A novel ion-imprinted carbon material induced by hyperaccumulation

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Functional Nanostructured Materials (including low-D carbon)

A novel ion-imprinted carbon material induced by hyperaccumulation pathway for the selective capture of uranium Jiahui Zhu, Qi Liu, Jingyuan Liu, Rongrong Chen, Hongsen Zhang, Jing Yu, Milin Zhang, Rumin Li, and Jun Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b09022 • Publication Date (Web): 01 Aug 2018 Downloaded from http://pubs.acs.org on August 1, 2018

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ACS Applied Materials & Interfaces

A

novel

ion-imprinted

carbon

material

induced

by

hyperaccumulation pathway for the selective capture of uranium Jiahui Zhu,a Qi Liu,*a,c Jingyuan Liu,a,c Rongrong Chen,b,c Hongsen Zhang,a,d Jing Yu,a Milin Zhang,a,e Rumin Li,a,c and Jun Wang,*a,b,c a. Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, Harbin Engineering University, Harbin 150001, China b. Institute of Advanced Marine Materials, Harbin Engineering University, Harbin 150001, China. c. Harbin Engineering University Capital Management Co. Ltd, Harbin 150001, China. d. Modern Analysis, Test and Research Center, Heilongjiang University of Science and Technology, Harbin 150027, China. e. College of Science, Heihe University, Heihe 164300, China.

＊Corresponding author: Jun Wang : Tel.: +86 451 8253 3026; Fax: +86 451 8253 3026; E-mail: [email protected] Qi Liu: Tel.: +86 451 8253 3026; Fax: +86 451 8253 3026; E-mail: [email protected]

Abstract The development of nuclear energy is significant for resource sustainability. Uranium is the main nuclear fuel and its effective absorption has captured the attention of researchers. In this study, the green technologies, hyperaccumulation effect of the plant and ion-imprinted technology were used to prepare the uranium ion-imprinted hierarchically porous carbon material (II-HPC). At the same time, a non-imprinted hierarchically porous carbon (HPC) was prepared for comparison. The adsorption isotherm was fitted to Langmuir model and maximum sorption capacity of II-HPC was 503.64 mg g-1 at 298K. The kinetic data followed the pseudo-second-order model, indicating a dominant role of chemisorption. Initial studies were performed on a lab-scale simulated continuous-flow system for the adsorption kinetics testing of II-HPC in simulated seawater. The results showed that the amount of uranium adsorbed after 35 days was 0.379 mg g -1, which determined that II-HPC adsorbent is a potential material for enrichment of U (VI) from the seawater.

Keywords: hyperaccumulation effect; ion-imprinted; hierarchical porous carbon; uranium (VI) adsorption; simulated seawater

1. Introduction Limited resource availability has motivated the interest for researchers in the development of new and cleaner energy technology. The International Atomic Energy Agency predicted that nuclear power will be the main energy sources over the period 2015–20301. For the main nuclear fuel, the enrichment of uranium is of critical importance in terms of sustainable development of the energy industry. The terrestrial uranium reserves are about 7.1 million tons which limits supply to about 100 years2. Therefore, researchers are directing their attention to seawater for the selective extraction of uranium. The total amount of uranium is estimated at 4.5 billion tons in the seawater, which provides a much longer sustainable resource for uranium supplying nuclear energy for thousands of years3-4. 1

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ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

However, there are many competing metal ions at different concentrations in seawater and the concentration of uranium is only 3.3 ppb5-6. So the selective capture of uranium from seawater presents a great enormous challenge. In recent times, a variety of separation methods, such as flotation 7, ion-exchange8, co-precipitation9 and adsorption10-11, have been applied to remove uranium from seawater. The adsorption method is regarded as one of the more effective and attractive process, because of its simple operation, low energy consumption and high adsorption capacity12. A series of adsorbents including organic polymers, metal-organic frameworks and activated carbon sorbents13-14, have been developed as the absorbent material. However, further application of the materials for the capture uranium from seawater is inhibited due to the lower adsorption capability in mild alkaline conditions. Therefore, the challenge is to prepare an adsorbent with chemical stability, high selectivity and high adsorption capacity for uranium. Carbon materials with large specific surface area, chemical stability and thermal stability, as an effective adsorbent, show excellent adsorption capacity15-17. In recent years, numerous studies on carbon materials have been carried out for the removal of uranium. Mellah et al. studied activated carbon for the adsorption of uranium (VI)18. Gu et al. synthesized carbon nanotubes aerogels for efficient uranium adsorption 19. Wang et al. described the enrichment of U(VI) by graphene oxide nanoribbons20. However, the practical application of these carbon materials for removing uranium from seawater is limited owing to the low selectivity for U (VI). To improve the selectivity of the materials, an ion-imprinting strategy has shown promise for the preparation of materials. It is based on the polymerization between monomers and the template ions, which provides a highly selective binding site21-22. For instance, Hua et al. synthesized ion-imprinted mesoporous silica adsorbent for the enrichment of uranium, which is considered as a promising selective material23. Preetha et al. evidenced the feasibility of removing uranium selectively from nuclear power reactor effluents by ion imprinted polymer materials24. Rao et al. investigated the molecular imprinted polymeric microbeads for the selective separation of uranium25. However, there are few studies on the capture of uranium in a flowing simulated seawater flume system by ion-imprinted materials. The exploration of biological engineering methods is an exciting research area and it provides new ideas for the design of green carbon material26. The researchers mimic biological structure to prepare promising advanced carbon materials for the application in different fields, which breaks through the conventional methods of chemical synthesis. Natural plants have a hierarchical architecture to facilitate efficient transport of electrolytes to the entire plants. Furthermore, the plants concentrate metal ions through adsorption by their roots for transferring to their shoots27. The term ―hyperaccumulation effect‖ was coined for the plants28. Therefore ， the ion-imprinted technology and hyperaccumulation effect of the plant were combined to prepare the uranium ion-imprinted hierarchically porous carbon material. Suaeda glauca as a halophytic plant is chosen due to its exceptional ability to accumulate metal ions, which can be converted into hierarchical porous carbon material by high temperature carbonization. The synthesized hierarchical carbon material maintains the memory effect on uranium for improvement of the selectivity and adsorption capacity of the material for uranium adsorption. More importantly, this material is different from the traditional carbon material in powder and it is the columnar in structure, which maintains stability for the dynamic measurement of adsorption in lab-scale simulated continuous-flow system. In this study, a novel ion-imprinted hierarchical porous carbon material (II-HPC) induced by hyperaccumulation pathway of the plant and non-imprinted hierarchically porous carbon composites (HPC) were prepared for the capture of uranium. The materials were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) to analyze the microstructure. Furthermore, the selectivity for uranium was evaluated in simulated seawater and adsorption kinetics was studied in a lab-scale simulated continuous-flow system. II-HPC adsorbent showed excellent performance for U (VI) enrichment. 2


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2.

Experimental Section

2.1 Preparation of II-HPC adsorbent Naturally grown suaeda glauca was collected and cultivated hydroponically in the uranium solution of concentration 200 mg L-1, which continued for 5 days to promote the hyperaccumulation of uranium (VI). In the process, uranium (VI) was absorbed by the roots and translocated to the entire plant. The plants were then harvested from the solution and the stems of the plants were picked out, washed and dried. The dried samples were carbonized for 2 h at 800 °C under N2 protection at a ramp rate of 2 °C min−1. After that, the samples were washed with 1M HNO3 to remove the imprinted uranium ions and chemical oxidation, which were then remained in the sodium hydroxide solutions for the activation 12 h. The II-HPC adsorbent was obtained after washing and dried. At the same time, the pure HPC sample was obtained from the stems of suaeda glauca without the hyperaccumulation of uranium ions. The details of the experimental process of uranium adsorption and material characterization are given in supporting information. 3. Results and discussion 3.1 Characterization

Fig. 1 The schematic illustration for the synthesis of ion-imprinted hierarchically porous carbon material (II-HPC).

Fig.1 illustrated the synthesis of II-HPC adsorbent. Suaeda glauca as the saline tolerance plant is chosen for its excellent ability to adsorb metal ions. It is cultivated hydroponically in high concentrations of uranium solution. We harvested the stems of the plants for analysis after washing and drying treatment. Then the sample was prepared by high temperature carbonization under the protection of nitrogen. Uranium (VI) was removed by HNO3 and uranium ion-imprinted hierarchically porous carbon composites (II-HPC) were obtained and non-imprinted hierarchically porous carbon composites (HPC) also was prepared for comparison. In particular, the uranium content also was monitored by Energy dispersive X-ray spectroscopy (EDS) and the results indicated that it was successfully removed as shown in Fig.S1. Elemental analysis was performed to determine the compositions of HPC and II-HPC. It demonstrated HPC and II-HPC consists of C, H, N and O elements as shown in Table S1.

3



Fig. 2 SEM images of II-HPC adsorbent. Longitudinal section (a), transversal surface (b), (c) and (d), sidewall of the channels (e).

Scanning electron microscopy (SEM) of the II-HPC adsorbent is shown in Fig. 2 (a-e) and which demonstrates the existence of the three-dimensional hierarchical porous structure. As seen from Fig. 2 (a), along with the longitudinal section, there are long parallel channels corresponding to vasculature and parenchymal cells in the plants. Fig. 2 (b) and (c) indicate a mass of pores of diameter ~5 um appearing on the transverse section. What's even more remarkable is the existence of many transverse pores of about 1~3 um in diameter in the sidewalls of these channels (Fig.2 (d) and (e)). These images demonstrate the porous nature of the hierarchical structures of II-HPC adsorbent. The porous architecture provides abundant and accessible sites for uranium ions. N2 adsorption–desorption measurements were performed to determine the pore structure of II-HPC and HPC in Fig. S2 (a) and (b). They are typical the mixture of reversible Type I and Type IV isotherms characteristic of micro-mesoporous materials with H4 hysteresis loop, which demonstrated the hierarchical structure of HPC and II-HPC29. The porosity of HPC and II-HPC are 18.79% and 15.92%. The Brunauer–Emmett–Teller (BET) specific surface area of II-HPC and HPC is 367.8 and 154.49 m2 g-1. After ion-imprinting, the surface area decreases and the pore diameter are slightly increased from 1.976 to 2.310 nm. These results attribute to that the adsorption of U (VI) is mainly dominated by ions recognition or specific adsorption30. The related parameters of the porous

HPC II-HPC

10

20

30

40

50

60

70

80

4000

1157 1627

2885

(100)

II-HPC

3439

Intensity (a.u.)

HPC

3500

3000

2000

1500 -1

2(degree)

1323

(b)

(002)

1489

(a)

1402

structure are shown in Table S2.

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Wavenumber (cm )

Fig. 3 XRD patterns (a) and FT-IR spectra (b) of the HPC and II-HPC adsorbent.

4


1000

Page 5 of 15

To determine the crystalline structure of prepared HPC and II-HPC adsorbents, XRD patterns measurement were conducted, as shown in Fig. 3(a). The broad peaks at 24.4°and 43.7°are assigned to (002) and (100) graphite planes, respectively31. From a comparison of XRD patterns of HPC and II-HPC, the hyperaccumulation pathway does not transform the crystal structure of the adsorbent. FT-IR spectra of HPC and II-HPC adsorbents are shown in Fig. 3(b). They have absorption bands of hydroxyl and free amine groups at 3439 cm-132. The peaks appearing at 2885 cm-1 are ascribed to the fatty acyl chains C–H groups33. Peaks around 1627 cm−1 represent the stretching vibration of C=N in HPC and II-HPC34. The appearance of another two peaks at 1489 and 1402 cm−1 are attributed to the symmetric COO- stretching bands35. We see that the C–N stretching vibrations of the aromatic amino amines appear near 1323 cm-1 and 1157cm-136, which are consistent with the protein in suaeda glauca. These results indicate that we have synthesized HPC and II-HPC successfully. 3.2 Effect of initial pH and ionic strength The pH and ionic strength of solution are critical in overall sorption process. In Fig.4 (a), we observe that the removal percentage of HPC and II-HPC increases with pH rising from 2.0 to 4.0. Almost all of the uranium (VI) were removed at pH 4.0 for HPC with uranium mainly in the forms of dioxo uranyl cation UO22+ at this stage37. The adsorption capacity of II-HPC changes slowly as the pH changes from 6 to 8 and then decreases at pH=9, which proved that II-HPC should have the capabilities for seawater uranium recovery. This advantage is attributed to the treatment process of ion-imprinted and alkali activation, which improves the adsorption capacity by providing more reactive sites38. At pH 6 to 8, the predominant uranium species are (UO2)3(OH)5+ and (UO2)4(OH)7+ and II-HPC coordinates well with them39. The optimal condition for the following adsorption experiment is chosen as pH=8. Ionic strength effects on the adsorption behaviour of II-HPC have been studied in Fig.4 (b), there is little effect on the removal of U (VI) with ionic strength (0.001-0.1 mol L-1), which indicates that inner-sphere surface complexation dominates the sorption of uranium (VI)40. 100

(a)

Removal percentage (%)

Removal percentage (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


80 60 40 20 HPC II-HPC

0 2

3

4

5

6

7

8

100

(b)

80 60 40 0.001 M NaClO4 20

0.01 M NaClO4 0.1 M NaClO4

0 2

9

3

4

5

6

7

8

9

pH

pH

Fig. 4 Effect of initial pH of HPC and II-HPC (a), ionic strength on adsorption property of II-HPC (b). pH = 2.0-9.0, T = 25 ºC, msorbent/Vsolution = 0.5 g·L-1, initial uranium concentration 30 mg L-1. 3.3 Sorption isotherms and adsorption thermodynamics The relationship between different uranium (VI) concentration (30–400 mg L−1) and the uptake capacity on HPC (Fig.5 (a)) and II-HPC (Fig. 5 (b)) shows that sorption capacity increases with initial uranium (VI) concentration until adsorption equilibrium. The plateau indicates that the most active sites in the II-HPC react with uranium (VI). To describe the sorption isotherms distinctly, the Langmuir (Eq. (S2)) and Freundlich (Eq. (S3)) equations were used. Langmuir model describes sorption processes that are homogenously monolayer adsorbed41. Freundlich model is an empirical equation, which assumes that sorption processes occur on the heterogeneous surface42. All parameters were calculated and listed in Table S3 for HPC adsorbent and Table S4 for II-HPC adsorbent. The isotherm on the II-HPC adsorbent fits by Langmuir model better with higher R2 values (>0.97), which demonstrated that monolayer sorption is the main adsorption mechanism. The theoretical maximum adsorption 5



capacity for HPC is 347.68 mg g-1 and for II-HPC is 503.64 mg g-1 at 298K. We compared the maximum sorption capacity of II-HPC for uranium (VI) with other materials as shown in Table 1, including covalent organic framework (COF), functionalized 2-D COF materials, conventional metal organic frameworks (MOFs), MOFs-composites and ion-imprinting materials. The results showed that the adsorbent amount of II-HPC is superior to those of other adsorbent, which demonstrated II-HPC adsorbent is a promising material for the enrichment of U (VI). 600

500

(b)

(a) 500

qe(mg L-1)

400

qe(mg L-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 15

300 HPC 25℃ HPC 35℃ HPC 45℃ Langmuir model fit Freundlich model fit

200 100

400 300

II-HPC 25℃ II-HPC 35℃ II-HPC 45℃ Langmuir model fit Freundlich model fit

200 100 0

0 0

20

40

60

80

-1

100

120

0

140

20

40

60

80

100

Ce (mg L-1)

Ce (mg L )

Fig. 5 Adsorption isotherm of HPC (a) and II-HPC (b) for uranium (VI) ions at different temperatures. pH = 8.0; temperature = 25–45 °C; msorbent/Vsolution = 0.5 g·L-1.

Table 1 The maximum adsorption capacity of different adsorbents for uranium (VI).

Adsorption Adsorbents

Capacity

Conditions

Ref.

mg-U/g-adsorbent MPCOF

71

T = 298 K, pH=1.5

[43]

COF-HBI

211

T = 298.15 K, pH = 4.5

[44]

PAF-1-CH2AO

304

T = 298 K, pH=6.0

[45]

UIMS-4

80

T = 298.15 K, pH = 5.2

[23]

SII-PNF

133.3

T = 298.15 K, pH = 8

[46]

IMCR

187.26

T = 298 K, pH =5

[47]

MOF-76

298

T = 298 K, pH =3

[48]

Carboxyl functionalized MIL-101

314

T = 298 K, pH=7.0

[12]

Mg-Co LDHs

915

T = 298.15 K, pH = 5

[49]

II-HPC

503.64

T = 298 K, pH = 8

this work

In order to evaluate the thermodynamic feasibility, the thermodynamic parameters for the adsorption process on II-HPC were investigated at 25, 35, 45 °C (Fig. S3). The standard free energy change entropy ΔS° (J mol-1·K-1), enthalpy ΔH° (kJ mol-1) and ΔG° (kJ mol-1) were obtained from the following equation50: ln Kd  H 0 / RT  S 0 / R

(1)

G   RT ln Kd

(2)

0

6


Page 7 of 15

Where Kd is equilibrium constant (mL g-1), R is the ideal gas constant (8.314 J mol-1·K-1). The calculated thermodynamics parameters are reported in Table S5. The negative ΔG° values reveal the spontaneity of adsorption. The positive value of ΔH° indicates that adsorption is an endothermic sorption process with high temperature facilitating the process of adsorption. 3.4 Sorption kinetic Because of the excellent adsorption performance of II-HPC for U (VI), we further measured the adsorption kinetics on II-HPC for removing U (VI) from simulated seawater with an initial U (VI) concentration of 500 ug L-1 (Fig. 6). The sorption of the II-HPC for uranium (VI) gradually increases and reaches a stable equilibrium state after 120 min. Intra-particle diffusion (Eq.(S3)), pseudo-first-order (Eq.(S4)) and pseudo-second-order models (Eq.(S5)) was used to fit the kinetics data of uranium enrichment by II-HPC 51-52.The results in the Fig. 6 and Table S6. show that they fit the pseudo-second-order model better with higher R2 values (0.99), which indicates that the chemical sorption is dominant sorption process 53. Intra-particle diffusion equation is expressed as54: (3) -1

1/2

Where kp (mg g min ) is the rate constant. The fitting curve of qt vs. t

1/2

is shown in Fig. 6 insert and it was not

pass through the origin, which indicated that intra-particle diffusion and surface adsorption were primarily controlled the adsorption process55. The initial straight line is the mass transfer of adsorbate molecules due to film diffusion56. A hierarchically porous structure facilitates II-HPC uranium diffusion to the inner surface in the second stage. The third step of chemisorption controls the adsorption rate between the active sites of II-HPC and uranium (VI). The order of intra-particle diffusion rate constants was obtained as k3 (third stage) < k2 (second stage) < k1 (first stage) in Table S7. This demonstrates that the chemisorption is the main adsorption mechanism, at the same time, a porous structure also promotes an effective adsorption57.

1000 900 800

UI-HPC Pseudo-first-order Pseudo-second-order

700 600 1000

500

900

qt (ug g-1)

qt (ug g-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


400

800 700 600 500

300

400

200

200

300

2

4

6

8

10

12

14

16

t1/2 (min1/2)

100 0

30

60

90 120 150 180 210 240 270

t (min) Fig. 6 Effect of contact time on the sorption of simulated seawater by II-HPC. pH = 8.0; temperature = 25°C; msorbent/Vsolution = 0.5 mg/mL.

7



Fig. 7 Schematic diagrams of flow-through experiments II-HPC adsorbent was selected for further adsorption kinetics testing in a lab-scale simulated continuous-flow system. Schematic diagrams of the adsorption experiments are shown in Fig. 7. In the flow-through experiments, the simulated seawater was drawn from a reservoir and forced through the pipeline using a pump. Then the solution was filtered and sterilized by ultraviolet radiation. The II-HPC adsorbent was packed in columns of 15 cm height and 2.5cm diameter. Twenty columns were placed in parallel in the multi-channel flow system. To keep II-HPC uniformly distributed along the columns, glass beads of 4 mm diameter were packed in the upper and lower ends of the column. More importantly, the adsorption process was quantitatively monitored for temperature, pH and flow rate. The adsorption testing was conducted at a temperature of 25 ± 2 °C. The initial uranium concentration was 3.5 ug L−1 at the pH 8.3±0.2 and simulated seawater was passed the columns at flow rates of 30 ±2 mL min-1. The adsorbent was collected from the column at regular intervals, and treated with acid solution to elute the metal ions. The experimental results showed that the amount of uranium adsorbed after 35 days in simulated seawater was 0.379 mg g-1. Adsorption conditions, including the initial concentration of uranium solution, flow rate, temperature, affected the adsorption performance. Many absorbent materials were used to remove uranium from nature seawater or simulated seawater, such as fiber adsorbents, grafted polymeric adsorbents, nonwoven fabric and MOFs. They showed excellent adsorption properties as shown in Table S8. Compared with these adsorbents, II-HPC as an environmentally friendly and low cost material is considered a potential adsorbent for U (VI) removal from seawater. 3.5 Removal mechanism The higher adsorption capacity is achieved on the II-HPC, which attributed that hyperaccumulation effect and ion imprinting technology are crucial importance for the removal of U (VI). II-HPC generated specific recognition sites by reversible immobilization of uranium (VI), so the imprinted material II-HPC can keep the memory effect toward uranium (VI) in size, shape and functionality[58-59], which can provide higher adsorption activity and absorbability for uranium (VI). The XPS analysis was used to describe interaction mechanism between II-HPC adsorbent and uranium (VI). From Fig. 8 (a), the XPS survey scan of the samples before and after the U (VI) reaction show peaks of N 1s, C 1s, and O 1s for II-HPC adsorbent and new peaks of U 4f for II-HPC-U, which reveals the presence of U 4f5/2 (393.28 eV and 392.66) and U 4f7/2 (382.62 eV and 381.88 eV), which further suggests that II-HPC-U adsorbs uranium successfully (Fig. 8 (b)). As shown in Fig. 8 (c), the O1s spectra could be decomposed into three 8


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components. The O1s peak with 531.00 eV is attributed to the C=O type oxygen60. The peak at around 532.16 eV is assigned to the C–O type oxygen in C–OH and COOR groups61. The binding energies around 533.56 eV are attributed to chemisorbed oxygen or strongly adsorb water molecules62-63. For the samples after U (VI) sorption, the C−O and C=O groups signal a shift to higher binding energies of 532.80 eV and 531.85 eV, which indicated the complexation exist between the oxygenic group and uranium species 64. In the high-resolution N 1s spectrum (Fig. 8 (d)), three peaks at 399.67 eV, 397.83 eV and 400.84 eV are fitted to pyrrolic N, pyridinic N and graphitic N are fitted to graphitic N, pyrrolic N and pyridinic N, respectively, which contribute to the π-conjugated system with a pair of p-electrons. A negative shift occurs of 0.15 eV, 0.81 eV and 0.53 eV after adsorption, which demonstrates the surface coordination of uranium (VI) with Nitrogen functional groups65. According to the above analysis, we propose a possible uptake mechanism in Fig. 9. U 4f

N 1s

II-HPC

Intensity (cps)

O 1s

Intensity (cps)

(b)

C 1s

(a)

U 4f

II-HPC

393.28 eV

381.88 eV

382.62 eV

392.66 eV

II-HPC-U

II-HPC-U

700

600

500

400

300

200

100

0

396

394

392

(c)

390

388

386

384

382

380

378

Binding energy (eV)

Binding energy (eV) (d)

532.16 eV

N 1s

399.67 eV

397.83 eV

400.84 eV

Intensity (cps)

533.56 eV

Intensity (cps)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


531.00 eV

II-HPC

531.85 eV

532.80 eV

II-HPC

399.82 eV 401.37 eV

398.64 eV

533.58 eV

II-HPC-U

II-HPC-U 538

536

534

532

530

528

404

403

402

401

400

399

398

397

Binding energy (eV) Binding energy (eV) Binding energy (eV) Fig. 8 XPS spectra (a), U 4f spectra (b), O 1s spectra (c) and N 1s spectra (d) of II-HPC and II-HPC-U.

Fig. 9 A schematic diagram of II-HPC for adsorption of uranium (VI) 9



3.6 Simulated seawater experiments II-HPC adsorbent was further investigated to discuss its selectivity for uranium (VI) and adsorption abilities. The preparation of simulated seawater is provided in support information. The sorption procedure was as follows, II-HPC was added into the simulated seawater of different concentrations (3 to 500 ppb) and the solid/liquid ratio of 0.5 mg mL-1, which was shaken for 24h to reach the absorption equilibrium at 25 °C. The results indicated that all of the removal efficiency for uranium (VI) are more than 88% (Fig.10 (a)). After that, II-HPC adsorbent was soaked in the simulated seawater contaminated with concentration of uranium of 3.3 ppb. At the same time, the pH was adjusted to be close to real seawater (Fig.10 (b)). The distribution coefficient (Kd) value of uranium (VI) with other competing ions is 1.02 × 104 mL g−1, which means that II-HPC adsorbent is an excellent adsorption for enriching uranium from seawater.

800

80

600

60

400

40

200

20

0

0 3

10

30

50

100

Removal efficiency (%)

100

1000

(a)

12000

(b)

10000

80

8000 60 6000 40

4000

20

2000 0

0 U

500

Initial concentration (ug L-1)

V Cr Al Co Li Ca K Fe Mg Sr Na

Fig. 10 Effect of initial trace concentration of uranium on its adsorption capacity from simulated seawater and removal rate (a) and selected results of II-HPC adsorbent for the extraction of uranium from simulated seawater (b) 3.7 Regeneration and reusability The regenerability is of significance for an economical and effective absorbent material. Therefore, the regeneration and reusability of II-HPC were evaluated by five cycles of sorption–desorption. The 0.1M HNO3 solution was chosen as universal reagent for desorption of uranium (VI) from the adsorbent. As revealed in Fig. S4, the removal efficiency on regenerated adsorbent was not diminished dramatically, which can reach up to 85% after five cycles. The slight decrease of the removal efficiency was mainly ascribed to the incomplete desorption of uranium (VI) onto II-HPC66. These results indicated that the II-HPC have an excellent reusability for uranium (VI) sorption. Therefore, the II-HPC manifested the excellent stability and reusability. 4. Conclusion A novel uranium ion-imprinted hierarchically porous carbon composite (II-HPC) was prepared to enrich uranium from simulated seawater (ppb level) and aqueous solution (ppm level). The effects of temperature, contact time, pH and initial uranium (VI) concentration on uranium (VI) sorption behavior were studied by adsorption experiments. The results showed that the saturation adsorption capacity, acquired from Langmuir isotherm, was 503.64 mg g-1 for II-HPC at 298K. The best description of adsorption kinetic in simulated seawater fitted the pseudo-second-order equation, which demonstrated the chemical adsorption characteristics of uranium onto II-HPC. In lab-scale simulated continuous-flow system, the amount of uranium adsorbed after 35 days was 0.379 mg g-1 in simulated seawater. The results in this study indicate that II-HPC adsorbent is a promising material and will be used for capturing uranium from seawater. Supporting Information Details about characterization, adsorption experiments, adsorption thermodynamics, adsorption dynamics and supplemental figures and tables. 10


Kd (mg L-1)

Removal efficiency (%)

100

qe(ug L-1)

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Conflict of Interest The authors declare no competing financial interest. Acknowledgements This work was supported by National Natural Science Foundation of China (NSFC 51603053), the Aplication Technology Research and Development Plan of Heilongjiang Province (GX16A009), Ph.D. Student Research and Innovation Fund of the Fundamental Research Funds for the Central Universities (HEUGIP201817) and Fundamental Research Funds of the Central University (HEUCF181003). References (1) Tsouris, C. Uranium Extraction: Fuel from Seawater. Nature Energy 2017, 2, 17022. (2) Das, S.; Brown, S.; Mayes, R. T.; Janke, C. J.; Tsouris, C.; Kuo, L.-J.; Gill, G.; Dai, S. Novel Poly (imide dioxime) Sorbents: Development and Testing for Enhanced Extraction of Uranium from Natural Seawater. Chem. Eng. J. 2016, 298, 125-135. (3) Davies, R.; Kennedy, J.; McIlroy, R.; Spence, R.; Hill, K. Extraction of Uranium From Sea Water. Nature 1964, 203, 1110-1115. (4) Yuan, Y.; Yang, Y.; Ma, X.; Meng, Q.; Wang, L.; Zhao, S.; Zhu, G. Molecularly Imprinted Porous Aromatic Frameworks and Their Composite Components for Selective Extraction of Uranium Ions. Adv. Mater. 2018, 30, 1706507. (5) Chen, L.; Bai, Z.; Zhu, L.; Zhang, L.; Cai, Y.; Li, Y.; Liu, W.; Wang, Y.; Chen, L.; Diwu, J. Ultrafast and Efficient Extraction of Uranium from Seawater Using an Amidoxime Appended Metal–Organic Framework. ACS Appl. Mater. Interfaces 2017, 9, 32446-32451. (6) Li, B.; Sun, Q.; Zhang, Y.; Abney, C. W.; Aguila, B.; Lin, W.; Ma, S. Functionalized Porous Aromatic Framework for Efficient Uranium Adsorption from Aqueous Solutions. ACS Appl. Mater. Interfaces 2017, 9, 12511-12517. (7) Rao, T. P.; Metilda, P.; Gladis, J. M. Preconcentration Techniques for Uranium (VI) and Thorium (IV) Prior to Analytical Determination—an Overview. Talanta 2006, 68, 1047-1064. (8) Mellah, A.; Chegrouche, S.; Barkat, M. The Removal of Uranium(VI) from Aqueous Solutions onto Activated Carbon: Kinetic and Thermodynamic Investigations. J. Colloid Interface Sci. 2006, 296, 434-441. (9) Mellah, A.; Chegrouche, S.; Barkat, M. The Precipitation of Ammonium Uranyl Carbonate (AUC): Thermodynamic and Kinetic Investigations. Hydrometallurgy 2007, 85, 163-171. (10) Callura, J. C.; Perkins, K. M.; Noack, C. W.; Washburn, N. R.; Dzombak, D. A.; Karamalidis, A. K. Selective Adsorption of Rare Earth Elements onto Functionalized Silica Particles. Green Chem. 2018, 20, 1515-1526. (11) Barber, P. S.; Kelley, S. P.; Griggs, C. S.; Wallace, S.; Rogers, R. D. Surface Modification of Ionic Liquid-Spun Chitin Fibers for the Extraction of Uranium from Seawater: Seeking the Strength of Chitin and the Chemical Functionality of Chitosan. Green Chem. 2014, 16, 1828-1836. (12) Li, L.; Ma, W.; Shen, S.; Huang, H.; Bai, Y.; Liu, H. A Combined Experimental and Theoretical Study on the Extraction of Uranium by Amino-Derived Metal–Organic Frameworks through Post-Synthetic Strategy. ACS Appl. Mater. Interfaces 2016, 8, 31032-31041. (13) Brown, S.; Chatterjee, S.; Li, M.; Yue, Y.; Tsouris, C.; Janke, C. J.; Saito, T.; Dai, S. Uranium Adsorbent Fibers Prepared by Atom-Transfer Radical Polymerization from Chlorinated Polypropylene and Polyethylene Trunk Fibers. Ind. Eng. Chem. Res. 2015, 55, 4130-4138. (14) Jin, J.; Li, S.; Peng, X.; Liu, W.; Zhang, C.; Yang, Y.; Han, L.; Du, Z.; Sun, K.; Wang, X. HNO 3 Modified Biochars for Uranium (VI) Removal from Aqueous Solution. Bioresour. Technol. 2018, 256, 247-253. 11



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A novel ion-imprinted carbon material induced by hyperaccumulation

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