Succinamic Acid Grafted Nanosilica for the Preconcentration of U(VI

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Succinamic Acid Grafted Nano-Silica for the Preconcentration of U(VI) from Aqueous Solution Fuyou Fan, Duoqiang Pan, Hanyu Wu, Tianjiao Zhang, and Wangsuo Wu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04652 • Publication Date (Web): 08 Feb 2017 Downloaded from http://pubs.acs.org on February 12, 2017

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Industrial & Engineering Chemistry Research

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Succinamic Acid Grafted Nano-Silica for the

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Preconcentration of U(VI) from Aqueous Solution

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Fuyou Fan1,2,3, Duoqiang Pan1,4*, Hanyu Wu1,4, Tianjiao Zhang5, Wangsuo Wu1,4*

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University, Lanzhou 730000, China

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Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China

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University of Chinese Academy of Sciences, Beijing 100049, China

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Key Laboratory of Special Function Materials and Structure Design, Ministry of

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Education, Lanzhou 730000, China

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Radiochemistry Laboratory, School of Nuclear Science and Technology, Lanzhou

The Second Medical College, Lanzhou University, Lanzhou 730000, China.

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Submitted to Industrial & Engineering Chemistry Research

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*Corresponding authors: Duoqiang Pan

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Tel: 86 931 8913594; Fax: 86 931 8913594

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Email: [email protected]

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Wangsuo Wu

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Email: [email protected]

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ACS Paragon Plus Environment


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Abstract

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Succinamic

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characterized and tested for hexavalent uranium preconcentration from contaminated

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aqueous solutions. The succinamic acid grafted nano-silica exhibited improved

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uranium preconcentration capacity in comparison with that of raw nano-silica. The

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effects of environmental conditions such as pH, ionic strength, solid concentration,

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foreign ions and temperature on uranium(VI) preconcentration performance were

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investigated by batch technique in detail, and the related mechanism was discussed

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with aid of XPS technique. Results showed that uranium(VI) preconcentration by

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SA@SiO2 was strongly dependent on pH while less so on ionic strength, the

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preconcentration was mainly dominated by inner-sphere surface complexation. The

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coexisting cations had no effects while anions influenced U(VI) preconcentration

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significantly. The preconcentration of U(VI) was favorable at lower temperature, the

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maximum preconcentration capacity was 44.5 mg/g at pH = 4.0 ± 0.1 and T = 298 K.

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Thermodynamic parameters indicated that the preconcentration process was

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exothermic and spontaneous. The SA@SiO2 exhibited desirable selectivity for

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uranium, and can be reused at least 5 times without decreasing capacity. Accordingly,

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the SA@SiO2 is a potential and suitable candidate for the preconcentration of U(VI)

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from considerable volume of contaminated water.

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Key Words: Succinamic Acid; Nano-silica, Uranium; Preconcentration

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1.

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Uranium is an important pollutant to water body around nuclear industrial sites, such

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as uranium mining, milling and nuclear waste disposal.1,2,3 Environmentally mobile

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uranium (hexavalent uranium) could migrate through natural geologic and hydrologic

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processes, then further accumulate in living creatures. Because of its chemical toxicity

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and radioactivity, the uranium contaminated water has potential to cause severe

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progressive or irreversible organism injury.4,5 Thus, preconcentration and elimination

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of uranium pollutant from contaminated water body is very crucial to mitigate the

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hazard of uranium to organism and ecology. Different techniques such as sorption,

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precipitation, reduction, membrane and ion exchange have been sought to

acid

functionalized

nano-silica

(SA@SiO2)

was

synthesized,

Introduction

2


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preconcentrate uranium from aqueous solutions, among which sorption technique has

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drawn many concerns because of its high efficiency, easy operation and low cost.

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Many sorbents such as minerals6, oxides7 and nano-materials8 were proposed so far on

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the preconcentration and purification of contaminated water body, however, the

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shortage that limited sorption selectivity for natural minerals, high cost and

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environmental unfriend for nanomaterials are restricting their further widely industrial

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application. Thus the economical and environmental friendly sorbents with prominent

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sorption capacity and selectivity need to be developed for the preconcentration of

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uranium contaminants from considerable volume of aqueous solutions around nuclear

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facilities.9

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Recently, the organic functional groups such as amidoxime, amide, displayed great

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coordination ability and selectivity with uranium. Accordingly, the grafting of these

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organic functional groups to a proper solid substrate is easily called in mind. Zhao et

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al.9 synthesized amidoxime functionalized Fe3O4@SiO2 core-shell magnetic

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microspheres and found it had highly efficient preconcentration toward U(VI). Wang

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et al.10 prepared iminodiacetic acid derivative functionalized SBA-15 and concluded

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that SBA-15-CyD3A possessed good selective sorption properties for U(VI). Carboni

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et al.11 synthesized a series of carboxyl-, amidoxime-, and phosphoryl functionalized

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mesoporous carbon materials and the uranium sorption results indicated that these

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materials were promising sorbents for U(VI) extraction. Starvin et al.12 used activated

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carbon modified by diarylazobisphenol in preconcentration and separation of trace

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quantities of uranium from other inorganics. Tashkhourian et al.13 prepared sodium

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dodecyl sulfate (SDS) and Schiff’s base ligand coated alumina for preconcentration of

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uranyl(VI) from water. The enrichment factor was more than 200 and the recovery

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was 99.5 %, the coexisting ions had no significant effect on the preconcentration

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process. Pan et al.14 synthesized chitosan attapulgite composite particles for extraction

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of uranyl ion from aqueous solutions, the adsorption capacity for uranyl ions was 53.5

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mg/g at 298 K and pH 5.5. Ulusoy et al.15 prepared gallocyanine (GC) functionalized

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polyacyril amide (PAA) for removal of uranyl ions from aqueous media, the

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maximum capacity was found to be 7.14 mg/g (298K), but the regeneration was poor 3



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due to the inferior stability of functional groups. Oyola et al.16 developed amidoxime

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grafted high surface-area polyethylene (PE) fibers for selective extraction of uranium

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from seawater, the proposed fibers performed good uranium extraction capacity.

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Silica in nano dimension not only possesses abundant surface and high chemical

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stability, but also can be modified irreversibly through the reaction of surface silanol

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group.17 Succinamic acid has strong tendency to form complexes with transition

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metals.18 In present work, a hybrid constituting of succinamic acid and nano-silica

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were synthesized, characterized and applied to preconcentrate hexavalent uranium

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from aqueous solution. Effect of environmental conditions such as pH, ionic strength,

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temperature and coexisting ions were investigated by batch technique, and the

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interaction mechanism between uranium and SA@SiO2 composite was discussed with

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the aid of X-ray photoelectron spectroscopy. The results indicated that SA@SiO2

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composite is an effective and promising agent for uranium preconcentration from

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considerable volume of aqueous solution.

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2. Experimental

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2.1 Materials

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Nano-silica with average particle size ~ 20 nm was purchased from Nanjing Haitai

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nano materials Co. Ltd. Toluene was distilled and dried before use according to

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conventional literature methods.19 Other chemicals used in the experiments were of

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analytical grade and used as received. U(VI) stock solution was prepared by

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dissolving U3O8 in concentrated nitric acid. The solution was heated until it was

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nearly dry and then 5 mL 0.01 M HNO3 was added, the obtained solution was

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transferred to 100 mL volumetric flask and diluted with 0.01 M HNO3. Other stock

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solutions and suspensions were prepared in double distilled water with electrical

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conductivity of 8.80 µS/cm.

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2.2 Preparation of SA@SiO2

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Firstly, Silica-aminopropyltriethoxysilane (Si-APTES) was prepared by refluxing

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2.7475 g activated nano-silica (treated overnight at 100 oC under vacuum) and 4.00

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mL 3-aminopropyltriethoxysilane (APTES) in 100 mL dry toluene medium under N2

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atmosphere for 18 h. The suspended solid product was filtered after cooling to room 4


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temperature, washed thoroughly with toluene and ethanol several times, dried at 80℃

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under vacuum overnight, and then Si-APTES was obtained.10 In this reaction, the

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surface silanol groups presented on silica gel reacted with APTES to form amino

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functionalized silica gel (Si-APTES). Secondly, SA@SiO2 was synthesized by the

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condensation reaction, succinic anhydride (1.7123 g) and Si-APTES (2.8029 g) were

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mixed in 100 mL tetrachloromethane at room temperature, then small amount of

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pyridine was added as an acid binding agent.10 The scheme of synthesis reaction was

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shown in Figure 1.

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2.3 Preconcentration procedures

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Stock suspensions of SA@SiO2, NaNO3 and UO2(NO3)2 stock solutions were mixed

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in the polyethylene tubes to achieve the desired concentrations of different

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components. The pH values of the solutions were adjusted by adding negligible

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volumes of 0.1 or 0.01 mol/L HNO3 or NaOH solution. After the suspensions were

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shaken on an orbital shaker for 48 h, the solid and liquid phases were separated by

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centrifugation at 10000 rpm for 30 min. The equilibrium pH values were measured by

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calibrated pH-meter (Sartorius, PB-10). The concentration of U(VI) in the supernatant

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(Ce) was analyzed by spectrophotometry at a wavelength of 652 nm using Arsenazo

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III. All the experimental data were the averages of duplicate experiments.20

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2.4 Characterization

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The obtained SA@SiO2 composite was characterized by X-ray diffraction (XRD,

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PANalytical X’Pert PRO), field emission scanning electron microscope (FESEM,

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Hitachi S-4800), transmission electron microscope (TEM, FEI Tecnai F30), N2

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adsorption-desorption (Micromeritics, TriStar II 3020), Elements analysis (Elementar,

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Vario EL), Fourier Transform Infrared spectra (FTIR, Nicolet Nexus) and X-ray

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photo-electron spectroscopy (XPS, Thermo ESCALab 220i-XL). XRD patterns were

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obtained from D/Max-r B equipped with a rotation anode using Cu Kα radiation in the

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range of 3° ≤ 2θ ≤ 70°. The XPS data were obtained using Al Kα radiation, the

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pressure in the analysis chamber was maintained below 5 × 10−10 mbar. The binding

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energies were corrected using C 1s peak at 284.80 eV as a reference.

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3. Results and discussion 5



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3.1 Characterization

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XRD patterns of raw nano-silica and SA@SiO2 composite (Figure 2-i) displayed a

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single broad peak around 23°, there is no evidence for the presence of any crystalline

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phases (i.e., amorphous characteristic of silica) or any other impurity. The similar

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XRD pattern for SA@SiO2 and raw nano-silica suggested that the phase structure of

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nano-silica was not changed during grafting process. According to SEM and TEM

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images, it can be seen that before and after modification there was a little change in

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the general topography (Figure 2-ii). SiO2 and its derivate exhibited smooth and

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spherical shape (from TEM images), and the particles were easy to aggregate in to

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gobbet due to high surface energy, which makes the morphology shapeless from SEM

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images. High specific surface area of SiO2 determined by N2 adsorption-desorption

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measurement is 207.6 m2/g, suggesting that nano-silica possibly possesses high

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sorption capacity and strong affinity to uranium. While for SA@SiO2, the surface area

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(124.9 m2/g) is smaller, which is because the adhesion of organic molecule on silica

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surface makes silica particles more aggregative. There was no plenty of micro and

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mesoporosity in raw SiO2 and SA@SiO2 from the nature of the isotherm (Figure

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2-iii).

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Figure 2-iv showed the FTIR spectra of raw and modified silica. Raw silica showed

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the typical adsorption bands at 1107 cm−1 (asymmetric Si-O-Si stretch), 804 cm−1

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(symmetric Si-O-Si stretch), and 471 cm−1 (Si-O-Si bending mode), the adsorption

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bands at 3431 cm−1 and 1633 cm−1 were assigned to the hydrated silane group and the

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bending vibration of surface hydroxide respectively.21,22 For SA@SiO2, the adsorption

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band at 1723 cm−1 was observed, it was assigned to COO- antisymmetric stretching

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vibrations. The wave numbers centered at 2939, 1555 and 1415 cm−1 were assigned to

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C-H, N-H and C-N bands respectively.23 These results support the fact that nano-silica

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was successfully modified with succinamic acid. Spectra after uranium sorption

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showed that COO- antisymmetric stretching vibrations shift toward higher wave

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number region (1633 cm−1), and the COO- symmetric stretching vibrations could be

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observed obviously at 1384 cm−1, which implied that the carboxyl group played an

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important role in uranium binding.10 The content of C, H, and N in the raw and 6


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modified nano-silica (Table 1) was determined by element analysis. In SA@SiO2, the

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N content of 1.14 % supported the fact that succinamic acid had been successfully

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grafted on the nano-silica. The grafting ratio for SA@SiO2 calculated from N element

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content was 0.811 mmol/g (Table 1).

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3.2 Effect of solid concentration

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The distribution coefficient (Kd) can be calculated from C0 (mol/L) and Ce (mol/L):

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Kd =

C 0 − Ce V × C0 m

(1)

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where V is the volume of the suspension, C0 is the initial concentration of U(VI) and

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Ce is the equilibrated U(VI) concentration after preconcentration, and m is the mass of

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solid. Preconcentration percentage of UO22+ increased with the solid concentration

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from ~11 % at 0.1 g/L to ~90 % at 0.8 g/L, and remained stable at ~90 % from 0.8 to

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2.5 g/L (Figure 3). There are more surface sites available to bind U(VI) at SA@SiO2

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surface with increasing solid concentration, but when solid concentration increased to

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certain extent, the interaction between solid particles restricts the performance of

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uranium preconcentration. Kd keeps almost constant in the whole range, this result is

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similar with sorption of U(VI) on Na-attapulgite24, Pb(II) on NKF-6 zeolite25.

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3.3 Effect of pH and ionic strength

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Preconcentration of UO22+ on raw and modified SiO2 was strongly dependent on pH

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values but less so on ionic strength (Figure 4-i, ii). The preconcentration of UO22+ on

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raw SiO2 increased sharply from ~10 % to ~100 % at pH range of 2.5-5.7, then

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reached a plateau at pH rang of 5.7-11.0. While for SA@SiO2, preconcentration

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percentage rose immediately from ~25 % to ~100 % at pH range of 2.5-4.1, then

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stabilized above pH 4.1. The modification by succinamic acid greatly enhanced

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uranium preconcentration performance at acidic condition because the adhesion of

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succinamic acid provided abundant coordinating functional groups for U(VI). It is

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clear that UO22+ is the main species in aqueous solution below pH 4, H+ ions emitted

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from the chelation reactions can be neutralized as pH rising, which reduces the

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repulsion between SA@SiO2 and UO22+ through deprotonation of the grafted groups

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and enhances the preconcentration amounts.9 7



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Different NaNO3 concentrations were used to study the ionic strength dependence of

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U(VI) preconcentration by SA@SiO2. From Figure 4-ii, ionic strength made little

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difference on uranium preconcentration over a wide pH range. Generally, the surface

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ion exchange and outer-sphere complexes can be influenced significantly by ionic

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strength, whereas inner-sphere complex is mainly affected by pH but ionic strength.

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The great pH dependence but less ionic strength dependence indicated that the

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inner-sphere surface complexation is the major mechanism rather than ion exchange

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or outer-sphere surface complexation.26 This also supported that chelating functional

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groups of succinamic acid on SA@SiO2 formed chelates with U(VI).9,27

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3.4 Effect of interfering ions

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Figure 4-iii demonstrated the preconcentration of U(VI) on SA@SiO2 as a function of

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pH in 0.1 M LiNO3, NaNO3, KNO3 and Mg(NO3)2 solutions, separately. One can see

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that the coexisting foreign cations (with different radius and charge) had little

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influence on U(VI) preconcentration, which indicated that the preconcentration of

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U(VI) was dominated by inner-sphere surface complexation rather than ion exchange.

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These results are consistent with the sorption of U(VI) on amidoxime-functionalized

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Fe3O4@SiO2 core-shell magnetic microspheres9, sorption of Th (IV) on silica28.

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Figure 4-iv showed the preconcentration curves of U(VI) on SA@SiO2 as a function

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of pH in 0.1 M NaClO4, NaNO3, and NaCl solutions. The preconcentration of U(VI)

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on SA@SiO2 in 0.1 M NaCl solution is the highest and that in 0.1 M NaClO4 is the

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lowest. The radius sequence of these anions is Cl− < NO3− < ClO4−, Cl− with smaller

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radius is easier to be attached to solid surface, which alters the surface electrostatic

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property and forms a negative charged circumstance for U(VI) preconcentration.6,29

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3.5 Thermodynamic studies

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The isotherms of U(VI) preconcentration on SA@SiO2 at different temperatures were

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shown in Figure 5. Langmuir and Freundlich models were employed to simulate the

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experimental isotherms of U(VI) preconcentration. The form of Langmuir isotherm

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can be described as:

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q=

bqmax Ce 1 + bCe

(2) 8


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where Ce (mol·L-1) is the equilibrium concentration of U(VI) remaining in aqueous

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solution, q (mol·g-1) is the quantity of preconcentrated U(VI) per unit weight of

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adsorbent after equilibrium, b (L·mol-1) is a constant associated with the enthalpy of

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preconcentration, and qmax (mol·g-1) is the maximum preconcentration capacity that

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indicates the quantity of U(VI) at complete monolayer coverage. The Freundlich

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model is an empirical model illustrating the sorption on a heterogeneous surface with

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tremendous identical sites, which can be explained by the following equation:

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q = k F Cen

(3)

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where Ce (mol·L-1) is the equilibrium aqueous concentration of U(VI), kF

245

(mol1-n·Ln·g-1) and n are the Freundlich empirical constants, representing the

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preconcentration capacity and preconcentration intensity respectively. The parameters

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calculated from two models were shown in Table 2. The results suggested that

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Langmuir model fitted the isothermic data of U(VI) preconcentration better than

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Freundlich model, indicating that the U(VI) preconcentrated on SA@SiO2 constituted

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a monolayer coverage and the major sorption mechanism was chemisorption.9 This is

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consistent with the strong chelation between U(VI) and succinamic acid functional

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groups. The qmax value of U(VI) preconcentration on SA@SiO2 was calculated to be

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44.5 mg·g-1 at 298 K, which is much higher than that of U(VI) preconcentration on

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other natural and man-made materials under similar experimental conditions. The qmax

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values of U(VI) preconcentration on these materials were listed in Table 3. By

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comparison with other materials, the SA@SiO2 nano-composites showed prominent

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capacity. From Figure 5, it can be seen that the preconcentration of U(VI) on

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SA@SiO2 is the lowest at 338K and the highest at 298K, which means that lower

259

temperature is advantageous for U(VI) preconcentration process. The thermodynamic

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parameters (∆H0, ∆S0 and ∆G0) of U(VI) preconcentration can be calculated by the

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temperature dependent isotherms. The Gibbs free energy changes (∆G0) are calculated

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by the following equation:

263 264

∆G o = − RT ln K 0

(4)

where T is the temperature in Kelvin, R is the ideal gas constant (8.314 J·mol-1·K-1) 9



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and K0 is the preconcentration equilibrium constant that can be extrapolated by

266

plotting ln Kd vs. Ce (Figure 6-i) when Ce is close to zero. The standard enthalpy

267

change (∆H0) and the standard entropy change (∆S0) can be calculated by the slope

268

and intercept of the following equation (Figure 6-ii):

269

ln K 0 =

∆S 0 ∆H 0 − R RT

(5)

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The negative ∆G0 values (-24.25, -25.40 and -26.06 kJ·mol-1 for 298, 318 and 338K,

271

respectively) reflected the spontaneous process of U(VI) preconcentration on

272

SA@SiO2. Negative ∆H0 value (-10.66 kJ·mol-1) indicated that the overall sorption

273

process was apparently exothermic, which was consistent with the reported results for

274

uranium preconcentration on SII-MM1 and SNI-MM30, MWCNTs31, and amino acid

275

functionalized chitosan magnetic particles32. The positive value of ∆S0 (45.84

276

kJ·mol-1) mainly was the result of release of hydration waters from hydrated U(VI)

277

species, which also reflected the affinity of U(VI) to SA@SiO2 in aqueous

278

solution.7,33

279

3.6 Preconcentration mechanism

280

The preconcentration mechanism of U(VI) on SA@SiO2 was explained with the aid

281

of XPS technique. The characteristic peak of uranium at 383.07 eV appeared in

282

survey spectra after U(VI) loading on SA@SiO2, which indicated that U(VI) was

283

concentrated on SA@SiO2 (Figure 7 (left)). It can be seen that the binding energy of

284

N 1s decreased after U(VI) loading, which meant that N was involved in

285

preconcentration process by forming complex with U(VI).34 The deconvoluted C 1s

286

spectrum of SA@SiO2 can be satisfactorily fitted by C-C/C-H at 284.84 eV, C-N at

287

287.08 eV, HN-C=O at 289.22 eV and O=C-OH at 292.72 eV (Figure 7 (right) &

288

Table 4).35, 36, 37 The binding energy shifts of C 1s and O 1s after U(VI) loading on

289

SA@SiO2 demonstrated the variation of the chemical environment of C and O,

290

namely, amide and carboxyl groups on SA@SiO2 chelated with U(VI). In

291

deconvoluted C 1s spectra, the peak area percentage of HN-C=O decreased from

292

68 % to 4 % while that of O=C-OH decreased from 7 % to 4 % after U(VI) loading

293

(Table 4), illustrating that both amide and carboxyl played important role in the 10


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process of U(VI) preconcentration on SA@SiO2.

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3.7 Regeneration and selectivity study

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The regeneration and reusability of a sorbent is essential to evaluate its performance

297

and application according to economic and environmental consideration. From the

298

results presented in Figure 4, few U(VI) is preconcentrated at very low pH values,

299

implying that acid treatment is a possible method for the regeneration of

300

uranium-loaded SA@SiO2. Therefore, the regeneration of SA@SiO2 was performed

301

in 0.05 mol/L HNO3 solution. The preconcentration efficiency was more than 96 %

302

after 5 consecutive cycles (Figure 8A). The results indicated that U(VI)-loaded

303

SA@SiO2 composite could be efficiently regenerated by 0.05 mol/L HNO3 and reused

304

without obvious decrease in U(VI) preconcentration capability. The proposed

305

SA@SiO2 nano-composite in present work possesses potential of long-term use with

306

low replacement cost, and is a promising candidate for the preconcentration of U(VI)

307

from aqueous solution.

308

Efficient preconcentration of uranium requires high selectivity as there usually exist

309

competitive metal ions in aqueous solutions. The selectivity performance of

310

SA@SiO2 and SiO2 to U(VI) preconcentration were investigated in aqueous solution

311

containing Ca2+, Mg2+, Sr2+, Zn2+, Co2+, Ni2+, Cd2+, Cu2+ and Eu3+ at a pH value of

312

about 4.0. The residual metal ions in supernatant after sorption were measured by

313

ICP-OES (Optima 8000). From Figure 8B, it is obvious that SA@SiO2 exhibited

314

desirable selectivity for U(VI) over a range of coexisting metal ions, and the

315

selectivity of SA@SiO2 for uranium was obviously improved comparing with that of

316

rare SiO2, validating that the modification by succinamic acid in this work is effective.

317

4. Conclusion

318

A novel succinamic acid functionalized silica gel (SA@SiO2) was prepared by a

319

post-grafting method, its preconcentration behaviors of U(VI) from aqueous solution

320

were investigated by batch techniques. The detailed characterization confirmed the

321

presence of succinamic moieties (0.811 mmol/g) on the surface of silica gel. The

322

preconcentration ability toward uranium was significantly enhanced after modification,

323

and the preconcentration was strongly dependent on pH while less so on ionic strength, 11



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Page 12 of 32

324

inner-sphere surface complexation dominated the sorption process. Coexisting cations

325

had little influence on U(VI) preconcentration over a wide pH while anions influenced

326

greatly at acidic pH range. Langmuir model fitted the preconcentration isotherms

327

better

328

preconcentration process of U(VI) on SA@SiO2 was a spontaneous and exothermic

329

process. XPS data illustrated that both amide and carboxyl were involved in

330

preconcentration process by forming complexes with U(VI). The SA@SiO2 exhibited

331

desirable selectivity for uranium, and can be reused at least 5 times without

332

decreasing capacity. The results in present work provide an effective candidate for the

333

preconcentration and recovery of U(VI) from considerable volume of contaminated

334

water around nuclear facilities.

335

Acknowledgments

336

The authors thank Zhu L. for the assistant on synthesis of SA@SiO2. This work was

337

supported by the National Natural Science Foundation of China (21327801, 41573128,

338

21601179); the Key Laboratory Project of Gansu Province (1309RTSA041); the

339

“100-Talent” Program from the Chinese Academy of Sciences in Lanzhou Center for

340

Oil and Gas Resources, Institute of Geology and Geophysics; the Fundamental

341

Research Funds for the Central University (lzujbky-2015-70, lzujbky-2016-34); and

342

open project of Key Laboratory for Magnetism and Magnetic Materials of the

343

Ministry of Education, Lanzhou University (lzummm2015011).

344

References

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spectroscopic characterizations of succinamic acid and succinimide platinum blues. J.

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experimental and theoretical calculations. Chem. Eng. J. 2016, 287, 448.

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Absorption Fine Structure Spectroscopy and by Modeling Techniques. Environ. Sci.

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Particles for Uranyl Sorption. Ind. Eng. Chem. Res. 2015, 54 (49), 12374.

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bio-nanocomposites as high performance adsorbents for the removal of radionuclides.

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Borassus flabellifer-based adsorbents. Langmuir. 2012, 28(46), 16038.

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(37) Guo, F.; Zhang, Z. Z.; Liu, W. M.; Su, F. H.; Zhang, H. J. Effect of plasma

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treatment of Kevlar fabric on the tribological behavior of Kevlar fabric/phenolic

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composites. Tribol. Inter. 2009, 42, 243.

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(38) Bryant, D. E.; Stewart, D. I.; Kee, T. P.; Barton, C. S. Development of a

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functionalized

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groundwater. Environ. Sci. Technol. 2003, 37(17), 4011.

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(39) Metilda, B. P.; Gladis, J. M.; Rao, T. P. Catechol functionalized aminopropyl

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silica gel: synthesis, characterization and preconcentrative separation of uranium(VI)

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from thorium(IV). Radiochim. Acta. 2005, 93(1), 219.

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(40) Simsek, S.; Ulusoy, U. Uranium and lead adsorption onto bentonite and zeolite

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modified with polyacrylamidoxime. J. Radioanal. Nucl. Chem. 2012, 292, 41.

461

(41) Venkatesan, K. A.; Sukumaran, V.; Antony, M. P.; Rao, P. R. V. Extraction of

462

uranium by amine, amide and benzamide grafted covalently on silica gel. J.

463

Radioanal. Nucl. Chem. 2004, 260(3), 443.

464

(42) Akyil, S.; Aslani, M. A. A.; Eral, M. Sorption characteristics of uranium onto

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composite ion exchangers. J. Radioanal. Nucl. Chem. 2003, 256(1), 45.

466

(43) Banerjee, C.; Dudwadkar, N.; Tripathi, S. C.; Gandhi, P. M.; Grover, V.;

467

Kaushik C. P. et al. Nano-cerium vanadate: a novel inorganic ion exchanger for

468

removal of americium and uranium from simulated aqueous nuclear waste. J. Hazard.

469

Mater. 2014, 280, 63.

polymer-coated

silica

for

the

removal

470

16


of

uranium

from

Page 17 of 32

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List of Tables

471 472

Table 1. Physical and chemical properties of raw SiO2 and SA@SiO2.

473

Table 2. Langmuir and Freundlich isoherms parameters.

474

Table 3. Comparison of the maximum preconcentration capacity of U(VI) on

475

SA@SiO2 with other materials.

476

Table 4. The binding energy and assignments of C 1s and O 1s XPS spectral bands

477

for SA@SiO2 and U(VI)-loaded SA@SiO2.

478

17



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

479

Page 18 of 32

Table 1

480

Nano-silica Si -APTES SA@SiO2 BET (m2 g-1)

207.6

/

124.9

Pore volume (cm3 g-1)

0.943

/

0.720

Pore size (nm)

18.162

/

23.047

C (weight %)

0.88

4.54

11.70

N (weight %)

0.00

1.41

1.14

H (weight %)

0.46

0.96

1.55

Functional groups content (mmol·g-1)

0

1.004

0.811

481 482

18


Page 19 of 32

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


483

Table 2

484

Parameters of the Langmuir and Freundlich models Langmuir model T(K)

qmax (mol·g-1)

298

1.874 × 10-4

318 338

b (L·mol-1)

Freundlich model kF (mol1-n·Ln·g-1)

n

R2

1.967 × 105 0.967

0.0079

0.415

0.834

1.663 × 10-4

1.664 × 105 0.967

0.0084

0.393

0.903

1.448 × 10-4

1.022 × 105 0.935

0.0093

0.385

0.884

R2

485 486

19



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

487

Page 20 of 32

Table 3

488

Materials

Experimental conditions

qmax (mg/g)

Ref

Functionalized polymer-coated silica

pH = 4.5, T = 298K

5.2

38

Catechol functionalized aminopropyl silica gel

pH = 5.0, T = 298K

15.94

39

p-DPMBT immobilized silica

pH = 5.0, T = 298K

1.19

4

Bentonite modified with polyacrylamidoxime

pH = 4, T = 298K

33.3

40

Amine modified silica gel

pH =4.0, T = 302K

35.86

41

MC-Ph-AO/PhCOOH

pH = 4.0, T = 298K

22.0

11

Ion exchanger (Composite C)

-

0.0429

42

Ion exchanger (nano-CeVO4)

pH 1-6

18.73

43

nano silica

pH = 5.0, T = 298K

6.95

8

SA@SiO2

pH = 4.0, T = 298K

44.5

This work

489 490

20


Page 21 of 32

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


491

Table 4

492

SA@SiO2

U(VI)-loaded SA@SiO2

Element

Assignments B.E. (eV)

Area %

B.E. (eV)

Area %

284.84

13

284.86

27

C-(C, H)

287.08

12

286.68

64

C-N

289.22

68

288.39

4

C=O

292.72

7

290.36

4

O=C-OH

532.24

11

532.41

28

CONH

535.17

37

533.63

32

C=O

536.64

51

534.73

40

COOH

C 1s

O 1s

493 494

21



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

List of Figures

495 496 497

Figure 1. Schematic illustration of the synthesis of SA@SiO2.

498

Figure 2. i): XRD of (a): nano-silica; (b): SA@SiO2. ii): SEM images of (a):

499

nano-silica; (b): SA@SiO2. TEM images of (c): nano-silica; (d): SA@SiO2. iii): N2

500

adsorption-desorption isotherms of raw SiO2 and SA@SiO2. iv): FTIR spectra of (a):

501

nano-silica, (b): SA@SiO2 and (c): U-loaded SA@SiO2.

502

Figure 3. Effect of the solid concentration on U(VI) preconcentration on SA@SiO2. I

503

= 0.01 mol/L NaNO3, pH = 5.0 ± 0.1, T = 25 °C, CU(VI) initial = 2.0 × 10-5 mol/L.

504

Figure 4. (i): Influence of pH on U(VI) preconcentration onto raw SiO2 and

505

SA@SiO2 (m/V = 0.4 g/L, T = 25 °C, CU(VI) initial = 2.0 × 10-5 mol/L). (ii): Influence of

506

pH and ionic strength on U(VI) preconcentration onto SA@SiO2 (m/V = 0.3 g/L, CU(VI)

507

initial =

508

preconcentration onto SA@SiO2 (m/V = 0.5 g/L, pH = 5.0 ± 0.1, T = 25 °C, CU(VI) initial

509

= 2.0 × 10-5 mol/L)). (iii) & (iv): Influence of cations and monovalent anions on U(VI)

510

preconcentration onto SA@SiO2 (m/V = 0.3 g/L, CU(VI) initial = 5.0 × 10-5 mol/L, T =

511

25 °C).

512

Figure 5. Isotherms of U(VI) preconcentration on SA@SiO2 at different temperatures.

513

m/V = 0.3 g/L, I = 0.01 mol/L NaNO3, pH = 4.0 ± 0.1.

514

Figure 6. (i): Effect of temperature on the distribution coefficients of U(VI) on

515

SA@SiO2; (ii): Linear plot of lnK0 versus 1/T for the preconcentration of U(VI) on

516

SA@SiO2.

517

Figure 7. The whole range XPS spectra (left) of SA@SiO2 and U(VI)-loaded

518

SA@SiO2. X-ray photoelectron high-resolution (right) (A): C 1s spectra of SA@SiO2;

519

(B): C 1s spectra of U(VI)-loaded SA@SiO2; (C): O 1s spectra of SA@SiO2 and (D):

520

O 1s spectra of U(VI)-loaded SA@SiO2.

521

Figure 8. (A): Recycling of SA@SiO2 in U(VI) preconcentration from aqueous

522

solution. CU(VI) initial = 5 × 10-5 mol/L, m/V = 0.3 g/L, I = 0.01 mol/L NaNO3, pH = 5.0

523

± 0.1, T = 25 oC. (B): Selectivity of SA@SiO2 and rare SiO2. (m/V = 1.0 g/L, I = 0.01

5.0 × 10-5 mol/L, T = 25 °C). (Insert figure: Influence of ionic strength on U(VI)

22


Page 22 of 32

Page 23 of 32

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524

mol/L NaNO3, CM initial = 1.0 × 10-4 mol/L, pH = 4.0 ± 0.1, T = 25 °C).

525

23



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

526 527

Figure 1

528

24


Page 24 of 32

0

ii

iv

d

0.0

0.2

0.4

0.6

0.8

a b c

4000

3200

2400

1600

Wavenumbers (cm-1)

529 530

1.0

Ralative pressure (P/P0)

Figure 2

531

25


472

iii

1106

i

803

b

c

60

100

1384

a

50

200

1630

40

SA@SiO2 Desorption

1732 1555 1415

30

2 Theta

300

Intensity (a.u.)

20

400

nano silica Adsorption nano silica Desorption SA@SiO2 Adsorption

500

2937

b 10

600

3431

a

Intensity

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


Quantity Adsorbed ( cm3/g)

Page 25 of 32

800


100

8

80

6

60 4 40 2

20 0

0.0

0.5

1.0

1.5

2.0

Solid Concentration (g/L) 532 533

Figure 3

534

26


2.5

0

Log Kd (mL/g)

Preconcentration (%)

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 26 of 32

Page 27 of 32

535 120

60 40 nano-silica SA@SiO2

20 2

80

4

6 pH

8

10

40 20 0


0.5M NaNO3

100 80 60 40 20 0 0.0

0.1

0.2

0.3

0.4

0.5

0.1M LiNO3 0.1M NaNO3 0.1M KNO3 0.1M Mg(NO3)2

40 20 2

2

3

4

5 pH

6

7

3

4

6

8

7

8

iv

80 60 40

0.1M NaClO4 0.1M NaNO3 0.1M NaCl

20

1

2

3

537 538

5 pH

0

C(NaNO3) mol/L

1

60

100 0.01M NaNO3 0.1M NaNO3

60

80

0

12


ii

100

536



80

0

iii

100

i

100


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


Figure 4

539

27


4

5 pH

6

7

8


1.8E-4 1.5E-4 Cs (mol/g)

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

1.2E-4 9.0E-5

298K 318K 338K Langmuir model Freundlich model

6.0E-5 3.0E-5 0

1E-5

2E-5

3E-5

4E-5

Ce (mol/L)

540 541

Figure 5

542

28


5E-5

Page 28 of 32

Page 29 of 32

9.6 9.3

298K 318K 338K

i

9.0

9.8 9.7 0

8.4

9.5 9.4

8.1

9.3

7.8 0.00

ii

9.6

8.7

Ln K

Ln Kd (mL/g)

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


1.50E-5 3.00E-5 Ce (mol/L)

9.2

4.50E-5

3.00E-3

543 544

Figure 6

545

29


3.15E-3 1/T (1/K)

3.30E-3

Intensity (a. u.)

O 1s

SA@SiO2 0

200

400 600 800 1000 1200 Binding Energy (eV)

Intensity (a. u.)

U 4f

U(VI)+SA@SiO2

N 1s

C 1s

Si 2p

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

Intensity (a. u.)


CONH

A

292

288

C=O

280

COOH 538

536

534

532

530

536

534

532

530

D

292

288

284

280

Binding Energy (eV)

546 547

284

B

296

CONH

C

C-N, C-H C-C

O-C=O 296

Page 30 of 32

Figure 7

548

30


538

Binding Energy (eV)

100

A

80 60 40 20 0 0

1

2

3

4

5

Cycle Number

80 Preconcentration (%)

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 31 of 32

B

SA@SiO2

60

rare SiO2

40 20 0

2+

2+

Ca Mg Sr2+ Zn2+ Co2+ Ni2+ Cd2+Cu2+ Eu3+ UO22+

549 550

Figure 8

551

31



120 100 Preconcentration (%)

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 32 of 32

80 60 40 nano-silica SA@SiO2

20 0

2

4

6 pH

8

552 553

TABLE OF CONTENT

32


10

12

Succinamic Acid Grafted Nanosilica for the Preconcentration of U(VI

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