Nano-TiO2 Imparts Amidoximated Wool Fibers with Good Antibacterial

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Cite This: Ind. Eng. Chem. Res. 2018, 57, 1826−1833

Nano-TiO2 Imparts Amidoximated Wool Fibers with Good Antibacterial Activity and Adsorption Capacity for Uranium(VI) Recovery Jun Wen,†,∥ Qiaoyu Li,†,‡,∥ Hao Li,† Min Chen,‡,§ Sheng Hu,† and Haiming Cheng*,‡,§ †

Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, China Key Laboratory of Leather Chemistry and Engineering of Ministry of Education, Sichuan University, Chengdu 610065, China § National Engineering Laboratory for Clean Technology of Leather Manufacture, Sichuan University, Chengdu 610065, China ‡

S Supporting Information *

ABSTRACT: Marine bacteria play a key role in marine ecosystems and are one of the main causes of biofouling. Biofouling of adsorbents that are used for uranium recovery usually results in a decrease in uranium recovery. A novel adsorbent with antibacterial activity for uranium recovery in bacterial environments was prepared in our study to address this concern. Amidoxime-functionalized wool fibers with nano-TiO2 particles (Wool-AO@TiO2) was synthesized by radiationinduced graft polymerization combined with in situ coprecipitation of nano-TiO2 particles onto the wool fibers. The presence of nano-TiO2 on the adsorbent was verified by scanning electron microscopy with energy-dispersive X-ray spectroscopy. The maximum uranium adsorption capacity of Wool-AO@TiO2, acquired from the Langmuir isotherm, was 113.12 mg/g. The introduced nano-TiO2 imparted excellent antibacterial activity to Wool-AO@TiO2. The inhibition of Staphylococcus aureus and Escherichia coli by Wool-AO@TiO2 was 95.2% and 90%, respectively. The adsorption capacity was mostly unaffected in bacterial environments, even after four cycles of culturing with bacteria. These results suggest that the prepared Wool-AO@TiO2 adsorbent may promote the development of novel antifouling adsorbents for uranium recovery from seawater.

1. INTRODUCTION Even though seawater has a uranium concentration of only 3.3 ppb, it is still considered a potential source of uranium because of the large amount it contains (∼4.5 billion tons), which is approximately 1000 times as much as that found in mineral ores on land.1,2 According to the Organization for Economic Cooperation and Development, the total amount of uranium available from land mining could be exhausted in approximately one century with the current nuclear energy consumption rate.3 Therefore, the development of processes for efficient uranium extraction from seawater plays an important role in the utilization of uranium and and nuclear electricity industry. Scientists in many countries have been involved in the development of such techniques in recent decades.4−7 Various materials have been developed as adsorbents for recovering uranium from seawater, such as polymeric fibers,8−10 biomaterials,11−13 inorganic materials,14−17 and nanomaterials.18,19 These studies focused mostly on how to enhance the adsorption capacity and selectivity for uranium. Biofouling due to marine bacteria, one of the essential factors that affect the adsorption of uranium from seawater, has been noted to reduce adsorption capacity. However, few studies have addressed this problem. Park et al.20 revealed that the adsorption performance of amidoxime adsorbents decreased dramatically owing to biofouling when exposed to raw seawater © 2018 American Chemical Society

in the presence of light. Although carrying out the recovery process below the photic zone would diminish this biofouling effect, the lower temperature at greater depth may result in poor adsorption capacity and rate. In addition, increasing the depth of operation will increase the technical difficulties and costs. For these reasons, the development of a uranium recovery adsorbent with antibacterial activity is very important. To the best of our knowledge, no report on this exists so far. Titanium dioxide (TiO2) has been proposed as a potential adsorbent for uranium(VI) recovery.21−23 Recently, nanoscale TiO2 (nano-TiO2) has received great attention because of its antibacterial activity, low cost, self-cleaning properties, good hydrophilicity, and stability.24 Nano-TiO2 can be activated when irradiated with ultraviolet (UV) light in the presence of water vapor, which generates superoxide anions and hydroxyl radicals. The various highly active oxygen-containing radicals can oxidize organic compounds/cells, resulting in the death of microorganisms. Herein, we present a novel adsorbent comprising amidoximefunctionalized wool fibers with nano-TiO2 (Wool-AO@TiO2), Received: Revised: Accepted: Published: 1826

October 23, 2017 January 19, 2018 January 29, 2018 January 29, 2018 DOI: 10.1021/acs.iecr.7b04380 Ind. Eng. Chem. Res. 2018, 57, 1826−1833

Article

Industrial & Engineering Chemistry Research Scheme 1. Synthesis of Amidoxime-Functionalized Wool Fibers with Nano-TiO2 (Wool-AO@TiO2)

composition of each adsorbent was determined by a 51XMX0019 X-Max energy-dispersive X-ray spectroscopy (EDXS) analyzer (Oxford Instruments, UK). Thermogravimetric analysis (TGA) of the samples was carried out on a TG 209 F (Netzsch, Germany) from 20 to 800 °C with a heating rate of 10 °C/min. The cell was purged with air at 60 mL/min during heating. The nitrogen adsorption isotherms of the samples were detected by a Tristar 3000 surface area and porosity analyzer (Micromeritics, USA) at liquid nitrogen temperature (77 K). The surface area of each sample was calculated using the Brunauer−Emmett−Teller (BET) equation. All tests were run in triplicate. 2.4. Adsorption Experiments. Uranium sorption experiments were performed in simulated seawater (consisting of UO2(NO3)2·6H2O (∼50 ppm), NaHCO3 (∼193 ppm), and NaCl (∼25600 ppm) in deionized water, with a pH of 8.0 ± 0.2). Briefly, 20 mg of the adsorbent and 20 mL of a uranium aqueous solution were added to a 50 mL plastic flask and shaken using a thermostat shaker (WS-300R, Wiggens) at 100 rpm for 24 h at 25 °C. The concentration of uranium was determined with inductively coupled plasma optical emission spectroscopy (ICP-OES). The amount of uranium adsorbed at equilibrium was calculated by eq 1:

synthesized by radiation-induced graft polymerization of acrylonitrile and methacrylic acid, combined with in situ coprecipitation of nano-TiO2 particles onto the wool fibers; this material shows good adsorption capacity of uranium(VI) and excellent antibacterial activity in aqueous solutions.

2. EXPERIMENTAL SECTION 2.1. Materials. Merino wool fibers were purchased from a local market. Acrylonitrile and methylacrylic acid were purchased from Sinopharm Chemical Reagents (Shanghai, China). Nano-TiO2 (size 25 nm) was purchased from Aladdin Chemicals (Shanghai, China) and dispersed in an emulsion for irradiation grafting reactions. Hydroxylamine hydrochloride and sodium hydroxide were obtained from KeLong Chemicals (Chengdu China). A standard solution of uranium(VI) (1000 ppm) was supplied by the National Analysis and Testing Center (Beijing, China). Finally, a stock solution (1000 ppm) of uranyl nitrate was prepared by dissolving uranyl nitrate hexahydrate into deionized water. All reagents were used as received without further treatment. 2.2. Preparation of Adsorbents. The Wool-AO@TiO2 composites were synthesized by radiation-induced polymerization in combination with an in situ emulsion co-precipitation method as shown in Scheme 1. Briefly, 1.0 g of wool fibers, monomers (3 mL of acrylonitrile and 3 mL of methylacrylic acid), and nano-TiO2 particles (0− 20 mg) were mixed in a transparent glass bottle and then sealed with foil. The mixtures were irradiated with an electron beam (electronic linear accelerator, VF-ProAcc-10/20, 10 MeV) at room temperature with a 200 kGy dose. The product was rinsed with acetone at 40 °C to remove the homopolymers and unreacted monomers and then washed thoroughly with deionized water and dried. The obtained product was designated Wool-AN@TiO2. To obtain amidoxime groups, 0.5 g of Wool-AN@TiO2 was mixed with 50 mL of NH2OH·HCl solution (methanol:water = 1:1) containing 4.0 g NH2OH·HCl and neutralized to pH 7 with 0.2 M NaOH. This mixture was refluxed at 75 °C for 5 h. Subsequently, the wool fibers were thoroughly washed by methanol and dried, and the obtained adsorbent was designated Wool-AO@TiO2. Wool-AN and Wool-AO fibers without added nano-TiO2 were also prepared as controls following the same procedures as described above. 2.3. Characterization. The Fourier transform infrared (FT-IR) spectra of pristine wool fibers, Wool-AN, and WoolAO were collected on a Nicolet iS10 FT-IR spectrophotometer (Thermo Scientific, USA) in KBr discs over a range from 4000 to 600 cm−1. The morphologies of the fibers were observed using a JSM-F7500 scanning electron microscope (SEM; Japan Electron Optical Laboratory Co., Ltd., Japan). The elemental

qe =

(C0 − Ce)V m

(1)

where qe (mg U/g) is the equilibrium sorption capacity, v (mL) the volume of solution, m (g) the adsorbent weight, and C0 (mg/L) and Ce (mg/L) the concentrations of uranium at the initial and equilibrium states, respectively. The effect of pH on the adsorption was studied by varying the pH values from 3 to 9 by slow adjustments with 0.1 M K2CO3 and 0.1 M HNO3. All adsorption experiments were conducted for 24 h at 25 °C with an initial metal ion concentration of 50 mg/L. The isotherm studies were conducted at pH 8.0 with initial uranium concentrations varying from 10 to 500 ppm. 2.5. Antibacterial Activity Analysis. To determine the antibacterial properties of the adsorbents, the dilution plate counting method was performed according to Chinese standard GB/T 20944. Briefly, sterile plate count agar (PCA) plates were prepared by pouring sterilized media onto the sterile plates under aseptic conditions. Then, 10 mg of sample was cultured with 20 mL of 30 mM phosphate buffer saline (PBS, 0.15 M NaCl, pH 7.4) containing bacteria species at a concentration of ∼105 CFU/mL and lysogeny broth (LB) medium. Afterward, the mixture was shaken at 150 rpm for 18 h at 24 °C in a water bath exposed to visible light. Subsequently, 0.2 mL of the supernatant was spread on PCA using a 10-fold dilution method. The number of colonies was counted after incubating 1827

DOI: 10.1021/acs.iecr.7b04380 Ind. Eng. Chem. Res. 2018, 57, 1826−1833

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Industrial & Engineering Chemistry Research at 37 °C for 24 h in a constant temperature incubator. The amount of inhibition by each sample was calculated by eq 2: I=

Wt − Q t Wt

× 100%

TGA of pristine wool, Wool-AO, and Wool-AO@TiO2 was conducted from 20 to 800 °C at a heating rate of 10 °C/min (see Figure S2 in the Supporting Information). The results are shown in Table 1, in which IDT means the initial decomposition temperature, FDT means the final decomposition temperature, and Tp means peak derivative temperature. Wool-AO@TiO2 exhibited the lowest Tp (300.1 °C) compared to Wool-AO (313.3 °C) and pristine wool (319.9 °C); however, Wool-AO@TiO2 exhibited the highest residual mass (26.1%) among the three samples. These differences can likely be explained by both the grafting and amidoximation processes and the loading of nano-TiO2 particles; the SEM images in Figure 2 show evidence of damage to the wool fibers during grafting and amidoximation, which causes a decrease in thermal stability. 3.2. Adsorption Experiments. 3.2.1. Effect of Dosage of Nano-TiO2 Particles on Adsorption Capacity. The influence of the amount of TiO2 on Wool-AO@TiO2 on the sorption of uranium(VI) was investigated by varying the TiO2 dosage deposited on the wool fibers; adsorption experiments were performed for 24 h at pH 8.0 and 25 °C with an initial metal ion concentration of 50 mg/L. As shown in Figure 4, the adsorption of uranium by Wool-AO@TiO2 increased as the amount of nano-TiO2 particles was increased from 0 to 1.5%, with a maximum adsorption capacity of 72.3 mg/g. This was possible because TiO2 has good uranium adsorption properties. Moreover, the higher specific surface area of Wool-AO@TiO2 than Wool-AO may play a role in adsorption as well. As shown in Table 1, the specific surface area of Wool-AO@TiO2 (dose of TiO2 of 1.5%) was 3.83 m2/g, notably higher than that of Wool-AO (2.51 m2/g). However, when further increasing the concentration of TiO2 to 2.0%, the adsorption capacity of uranium decreased to 57.1 mg/g. The reason may be agglomeration of nano-TiO2 particles, which is much more probable with increasing TiO2 dosages; this agglomeration may have resulted in TiO2 particles that are larger than nanoparticle size.26 Because the metal ion adsorption capacity of nano-TiO2 particles depends on their size,27−29 this may have caused the decrease in adsorption capacity at the nano-TiO2 concentration of 2.0%. 3.2.2. Effect of Initial pH on Adsorption. The initial pH of the solution plays a key role in the adsorption capacity because pH affects both the speciation of uranium in aqueous solutions and the activity of the binding groups on the adsorbents. The effect of pH on adsorption of uranium(VI) onto Wool-AO@ TiO2 was investigated by varying the pH from 3.0 to 9.0. The results are shown in Figure 5. The adsorbed amount of uranium(VI) on Wool-AO increased from 6.52 to 31.1 mg/g as the pH was increased from 3.0 to 6.0 but then slightly decreased at higher pH values, staying relatively constant. For Wool-AO@TiO2, the amount of adsorbed uranium increased rapidly between pH 3.0 and 6.0, from 29.8 to 67.5 mg/g, and then slowly further increased until reaching 74.1 mg/g at the pH of 9.0. At the same pH, uranium uptake by Wool-AO@ TiO2 was therefore higher than by Wool-AO. When the initial pH was lower than 3.0, the adsorbed amount for uranium recovery by Wool-AO was only 6.52 mg/g. The latter could be explained by UO22+ being the predominant species of uranyl when the pH is below 3;30 at the same time, most amidoxide groups on Wool-AO are protonated, providing few binding sites for the cationic uranium.31 When increasing the initial pH, the protonated amidoxime groups gradually deprotonate, while UO22+ hydrolyzes to form less positively

(2)

where I (%) is the inhibition rate, and Wt and Qt are the amounts of colonies of the test and control sample, respectively. Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) were selected as the test species, and pristine wool fiber was used as the control sample.

3. RESULTS AND DISCUSSION 3.1. Characterization. The FT-IR spectra of pristine wool, Wool-AN@TiO2, and Wool-AO@TiO2 are shown in Figure 1.

Figure 1. Fourier transform infrared (FT-IR) spectra of wool, wool fibers with nano-TiO2 without amidoxime groups (Wool-AN@TiO2), and Wool-AO@TiO2.

The spectrum of pristine wool fibers shows typical peaks at 1632.8 cm−1 for CO (amide I), 1545.7 cm−1 for N−H (amide II), and 1387.7 cm−1 for C−N (amide III).25 After grafting, in Wool-AN@TiO2, new bands can be observed at 2246.1 and 1735.6 cm−1 (Figure 1); these can be attributed to nitrile and carboxyl groups, respectively, suggesting that acrylonitrile and methylacrylic acid were successfully grafted onto the wool fibers. In the spectrum for Wool-AO@TiO2, the disappearance of nitrile stretching bands and appearance of signatures for N−O (927.7 cm−1) and CO (1646.6 cm−1) can clearly be observed after amidoximation,12 which indicates that the nitrile groups were converted to amidoxime groups. SEM images of pristine wool, Wool-AO, and Wool-AO@ TiO2 are shown in Figure 2. It can clearly be observed that grafting and amidoximation damaged or caused damage to the scale layer of the pristine wool fibers (Figure 2b). Moreover, many nanoparticles appeared (sizes ranging from 20−40 nm to 300−500 nm) on the surface of Wool-AO@TiO2 (Figure 2d), illustrating that nano-TiO2 had successfully been affixed onto the wool fibers by in situ coprecipitation. The SEM-EDXS profiles (Figure 3b) show the presence of elemental Ti on Wool-AO@TiO2, which further indicates that nano-TiO2 particles were successfully loaded onto the wool fibers. 1828

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Figure 2. Scanning electron microscope (SEM) profiles: (a) pristine wool, (b) amidoxime-functionalized wool fibers without TiO2 (Wool-AO), and (c,d) Wool-AO-TiO2.

Figure 3. SEM-energy-dispersive X-ray spectroscopy (EDXS) profiles: (A) wool and (B) Wool-AO@TiO2.

6.0−7.034,35 than amidoxime groups (pHZCP 4.3),27 the adsorption capacity of Wool-AO@TiO2 is more stable at a higher pH value, with an optimum pH of 7.0−8.0. To ensure that the pH of the experimental system is consistent with that of seawater, all following experiments were performed at pH 8.0. The effect of contact time, adsorption kinetics, and equilibrium studies are described in detail in the Supporting Information. The results show that the equilibrium times of Wool-AO and Wool-AO@TiO2 were about 7 and 10 h,

charged species such as UO2(OH)2+ and UO2NO3+. As a result, repulsion decreases and uranyl species can more easily coordinate with amidoxime groups,32 leading to enhanced adsorption. When the pH is higher than 6.0, UO22+ undergoes further hydrolysis, forming some species that are neutral, negatively charged, or precipitate. The amidoxime groups easily react with OH− to form a negatively charged substance, leading to another electrostatic repulsion that is not beneficial to the adsorption of uranium.33 As a consequence, the optimal pH of Wool-AO is at 6.0. Because nano-TiO2 has a higher pHZCP of 1829

DOI: 10.1021/acs.iecr.7b04380 Ind. Eng. Chem. Res. 2018, 57, 1826−1833

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the addition of nano-TiO2 on Wool-AO improved its uranium(VI) adsorption capacity. 3.3. Antibacterial Activity. Many reports have been concerned with improving adsorption capacities from aqueous solutions, especially from seawater. However, biofouling is a critical factor that may invalidate these previous efforts. Therefore, the antibacterial activity of adsorbents should be of concern as well. Herein, Gram-negative E. coli and Grampositive S. aureus were selected to investigate the antibacterial activity of Wool-AO@TiO2 in aqueous solutions, as those are the most common models for antibacterial studies.36 3.3.1. Effect of the Dosage of TiO2 Nanoparticles. The effect of the amount of TiO2 on Wool-AO@TiO2 on its antibacterial activity was investigated, with results shown in Figure 6 (all data in triplicate). This shows that the use of TiO2

Table 1. Thermogravimetric Analysis (TGA) Parameters and Specific Surface Areas of Wool, Wool-AO, and Wool-AO@ TiO2a TGA sample pristine wool Wool-AO Wool-AO@ TiO2

specific area (m2/g)

IDT (°C)

FDT (°C)

residual mass (%)

Tp (°C)

2.35 2.51 3.83

266.5 262.9 264.5

383.8 380.0 361.7

17.8 13.4 26.1

319.9 313.3 300.1

a IDT, initial decomposition temperature; FDT, final decomposition temperature; Tp, peak derivative temperature.

Figure 4. Effect of dosage of TiO2 on adsorption. Conditions: pH 8.0, temperature (T) 25 °C, initial uranium(VI) concentration (C0) 50 ppm, and time = 24 h. Figure 6. Effect of dosage of TiO2 on antibacterial activity.

nanoparticles improved the antibacterial activity of Wool-AO; within the experimental range, the extent of E. coli inhibition by Wool-AO@TiO2 increased with increasing dosage of TiO2 nanoparticles, with the inhibition reaching a maximum of 90% at a TiO2 dosage of 1.5−2.0%. Similarly, the S. aureus inhibition increased sharply when the dosage of TiO 2 nanoparticles was less than 1.0%, then increased slower ay higher dosages, ultimately reaching a maximum of 95.2% at a 1.5−2.0% TiO2 dose. According to these results, Wool-AO@ TiO2 exhibited greater inhibition of S. aureus than of E. coli, which may be due to the different bacterial cell structures.37 It is known that Gram-negative bacteria (e.g., E. coli) have a triplelayer cell wall with an inner membrane, a thin peptidoglycan layer, and an outer membrane, whereas Gram-positive bacteria (e.g., S. aureus) have a thicker peptidoglycan layer and no outer membrane. Similar results have been reported in several other studies.36,38−40 Photographs in Figure 7 depict the antibacterial activity of Wool-AO and Wool-AO@TiO2 against E. coli. 3.3.2. Uranium(VI) Adsorption in Bacterial Environments. To investigate the adsorption behavior of Wool-AO@TiO2 in bacterial environments, adsorption experiments at 25 °C were also performed in 30 mM PBS buffer (pH 8.0) with 105 CFU/ mL bacteria and an initial uranium(VI) concentration of 50 ppm. The results, shown in Figure 8 (all data in triplicate), indicate that the adsorption processes reached equilibrium states earlier (after 4−6 h) and yielded higher uranium adsorption capacities in bacterial environments (87.5 mg/g

Figure 5. Effect of initial pH on adsorption. Conditions: T = 25 °C, C0 = 50 ppm, time = 24 h.

respectively (Supporting Information, Figure S3). The Langmuir model was suitable to describe the adsorption process of uranium for both Wool-AO and Wool-AO@TiO2, implying a monolayer coverage of uranium onto both materials. The maximum uranium adsorption capacity (qm) of WoolAO@TiO2, acquired from Langmuir isotherms, was 113.12 mg/g, which is higher than that of Wool-AO (49.6 mg/g) (Supporting Information, Table S1). These results indicate that 1830

DOI: 10.1021/acs.iecr.7b04380 Ind. Eng. Chem. Res. 2018, 57, 1826−1833

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Figure 7. Antibacterial activity of adsorbents against E. coli: (a) control, (b) Wool-AO, and (c) Wool-AO@TiO2 with 1.5% TiO2.

Figure 8. Adsorption of uranium in bacterial environments. Conditions: T = 25 °C, C0 = 50 ppm, and 105 CFU/mL bacteria in 30 mM PBS buffer (pH 8.0).

Figure 9. Antibacterial testing over four cycles.

remained at relatively high levels of 88.4 and 89%, respectively, of the initial inhibition amounts. The adsorption capacity of the material in each bacterial culture is listed in Table 2. WoolAO@TiO2 still exhibited good adsorption capability for uranium(VI) even after four cycles, indicating the good reusability properties of Wool-AO@TiO2.

with E. coli, 104.1 mg/g with S. aureus) than in environments without bacteria (7−10 h and 72.3 mg/g, see also Supporting Information, Figure S3). This may be explained by phosphate in the bacterial system possibly being beneficial to uranium adsorption (Supporting Information, Figure S6).41−43 Furthermore, the uranium(VI) adsorption capacity of Wool-AO@ TiO2 in the presence of S. aureus was greater than in the presence of E. coli, which implies that the influence of S. aureus on adsorption is easier to avoid. 3.3.3. Cyclic Antibacterial Testing. To evaluate long-term bacterial resistance, Wool-AO@TiO2 and bacterial solution were cultured continuously for four cycles. The antibacterial tests were performed as described above. At the end of each culture cycle, the solution was removed by centrifugation and the adsorption capacity measured by ICP-OES. The WoolAO@TiO2 with adsorbed uranium(VI) was then placed in a 0.1 M Na2CO3 solution (100 mL) for regeneration at 25 °C for 24 h. The regenerated adsorbent was subsequently placed in a newly activated bacterial solution with 50 ppm uranium(VI) for another culture run. The results, shown in Figure 9 (each data point in triplicate), indicate that the antibacterial activity of Wool-AO@TiO2 decreases slightly with an increasing number of cycles. After four cycles, E. coli and S. aureus inhibitions still

Table 2. Adsorption after Cyclic Antibacterial Testing Wool-AO@TiO2 cycle cycle cycle cycle

1 2 3 4

adsorption after culture with E. coli (mg/g)

adsorption after culture with S. aureus (mg/g)

87.5 86.4 85.7 83.4

104.1 102.6 100.4 97.3

4. CONCLUSIONS In summary, a novel adsorbent comprising amidoximefunctionalized wool fibers with nano-TiO2 (Wool-AO@TiO2) was prepared by radiation-induced copolymerization, and its adsorption properties and antibacterial activity were investigated. Wool-AO@TiO2 exhibited pH-dependent uranium(VI) adsorption capacity with good adsorption efficiency in the pH range from 6.0 to 9.0. The adsorption process followed 1831

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(8) Kim, J. S.; Tsouris, C.; Oyola, Y.; Janke, C. J.; Mayes, R. T.; Dai, S.; Gill, G.; Kuo, L. J.; Wood, J.; Choe, K. Y.; Schneider, E.; Lindner, H. Uptake of uranium from seawater by amidoxime-based polymeric adsorbent: field experiments, modeling, and updated economic assessment. Ind. Eng. Chem. Res. 2014, 53, 6076−6083. (9) Schenk, H. J.; Astheimer, L.; Witte, E. G.; Schwochau, K. Development of sorbers for the recovery of uranium from seawater 0.1. assessment of key parameters and screening studies of sorber materials. Sep. Sci. Technol. 1982, 17, 1293−1308. (10) Brown, S.; Yue, Y. F.; Kuo, L. J.; Mehio, N.; Li, M. J.; Gill, G.; 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. (11) Anirudhan, T. S.; Deepa, J. R.; Binusreejayan. Synthesis and characterization of multi-carboxyl-functionalized nanocellulose/nanobentonite composite for the adsorption of uranium(VI) from aqueous solutions: kinetic and equilibrium profiles. Chem. Eng. J. 2015, 273, 390−400. (12) Yin, Z. L.; Xiong, J.; Chen, M.; Hu, S.; Cheng, H. M. Recovery of uranium(VI) from aqueous solution by amidoxime functionalized wool fibers. J. Radioanal. Nucl. Chem. 2016, 307, 1471−1479. (13) Hazer, O.; Kartal, S. Use of amidoximated hydrogel for removal and recovery of U(VI) ion from water samples. Talanta 2010, 82, 1974−1979. (14) Guerra, D. L.; Leidens, V. L.; Viana, R. R.; Airoldi, C. Amazon kaolinite functionalized with diethylenetriamine moieties for U(VI) removal: thermodynamic of cation-basic interactions. J. Hazard. Mater. 2010, 180, 683−692. (15) Zakutevskii, O. I.; Psareva, T. S.; Strelko, V. V.; Kartel’, N. T. Sorption of U(VI) from aqueous solutions with carbon sorbents. Radiochemistry 2007, 49, 67−71. (16) Ding, C.; Cheng, W.; Nie, X.; Yi, F. Synergistic mechanism of U(VI) sequestration by magnetite-graphene oxide composites: Evidence from spectroscopic and theoretical calculation. Chem. Eng. J. 2017, 324, 113−121. (17) Guo, Z. J.; Yan, Z. Y.; Tao, Z. Y. Sorption of uranyl ions on TiO2: effects of contact time, ionic strength, concentration, and humic substance. J. Radioanal. Nucl. Chem. 2004, 261, 157−162. (18) Tan, L.; Zhang, X.; Liu, Q.; Jing, X.; Liu, J.; Song, D.; Hu, S.; Liu, L.; Wang, J. Synthesis of Fe3O4 @TiO2, core−shell magnetic composites for highly efficient sorption of uranium(VI). Colloids Surf., A 2015, 469, 279−286. (19) Khajeh, M.; Jahanbin, E. Application of cuckoo optimization algorithm−artificial neural network method of zinc oxide nanoparticles−chitosan for extraction of uranium from water samples. Chemom. Intell. Lab. Syst. 2014, 135, 70−75. (20) Park, J.; Gill, G. A.; Strivens, J. E.; Kuo, L. J.; Jeters, R. T.; Avila, A.; Wood, J. R.; Schlafer, N. J.; Janke, C. J.; Miller, E. A.; Thomas, M.; Addleman, R. S.; Bonheyo, G. T. Effect of biofouling on the performance of amidoxime-based polymeric uranium adsorbents. Ind. Eng. Chem. Res. 2016, 55, 4328−4338. (21) Davies, R. V.; Kennedy, J.; McIlroy, R. W.; Spence, R.; Hill, K. M. Extraction of uranium from seawater. Nature 1964, 203, 1110− 1115. (22) Wazne, M.; Meng, X.; Korfiatis, G. P.; Christodoulatos, C. Carbonate effects on hexavalent uranium removal from water by nanocrystalline titanium dioxide. J. Hazard. Mater. 2006, 136, 47−52. (23) Jaffrezic-Renault, N.; Poirier-Andrade, H.; Trang, D. H. Models for the adsorption of uranium on titanium dioxide. J. Chromatogr. A 1980, 201, 187−192. (24) Liou, J. W.; Chang, H. H. Bactericidal effects and mechanisms of visible light-responsive titanium dioxide photocatalysts on pathogenic bacteria, Arch. Immunol. Arch. Immunol. Ther. Exp. 2012, 60, 267− 275. (25) Monier, M.; Nawar, N.; Abdel-Latif, D. A. Preparation and characterization of chelating fibers based on natural wool for removal of Hg(II), Cu(II) and Co(II) metal ions from aqueous solutions. J. Hazard. Mater. 2010, 184, 118−125.

Langmuir isotherm adsorption model and pseudo-second-order kinetics. The maximum uranium adsorption capacity of WoolAO@TiO2, acquired from the Langmuir isotherm, was 113.12 mg/g. The increase in specific surface area of Wool-AO@TiO2 after TiO2 functionalization may have led to an enhancement of adsorption capacity. It should also be noted that Wool-AO@ TiO2 showed good antibacterial activity, effectively inhibiting growth of the model bacteria S. aureus and E. coli with 95.2 and 90%, respectively. At the same time, the adsorption of uranium(VI) in bacterial environments was not negatively affected. Even after a four-cycle culture in the presence of bacteria, the adsorption capacity did not significantly decrease. Therefore, the synthesized antibacterial adsorbent may potentially be applicable for the extraction of uranium from seawater and promote the development of new types of efficient adsorption materials.

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ASSOCIATED CONTENT

S Supporting Information *

Detailed experimental procedures and compound characterization. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/ acs.iecr.7b04380. (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Phone: +86-28-8540-5839. Fax: +86-28-8540-5237. E-mail: [email protected]. ORCID

Haiming Cheng: 0000-0002-1686-5354 Author Contributions ∥

J.W. and Q.Y.L. made equal contributions to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for the financial support of the Radiochemistry 909 Project in the China Academy of Engineering Physics, the Key Research Program of Sichuan Province of China (2017GZ0268, 2017TD0010).

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REFERENCES

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