Efficient Iodine Removal by Porous Biochar-Confined Nano-Cu2O/Cu0: Rapid and Selective Adsorption of Iodide and Iodate Ions

Iodine is a nuclide of crucial concern in radioactive waste management. Nanomaterials selectively adsorb iodine from water; however, the efficient application of nanomaterials in engineering still needs to be developed for radioactive wastewater deiodination. Artemia egg shells possess large surface groups and connecting pores, providing a new biomaterial to remove contaminants. Based on the Artemia egg shell-derived biochar (AES biochar) and in situ precipitation and reduction of cuprous, we synthesized a novel nanocomposite, namely porous biochar-confined nano-Cu2O/Cu0 (C-Cu). The characterization of C-Cu confirmed that the nano-Cu2O/Cu0 was dispersed in the pores of AES biochar, serving in the efficient and selective adsorption of iodide and iodate ions from water. The iodide ion removal by C-Cu when equilibrated for 40 min exhibited high removal efficiency over the wide pH range of 4 to 10. Remarkable selectivity towards both iodide and iodate ions of C-Cu was permitted against competing anions (Cl−/NO3−/SO42−) at high concentrations. The applicability of C-Cu was demonstrated by a packed column test with treated effluents of 1279 BV. The rapid and selective removal of iodide and iodate ions from water is attributed to nanoparticles confined on the AES biochar and pore-facilitated mass transfer. Combining the advantages of the porous biochar and nano-Cu2O/Cu0, the use of C-Cu offers a promising method of iodine removal from water in engineering applications.


Introduction
Nuclear power produces about 10% of the total global electricity and about 5% of the total in China, and it will continue to be a viable alternative to fossil fuels in the future [1]. While nuclear power contributes to electricity supply and reduces CO 2 emissions, it also poses significant challenges in terms of radioactive waste treatment and disposal. The radionuclides produced by nuclear reaction processes such as in uranium fission mainly contain 129/131 I, 127 Xe, 134/137 Cs, 90 Sr, 99 Tc, and 79 Se [1]. Among these, iodine is particularly problematic due to its volatility. Before treatments involving high temperatures such as vitrification, the liquidus iodine needs to be captured efficiently to avoid the release of gaseous wastes [2]. Additionally, the emergency accident in Fukushima, Japan, released radioactive iodine into the water and soil [3,4]. Radioactive iodine poses a significant threat to living creatures, including humans, and is considered one of the most dangerous radionuclides. As one of the halogen elements, iodine is highly soluble and mobile in terms of its chemical properties. It can quickly enter the human body through the food chain and can cause damage due to its chemical toxicity and radioactivity. Therefore, it is necessary to develop efficient methods to remove radioactive iodine.
Among the different halide removal treatments, adsorption still attracts significant interest because of its operational simplicity and flexibility [5,6]. Activated carbon removes gaseous iodine via physical adsorption, and the ion exchange resin enriches iodine in the As the raw material of the biochar, Artemia egg shells were washed with deionized water to remove salt and impurities. The washed Artemia egg shells were calcinated under vacuum at 550 • C for 3 h with a nitrogen flow rate of 60 mL/min, and the resulting product was Artemia egg shell biochar, noted as AES biochar. The Cu + precursor solution was prepared with 1.06 g of polyethyleneimine (PEI) and 1.52 g of Cu(NO 3 ) 2 ·3H 2 O dissolved in 100 ml of deionized water. The Cu + precursor solution and 1.0 g of AES biochar were vigorously mixed by stirring of 12 h. The mixture was then transferred to a 200 mL tetrafluoroethylene hydrothermal reactor and heated hermetically at 220 • C for 2 h. The solid was then filtered and dried at 60 • C to obtain Artemia egg shell biochar-hosted nano-Cu 2 O/Cu 0 , denoted as C-Cu. The copper concentration in the filtrate was determined via atomic absorption spectrometry (AAS, AA6800, Shimadzu, Kyoto, Japan) to calculate the copper content of the C-Cu.

Characterization
The morphology and structure of the adsorbents were recorded using a scanning electron microscope (SEM, S-3400N II, Hitachi, Tokyo, Japan) and transmission electron microscope (TEM, JEM-2010FX, JEOL, Tokyo, Japan). The specific surface area (SSA) and pore size distribution of the C-Cu and AES biochar were determined via N 2 adsorption/desorption with a surface area and pore size analyzer (ASAP 2420, Micromeritics, Norcross, GA, USA). The specific surface areas were calculated from the Brunauer-Emmett-Teller (BET) equation. The total pore volumes were estimated using the adsorbed N 2 amount at the relative pressure P/P 0 of 0.99, and the micropore volumes were calculated from the t-plot method. The pore size distribution was obtained based on the Barrett-Joyner-Halenda (BJH) method. X-ray diffraction (XRD) data for the Cu 2 O, AEC biochar, and Cu-C were collected using an X-ray diffractometer (D/max2550PC, Rigaku, Tokyo, Japan) at a scanning speed of 5 • 2θ/min over a range of 10 • to 100 • . The zeta potentials of the C-Cu, AES biochar, and Cu 2 O were determined at different pH values using a Zetasizer (Nano ZS-90) from Malvern Instruments, Malvern, UK.

Iodine Adsorption
In the iodine adsorption experiments, stable isotopes of 127 I was used instead of radioactive iodine 129/131 I. Solutions containing I − or IO 3 − were prepared with sodium iodide or sodium iodate, respectively. Batch experiments were used for static adsorption, and the C-Cu was placed into solutions with 10 mg/L of I − or IO 3 − at pH = 7.0 ± 0.2. The adsorption system was maintained at 25 • C using a thermostatic shaker with an agitation speed of 180 rpm. The dosage of C-Cu during the kinetic initiation process was 1.0 g and the solution volume was 1000 mL. As the adsorption process continued to various time points, supernatant samples were taken and analyzed using a spectrophotometer for the concentrations of I − or IO 3 − [27]. In the isotherm experiments, 50 mL I − or IO 3 − solutions with different initial concentrations of 1, 5, 10, 20, 50, 100, and 200 mg/L were contacted with 0.025 g of C-Cu for 24 h to allow adsorption equilibrium to be achieved. The pH of the solutions was adjusted to different values ranging between 2 and 12 to investigate the effect of the solution pH on the iodide and iodate ion adsorption onto the C-Cu. Na 2 SO 4 , NaCl, and NaNO 3 were used in the selective adsorption experiments, and the competing anions of SO 4 2− , Cl − , and NO 3 − had molar ratios of 1, 5, 10, 20, 50, and 100 mol/mol. Cu 2 O and AEC biochar were used as the reference materials for the static adsorption experiments.
The column adsorption experiment was conducted to evaluate the working conditions of the adsorbents in the fixed-bed reactor to investigate the removal efficiency in engineering applications. A column with a 10 mm inner diameter was packed with 1.5 g of C-Cu to form a 25-mm-high fixed bed. The influent-simulated radioactive wastewater was percolated into the column at a constant flow rate using a peristaltic pump containing I − = 2 mg/L, Cl − = 150 mg/L, SO 4 2− = 50 mg/L, NO 3 − = 50 mg/L, F − = 50 mg/L, ReO 4 − = 10 mg/L, and HCO 3 − = 50 mg/L. An automatic collector collected the effluent samples for the iodide ion concentration measurements.

Characterization
The microstructure and chemical components of the Artemia egg shell biochar-hosted nano-Cu 2 O/Cu 0 (C-Cu) is shown in Figure 1.
points, supernatant samples were taken and analyzed using a spectrophotometer for the concentrations of I − or IO3 − [27]. In the isotherm experiments, 50 mL I − or IO3 − solutions with different initial concentrations of 1, 5, 10, 20, 50, 100, and 200 mg/L were contacted with 0.025 g of C-Cu for 24 h to allow adsorption equilibrium to be achieved. The pH of the solutions was adjusted to different values ranging between 2 and 12 to investigate the effect of the solution pH on the iodide and iodate ion adsorption onto the C-Cu. Na2SO4, NaCl, and NaNO3 were used in the selective adsorption experiments, and the competing anions of SO4 2− , Cl − , and NO3 − had molar ratios of 1, 5, 10, 20, 50, and 100 mol/mol. Cu2O and AEC biochar were used as the reference materials for the static adsorption experiments.
The column adsorption experiment was conducted to evaluate the working conditions of the adsorbents in the fixed-bed reactor to investigate the removal efficiency in engineering applications. A column with a 10 mm inner diameter was packed with 1.5 g of C-Cu to form a 25-mm-high fixed bed. The influent-simulated radioactive wastewater was percolated into the column at a constant flow rate using a peristaltic pump containing I − = 2 mg/L, Cl − = 150 mg/L, SO4 2− = 50 mg/L, NO3 − = 50 mg/L, F − = 50 mg/L, ReO4 − = 10 mg/L, and HCO3 − = 50 mg/L. An automatic collector collected the effluent samples for the iodide ion concentration measurements.

Characterization
The microstructure and chemical components of the Artemia egg shell biochar-hosted nano-Cu2O/Cu 0 (C-Cu) is shown in Figure 1. The C-Cu sample possessed a rough surface (Figure 1a) and the length and width were around 2-3 μm (Figure 1b). Fine particles can be observed in the TEM images in Figure 1b,c. In the XRD pattern in Figure 1d, the AES biochar is mainly amorphous carbon, which is also shown in the C-Cu sample. The characteristic lines of Cu2O (JCPDS No. 65-3288) exposed well-crystalized Cu2O in the commercial cuprous oxide and C-Cu, while Cu 0 (JCPDS No. 04-0836) was only detected in the C-Cu. The particle sizes of the Cu2O and Cu 0 in the C-Cu calculated from Scherrer's formula were 36 nm and 35 nm, respectively. The lattices in the HR-TEM images clearly present Cu2O (111) and The C-Cu sample possessed a rough surface (Figure 1a) and the length and width were around 2-3 µm (Figure 1b). Fine particles can be observed in the TEM images in Figure 1b,c. In the XRD pattern in Figure 1d, the AES biochar is mainly amorphous carbon, which is also shown in the C-Cu sample. The characteristic lines of Cu 2 O (JCPDS No. 65-3288) exposed well-crystalized Cu 2 O in the commercial cuprous oxide and C-Cu, while Cu 0 (JCPDS No. 04-0836) was only detected in the C-Cu. The particle sizes of the Cu 2 O and Cu 0 in the C-Cu calculated from Scherrer's formula were 36 nm and 35 nm, respectively. The lattices in the HR-TEM images clearly present Cu 2 O (111) and Cu 0 (111) planes in Figure 1e,f. As listed in Table 1, the Brunauer-Emmett-Teller (BET) specific surface area and pore volume of C-Cu decreased after the dispersion of Cu species. However, the micropore volume and the average Barrett-Joyner-Halenda (BJH) pore size were comparable to the AES biochar. The AES biochar showed a micro-meso-macro pore distribution (Figure 1h inset) with the most probable pore size of 4.8 nm, in accordance with the desorption hysteresis typical for mesoporous materials (Figure 1h). However, the mesopore and macropore volumes of the C-Cu were about 50% of those of the AES biochar, indicating that the dispersed nanoparticles of Cu 2 O and Cu 0 blocked some of the mesopores and macropores of the C-Cu. Thus, the hierarchical porous structure of the AES (Figure 1g) remained in the C-Cu, with the pores confined to the nanoparticle dispersion. The characterization results demonstrated that nanoparticles of Cu 2 O and Cu 0 were loaded successfully on the AES biochar using the abovementioned synthesis method. The content of Cu in the C-Cu was 117.8 mg/g. Table 1. Specific surface area, pore volume, and pore size values of AES biochar and C-Cu.

Iodine Removal Efficiency by C-Cu
The iodine removal efficiency was evaluated using the removal kinetics and isotherm adsorption of the C-Cu, and the experimental data and fitting results are illustrated in Figures 2 and 3, respectively. Pseudo-first order and pseudo-second order models are shown in Equations (1) and (2), respectively [28].
Pseudo-first order model: Pseudo-second order model: Here, Q t (mg/g) is the adsorbed amount of iodide ions or iodate ions at a certain time t (min); Q e (mg/g) is the adsorption capacity of the iodide ions or iodate ions at equilibrium; k 1 (1/min) and k 2 (g·mg −1 ·min −1 ) are the kinetic rate constants of the pseudo-first order and pseudo-second order models, respectively.
It is clear from the kinetic data of the removal of iodide ions by C-Cu in Figure 2a that the rate of iodide ion adsorption was very rapid, reaching 50% of the maximum adsorption capacity at 10 min and the adsorption equilibrium at 40 min. In Figure 2b, the iodate ion adsorption capacity reached half of its maximal capacity at 20 min, and then the adsorption rate slowed and equilibrated at 60 min. The adsorption of iodide and iodate ions onto C-Cu was fitted using pseudo-first order and pseudo-second order models, and the results more consistent with the pseudo-second order kinetic model ( Table 2). This kinetic fitting results explained the external and internal diffusion and adsorption of iodide and iodate anions onto the active sites of the porous C-Cu [28].
The Langmuir and Freundlich models shown in Equations (3) and (4) are used to fit the isotherm adsorption data, respectively [29].
Langmuir isotherm model: Freundlich isotherm model: Here, Q e (mg/g) and C e (mg/L) are the adsorbed amount and concentration of iodide ions or iodate ions at equilibrium; Q m (mg/g) is the maximum adsorption capacity of the Langmuir model; K L (L/mg) is the ratio of the adsorption and desorption rates; K F (L 1/n ·mg (1−1/n) ·g −1 ) and n are the Freundlich model constants.
for C-Cu to adsorb iodide ions. At 20 °C, the maximum adsorption capacity reached 86.8 mg/g. Regarding the adsorption of iodate ions onto the C-Cu, the temperature presented opposite effects on the capacity compared with the iodide ions; the maximum adsorption capacity values increased with the increases in temperature to 29.8 mg/g, 37.4 mg/g, and 43.1 mg/g at 20 °C, 40 ℃, and 60 °C, respectively. Table 3 shows the regression coefficients of the iodine adsorption data onto C-Cu fitted by the Langmuir and Freundlich isothermal models, where the data are more consistent with the Freundlich model.  mg/g. Regarding the adsorption of iodate ions onto the C-Cu, the temperature presented opposite effects on the capacity compared with the iodide ions; the maximum adsorption capacity values increased with the increases in temperature to 29.8 mg/g, 37.4 mg/g, and 43.1 mg/g at 20 °C, 40 ℃, and 60 °C, respectively. Table 3 shows the regression coefficients of the iodine adsorption data onto C-Cu fitted by the Langmuir and Freundlich isothermal models, where the data are more consistent with the Freundlich model.   In Figure 3, the maximum adsorption capacity values of the iodide ions decreased with the increase in temperature, indicating that low temperatures were more favorable for C-Cu to adsorb iodide ions. At 20 • C, the maximum adsorption capacity reached 86.8 mg/g. Regarding the adsorption of iodate ions onto the C-Cu, the temperature presented opposite effects on the capacity compared with the iodide ions; the maximum adsorption capacity values increased with the increases in temperature to 29.8 mg/g, 37.4 mg/g, and 43.1 mg/g at 20 • C, 40°C, and 60 • C, respectively. Table 3 shows the regression coefficients of the iodine adsorption data onto C-Cu fitted by the Langmuir and Freundlich isothermal models, where the data are more consistent with the Freundlich model. The removal mechanism of iodine by C-Cu was extrapolated using XRD patterns of the C-Cu before and after iodine adsorption, with Compared with the iodine removal materials listed in Table 4, the as-prepared Artemia egg shell biochar-hosted nano-Cu 2 O/Cu 0 showed effective iodine removal performance in terms of the adsorption kinetics and maximum actual adsorption capacity (Q a ) [30][31][32][33]. The hierarchical porous structure of the Artemia egg shell biochar facilitates the faster mass transfer of iodide and iodate anions onto the C-Cu surface, leading to equilibrium being achieved much quicker at 40 min. Moreover, the hierarchical porous structure promotes nano-Cu 2 O and Cu 0 dispersion on the AES biochar surface, which provides abundant active sites for iodide or iodate ion sorption. Thus, high maximal adsorption capacities are achieved for iodide and iodate ions.

Effect of Solution pH on Iodine Removal
The iodine species vary at different solution pH levels, mainly occurring as iodide anions and iodate anions [13]. The effects of the solution pH on iodide and iodate anions are illustrated in Figure 4. In the experiment, the AES biochar removed 2.6% to 10.5% of the iodine as both iodide and iodate anions in the pH range of 2.1 to 12.0, while the C-Cu achieved good iodine removal at neutral pH. Over a wide pH range of 4.0 to 9.1, C-Cu maintained iodide ion removal rates higher than 81.5%, with maximum removal rates of around 96.4% at pH = 6.1 and 7.2. With increasing pH levels of 10.0, 10.9, and 12.0, the rate of iodide ion removal by C-Cu rapidly declined, reaching only 10.9% at 12.0. This pattern was consistent with the iodide ion removal by Cu 2 O, but due to the wider pH range and higher iodine uptake rates, the C-Cu was more efficient for iodine removal. The removal rate was related to the nanoparticle stability at different solution pH levels, as shown in Table 5. In acid solutions, the nanoparticles on the C-Cu leached by up to 26.8% at pH 3.1, which decreased the iodide and iodate ion adsorption and removal rates at acidic pH values. On the other hand, the nanoparticles remained stable in near-neutral to alkaline solutions, with a leaching rate of 2.0% at pH 7.2. Moreover, the zeta potentials of the AES biochar, Cu 2 O, and C-Cu, as illustrated in Figure 4c, can be used to explain the iodide ion removal efficiency. All sorbents showed decreased seta potentials with increasing pH values, but the AES biochar showed negative zeta potentials across the majority of the experimental pH range, which increased the repulsion towards the iodide anions on the biochar surface. In contrast, both Cu 2 O and C-Cu showed positive zeta potentials in the acidic to near-neutral pH range, with zero charge potentials of 5. achieved good iodine removal at neutral pH. Over a wide pH range of 4.0 to 9.1, C-Cu maintained iodide ion removal rates higher than 81.5%, with maximum removal rates of around 96.4% at pH = 6.1 and 7.2. With increasing pH levels of 10.0, 10.9, and 12.0, the rate of iodide ion removal by C-Cu rapidly declined, reaching only 10.9% at 12.0. This pattern was consistent with the iodide ion removal by Cu2O, but due to the wider pH range and higher iodine uptake rates, the C-Cu was more efficient for iodine removal. The removal rate was related to the nanoparticle stability at different solution pH levels, as shown in Table 5. In acid solutions, the nanoparticles on the C-Cu leached by up to 26.8% at pH 3.1, which decreased the iodide and iodate ion adsorption and removal rates at acidic pH values. On the other hand, the nanoparticles remained stable in near-neutral to alkaline solutions, with a leaching rate of 2.0% at pH 7.2. Moreover, the zeta potentials of the AES biochar, Cu2O, and C-Cu, as illustrated in Figure 4c, can be used to explain the iodide ion removal efficiency. All sorbents showed decreased seta potentials with increasing pH values, but the AES biochar showed negative zeta potentials across the majority of the experimental pH range, which increased the repulsion towards the iodide anions on the biochar surface. In contrast, both Cu2O and C-Cu showed positive zeta potentials in the acidic to near-neutral pH range, with zero charge potentials of 5.

High Selectivity of Iodide and Iodate Ions against Competitive Anions
As shown in Figure 5, C-Cu demonstrated remarkable selectivity towards both iodide and iodate ions against competing anions (Cl − /NO 3 − /SO 4 2− ) at high concentrations. Neither the competing anion species nor the concentration significantly weakened the adsorption of iodide ions onto C-Cu in the experimental. The distribution coefficient K d increased by 18-fold when compared to the AES biochar, indicating that C-Cu has an extraordinarily high affinity for iodide ions that is not only brought about by electrostatic effects. The adsorption selectivity of C-Cu for iodide ions increased by around 20% over that of Cu 2 O, which should also be mentioned because it suggested that the affinity sites were used to their greater potential. The hierarchical porous structure of the AES biochar promoted the in situ generation of nano-Cu 2 O and Cu 0 and uniform nanoparticle dispersion on the porous surface, which was attributed to the presence of high-affinity sites for iodide ions. The high selectivity of C-Cu towards iodine was also exhibited by the iodate ion adsorption. Even while the adsorption of C-Cu towards the iodate ions was somewhat reduced by the three competing anions with high concentrations, the K d value of the iodate ions against 100-fold Cl − (mol/mol) for the C-Cu was still 8 times higher than that of the AES biochar. Therefore, C-Cu offered superior iodine removal performance for natural water sources where large amounts of anions were present.
As shown in Figure 5, C-Cu demonstrated remarkable selectivity towards both iodide and iodate ions against competing anions (Cl − /NO3 − /SO4 2− ) at high concentrations. Neither the competing anion species nor the concentration significantly weakened the adsorption of iodide ions onto C-Cu in the experimental. The distribution coefficient Kd increased by 18-fold when compared to the AES biochar, indicating that C-Cu has an extraordinarily high affinity for iodide ions that is not only brought about by electrostatic effects. The adsorption selectivity of C-Cu for iodide ions increased by around 20% over that of Cu2O, which should also be mentioned because it suggested that the affinity sites were used to their greater potential. The hierarchical porous structure of the AES biochar promoted the in situ generation of nano-Cu2O and Cu 0 and uniform nanoparticle dispersion on the porous surface, which was attributed to the presence of high-affinity sites for iodide ions. The high selectivity of C-Cu towards iodine was also exhibited by the iodate ion adsorption. Even while the adsorption of C-Cu towards the iodate ions was somewhat reduced by the three competing anions with high concentrations, the Kd value of the iodate ions against 100-fold Cl − (mol/mol) for the C-Cu was still 8 times higher than that of the AES biochar. Therefore, C-Cu offered superior iodine removal performance for natural water sources where large amounts of anions were present.

Continuous Adsorption Performance
To further investigate the applicability of C-Cu in an engineering continuous flow treatment system, a fixed-bed column adsorption experiment was conducted, with commercial Cu2O powder used as a comparison, and the experimental data are shown in Figure 6. The concentration of iodide ions in the influent was 2.0 mg/L, and the concentration in the effluent of 941 BV remained stable at about 0.78 mg/L, which provided an iodide ion removal rate of about 61%. After this, the Iconcentration in the effluent started to rise and a breakthrough occurred when the effluent reached 1279 BV. The fixed-bed column packed with C-Cu processed more than four times as much water

Continuous Adsorption Performance
To further investigate the applicability of C-Cu in an engineering continuous flow treatment system, a fixed-bed column adsorption experiment was conducted, with commercial Cu 2 O powder used as a comparison, and the experimental data are shown in Figure 6. The concentration of iodide ions in the influent was 2.0 mg/L, and the concentration in the effluent of 941 BV remained stable at about 0.78 mg/L, which provided an iodide ion removal rate of about 61%. After this, the I − concentration in the effluent started to rise and a breakthrough occurred when the effluent reached 1279 BV. The fixed-bed column packed with C-Cu processed more than four times as much water as the Cu 2 O column did, while also having a lower iodide ion concentration in the effluent, which was ascribed to the hierarchical porous structure of the C-Cu and pore-confined nanoparticles. The large water treatment volumes and high iodine removal performance rates under engineering conditions demonstrated the application potential of C-Cu for the deep treatment of iodine-containing wastewater.
as the Cu2O column did, while also having a lower iodide ion concentration in the effluent, which was ascribed to the hierarchical porous structure of the C-Cu and pore-confined nanoparticles. The large water treatment volumes and high iodine removal performance rates under engineering conditions demonstrated the application potential of C-Cu for the deep treatment of iodine-containing wastewater.

Conclusions
A novel adsorbent was synthesized via the in situ precipitation and reduction of Cu2O and Cu 0 on a porous biomatrix of Artemia egg shell biochar. SEM, TEM, XRD, and BET analyses confirmed that approximately 35 nm of nano-Cu2O/Cu 0 dispersed in the pores of the AES biochar. The C-Cu induced a rapid adsorption equilibrium for iodide and iodate ions. The adsorption isotherm experiments showed that the maximum actual adsorption capacities of the iodide and iodate ions by C-Cu reached 86.8 and 43.1 mg/g at pH = 7.0 ± 0.2, respectively. Moreover, for the iodide and iodate ions, the C-Cu achieved Kd values about 18 and 8 times greater than for the AES biochar against Cl − at a 100-fold molar ratio. These excellent adsorption performance results were attributed to mechanisms including electrostatic interactions and precipitation. The continuous adsorption experiments demonstrated the potential of C-Cu for engineering applications. Overall, the rapid and selective adsorption of iodide and iodate ions onto C-Cu makes this nanocomposite attractive for efficiently removing radioactive iodine from water.

Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.

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

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

Conclusions
A novel adsorbent was synthesized via the in situ precipitation and reduction of Cu 2 O and Cu 0 on a porous biomatrix of Artemia egg shell biochar. SEM, TEM, XRD, and BET analyses confirmed that approximately 35 nm of nano-Cu 2 O/Cu 0 dispersed in the pores of the AES biochar. The C-Cu induced a rapid adsorption equilibrium for iodide and iodate ions. The adsorption isotherm experiments showed that the maximum actual adsorption capacities of the iodide and iodate ions by C-Cu reached 86.8 and 43.1 mg/g at pH = 7.0 ± 0.2, respectively. Moreover, for the iodide and iodate ions, the C-Cu achieved K d values about 18 and 8 times greater than for the AES biochar against Cl − at a 100-fold molar ratio. These excellent adsorption performance results were attributed to mechanisms including electrostatic interactions and precipitation. The continuous adsorption experiments demonstrated the potential of C-Cu for engineering applications. Overall, the rapid and selective adsorption of iodide and iodate ions onto C-Cu makes this nanocomposite attractive for efficiently removing radioactive iodine from water.