Graphene Oxide

Research Article pubs.acs.org/journal/ascecg

Decontamination of Sr(II) on Magnetic Polyaniline/Graphene Oxide Composites: Evidence from Experimental, Spectroscopic, and Modeling Investigation Baowei Hu,† Muqing Qiu,† Qingyuan Hu,† Yubing Sun,*,‡ Guodong Sheng,*,† Jun Hu,§ and Jingyuan Ma⊥ †

School of Life Science, Shaoxing University, Huancheng West Road 508, Shaoxing 312000, P.R. China Key Lab of New Thin Film Solar Cells, Institute of Plasma Physics, Chinese Academy of Science, P.O. Box 1126, Hefei 230031, P.R. China § School of Electronic Engineering, Dongguan University of Technology, Guangdong 523808, P.R. China ⊥ Shanghai Synchrotron Radiation Facility (SSRF), Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, P.R. China ‡

S Supporting Information *

ABSTRACT: The interaction of Sr(II) on magnetic polyaniline/ graphene oxide (PANI/GO) composites was elucidated by batch, EXAFS, and surface complexation modeling techniques. The batch experiments showed that decreased uptake of Sr(II) on magnetic PANI/GO composites was observed with increasing ionic strength at pH 5.0. The maximum uptake capacity of magnetic PANI/GO composites derived from the Langmuir model at pH 3.0 and 293 K was 37.17 mg/g. The outersphere surface complexation controlled the uptake of Sr(II) on magnetic PANI/GO composites at pH 3.0 due to the similarity to the EXAFS spectra of Sr2+ in aqueous solutions, but the Sr(II) uptake at pH 7.0 was inner sphere complexation owing to the occurrence of the Sr−C shell. According to the analysis of surface complexation modeling, uptake of Sr(II) on magnetic PANI/ GO composites was well simulated using a diffuse layer model with an outer-sphere complex (SOHSr2+ species) and two innersphere complexes (i.e., (SO)2Sr(OH)− and SOSr+ species). These findings are crucial for the potential application of magnetic nanomaterials as a promising candidate for the uptake of radionuclides for environmental remediation. KEYWORDS: Sr(II), Magnetic graphene oxide, Polyaniline, EXAFS, Modeling

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INTRODUCTION The safe disposal of radionuclides is of great importance for sustainable waste treatment strategies.1−3 90Sr is the most ubiquitous radioactive element observed in practical wastewater from reactions and reprocessing plants. Generally, the uptake process is one of the most important methods controlling contaminant mobility in dilute systems.4−6 In the past several decades, Sr(II) uptake in various clay minerals/metal (hydr)oxides has been extensively investigated owing to the ubiquity of Sr(II) in radioactive wastes.7−12 In these studies, it was demonstrated that cation-exchange reactions/outer sphere complexation control Sr(II) uptake, indicating that clay minerals/metal (hydr)oxides are important sorbents responsible for retarding the transport and fate of radionuclides in water bodies and that they are generally regarded in remediation and treatment processes. However, limited sorption capacities of theses natural adsorbents were observed (e.g., 1.17 and 21.41 mg/g for dolomite13 and sericite,14 © 2017 American Chemical Society

respectively), which blocked the practical application in environmental cleanup, particularly in low concentration conditions. It has been determined that the uptake of radionuclides by nanomaterials has been known as a remediation strategy available for the stabilization of radionuclides.15−20 Graphene oxide (GO, as an excellent adsorbent) has been widely employed to remove various organic and inorganic pollutants in recent years.4,21−27 It has been proven that GO displays the high effective adsorption capacity due to the occurrence of abundance of oxygenated functional groups, including -OH and -COOH groups. However, the excellent dispersibility of GO in aqueous solutions cannot easily be separated from liquid phase in terms of centrifugation. Therefore, magnetic GO composites Received: April 12, 2017 Revised: June 9, 2017 Published: June 19, 2017 6924

DOI: 10.1021/acssuschemeng.7b01126 ACS Sustainable Chem. Eng. 2017, 5, 6924−6931

Research Article

ACS Sustainable Chemistry & Engineering

Figure 1. Characterization of magnetic PANI/GO composites. (A and B) SEM images before and after Sr(II) uptake, respectively; (C) XPS spectra; (D) FTIR spectra.

composite matrices (e.g., magnetic GO-based composites) using EXAFS and modeling is still poorly understood.42 In this study, the Sr(II) uptake mechanism was investigated using sodium nitrate as the background electrolyte and magnetic PANI/GO composites as the adsorbents. The objectives of this manuscript were to (1) characterize the magnetic PANI/GO composites using FT-IR, SEM, XPS, XRD, and magnetic properties; (2) elucidate the effect of environmental factors (i.e., reaction time, pH, ionic strength and temperature) on Sr(II) uptake by magnetic PANI/GO composites by batch techniques; (3) demonstrate the interaction mechanism of Sr(II) on magnetic PANI/GO composites by XPS and EXAFS spectra; and (4) simulate the progress of Sr(II) uptake on magnetic PANI/GO composites using the surface complexation model. This manuscript highlights the uptake mechanism of Sr(II) on magnetic PANI/GO composites using modeling and spectroscopic similar technique.

have been synthesized in recent years to remove various environmental pollutants.28−32 Sun et al. demonstrated that the maximum sorption capacity of GO-supported polyaniline (PANI/GO) composites were 245.14 and 250.8 mg/g for U(VI) and Eu(III), respectively.13 The authors, based on XPS analysis, demonstrated that the function of GO and PANI was to enhance the adsorption performance and chemical affinity toward radionuclides, respectively. Nevertheless, few studies concerning the interaction mechanisms between Sr(II) and magnetic GO-based nanoparticles are currently available.33 Understanding the uptake mechanism of radionuclides under various environmental conditions by the surface complexation model, and advanced spectroscopic techniques are crucial for evaluating the transport and fate of radionuclides in the subsurface environment. Surface complexation modeling as a powerful tool can predict radionuclide uptake under limited experimental conditions.21,34,35 Chen et al. fitted the uptake of Sr(II) on oxidized multiwall carbon nanotube using a diffuse layer model with hydroxyl and deprotonated carboxyal groups.36 However, these optimized parameters are generally correlated with experimental data and complexation reactions used. The spectroscopic technique (e.g., XPS, EXAFS) can give insight into the speciation of radionuclides at local environments and microstructures of radionuclides at water−solid interface.37−41 It is demonstrated that the uptake of Sr(II) at various water-minerals was outer-sphere surface complexation. To the authors’ knowledge, Sr(II) binding in these complex

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EXPERIMENTAL SECTION

Materials. Flake graphite (99.9%, SigmaAldrich) dissolved into 0.1 mol/L HNO3 solutions. Synthesis and Characterization of Magnetic PANI/GO Composites. Magnetic PANI/GO composites were obtained by simple hydrothermal reactions.43 First of all, GO was obtained by 6925


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ACS Sustainable Chemistry & Engineering oxidizing graphite under concentrated H2SO4 conditions according to the modified version of Hummers method.44 Then, PANI/GO composites were obtained according to polymerizing aniline on the GO and (NH4)2S2O8 flowing procedure as previously reported elsewhere.45 The synthesis processes of magnetic PANI/GO composites were as follows: 0.92 g of ferric chloride and 0.52 g of ferrous chloride were mixed in 250 mL of 0.5 g/L PANI/GO solutions under a glovebox filled with N2 atmosphere conditions. Then, the pH value was adjusted to 10 using 30% ammonia. Ten milliliters of hydrazine-hydrate was provided into the aforementioned suspension at 363 K under constant stirring. The suspension solution was stirred rapidly for 4 h. Next, magnetic PANI/GO composites were filtered from the suspension solution and finally dried in vacuum. The nanostructure and morphology of magnetic PANI/GO was visualized by SEM (JEOL JSM-6700, Tokyo, Japan) and FT-IR (Nicolet 8700 FTIR spectrometer, Thermo Scientific). The changes in the chemical and electronic states of the magnetic PANI/GO before and after adsorption were characterized by XPS (Thermo ESCALAB 250 electron spectrometer) using a multidetection analyzer with Mg Kα radiation (1253.6 eV) under 10−9 Torr pressure. All peaks were referenced with the C 1s line at 284.4 eV and were fitted in terms of the XPSPEAK41 mode. Batch Uptake Experiments. Batch experiments were carried out in triplicate in a glovebox under N2 conditions (O2 and CO2 < 2 ppm) at ambient conditions (293 K). Briefly, 0.5 g/L of magnetic PANI/GO composites with electrolyte solution (0.01 mol/L NaNO3) were added to 10 mL of polycarbonate to pre-equilibrate for 24 h, and then a certain amount of Sr(II) solution (10.0 mg/L) was provided. Then, suspensions were reacted for 2 days at 293 K under vigorous stirring conditions. After equilibration, the suspensions were separated at 9800 rpm for 20 min. The concentration of Sr(II) in the supernatant was detected using atomic absorption spectroscopy (AAS-6300C, Shimadzu, Japan). The percentage of adsorbed Sr(II) can be calculated by the difference in initial Sr(II) and Sr(II) concentration at the supernatant after adsorption equilibrium. Analysis of EXAFS Spectra. The samples for EXAFS analysis at different pH were performed in the glovebox at room temperature. Strontium K-edge EXAFS spectra (at 16105 eV) were carried out with BL14W beamlines of the Shanghai synchrotron radiation facility by fluorescence mode with a 16 elements Ge detector using silicon (220) double-crystal monochromator at 77 K to decrease the thermal disorder. Analysis of EXAFS spectra were performed by Athena software, and then the Artemis package was used to fit the EXAFS data. The structural parameters of the sorption samples were analyzed by fitting the experimental data with theoretical calculations of reference standards. These parameters (i.e., Debye−Waller factor (σ2), ΔE0 (the energy at k = 0), and amplitude reduction factor (S02)) were set to guess. The fittings of Sr−O and Sr−C shells were obtained from Sr2+ and strontianite.46 The preparation and analysis of XPS, XANES, and EXAFS are provided in the Supporting Information (SI). Surface Complexation Model. The uptake data was simulated using double layer modeling (DLM) by Visual MINTEQ v. 2.6 mode.47 The parameters of log K+ and K− (protonation and deprotonation) were optimized potentiometric titration of magnetic PANI/GO composites. The reactions of surface complexation modeling selected in this study by assuming that combination of SOH (amphoteric hydroxide functional groups) with Sr(II) at different complexation types. The concentration of the reactive site (mol/g) was optimized by the potentiometric titration data. The optimized parameters were obtained by repeatedly altering the equilibration constants.

shown in Figure 1C, the O 1s XPS spectra of magnetic PANI/ GO composites can be deconvoluted into three bands at 532.0, 532.9, and 933.8 eV, which were assigned to Fe−O, N/C−O, and adsorbed H2O, respectively. After adsorption, however, the binding energies of the three bands were shifted to lower energies. In addition, the relative intensities of Fe−O and adsorbed H2O were significantly enhanced, whereas the C/N− O peaks were decreased, indicating that the high uptake of Sr(II) by magnetic PANI/GO composites was ascribed to the nitrogen/oxygenated functional groups. As shown by FT-IR spectra in Figure 1D, the bands at ∼3400, 1750, 1630, 1420, and 1180 cm−1 could be attributed to the stretching vibration of −OH, CO, CC, C−C, and C−O/N groups, respectively.48−50 The bands at 790 and 585 cm−1 were ascribed to the Fe−O groups.51,52 The results of FT-IR spectra indicated that the magnetite nanoparticles were successfully grafted on the PANI/GO surface. As shown in Figure S1A, the peaks at 2θ = 30.25, 35.70, 43.42, 54.11, 57.35, and 62.75° can be indexed to the (220), (311), (400), (422), (511), and (440) planes of magnetite (JCPDS, No. 75-0033), indicating that magnetic magnetite was synthesized using this method.28 According to the analysis of the magnetic hysteresis loop (Figure S1B), it is demonstrated that the as-prepared composites were magnetic composites. As shown in Table 1, the N2−BET surface area of Table 1. Selective Properties of Magnetic PANI/GO Composites C (at %)a N (at %) O (at %) H (at %) Fe (at %) SBET (m2/g) zeta potential (mV) a

59.64 1.96 23.71 1.83 13.86 86.53 0 at pH 1.98

Determined by XPS analysis.

magnetic PANI/GO composites calculated from the BET method was 86.53 m2/g. The main components of magnetic PANI/GO composites determined from XPS analysis were C (59.64 at %), O (23.71 at %), H (1.96 at %), N (1.83 at %), and Fe (13.86 at %). These characterizations revealed magnetic PANI/GO composites with oxygen- and nitrogen-containing functional groups. Adsorption Kinetics. Figure 2A shows the effect of reaction time on Sr(II) uptake by magnetic PANI/GO composites at pH 7.0 and 3.5. Sr(II) uptake was fast and increased linearly within 6 h; then, uptake equilibrium was attained at a reaction time of 12 h. Approximately 100 and 55% of Sr(II) was removed by magnetic PANI/GO composites at pH 7.0 and 3.5, respectively. The uptake kinetics of Sr(II) on magnetic PANI/GO composites were simulated using pseudofirst- and pseudo-second-order kinetic models. More details concerning the pseudo-first- and pseudo-second-order kinetic models were provided in the SI. As listed in Table S1, the uptake of Sr(II) on magnetic PANI/GO composites was wellsimulated by a pseudo-second-order-kinetic model with a high correlation coefficient (R2 > 0.9995) compared to that of the pseudo-first-order kinetic model (R2 < 0.95), indicating that Sr(II) uptake by magnetic PANI/GO composites might be controlled by rate-limiting uptake.53−55 Effect of pH and Ionic Strength. Figure 2B shows the Sr(II) uptake by magnetic PANI/GO composites at different

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RESULTS AND DISCUSSION Characterization. Panels A and B in Figure 1 show SEM images of magnetic PANI/GO composites before and after Sr(II) adsorption, respectively. The nanosheets of magnetic PANI/GO composites were aggregated tightly (Figure 1A).15 After Sr(II) adsorption, the morphology of magnetic PANI/ GO composites had not significantly changed (Figure 1B). As 6926


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Figure 2. (A) Uptake kinetics of Sr(II) on magnetic PANI/GO composites, C0 = 10.0 mg/g, m/v = 0.5 g/L, pH 3.0, I = 0.01 mol/L NaNO3, T = 293 K. (B) Effect of pH and ionic strength on Sr(II) uptake on magnetic PANI/GO composites, C0 = 10.0 mg/g, m/v = 0.5 g/L, T = 293 K.

Figure 3. (A) Uptake isotherms of Sr(II) on magnetic PANI/GO composites at different temperatures, m/v = 0.5 g/L, pH 3.0, I = 0.01 mol/L NaNO3; (B) regeneration of Sr(II) on magnetic PANI/GO composites, m/v = 0.5 g/L, pH 3.0, I = 0.01 mol/L NaNO3, T = 293 K.

sites at low pH conditions. Sr(II) uptake on magnetic PANI/ GO composites wsa remarkably enhanced with the increase in temperature from 293 to 333 K. The data were fitted using the Langmuir and Freundlich models. A more detailed description of the Langmuir and Freundlich models is provided in the SI. As shown in Table S2, the adsorption isotherms of Sr(II) on magnetic PANI/GO composites were well simulated by the Langmuir model due to the higher correlation coefficient (R2 > 0.998) comparing with Freundlich model (R2 < 0.995). The maximum sorption capacity of magnetic PANI/GO composites was 37.17 mg/g for Sr(II) at pH 3.0 and 293 K. As listed in Table 2, the maximum uptake capacities of magnetic PANI/GO composites were comparable to those of the other carbonbased nanomaterials such as activated carbon (44.41 mg/g at

ionic strengths and pH conditions. Uptake of Sr(II) was significantly enhanced with increasing pH of 1.0−5.0, whereas the uptake plateaued at pH >6.0. A previous study demonstrated that Sr(II) species in solution was Sr2+ at pH 2.0. Thus, the uptake of Sr(II) on magnetic PANI/GO composites at pH >2.0 was ascribed to the electrostatic attraction of positive Sr2+ and negative magnetic PANI/GO composites. As shown in Figure 2B, Sr(II) uptake on magnetic PANI/GO composites at pH 5.0. Previous studies reported that outerspherical complexation was controlled by the effect of ionic strength but that inner-spherical complexation was insensitive to ionic strength.17,56−69 Thus, the uptake mechanism of Sr(II) on magnetic PANI/GO composites at pH 5.0. Adsorption Isotherms. Figure 3A shows the adsorption isotherms (adsorption amount (Qe; mg/g) vs equilibrated concentration (Ce; mg/L) of Sr(II) on magnetic PANI/GO composites at 0.01 mol/L NaNO3 and pH 3.0. Generally, the value of solution pH for nuclear wastewater is very low (pH 2.0−3.0). Thus, uptake isotherms were conducted at pH 3.0 to investigate the adsorption performance of PANI/GO compo-

Table 2. Adsorption Capacity of Various Adsorbents for Sr(II) Uptake adsorbent activated carbon magnetic CNT carbon nanofibers GO PANI/GO magnetic GO magnetic PANI/GO 6927

exp. conditions pH pH pH pH pH pH pH

5.0, 6.4, 4.5, 3.0, 3.0, 4.0, 3.0,

293 298 293 298 298 293 293

K K K K K K K

Qm (mg/g)

ref

44.41 9.81 67.11 48.72 147.06 14.71 37.17

68 69 18 15 15 70 this study


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Figure 4. (A) Sr K-edge EXAFS spectra and (B) corresponding Fourier transmission of reference and uptake samples at pH 3.0 and 7.0, C0 = 10.0 mg/g, m/v = 0.5 g/L, I = 0.01 mol/L NaNO3, T = 293 K; dots: experimental data; lines: fitted results.

pH 5.0 and 293 K),70 magnetic carbon nanotubes (9.81 mg/g at pH 6.4 and 298 K),71 GO (48.72 mg/g at pH 3.0 and 298 K),15 and magnetic GO (14.71 mg/g at pH 4.0 and 293 K).72 However, the adsorption capacity of PANI/GO composite toward Sr(II) (147.06 mg/g at pH 3.0 and 298 K)15 was significantly higher than that of magnetic PANI/GO composites due to the occupation of surface reactive sites by magnetite nanoparticles. On the other hand, Sr(II) uptake was significantly enhanced at higher reaction temperature. Thus, the high uptake capacity of PANI/GO could be attributed to the high reaction temperature used (298 K) compared to that for magnetic PANI/GO composites used in this study (293 K). Therefore, magnetic PANI/GO composites can be considered as a candidate for uptake of radionuclides in environmental cleanup. The regeneration and reusability experiments were significant for accessing potential application in radionuclide remediation. Figure 3B shows the regeneration experiments of Sr(II) uptake on magnetic PANI/GO composites at 5 successive cycling times. The maximum adsorption capacity of magnetic PANI/ GO composites slightly decreased from 37.17 to 32.55 mg/g after 5 cycling times, indicating that PANI/GO composites can be considered as a renewable adsorbent to remove radionuclides in practical aquatic systems. EXAFS Analysis. Knowledge of the interaction mechanisms of Sr(II) on magnetic PANI/GO composites by the analysis of EXAFS spectra at molecular scale is crucial for evaluating behavior of Sr(II) in the geologic repository long term. Panels A and B in Figure 4 show the Sr K-edge EXAFS spectra and the corresponding Fourier transformed spectra, respectively. Table 3 summarizes the optimized parameters of Sr(II) reference and Sr(II) uptake under different pH conditions. The EXAFS spectra for references and adsorption samples showed similar single frequencies (Figure 4A). As shown in Figure 4B, the first coordination shell at ∼2.05 Å was well simulated using sevento-eight O located at a distance of ∼2.6 Å, which was agreement with previous studies.73 Quantitative fits of Sr(II) uptake at pH 3.0 were similar to those of the aqueous Sr2+ species, whereas it could not be fit with Sr−C and/or Sr−Sr shell, indicating outer-spherical complexation of Sr(II) uptake at pH 3.0.74 The high coordination number revealed that the Sr(II) had not lost its waters of hydration upon uptake.75 For samples at pH 7.0, the CN value of first shell oxygen atoms

Table 3. Structural Parameters Obtained from Sr K-Edge EXAFS Data Analysis for Reference and Uptake Samples sample 2+

Sr aq SrCO3

mPANI/GO_pH3.0 mPANI/GO_pH7.0

shell

R (Å)

CN

σ2 (Å2)

Sr−O Sr−O Sr−C Sr−Sr Sr−O Sr−O Sr−C

2.62 2.57 3.14 3.95 2. 59 2.58 3.12

7.5 6.8 2.2 5.2 7.5 7.1 2.1

0.007 0.0075 0.0089 0.0425 0.0065 0.0052 0.0094

(CN = 7.1) was higher than that of SrCO3 (s) (CN = 6.8), but lower than that of aqueous Sr2+ species (CN = 7.5), which indicated that Sr(II) had a small coordination shell compared to that of hydrated aqueous Sr(II). The presence of a Sr−C shell indicated that Sr was taken up as a monodentate and mononuclear inner-sphere surface complex.76 The other weak oscillation was likely to be Sr−O shell multiple backscattering. The EXAFS results revealed that Sr(II) uptake on magnetic PANI/GO composites was outer-sphere complexation at pH 3.0, but Sr(II) uptake at pH 7.0 was inner spherical complexation. Surface Complexation Modeling. Panels A and B in Figure 5 show pH edge and isotherms of Sr(II) uptake, respectively. The optimized constants of surface complexation modeling are summarized in Table 4. As shown in Figure 5A, the uptake of Sr(II) on magnetic PANI/GO composites at different pH conditions was well simulated using DLM with an outer spherical site (SOHSr2+) and two inner spherical sites (SOSr+ and (SO)2Sr(OH)− species). As shown in Figure 5A, the main species of Sr(II) uptake on magnetic PANI/GO composites was SOHSr2+ at pH 5.0, respectively. The simulated results showed that outerspherical complexation controlled Sr(II) uptake on magnetic PANI/GO composites at pH < 4.0, whereas Sr(II) uptake on magnetic PANI/GO composites at pH >5.0 was the innerspherical complexation. These reactions and corresponding parameters were used to simulate the isothermal uptake of Sr(II) on magnetic PANI/GO composites (Figure 5B). Adsorption isotherms of Sr(II) can be simulated using these parameters, whereas slight overevaluation was observed at high 6928


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Figure 5. Surface complexation modeling of Sr(II) uptake onto magnetic PANI/GO composites at (A) different pH and (B) initial Sr(II) concentration conditions; solid squares and lines refer to experimental data and fitted results, respectively, C0 = 10.0 mg/g, m/v = 0.5 g/L, pH 3.0, I = 0.01 mol/L NaNO3, T = 293 K.

Table 4. Optimized Parameters for Surface Complexation Modeling of Sr(II) Sorption on Magnetic PANI/GO Composites Using the DLM Model equation +

= SOH2+ − +

SOH + H SOH = SO + H SOH + Sr2+ = SOHSr2+ SOH + Sr2+ = SOSr+ + H+ 2SOH + Sr2+ + H2O = (SO)2Sr(OH)− + 3H+

log K 4.21 −5.36 3.24 2.62 −2.97

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REFERENCES

(1) Sun, Y. B.; Li, J. X.; Wang, X. K. The retention of uranium and europium onto sepiolite investigated by macroscopic, spectroscopic and modeling techniques. Geochim. Cosmochim. Acta 2014, 140, 621− 643. (2) Sheng, G.; Yang, P.; Tang, Y.; Hu, Q.; Li, H.; Ren, X.; Hu, B.; Wang, X.; Huang, Y. New insights into the primary roles of diatomite in the enhanced sequestration of UO22+ by zerovalent iron nanoparticles: An advanced approach utilizing XPS and EXAFS. Appl. Catal., B 2016, 193, 189−197. (3) Sheng, G.; Alsaedi, A.; Shammakh, W.; Monaquel, S.; Sheng, J.; Wang, X.; Li, H.; Huang, Y. Enhanced sequestration of selenite in water by nanoscale zero valent iron immobilization on carbon nanotubes by a combined batch, XPS and XAFS investigation. Carbon 2016, 99, 123−130. (4) Sun, Y. B.; Wang, Q.; Chen, C. L.; Tan, X. L.; Wang, X. K. Interaction between Eu(III) and graphene oxide nanosheets investigated by batch and extended X-ray absorption fine structure spectroscopy and by modeling techniques. Environ. Sci. Technol. 2012, 46 (11), 6020−6027. (5) Ding, C. C.; Cheng, W. C.; Sun, Y. B.; Wang, X. K. Novel fungusFe3O4 bio-nanocomposites as high performance adsorbents for the removal of radionuclides. J. Hazard. Mater. 2015, 295, 127−137. (6) Cheng, W. C.; Ding, C. C.; Sun, Y. B.; Wang, X. K. Fabrication of fungus/attapulgite composites and their removal of U(VI) from aqueous solution. Chem. Eng. J. 2015, 269, 1−8. (7) Yang, D. J.; Zheng, Z. F.; Zhu, H. Y.; Liu, H. W.; Gao, X. P. Titanate nanofibers as intelligent absorbents for the removal of radioactive ions from water. Adv. Mater. 2008, 20 (14), 2777−2781. (8) Bekhit, H. M.; Hassan, A. E.; Harris-Burr, R.; Papelis, C. Experimental and numerical investigations of effects of silica colloids on transport of strontium in saturated sand columns. Environ. Sci. Technol. 2006, 40 (17), 5402−5408. (9) Duff, M. C.; Hunter, D. B.; Hobbs, D. T.; Fink, S. D.; Dai, Z.; Bradley, J. P. Mechanisms of strontium and uranium removal from high-level radioactive waste simulant solutions by the sorbent

CONCLUSIONS The uptake mechanism between Sr(II) and magnetic PANI/ GO composites has been addressed by batch, EXAFS, and modeling techniques. Outer- and inner-spherical complexations appear to be the prevailing mechanism of Sr(II) uptake by magnetic PANI/GO composites at pH 5, respectively. These findings are crucial for the immobilization and retardation of radionuclides in deep geologic repositories. ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b01126. Additional characterization such as thermal gravity analysis and TEM images, calculations of adsorption kinetics, solubility products, radionuclides in aqueous solutions, Langmuir and Freundlich models, and analysis of XPS and EXAFS (PDF)

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ACKNOWLEDGMENTS

We want to thank Prof. Yuying Huang from Shanghai Institute of Applied Physics, Chinese Academy of Sciences for the measurement and analysis of EXAFS spectra. Financial support from the Natural Science Foundation of China (21207092, 21577093), the priority Academic program development of Jiangsu Higher Education Institutions, and the Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Key Lab of Novel Thin Film Solar Cells, Chinese Academy of Sciences and Science and Technology Project of Shaoxing (2014B70041) are acknowledged.

Sr(II) loading conditions. The main adsorption sites of uptake isotherm of Sr(II) were SOHSr2+ species, which was accordance with pH edge uptake.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Phone: +86-551-65593308. Fax: 86-551-65591310. ORCID

Yubing Sun: 0000-0003-4931-8039 Notes

The authors declare no competing financial interest. 6929


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ACS Sustainable Chemistry & Engineering monosodium titanate. Environ. Sci. Technol. 2004, 38 (19), 5201− 5207. (10) Lea, A. S.; Amonette, J. E.; Baer, D. R.; Liang, Y.; Colton, N. G. Microscopic effects of carbonate, manganese, and strontium ions on calcite dissolution. Geochim. Cosmochim. Acta 2001, 65 (3), 369−379. (11) Parkman, R. H.; Charnock, J. M.; Livens, F. R.; Vaughan, D. J. A study of the interaction of strontium ions in aqueous solution with the surfaces of calcite and kaolinite. Geochim. Cosmochim. Acta 1998, 62 (9), 1481−1492. (12) Axe, L.; Anderson, P. R. Experimental and theoretical diffusivities of Cd and Sr in hydrous ferric oxide. J. Colloid Interface Sci. 1997, 185 (2), 436−448. (13) Ghaemi, A.; Torab-Mostaedi, M.; Ghannadi-Maragheh, M. Characterizations of strontium(II) and barium(II) adsorption from aqueous solutions using dolomite powder. J. Hazard. Mater. 2011, 190 (1−3), 916−921. (14) Hu, B. W.; Hu, Q. Y.; Xu, D.; Chen, C. G. Macroscopic and microscopic investigation on adsorption of Sr(II) on sericite. J. Mol. Liq. 2017, 225, 563−568. (15) Sun, Y. B.; Shao, D. D.; Chen, C. L.; Yang, S. B.; Wang, X. K. Highly efficient enrichment of radionuclides on graphene oxidesupported polyaniline. Environ. Sci. Technol. 2013, 47 (17), 9904− 9910. (16) Cheng, W. C.; Ding, C. C.; Wang, X. X.; Wu, Z.-Y.; Sun, Y. B.; Yu, S.-H.; Hayat, T.; Wang, X. K. Competitive sorption of As(V) and Cr(VI) on carbonaceous nanofibers. Chem. Eng. J. 2016, 293, 311− 318. (17) Sheng, G.; Tang, Y.; Linghu, W.; Wang, L.; Li, J.; Li, H.; Wang, X.; Huang, Y. Enhanced immobilization of ReO4− by nanoscale zerovalent iron supported on layered double hydroxide via an advanced XAFS approach: Implications for TcO4− sequestration. Appl. Catal., B 2016, 192, 268−276. (18) Sun, Y. B.; Wu, Z.-Y.; Wang, X. X.; Ding, C. C.; Cheng, W. C.; Yu, S.-H.; Wang, X. K. Macroscopic and microscopic investigation of U(VI) and Eu(III) adsorption on carbonaceous nanofibers. Environ. Sci. Technol. 2016, 50 (8), 4459−4467. (19) Ding, C. C.; Cheng, W. C.; Sun, Y. B.; Wang, X. K. Determination of chemical affinity of graphene oxide nanosheets with radionuclides investigated by macroscopic, spectroscopic and modeling techniques. Dalton Trans. 2014, 43 (10), 3888−3896. (20) Sun, Y. B.; Wang, X. X.; Ding, C. C.; Cheng, W. C.; Chen, C. L.; Hayat, T.; Alsaedi, A.; Hu, J.; Wang, X. K. Direct synthesis of bacteriaderived carbonceous nanofibers as a highly efficient material for radionuclides elimination. ACS Sustainable Chem. Eng. 2016, 4 (9), 4608−4616. (21) Sun, Y. B.; Wang, X. X.; Song, W. C.; Lu, S. H.; Chen, C. L.; Wang, X. K. Mechanistic insights into the decontamination of Th(IV) on graphene oxide-based composites by EXAFS and modeling techniques. Environ. Sci.: Nano 2017, 4, 222−232. (22) Song, W. C.; Yang, T. T.; Wang, X. X.; Sun, Y. B.; Ai, Y. J.; Sheng, G. D.; Hayat, T.; Wang, X. K. Experimental and theoretical evidence for competitive interactions of tetracycline and sulfamethazine with reduced graphene oxides. Environ. Sci.: Nano 2016, 3, 1318− 1326. (23) Sun, Y. B.; Yang, S. B.; Ding, C. C.; Jin, Z. X.; Cheng, W. C. Tuning the chemistry of graphene oxides by a sonochemical approach: application of adsorption properties. RSC Adv. 2015, 5 (32), 24886− 24892. (24) Sun, Y. B.; Ding, C. C.; Cheng, W. C.; Wang, X. K. Simultaneous adsorption and reduction of U(VI) on reduced graphene oxide-supported nanoscale zerovalent iron. J. Hazard. Mater. 2014, 280, 399−408. (25) Jin, Z. X.; Sheng, J.; Sun, Y. B. Characterization of radioactive cobalt on graphene oxide by macroscopic and spectroscopic techniques. J. Radioanal. Nucl. Chem. 2014, 299 (3), 1979−1986. (26) Sun, Y. B.; Yang, S. B.; Zhao, G. X.; Wang, Q.; Wang, X. K. Adsorption of polycyclic aromatic hydrocarbons on graphene oxides and reduced graphene oxides. Chem. - Asian J. 2013, 8 (11), 2755− 2761.

(27) Sun, Y. B.; Chen, C. L.; Shao, D. D.; Li, J. X.; Tan, X. L.; Zhao, G. X.; Yang, S. B.; Wang, X. K. Enhanced adsorption of ionizable aromatic compounds on humic acid-coated carbonaceous adsorbents. RSC Adv. 2012, 2 (27), 10359−10364. (28) Jin, Z. X.; Wang, X. X.; Sun, Y. B.; Ai, Y. J.; Wang, X. K. Adsorption of 4-n-nonylphenol and bisphenol-A on magnetic reduced graphene oxides: A combined experimental and theoretical studies. Environ. Sci. Technol. 2015, 49 (15), 9168−9175. (29) Liu, M.; Chen, C.; Hu, J.; Wu, X.; Wang, X. Synthesis of magnetite/graphene oxide composite and application for cobalt (II) removal. J. Phys. Chem. C 2011, 115 (51), 25234−25240. (30) Sun, H.; Cao, L.; Lu, L. Magnetite/reduced graphene oxide nanocomposites: one step solvothermal synthesis and use as a novel platform for removal of dye pollutants. Nano Res. 2011, 4 (6), 550− 562. (31) Yoon, Y.; Park, W. K.; Hwang, T.-M.; Yoon, D. H.; Yang, W. S.; Kang, J.-W. Comparative evaluation of magnetite-graphene oxide and magnetite-reduced graphene oxide composite for As(III) and As(V) removal. J. Hazard. Mater. 2016, 304, 196−204. (32) Zhang, Y.; Cheng, Y.; Chen, N.; Zhou, Y.; Li, B.; Gu, W.; Shi, X.; Xian, Y. Recyclable removal of bisphenol A from aqueous solution by reduced graphene oxide−magnetic nanoparticles: Adsorption and desorption. J. Colloid Interface Sci. 2014, 421, 85−92. (33) Yang, S.; Chen, C.; Chen, Y.; Li, J.; Wang, D.; Wang, X.; Hu, W. Competitive adsorption of Pb(II), Ni(II), and Sr(II) ions on graphene oxides: A combined experimental and theoretical study. ChemPlusChem 2015, 80 (3), 480−484. (34) Sun, Y. B.; Zhang, R.; Ding, C. C.; Wang, X. X.; Cheng, W. C.; Chen, C. L.; Wang, X. K. Adsorption of U(VI) on sericite in the presence of Bacillus subtilis: A combined batch, EXAFS and modeling techniques. Geochim. Cosmochim. Acta 2016, 180, 51−65. (35) Huang, J. Y.; Wu, Z. W.; Chen, L. W.; Sun, Y. B. Surface complexation modeling of adsorption of Cd(II) on graphene oxides. J. Mol. Liq. 2015, 209, 753−758. (36) Chen, C.; Hu, J.; Xu, D.; Tan, X.; Meng, Y.; Wang, X. Surface complexation modeling of Sr(II) and Eu(III) adsorption onto oxidized multiwall carbon nanotubes. J. Colloid Interface Sci. 2008, 323 (1), 33− 41. (37) Chorover, J.; Choi, S.; Rotenberg, P.; Serne, R. J.; Rivera, N.; Strepka, C.; Thompson, A.; Mueller, K. T.; O’Day, P. A. Silicon control of strontium and cesium partitioning in hydroxide-weathered sediments. Geochim. Cosmochim. Acta 2008, 72 (8), 2024−2047. (38) Sun, Y. B.; Chen, C. L.; Tan, X. L.; Shao, D. D.; Li, J. X.; Zhao, G. X.; Yang, S. B.; Wang, Q.; Wang, X. K. Enhanced adsorption of Eu(III) on mesoporous Al2O3/expanded graphite composites investigated by macroscopic and microscopic techniques. Dalton Trans. 2012, 41 (43), 13388−13394. (39) Ding, C. C.; Cheng, W. C.; Sun, Y. B.; Wang, X. K. Effects of Bacillus subtilis on the reduction of U(VI) by nano-Fe0. Geochim. Cosmochim. Acta 2015, 165, 86−107. (40) Liu, H. B.; Zhu, Y. K.; Xu, B.; Li, P.; Sun, Y. B.; Chen, T. H. Mechanical investigation of U(VI) on pyrrhotite by batch, EXAFS and modeling techniques. J. Hazard. Mater. 2017, 322, 488−498. (41) Sun, Y. B.; Yang, S. B.; Chen, Y.; Ding, C. C.; Cheng, W. C.; Wang, X. K. Adsorption and desorption of U(VI) on functionalized graphene oxides: A combined experimental and theoretical study. Environ. Sci. Technol. 2015, 49 (7), 4255−4262. (42) Choi, S.; O’Day, P. A.; Rivera, N. A.; Mueller, K. T.; Vairavamurthy, M. A.; Seraphin, S.; Chorover, J. Strontium speciation during reaction of kaolinite with simulated tank-waste leachate: Bulk and microfocused EXAFS analysis. Environ. Sci. Technol. 2006, 40 (8), 2608−2614. (43) Zhao, J.; Lin, J. P.; Xiao, J. P.; Fan, H. L. Synthesis and electromagnetic, microwave absorbing properties of polyaniline/ graphene oxide/Fe3O4 nanocomposites. RSC Adv. 2015, 5 (25), 19345−19352. (44) Hummers, W. S.; Offeman, R. E. Preparation of graphitic oxide. J. Am. Chem. Soc. 1958, 80 (6), 1339−1339. 6930


Research Article

ACS Sustainable Chemistry & Engineering (45) Kumar, N. A.; Choi, H. J.; Shin, Y. R.; Chang, D. W.; Dai, L. M.; Baek, J. B. Polyaniline-grafted reduced graphene oxide for efficient electrochemical supercapacitors. ACS Nano 2012, 6 (2), 1715−1723. (46) Sahai, N.; Carroll, S. A.; Roberts, S.; O’Day, P. A. X-ray absorption spectroscopy of strontium(II) coordination - II. Sorption and precipitation at kaolinite, amorphous silica, and goethite surfaces. J. Colloid Interface Sci. 2000, 222 (2), 198−212. (47) Gustafsson, J. P. A windows version of MINTEQ, 2009; http:// www.lwr.kth.se/English/OurSOrware/vminteq/index.htm. (48) Xing, M.; Xu, L.; Wang, J. Mechanism of Co(II) adsorption by zero valent iron/graphene nanocomposite. J. Hazard. Mater. 2016, 301, 286−296. (49) Wang, J.; Chen, B.; Xing, B. Wrinkles and folds of activated graphene nanosheets as fast and efficient adsorptive sites for hydrophobic organic contaminants. Environ. Sci. Technol. 2016, 50 (7), 3798−3808. (50) Stankovich, S.; Dikin, D. A.; Piner, R. D.; Kohlhaas, K. A.; Kleinhammes, A.; Jia, Y.; Wu, Y.; Nguyen, S. T.; Ruoff, R. S. Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide. Carbon 2007, 45 (7), 1558−1565. (51) Yang, X. Y.; Zhang, X. Y.; Ma, Y. F.; Huang, Y.; Wang, Y. S.; Chen, Y. S. Superparamagnetic graphene oxide-Fe3O4 nanoparticles hybrid for controlled targeted drug carriers. J. Mater. Chem. 2009, 19, 2710−2714. (52) Chandra, V.; Park, J.; Chun, Y.; Lee, J. W.; Hwang, I.-C.; Kim, K. S. Water-dispersible magnetite-reduced graphene oxide composites for arsenic removal. ACS Nano 2010, 4 (7), 3979−3986. (53) Lu, S. H.; Hu, J. S.; Chen, C. L.; Chen, C. J.; Yu, G.; Sun, Y. B.; Tan, X. L. Spectroscopic and modeling investigation of efficient removal of U(VI) on a novel magnesium silicate/diatomite. Sep. Purif. Technol. 2017, 174, 425−431. (54) Hu, B. W.; Hu, Q. Y.; Di, X.; Chen, C. G. The adsorption of U(VI) on carbonaceous nanofibers: A combined batch, EXAFS and modeling techniques. Sep. Purif. Technol. 2017, 175, 140−146. (55) Hu, B. W.; Hu, Q. Y.; Chen, C. G.; Sun, Y. B.; Xu, D.; Sheng, G. D. New insights into Th(IV) speciation on sepiolite: Evidence for EXAFS and modeling investigation. Chem. Eng. J. 2017, 322, 66−72. (56) Sheng, G.; Yang, Q.; Peng, F.; Li, H.; Gao, X.; Huang, Y. Determination of colloidal pyrolusite, Eu(III) and humic substance interaction: A combined batch and EXAFS approach. Chem. Eng. J. 2014, 245, 10−16. (57) Yang, S. T.; Zhao, D. L.; Sheng, G. D.; Guo, Z. Q.; Sun, Y. B. Investigation of solution chemistry effects on sorption behavior of radionuclide Cu-64(II) on Illite. J. Radioanal. Nucl. Chem. 2011, 289 (2), 467−477. (58) Sheng, G.; Shen, R.; Dong, H.; Li, Y. Colloidal diatomite, radionickel, and humic substance interaction: a combined batch, XPS, and EXAFS investigation. Environ. Sci. Pollut. Res. 2013, 20 (6), 3708− 3717. (59) Sheng, G.; Hu, B. Role of solution chemistry on the trapping of radionuclide Th(IV) using titanate nanotubes as an efficient adsorbent. J. Radioanal. Nucl. Chem. 2013, 298 (1), 455−464. (60) Yang, S. B.; Ding, C. C.; Cheng, W. C.; Jin, Z. X.; Sun, Y. B. Effect of microbes on Ni(II) diffusion onto sepiolite. J. Mol. Liq. 2015, 204, 170−175. (61) Sheng, G.; Dong, H.; Shen, R.; Li, Y. Microscopic insights into the temperature-dependent adsorption of Eu(III) onto titanate nanotubes studied by FTIR, XPS, XAFS and batch technique. Chem. Eng. J. 2013, 217, 486−494. (62) Sun, Y. B.; Yang, S. T.; Sheng, G. D.; Wang, Q.; Guo, Z. Q.; Wang, X. K. Removal of U(VI) from aqueous solutions by the nanoiron oxyhydroxides. Radiochim. Acta 2012, 100 (10), 779−784. (63) Sheng, G.; Ye, L.; Li, Y.; Dong, H.; Li, H.; Gao, X.; Huang, Y. EXAFS study of the interfacial interaction of nickel(II) on titanate nanotubes: Role of contact time, pH and humic substances. Chem. Eng. J. 2014, 248, 71−78. (64) Sun, Y. B.; Yang, S. T.; Sheng, G. D.; Guo, Z. Q.; Wang, X. K. The removal of U(VI) from aqueous solution by oxidized multiwalled carbon nanotubes. J. Environ. Radioact. 2012, 105, 40−47.

(65) Sun, Y. B.; Yang, S. T.; Sheng, G. D.; Guo, Z. Q.; Tan, X. L.; Xu, J. Z.; Wang, X. K. Comparison of U(VI) removal from contaminated groundwater by nanoporous alumina and non-nanoporous alumina. Sep. Purif. Technol. 2011, 83, 196−203. (66) Ma, M. H.; Gao, H. Y.; Sun, Y. B.; Huang, M. S. The adsorption and desorption of Ni(II) on Al substituted goethite. J. Mol. Liq. 2015, 201, 30−35. (67) Sun, Y. B.; Yang, S. B.; Wang, Q.; Alsaedi, A.; Wang, X. K. Sequestration of uranium on fabricated aluminum co-precipitated with goethite (Al-FeOOH). Radiochim. Acta 2014, 102 (9), 797−804. (68) Sheng, G.; Hu, J.; Li, H.; Li, J.; Huang, Y. Enhanced sequestration of Cr(VI) by nanoscale zero-valent iron supported on layered double hydroxide by batch and XAFS study. Chemosphere 2016, 148, 227−232. (69) Sun, Y. B.; Wang, Q.; Yang, S. T.; Sheng, G. D.; Guo, Z. Q. Characterization of nano-iron oxyhydroxides and their application in UO22+ removal from aqueous solutions. J. Radioanal. Nucl. Chem. 2011, 290 (3), 643−648. (70) Chegrouche, S.; Mellah, A.; Barkat, A. Removal of strontium from aqueous solutions by adsorption onto activated carbon: kinetic and thermodynamic studies. Desalination 2009, 235 (1−3), 306−318. (71) Chen, C. C.; Hu, J.; Shao, D. D.; Li, J. X.; Wang, X. K. Adsorption behavior of multiwall carbon nanotube/iron oxide magnetic composites for Ni(II) and Sr(II). J. Hazard. Mater. 2009, 164, 923−928. (72) Li, D. M.; Zhang, B.; Xuan, F. Q. The sequestration of Sr(II) and Cs(I) from aqueous solutions by magnetic graphene oxides. J. Mol. Liq. 2015, 209, 508−514. (73) Chen, C. C.; Coleman, M. L.; Katz, L. E. Bridging the gap between macroscopic and spectroscopic studies of metal ion sorption at the oxide/water interface: Sr(II), Co(II), and Pb(II) sorption to quartz. Environ. Sci. Technol. 2006, 40 (1), 142−148. (74) Chen, C. C.; Hayes, K. F. X-ray absorption spectroscopy investigation of aqueous Co(II) and Sr(II) sorption at clay-water interfaces. Geochim. Cosmochim. Acta 1999, 63 (19−20), 3205−3215. (75) Axe, L.; Bunker, G. B.; Anderson, P. R.; Tyson, T. A. An XAFS analysis of strontium at the hydrous ferric oxide surface. J. Colloid Interface Sci. 1998, 199 (1), 44−52. (76) Langley, S.; Gault, A. G.; Ibrahim, A.; Takahashi, Y.; Renaud, R.; Fortin, D.; Clark, I. D.; Ferris, F. G. Sorption of strontium onto bacteriogenic iron oxides. Environ. Sci. Technol. 2009, 43 (4), 1008− 1014.

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