Research Article Cite This: ACS Sustainable Chem. Eng. 2018, 6, 2462−2473
A New Application of a Mesoporous Hybrid of Tungsten Oxide and Carbon as an Adsorbent for Elimination of Sr2+ and Co2+ from an Aquatic Environment Yanan Wang,† Huiyan Huang,‡ Shengxia Duan,†,‡ Xia Liu,† Ju Sun,† Tasawar Hayat,⊥,∥ Ahmed Alsaedi,⊥ and Jiaxing Li*,†,§,⊥ †
CAS Key Laboratory of Photovoltaic and Energy Conservation Materials, Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei 230031, P.R. China ‡ School of Chemical and Environmental Engineering, Wuyi University, Jiangmen 529020, China § Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Suzhou 215123, P.R. China ⊥ NAAM Research Group, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia ∥ Department of Mathematics, Quaid-I-Azam University, Islamabad 44000, Pakistan ABSTRACT: The mesoporous tungsten oxide and carbon (WOx/C) nanowire network was successfully synthesized using an environmentally friendly solvothermal method. The as-prepared composite was applied as an adsorbent for metal ion elimination from wastewater via batch experiments. The adsorption results suggested that the adsorption interactions between WOx/C and Sr2+ and Co2+ were pH-dependent, while the effect of ionic strength toward sorption capacity depended on the solution acidity and adsorbates. The sorption process followed the Langmuir model with the maximum sorption capacity of Sr2+ and Co2+ onto WOx/C being 175.0 and 326.0 mg/g at 308 K, respectively. Thermodynamic parameters, namely, ΔS°, ΔH°, and ΔG°, indicated an endothermic, but spontaneous adsorption process. All the exhibited results demonstrated that the as-synthesized WOx/C nanowire network has the potential to be an effective adsorbent for heavy metal ion remediation from aqueous solutions. KEYWORDS: Tungsten oxide and carbon, Sr2+, Co2+, adsorption
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INTRODUCTION With the increasing demand for energy and the fast consumption of fossil fuels, nuclear energy has been considered as a promising alternative to alleviate the resource shortage due to its effectiveness and cleanliness. However, environmentally hazardous nuclides are inevitably produced and can be released into the environment in processing of nuclear fuel and treatment of spent fuels, posing a threat to public health. Among the hazardous nuclides, strontium (Sr) and cobalt (Co), both in stable and in radioactive forms, are two nonnegligible toxic elements existing not only in nuclear waste repositories but also in petrochemical, mineral mining, and smelting wastewaters.1 Moreover, the development in advanced technology also increased the possibility of Sr and Co emission to the environment. For example, 90Sr, a pure β radiator usually derived from the fission process, has been applied to thickness gauge2 and radiotherapy.3 However, 90Sr is one of the most dangerous radionuclides for human beings due to its long halflife and chemical properties. Specifically, Sr2+ can be easily assimilated in the human body through the alimentary tract thereby depositing in the liver, lungs, and kidneys because of its high solubility. Once taken into the human body, Sr2+ can easily © 2017 American Chemical Society
replace the calcium (Ca) in bones and other human organs and tissues due to its similarity to Ca, causing anemia and leukemia, along with other chronic diseases.4,5 Moreover, the application of Co is even more extensive, ranging from Co-containing alloy materials of various properties6−8 to dyeing,9 electroplating,10 and so forth. The discharge of Co2+ by these aforementioned industries can cause severe threats to human health, such as asthma-like allergies, heart disease, thyroid damage, and bleeding, considering its non-biodegradable properties in natural conditions and accumulation propensity in living organisms. Therefore, it is crucial to restrict the concentration of Sr2+ and Co2+ to acceptable levels in the environment. Recently, numerous techniques have been developed for elimination of Sr2+ and Co2+ from aqueous solutions, including precipitation, adsorption, and ion-exchange. Among these methods, adsorption has been proven to be the most effective one with the advantages of simplicity, high efficiency, low cost, etc. Researchers have performed extensive work to investigate Received: October 27, 2017 Revised: December 4, 2017 Published: December 12, 2017 2462
DOI: 10.1021/acssuschemeng.7b03818 ACS Sustainable Chem. Eng. 2018, 6, 2462−2473
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ACS Sustainable Chemistry & Engineering
stronger chelating ability toward heavy metal ions and have been used to functionalize the inorganic adsorbents to improve their adsorption performance. Therefore, we envision that a combination of tungsten oxide 1D framework with carbonaceous materials would fabricate a superior adsorbent with unique heterogeneous surface and strong affinity for heavy metal ions and organic dyes in a one-pot and scalable approach. In this work, an inorganic−organic carbon encapsulated W18O49 hybrid network (WOx/C) was successfully fabricated via a simple one-pot solvothermal method and was adopted as adsorbent to remove heavy metal ions of Sr2+ and Co2+ from aqueous solution. Influencing factors, such as sorption temperature, pH, and ionic strength (I) were investigated. The results suggested that the WOx/C hybrid network can be potentially applied as an adsorbent for water purification.
appropriate adsorbents for removal of hazardous nuclides from aqueous solutions, including carbon materials,11−14 titanate materials,15 clay composites,16,17 chitosan-based materials,18,19 etc. However, these adsorbents either have poor adsorption properties or may produce secondary pollution during the synthetic or application process. For instance, graphene nanomaterials have presented desirable performance in the adsorption of Sr2+ and Co2+ due to the large surface area, abundant functional groups, and excellent dispersity in aqueous solution.20−22 However, recent research23−26 revealed that graphene nanomaterials released to the environment can be accumulated by organisms, which can subsequently interfere in their biophysical activities like metabolism, leading to unpredictable effects in the long run. Specifically, metal oxides have attracted great attention from many researchers for dangerous heavy metal ion treatment with the advantages of low cost, simple synthetic process, and desirable adsorption performance. Recent years have witnessed great progress in water purification techniques by applying metal oxides, such as iron oxides, aluminum oxides, zinc oxides, and manganese oxides.27−32 For example, Lukashev et al.33 reported a maximum sorption capacity of 0.43 mmol/g Co(II) onto mechanically activated γ-Fe2O3.34 A selective extraction method presented by Dong et al.35 revealed the importance of Mn and Fe oxides for Pb and Cd adsorption. In addition to inorganic heavy metal ions, the laterally grown ZnO nanorods on reduced graphene oxide hydrogel contributed to excellent methylene blue (MB) elimination efficiency because of improved photocatalytic activity.36 Although some achievements have been made with these metal oxides in the adsorption of heavy metal ions from aqueous solutions, limitations such as somewhat lower adsorption capacity, slow adsorption kinetics and lack of acid resistance restrict their practical application in water purification. Hence, it is imperative to explore new metal oxides with both remarkable adsorption performance and acid resistance. Tungsten oxides WO3−x (x = 0−1) are promising candidates for heavy metal ion adsorption due to their attractive properties such as uniform size and shape, resistance to acid, thermal stability, and low cytotoxicity.37−41 Therefore, tungsten oxides, especially W18O49, are favored by researchers from photoelectric to semiconductor fields. W18O49 was reported to be applied for heavy metal ion adsorption. Additionally, W18O49, as an interesting non-stoichiometric tungsten oxide, possesses abundant oxygen vacancies on the surface, which might provide many active sites for metal ion complexation. Furthermore, most metal oxides cannot compete with other materials in adsorption capacity in many circumstances, thereby limiting their application in water purification. To further improve its adsorption capacity, incorporating organic functional groups with favorable affinity to the heavy metal ions and organic dyes into the WOx, namely, inorganic−organic hybrid WOx-based composites, may be an effective approach. These organic functional groups including thiol, amino, carboxylic, and sulfur groups possess stronger complexation or chelating ability toward heavy metal ions and have been used to functionalize the inorganic adsorbents to improve their adsorption performance. Hu et al.42 synthesized Zn2GeO4-ethylenediamine inorganic− organic hybrid nanowires using ethylenediamine as solvent, which showed superb removal capacity for Pb2+. Carbonaceous materials via hydrothermal carbonization of glucose, with abundant hydrophilic functional groups, commonly possessed
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EXPERIMENTAL SECTION
Materials. Adsorbate (Sr2+ and Co2+) stock solutions were prepared by dissolving their nitrate salts (99.9%, Sigma−Aldrich) in 0.01 M HNO3 solution and then diluted to desired concentrations. All reagents in this experiment were commercially ordered and used without further purification. Deionized water was adopted for all experimental work. Preparation of WOx/C Inorganic−Organic Nanowire Network. A simple solvothermal method was adopted to produce WOx/C using WCl6 as a precursor and tri(ethylene glycol) as solvent. Specifically, 0.8 g of WCl6 was dissolved into 40 mL of tri(ethylene glycol) under vigorous stirring to form a precursor solution. Glucose (0.6 g, used as carbon source) was added into the precursor solution, and the mixture was stirred for 1 h. The mixed solution was transferred into a 100 mL Teflon-lined stainless steel autoclave and kept at 200 °C for 6 h. After naturally cooling to room temperature, the product was collected via centrifugation and washed with deionized water and ethanol several times to remove the inorganic and organic impurities. Finally, after freeze-drying overnight, the obtained samples are collected as WOx/C and WOx. Characterizations. The surface morphologies of pristine WOx/C coupled with WOx/C adsorbed Sr2+ and Co2+ were characterized through scanning electron microscopy (SEM, S-4800, field emission) equipped with a GENESIS4000 energy dispersive X-ray spectroscope. Fourier transform infrared spectroscopy (Nicolet-8700 FT−IR spectrophotometer) with KBr pellets was applied to verify the surface functional groups in the 4000−400 cm−1 region. X-ray powder diffraction (XRD), equipped with a Cu Kα radiation source (λ = 1.5406 Å) scanning from 20−80° with a step size of 0.02°, was also adopted to identify WOx/C samples before and after adsorption. In addition, X-ray photoelectron spectroscopy (XPS) was carried out on Thermo Escalab 250, conducting at 150 W with Al Kα radiation. Specific surface area was analyzed by N2 adsorption−desorption isotherm recorded from a Micromeritics ASAP 2010 surface area analyzer. Zeta potential was measured with Zetasizer Nano ZS (Malvern, England). Batch Sorption Experiment. The sorption experiments of Sr2+ and Co2+ onto WOx/C were performed in polyethylene tubes by batch techniques. In the process, the solution pH was adjusted by adding negligible amounts of 0.01−1 M HNO3 or NaOH solutions. The sorption isotherms were conducted at 288, 308, and 328 K at pH of 5.5 and 4.5, respectively, for Sr2+ and Co2+ to make sure that no precipitation existed within the concentration range of 2−27 mg/L for Sr2+ and 4−80 mg/L for Co2+. The suspension of WOx/C and NaNO3 was pre-equilibrated for 24 h, and then stock solution of Sr2+ and Co2+ was gradually injected into this prepared suspension. After being adjusted to the desired pH, the suspensions were immediately transferred to a shaker, constantly shaking for 24 h to reach complete reaction equilibrium. After that, the suspensions were centrifuged to separate the solid and liquid phase. The Sr2+ concentration of the supernatant was determined by inductively coupled plasma−atomic emission spectroscopy (ICP−AES, iCAP6000, Thermo Fisher 2463
DOI: 10.1021/acssuschemeng.7b03818 ACS Sustainable Chem. Eng. 2018, 6, 2462−2473
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ACS Sustainable Chemistry & Engineering
Figure 1. XRD patterns (A), FTIR spectra (B), ζ potential (C), and BET analysis (D) of the synthesized WOx/C.
Figure 2. XPS spectra of (A) low-resolution and (B) high-resolution W 4f, (C) O 1s, and (D) C 1s of WOx/C. Scientific) while Co2+ concentration was measured by atomic absorption spectroscopy (AAS-6300C, Shimadzu, Japan). The sorption capacity of metal ions (sorption percentage (%) and Qe (mg/g)) can be calculated according to the following equations:
sorption (%) =
Q e(mg/g) =
(C0 − Ce) × 100% C0
V (C0 − Ce) m
mass of WOx/C adsorbent and the total volume of the suspension, respectively. The reported experimental data were the average value of duplicate data within 5% relative errors.
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RESULTS AND DISCUSSION Characterization. XRD pattern was applied to characterize the crystal structure of the synthesized WOx/C material (Figure 1A). Two peaks located at 2θ 23.46° and 48.03° in pristine WOx/C correspond to (010) and (020) from the monoclinic phase of W18O49 with cell diameters of a = 18.23073 Å, b = 3.79557 Å, c = 14.11241 Å, and β = 116.1579° (JCPDS Card no.
(1)
(2)
where C0 (mg/L) is the initial concentration, Ce (mg/L) is the equilibrium concentration after adsorption, and m (g) and V (L) are the 2464
DOI: 10.1021/acssuschemeng.7b03818 ACS Sustainable Chem. Eng. 2018, 6, 2462−2473
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ACS Sustainable Chemistry & Engineering 71-2450), revealing the main component of WOx. The existence of carbon can be proved in the FT-IR spectra (Figure 1B), where carbon related functional groups were clearly observed in 2800− 2900 cm−1 (characteristic −CH stretching), 1710 and 1400 cm−1 for CO, 1620 cm−1 for CC, and 980 for C−O bonds.43 The abundant carbonaceous functional groups were ascribed to the possibly incomplete carbonization of glucose at the hydrothermal temperature of 200 °C on the surface of tungsten oxide,44 indicating the preparation of WOx/C. To investigate the surface charged species of WOx/C as a function of solution pH, the ζ potential analysis was conducted by determining the species’ activities in solution, and the result is given in Figure 1C. The negatively charged surface of WOx/C is probably due to the deprotonation of its surface functional groups such as −OH, −COOH, CO, etc., providing easier accessibility for positively charged contaminants. Figure 1D shows the N 2 adsorption−desorption isotherm of the mesoporous WOx/C. Based on the BET data, the specific surface area of mesoporous WOx/C nanowire network is calculated to be 92.5 m2/g, a large surface area for the immobilization of contaminants from aqueous solutions. XPS technique was applied to obtain further insight into the composition and surface functional groups of WOx/C. As shown in Figure 2A, the presence of a strong C 1s peak revealed that the surface of tungsten oxide was successfully functionalized by carbonaceous species during the synthetic process. The peaks at 491.88 and 428.49 eV were assigned to W 4p core level, while peaks at 259.81 and 246.60 eV corresponded to W 4d core level. The double peak appearing at 35.60 and 37.70 eV was assigned to W 4f7/2 and W 4f5/2 sublevels because of the spin-orbit splitting.45 The deconvolution of W 4f, O 1s, and C 1s XPS spectra are presented in Figure 2B−D, where the W 4f XPS spectra of WOx/C could be perfectly fitted by three oxidation states. The peaks appearing at 37.7 and 35.65 eV were associated with W6+.46 The peaks observed at binding energy of 36.5 and 34.86 eV corresponded to W5+.47 The rather short W−W distance of 0.26 nm and the oxygen vacancy occurring at the shear planes provided places for W5+ to be formed. Moreover, the peak found at 34.2 eV indicated the presence of W4+ oxidation state, which might be derived from the dismutation of W5+.48 The different oxidation states of W6+, W5+, and W4+ were the typical nonstoichiometric characteristics of W18O49 nanomaterials.47,49 All the results indicated a successful preparation of WOx/C. The O 1s XPS spectra (Figure 2C) exhibited two peaks, 530.41 and 532.22 eV, in accordance with the W−O−W bonds and the O atoms in the vicinity of an O vacancy in the W18O49 nanowire network50,51 or the residual water or C−O bonds derived from the residual adsorbed molecules.52 The C 1s spectra were deconvoluted to three peaks, corresponding to CO/O−CO, C−O, and CC, respectively (Figure 2D). The XPS results are totally conformed to the FT-IR analysis, revealing the generation of abundant carbonaceous species and various oxygen containing functional groups on the surface of WOx. The morphologies of WOx/C were detected through TEM to corroborate its nanowires morphology (Figure 3). The TEM image clearly showed that a large quantity of loose twisted nanowires with length up to several micrometers contained in the WOx/C network exhibited remarkable flexibility compare with pristine WOx, which was aggregated and assembled from the radial nanowires. These loose structures indicated that they are more conducive to the adsorption of pollutants. The diameter of the single WOx/C nanowires is ∼1−2 nm.
Figure 3. TEM image of WOx (A) and WOx/C (B).
The microstructure for the as-synthesized WOx/C is captured through SEM (Figure 4A,B). Figure 4A,B exhibits the
Figure 4. SEM images of (A) pristine, (C) Sr2+-adsorbed, and (E) Co2+-adsorbed WOx/C; (B, D, F) respective SEM images in higher magnification.
morphology of the WOx/C nanowire network, which consists of nanowires with diameter of several to dozens of nanometers and length of several hundred nanometers, adhering to and intertwining with each other to form porous structures, which provides large surface area and easy access for outside substances to its inner space. As a comparison, the surface morphologies of WOx/C after adsorption are also presented (Figure 4C−F). As depicted in Figure 4C,D, in spite of the existence of extra aggregates in the WOx/C, the basic porous inner structures can still be easily distinguished. This result suggested that Sr2+ ions entered into the pores of WOx/C and caused aggregation, while the number of Sr2+ ions was not enough to fill up the WOx/C. Although several bumps were observed in Co2+-adsorbed WOx/ C (Figure 4E), which seems to differ from the original one (Figure 4A) largely, the inner porous structure almost remains intact as a matter of fact (as shown in Figure 4F). This may result from the interaction of Co2+ ions mainly with the outer surface 2465
DOI: 10.1021/acssuschemeng.7b03818 ACS Sustainable Chem. Eng. 2018, 6, 2462−2473
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ACS Sustainable Chemistry & Engineering
Figure 5. Adsorption kinetics of (A) Sr2+ and (B) Co2+ on WOx/C and fitting to three kinetic equations: solid line for pseudo-first-order model, dashed line for pseudo-second-order model, and dotted line for intraparticle diffusion model; (C, D) linear plots of intraparticle diffusion model for Sr2+ and Co2+, m/V = 0.1 g/L, I = 0.01 M NaNO3, pHSr = 5.5, pHCo = 4.5, T = 288 K.
of WOx/C. According to the SEM images before and after adsorption, the adsorption mechanism between Sr2+ and WOx/ C seems to be inner-sphere complexation, while the Co2+ ions tend to be immobilized by WOx/C via outer-sphere chelation or ion exchange, which is in accordance with the adsorption results. Adsorption Performance. Kinetic Study. The adsorption kinetics is very important because it can reflect the ratecontrolling step of the adsorption process. The adsorption kinetics were studied at the concentrations of 0.1 g/L WOx/C, 21 mg/L Sr2+, and 80 mg/L Co2+ (Figure 5). The reaction equilibrium can be reached within 10 and 120 min for Sr2+ and Co2+, respectively. To obtain insights into the adsorption behavior of WOx/C toward the two heavy metal ions, three kinetic models, namely, pseudo-first-order, pseudo-second-order, and intraparticle diffusion models,53,54 were utilized to study the adsorption process. The equations of three models are given as follows: qt = qe(1 − e−k1t )
Table 1. Parameters for the Three Kinetic Models model
pseudo-firstorder
qt = k intt
0.5
+C
qt = qe(1 − e
−k1t
) Co2+
Sr2+ pseudosecondorder
2
qt =
k 2qe t 1 + k 2qet
Co2+
(3)
Sr2+
k 2qe t 1 + k 2qet
adsorbate Sr2+
2
qt =
equation (linearization)
intraparticle diffusion
(4)
qt = k intt
0.5
+C Co2+
(5)
parameters k1 = 0.407 min−1 qe = 87.780 mg· g−1 k1 = 0.152 min−1 qe = 105.291 mg·g−1 k2 = 0.0238 g· mg−1·min−1 qe = 88.602 mg· g−1 k2 = 0.0023 g· mg−1·min−1 qe = 111.100 mg·g−1 kint = 0.349 mg· g−1·min−0.5 C = 83.966 mg· g−1 kint = 1.938 mg· g−1·h−0.5 C = 81.848 mg· g−1
R2 0.996
0.946
0.997
0.981
0.937
0.814
chemisorption process as the rate-limiting step.55 The intraparticle diffusion is not the only rate controlling step in the adsorption reaction according to the nonzero value of C13 and multilinearity in Figure 5C,D, suggesting that the adsorption process onto WOx/C consists of several steps. Specifically, the heavy metal ions in the solution first transfer to the external surface of WOx/C, which can be reflected from the initial linear portion in Figure 5C,D. The second linear part stands for the gradual adsorption stage, in which the heavy metal ions diffuse through the pores of WOx/C. For the adsorption of Co2+ ions,
where qt (mg/g) and qe (mg/g) represent the adsorption amount at reaction time t and after equilibrium, k1 (min−1) and k2 (g·mg−1·min−1) are denoted as the kinetic adsorption rate constant of the first- and second-pseudo-kinetic models, respectively, kint (mg·g−1·min−0.5) is the intradiffusion rate constant, and C is a constant related to thickness and interlayer. The parameters and fitting coefficients are listed in Table 1. The adsorption process can be fitted by the pseudo-second-order model both for both metal ions with the correlation coefficient of 0.997 and 0.981, respectively, demonstrating a possible 2466
DOI: 10.1021/acssuschemeng.7b03818 ACS Sustainable Chem. Eng. 2018, 6, 2462−2473
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ACS Sustainable Chemistry & Engineering
Figure 6. Effect of pH and ionic strength on the sorption of (A) Sr2+ and (B) Co2+ onto WOx/C, in which orange spheres represent the percentage of metal ions remaining in the solution; the species distribution of (C) Sr2+ and (D) Co2+ as a function of pH in aqueous solution, C0 = 21 and 80 mg/L for Sr2+ and Co2+, respectively, m/V = 0.1 g/L, T = 288 K.
Figure 7. Sorption isotherms of (A) Sr2+ (pH 5.5) and (B) Co2+ (pH 4.5) at various temperatures as well as their fitting results, solid lines for Langmuir models and dotted lines for Freundlich models; plots of ln K° versus 1/T for (C) Sr2+ and (D) Co2+ coupled with their linear fittings, m/V = 0.1 g/L, I = 0.01 M NaNO3.
there is a final equilibrium stage in which the intraparticle diffusion begins to slow down due to the sharply decreased ions concentration in aqueous solution and the reduction of available adsorption sites on WOx/C. The slope of the linear portion can be interpreted as the indication of the rate of the adsorption process that the adsorption rate for Sr2+ is remarkable in the first 10 min and then decreases afterward. In contrast, the adsorption rate for Co2+ is much slower. The ever-decreasing adsorption rate with time can be explained as the ions diffusing into the
inner part of WOx/C blocking the pores so that the free path of heavy metal ions is narrowed. Effect of Solution Acidity and Ionic Strength. The influence of solution pH values on the sorption performance toward Sr2+ and Co2+ on WOx/C is exhibited in Figure 6. The results of the samples without adsorbent at varied solution pH were also given in Figure 6 to estimate the contribution of the precipitation process, from which we can learn that the precipitation process can be ignored for Sr2+ adsorption throughout the experimental 2467
DOI: 10.1021/acssuschemeng.7b03818 ACS Sustainable Chem. Eng. 2018, 6, 2462−2473
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ACS Sustainable Chemistry & Engineering Table 2. Parameters for the Langmuir and Freundlich Models Langmuir model
Freundlich model
adsorbate
T (K)
Cs,max (mg·g−1)
b (L·mg−1)
R2
KF (mg1−n·Ln·g−1)
n
R2
Sr2+
288 308 328 288 308 328
114.0 175.0 269.7 269.8 326.0 374.9
0.076 0.059 0.042 0.009 0.008 0.009
0.904 0.871 0.907 0.964 0.996 0.988
10.8 12.2 12.4 4.1 4.3 5.0
0.632 0.703 0.791 0.759 0.783 0.812
0.845 0.814 0.875 0.976 0.991 0.984
Co2+
where Ce (mg·L−1) is the concentration of adsorbate at equilibrium, Q e (mg·g −1 ) is the amount of adsorbate immobilized by WOx/C, Cs,max represents the maximum sorption capacity of WOx/C toward an adsorbate, corresponding to a complete adsorbate coverage on WOx/C’s surface at high concentration of an adsorbate, and b (L·g−1) refers to the Langmuir constant, while KF and n in the Freundlich model are denoted as Freundlich constants with respect to the sorption capacity and sorption intensity, respectively. As depicted in Figure 7A,B, Langmuir model exhibited a better fitting results compared to the Freundlich model for both adsorbates’ sorption. Table 2 lists the relative parameters of both Langmuir and Freundlich models. The saturated sorption capacity of WOx/C derived from the Langmuir model was 175.0 and 326.0 mg·g−1 for Sr2+ and Co2+ at T = 308 K, superior to many other reported adsorbents (Table 3).
pH while for Co2+ the effect of precipitation is unnoticeable when solution pH < 7. In addition, the sorption capacity increased with increasing pH values in the range of 2.0−6.0, which could be explained by the electrostatic attraction between positively charged metal species (Figure 6C,D) and increasingly negatively charged WOx/C surface (Figure 1C). However, when the solution pH continued to escalate, the sorption behavior of the two metal ions showed apparent differences (Figure 6A,B): for Sr2+, the adsorption capacity remained the maximum value at pH 6.0−9.0, while WOx/C exhibited an increasing sorption tendency throughout the experimental pH toward Co2+ and the increment in the pH range of 7.0−8.0 was noticeable. A possible explanation for this phenomenon is that the binding sites for Sr2+ ions on the WOx/C have reached saturation at pH 6.0 and further increment in solution pH could not lead to larger adsorption capacity. In addition, Figure 6A also demonstrates that ionic strength has negligible impact on Sr2+ sorption onto WOx/C in the pH range from 2.0−6.0, which demonstrated the inner-sphere chelation,56 which confirms the previous SEM analysis result. When solution pH exceeded 6.0, although very little, the restricting effect of high ionic strength on Sr2+ adsorption can still be observed, suggesting an ion exchange adsorption mechanism in basic solution. The sorption capacity of Co2+ was positively related to the solution pH in the whole range, and sorption capacity in ionic strength of 0.001 M NaNO3 was larger than that of both 0.01 M and 0.1 M NaNO3 (Figure 6B). The consistently increasing trend resulted from the positively charged Co2+ ions (Figure 6D) and gradually increasing negatively charged WOx/C surface with the increase of pH. The ionic strength dependence revealed an ionic exchange sorption mechanism. The ever-decreasing discrepancy under various ionic strength conditions at high pH might be related to the production of Co(OH)2(aq) (Figure 6D). As a result, solution pH of 5.5 and 4.5 was determined for the following thermodynamic study of Sr2+ and Co2+ adsorption onto WOx/C, respectively, to ensure that no precipitation occurs during the adsorption process. Sorption Isotherms and Thermodynamics. To investigate the thermodynamic properties of metal ion sorption onto WOx/ C, the sorption isotherms of Sr2+and Co2+ were measured at three different temperatures (Figure 7A,B). Considering the precipitation possibility of metal ions in basic solutions, the isotherms were obtained at low pH conditions, 5.5 for Sr2+ and 4.5 for Co2+. The Langmuir and Freundlich models are denoted as follows: Qe =
Table 3. Sorption Capacity of Co(II) and Sr(II) by Some Adsorbents
Q e = KFCe n
adsorbate
T (K)
6.8 6.8 4.5
Co(II) Co(II) Co(II)
303 303 308
zero-valent iron nanoparticles nZVI−graphene composite γ-Fe2O3 nanotubes graphene oxide− magnetite hybrid Fe3O4 WOx/C
>6.5
Co(II)
5.7
Co(II)
303
6.0 7.0
Co(II) Co(II)
298 318
60.6 23
6.9 5.5
Co(II) Sr(II)
295 308
17.4 175
thiacalixarenefunctionalized GO titanate nanotubes magnetic zeolite composite APTES-Mt graphene oxide− magnetite hybrid
7.0
Sr(II)
298
101
8.0
Sr(II) Sr(II)
298
91.7 83.7
63 64
Sr(II) Sr(II)
301 318
65.6 18
65 60
ozonized GO GO WOx/C
8.5 7.0
Cs,max (mg·g−1) 372 198 326
ref 11
172
this study 57
134
58 59 60 61 this study 62
Thermodynamic Data. Further analysis about how temperature affected adsorbate sorption efficiency onto WOx/C was carried out as well. Figure 7C,D presented the plots of ln K° versus 1/T and their linear fitting lines, based on which the thermodynamic parameters, namely, ΔG°, ΔS°, and ΔH°, are calculated according to the following equations:
bCs,maxCe 1 + bCe
pH
adsorbent
(6) (7)
ΔG° = −RT ln K ° 2468
(8) DOI: 10.1021/acssuschemeng.7b03818 ACS Sustainable Chem. Eng. 2018, 6, 2462−2473
Research Article
ACS Sustainable Chemistry & Engineering ΔS° ΔH ° − (9) R RT where K° and R (8.314 J mol−1·K−1) represent the sorption equilibrium constant and the ideal gas constant and T is the temperature in kelvin. According to eq 9, ΔS° and ΔH° can be calculated by multiplying R and −R with the intercept and slope in Figure 7C,D, respectively. As shown in Table 4, the negative
Possible Adsorption Mechanism. A comparison adsorption experiment was conducted to determine whether the high adsorption capacity toward Sr2+ and Co2+ was attributed to the WOx or the introduced carbonaceous species and oxygen containing functional groups in functionalization process. Herein, reacting conditions using single WOx and WOx/C samples as adsorbent were kept the same for the Sr2+ and Co2+ adsorption. As depicted in Figure 9A,B, the sorption isotherms of the two samples exhibited similar trend except that WOx/C had a higher adsorption capacity than WOx for both Sr2+ and Co2+, implying that carbon functionalization on WOx was conducive to metal ion immobilization. But which part of WOx/ C is responsible for the metal ion binding remains unclear. Therefore, characterization of WOx/C after metal ion loading was collected and analyzed. From Figure 9C, it can be clearly seen that no predominant new peaks but the (010) and (020) peak shifting to a slightly lower diffraction angle was observed in Sr2+- and Co2+-adsorbed WOx/C compared to the pristine WOx/C (Figure 1A), from which we could conclude that the adsorption of Sr2+ and Co2+ barely affected its lattice structure apart from the slightly expanded interlayer spacing because of outer heavy metal ion intrusion. The FT-IR spectra of the raw WOx/C and metal ionloaded WOx/C were measured to detect the surface functional group changes before and after adsorption, as exhibited in Figure 9D. The characteristic band at 3423 cm−1 indicated the vibration of O−H of water arising from the hydrothermal carbonization process. The absorption band in the region 580−940 cm−1 was ascribed to the stretching vibration of short WO bonds, while small bands around 819 and 725 cm−1 were attributed to the O− W−O stretching modes.67 Moreover, the peaks at 655 and 582 cm−1 were related to the W−O−W stretching vibration.68 Meanwhile, the peak at 1623 cm−1 is associated with the W− OH, also known as the oxygen vacancies. The disappearance of the small peak at ∼980 cm−1, which was assigned to the C−O vibration, was observed for both Sr2+- and Co2+-loaded samples compared to the pristine WOx/C (Figure 1B). This is probably because of the binding reaction between C−O and heavy metal ions, suggesting that the enhanced adsorption capacity of WOx/ C is mainly arising from the introduced carbonaceous functional groups. Considering that the tiny changes can be overlapped by the strong peaks in FT-IR spectra, XPS analysis was applied to detect changes in bonds. In the full XPS spectra, characteristic peaks of heavy metal ions were observed at 133.94 and 781.92 eV, respectively, for Sr2+ and Co2+ after sorption (Figure 10A), confirming the strong sorption ability of WOx/C. After adsorption, only two sharp peaks could be observed in the deconvolution XPS spectra of W 4f (Figure 10B,C), suggesting partial conversion of W5+ to W4+ and W6+ in comparison to pristine WOx/C (Figure 2B). The detailed information about each peak, including the binding energy, corresponding oxidation state, and functional groups as well as their percentage in WOx/C before and after adsorption are listed in Tables 5 and 6. Slight shifting of binding energy could be observed for both metal ion-loaded samples, similar to previously reported results.69 The fitted O 1s results of heavy metal ion-loaded WOx/C (Figure 10D,E) showed a conformed trend toward higher binding energy (0.24 eV for Sr and 0.34 eV for Co) relative to pure WOx/C (as shown in Table 5), indicating a change of the local bonding environments.70 The decreased percentage of O vacancies after heavy metal ion adsorption (as shown in Table 6) suggests that the adsorbed metal ions may take up the O vacancies through the formation of
ln K ° =
Table 4. Thermodynamic Parameters for Heavy Metal Ion Sorption on WOx/C. adsorbate 2+
Sr
Co2+
T (K)
ΔG° (kJ·mol−1)
ΔS° (J·mol−1·K−1)
ΔH° (kJ·mol−1)
288 308 328 288 308 328
−5.7(2) −5.7(6) −5.8 −2.0 −2.4 −3.2
34.9
5.0
29.4
6.5
ΔG° values indicate spontaneous sorption processes of Sr2+ and Co2+. Increasing sorption temperature gave even more negative ΔG°, suggesting a sorption process favored by higher temperature, which is in accordance with the fact that higher reaction temperature always came along with larger sorption capacity. The positive value of ΔH° (34.9 and 6.5 kJ·mol−1 for Sr2+ and Co2+, respectively) revealed endothermic sorption processes. The most widely accepted explanation for this phenomenon was that the energy absorbed for the dehydration of ionic adsorbates from their aqueous complex exceeded that of releasing from their attaching process to the solid surface of WOx/C.66 The positive ΔS° (34.9 and 29.4 for Sr2+ and Co2+, respectively) indicated structural changes during the immobilization process. Based on the calculated data, it can be concluded that the disorder of the solid-solution system increased with the order of Co2+ and Sr2+. Additionally, the recyclability of WOx/C was investigated by five successive adsorption−desorption experiments, using 0.1 M HNO3 solution as the desorption agent. As depicted in Figure 8,
Figure 8. Adsorption recyclability of Sr2+ and Co2+ on WOx/C over five cycles, pH 5.5 for Sr2+ and 4.5 for Co2+, m/V = 0.1 g/L, T = 288 K.
a slight decline in adsorption percentage was observed for both the Sr2+ and Co2+ after five cycles, from ∼38% to ∼34% for Sr2+ and from ∼15% to ∼12% for Co2+, which could be the result of the mass loss of the adsorbent during adsorption/desorption process. The regeneration results also suggested that the prepared WOx/C possessed desirable recyclability and recoverability when used as an adsorbent for heavy metal ion elimination from aquatic environments. 2469
DOI: 10.1021/acssuschemeng.7b03818 ACS Sustainable Chem. Eng. 2018, 6, 2462−2473
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ACS Sustainable Chemistry & Engineering
Figure 9. Adsorption isotherms of (A) Sr and (B) Co at 328 K by WOx and WOx/C; (C) XRD patterns and (D) FTIR spectra of heavy metal ion loaded WOx/C.
Figure 10. XPS spectra of Sr2+- and Co2+-loaded WOx/C (A) and corresponding deconvolution of W 4f, O 1s, and C 1s spectra (B, D, and F for Sr2+ loaded WOx/C and C, E, and G for Co2+ loaded WOx/C).
eV decrease after Sr2+ and Co2+ immobilization, respectively (Table 5). A remarkable decline of C−O functional groups in C 1s spectra after adsorption, from 43% to 26% for Sr2+ and 32% for Co2+, is presented in Table 6, implying binding of Sr2+−OC and Co2+−OC for Sr2+ and Co2+ with WOx/C, respectively. To summarize, the high adsorption capacity of WOx/C toward Sr2+
W−O−Sr and W−O−Co bonds. The deconvoluted C 1s spectra are exhibited in Figure 10F,G. The C 1s spectra consist of three peaks corresponding to CO/O−CO, C−O, and CC, respectively. Contrary to the O 1s spectra, a slight shift to lower binding energy of WOx/C after adsorption was observed, especially for the peak referring to C−O bond with 0.27 and 0.51 2470
DOI: 10.1021/acssuschemeng.7b03818 ACS Sustainable Chem. Eng. 2018, 6, 2462−2473
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ACS Sustainable Chemistry & Engineering
Program Development of Jiangsu Higher Education Institutions is acknowledged.
Table 5. Binding Energy and Assignment of W 4f and O 1s XPS Spectral Bands for Pure and Metal Ion-Loaded WOx/C
■
heavy metal ionloaded WOx/C (eV) element W 4f
O 1s C 1s
Sr2+
WOx/C (eV) 37.7 35.7 36.5 34.9 34.2 532.2 530.4 286.6 285.8 284.6
37.8 35.7 36.8 35.6 34.8 532.6 530.6 286.6 285.5 284.6
Co2+
assignments
37.8 36.6 36.4 35.4 35.0 532.6 530.8 286.5 285.2 284.6
6+
(1) Liu, X.; Wang, X.; Li, J.; Wang, X. Ozonated graphene oxides as high efficient sorbents for Sr(II) and U(VI) removal from aqueous solutions. Sci. China: Chem. 2016, 59, 869−877. (2) Gardner, R. P.; Metwally, W. A.; Shehata, A. A semi-empirical model for a 90Sr beta-particle transmission thickness gauge for aluminum alloys,. Nucl. Instrum. Methods Phys. Res., Sect. B 2004, 213, 357−363. (3) Fraunholz, I. B.; Gerstenhauer, A.; Bottcher, H. D. Results of postoperative (90)Sr radiotherapy of keloids in view of patients’ subjective assessment. Strahlenther. Onkol. 2005, 181, 724−729. (4) Blaschko, S. D.; Chi, T.; Miller, J.; Flechner, L.; Fakra, S.; Kapahi, P.; Kahn, A.; Stoller, M. L. Strontium substitution for calcium in lithogenesis. J. Urol. 2013, 189, 735−739. (5) Wang, M.; Xu, L.; Peng, J.; Zhai, M.; Li, J.; Wei, G. Adsorption and desorption of Sr(II) ions in the gels based on polysaccharide derivates. J. Hazard. Mater. 2009, 171, 820−826. (6) Sato, J.; Omori, T.; Ohnuma, I.; Ishida, K.; Oikawa, K.; Kainuma, R. Cobalt-base high-temperature alloys. Science 2006, 312, 90−91. (7) Inoue, A.; Kong, F. L.; Man, Q. K.; Shen, B. L.; Li, R. W.; AlMarzouki, F. Development and applications of Fe- and Co-based bulk glassy alloys and their prospects. J. Alloys Compd. 2014, 615, S2−S8. (8) Han, Y.; Inoue, A.; Kong, F. L.; Chang, C. T.; Shu, S. L.; Shalaan, E.; Al-Marzouki, F. Softening and good ductility for nanocrystaldispersed amorphous Fe−Co−B alloys with high saturation magnetization above 1.7 T. J. Alloys Compd. 2016, 657, 237−245. (9) Gilabert, J.; Palacios, M. D.; Sanz, V.; Mestre, S. Solution combustion synthesis of (Co,Ni)Cr2O4 pigments: Influence of initial solution concentration. Ceram. Int. 2017, 43, 10032−10040. (10) Glushkova, M. O.; Ved, M. V.; Sakhnenko, M. D. Corrosion properties of cobalt-silver alloy electroplates. Mater. Sci. 2013, 49, 292− 297. (11) Liu, X.; Huang, Y.; Duan, S.; Wang, Y.; Li, J.; Chen, Y.; Hayat, T.; Wang, X. Graphene oxides with different oxidation degrees for Co(II) ion pollution management. Chem. Eng. J. 2016, 302, 763−772. (12) Duan, S.; Wang, Y.; Liu, X.; Shao, D.; Hayat, T.; Alsaedi, A.; Li, J. Removal of U(VI) from aqueous solution by amino functionalized flake graphite prepared by plasma treatment. ACS Sustainable Chem. Eng. 2017, 5, 4073−4085. (13) Duan, S.; Li, J.; Liu, X.; Wang, Y.; Zeng, S.; Shao, D.; Hayat, T. HF-Free synthesis of nanoscale metal−organic framework NMIL100(Fe) as an efficient dye adsorbent. ACS Sustainable Chem. Eng. 2016, 4, 3368−3378. (14) Fang, F.; Kong, L.; Huang, J.; Wu, S.; Zhang, K.; Wang, X.; Sun, B.; Jin, Z.; Wang, J.; Huang, X.-J.; Liu, J. Removal of cobalt ions from aqueous solution by an amination graphene oxide nanocomposite. J. Hazard. Mater. 2014, 270, 1−10. (15) Kohli, V.; Zhang, Z.; Park, C.; Fenter, P. Rb+ and Sr2+ Adsorption at the TiO2 (110)-electrolyte interface observed with resonant anomalous X-ray reflectivity. Langmuir 2010, 26, 950−958. (16) Lazarevic, S.; Jankovic-Castvan, I.; Jovanovic, D.; Milonjic, S.; Janackovic, D.; Petrovic, R. Adsorption of Pb2+, Cd2+ and Sr2+ ions onto natural and acid-activated sepiolites. Appl. Clay Sci. 2007, 37, 47−57. (17) Smiciklas, I.; Dimovic, S.; Plecas, I. Removal of Cs1+, Sr2+ and Co2+ from aqueous solutions by adsorption on natural clinoptilolite. Appl. Clay Sci. 2007, 35, 139−144. (18) Wu, S.-P.; Dai, X.-Z.; Kan, J.-R.; Shilong, F.-D.; Zhu, M.-Y. Fabrication of carboxymethyl chitosan−hemicellulose resin for adsorptive removal of heavy metals from wastewater. Chin. Chem. Lett. 2017, 28, 625−632. (19) Zhu, Y.; Bai, Z.-S.; Wang, H.-L. Microfluidic synthesis of thiourea modified chitosan microsphere of high specific surface area for heavy metal wastewater treatment. Chin. Chem. Lett. 2017, 28, 633−641. (20) Chen, H.; Li, J.; Shao, D.; Ren, X.; Wang, X. Poly(acrylic acid) grafted multiwall carbon nanotubes by plasma techniques for Co(II) removal from aqueous solution. Chem. Eng. J. 2012, 210, 475−481.
W W6+ W5+ W5+ W4+ O vacancy W−O−W CO/O−CO C−O CC
Table 6. Fraction (%) of Oxidation States and Functional Groups in High-Resolution W 4f, O 1s, and C 1s Spectra of Pure and Sr2+ and Co2+ Loaded WOx/C WOx/C
WOx/C + Sr
WOx/C + Co
84 14 2 49 51 9 43 48
87 9 5 32 68 21 25 54
88 8 4 28 72 21 32 47
6+
W W5+ W4+ O vacancy W−O−W CO/O−CO C−O CC
and Co2+ is the synergistic result of O vacancies and C−O functional groups.
■
CONCLUSION A WOx/C nanowire network was successfully fabricated, and its sorption capacity and efficiency toward Sr2+ and Co2+ were examined. The immobilization of Sr2+ was processed via innersphere complexes, while ionic exchange or outer-sphere complexation was applied for Co2+ sorption. Spectroscopic analysis revealed that the C−O functional groups and O vacancies provided by WOx/C are active sorption sites for adsorbate sorption from aqueous solutions. The calculated maximum sorption capacity was 175.0 and 326.0 mg/g for Sr2+ (pH 5.5) and Co2+ (pH 4.5) at 308 K, respectively. This study provided a potential application of WOx/C as an adsorbent for metal ion removal from aqueous solutions, considering its easy fabrication, excellent sorption efficiency, and easy separation process.
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REFERENCES
AUTHOR INFORMATION
Corresponding Author
*Tel: +86-551-65596617. E-mail:
[email protected] (J. Li). ORCID
Jiaxing Li: 0000-0002-7683-2482 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS Financial support from National Natural Science Foundation of China (21677146) and the Jiangsu Provincial Key Laboratory of Radiation Medicine and Protection and the Priority Academic 2471
DOI: 10.1021/acssuschemeng.7b03818 ACS Sustainable Chem. Eng. 2018, 6, 2462−2473
Research Article
ACS Sustainable Chemistry & Engineering (21) Sun, Y.; Shao, D.; Chen, C.; Yang, S.; Wang, X. Highly efficient enrichment of radionuclides on graphene oxide-supported polyaniline. Environ. Sci. Technol. 2013, 47, 9904−9910. (22) Chang, K.; Li, X.; Liao, Q.; Hu, B.; Hu, J.; Sheng, G.; Linghu, W.; Huang, Y.; Asiri, A. M.; Alamry, K. A. Molecular insights into the role of fulvic acid in cobalt sorption onto graphene oxide and reduced graphene oxide. Chem. Eng. J. 2017, 327, 320−327. (23) Chen, Y.; Ren, C.; Ouyang, S.; Hu, X.; Zhou, Q. Mitigation in multiple effects of graphene oxide toxicity in zeebrafish embryogenesis driven by humic acid. Environ. Sci. Technol. 2015, 49, 10147−10154. (24) Yousefi, M.; Dadashpour, M.; Hejazi, M.; Hasanzadeh, M.; Behnam, B.; de la Guardia, M.; Shadjou, N.; Mokhtarzadeh, A. Antibacterial activity of graphene oxide as a new weapon nanomaterial to combat multidrug-resistance bacteria. Mater. Sci. Eng., C 2017, 74, 568−581. (25) Dziewiecka, M.; Karpeta-Kaczmarek, J.; Augustyniak, M.; RostRoszkowska, M. Short-term in vivo exposure to graphene oxide can cause damage to the gut and testis. J. Hazard. Mater. 2017, 328, 80−89. (26) Wang, Y.; Liu, X.; Huang, Y.; Hayat, T.; Alsaedi, A.; Li, J. Interaction mechanisms of U(VI) and graphene oxide from the perspective of particle size distribution. J. Radioanal. Nucl. Chem. 2017, 311, 209−217. (27) Zhao, Y.; Li, J.; Zhao, L.; Zhang, S.; Huang, Y.; Wu, X.; Wang, X. Synthesis of amidoxime-functionalized Fe3O4@SiO2 core−shell magnetic microspheres for highly efficient sorption of U(VI). Chem. Eng. J. 2014, 235, 275−283. (28) Song, W.; Liu, M.; Hu, R.; Tan, X.; Li, J. Water-soluble polyacrylamide coated-Fe3O4 magnetic composites for high-efficient enrichment of U(VI) from radioactive wastewater. Chem. Eng. J. 2014, 246, 268−276. (29) Zhang, S.; Yang, H.; Huang, H.; Gao, H.; Wang, X.; Cao, R.; Li, J.; Xu, X.; Wang, X. Unexpected ultrafast and high adsorption capacity of oxygen vacancy-rich WOx/C nanowire networks for aqueous Pb2+ and methylene blue removal. J. Mater. Chem. A 2017, 5, 15913−15922. (30) de Rudder, J.; Van de Wiele, T.; Dhooge, W.; Comhaire, F.; Verstraete, W. Advanced water treatment with manganese oxide for the removal of 17 alpha-ethynylestradiol (EE2). Water Res. 2004, 38, 184− 192. (31) Kim, K.-J.; Jang, A. Evaluation of natural organic matter adsorption on Fe-Al binary oxide: Comparison with single metal oxides. Chemosphere 2017, 185, 247−257. (32) Alvarez-Ayuso, E.; Garcia-Sanchez, A.; Querol, X. Adsorption of Cr(VI) from synthetic solutions and electroplating wastewaters on amorphous aluminium oxide. J. Hazard. Mater. 2007, 142, 191−198. (33) Lukashev, R. V.; Zanaveskin, K. L.; Kuz’min, A. G. Sorption of Co(II) ions onto mechanically activated gamma-Fe2O3 powders. Russ. J. Appl. Chem. 2014, 87, 1359−1363. (34) Wang, B.; Wu, H.; Yu, L.; Xu, R.; Lim, T. T.; Lou, X. W. D. Template-free formation of uniform urchin-like alpha-FeOOH hollow spheres with superior capability for water treatment. Adv. Mater. 2012, 24, 1111−1116. (35) Dong, D. M.; Nelson, Y. M.; Lion, L. W.; Shuler, M. L.; Ghiorse, W. C. Adsorption of Pb and Cd onto metal oxides and organic material in natural surface coatings as determined by selective extractions: new evidence for the importance of Mn and Fe oxides. Water Res. 2000, 34, 427−436. (36) Luan, V. H.; Tien, H. N.; Hur, S. H. Fabrication of 3D structured ZnO nanorod/reduced graphene oxide hydrogels and their use for photo-enhanced organic dye removal. J. Colloid Interface Sci. 2015, 437, 181−186. (37) Mu, W.; Yu, Q.; Li, X.; Wei, H.; Jian, Y. Efficient removal of Cs+ and Sr2+ from aqueous solution using hierarchically structured hexagonal tungsten trioxide coated Fe3O4. Chem. Eng. J. 2017, 319, 170−178. (38) Hai, G.; Huang, J.; Cao, L.; Jie, Y.; Li, J.; Wang, X.; Zhang, G. Influence of oxygen deficiency on the synthesis of tungsten oxide and the photocatalytic activity for the removal of organic dye. J. Alloys Compd. 2017, 690, 239−248.
(39) Zheng, H.; Ou, J. Z.; Strano, M. S.; Kaner, R. B.; Mitchell, A.; Kalantar-zadeh, K. Nanostructured tungsten oxideproperties, synthesis, and applications. Adv. Funct. Mater. 2011, 21, 2175−2196. (40) Li, Y.; Luo, W.; Qin, N.; Dong, J.; Wei, J.; Li, W.; Feng, S.; Chen, J.; Xu, J.; Elzatahry, A. A.; Es-Saheb, M. H.; Deng, Y.; Zhao, D. Highly ordered mesoporous tungsten oxides with a large pore size and crystalline framework for H2S sensing. Angew. Chem., Int. Ed. 2014, 53, 9035−9040. (41) Zhu, Y.; Zhao, Y.; Ma, J.; Cheng, X.; Xie, J.; Xu, P.; Liu, H.; Liu, H.; Zhang, H.; Wu, M.; Elzatahry, A. A.; Alghamdi, A.; Deng, Y.; Zhao, D. Mesoporous tungsten oxides with crystalline framework for highly sensitive and selective detection of foodborne pathogens. J. Am. Chem. Soc. 2017, 139, 10365−10373. (42) Yu, L.; Zou, R.; Zhang, Z.; Song, G.; Chen, Z.; Yang, J.; Hu, J. A Zn2GeO4-ethylenediamine hybrid nanoribbon membrane as a recyclable adsorbent for the highly efficient removal of heavy metals from contaminated water,. Chem. Commun. 2011, 47, 10719−10721. (43) Qin, Y.; Zhang, X.; Liu, Y.; Xie, W. Highly aligned array of W18O49/CuO core−shell nanorods and its promising NO2 sensing properties. J. Alloys Compd. 2016, 673, 364−371. (44) Qian, H.-S.; Yu, S.-H.; Luo, L.-B.; Gong, J.-Y.; Fei, L.-F.; Liu, X.M. Synthesis of uniform Te@carbon-rich composite nanocables with photoluminescence properties and carbonaceous nanofibers by the hydrothermal carbonization of glucose. Chem. Mater. 2006, 18, 2102− 2108. (45) Saleem, M.; Al-Kuhaili, M. F.; Durrani, S. M. A.; Hendi, A. H. Y.; Bakhtiari, I. A.; Ali, S. Influence of hydrogen annealing on the optoelectronic properties of WO3 thin films. Int. J. Hydrogen Energy 2015, 40, 12343−12351. (46) Chang, X.; Dong, L.; Yin, Y.; Sun, S. A novel composite photocatalyst based on in situ growth of ultrathin tungsten oxide nanowires on graphene oxide sheets,. RSC Adv. 2013, 3, 15005−15013. (47) Jeon, S.; Yong, K. Direct synthesis of W18O49 nanorods from W2N film by thermal annealing. Nanotechnology 2007, 18, 245602− 245609. (48) Chen, P.; Qin, M.; Zhang, D.; Chen, Z.; Jia, B.; Wan, Q.; Wu, H.; Qu, X. Combustion synthesis and excellent photocatalytic degradation properties of W18O49. CrystEngComm 2015, 17, 5889−5894. (49) Guo, C.; Yin, S.; Dong, Q.; Sato, T. The near infrared absorption properties of W18O49,. RSC Adv. 2012, 2, 5041−5043. (50) Lei, F.; Sun, Y.; Liu, K.; Gao, S.; Liang, L.; Pan, B.; Xie, Y. Oxygen vacancies confined in ultrathin indium oxide porous sheets for promoted visible-light water splitting. J. Am. Chem. Soc. 2014, 136, 6826−6829. (51) Sun, Y.; Wang, W.; Qin, J.; Zhao, D.; Mao, B.; Xiao, Y.; Cao, M. Oxygen vacancy-rich mesoporous W18O49 nanobelts with ultrahigh initial Coulombic efficiency toward high-performance lithium storage, Electrochimica. Electrochim. Acta 2016, 187, 329−339. (52) Guo, C.; Yin, S.; Yan, M.; Kobayashi, M.; Kakihana, M.; Sato, T. Morphology-controlled synthesis of W18O49 nanostructures and their near-infrared absorption properties. Inorg. Chem. 2012, 51, 4763−4771. (53) Gao, Q.; Xie, J.-F.; Shao, Y.-T.; Chen, C.; Han, B.; Xia, K.-S.; Zhou, C.-G. Ultrafast and high-capacity adsorption of Gd(III) onto inorganic phosphorous acid modified mesoporous SBA-15. Chem. Eng. J. 2017, 313, 197−206. (54) Zhang, S.; Gao, H.; Li, J.; Huang, Y.; Alsaedi, A.; Hayat, T.; Xu, X.; Wang, X. Rice husks as a sustainable silica source for hierarchical flower-like metal silicate architectures assembled into ultrathin nanosheets for adsorption and catalysis. J. Hazard. Mater. 2017, 321, 92−102. (55) Zou, Y.; Wang, X.; Ai, Y.; Liu, Y.; Li, J.; Ji, Y.; Wang, X. Coagulation behavior of graphene oxide on nanocrystallined Mg/Al layered double hydroxides: Batch experimental and theoretical calculation study. Environ. Sci. Technol. 2016, 50, 3658−3667. (56) Fuller, A. J.; Shaw, S.; Peacock, C. L.; Trivedi, D.; Burke, I. T. EXAFS study of Sr sorption to Illite, goethite, chlorite, and mixed sediment under hyperalkaline conditions. Langmuir 2016, 32, 2937− 2946. 2472
DOI: 10.1021/acssuschemeng.7b03818 ACS Sustainable Chem. Eng. 2018, 6, 2462−2473
Research Article
ACS Sustainable Chemistry & Engineering (57) Ü züm, Ç .; Shahwan, T.; Eroğlu, A. E.; Lieberwirth, I.; Scott, T. B.; Hallam, K. R. Application of zero-valent iron nanoparticles for the removal of aqueous Co2+ ions under various experimental conditions. Chem. Eng. J. 2008, 144, 213−220. (58) Xing, M.; Wang, J. Nanoscaled zero valent iron/graphene composite as an efficient adsorbent for Co(II) removal from aqueous solution. J. Colloid Interface Sci. 2016, 474, 119−128. (59) Roy, A.; Bhattacharya, J. A binary and ternary adsorption study of wastewater Cd(II), Ni(II) and Co(II) by γ-Fe2O3 nanotubes,. Sep. Purif. Technol. 2013, 115, 172−179. (60) Tayyebi, A.; Outokesh, M.; Moradi, S.; Doram, A. Synthesis and characterization of ultrasound assisted “graphene oxide−magnetite” hybrid, and investigation of its adsorption properties for Sr(II) and Co(II) ions. Appl. Surf. Sci. 2015, 353, 350−362. (61) Uheida, A.; Salazar-Alvarez, G.; Bjorkman, E.; Yu, Z.; Muhammed, M. Fe3O4 and gamma-Fe2O3 nanoparticles for the adsorption of Co2+ from aqueous solution. J. Colloid Interface Sci. 2006, 298, 501−507. (62) Zhang, P.; Wang, Y.; Zhang, D. Removal of Nd(III), Sr(II), and Rb(I) Ions from aqueous solution by thiacalixarene-functionalized graphene oxide composite as an adsorbent. J. Chem. Eng. Data 2016, 61, 3679−3691. (63) Ryu, J.; Kim, S.; Hong, H.-J.; Hong, J.; Kim, M.; Ryu, T.; Park, I.S.; Chung, K.-S.; Jang, J. S.; Kim, B.-G. Strontium ion (Sr2+) separation from seawater by hydrothermally structured titanate nanotubes: Removal vs. recovery. Chem. Eng. J. 2016, 304, 503−510. (64) Faghihian, H.; Moayed, M.; Firooz, A.; Iravani, M. Evaluation of a new magnetic zeolite composite for removal of Cs+ and Sr2+ from aqueous solutions: kinetic, equilibrium and thermodynamic studies. C. R. Chim. 2014, 17, 108−117. (65) Wu, P.; Dai, Y.; Long, H.; Zhu, N.; Li, P.; Wu, J.; Dang, Z. Characterization of organo-montmorillonites and comparison for Sr(II) removal: equilibrium and kinetic studies. Chem. Eng. J. 2012, 191, 288−296. (66) Tahir, S. S.; Rauf, N. Thermodynamic studies of Ni(II) adsorption onto bentonite from aqueous solution. J. Chem. Thermodyn. 2003, 35, 2003−2009. (67) Bhuyan, B.; Paul, B.; Dhar, S. S.; Vadivel, S. Facile hydrothermal synthesis of ultrasmall W18O49 nanoparticles and studies of their photocatalytic activity towards degradation of methylene blue. Mater. Chem. Phys. 2017, 188, 1−7. (68) Yayapao, O.; Thongtem, T.; Phuruangrat, A.; Thongtem, S. CTAB-assisted hydrothermal synthesis of tungsten oxide microflowers. J. Alloys Compd. 2011, 509, 2294−2299. (69) Liu, X.; Li, J.; Wang, X.; Chen, C.; Wang, X. High performance of phosphate-functionalized graphene oxide for the selective adsorption of U(VI) from acidic solution. J. Nucl. Mater. 2015, 466, 56−64. (70) Gong, J.; Liu, T.; Wang, X.; Hu, X.; Zhang, L. Efficient removal of heavy metal ions from aqueous systems with the assembly of anisotropic layered double hydroxide nanocrystals@carbon nanosphere. Environ. Sci. Technol. 2011, 45, 6181−6187.
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