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Amino Siloxane Oligomer Modified Graphene Oxide Composite for the Efficient Capture of U(VI) and Eu(III) from Aqueous Solution Donglin Zhao, LiLi Chen, Mingwenchan Xu, Shaojie Feng, Yi Ding, M. Wakeel, Njud S. Alharbi, and Changlun Chen ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02316 • Publication Date (Web): 03 Oct 2017 Downloaded from http://pubs.acs.org on October 7, 2017

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ACS Sustainable Chemistry & Engineering

Amino Siloxane Oligomer Modified Graphene Oxide Composite for the Efficient Capture of U(VI) and Eu(III) from Aqueous Solution Donglin Zhao,† Lili Chen,†, ‡ Mingwenchan Xu, ‡ Shaojie Feng,† Yi Ding,*† M. Wakeel,‼ Njud S. Alharbi,§ Changlun Chen*‡,§ †

Key Laboratory of Functional Molecule Design and Interface Process, Anhui Jianzhu

University, Hefei, 230601, PR China ‡

CAS Key Laboratory of Photovoltaic and Energy Conservation Materials, Institute

of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei 230031, PR China ‼

School of Environment, Beijing Normal University, Beijing, China

§

Department of Biological Sciences,

Faculty of Science, King Abdulaziz University,

Jeddah, 21589, Saudi Arabia *Corresponding author: [email protected] (C.L. Chen), [email protected] (Y. Ding),; Phone: +86-551-65592788. Fax: 86-551-65591310.

1

ACS Paragon Plus Environment


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ABSTRACT Poly 3-aminopropyltriethoxysilane is highly reactive high-molecular polymer because of the existence of abundant amino groups, which presents a strong affinity towards different metal cations. In view of this, the novel poly amino siloxane oligomer-modifed graphene oxide composite (PAS-GO) was fabricated by a facile cross-linking reaction and applied to capture U(VI)/Eu(III) ions from aqueous solution. The interaction mechanisms between the PAS-GO and U(VI)/Eu(III) were elaborated. The modification by -NH2 increased the sorption sites and improved the sorption capacities because of the synergistic effect of chelation with U(VI)/Eu(III). X-ray photoelectron spectroscopy revealed that nitrogen groups involved in the removal of U(VI)/Eu(III) since nitrogen atoms of amine groups provided the lone pair of electron with U(VI)/Eu(III) species. The maximum sorption capacity of U(VI) and Eu(III) on the PAS-GO at 298 K calculated by the Langmuir isotherm model was 310.63 and 243.90 mg/g, respectively. The PAS-GO could be repeatedly used for more than five cycles with slight degradation of sorption. High sorption efficiency and excellent reusability make PAS-GO composite an ideal candidate for the capture of U(VI)/Eu(III) from aqueous solution.

KEYWORDS: Graphene oxide, Sorption, U(VI), Eu(III)

2


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■ INTRODUCTION With the development of the nuclear industry, a large amount of radioactive elements are widely used, which results in a series of environmental problems.1-4 Therefore, it is an urgent important to find effective methods for radionuclide treatment. Sorption is considered an effective and economical method to capture trace level concentrations of radionuclides from aqueous solution as compared with other conventional sewage treatment methods.5-7 In addition, many types of sorbents like porous carbonaceous materials have been applied in removing organic and inorganic contaminants from wastewater because of their high surface areas and high sorption capacity.8-15 Graphene oxide (GO), obtained via the oxidation of graphite,16, 17 has attracted widespread interest because of its utility as a promising replacements for other conventional sorbents in waste treatment.18-23 The oxygen-containing functional groups play crucially important roles in removing organic compounds and heavy metal ions from wastewater, since they can provide strong coordination with metal ions by cation exchange, surface complexation and electrostatic interaction.24-27 However, the number of functional groups on GO surfaces is not enough to effectively eliminate radioactive elements from wastewater. According to the previous reports,

28-31

metal

ions.

the nitrogen-containing functional groups can form stable chelation with Poly

3-aminopropyltriethoxysilane

(PAS)

is

highly

reactive

high-molecular polymer because of the existence of abundant amino groups, which presents a strong affinity towards different metal cations.32, 33 Motivated by this, PAS-GO was synthesized by a simple cross-linking reaction 3



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between GO and oligomeric poly 3-aminopropyltriethoxysilane and applied to capture U(VI)/Eu(III) from aqueous solution. The sorption performance of PAS-GO was studied as a function of pH, contact time, initial concentration and temperature. The Langmuir and Freundlich models were evaluated based on the sorption equilibrium data, and the pseudo-first-order and pseudo-second-order kinetic models were described kinetics sorption data. The sorption mechanisms of U(VI)/Eu(III) onto PAS-GO were also elaborated by X-ray photoelectron spectroscopy (XPS) analysis.

■ EXPERIMENTAL SECTION Materials. Graphite powder, potassium permanganate (KMnO4), sodium acetate (NaAc), sulfuric acid (H2SO4, 98%), hydrogen peroxide (H2O2, 30%) and ethylene glycol (EG) were purchased. U(VI) stock solution at 120 mg/L was prepared by dissolving UO2(NO3)2·6H2O. Eu(III) stock solution at 60 mg/L was prepared from diluting Eu(NO3)3. All other reagents were of analytical reagent grade and used without further purification. Milli-Q water was used in all experiments. Preparation of PAS-GO. GO was prepared from natural graphite powder according to the improved Hummers method,34 2.0 g of graphite powder was added to 50 mL 98% H2SO4 in an ice bath under continuous stirring. While maintaining vigorous stirring, 6.0 g of KMnO4 was slowly added and the temperature was kept below 15 oC. The mixture was persistently stirred at 35 oC for 24 h. Subsequently, a 10 mL portion of 30% H2O2 solution was dropwise added until the color of the mixture became bright yellow. The mixture was centrifuged and washed with 0.2 M HCl, followed by washing with Milli-Q water and ethyl alcohol. Finally, the 4


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as-received solid was then dried at 50 °C for 48 h under vacuum. The PAS-GO composite was synthesized as follows. Firstly, 250 mg of GO was mixed with 100 mL deionized

water

under

ultra-sonication

for

24

h.

Then,

2

mL

3-aminopropyltriethoxysilane (AS) and 100 mL Milli-Q water were added into other beaker with constantly stirring to get PAS oligomer at 318 K for 5 h. Subsequently, the above mixture was transferred into GO solution under vigorous stirring until the tawny solution became brown flock. Finally, the suspension was separated and washed several times with Milli-Q water, and the as-received solid was dried by vacuum freeze-drying equipment for 24 h. The synthesis of PAS-GO are presented in Scheme 1. The detailed characterization was shown in Supporting Information. Sorption Experiments. Batch sorption experiments were carried out to study the sorption performances of U(VI)/Eu(III) on the PAS-GO. The sorption capacity of the PAS-GO towards U(VI)/Eu(III) was studied at a room temperature of 25 ± 2 ºC. In addition, the pH values of U(VI)/Eu(III) solutions were adjusted to 5.5 ± 0.1 by adding 0.01M HNO3 or NaOH. The effect of temperature was investigated at 298, 308 and 318 K to study the sorption thermodynamics of U(VI)/Eu(III). The mixture was shaken for 24 h to make sure that the sorption process reached full equilibrium and sorbent was separated by centrifugation at 10000 rpm for 10 min. The residual concentration of U(VI)/Eu(III) in liquid phase was measured by ICP-MS (Agilent 7900, USA). The amounts of U(VI)/Eu(III) sorbed by the PAS-GO were calculated by the mass balance equation: 5



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Sorption (%) = (C0 − Ce)/C0 × 100%

(1)

qe = (C0 − Ce) × V/m

(2)

where C0 and Ce represent the initial and equilibrium concentrations of the U(VI)/Eu(III) in the solution (mg/L), respectively. V is the volume of solution (L), and m is the quality of the sorbent (g).

■ RESULTS AND DISCUSSION Characteristics. The SEM image (Figure 1a) shows that GO exhibits slightly wrinkle because of its strong interactions between crystals.35 As shown in Figure 1b, the as-prepared PAS-GO presents lamellar wrinkled structures, which indicates that PAS is decorated onto the surface of GO sheets. The TEM image was used to further characterize the crystal structure and morphology of the PAS-GO. Figure 1d shows the PAS-GO stacks few-layered carbon sheets compared to the TEM image of GO (Figure 1c), indicating that the PAS-GO is successfully synthesized and multi-arm PAS prevents GO sheets from aggregation. Compared to its morphology before sorption (Figure 1d), the PAS-GO layered features are still maintained after sorption (Figure 1e and f), which implies PAS-GO has excellent structural stability. The FTIR spectra of GO and the PAS-GO were used to study the type of oxygen-containing groups and -NH2 groups. The FTIR results are shown in Figure 2a. In GO, a strong and broad absorption peak at ~3420 cm-1 is observed due to the O-H stretching vibration. The FTIR spectrum of the PAS-GO shows the presence of C=C (1630 cm−1), C=O (1218 cm−1) and C–O (1035 cm−1). The peaks at 3420 and 2927 cm−1 in PAS-GO ascribe to the presence of NH stretching vibration frequency of the 6


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-NH2 groups and the methylene stretching vibration bond. 32, 35, 37 The XRD patterns of GO and the PAS-GO are shown in Figure 2b. The characteristics diffraction peaks of GO is observed at 2θ values of 11.2°, which corresponds to the (002) layer planes of GO sheets.19,25 While, there is no obvious diffraction peak of the GO sheets observed in the PAS-GO, which indicates the PAS-GO has been successfully prepared and further confirms the as-prepared PAS-GO is effectively exfoliated. Figure 2c shows the Raman spectra of GO and the PAS-GO. Both of samples show D band at approximately 1352 cm −1 associated with the sp3 carbon atom vibration and G band at 1595 cm−1 of the sp2 carbon atom vibration.38, 39 However, a new peak is observed at 1150 cm−1 in the PAS-GO, which may be caused by the antisymmetric stretching vibration of Si-O-Si. The thermal stabilities of PAS, PAS-GO and GO were showed in Figure 2d. In PAS-GO, the first stage can be seen between 30 and 152 oC which there is 10.2% weight loss, owing to the removal of adsorbed water and the decomposition of labile oxygen functional groups. Then, an abrupt weight loss (17.4%) occurs from 152 to 225

o

C, which can be attributed to the decomposition of the oxygen or

nitrogen-containing functional groups. The weight loss at higher temperature should be due to the pyrolysis of carbon skeleton of GO.32, 40 As shown in Figure 2d, the thermal stability of PAS-GO is better than that of GO obviously. In addition, according to the thermogravimetric test results, we can draw that the amount of PAS grafted on the surface of GO are calculated to be 2.6%. 7



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The N2 adsorption/desorption isotherms of GO and the PAS-GO are shown in Figure 2e and 2f. The BET surface area of the GO and PAS-GO are calculated to be 20.66 and 36.24 m2 g−1, respectively. And the pore volume for PAS-GO is calculated to be 0.18 cm3 g−1 and the average pore size of 3.5 nm is obtained, indicating the mesoporous structure of the prepared PAS-GO.41 From Figure S1, it can be seen that the sizes of PAS-GO in solution have no obvious effect on the sorption capacity. The zeta potential of the PAS-GO was investigated at room temperature and shown in Figure 2g. The pHzpc of the PAS-GO is 5.3. The PAS-GO was negatively charged when pH > 5.3. The zeta potential of the PAS-GO is getting more negative as the pH value increase, which means the PAS-GO is negatively charged in natural water system, which promotes the sorption capacities of cation pollutants. Therefore, positive charge metal ions were attracted to the surface of PAS-GO by the surface complexation.42 To study the chemical states of elements on sorbent surface, the XPS analysis of the PAS-GO was measured. The survey spectrum of the PAS-GO is shown in Figure 2h, there are C (284.77 eV), N (399.71 eV) and O (531.99 eV) elements. In addition, the presence of N1s peak of PAS-GO at around 400.1 eV further indicates the formation of amino groups in the composites.43 Effect of pH. Figure 3 presents the effect of initial pH values ranging from 2 to 10 on the removal of U(VI)/Eu(III) by the PAS-GO. Figure 3 shows that the sorption of U(VI)/Eu(III) on PAS-GO increases as pH values varying from 2.5 to 6.5. Since the high concentration of H+ has a competitive sorption with U(VI) and Eu(III) and makes 8


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the amino groups of PAS-GO protonated under the low pH condition, and make only few of –NH2 present a strong affinity toward U(VI) and Eu(III). R-NH2 + H+↔ R-NH3+ (amino protonate)

(3)

The variation of pH in solution during the sorption process is shown in Table S1. The solution pH after sorption increases a little under acidic conditions because of the protonation reaction on the surfaces of PAS-GO. However, the solution pH decreases under alkaline conditions because of surface deprotonation process. In addition, the PAS-GO is negative charged at solution pH > 5.3 (the pHzpc of PAS-GO is close to 5.3) and occurs the electrostatic forces of attraction between cation pollutants, which promotes the sorption at a relatively high pH value. As pH increased, the majority of -OH are released into the solution, which prevents - NH2 translating into NH3+ and results in the surface of PAS-GO having more -NH2 to establish the combination of U(VI)/Eu(III). The main U(VI) species in aqueous solution as a function of pH are predominated by (UO2)3(OH)7− and UO2(CO3)22− species at pH > 6.5 according to the thermodynamic data.44 The distribution of aqueous U(VI) species in water solution is given in Figure S2. The removal of U(VI) on the PAS-GO decrease because of the electrostatic repulsion between negatively charged species ((UO2)3(OH)7− or UO2(CO3)22−) and the negative charged PAS-GO. However, the amounts of Eu(III) sorbed on the PAS-GO basically remain constant, which contributes to electrostatic attractions between Eu2(OH)24+ species and the negatively charged PAS-GO in aqueous solution at pH > 6.5.45 Typically, the initial pH values for the sorption of U(VI) ranges from 5.0 to 6.0.46 Therefore, the sorption of U(VI) was performed at pH 9



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5.5 ± 0.1 in the following experiments. Similarly, the sorption of Eu(III) on the PAS-GO was studied at pH 5.5 ± 0.1. Sorption Kinetics. Generally, the sorption is a time-consuming process that draws considerable interest in economical wastewater treatment plants.47 Figure S3 shows the kinetics of U(VI)/Eu(III) sorption onto the PAS-GO. As shown in Figure S3a, the sorption increases with contact time and U(VI) is removed by the PAS-GO within approximately 30 min at 298 K. Figure S3b shows that the sorption of Eu(III) on the PAS-GO attains equilibrium rapidly in the first 50 min at 298 K. Two kinetic models have been explored the sorption mechanisms of PAS-GO. The pseudo-first-order

model

is

widely

used

for

sorption

process,

and

its

linearized-integral form is expressed by the following equation: 48 ln(qe − qt ) = ln qe − k1t

(4)

where k1 is the pseudo-second-order constant. The pseudo-second-order kinetic model is described as:49

t 1 t = + 2 qt k2 qe qe

(5)

where k2 is the sorption rate constant of the pseudo-first-order. A series of parameters (qe values, kinetic constants and correlation coefficients) about pseudo-first-order and pseudo-second-order kinetic models are shown in Table S2. According to the correlation coefficients (R2) of the linear plots, the pseudo-second-order model well fits the experimental values of the removal of U(VI) / Eu(III) by the PAS-GO.50

Sorption Isotherm. The removal of U(VI) and Eu(III) by the PAS-GO was carried out at the temperature of 298, 308 and 318 K with a constant pH of 5.5 ± 0.1 (Figure S4a and 4b). The Langmuir theory assumes that monolayer sorption onto a surface 10


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contains a certain number of identical and energetically equivalent sorption sites. The Freundlich isotherm model is an empirical theory that represents the sorption sites with different sorption energy on heterogeneous surfaces, which suggests the capacity of sorption is related to the equilibrium concentration of sorbates. The Langmuir model is represented as: 51

Ce C K = e + L qe qmax qmax

(6)

The Freundlich model is described as follows

1 ln qe = ln K F + ln Ce n

(7)

where Ce (mg/L) is the equilibrium concentration of U(VI) / Eu(III) in solution, qe (mg/g) is the amount of U(VI) / Eu(III) sorbed at equilibrium, qmax (mg/g) is the maximum sorption capacity of the PAS-GO, KL (mg/L) is a constant that relates to the heat of sorption, KF (mg1−n Ln·g-1) is the constant related to the sorption capacity and n is the Freundlich constant depended on the sorption at equilibrium concentration. The results of the isotherm constants based on the experimental data as well as the correlation coefficients are shown in Table S3. The values of correlation coefficients of the Langmuir model are higher than those of the Freundlich model at 298, 308 and 318 K. The Langmuir model better describes the sorption equilibrium than the Freundlich model within the studied temperature range. The maximum sorption capacity of U(VI) and Eu(III) on the PAS-GO at 298 K calculated by the Langmuir isotherm model was 310.63 and 243.90 mg/g, respectively. A comparison of maximum sorption capacities with other sorbents is shown in Table S4. The PAS-GO presents much higher sorption capacity.

Sorption Thermodynamics. The Gibb´s free energy (∆G), entropy (∆S) and enthalpy change (∆H) are used to investigate sorption thermodynamics at 298, 308 11



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and 318 K, which can be determined from the following equation: ∆G = -RT ln K d

(8)

ln K d = ∆S − ∆Η

(9)

R

RT

where R (8.314 J·mol-1·K-1) is the universal gas constant, T is the temperature in Kelvin, Kd is the thermodynamic equilibrium constants, which can be obtained by the linear plot of qe/Ce under different temperatures. Plotting lnKd versus Ce (Figure S4c and 4d) gives intercept equal to lnK0 when Ce is about to zero. Values of ∆H/R and ∆S/R are obtained from the slope and intercept by potting lnKd against 1/T. The result of ∆G, ∆S and ∆H are listed in Table S5, the values of ∆G are negative for U(VI)/Eu(III) at different temperatures, which demonstrated the sorption process is spontaneous. In addition, the U(VI) and Eu(III) sorption increases with the increase of temperature. The positive value of ∆H confirms that the sorption process of U(VI) /Eu(III) is endothermic.

Regeneration Study. The recycling of the PAS-GO in removing U(VI)/Eu(III) ions was also investigated. In brief, 150 mL 0.05 M NaOH used as sorbing agent solution to disperse the sorbent after sorption, after shaken for 12 h, the U(VI)/Eu(III)-sorbent was separated and washed by 0.05 M HNO3 and deionized water, finally, the PAS-GO was dried by freeze-drying and reused. From Figure S5, the sorption efficiency of U(VI) on PAS-GO decreases slightly from 87.39% to 82.70% after five consecutive process of sorption/desorption cycles while the sorption efficiency of Eu(III) declines from 84.79% to 70.36%. Therefore, the PAS-GO shows a good reusability after 5 cycles.

Sorption Mechanisms. The FTIR spectra of the PAS-GO before and after sorption shown in Figure 4 were used to identify the interaction mechanisms between PAS-GO 12


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and U(VI) and Eu(III). It can be seen that the peaks at 696 and 472 cm-1 disappear and a new band is observed at 1385 cm-1 after sorption, suggesting the bond formation between oxygen-containing groups and U(VI)/Eu(III).52 The elemental mapping analysis of the PAS-GO after sorbing U(VI)/Eu(III) are shown in Figure S6. The elemental mapping images indicate N element uniformly disperse on the surface of GO and the successful synthesis of PAS-GO. In addition, in agreement with the results of FTIR results, the existence of element U and Eu mapping for PAS-GO further confirm that the lost U and Eu in solution is sorbed by the PAS-GO. In order to get better understand the removal mechanisms of U(VI)/Eu(III) on the PAS-GO, the XPS of samples was measured to identify surface complexation and XPS spectra of the PAS-GO after sorption are given in Figure 5. The occurrence of U 4f and Eu 3d in wide scan spectra (Figure 5a) and the high-resolution XPS spectra of U (Figure 5b) and Eu (Figure 5c) clearly confirm the presence of U(VI)/Eu(III) on the PAS-GO. The high-resolution XPS spectra of N 1s is shown in Figure 5d. The shifts of binding energy for both peaks are observed after the sorption of U(VI)/Eu(III). In the case of the PAS-GO-Eu systems, the binding energy of the N 1s peak is shifted from 399.71 to 400.08 eV (Figure 5d) and the peak width (W) increased from 3.08 to 3.95 eV compared with the corresponding binding energy of PAS-GO, which demonstrates that nitrogen groups involve in the Eu(III) sorption since nitrogen atoms of amine groups provide the lone pair of electron with Eu(III) species.53 In addition, the one peak (C=NOH) shifted from 401.06 to 401.49 eV and another shift (N≡C-CH) increased from 399.14 to 399.46 eV after sorbing Eu(III), further indicating the formation of the coordination bond of N-Eu(III). Based on the XPS measurement, the same analysis of the sorption mechanism of U(VI) on the PAS-GO is similar to that of Eu(III). 13



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■ CONCLUSIONS In the study, the PAS-GO was successfully prepared in site polymerizing PAS onto GO and was studied as a highly efficient sorbent in removing U(VI)/Eu(III). Sorption isotherms and kinetics studies suggested that the sorption of U(VI)/Eu(III) followed the Langmuir isotherm and pseudo-second-order kinetic models. The maximum sorption capacities of U(VI) and Eu(III) on the PAS-GO at 298 K calculated by the Langmuir model were 310.63 and 243.90 mg/g, respectively. The modification by -NH2 increased the sorption sites, caused chelation with U(VI)/Eu(III), and thus improved the sorption capacities. XPS analysis revealed that nitrogen groups involved in the U(VI)/Eu(III) sorption since nitrogen atoms of amine groups provided the lone pair of electron with U(VI) and Eu(III) species. The PAS-GO has a good stability and reusability. The results revealed that the PAS-GO represented potentially suitable material in removing U(VI)/Eu(III) ions from radioactive polluted water. However, the practical application of PAS-GO as a sorbent is limited because of the difficulty in traditional centrifugation and filtration from aqueous solutions. Further research is needed to evaluate some iron oxide nanomaterials composited with PAS-GO as magnetic sorbents.

■ ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge via the Internet at DOI: 10.1021/acssuschemeng. Characterization, effect of particle size on sorption of

U(VI)/Eu(III), the

distribution of aqueous U(VI) species in water solution, sorption kinetics, sorption 14


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isotherms, recycling of the PAS-GO for the removal of U(VI)/Eu(III) ions, the elemental mapping images of PAS-GO samples after U(VI)/Eu(III) sorption calculated by TEM, the initial and final pH in the sorption system of U(VI)/Eu(III) onto PAS-GO, kinetic parameters and isotherm parameters for U(VI)/Eu(III) sorption, thermodynamic parameters, and comparison of the maximum U(VI)/Eu(III) sorption capacity of on PAS-GO with other sorbents.

■ AUTHORS INFORMATION Corresponding Author *Tel: +86-551-65592788; Fax: +86-551-65591310. Email: [email protected] (C.L. Chen),

dyrqf@ ahjzu.edu.cn (Y. Ding); Phone: +86-551-65592788. Fax: 86-551-65591310. Notes The authors declare no competing financial interest.

■ ACKNOWLEDGEMENT Financial support from the National Natural Science Foundation of China (21377005 and 21477133), and Natural Science Fund of Education Department of Anhui province (KJ2015ZD15) are acknowledged.

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Figure Caption Scheme 1. Schematic illustration of the synthesis procedure of PAS-GO. Figure 1. SEM images of

GO (a) and

PAS-GO (b); TEM images of GO (c) and

PAS-GO (d); TEM images of PAS-GO after sorption U(VI) (e) and Eu(III) (f).

Figure 2. FTIR spectra of GO and PAS-GO (a); XRD patterns of GO and PAS-GO (b); Raman spectra of GO and PAS-GO (c); TGA curves of GO and PAS-GO (d); N2 adsorption−desorption isotherms of GO (e) and PAS-GO (f) (inset of (e) and (f) are the pore size distribution curves, correspondingly); Zeta potential of PAS-GO (g) and XPS spectra of PAS-GO (h).

Figure 3. Effect of pH on sorption of U(VI) (a) and Eu(III) (b), T = 298 K, m/V = 0.1 g/L, C0 = 16 and 6 mg/L, respectively.

Figure 4. FTIR spectra of PAS-GO samples before and after Eu(III) and U(VI) sorption.

Figure 5. Spectra of PAS-GO with Eu(III) and U(VI) sorbed: survey scans of Eu(III) and U(VI) sorbed on PAS-GO (a); high-resolution spectra of U 4f (b) and N 1s spectra of U(VI) and Eu(III) sorbed on PAS-GO (d).

24


Eu 3d (c);

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1. H2SO4 00C 2. KMnO4

Graphite GO PAS

PAS-GO

Scheme 1. Schematic illustration of the synthesis procedure of PAS-GO.

25



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Figure 1. SEM images of

GO (a) and

PAS-GO (b); TEM images of GO (c) and

PAS-GO (d); TEM images of PAS-GO after sorption U(VI) (e) and Eu(III) (f).

26


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b

Transmittance(%)

a

3420 2927

2θ=11.2

GO

PAS-GO PAS-GO

GO 3500 3000 2500 2000 1500 1000 500 -1 Wavenumber (cm )

GO

15 10

0.007 0.006 0.005 0.004 0.003 0.002 0.001 0.000 0

1800

f 5 10 15 20 25

Pore Diameter (nm)

5

Adsorption Desorption

0

30

0.2 0.4 0.6 0.8 Relative pressure (P/P0)

40 60 2θ (degree)

1.0

35 30 25 20 15

200 400 600 Temperature (°C)

800

0.006 0.005 0.004 0.003 0.002 0.001 0.000 0 5 10 15 20 25 30

Pore Diameter (nm)

10

Adsorption Desorption

5 0 0.0

0.2 0.4 0.6 0.8 Relative pressure (P/P0)

h

20

80

PAS PAS-GO GO

0 Quantity adsorbed (cm3/g)

Pore Volume (cm3/g)

Quantity adsorbed (cm3/g)

20

1200 1400 1600 -1 Raman shift (cm )

0.0

g

Weight (%)

Intensity (a. u.)

PAS-GO

1000

e

d

1592

1352

1150

20 110 100 90 80 70 60 50 40 30 20

Pore Volume (cm3/g)

c

Zeta Potential (mV)

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


1.0

O 1s

10

C 1s

0 394 396 398 400 402 404 406 408

-10

Binding Energy(eV)

-20

Si 2s Si 2p

N 1s

-30 -40 2

3

4

5

6 7 pH

8

9

0

10

200 400 600 800 1000 1200 1400 Binding Energy(eV)

Figure 2. FTIR spectra of GO and PAS-GO (a); XRD patterns of GO and PAS-GO (b); Raman spectra of GO and PAS-GO (c); TGA curves of GO and PAS-GO (d); N2 adsorption−desorption isotherms of GO (e) and PAS-GO (f) (inset of (e) and (f) are the pore size distribution curves, correspondingly); Zeta potential of PAS-GO (g) and XPS spectra of PAS-GO (h).

27



90

a

Removal Percentage (%)

100 Removal Percentage (%)

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

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80 60 40 20

PAS-GO GO

0

b

80 70 60 50 40 30

PAS-GO GO

20 10

2

4

6 pH

8

2

10

4

6

8

10

pH

Figure 3. Effect of pH on sorption of U(VI) (a) and Eu(III) (b), T = 298 K, m/V = 0.1 g/L, C0 = 16 and 6 mg/L, respectively.

28


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140 120 Transmittance(%)

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


100

PAS-GO 3420

80 60

PAS-GO-U(VI) 3431

40 20 4000

1630

2927

696 1035 472

3412

3500

PAS-GO-Eu(III) 2919 1641

3000

1094

1639

2916

1385

2500 2000 1500 -1 Wavenumber (cm )

1081

1000

500

Figure 4. FTIR spectra of PAS-GO samples before and after Eu(III) and U(VI) sorption.

29



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a C 1s

N 1s

O 1s PAS-GO

Page 30 of 31

U 4f

b

O 1s C 1s U 4f N 1s C 1s

0

200

PAS-GO-U(VI)

O 1s Eu 3d N 1s PAS-GO-Eu(III)

400

600

800

Binding Energy (eV)

c

1000

1200

375

380

385

1140

1155

1170

Binding Energy (eV)

395

d

Eu 3d

W=3.78eV Eb=400.08eV W=3.95eV

PAS-GO-Eu(III)

1125

390

Binding Energy (eV) C=NOH N≡C-CH Eb=399.71eV W=3.08eV PAS-GO PAS-GO-U(VI) Eb=399.76eV

1185 394

396

398

400

402

Binding Energy (eV)

404

406

Figure 5. Spectra of PAS-GO with Eu(III) and U(VI) sorbed: survey scans of Eu(III) and U(VI) sorbed on PAS-GO (a); high-resolution spectra of U 4f (b) and Eu 3d (c); N 1s spectra of U(VI) and Eu(III) sorbed on PAS-GO (d).

30


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Table of Contents

Synopsis: Schematic for the synthesis PAS-GO and the application of the removal of U(VI) and Eu(III)

+

U 、Eu


Amino Siloxane Oligomer Modified Graphene ... - ACS Publications

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