Magnetic Graphene Oxide Composite

Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

pubs.acs.org/jced

Preparation of Polyamidoxime/Magnetic Graphene Oxide Composite and Its Application for Efficient Extraction of Uranium(VI) from Aqueous Solutions in an Ultrasonic Field Zhongran Dai,† Hui Zhang,† Yang Sui,‡,§ Dexin Ding,*,† and Le Li† Key Discipline Laboratory for National Defense for Biotechnology in Uranium Mining and Hydrometallurgy, and ‡School of Environment and Safety Engineering, University of South China, Hengyang 421001, China § Fujian Fuqing Nuclear Power Co., Ltd., Fuqing, 350300, China Downloaded via UNIV OF TEXAS SW MEDICAL CTR on October 13, 2018 at 06:58:27 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

†

S Supporting Information *

ABSTRACT: In this work, the polyamidoxime functionalized magnetic graphene oxide (mGO-PAO) was prepared via the surface-initiated reversible addition−fragmentation chain transfer (RAFT) polymerization, characterized by TEM, FT-IR, VSM, and TGA techniques, and applied for the extraction of uranium(VI) from aqueous solutions in an ultrasonic field. The effects of pH, contact time, initial uranium(VI) concentration, temperature, and competitive ions on the adsorption of U(VI) were investigated. The adsorption speed of mGO-PAO for U(VI) was found to be 18 times faster in the ultrasonic field than in the shaking mode, and the adsorption equilibrium, to be reached within 2 min. When the U(VI) concentration was 10 mg/L, the temperature, 298 K, and pH, 6.0, the removal rate of U(VI) reached 98.24% with high selectivity. The adsorption kinetics and isotherm data were well described by the pseudo-second-order and Langmuir models, respectively. The thermodynamic parameters suggested that the adsorption of U(VI) was a typical spontaneous and endothermic process. XPS analysis suggested that the mGO-PAO bound the U(VI) through the η2-N,O binding mode. Moreover, the mGO-PAO exhibits excellent adsorption performance in actual radioactive wastewater with an assist of ultrasound. This work provides a new approach for highly effective extraction of U(VI) from the actual radioactive wastewater.

1. INTRODUCTION Over the past years, a large amount of uranium-containing radioactive wastewater was produced with the development of nuclear power. Once U(VI) enters into the environment, its radiation can cause an irreversible and persistent damage to the ecological balance and to human health.1−3 Therefore, the efficient removal of uranium(VI) from radioactive wastewater is of the utmost importance. To make the removal of uranium(VI) from radioactive wastewater economically feasible, the adsorbents must possess the properties of high adsorption capacity, adsorption speed, reusability, and selectivity. Up to now, most research focuses on the application of adsorbents for uranium(VI) removal due to its © XXXX American Chemical Society

ease of operation, low cost, efficiency and wide adaptability. Many adsorbents such as magnetic materials, activated carbon, metal organic frameworks, ion-imprinted polymer, and other materials have been used to eliminate U(VI) from aqueous solutions.4−36 Nevertheless, it is still a challenge to develop efficient adsorbents for the removal of U(VI) with high adsorption capacity, high adsorption speed, reusability, and high selectivity. Polymers are popular adsorbents for extraction of U(VI) from wastewater due to their low cost simple operation, Received: August 12, 2018 Accepted: October 3, 2018

A

DOI: 10.1021/acs.jced.8b00703 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

washed with ethanol and ultrapure water, and dried at 50 °C in vacuum. 2.2.2. Synthesis of mGO-PAO. A 200 mg sample of mGOPAN and 1 mL of NH2OH (50% in water) were dispersed into 40 mL of methanol−water (Vm/Vw = 1/1) solution. Subsequently, the suspension was stirred at 80 °C for 12 h. Then, the solid was obtained by using a magnet. Finally, the product was washed with ethanol and ultrapure water, and dried at 50 °C in vacuum. 2.3. Batch Adsorption Experiments. The effects of pH, contact time, initial uranium concentrations, temperature, and coexisting ions on the U(VI) adsorption by mGO-PAO were investigated. Typically, the mGO-PAO (20 mg) was added to the 50 mL U(VI) solution with appropriate concentration and appropriate pH value in a 250 mL conical flask at the appropriate temperature in an air bath oscillator (180 rpm) or in an ultrasonic field (40 W, 40 kHz). The pH was adjusted by dilute HCl and NaOH. After a predetermined time, the solid−liquid separation was carried out using a magnet. All U(VI) adsorption data represented the average value after duplicate determinations. The equilibrium adsorption capacity qe (mg/g) and distribution coefficient Kd (mL/g) were calculated by the following formulas:

and they are environmental benign. Among them, poly(acrylamidoximes) (PAOs) are commonly used because of their ability to bind the uranyl ion (UO22+).7,13,37−40 Owing to its good dispersibility and high surface area, graphene oxide (GO) is being used as an adsorbent in the removal of U(VI). There are many functional groups on the surface of GO, such as epoxy, hydroxyl, and carboxyl groups, which render its excellent adsorption performance for U(VI) and make it easier for surface functionalization.14−16 Magnetic adsorbents have attracted considerable attention since they can be conveniently and rapidly separated from the aqueous solutions through the application of a magnetic field. Compared with traditional separation methods (filtration and centrifugation), magnetic separation requires less energy and can achieve better results, especially for adsorbents of a small size. However, the surface area of magnetic adsorbent will significantly decrease with the aggregation of magnetic powders, which results in a decrease of the adsorbent performance. To address this problem, many investigators use the functional modified magnetic materials to prevent aggregation of the adsorbent.7,41−43 Ultrasound is a potential method for resolving the aggregation problem due to its powerful dispersion function. Ultrasonic vibrations in the liquids can induce formation and implosion of microscopic bubbles, and the transport of heat and mass can be improved by high temperatures and pressures from the cavitation bubbles collapse. Previous studies have indicated that ultrasonic vibrations have advantages over the classical methods.44,45 For instance, Zhang et al.46 indicated that the adsorption rate of Fe3O4 magnetic particle for Cr(VI) could be increased 1.7−2.1 times by ultrasound. To make use of the advantages of polymer, magnetic sensitivity. and graphene oxide, the polyamidoxime functionalized magnetic graphene oxide (mGO-PAO) was fabricated for the extraction of U(VI) from aqueous solutions in this study. The properties of the adsorbent were characterized by TEM, FT-IR, TGA, VSM, and XPS. The U(VI) adsorption behavior on the mGO-PAO was studied at various pH values, contact times, initial U(VI) concentration, temperatures, and competitive ions. In addition, an adsorption mechanism is proposed based on the characterization by XPS. More importantly, the influence of ultrasound on the adsorption process was investigated. The objective of this research was to provide a new adsorbent for rapid U(VI) extraction with high selectivity from the actual radioactive wastewater.

qe = Kd =

(CO − Ce)V m C0 − Ce 1000V × Ce m

(1)

(2)

where C0 and Ce are the concentrations of U(VI) before and after adsorption (mg/L), V is the volume (L), and m is the amount of adsorbent (g). 2.4. Desorption and Regeneration Studies. In brief, 20 mg of adsorbent and 50 mL of uranium(VI) solution were put into to a 250 mL conical flask which was shaken for 2 h in air bath oscillator at pH 6.0 and 298 K. Then, the adsorbent was separated by using a magnet. After the adsorption, the U(VI)-laded adsorbent was eluted by 50 mL of 0.1 M HCl solution as eluent, and washed with ultrapure water. The process of uranium adsorption was repeated five times as before.

3. RESULTS AND DISCUSSION 3.1. Characterization. The micromorphology and microstructure of GO, mGO, mGO-PAN, and mGO-PAO were characterized by TEM images. Figure 1A shows that the surface of GO was smooth. After modification, the Fe3O4 nanoparticles were homogeneously dispersed on the surface of GO sheets (Figure 1B). The presence of the wrinkle on the surface of mGO can be found (Figure 1C,D) due to the surface initiated RAFT polymerization and the polyacrylonitrile (PAN) and PAO growing on the surface of GO. To further explore the composition of mGO-PAO after adsorption of U(VI) (mGO-PAO-U), elemental mapping was conducted to study the TEM elemental distributions in the sheet of mGO-PAO-U, as described in Figure 2. The U, O, N, C, and Fe elements were homogeneously distributed in the mGO-PAO-U. The results further suggest that the mGO-PAO was successfully prepared, and that the U(VI) in the solution was adsorbed by the mGO-PAO. To better understand the structures of the materials, the FT-IR spectra of GO, mGO, mGO-PAN, mGO-PAO, and mGO-PAO-U were performed as shown in Figure 3. For GO,

2. EXPERIMENTAL SECTION 2.1. Materials. Acrylonitrile (AN) and 2,2-Azobis(isobutyronitrile) (AIBN) were purchased from Tianjin Kermel Chemical Reagents Development Center (Tianjin, China), and 2-bromopropionyl bromide and ethyl potassium dithiocarbonate, from TCI (Shanghai) Development Co., Ltd. 2.2. Synthesis of mGO-PAO Composite. The mGO-PAO was synthesized by modifying the surface of magnetic graphene oxide (mGO) using the surface-initiated RAFT polymerization according to our previous study.47 The procedure was illustrated in Scheme 1. The mGO and mGO-SCSOEt were synthesized according to the reported procedure.48,49 2.2.1. Synthesis of mGO-PAN. Under nitrogen gas protection, 1.5 g of mGO-SCSOEt, 3.5 mL of acrylonitrile and 60 mg of AIBN were dispersed into 6 mL of THF solution. Subsequently, the suspension was stirred at 60 °C for 2 h. Then, the solid was obtained by using a magnet. Finally, the product was B



Article

Scheme 1. Procedure for Synthesizing the Poly-Amidoxime Functionalized Magnetic Graphene Oxide Composite (mGO-PAO)

Moreover, the characteristic peak of CN stretching vibration at 2245 cm−1 was found in the spectrum of mGO-PAN, which indicates that polyacrylonitrile was growing on the surface of mGO. After reaction with hydroxylamine, the peak at 2245 cm−1 disappeared, suggesting that the nitrile groups in mGO-PAN were converted to the amidoxime groups. In comparison with the mGO-PAO, the peak of UO22+ antisymmetric vibration was found at 895 cm−1, indicating that the U(VI) was successfully adsorbed onto mGO-PAO.40,50 The TGA curves of the GO, mGO, and mGO-PAO were shown in Figure 4. GO exhibit a sharp weight loss below 150 °C due to the decomposition of labile oxygen-containing functional groups. For mGO-PAO, remarkable weight loss was found at about 320 and 620 °C, which was attributed to the decomposition of amidoxime and polymerized amidoxime groups, respectively.51,52 The results of TGA analysis proved not only the thermal stability of mGO-PAO but also the successful synthesis of the adsorbent. The magnetism of mGO-PAO was explored by gauging the magnetization curves. As shown in Figure 5, the magnetic curves of both mGO and mGO-PAO showed a typical feature of superparamagnetism. The saturation magnetization (Ms) values of mGO and mGO-PAO were 36.3 and 25.8 emu g−1, respectively. The magnetic saturation value of mGO-PAO is less than that of mGO, and the reason might be due to the

Figure 1. TEM images of (A) GO, (B) mGO, (C) mGO-PAN, and (D) mGO-PAO.

the peak at 3412 cm−1 was ascribed to the −OH stretching vibration. The absorption peaks at 1730, 1621, and 1070 cm−1 belong to the CO, CC, and C−O vibrations, respectively. Compared with GO, the characteristic peak of Fe−O vibration at 584 cm−1 appeared in the FI-IR spectrum of mGO, indicating that the magnetic graphene oxide was successfully obtained. C



Article

Figure 2. TEM image and elemental mapping of mGO-PAO-U.

Figure 5. Magnetization curves of mGO and mGO-PAO. Figure 3. FT-IR spectra of GO, mGO, mGO-PAN, mGO-PAO, and mGO-PAO-U.

presence of PAO polymer brushes on the surface of mGO. In addition, no obvious hysteresis was observed and the remanence was negligible due to the superparamagnetic peculiarity of mGO-PAO. These favorable magnetic properties would provide great benefits for the magnetic separation process. 3.2. Effect of pH. The pH value plays a key role on the performance of adsorbent, as shown in Figure 6A. Clearly, the adsorption capacity of mGO-PAO increases with the increase of pH from 3 to 6, while decreases with further increase of pH from 6 to 8. This phenomenon could be illustrated by the surface protonation reaction of amidoxime groups and the species distribution of U(VI) in aqueous solutions. The species distribution of U(VI) in aqueous solutions was calculated by the Visual MINTEQ.53 As shown in Figure 6B, U(VI) was almost positively charged in the pH range of 2−6, including UO22+, UO2OH+, (UO2)2(OH)22+, and (UO2)3(OH)5+; at the same time, the amidoxime groups on mGO-PAO can be protonated with the decrease of pH value in solution. Therefore, this will prevent the chelating reaction between the amidoxime ligands and uranyl ions due to the electrostatic repulsion. On the other hand, U(VI) was neutral or negatively charged under the basis conditions (pH is higher than 6.0), and the

Figure 4. TGA curves of GO, mGO, and mGO-PAO. D



Article

Figure 6. (A) Effect of pH on the U(VI) adsorption by mGO-PAO (m = 20 mg, V = 50 mL, Co = 10 mg/L, T = 298 K, t = 24 h) and (B) species distribution of U(VI) in aqueous solutions.

amidoxime groups on mGO-PAO can easily react with OH− to form a negatively charged substance. Thus, the adsorption capacity of mGO-PAO will be decreased at pH > 6 due to the electronic repulsion between the U(VI) and the adsorbent surfaces.54 As a consequence, for mGO-PAO, the optimal pH value for the adsorption toward uranyl ions was determined to be 6.0, and all following experiments were performed at pH 6.0. 3.3. Effect of Contact Time and Adsorption Kinetics. Figure 7 shows the effect of contact time on the U(VI) adsorption

where the qe and qt are the adsorption capacities of U(VI) (mg/g) at equilibrium time and time t (min), respectively. The k1 and k2 are the rate constants of the pseudo-first-order and pseudo-second-order models, respectively. The parameter of the different kinetic models was listed in Table 1 and Figure S1. Compared with the pseudo-first-order Table 1. Kinetic Parameters of U(VI) Adsorption on mGO-PAO pseudo-first-order k1 (min−1)

qe (cal) (mg/g)

R2

24.56

0.0348

8.04

0.963

k2 qe (cal) (g·mg−1·min−1) (mg/g) 0.0148

24.89

R2 0.999

Langmuir model:

by mGO-PAO. The rate of adsorption increases very fast within the first 20 min, and the adsorption equilibrium was reached at 120 min. To explore the adsorption kinetics and rate-controlling step, the experimental data were analyzed by pseudo-first-order and pseudo-second-order models.

Ce 1 1 = + Ce qe qmbL qm

(5)

Freundlich model: ln qe = ln KF +

The pseudo-first-order equation:

The pseudo-second-order equation: t 1 1 = + t qt qe k 2qe2

qe (exp) (mg/g)

model, the calculated value of qe from the pseudo-second-order model (qe = 24.89 mg/g) was closer to the experimental values (qe = 24.56 mg/g) and has a relatively high regression coefficient (R2 = 0.999). The results indicated that the pseudosecond-order model was more appropriate for describing the kinetics of uranium(VI) adsorption on mGO-PAO and the chemisorption is rate-controlling step. 3.4. Effect of Initial Uranium(VI) Concentrations and Adsorption Isotherms. To understand the mechanism for the U(VI) adsorption by mGO-PAO, the adsorption isotherms at different temperatures were depicted in Figure 8. Furthermore, the adsorption data were simulated by Langmuir and Freundlich isotherm models, and these two models were given below:

Figure 7. Effect of contact time on the U(VI) adsorption by mGOPAO (m = 20 mg, V = 50 mL, Co = 10 mg/L, pH = 6.0, T = 298 K).

ln(qe − qt ) = lnqe − k1t

pseudo-second-order

1 ln Ce nF

(6)

where Ce is the concentration of U(VI) at equilibrium (mg/L), qe is the amount of U(VI) adsorbed at equilibrium (mg/g), qm is the maximum adsorption capacity, bL is the Langmuir constant related to adsorption energy, and KF and nF are Freundlich constants related to adsorption capacity and adsorption intensity, respectively.

(3)

(4) E



Article

3.5. Effect of Temperature and Thermodynamic Studies. The effect of temperature on the U(VI) adsorption by mGO-PAO was studied, and the results are shown in Figure 9. It can be seen that the adsorption capacity of U(VI) increased with increasing temperature, indicating that high temperature can help to the adsorption of U(VI). The thermodynamic parameters were calculated using the Van’t Hoff equation, which is as follows: ln Kd =

ΔS 0 ΔH 0 − R RT

(7)

where Kd is the distribution coefficient (mL/g), ΔS is the standard entropy (J·mol−1·K−1), ΔH0 is the standard enthalpy (kJ·mol−1), T is the reaction temperature (K), and R is the gas constant (8.314 J·mol−1·K−1). The standard Gibbs free energy (ΔG0) values were calculated using the Gibbs−Helmholtz equation, which is as follows: 0

ΔG 0 = ΔH 0 − T ΔS 0

Figure 8. Effect of initial uranium(VI) concentrations on the U(VI) adsorption by mGO-PAO (m = 20 mg, V = 50 mL, pH = 6.0, t = 24 h).

(8) 0

Thus, the standard enthalpy change (ΔH , kJ/mol), standard entropy change (ΔS0, J/(mol·K)), and standard free energy change (ΔG0, kJ/mol)) of U(VI) adsorption by mGO-PAO were obtained (Table 3 and Table 4). The positive ΔH0

The parameters of isotherm models were obtained and presented in Table 2 and Figure S2. On the basis of Table 2, the correlation coefficient (R2) of the Langmuir model was higher than that of the Freundlich model, implying that the adsorption mainly is a simple monolayer adsorption process on a homogeneous surface of adsorbent. The adsorption isotherms analysis indicated that the adsorption behavior of mGO-PAO was well fitted by the Langmuir model, and the maximum adsorption capacity (qm) was computed to be 89.93 mg·g−1 at 298 K.

Table 3. Parameters for U(VI) Adsorption by mGO-PAO ΔH0 (kJ/mol)

ΔS0 (J/mol·K)

R2

75.04

254.93

0.988

(ΔH0 = 75.04 kJ/mol) and negative ΔG0 values indicate that the adsorption of U(VI) was an endothermic and spontaneous

Table 2. Parameters Calculated from the Langmuir and Freundlich Model T (K) model

parameters

298

303

308

313

318

Langmuir

qm (mg/g) bL R2 KF nF R2

89.93 0.85 0.997 28.66 2.9 0.943

105.93 0.98 0.998 33.6 2.74 0.959

116.69 1.19 0.998 38.32 2.65 0.956

125.63 1.82 0.999 48.74 2.92 0.933

134.23 2.29 0.999 52.26 2.64 0.939

Freundlich

Figure 9. Effect of temperature on the U(VI) adsorption by mGO-PAO (a) and the relationship between ln Kd and 1/T (b) (m = 20 mg, V = 50 mL, C0 = 50 mg/L, pH = 6.0, t = 2 h). F



Article

Table 4. ΔG0 for U(VI) Adsorption by mGO-PAO at Different Temperatures ΔG0 (kJ/mol)

T/K = 298

T/K = 303

T/K = 308

T/K = 313

T/K = 318

−0.97

−2.24

−3.52

−4.79

−6.07

process. The positive value of ΔS0 (ΔS0 = 254.93 J/mol·K) indicates the increased randomness during the U(VI) adsorption process. Moreover, the value of ΔG0 was decreased with increasing temperature, implying that the adsorption process was more favorable at higher temperatures. 3.6. Effect of Competitive Ions. As we know, the wastewater contains not only uranium(VI) but also other heavy metal ions. Therefore, the interference of heavy metal ions for the uptake of uranium(VI) from aqueous solutions must be considered, as shown in Figure 10. Some representative ions in

Figure 11. Recycling of mGO-PAO in the U(VI) adsorption (m = 20 mg, V = 50 mL, pH = 6.0, C0 = 10 mg/L, T = 298 K, t = 2 h).

in Figure 13. In Figure 13a, the N 1s spectrum of mGO-PAO was fitted with two peaks at 400.18 and 399.72 eV, which are related to the H2N−CN−OH and H2N-CN−OH, respectively. After U(VI) adsorption, the peak related to the H2N−CN−OH produced a shift of 0.36 eV (Figure 13b), while the H2N−CN−OH peak of mGO-PAO remained unchanged, indicating that U(VI) can interact with the H2N− CN−OH groups. The detailed spectrum of O 1s was shown in Figure 13c and Figure 13d. Obviously, the O 1s spectrum of mGO-PAO fitted with two peaks at 531.62 and 530.28 eV, which are related to the CN−OH peak and the adsorbed water peaks, respectively. After U(VI) adsorption, the peak related to the CN−OH produced a shift of 0.16 eV (Figure 13d), indicating that U(VI) can interact with the CN−OH groups. On the whole, the peaks of mGO-PAO became wider and shifted to higher binding energy after adsorption of U(VI), which is consistent with the result reported in the literature.55,56 On the basis of the XPS analysis, it can be concluded that the U(VI) was adsorbed onto mGO-PAO through the complexation of U(VI) with the imine and the hydroxyl, which probably is due to the η2 chelation,57,58 as shown in Figure 14. The results of XPS analysis also indicated the successful preparation of mGO-PAO. 3.9. Effect of Ultrasound on the Adsorption. The ultrasound was used to improve the adsorption performance of U(VI) by mGO-PAO. The FT-IR spectra of mGO-PAO before and after ultrasonic treatment are shown in Figure S3, and they were used to identify the effect of ultrasound on the structure of the adsorbent. It can be seen that the adsorbent did not change before and after ultrasonic treatment, indicating that the ultrasound did not destroy the functional groups of mGO-PAO. Figure 15 shows the effect of contact time on the U(VI) adsorption by mGO-PAO in the presence of ultrasound. Compared with that of the the shake mode, the adsorption rate of mGO-PAO significantly improved with ultrasonic agitation, and the adsorption equilibrium could be reached in 2 min at pH = 6.0. These data were also analyzed by pseudo-first-order and pseudo-second-order models, and the results were shown

Figure 10. Selective adsorption of U(VI) by mGO-PAO (m = 20 mg, V = 50 mL, pH = 6.0, T = 298 K, t = 2 h, C0 = 0.1 mmol/L for all metal ions).

wastewater, including Ca(II), Mn(II), Mg(II), Cd(II), Zn(II), Co(II), and Pb(II) ions, were selected to evaluate the adsorption selectivity of mGO-PAO for uranium(VI). Obviously, the mGO-PAO exhibits considerable selectivity toward U(VI) in the presence of other heavy metal ions with a high removal rate (97.6%). The excellent selectivity of mGO-PAO toward U(VI) was mainly attributed to the coordination capability of the amidoxime group for U(VI). 3.7. Desorption and Reusability. Reusability is an important parameter to evaluate the potential of an adsorbent in practical applications. The mGO-PAO adsorption−desorption cycles were studied, and the results were shown in Figure 11. In this work, 0.1 mol L−1 HCl was used as eluent for the recycling of the adsorbent. After five cycles, the adsorption efficiency decreased slightly in the U(VI) adsorption process and still maintained over 80%. The results indicated that mGO-PAO could be efficiently regenerated by 0.1 mol L−1 HCl and the adsorbent had good reusability. 3.8. Interaction Mechanism. To elucidate the interaction mechanism of U(VI) with mGO-PAO, the XPS spectra of mGO-PAO before and after U(VI) adsorption were measured. As shown in Figure 12, the double peak of U 4f can be clearly observed after adsorption, which indicates that U(VI) was successfully adsorbed onto the surface of mGO-PAO. To further verify the microscopic interaction between mGO-PAO and U(VI), the detailed spectra of N 1s and O 1s were shown G



Article

Figure 12. XPS spectra of mGO-PAO and mGO-PAO-U.

Figure 13. XPS spectra of N 1s for (a) mGO-PAO and (b) mGO-PAO-U, and XPS spectra of O 1s for (c) mGO-PAO and (d) mGO-PAO-U.

in Figure S4 and listed in Table 5. The results also indicated that the pseudo-second-order model was more appropriate for describing the kinetics of the adsorption of U(VI) by mGOPAO. It can be found from Table 5 that the value of k2 was 0.0046 g·mg−1·s−1 in the presence of ultrasound. However, the value of k2 was 0.0148 g·mg−1·min−1 in the absence of ultrasound (Table 1). Obviously, the adsorption speed of U(VI) by

mGO-PAO was increased by about 18 times due to the good dispersion of the magnetic powders by ultrasound.46 Next, the effect of ultrasound on the adsorption isotherms and selectivity were also studied in detail. In the presence of ultrasound, the adsorption process of uranium(VI) was also more suitably described by the Langmuir model (Figure S5 and Figure S6). The maximum U(VI) adsorption capacity (qm) H



Article

Figure 14. Possible η2 chelation in U(VI) adsorption by mGO-PAO.

Figure 16. Effect of contact time on the U(VI) adsorption from actual radioactive wastewater by mGO-PAO in the presence of ultrasound (m = 20 mg, V = 50 mL, T = 298 K).

and structure were well characterized by TEM, FT-IR, TGA, VSM, and XPS. The results of the adsorption experiments revealed that the U(VI) could be effectively removed by mGOPAO with high selectivity and the adsorbent had good reusability. Adsorption kinetics and isotherms studies suggested that the adsorption of U(VI) followed the pseudo-secondorder and Langmuir isotherm models, indicating that the chemisorption was the rate-limiting step and the adsorption was a monolayer adsorption. The thermodynamic study suggested that the adsorption process was spontaneous, feasible, and endothermic. In the presence of ultrasound, the mGOPAO showed ultrafast removal kinetics (equilibrium can be reached within 2 min) and high removal rate (91.98%) of U(VI) from the actual radioactive wastewater. This study not only provides a new adsorbent for rapid uranium(VI) extraction with high selectivity from radioactive wastewater but also demonstrates that ultrasound can be of great help to increase its adsorption speed.

Figure 15. Effect of contact time on the U(VI) adsorption by mGOPAO in the presence of ultrasound (m = 20 mg, V = 50 mL, C0 = 10 mg/L, pH = 6.0, T = 298 K).

Table 5. Kinetic Parameters of U(VI) Adsorption by mGOPAO in the Presence of Ultrasound pseudo-first-order

pseudo-second-order

qe (exp) (mg/g)

k1 (s−1)

qe (cal) (mg/g)

R2

k2 (g·mg−1·s−1)

qe (cal) (mg/g)

R2

24.85

0.0446

22.846

0.917

0.0046

26.254

0.999

of mGO-PAO was computed to be 89.928 mg/g (Table S1). In addition, the high adsorption selectivity of mGO-PAO toward U(VI) was also obtained (Figure S7 and Table S2). Obviously, these results are consistent with the previous experiments in the absence of ultrasound, indicating that the ultrasound has no significant influence on the adsorption isotherms and selectivity in this work. 3.10. Uranium Removal from Actual Radioactive Wastewater. To evaluate the adsorption capacity of mGOPAO for uranium extraction from wastewater, the experiments were carried out on the adsorption of uranium(VI) from actual radioactive wastewater in the presence of ultrasound. The actual radioactive wastewater was taken from a uranium mine in South China. The concentration of uranium ions in it is 123.75 μg/L and the pH = 5.84. As shown in Figure 16, the adsorption equilibrium can be quickly reached at 2 min, with the removal rate being 91.98%. The concentrations of uranium(VI) in solutions can be decreased to the level lower than maximum U(VI) concentration in drinking water at 30 μg·L−1 (U.S. Environmental Protection Agency, 2012). The experiments demonstrate that mGO-PAO has great potential in the extraction of U(VI) from actual radioactive wastewater.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b00703. Pseudo-first-order and pseudo-second-order adsorption kinetics model; Langmuir and Freundlich adsorption isotherm model; selective adsorption of uranium(VI) by mGO-PAO in the presence of ultrasound (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Dexin Ding: 0000-0002-7304-4376 Funding

This work was supported by the National Natural Science Foundation of China (U1401321 and 51704170), the Natural Science Foundation of Hunan Province (2018JJ3423), and the Postdoctoral Science Foundation of China (2017M612569).

4. CONCLUSION In summary, polyamidoxime functionalized magnetic graphene oxide (mGO-PAO) was successfully synthesized. The morphology

Notes

The authors declare no competing financial interest. I



■

Article

(17) Zhuang, S.; Cheng, R.; Kang, M.; Wang, J. Kinetic and equilibrium of U(VI) adsorption onto magnetic amidoxime-functionalized chitosan beads. J. Cleaner Prod. 2018, 188, 655−661. (18) Pang, H.; Huang, S.; Wu, Y.; Yang, D.; Wang, X.; Yu, S.; Chen, Z.; Alsaedi, A.; Hayat, T.; Wang, X. Efficient elimination of U(VI) by polyethyleneimine decorated fly ash. Inorg. Chem. Front. 2018, DOI: 10.1039/C8QI00253C. (19) Gładysz-Płaska, A.; Majdan, M.; Tarasiuk, B.; Sternik, D.; Grabias, E. The use of halloysite functionalized with isothiouronium salts as anorganic/inorganic hybrid adsorbent for uranium(VI) ions removal. J. Hazard. Mater. 2018, 354, 133−144. (20) Sun, Q.; Aguila, B.; Perman, J.; Ivanov, A. S.; Bryantsev, V. S.; Earl, L. D.; Abney, C. W.; Wojtas, L.; Ma, S. Bio-inspired nano-traps for uranium extraction from seawater and recovery from nuclear waste. Nat. Commun. 2018, 9, 1644−1652. (21) Li, W.; Liu, Q.; Chen, R.; Yu, J.; Zhang, H.; Liu, J.; Li, R.; Zhang, M.; Liu, P.; Wang, J. Efficient removal of U(VI) from simulated seawater with hyperbranched polyethylenimine (HPEI) covalently modified SiO2 coated magnetic microspheres. Inorg. Chem. Front. 2018, 5, 1321−1328. (22) Wang, X.; Yu, S.; Wu, Y.; Pang, H.; Yu, S.; Chen, Z.; Hou, J.; Alsaedi, A.; Hayat, T.; Wang, S. The synergistic elimination of uranium(VI) species from aqueous solution using bi-functional nanocomposite of carbon sphere and layered double hydroxide. Chem. Eng. J. 2018, 342, 321−330. (23) Zhang, Z.; Dong, Z.; Wang, X.; Ying, D.; Niu, F.; Cao, X.; Wang, Y.; Hua, R.; Liu, Y.; Wang, X. Ordered mesoporous polymer− carbon composites containing amidoxime groups for uranium removal from aqueous solutions. Chem. Eng. J. 2018, 341, 208−217. (24) Wang, Z.; Xu, C.; Lu, Y.; Wei, G.; Ye, G.; Sun, T.; Chen, J. Microplasma electrochemistry controlled rapid preparation of fluorescent polydopamine nanoparticles and their application in uranium detection. Chem. Eng. J. 2018, 344, 480−486. (25) Huang, Z. W.; Li, Z. J.; Wu, Q. Y.; Zheng, L. R.; Zhou, L. M.; Chai, Z. F.; Wang, X. L.; Shi, W. Q. Simultaneous elimination of cationic uranium(VI) and anionic rhenium(VII) by graphene oxide− poly(ethyleneimine) macrostructures: a batch, XPS, EXAFS, and DFT combined study. Environ. Sci.: Nano 2018, 5, 2077. (26) Zhang, Z. H.; Duan, S. X.; Chen, H. Y.; Zhang, F. S.; Hayat, T.; Alsaedi, A.; Li, J. X. Synthesis of Porous Magnetic Ni0.6Fe2.4O4 Nanorods for Highly Efficient Adsorption of U(VI). J. Chem. Eng. Data 2018, 63, 1810−1820. (27) Liu, X.; Xu, X. T.; Sun, J.; Alsaedi, A.; Hayat, T.; Li, J. X.; Wang, X. K. Insight into the impact of interaction between attapulgite and graphene oxide on the adsorption of U(VI). Chem. Eng. J. 2018, 343, 217−224. (28) Duan, S. X.; Xu, X. T.; Liu, X.; Wang, Y. N.; Hayat, T.; Alsaedi, A.; Meng, Y. D.; Li, J. X. Highly enhanced adsorption performance of U(VI) by non-thermal plasma modified magnetic Fe3O4 nanoparticles. J. Colloid Interface Sci. 2018, 513, 92−103. (29) Duan, S. X.; Wang, Y. N.; Liu, X.; Shao, D. D.; Hayat, T.; Alsaedi, A.; Li, J. X. Removal of U(VI) from Aqueous Solution by Amino Functionalized Flake Graphite Prepared by Plasma Treatment. ACS Sustainable Chem. Eng. 2017, 5, 4073−4085. (30) Li, Z. J.; Huang, Z. W.; Guo, W. L.; Wang, L.; Zheng, L. R.; Chai, Z. F.; Shi, W. Q. Enhanced Photocatalytic Removal of Uranium(VI) from Aqueous Solution by Magnetic TiO2/Fe3O4 and Its Graphene Composite. Environ. Sci. Technol. 2017, 51, 5666−5674. (31) Huang, Z. W.; Li, Z. J.; Zheng, L. R.; Zhou, L. M.; Chai, Z. F.; Wang, X. L.; Shi, W. Q. Interaction Mechanism of Uranium(VI) with Three-Dimensional Graphene Oxide-Chitosan Composite: Insights from Batch Experiments, IR, XPS, and EXAFS Spectroscopy. Chem. Eng. J. 2017, 328, 1066−1074. (32) Lan, J. H.; Chai, Z. F.; Shi, W. Q. A combined DFT and molecular dynamics study of U(VI)/calcite interaction in aqueous solution. Sci. Bull. 2017, 62, 1064−1073. (33) Wang, Y. N.; Liu, X.; Huang, Y. S.; Hayat, T.; Alsaedi, A.; Li, J. X. Interaction mechanisms of U(VI) and graphene oxide from the

REFERENCES

(1) Burns, P. C.; Ewing, R. C.; Navrotsky, A. Nuclear fuel in a reactor accident. Science 2012, 335, 1184−1188. (2) Yao, W.; Wang, X. X.; Liang, Y. S.; Yu, J.; Gu, P. C.; Sun, Y. B.; Xu, C.; Chen, J.; Hayat, T.; Alsaedi, A.; Wang, X. K. Synthesis of novel flower-like layered double oxides/carbon dots nanocomposites for U(VI) and 241Am(III) efficient removal: Batch and EXAFS studies. Chem. Eng. J. 2018, 332, 775−786. (3) Chen, Z.; Liang, Y.; Jia, D. S.; Chen, W. Y.; Cui, Z. M.; Wang, X. K. Layered Silicate RUB-15 for Efficient Removal of UO22+ and Heavy Metal Ions by Ion-exchange. Environ. Sci.: Nano 2017, 4, 1851−1858. (4) Zhang, S.; Zhao, X.; Li, B.; Bai, C.; Li, Y.; Wang, L.; Wen, R.; Zhang, M.; Ma, L.; Li, S. ″Stereoscopic″ 2D Super-Microporous Phosphazene-Based Covalent Organic Framework: Design, Synthesis and Selective Sorption towards Uranium at High Acidic Condition. J. Hazard. Mater. 2016, 314, 95−104. (5) Brown, S.; Chatterjee, S.; Li, M.; Yue, Y.; Tsouris, C.; Janke, C. J.; Saito, T.; Dai, S. Uranium Adsorbent Fibers Prepared by AtomTransfer Radical Polymerization from Chlorinated Polypropylene and Polyethylene Trunk Fibers. Ind. Eng. Chem. Res. 2016, 55, 4130− 4138. (6) Brown, S.; Yue, Y.; Kuo, L.-J.; Mehio, N.; Li, M.; Gill, G. A.; Tsouris, C.; Mayes, R. T.; Saito, T.; Dai, S. Uranium Adsorbent Fibers Prepared by Atom-Transfer Radical Polymerization (ATRP) from Poly(vinyl chloride)-co-chlorinated Poly(vinyl chloride) (PVC-coCPVC) Fiber. Ind. Eng. Chem. Res. 2016, 55, 4139−4148. (7) Yang, Y.; Wang, J.; Wu, F.; Ye, G.; Yi, R.; Lu, Y.; Chen, J. Surface-initiated SET-LRP mediated by mussel-inspired polydopamine chemistry for controlled building novel core-shell magnetic nanoparticles for highly-efficient uranium enrichment. Polym. Chem. 2016, 7, 2427−2435. (8) Li, Y.; Wang, L.; Li, B.; Zhang, M.; Wen, R.; Guo, X.; Li, X.; Zhang, J.; Li, S.; Ma, L. Pore-free matrix with cooperative chelating of hyperbranched ligands for high-performance separation of uranium. ACS Appl. Mater. Interfaces 2016, 8, 28853−28861. (9) Zhu, J.; Liu, Q.; Li, Z.; Liu, J.; Zhang, H.; Li, R.; Wang, J.; Emelchenko, G. A. Recovery of uranium(VI) from aqueous solutions by the modified honeycomb-like porous carbon material. Dalton Trans. 2017, 46, 420−429. (10) Li, R.; Che, R.; Liu, Q.; Su, S.; Li, Z.; Zhang, H.; Liu, J.; Liu, L.; Wang, J. Hierarchically structured layered-double-hydroxides derived by ZIF-67 for uranium recovery from simulated seawater. J. Hazard. Mater. 2017, 338, 167−176. (11) Wu, F.; Pu, N.; Ye, G.; Sun, T.; Wang, Z.; Song, Y.; Wang, W.; Huo, X.; Lu, Y.; Chen, J. Performance and Mechanism of Uranium Adsorption from Seawater to Poly(dopamine)-Inspired Sorbents. Environ. Sci. Technol. 2017, 51, 4606−4614. (12) Dong, Y.; Dong, Z.; Zhang, Z.; Liu, Y.; Cheng, W.; Miao, H.; He, X.; Xu, Y. POM Constructed from Super-Sodalite Cage with Extra-Large 24-Membered Channels: Effective Sorbent for Uranium Adsorption. ACS Appl. Mater. Interfaces 2017, 9, 22088−22092. (13) Zeng, J.; Zhang, H.; Sui, Y.; Hu, N.; Ding, D.; Wang, F.; Xue, J.; Wang, Y. New Amidoxime Based Material TMP-g-AO for Uranium Adsorption under Seawater Conditions. Ind. Eng. Chem. Res. 2017, 56, 5021−5032. (14) Linghu, W.; Yang, H.; Sun, Y.; Sheng, G.; Huang, Y. One-Pot Synthesis of LDH/GO Composites as Highly Effective Adsorbents for Decontamination of U(VI). ACS Sustainable Chem. Eng. 2017, 5, 5608−5616. (15) Yang, P.; Liu, Q.; Zhang, H.; Liu, J.; Chen, R.; Li, R.; Wu, D.; Bai, X.; Wang, J. Phosphatidyl-assisted fabrication of graphene oxide nanosheets with multi-active sites for uranium(VI) capture. Environ. Sci.: Nano 2018, 5, 1584−1594. (16) Zhao, D.; Gao, X.; Chen, S.; Xie, F.; Feng, S.; Alsaedi, A.; Hayat, T.; Chen, C. Interaction between U(VI) with sulfhydryl groups functionalized graphene oxides investigated by batch and spectroscopic techniques. J. Colloid Interface Sci. 2018, 524, 129−138. J



Article

perspective of particle size distribution. J. Radioanal. Nucl. Chem. 2017, 311, 209−217. (34) Liu, X.; Huang, Y. S.; Duan, S. X.; Wang, Y. N.; Li, J. X.; Chen, Y. T.; Hayat, T.; Wang, X. K. Graphene oxides with different oxidation degrees for Co(II) ion pollution management. Chem. Eng. J. 2016, 302, 763−772. (35) Liu, X.; Li, J. X.; Wang, X. X.; Chen, C. L.; Wang, X. K. High performance of phosphate-functionalized graphene oxide for the selective adsorption of U(VI) from acidic solution. J. Nucl. Mater. 2015, 466, 56−64. (36) Zhang, S. W.; Zeng, M. Y.; Li, J. X.; Li, J.; Xu, J. Z.; Wang, X. K. Porous magnetic carbon sheets from biomass as an adsorbent for the fast removal of organic pollutants from aqueous solution. J. Mater. Chem. A 2014, 2, 4391−4397. (37) Horzum, N.; Shahwan, T.; Parlak, O.; Demir, M. M. Synthesis of amidoximated polyacrylonitrile fibers and its application for sorption of aqueous uranyl ions under continuous flow. Chem. Eng. J. 2012, 213, 41−49. (38) Barber, P. S.; Kelley, S. P.; Griggs, C. S.; Wallace, S.; Rogers, R. D. Surface modification of ionic liquid-spun chitin fibers for the extraction of uranium from seawater: seeking the strength of chitin and the chemical functionality of chitosan. Green Chem. 2014, 16, 1828−1836. (39) Oyola, Y.; Dai, S. High surface-area amidoxime-based polymer fibers co-grafted with various acid monomers yielding increased adsorption capacity for the extraction of uranium from seawater. Dalton Trans. 2016, 45, 8824−8834. (40) Zhang, L.; Yang, S.; Qian, J.; Hua, D. Surface Ion-Imprinted Polypropylene Nonwoven Fabric for Potential Uranium Seawater Extraction with High Selectivity over Vanadium. Ind. Eng. Chem. Res. 2017, 56, 1860−1867. (41) Husnain, S. M.; Um, W.; Chang, Y.-Y.; Chang, Y.-S. Recyclable superparamagnetic adsorbent based on mesoporous carbon for sequestration of radioactive Cesium. Chem. Eng. J. 2017, 308, 798− 808. (42) Min, X.; Yang, W.; Hui, Y.-F.; Gao, C.-Y; Dang, S.; Sun, Z.-M. Fe3O4@ZIF-8: A Magnetic Nanocomposite for Highly Efficient UO22+ Adsorption and Selective UO22+/Ln3+ Separation. Chem. Commun. 2017, 53, 4199−4202. (43) Cheng, M.; Wang, Z.; Lv, Q.; Li, C.; Sun, S.; Hu, S. Preparation of amino-functionalized Fe3O4@mSiO2 core-shell magnetic nanoparticles and their application for aqueous Fe3+ removal. J. Hazard. Mater. 2018, 341, 198−206. (44) Asfaram, A.; Ghaedi, M.; Goudarzi, A.; Rajabi, M. Response surface methodology approach for optimization of simultaneous dye and metal ion ultrasound-assisted adsorption onto Mn doped Fe3O4NPs loaded on AC: kinetic and isothermal studies. Dalton Trans. 2015, 44, 14707−14723. (45) Huang, L.; Zhou, S.; Jin, F.; Huang, J.; Bao, N. Characterization and mechanism analysis of activated carbon fiber felt-stabilized nanoscale zero-valent iron for the removal of Cr(VI) from aqueous solution. Colloids Surf., A 2014, 447, 59−66. (46) Zhang, W.-B.; Deng, M.; Sun, C.-X.; Wang, S.-B. UltrasoundEnhanced Adsorption of Chromium(VI) on Fe3O4 Magnetic Particles. Ind. Eng. Chem. Res. 2014, 53, 333−339. (47) Dai, Z. R.; Zhang, H.; Sui, Y.; Ding, D. X.; Hu, N.; Li, L.; Wang, Y. D. Synthesis and characterization of a novel core−shell magnetic nanocomposite via surface-initiated RAFT polymerization for highly efficient and selective adsorption of uranium(VI). J. Radioanal. Nucl. Chem. 2018, 316, 369−382. (48) Zhao, Y.; Zhang, L.; Chu, Z.; Xiong, Z.; Zhang, W. Ti4+immobilized chitosan coated magnetic graphene oxide for highly selective enrichment of phosphopeptides. Anal. Methods 2017, 9, 443−449. (49) Wilczewska, A. Z.; Markiewicz, K. H. Surface-Initiated RAFT/ MADIX Polymerization on Xanthate-Coated Iron Oxide Nanoparticles. Macromol. Chem. Phys. 2014, 215, 190−197. (50) Wei, Y.; Qian, J.; Huang, L.; Hua, D. Bifunctional polymeric microspheres for efficient uranium sorption from aqueous solution:

synergistic interaction of positive charge and amidoxime group. RSC Adv. 2015, 5, 64286−64292. (51) Lu, X.; He, S. N.; Zhang, D. X.; Reda, A. T.; Liu, C.; Feng, J.; Yang, Z. Synthesis and characterization of amidoxime modified calix[8]arene for adsorption of U(VI) in low concentration uranium solutions. RSC Adv. 2016, 6, 101087−101097. (52) Shao, D. D.; Wang, X. X.; Wang, X. L.; Hu, S.; Hayat, T.; Alsaedi, A.; Li, J. X.; Wang, S. H.; Hu, J.; Wang, X. K. Zero valent iron/poly(amidoxime) adsorbent for the separation and reduction of U(VI). RSC Adv. 2016, 6, 52076−52081. (53) Gustafsson, J. P. Visual MINTEQ, ver. 3.1; Department of Land and Water Resources Engineering, KTH: Stockholm, Sweden; https://vminteq.lwr.kth.se/download/ (accessed May 22, 2018). (54) Cai, Y.; Wu, C.; Liu, Z.; Zhang, L.; Chen, L.; Wang, J.; Wang, X.; Yang, S.; Wang, S. Fabrication of Phosphorylated Graphene Oxide-Chitosan Composite for Highly Effective and Selective Capture of U(VI). Environ. Sci.: Nano 2017, 4, 1876−1886. (55) Tian, Y.; Fu, J.; Zhang, Y.; Cao, K.; Bai, C.; Wang, D.; Li, S.; Xue, Y.; Ma, L.; Zheng, C. Ligand-Exchange Mechanism: New Insight into Solid-Phase Extraction of Uranium Based on A Combined Experimental and Theoretical Study. Phys. Chem. Chem. Phys. 2015, 17, 7214−7223. (56) Li, B.; Bai, C.; Zhang, S.; Zhao, X.; Li, Y.; Wang, L.; Ding, K.; Shu, X.; Li, S.; Ma, L. An Adaptive Supramolecular Organic Framework for Highly Efficient Separation of Uranium via an in situ Induced Fit Mechanism. J. Mater. Chem. A 2015, 3, 23788− 23798. (57) Vukovic, S.; Watson, L. A.; Kang, S. O.; Custelcean, R.; Hay, B. P. How Amidoximate Binds the Uranyl Cation. Inorg. Chem. 2012, 51, 3855−3859. (58) Parker, B. F.; Zhang, Z.; Rao, L.; Arnold, J. An overview and recent progress in the chemistry of uranium extraction from seawater. Dalton Trans. 2018, 47, 639−644.

K


Magnetic Graphene Oxide Composite

Recommend Documents