbents getting covered by an excess amount of I − . The desalination performance was also evaluated in other environments, such as varied pH values, river waters, and elevated temperatures. More than 99% of the radioactive iodines were captured by Ag/Fe 3 O 4 in 1 h in these environments as well. These results demonstrated that Ag/Fe 3 O 4 successfully and selectively captures I − in the presence of mixed ion species. Next, the reusability of Ag/Fe 3 O 4 was explored via the repetitive adsorption of radioiodine (150 µCi) from water. As shown in Figure 6b, a high removal efficiency (>99%) was observed in seven consecutive processes, suggesting that the adsorbent retained its stability. Moreover, the adsorbed radioiodine anions on the adsorbents were not readily released during the repeated operations.
Several studies have described various silver metal or silver oxide composite nanomaterials that can remove radioactive iodines [3,41]. Removal of unsettled adsorbents after water treatment requires further separation processes. Compared with the previous studies, this method offers a simpler and more efficient method for capturing radioactive materials from different aqueous solutions. Through a single operation for 1 h, most of the radioactive components were selectively captured by Ag/Fe 3 O 4 . Thereafter, the magnetic separation successfully recovered the I − -loaded adsorbent from the aqueous solvent. Additionally, the observed Q max value was favorable compared with those obtained in previous studies (Table S3). As a result of the large-scale synthesis and characterization of Fe 3 O 4 as well as the establishment of the formation of the silver layer, a large number of adsorbents that were used in this study can be easily prepared in a short time. These advantages strongly demonstrate that desalination using Ag/Fe 3 O 4 would be beneficial for the efficient treatment of radioiodine waste. To date, different silver-coated magnetic nanomaterials have been employed in a wide range of applications for specific purposes, including catalysis [42], antibacterial agents [43], imaging [44], and biosensing [45], because of their unique physical and chemical properties. This study would widen the scope of engineered nanomaterials in the field of environmental remediation. However, further optimization and validation of the process is required to investigate the industrial-scale remediation process of radioactive waste.

Conclusions
In this study, we synthesized an Ag/Fe3O4 nanoadsorbent for the desalination of radioiodine. The synthesized nanomaterials were characterized via SEM, TEM, EDS, and XRD. The composite material exhibited high adsorption capacity for I − (847 mg/g) in water. The Ag/Fe3O4 composite nanoadsorbents exhibited high removal efficiency as well as ion-selective desalination in the presence of several competing ions. The material was easily recovered from the treated water by applying an external magnetic field without the significant desorption of radioactivity. Moreover, the adsorbent maintained good desalination performance during seven consecutive remediations. Consequently, it is expected that Ag/Fe3O4-based desalination will present a promising direction and can be developed as a practical method for wastewater treatment.

Conclusions
In this study, we synthesized an Ag/Fe 3 O 4 nanoadsorbent for the desalination of radioiodine. The synthesized nanomaterials were characterized via SEM, TEM, EDS, and XRD. The composite material exhibited high adsorption capacity for I − (847 mg/g) in water. The Ag/Fe 3 O 4 composite nanoadsorbents exhibited high removal efficiency as well as ion-selective desalination in the presence of several competing ions. The material was easily recovered from the treated water by applying an external magnetic field without the significant desorption of radioactivity. Moreover, the adsorbent maintained good desalination performance during seven consecutive remediations. Consequently, it is expected that Ag/Fe 3 O 4 -based desalination will present a promising direction and can be developed as a practical method for wastewater treatment.  Figure S3: Figure S3. EDS analysis of iron oxide nanoparticles; Figure S4: Figure S4. TEM images of Ag/Fe 3 O 4 nanocomposite; Figure S5: Calibration curve to determine the unknown concentration using UV-Visible Spectrometer at 226 nm; Figure S6: (a) Pseudo-second-order kinetics study for Ag/Fe 3 O 4 , (b) Pseudo-first-order kinetics study for Ag/Fe 3 O 4 ;

Data Availability Statement:
The data presented in this article are available on request from the corresponding authors.

Conflicts of Interest:
The authors declare no conflict of interest.