Ion-Imprinted Mesoporous Silica for Selective Removal of Uranium

Aug 7, 2017 - It is strategically important to recycle uranium from radioactive liquid wastes for future uranium supply of nuclear energy. However, it...
0 downloads 0 Views 2MB Size
Download PDF
Research Article www.acsami.org

Ion-Imprinted Mesoporous Silica for Selective Removal of Uranium from Highly Acidic and Radioactive Effluent Sen Yang,† Jun Qian,† Liangju Kuang,‡ and Daoben Hua*,†,§ †

Downloaded via KAOHSIUNG MEDICAL UNIV on August 18, 2018 at 03:59:59 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

School for Radiological and Interdisciplinary Sciences (RAD-X) & College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China ‡ Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, Indiana 47907, United States § Collaborative Innovation Center of Radiological Medicine of Jiangsu Higher Education Institutions, Suzhou 215123, China S Supporting Information *

ABSTRACT: It is strategically important to recycle uranium from radioactive liquid wastes for future uranium supply of nuclear energy. However, it is still a challenge to adsorb uranium selectively from highly acidic and radioactive waste. In this paper, we report a novel strategy for effective uranium removal from highly acidic and radioactive media by surface ion-imprinted mesoporous silica sorbent. The sorbent was successfully synthesized by a co-condensation method with uranyl as the template ion and diethylphosphatoethyltriethoxysilane as the functional ligands. The pseudo-second-order model and Langmuir model showed better correlation with the sorption kinetic and isotherm data, and the sorption equilibrium could be reached within 40 min, the maximum adsorption capacity from Langmuir model was 80 mg/g in 1 mol/L nitric acid (HNO3) solution at 298.15 K. The sorbent showed faster kinetics and higher selectivity toward uranium over other ions compared with nonimprinted mesoporous and other previous sorbents. Furthermore, the ion-imprinted materials exhibited remarkable radioresistance stability and could be regenerated efficiently after five cycles. This work may provide a new approach for highly efficient sorption of uranium from strong HNO3 and radioactive media. KEYWORDS: uranium sorption, ion-imprinting, mesoporous silica, radioactive, strong acid

1. INTRODUCTION A large number of radioactive wastes are being produced with the development of nuclear industry. Uranium is considered one of the main contaminants and a hazard to the environment and humans due to its radioactive and chemical toxicity.1,2 Meanwhile, uranium is also the crucial raw material of the nuclear industry. Therefore, it is important to extract uranium from radioactive liquid wastes for sustainable development of the nuclear industry.3 In the past few decades, liquid−liquid extraction has been the most common technique employed for separation of radionuclide from nuclear waste.4 In comparison with liquid−liquid extraction, solid phase sorption has received much attention recently due to its flexibility, simplicity, economy and lower environmental pollution.5,6 To date, a variety of sorbents have been developed for exaction of uranium from highly acidic and/or radioactive medium, such as synthetic resins,7−9 mesoporous silica10−12 and covalent organic framework.13 For example, Subramanian et al.8 reported the extraction of thorium and uranium using a polymeric resin from simulated nuclear spent fuel mixtures; Chen et al.12 synthesized a category of mesoporous silicas functionalized with different phosphine oxide ligands for adsorbing uranium from strong HNO3 solutions; Li et al.13 prepared a covalent organic framework material for removal of © 2017 American Chemical Society

uranium in high acidic media (1 mol/L HNO3). Although great progress has been achieved, some challenges are still subsistent for uranium sorption from radioactive liquid wastes, such as strong acidity, high radioactivity and variety of competing metal ions.12,14,15 Therefore, it still has great significance to develop new sorbents for uranium sorption with good radioresistance, high selectivity and stability in strong acidic media. To improve the selectivity of sorbents, an ion-imprinting technique is introduced into the sorption field. The affinity between organic ligand and templated ions as well as the size of the generated cavities contribute to the high selectivity.16,17 For instance, Meng et al.18 synthesized a surface ion-imprinted polymer for the selective uranium sorption at pH 5.0 by graft polymerization with uranium(VI)−methacrylic acid complex; Qian et al.19 prepared uranyl ion-imprinted polymer-functionalized composites by locating polymerization for efficient uranium removal from aqueous solution of pH 5.0. However, to our best knowledge, there are few reports on ion-imprinted materials for uranium removal in highly acidic and radioactive media. Received: June 29, 2017 Accepted: August 7, 2017 Published: August 7, 2017 29337

DOI: 10.1021/acsami.7b09419 ACS Appl. Mater. Interfaces 2017, 9, 29337−29344

Research Article

ACS Applied Materials & Interfaces Scheme 1. Schematic for Synthesis of Uranyl Ion-Imprinted Mesoporous Silica (UIMS)

(Figure S1, Supporting Information). Energy-dispersive X-ray (EDX) analysis was used to confirm that uranyl ions were removed completely. Finally, the UIMS was obtained and desiccated in the vacuum oven at 40 °C. Analogous samples were prepared by the same procedure using the different TEOS/DPTS molar ratios (Table 1). For comparison, the

It is acknowledged that mesoporous silica is a promising matrix owing to its high specific surface area, mechanical and thermal stability, chemical and irradiation durability, and easy organic modification.20−23 In addition, organophosphorus compounds have the remarkable coordination ability to fission products and high chemical and mechanical stability in strong acidic and radioactive media.24−28 Motivated by these findings, we report herein novel ion-imprinted mesoporous silica functionalized by phosphorus ligands for selective removal of uranium from highly acidic and radioactive media. Specifically, the sorbent was prepared by a co-condensation method with UO22+ as template ion, tetraethoxysilane (TEOS) as silica source, triblock copolymers (P123) as porous template, and diethylphosphatoethyltriethoxysilane (DPTS) as functional ligands (Scheme 1). The ion-imprinted mesoporous silica can be obtained after the elution of the uranyl ion and P123 using ethanol−hydrochloric acid (37 wt %) mixture (9/1, v/v). The recognition cavities for UO22+ in size, shape and chemical functionality were formed on the surface of mesoporous silica. Therefore, it is expected that the obtained uranyl ion-imprinted mesoporous silica (UIMS) could effectively adsorb uranyl ions from strongly acidic and radioactive media.

Table 1. Feeding Ratio, Elemental Content and Organic Content of Functional Silica feeding ratio sorbents

TEOS (mmol)

DPTS (mmol)

UO22+ (mmol)

organic contenta (%)

UIMS-1 NIMS-1 UIMS-2 UIMS-3 UIMS-4 NIMS-4

40.0 40.0 40.0 40.0 40.0 40.0

2.00 2.00 5.00 10.0 20.0 20.0

0.500

2.80 2.92 5.10 10.4 12.3 13.6

a

0.500 0.500 0.500

Determined by thermogravimetric analysis (TGA).

nonimprinted mesoporous silica (NIMS-1 and NIMS-4) was prepared in the same way in the absence of uranyl ions, and mesoporous silica (SBA-15) was synthesized according to the literature methods (Supporting Information).30 2.3. Uranium Sorption Experiments. All sorption experiments were executed in polyethylene plastic tubes. Solutions of uranium(VI) were obtained by dissolving UO2(NO3)2·6H2O in HNO3 and further diluting with ultrapure water. The pH values of the solutions of uranium were adjusted by HNO3 (2 mol/L) and sodium carbonate solution (2 mol/L). A typical sorption procedure was as follows: the sorbent (5.0 mg) was added into uranyl ion solution (5.0 mL) in polyethylene tube and shaken for 12 h until the sorption equilibrium was achieved. The concentration of uranyl ion before and after sorption was tested by ICP-MS. The equilibrium sorption amount (qe, mg/g), distribution ratio (Kd) and sorption efficiency (SE) were calculated according to eqs 1, 2 and 3, respectively:

2. EXPERIMENTAL SECTION 2.1. Materials and Reagents. Diethylphosphatoethyltriethoxysilane (DPTS, 92%) was purchased from J&K Scientific Co., Ltd. Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) copolymer (P123) was purchased from SigmaAldrich Co., Ltd. Hydrochloric acid (37 wt %, GR), tetraethoxysilane (TEOS, AR), ethanol (AR) and nitric acid (AR) were from Sinopharm Chemical Reagent Co., Ltd. UO2(NO3)2·6H2O was purchased from Sigma-Aldrich Fluka. Characterization methods for all the samples are shown in Supporting Information. 2.2. Synthesis of Uranyl Ion-Imprinted Mesoporous Silica (UIMS). UIMS was synthesized according to the modified literature method. 29 The typical procedure was described as follows: UO2(NO3)2·6H2O (0.25 g, 5.0 × 10−4 mol) and a certain amount of DPTS were added into ultrapure water (10 mL), and stirred magnetically at 35 °C for 16 h to obtain a preassembly solution. In the meantime, P123 (4.0 g, 6.9 × 10−4 mol) was dissolved in 30 mL of ultrapure water and 120 mL of HCl solution (2 mol/L) under stirring for 16 h at 35 °C. The two solutions were mixed together dropwise for 1 h and continue to be stirred for 2 h. TEOS (8.5 g, 4.0 × 10−2 mol) was then added into the mixture dropwise under stirring. After stirring for 24 h, the solution was transferred into an autoclave and heated to 100 °C for another 24 h. The mixture was then filtered and washed with ultrapure water (500 mL × 3), and desiccated in a vacuum oven at 40 °C. P123 and UO22+ were removed by Soxhlet extraction with a solution of ethanol−hydrochloric acid (v/v, 9/1, 50 mL per 1 g sample) at 80 °C for 24 h. FT-IR spectra of UIMS-4 verified diethylphosphonate ester was not hydrolyzed after Soxhlet extraction

qe = (C0 − Ce) Kd =

V M

C0 − Ce V × Ce M

SE (%) =

C0 − Ce × 100 C0

(1) (2) (3)

where C0 and Ce (mg/L) are the initial and residual concentration of uranium(VI) in solution, respectively. M (g) is the dry sorbent weight, and V (L) is the volume of aqueous solution. The effects of sorbent dose, acidity/pH, competing ions and contact time on the sorption were studied. The isotherm experiments were carried out with the different initial uranium concentrations of 29338

DOI: 10.1021/acsami.7b09419 ACS Appl. Mater. Interfaces 2017, 9, 29337−29344

Research Article

ACS Applied Materials & Interfaces uranium in the solution of 1 mol/L HNO3 at 298.15 K. Kinetic studies were investigated using 1 × 10−4 mol/L of uranium in the solution of 1 mol/L HNO3 at 298.15 K. The competing sorption was performed in the solution of 1 mol/L HNO3 with 5.0 mg of sorbent and a mixture of UO2(NO3)2·6H2O, ZnCl2, CoCl2, Ba(NO3)2, MnCl2·4H2O, CsNO3, Ni(NO3)2·6H2O, CrCl3·6H2O, SrCl2·6H2O, NaNO3, Nd(NO3)3, EuCl3·6H2O, Sm(NO3)3·6H2O, ZrCl4, Gd(NO3)3·6H2O and La(NO3)2·6H2O. 2.4. Regeneration Studies. The reusability of UIMS was evaluated by five sorption−desorption cycles with the same concentration of sorbent (1.0 mg/mL) in the solution of 1 mol/L HNO3 (5.0 mL, 1 × 10−4 mol/L) at 298.15 K for 1 h until the sorption equilibrium was achieved. After saturated sorption, UIMS− uranium complex was eluted with a solution of ethanol−hydrochloric acid (9/1, v/v) by Soxhlet extraction at 80 °C under stirring for 24 h. 2.5. Irradiation Stability Study. The radioresistance of modified mesoporous silica was evaluated by 60Co γ-ray irradiation at a 15 Gy/ min of dose rate. A typical irradiation process was depicted as follows: 50.0 mg of UIMS-4 was irradiated with different irradiation doses (such as 100, 300 and 500 kGy) under ambient atmosphere or HNO3 solution (1 mol/L).

organic ligands (Figure S3, Supporting Information). The porosity analysis of all the sorbents indicated that the BET specific surface areas and average pore diameters decreased when the amount of organic ligands was increased (Table 2; Table 2. Parameters of the Porous Structure for the Obtained Materials material

specific surface areas (m2/g)

pore volume (cm3/g)

pore diameter (nm)

SBA-15 UIMS-1 NIMS-1 UIMS-2 UIMS-3 UIMS-4 NIMS-4

681 588 561 454 382 286 224

1.00 0.716 0.709 0.580 0.506 0.146 0.125

9.55 7.61 7.78 6.70 6.20 1.06 1.17

Figure S4, Supporting Information). Moreover, the pore sizes of uranyl ion-imprinted mesoporous silica are smaller than those of nonimprinted ones because they are the average values of the mesopore of the silica and the uranyl ion-imprinted cavities. It is also noticed that BET surface area and pore volumes for ion-imprinted mesoporous silica are larger than those of nonimprinted ones, which should be attributed to the sum of the above-mentioned two kinds of pores.19,31 The chemical structures of the sorbents were characterized by FT-IR spectra and EDX. Compared with bare SBA-15 (Figure 1G, trace a), the vibration band of PO (1412 cm−1)32 and Si-CH2 (673 cm−1)33 (Figure 1G, trace b, c, d, e, f and g) suggested the successful synthesis of UIMS-1−4 and NIMS-1, 4. The appearance of P elements in EDX spectra further verified DTPS was introduced into the sorbents successfully (Figure S5, Supporting Information). Thermogravimetric analysis (TGA) was conducted to study the chemical content of the samples, and three stages of mass loss is shown in Figure 1H: stage I was the desorption of crystal water; stage II was the process of decomposition of the organic groups in the range of temperatures between 200 and 450 °C, which was proportional to the amount of DPTS (Table 1); and stage III can be attributed to the condensation of the neighboring silanol groups to form siloxane bonds at 500− 700 °C.34 3.2. Effects of Sorbent Dose and Acidity/pH on Uranium Sorption. The sorption performance of sorbent toward uranium is always affected by different experimental conditions. First, we studied the effects of sorbent dose and acidity/pH on uranium sorption. The sorption efficiency increases quickly with the increase of sorbent dose, and reaches an equilibrium at 1.0 g/L sorbent content at pH 5.9 (Figure 2A). Therefore, 1.0 g/L was chosen as the optimum dose for the next sorption experiments. As shown in Figure 2B, the sorption efficiency of uranium in strong acidic environment (such as 1, 2 and 3 mol/L) was calculated as 66.33%, 34.54% and 14.63%, respectively. This sorption behavior of sorbent in strong acidic solution was due to the enhanced protonation of phosphonate ligands with the increase of HNO3 concentration. It is known that UO22+ is the main species of uranium(VI) in strong acid solution, and is not favored by the positively charged ligands owing to the electrostatic repulsion, resulting in a lower sorption capacity.28,35 In addition, the sorption efficiency of uranyl ions onto the UIMS-4 exceeded 90% at pH 1−7, which may be

3. RESULTS AND DISCUSSION 3.1. Characterization of UIMS. The morphological features of ion-imprinted mesoporous silicas were characterized by transmission electron microscopy (TEM) (Figure 1).

Figure 1. TEM images of (A) SBA-15, (B) UIMS-1, (C) UIMS-2, (D) UIMS-3, (E) UIMS-4 and (F) NIMS-4 (scale bar: 50 nm). (G) FT-IR spectra and (H) TGA curves of (a) SBA-15, (b) UIMS-1, (c) NIMS-1, (d) UIMS-2, (e) UIMS-3, (f) UIMS-4 and (g) NIMS-4.

Ordered hexagonal lattice arrangement was observed clearly for SBA-15, UIMS-1 and NIMS-1 (Figure 1A,B and Figure S2, Supporting Information). However, the ordered structures were observably degraded for UIMS samples with an increasing amount of organic ligand (Figure 1B−E). It was noticed that UIMS-4 and NIMS-4 did not show ordered mesoporous structure, which may be ascribed to the larger amount of organic ligands in their preparation. The small angle XRD patterns further demonstrate this point. For SBA-15, there were three well-resolved peaks that were indexed to (100), (110) and (200), indicating the ordering degree of the mesoporous structure; whereas, the diffraction peaks are not obvious for all modified mesoporous silica because of the introduction of 29339

DOI: 10.1021/acsami.7b09419 ACS Appl. Mater. Interfaces 2017, 9, 29337−29344

Research Article

ACS Applied Materials & Interfaces

uranium. Furthermore, the relative selectivity coefficient (βr) was much larger than 1, which indicated much better selectivity for imprinted mesoporous silica to uranium than that for nonimprinted ones. This result may be ascribed to the specific recognition cavities toward uranium generated through surface ion-imprinted technique, which were close to the diameter of uranyl ion of 0.36 nm.16,40 Noticeably, there was relatively low Kd of UIMS for Na(I), Cs(I), Co(II), Ba(II), Ni(II), Zn(II), Cr(III) and Zr(IV), which may be physically embedded into the cavities of imprinted mesoporous silica. Whereas, the Kd values of UIMS for most lanthanides, such as Nd(III), Sm(III), Gd(III), La(III) and Eu(III), were much larger than the other ions except uranium(VI). The results may be related to the average pore diameters of mesoporous silica materials besides the affinity between PO group and lanthanide ions.12,41 The hydrated lanthanide ions with larger sizes are relatively closer to the average pore diameters of UIMS-4 (1.06 nm), which are relatively difficult for the ions to go out of pore channel, thereby leading to be easily captured by the materials. In contrast, the ions with smaller size could go in and out of the framework more freely.13,40 The selectivity of UIMS-4 at pH of 5.2 was also studied (Table S1, Supporting Information). The relative selectivity coefficients (βr) at pH 5.2 were larger than 1, which was consistent with that in 1 mol/L HNO3 solution. This result reveals that imprinted mesoporous silica possess better selecatively both in strong and weak acidic solutions because of the specific recognition cavities toward uranium. In addition, we noticed that the βr in 1 mol/L HNO3 solution was larger than those at pH 5.2, which indicated that UIMS-4 possessed better selectivity compared with nonimprinted ones in a higher acidic solution. In other words, the imprinted cavities could greatly improve the selectivity for uranium in strong acidic condition compared with nonimprinted materials. Therefore, the ion-imprinted technique plays an important role in the selectivity toward uranium in strong acidic solution. The Kd and selectivity coefficients of UIMS-1 and NIMS-1 are listed in Table S2 (Supporting Information). The relative selectivity coefficient (βr) was much larger than 1, which was consistent with UIMS-4 and NIMS-4. The result further verified the better selectivity of ion-imprinted mesoporous silica. Moreover, the selectivity coefficient (β) of UIMS-1 was larger than UIMS-4 (Table 3), which indicated better selectivity to uranium. This result may be ascribed that most of the diethylphosphonate ester in UIMS-1 was imprinted to form the cavities due to a relatively small ratio of DPTS/uranyl ion. 3.4. Sorption Kinetics. In this study, the effect of initial uranium concentration on sorption efficiency was first investigated (Figure S6, Supporting Information). The sorption efficiency increases with initial uranium concentration from 1 × 10−6 to 1 × 10−4 mol/L. The similar phenomenon was also observed in the previous literature.42,43 The sorption was associated with the relatively weak affinity between uranyl ions and imprinted cavities. The driving force of sorption may depend on the diffusion of uranyl ions. The higher initial concentration leads to larger concentration gradient and diffusion between solution and sorbent, which will promote the sorption of larger portion of uranyl ions. However, when the initial concentration is over 1 × 10−4 mol/L, sorption efficiency began to decrease, which may be ascribed to the presence of excessive uranyl ions in solution compared to the available active sites on the UIMS-4. Therefore, we choose 1 ×

Figure 2. (A) Effects of sorbent dose on the sorption of uranium by UIMS-4; (B) The effect of acidity/pH on the sorption of uranium(VI) onto UIMS-4. (Experimental conditions: 5.0 mg sorbent dose, 1 × 10−4 mol/L uranium(VI), contact time = 12 h, 298.15 K, acidity/pH: (A) pH = 5.9, (B) from 3 M to pH = 7.)

ascribed to the generated cavities and surface silanol groups toward uranium(VI). The dominant uranium(VI) species was UO22+ at pH < 5,36 which can match with the imprinted cavities. However, the main uranium(VI) species was not UO22+ at pH > 5. The good sorption behavior may be attributed to the surface silanol groups.12,37 The results showed that it could be used to recover uranium from strong acidic media. 3.3. Effects of Competing Ions on Uranium Sorption. The most advantage of ion-imprinted technique is the ability to enhance the selectivity for the imprinting metal ion. To evaluate the selectivity of ion-imprinted materials, competitive experiments were carried out with the common ions in simulated high-level liquid waste (like Nd, Eu, Sm, La, Gd, Zr, Na, U, Sr, Cs, Ni, Mn, Co, Cr, Ba and Zn)38,39 at pH = 5.2 and 1 mol/L HNO3 solution, respectively. The values of Kd and selectivity coefficients are listed in Table 3. The Kd of UIMS-4 for uranyl ions was remarkably larger than other ions, suggesting a much higher selectivity for Table 3. Selective Sorption of Uranium on UIMS-4 and NIMS-4a βb

Kd (mL/g) competing ions

initial concentration mg/L

UIMS

NIMS

UIMS

NIMS

βrc

U(VI) Na(I) Cs(I) Sr(II) Ni(II) Zn(II) Co(II) Mn(II) Ba(II) Cr(III) Zr(IV) Nd(III) Sm(III) La(III) Eu(III) Gd(III)

93.5 136 167 126 138 209 125 131 129 117 209 58.5 37.2 102 73.9 24.4

412 12.6 18.9 35.0 23.3 10.3 16.9 31.0 12.4 15.6 14.4 128 34.6 38.8 92.3 62.4

184 62.6 86.4 69.9 71.3 77.0 60.8 68.0 67.9 83.3 56.4 154 72.1 111 129 120

32.7 21.8 11.8 17.7 40.0 24.4 13.3 33.4 26.4 28.7 3.23 11.9 10.6 4.47 6.62

2.94 2.13 2.64 2.58 2.39 3.03 2.71 2.71 2.21 3.27 1.20 2.55 1.67 1.43 1.53

11.1 10.2 4.47 6.85 16.7 8.06 4.91 12.3 11.9 8.76 2.70 4.67 6.38 3.13 4.32

a

Experiment conditions: 5.0 mg sorbent dose, 5.0 mL HNO3 solution (1 mol/L), 298.15 K, contact time = 12 h. bβ = Kd(U)/Kd(M), Kd(U) and Kd(M) are the dispersion coefficient of uranium and competing ions, respectively. cβr = βimprinted/βnonimprinted, βimprinted and βnonimprinted represent the selectivity coefficients of UIMS-4 and NIMS-4, respectively. 29340

DOI: 10.1021/acsami.7b09419 ACS Appl. Mater. Interfaces 2017, 9, 29337−29344

Research Article

ACS Applied Materials & Interfaces 10−4 mol/L as the initial uranium concentration to do the effect of contact time on the uranium sorption. Sorption kinetics of imprinted sorbents and nonimprinted mesoporous silica were studied in HNO3 solution (1 mol/L) and 298.15 K. Figure 3 shows the relationship between sorption

Figure 4. Sorption isotherm plots for uranium sorption by (a) UIMS1, (b) UIMS-2, (c) UIMS-3, (d) UIMS-4 and (e) NIMS-4, respectively. (Experimental conditions: 5.0 mg sorbent dose, 5.0 mL HNO3 solution (1 mol/L), 298.15 K.)

Table 5. Parameters of Langmuir and Freundlich Models for Uranium Sorption by UIMS-1, UIMS-2, UIMS-3, UIMS-4 and NIMS-4a

Figure 3. Effect of contact time on the uranium sorption by (a) UIMS2, (b) UIMS-3, (c) UIMS-4 and (d) NIMS-4, respectively. (Experimental conditions: 5.0 mg sorbent dose, 5.0 mL HNO3 solution (1 mol/L), 1 × 10−4 mol/L uranium(VI), 298.15 K.)

Langmuir

amount and contact time in uranium sorption. The sorption equilibrium could be reached within 40 min for all imprinted sorbents and within 3 h for the nonimprinted sorbents. And we can find that the equilibrium time would change when the initial concentration of uranium increased (Figure S7, Supporting Information). Furthermore, it can be seen that the sorption on UIMS is faster than most of other previous porous sorbents in 1 mol/L HNO3 solution (Table S3, Supporting Information). The pseudo-first-order and pseudosecond-order models were used to simulate kinetic profiles, respectively (Figure S8, Supporting Information). As shown in Table 4, the relatively larger correlation coefficients (R2) and the more accurate calculated qe indicated that pseudo-second-order model was more suitable for the description of kinetic processes. The k2 for imprinted sorbents was much larger than that for NIMS-4, implying the faster sorption, which may be ascribed to the strong complexation and geometric shape memory between UO22+ and corresponding cavities.44 Meanwhile, the k2 for UIMS-2 was larger than those for UIMS-3 and UIMS-4, which may be ascribed to the larger specific surface area and pore diameter (Table 2). 3.5. Sorption Isotherms. To understand the sorbent capacity, sorption isotherms studies were carried out with the initial concentrations of uranium from 8.40 × 10−5 to 1.68 × 10−3 mol/L in 1 mol/L HNO3 solution at 298.15 K. The relationship between equilibrium sorption amount qe and residual uranyl concentration Ce is shown in Figure 4. The sorption profiles were simulated with Langmuir and Freundlich models, respectively (Figure S9, Supporting Information). As shown in Table 5, the relatively larger R2 indicated that the adsorption process could be well described by Langmuir

sorbent

qmax (mg/g)

b (L/g)

UIMS-1 UIMS-2 UIMS-3 UIMS-4 NIMS-4

12.3 24.3 44.0 79.5 79.2

1.87 8.90 7.90 8.47 12.4

Freundlich R2

KF (mol1−nLn/g)

1/n

R2

0.990 0.999 0.997 0.995 0.999

0.0480 1.20 2.06 4.25 7.38

0.799 0.475 0.479 0.459 0.379

0.987 0.971 0.983 0.957 0.971

a

Experimental conditions: 5.0 mg sorbent dose, 5.0 mL HNO3 solution (1 mol/L), 298.15 K.

isotherm model, implying monolayer sorption because of the homogeneous distribution of active sites on the surface of mesoporous silica. The sorption capacity increased with the content of P element on the surface of sorbents (Figure S5, Supporting Information). Furthermore, the sorption capacities of UIMS-4 and NIMS-4 are similar due to the similar content of organic functionalities and BET surface area (Table1 and Table 2). Moreover, it can be seen that the sorption capacity of UIMS-4 in 1 mol/L HNO3 solution is larger than most of other previous porous sorbents in 1 mol/L HNO3 solution (Table S3, Supporting Information). In addition, there was a smaller equilibrium constant b value of 8.47 for UIMS-4 than that for NIMS-4, which may be attributed to the weaker affinity of imprinted cavities for UIMS-4 than that for NIMS-4, which was consistent with the finding in our previous work.45 The results indicated that the imprinted mesoporous silica may be an ideal sorbent because of its large capacity in strongly acidic solution. 3.6. Effect of Irradiation Stability on Uranium Sorption. Irradiation durability of sorbents is an important issue when used in radioactive waste liquids. Herein, γ-ray irradiation tests of ion-imprinted mesoporous silicas were performed with different irradiation doses under air atmosphere and in HNO3 solution, respectively. Solid-state 31P NMR

Table 4. Kinetic Parameters for Uranium Sorption by UIMS-2, UIMS-3, UIMS-4 and NIMS-4a pseudo-first order

a

pseudo-second order

samples

qe,exp (mg/g)

k1 (h−1)

qe,cal (mg/g)

R2

k2 (g/mg/h)

qe,cal (mg/g)

R2

UIMS-2 UIMS-3 UIMS-4 NIMS-4

4.97 9.02 16.2 16.7

1.60 3.18 1.05 0.815

0.742 1.14 1.19 10.6

0.277 0.184 0.120 0.875

2.76 2.02 0.801 0.108

5.09 9.28 16.5 18.4

0.999 0.998 0.998 0.995

Experimental conditions: 5.0 mg sorbent dose, 5.0 mL HNO3 solution (1 mol/L), 1 × 10−4 mol/L uranium(VI), 298.15 K. 29341

DOI: 10.1021/acsami.7b09419 ACS Appl. Mater. Interfaces 2017, 9, 29337−29344

Research Article

ACS Applied Materials & Interfaces

The sorption kinetic and isotherm data fit well with the pseudosecond-order model and Langmuir model, respectively, and the sorption equilibrium could be reached within 40 min, the maximum adsorption capacity from Langmuir model was 80 mg/g in 1 mol/L HNO3 solution at 298.15 K. The UIMS-4 showed faster sorption kinetics and higher selectivity toward uranium over other ions compared with nonimprinted mesoporous silicas. Furthermore, the surface ion-imprinted mesoporous silica sorbent can be used in strong acidic media compared with other ion-imprinted materials,19 and possesses better selectivity toward uranium in comparison with organophosphorus-functionalized mesoporous silica in strong HNO3 media.12 In addition, the UIMS-4 exhibited remarkable radioresistance stability and could be regenerated efficiently after five cycles. As far as we know, this is the first report on surface ion-imprinted mesoporous silica which can efficiently separate uranium from highly acidic and radioactive media.

spectroscopy was conducted to examine the chemical structure of UIMS-4 before and after γ-ray irradiation. As shown in Figure 5A, all the samples showed an intense peak at about 33

Figure 5. (A) Solid-state 31P NMR spectra of UIMS-4 before (a) and after irradiation in air (b, 100 kGy; d, 300 kGy; f, 500 kGy) and 1 mol/ L HNO3 solution (c, 100 kGy; e, 300 kGy; g, 500 kGy), respectively. Asterisk (*) indicates spinning sideband in the 31P NMR spectra. (B) Sorption of uranium(VI) by UIMS-4 before and after irradiation. (Experimental conditions: 5.0 mg sorbent, 5.0 mL HNO3 solution (1 mol/L), 1 × 10−4 mol/L uranium(VI), 298.15 K.)

■

ASSOCIATED CONTENT

S Supporting Information *

ppm, suggesting that structural integrity of the sorbents was well preserved after irradiation in air and HNO3 solution. The sorption capacity of UIMS-4 was further checked before and after γ-ray irradiation toward uranium. As shown in Figure 5B, the sorption capacity of uranyl ions remained almost unchanged after irradiation up to a dose of 500 kGy. The results indicated that the UIMS-4 had good radioresistance and could be a potential sorbent in an irradiation environment. 3.7. Regeneration Studies. Regenerability is of significance for an effective and economical adsorbent. In this research, the reusability of the sorbents was evaluated by five cycles of sorption−desorption with ethanol−hydrochloric acid (37 wt %) solution (9/1, v/v) as the desorbing agent. As shown in Figure 6A, the sorption efficiency almost remained

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b09419. Characterization methods, synthesis of SBA-15, sorption kinetics and isotherms, comparison of sorption kinetics sorption capacity, EDX spectrum, N2 sorption−desorption isotherms and pore size distribution, effects of competing ions on uranium sorption, FT-IR spectra of UIMS-4 before and after Soxhlet extraction, TEM image of NIMS-1, small angle X-ray diffraction patterns, effect of initial uranium concentration (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*Email: [email protected]; Tel/Fax: (+) 86-51265883261 (D.H.). ORCID

Daoben Hua: 0000-0003-1813-6988 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work is supported by Natural Science Foundation of China (91326202, U1532111), Key Project of Natural Science Foundation of the Higher Education Institutions of Jiangsu Province (16KJA310001), a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), the Qing-Lan Project of Jiangsu Province, and Jiangsu Key Laboratory of Radiation Medicine and Protection.

Figure 6. (A) Recycling of UIMS-4 for uranium sorption and (B) FTIR spectra of UIMS-4 (a) before and (b) after five cycles. (Experimental conditions: 5.0 mg sorbent, 5.0 mL 1 mol/L HNO3 solution, 1 × 10−4 mol/L uranium(VI), 298.15 K.)

unchanged after five cycles. Furthermore, there was no obvious change in FT-IR spectra of UIMS-4 before and after five cycles (Figure 6B), suggesting that the chemical structure of imprinted materials was well preserved during the sorption− desorption cycles. These results indicated that the sorbents have an excellent reusability for uranium(VI) sorption.

■

4. CONCLUSION In summary, we demonstrate a novel strategy for selective uranium removal from highly acidic and radioactive media by surface ion-imprinted mesoporous silica sorbent. The sorbent was prepared by co-condensation method with uranyl as the template ion. The effects of sorbent dose, acidity/pH, competing ions, contact time, initial concentration, and irradiation stability on uranium sorption were investigated.

■

ABBREVIATIONS DPTS, diethylphosphatoethyltriethoxysilane UIMS, uranyl ion-imprinted mesoporous silica NIMS, nonimprinted mesoporous silica P123, poly(ethylene glycol)-block-poly(propylene glycol)block-poly(ethylene glycol) copolymer TEOS, tetraethoxysilane REFERENCES

(1) Boice, J. D., Jr. Radiation Epidemiology: A Perspective on Fukushima. J. Radiol. Prot. 2012, 32, N33−N40.

29342

DOI: 10.1021/acsami.7b09419 ACS Appl. Mater. Interfaces 2017, 9, 29337−29344

Research Article

ACS Applied Materials & Interfaces (2) World Health Organization. Guidelines for Drinking-water Quality, Fourth ed.; World Health Organization, 2011. (3) Craft, E.; Abu-Qare, A.; Flaherty, M.; Garofolo, M.; Rincavage, H.; Abou-Donia, M. Depleted and Natural uranium: Chemistry and Toxicological Effects. J. Toxicol. Environ. Health, Part B 2004, 7, 297− 317. (4) Veliscek-Carolan, J. Separation of Actinides from Spent Nuclear Fuel: A review. J. Hazard. Mater. 2016, 318, 266−81. (5) Yusan, S. D.; Akyil, S. Sorption of Uranium(VI) from Aqueous Solutions by Akaganeite. J. Hazard. Mater. 2008, 160, 388−395. (6) Mohan, D.; Pittman, C. U., Jr. Reply to The Comments on HAZMAT 142 (2007) 1−53 ’Arsenic Removal from Water/Wastewater Using Adsorbents–a Critical Review’ by D. Mohan and C.U. Pittman Jr. made by Zhenze Li et al. [HAZMAT 175 (2010) 1116− 1117]. J. Hazard. Mater. 2011, 185 (185), 1614−1617. (7) Nogami, M.; Ishihara, T.; Maruyama, K.; Ikeda, Y. Effect of Chemical Structure of Monoamide Resins on Adsorptivity to Uranium(VI) in Nitric Acid Media. Prog. Nucl. Energy 2008, 50, 462−465. (8) Kesava Raju, C. S.; Subramanian, M. S. Sequential Separation of Lanthanides, Thorium and Uranium Using Novel Solid Phase Extraction Method from High Acidic Nuclear Wastes. J. Hazard. Mater. 2007, 145, 315−322. (9) Nogami, M.; Sugiyama, Y.; Kawasaki, T.; Harada, M.; Kawata, Y.; Morita, Y.; Kikuchi, T.; Ikeda, Y. Stability of Polyvinylpolypyrrolidone Against Gamma-Ray Irradiation in HNO3 Media. J. Radioanal. Nucl. Chem. 2012, 296, 423−427. (10) Zhang, W.; Ye, G.; Chen, J. New Insights into the Uranium Adsorption Behavior of Mesoporous SBA-15 Silicas Decorated with Alkylphosphine Oxide Ligands. RSC Adv. 2016, 6, 1210−1217. (11) Zhang, W.; Ye, G.; Chen, J. Study on the Gamma-Ray Irradiation Behavior of Mesoporous Silica Adsorbents Functionalized with Phosphine Oxide and Phosphonic Acid Ligands. J. Radioanal. Nucl. Chem. 2016, 307, 1445−1451. (12) Zhang, W.; Ye, G.; Chen, J. Novel Mesoporous Silicas Bearing Phosphine Oxide Ligands with Different Alkyl Chains for the Binding of Uranium in Strong HNO3 Media. J. Mater. Chem. A 2013, 1, 12706−12709. (13) Zhang, S.; Zhao, X. S.; Li, B.; Bai, C. Y.; Li, Y.; Wang, L.; Wen, R.; Zhang, M. C.; Ma, L. J.; Li, S. J. ″Stereoscopic″ 2D SuperMicroporous Phosphazene-Based Covalent Organic Framework: Design, Synthesis and Selective Sorption towards Uranium at High Acidic Condition. J. Hazard. Mater. 2016, 314, 95−104. (14) Zhao, Y.; Li, J.; Zhao, L.; Zhang, S.; Huang, Y.; Wu, X.; Wang, X. Synthesis of Amidoxime-Functionalized Fe3O4@SiO2 Core-Shell Magnetic Microspheres for Highly Efficient Sorption of U(VI). Chem. Eng. J. 2014, 235, 275−283. (15) Raju, C. S. K.; Subramanian, M. S. A Novel Solid Phase Extraction Method for Separation of Actinides and Lanthanides from High Acidic Streams. Sep. Purif. Technol. 2007, 55, 16−22. (16) Branger, C.; Meouche, W.; Margaillan, A. Recent Advances on Ion-Imprinted Polymers. React. Funct. Polym. 2013, 73, 859−875. (17) Lu, Y. K.; Yan, X. P. An Imprinted Organic-Inorganic Hybrid Sorbent for Selective Separation of Cadmium from Aqueous Solution. Anal. Chem. 2004, 76, 453−457. (18) Meng, H.; Gao, Q. H.; Li, Z.; Wang, X. N.; Ma, F. Y.; Zhou, W.; Zhang, L. Synthesis of a Highly Dense and Selective Imprinted Polymer via Pre-Irradiated Surface-Initiated Graft Polymerization. J. Mater. Chem. A 2015, 3, 13237−13243. (19) Qian, J.; Zhang, S.; Zhou, Y.; Dong, P.; Hua, D. Synthesis of Surface Ion-Imprinted Magnetic Microspheres by Locating Polymerization for Rapid and Selective Separation of Uranium(VI). RSC Adv. 2015, 5, 4153−4161. (20) Lebeau, B.; Galarneau, A.; Linden, M. Introduction for 20 Years of Research on Ordered Mesoporous Materials. Chem. Soc. Rev. 2013, 42, 3661−3662. (21) Mizoshita, N.; Tani, T.; Inagaki, S. Syntheses, Properties and Applications of Periodic Mesoporous Organosilicas Prepared from Bridged Organosilane Precursors. Chem. Soc. Rev. 2011, 40, 789−800.

(22) Wang, Z.; Xu, C.; Lu, Y. X.; Wu, F. C.; Ye, G.; Wei, G. Y.; Sun, T. X.; Chen, J. Visualization of Adsorption: Luminescent Mesoporous Silica-CarbonDots Composite for Rapid and Selective Removal of U(VI) and in Situ Monitoring the Adsorption Behavior. ACS Appl. Mater. Interfaces 2017, 9, 7392−7398. (23) Huynh, J.; Palacio, R.; Safizadeh, F.; Lefevre, G.; Descostes, D.; Eloy, L.; Guignard, N.; Rousseau, J.; Royer, S.; Tertre, E.; BatonneauGener, I. Adsorption of Uranium over NH2-Functionalized Ordered Silica in Aqueous Solutions. ACS Appl. Mater. Interfaces 2017, 9, 15672−15684. (24) Nasab, M. E. Solvent Extraction Separation of Uranium(VI) and Thorium(IV) with Neutral Organophosphorus and Amine Ligands. Fuel 2014, 116, 595−600. (25) Rajeswari, B.; Dhawale, B. A.; Bangia, T. R.; Mathur, J. N.; Page, A. G. Role of Cyanex-272 as an Extractant for Uranium in the Determination of Rare Earths by ICP-AES. J. Radioanal. Nucl. Chem. 2002, 254, 479−483. (26) Zhu, Y. J.; Jiao, R. Z. Chinese Experience in the Removal of Actinides from Highly-Active Waste by Trialkylphosphine-Oxide Extraction. Nucl. Technol. 1994, 108, 361−369. (27) Lebed, P. J.; de Souza, K.; Bilodeau, F.; Lariviere, D.; Kleitz, F. Phosphonate-Functionalized Large Pore 3-D Cubic Mesoporous (KIT-6) Hybrid as Highly Efficient Actinide Extracting Agent. Chem. Commun. 2011, 47, 11525−11527. (28) Yuan, L. Y.; Liu, Y. L.; Shi, W. Q.; Lv, Y. L.; Lan, J. H.; Zhao, Y. L.; Chai, Z. F. High Performance of Phosphonate-Functionalized Mesoporous Silica for U(VI) Sorption from Aqueous Solution. Dalton Trans. 2011, 40, 7446−7453. (29) He, R.; Li, W.; Deng, D.; Chen, W.; Li, H.; Wei, C.; Tang, Y. Efficient Removal of Lead from Highly Acidic Wastewater by Periodic Ion Imprinted Mesoporous SBA-15 Organosilica Combining Metal Coordination and Co-Condensation. J. Mater. Chem. A 2015, 3, 9789− 9798. (30) Zhao, D. Y.; Feng, J. L.; Huo, Q. S.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G. D. Triblock Copolymer Syntheses of Mesoporous Silica with Periodic 50 to 300 Angstrom Pores. Science 1998, 279, 548−552. (31) Younis, M. R.; Bajwa, S. Z.; Lieberzeit, P. A.; Khan, W. S.; Mujahid, A.; Ihsan, A.; Rehman, A. Molecularly Imprinted Porous Beads for the Selective Removal of Copper ions. J. Sep. Sci. 2016, 39, 793−798. (32) Wei, Y.; Zhang, L.; Shen, L.; Hua, D. Positively Charged Phosphonate-Functionalized Mesoporous Silica for Efficient Uranium Sorption from Aqueous Solution. J. Mol. Liq. 2016, 221, 1231−1236. (33) Meng, X. G.; Liu, Y.; Meng, M. J.; Gu, Z. Y.; Ni, L.; Zhong, G. X.; Liu, F. F.; Hu, Z. Y.; Chen, R.; Yan, Y. S. Synthesis of Novel IonImprinted Polymers by Two Different RAFT Polymerization Strategies for the Removal of Cs(I) from Aqueous Solutions. RSC Adv. 2015, 5, 12517−12529. (34) Dudarko, O. A.; Gunathilake, C.; Wickramaratne, N. P.; Sliesarenko, V. V.; Zub, Y. L.; Gorka, J.; Dai, S.; Jaroniec, M. Synthesis of Mesoporous Silica-Tethered Phosphonic Acid Sorbents for Uranium Species from Aqueous Solutions. Colloids Surf., A 2015, 482, 1−8. (35) Wang, Y. L.; Zhu, L.; Guo, B. L.; Chen, S. W.; Wu, W. S. Mesoporous Silica SBA-15 Functionalized with Phosphonate Derivatives for Uranium Uptake. New J. Chem. 2014, 38, 3853−3861. (36) Yang, S.; Zong, P.; Hu, J.; Sheng, G.; Wang, Q.; Wang, X. Fabrication of β-Cyclodextrin Conjugated Magnetic HNT/Iron Oxide Composite for High-Efficient Decontamination of U(VI). Chem. Eng. J. 2013, 214, 376−385. (37) Wang, X.; Zhu, G.; Guo, F. Removal of Uranium (VI) Ion from Aqueous Solution by SBA-15. Ann. Nucl. Energy 2013, 56, 151−157. (38) Onodera, Y.; Mimura, H.; Iwasaki, T.; Hayashi, H.; Ebina, T.; Chatterjee, M. A New Granular Composite with High Selectivity for Cesium Ion Prepared from Phosphomolybdic Acid Hydrate and Inorganic Porous Material. Sep. Sci. Technol. 1999, 34, 2347−2354. 29343

DOI: 10.1021/acsami.7b09419 ACS Appl. Mater. Interfaces 2017, 9, 29337−29344

Research Article

ACS Applied Materials & Interfaces (39) Parajuli, D.; Hirota, K.; Seko, N. Effective Separation of Palladium from Simulated High Level Radioactive Waste. J. Radioanal. Nucl. Chem. 2011, 288, 53−58. (40) Han, X.; Xu, M.; Yang, S.; Qian, J.; Hua, D. AcetylcysteineFunctionalized Microporous Conjugated Polymers for Potential Separation of Uranium from Radioactive Effluen. J. Mater. Chem. A 2017, 5, 5123−5128. (41) Lebed, P. J.; Savoie, J. D.; Florek, J.; Bilodeau, F.; Lariviere, D.; Kleitz, F. Large Pore Mesostructured Organosilica-Phosphonate Hybrids as Highly Efficient and Regenerable Sorbents for Uranium Sequestration. Chem. Mater. 2012, 24, 4166−4176. (42) Malik, R.; Dahiya, S.; Lata, S. An experimental and quantum chemical study of removal of utmostly quantified heavy metals in wastewater using coconut husk: A novel approach to mechanism. Int. J. Biol. Macromol. 2017, 98, 139−149. (43) Shen, J.; Duvnjak, Z. Effects of Temperature and pH on Adsorption Isotherms for Cupric and Cadmium Ions in Their Single and Binary Solutions Using Corncob Particles as Adsorbent. Sep. Sci. Technol. 2004, 39, 3023−3041. (44) Yavuz, H.; Say, R.; Denizli, A. Iron Removal from Human Plasma Based on Molecular Recognition Using Imprinted Beads. Mater. Sci. Eng., C 2005, 25, 521−528. (45) Zhang, L.; Yang, S.; Qian, J.; Hua, D. Surface Ion-Imprinted Polypropylene Nonwoven Fabric for Potential Uranium Seawater Extraction with High Selectivity over Vanadium. Ind. Eng. Chem. Res. 2017, 56, 1860−1867.

29344

DOI: 10.1021/acsami.7b09419 ACS Appl. Mater. Interfaces 2017, 9, 29337−29344