Article pubs.acs.org/EF
Synthesis of Nanocontainer Chabazites from Fly Ash with a Template- and Fluoride-Free Process for Cesium Ion Adsorption Tao Du,† Xin Fang,† Yichao Wei,† Jin Shang,‡ Bin Zhang,† and Liying Liu*,† †
SEP Key Laboratory of Eco-Industry, Northeastern University, Shenyang, Liaoning 110819, People’s Republic of China School of Energy and Environment, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Kowloon, Hong Kong
‡
ABSTRACT: Chabazite (CHA)-type zeolites were prepared using three different types of fly ashes in this investigation. The demonstrated universal synthetic strategy, which was template- and fluoride-free, consisted of fusion and hydrothermal reaction. The adsorption properties of cesium ions on prepared CHA were then investigated in static adsorption experiments combined with thermodynamic analysis. As-synthesized CHA, with typical CHA crystal structures, exhibited walnut-like particles in morphology. In the case of physical adsorption analysis, the as-synthesized sample showed pore blockage under N2 flow, whereas the CO2 isotherm revealed its considerable specific surface area of 336 m2/g, which, in return, ensured its notable properties for adsorption of ions. The removal efficiencies of cesium ions onto the CHA samples were as high as 99% in dilute solution. Furthermore, the obtained CHA-type zeolite maintained high adsorption capacities within a wide temperature range, thus demonstrating that it could be employed as a nanocontainer in radioactive wastewater management.
1. INTRODUCTION Chabazite (CHA)-type zeolite, one remarkable category of tect osilicate minerals w ith chemical formula of Mi/nn+AliSi36 − iO72 (where M represents the extra-framework cation, i is a positive number representing the quantity of aluminum atoms per unit cell, and n is an integer representing the valency), is acknowledged to have promising properties in catalysis, gas separation, pollution abatement, etc.1 Within its connected and cage-like microstructure, there exist certain locations to accommodate extra-framework cations, which counterbalance the framework charges and adsorption sites to contain guest molecules.2 Once the molecules succeed in passing through the eight-membered ring pore aperture (8MR, 3.8 × 3.8 Å) and entering the ellipsoidal cages (6.7 × 10 Å), they are “adsorbed”. Thanks to its specific pore aperture size that is similar to many small gas molecules and metal ions, CHA exhibits favorable size/shape selectivity, which, in turn, enables its wide applications. Various CHA-type zeolites as well as synthetic procedures have been developed recently. One of the typical CHA zeolites is SSZ-13 (aluminasilicate with a Si/Al ratio of 24). Commonly, it cannot be prepared without the assistance of N,N,Ntrimethyl-1-adamantammonium (TMAda+), but this organic structure-directing agent (OSDA) is both expensive and toxic. Even though some researchers attempted to reduce the synthesis cost and achieved remarkable results, it is still not environmentally friendly as a whole.3,4 Accordingly, researchers proposed an improved synthesis, viz., interzeolite conversion. The investigated method usually proceeds in hydrothermal systems, where faujasite (FAU)- or levynite (LEV)-type zeolite transforms into CHA zeolite under controlled conditions.5,6 This process avoids using poisonous OSDA but has a long synthetic cycle (usually more than 12 days), making it hard to meet the demands of mass production. Thus, compound mineralizers, e.g., fluorides,7,8 are employed to accelerate the crystallization and shorten the synthesis time. Similar scenarios © XXXX American Chemical Society
are encountered in other CHAs, such as SAPO-34 (silicoaluminophosphate with CHA topology),9 AIPO-34 (aluminophosphate with CHA topology),10 and K-CHA (aluminasilicate with a Si/Al ratio of 2.5).11 On the other hand, notable alternative strategies have emerged in recent years that use waste fly ashes to synthesize zeolites, which would effectively cut the cost and improve the economy of reclamations.12 Zeolites X,13 Y,14 A,15 etc. have been obtained from coal fly ashes via succinct methods. The synthesis of CHA-type zeolites (especially K-CHAs), however, still seems a tricky task because of their sensitivities to reaction conditions. Hard to obtain as they are, the CHA-type zeolites have important applications in many fields. Apart from the conventional utilizations, Cu-CHAs are promising catalysts in selective catalytic reduction (SCR) to mitigate the emissions of NOx.16,17 Cs-CHAs are known as the most efficient adsorbents in CO2/N2 and CO2/CH4 separations.18,19 K-CHAs are potential nanocontainers for gas encapsulations20 and capable of temperature-controlled invertible selective adsorption of N2 and CH4.21 Currently, nuclear power is playing an increasingly crucial role in the contemporary society as a promising clean energy. Widely used as it is, an increasing amount of reductive wastewater is generated annually, in which one of the main pollutants is cesium ion (Cs137). If the abundant radionuclide in the effluent is not managed properly, it would long contaminate the soil and water for centuries. However, the cesium ions are too chemically active to be removed by common methods. Although various porous materials (zirconium molybdoarsenates, dioctahedral smectites, etc.) have been used to treat Cs137,22−24 it is still urgent to find economic and efficient adsorbents to remove or reduce the pollutant for safe discharge. In consideration of the situation, we expected that the CHAReceived: December 23, 2016 Revised: March 10, 2017 Published: March 16, 2017 A
DOI: 10.1021/acs.energyfuels.6b03429 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels
2.2. Synthesis. In this investigation, the CHA-type zeolite was prepared using the raw ashes above in accordance with the synthesis procedure, viz., fusion and hydrothermal reaction. To start with, a certain Si/Al ratio [n(Si/Al) = 2] of raw materials was preset in all cases by mixing fly ashes with a certain amount of extra SiO2 or Al2O3 powders. The obtained mixture was then uniformly blended with KOH powders (KOH/mixture mass ratio of 2) and fused at 923 K for 1.5 h. After cooling to the ambient temperature, the resulting products were dissolved in deionized water with a water/product mass ratio of 4:1 and transferred to an autoclave, where hydrothermal reactions were conducted at 368 K for 4 days. Finally, the precipitates were centrifuged, washed, and dried overnight to obtain fly-ash-based CHAtype zeolites. Samples prepared from R1, R2, R3, and R2 and R3, for comparison, were labeled as R1-Si, R2-Si, R3-Al, and R23, respectively. Another comparative experiment was additionally designed to analyze the effects of impurities, such as calcium and iron. Hereby, only basic chemicals SiO2 and Al2O3 were mixed to obtain the powders with the Si/Al molar ratio of 2, and the following operations were identical with the other three samples. The as-synthesized sample was then labeled as Si-Al. 2.3. Characterization. Chemical compositions of all samples were determined by XRF (ZSXPrimus II, Rigaku). The crystal phase was examined by powder XRD using a Cu Kα radiation source with a scanning rate of 2°/min from 5° to 60° (XRD-7000, Shimadzu). Morphologies of samples were determined on field emission scanning electron microscopy (Superscan SSX-500, Hitachi). All samples were coated with a thin layer of gold for distinct observation prior to measurement. Surface area (SA) measurements were conducted on a physical adsorption analyzer (ASAP 2020). The Brunauer−Emmett− Teller (BET) SA was measured as usual using N2 at 77 K. As a result of the phenomenon of pore blockage in CHAs, we did the measurement with the probe of the CO2 molecule at 303 K to investigate the SA of samples on the basis of the Toth model. 2.4. Adsorption Properties of Cesium Ions. Adsorption properties of cesium ions on a representative sample (CHA-type zeolite, R1-Si) were measured in static adsorption experiments under three different temperatures (293, 323, and 353 K). Prior to adsorption experiments, 100 mmol L−1 of mother solution was prepared by dissolving solid cesium nitrate (CsNO3) in the deionized water and other standard liquids with various concentrations (10, 25, 50, 75, and 100 mmol L−1) were obtained by attenuation. In a typical adsorption experiment, 0.2 g of sample was mixed with 10 mL of standard liquid and stirred at a designed temperature for a period of time. Afterward, the supernatant in each single experiment was separated by centrifugation and measured on an atomic emission spectrometer (Z-2300, Hitachi) to determine the cesium concentration.
type zeolite would serve as a nanocontainer to removal the cesium ions in effluents. To the best of our knowledge, the adsorption properties of cesium ions on CHAs have not been investigated systematically. In this investigation, we demonstrated the preparation of CHA-type zeolite, with a general synthesis procedure, using different types of coal fly ashes. The as-obtained samples were then characterized by X-ray fluorescence (XRF) spectrometry, X-ray diffraction (XRD) detection, scanning electron microscopy (SEM), and static adsorption experiments to examine the performance in adsorbing cesium ions. Finally, the thermodynamic features and sorption process were analyzed to assess their properties as nanocontainers for cesium ions.
2. MATERIALS AND METHODS 2.1. Materials and Reagents. Fly ashes used in the present work, labeled as R1, R2, and R3, were collected from three power plants in Inner Mongolia, China. Each ash differs from the others in both compositions and properties, as shown by XRF (Table 1) and XRD
Table 1. Chemical Compositions of Raw Ashes and Prepared CHAs (wt %) composition materiala
SiO2
Al2O3
R1 R2 R3 R1-Si R2-Si R3-Al R23 Si-Al
48.5 41.9 68.3 44.1 43.7 36.4 38.1 47.3
40.8 43.0 16.0 22.5 22.1 22.9 21.0 23.7
K2O
CaO
Fe2O3
others
Si/Al mole ratio
28.7 27.9 31.1 27.1 28.4
3.3 3.7 5.3 1.4 2.7 3.1 4.6 0
2.0 2.8 5.7 2.1 2.2 5.4 7.5 0
5.4 8.6 4.7 1.2 1.4 1.1 1.7 0.6
1.01 0.83 3.62 1.94 1.68 1.35 1.54 1.70
a
R1, raw ash 1; R2, raw ash 2; R3, raw ash 3; R1-Si, CHA sample synthesized with R1 and SiO2; R2-Si, CHA sample synthesized with R2 and SiO2; R3-Al, CHA sample synthesized with R3 and Al2O3; R23, CHA sample synthesized with R2 and R3; and Si-Al, CHA sample synthesized with SiO2 and Al2O3.
(Figure 1). Other regents (SiO2, Al2O3, and KOH) used in our experiments were of analytical purity and bought from Sinopharm Chemical Reagent Co., Ltd. All reagents were used without further purification.
3. RESULTS AND DISCUSSION 3.1. Properties of Raw Fly Ashes. It is recognized that all fly ashes mainly consist of aluminosilicate along with some compounds, e.g., CaO and Fe2O3.25 The inconsistent chemical compositions among ashes are usually associated with the original coals and combustion conditions. As presented in Table 1, all ashes employed in this study contain more than 84 wt % intermediate glass but their Si/Al molar ratios show great differences from 0.83 to 3.62, which reflect their natural diverse characters. The XRD patterns of raw ashes are shown in Figure 1. The main crystalline phases in three ashes, recognized by comparing characteristic peaks at the corresponding positions, are mullite (3Al2O3·2SiO2), quartz (SiO2), hematite (Fe2O3), and calcia (CaO). The amorphous phases in the three ashes are reflected by the presence of the broad peak near 2θ = 21°. Generally, recycling means for different ashes are quite limited in the fields of landfill, construction, and agriculture.
Figure 1. XRD patterns of raw ashes (a) R1, (b) R2, and (c) R3. B
DOI: 10.1021/acs.energyfuels.6b03429 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels
microstructure with the other three samples obtained from fly ash, while there are no calcium or iron ions in the synthetic process. Thus, neither calcium nor iron ions seem to be the crucial factor affecting the crystal formation, and samples may display such a morphology on account of the subtle interactions between potassium and aluminosilicate in the hydrothermal system. Among all samples, R1-Si appears most favorable in aspects of the particle size and structural integrity under current synthetic conditions, and the properties of other samples would be improved by slightly adjusting the detailed synthesis factors as well. On the basis of this point, we deeply analyzed sample R1-Si in the following study. The specific SA of the as-synthesized sample presents the featured characters. The BET specific SA of sample R1-Si, measured at 77 K under N2 flow, is only 16.8 m2/g, which is likely attributed to the pore blockage in K-CHA.27 To investigate the details of textural properties of as-synthesized CHA, the gas adsorption isotherm of smaller diameter CO2 was carried out at 303 K. We analyzed the CO2 adsorption isotherm based on the Toth model and calculated the SA (Figure 4). A relatively high value of 336 m2/g illustrates its porous nature and promising application in cesium ion removal. Table 2 concludes some typical fly-ash-based zeolites and Cs ion sorbents. Although different models are used in the SA calculation, sample R1-Si presents a considerable SA value among fly-ash-based zeolites, especially in cases where OSDCs are excluded. On the other hand, sample R1-Si also has an adsorption capacity similar to the current most efficient sorbents. Commonly higher SAs benefit the adsorption capacity, yet an interesting phenomenon occurs that some sorbents with small BET SAs exhibit nice sorption properties (see sample R1-Si and nanometer-sized zeolite A in Table 2). According to the zeolite database of the International Zeolite Association (IZA), apertures of zeolite K-CHA (R1-Si) and 4A (nanometer-sized zeolite A) are 0.38 and 0.42 nm, respectively. Their small sizes will often lead to underestimations in BET SA tests, yet the strong interactions between their compact frameworks and cesium cations may promote the sorption properties in return. This provides us some insight in future material design. 3.3. Removal Efficiency. The removal efficiency (RE) of cesium ion (R, %) and distribution coefficient (Kd) were calculated as follows:
Therefore, a generally applicable strategy for fly ash reclamation is urgently needed. 3.2. Characterizations of Synthetic CHA-Type Zeolites. Compositions of the synthetic CHA-type zeolites are significantly different from the raw ashes (Table 1). The Si/Al molar ratios of R1-Si, R2-Si, R3-Al, R23, and Si-Al are 1.94, 1.68, 1.35, 1.54, and 1.70, respectively. The Si/Al ratios of R1-Si and R23 are higher than those of the original raw fly ashes, but the parameter of R2-Al is obviously lower than R2. This remarkable change in composition not only occurs in the cases of R1-Si, R2-Si, and R3-Al but also appears when both ashes are used (R23). That demonstrates that compositions of all samples have been well-adjusted as desired. Moreover, the concentration of unwanted impurities in the zeolites decreases dramatically by 6.1% on average. The crystals in samples involve a great transformation as well. According to the XRD results listed in Figure 2, the major
Figure 2. XRD patterns for samples (a) R1-Si, (b) R2-Si, (c) R3-Al, (d) R23, and (e) Si-Al.
crystalline phase turns out to be zeolite CHA in the samples. Fingerprint lines in the patterns are clearly at 2θ = 12.6°, 20.4°, and 30.3°, indicating the presence of specific cage structures that constitute the framework of CHA-type zeolites. Another crystal is recognizable in the sample, which turns out to be an unnamed potassium aluminum silicate hydrate. However, characteristic lines of other crystals, such as phillipsite (a common concomitant in CHAs), on the other hand, are either too weak to be distinguished or absent in any sample. Therefore, the synthesis procedure plays a crucial role in leaching the available Si and Al in the ashes and, at the same time, promotes the formation of a new crystal of CHA-type zeolite. Generally, the samples belong to CHA-type zeolites, but they show different features in morphologies when compared to traditional CHAs. As confirmed by SEM (Figure 3), each sample consists of walnut-like spherical particles with uniform sizes ranging from 4 to 8 μm. Although materials with similar microstructures have been prepared in fluoride media,26 most reported zeolite CHAs exhibit cubic crystal characteristics.23 We contend that potassium (K+) partially replaces the OSDA or zeolite seed during the synthetic process to direct the formation of the CHA structure. This assumption is on the basis of sample Si-Al. It presents identical morphology and
R = (C0 − Ce) × 100%/C0
(1)
Kd = (C0 − Ce)/CeV /m × 103
(2)
−1
where C0 (mmol L ) is the initial concentration of cesium ions in the solution, Ce (mmol L−1) is the equilibrium concentration of cesium ions in the solution, V (L) is the volume, and m (g) is the weight of sample R1-Si. Figure 5 presents the plots of REs of cesium ions at various conditions. Within the studied temperature range, the sample encounters obvious nonlinearly declination in RE when the initial concentration increases from 10 to 100 mmol L−1. The REs, to be precise, remain at approximately 95% once the initial concentration reduces to 25 mmol L−1 at higher adsorption temperature of 323 and 353 K. On the other hand, a higher adsorption temperature seems to promote the REs, whereas the attenuation of RE appears to be less strong at a mild temperature of 323 K. The underlying reason lies in the specific microstructure built up from corner-sharing TO4 tetrahedrons. C
DOI: 10.1021/acs.energyfuels.6b03429 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels
Figure 3. SEM images of products (a) R1-Si, (b) R2-Si, (c) R3-Al, (d) R23, and (e) Si-Al.
Table 2. Property Comparisons of Typical Fly-Ash-Based Zeolites and Cs Ion Sorbents sample R1-Si (CHA zeolite) hydrophobic zeolite Na-X zeolite Na−P1 zeolite sodalite GIS zeolite micrometer-sized zeolite A nanometer-sized zeolite A K@RWY (zeolitic chalcogenide)
feedstock fly ash fly ash fly ash fly ash fly ash fly ash commercial zeolite commercial zeolite basic chemicals
SA (m2/g)
Cs+ adsorption amount (mmol/g)
16.8a/ 336b 404
NA
166 71 33 46 1
NA NA NA NA 1.3
58
3.2
NA
2.4
2.8
reference this work 28 29
30 31
32
Figure 4. Adsorption isotherms of CO2 (303 K) and N2 (77 K) on sample R1-Si.
a
The isotherms of cesium ions onto sample R1-Si at different temperatures were shown in Figure 6, where the Langmuir adsorption model was employed to fit the isotherms. Although tiny differences are there in the adsorption capacities when cesium ion concentrations are low, the adsorption capacities, in
cases of high initial concentrations, increase apparently along with the temperature rise (from 293 to 323 K). However, a continually higher temperature (353 K) will not further promote the adsorption strongly. Instead, adsorption amounts of cesium ions onto the prepared sample are similar at 323 and D
Calculated from the BET model. bCalculated from the Toth model.
DOI: 10.1021/acs.energyfuels.6b03429 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels
Figure 5. Effect of the initial concentrations on the removal efficiencies at 293, 323, and 353 K.
3.4. Thermodynamic Analysis. The Gibbs free energy change is solved according to the following equation: ΔG° = −RT ln Kc
(3)
where ΔG° (kJ/mol) is the Gibbs free energy change, R is the gas constant, T (K) is the adsorption temperature, and Kc is the equilibrium constant, which can be calculated as Kc = Fe/(1 − Fe)
(4)
where Fe is the fraction attainment of cesium at equilibrium. Additionally, ΔG° can also be represented as (5)
ΔG° = ΔH ° − T ΔS°
where ΔH° (kJ/mol) is the enthalpy change and ΔS° (J mol−1 K−1) is the entropy change. The equilibrium characteristics and thermodynamic parameters were calculated with eqs 2−5 and summarized in Table 3. Apparently, the equilibrium adsorption capacities (qe) of cesium ions rise slightly with the increasing temperature, demonstrating a potential effect of the temperature on the sorption process. The calculated distribution coefficients (Kd) again reveal a similar tendency. Hence, they both prove that the adsorption of cesium ions on the sample is endothermic in thermodynamics. The interaction strength between the cesium ions and assynthesized samples increases with the temperature, as indicated by the increase in Kc with the temperature. This benefits the easier dehydration of the cesium ion at higher temperatures, so that the individual ion better fits the pore system of as-synthesized CHA-type zeolite in size and vice versa. Moreover, the negative values of ΔG° confirm the spontaneous nature of the studied process. The relationship between Gibbs free energy change (ΔG°) and temperature of adsorption was fitted using eq 5 and also concluded in Table 3. Because the enthalpy change (ΔH°) turns out to be positive in value, it again verified that the
Figure 6. Adsorption isotherms of cesium ions on sample R1-Si at 293, 323, and 353 K.
353 K, which turns out to be a result of mutual effects. A higher temperature will certainly accelerate the cesium ion motions in aqueous solution. The more active the cations, the more difficult they are to adsorb. Therefore, the adsorption capacities decrease. Meanwhile, a higher temperature will also help to expand frameworks of CHAs. More adsorption sites are exposed under the condition, which benefits the adsorption processes. Each of both effects compete with each other, and hence, the adsorbed amounts of cesium ions just keep the same level, even though the temperature has been raised by 30 K. The above results well prove the notable adsorption properties, suggesting that prepared fly-ash-based CHA is applicable and reliable in most practical situations, where both initial concentrations and adsorption temperatures are within this research scope.
Table 3. Equilibrium Characteristics and Thermodynamic Parameters of Cesium Ion Adsorption T (K)
qe (mmol/g)
Kd (mL/g)
Kc
ΔG° (kJ/mol)
ΔH° (kJ/mol)
ΔS° (J mol−1 K−1)
293 323 353
0.483 0.484 0.486
1426.67 1532.26 1698.82
1.43 1.53 1.70
−0.87 −1.15 −1.56
2.52
11.5
E
DOI: 10.1021/acs.energyfuels.6b03429 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels
4. CONCLUSION Fly-ash-based CHA was prepared following a novel general synthetic strategy, with the feedstock of various waste fly ashes. All of the prepared CHAs consist of a high-purified CHA crystal phase and present similar chemical compositions. Furthermore, their morphologies are walnut-like, and their porosity cannot be directly detected by N2 at 77 K because of the pore blockage but is confirmed by CO2 adsorption at 273 K. The cesium adsorption experiments demonstrate that the removal efficiencies of cesium ions decrease with the increase in the initial concentrations. Remarkably, the as-synthesized sample exhibits stable properties for cesium removal within a wide range of temperatures and is not compromised at high temperatures, such as most commercial adsorbents. Hence, the present investigation provides a promising solution in both waste managements of ashes and effluents.
process adsorbs heat from the environment. The entropy change (ΔS°) is also greater than zero and, hence, demonstrates that there comes increased randomness in the adsorption system, which may lie in some structural transformations at the interfaces as well as microstructures. Meanwhile, the adsorption is spontaneous when the temperature is higher than 219 K; therefore, no additional energy is required in practice. 3.5. Adsorption Process. The kinetic experiments, to better understand the adsorption process, were designed and conducted with the results given in Figure 7. If the temperature
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Jin Shang: 0000-0001-5165-0466 Liying Liu: 0000-0002-5842-7846 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS The authors gratefully acknowledge the financial support of the Natural Science Foundation of China (Grants 51474067 and 51406029), the National Key Research and Development Project (2016YFB0601301 and 2016YFB0601305), the “123” Project of China Environment Protection Foundation (CEPF 2013-123-2-14), and the National Department of Education (Funding N150204015).
Figure 7. Adsorption process of sample R1-Si at 293 K.
is over 323 K at the initial cesium concentration of 10 mmol L−1, the adsorption reaches equilibrium in less than 20 min. In particular, the adsorption capacity rapidly scores approximately 0.48 mmol g−1 at both 323 and 353 K, which is unconventional, especially in adsorption, because the temperature affects the process fractionally. In contrast, the case at 293 K displays the whole process clearly (Figure 7). Generally, there are three consecutive stages proceeding according to the adsorption dynamics of ions by porous materials,33 viz., (1) membrane diffusion, in which the solute transfers to the external surface along with a fluid stagnant film, (2) intraparticle diffusion, in which the solute enters the internal microstructures, and (3) adsorption, occurring at the adsorption sites. In this investigation, the main crystal phase in products is CHA-type zeolite that is hydrophilic with a tiny pore diameter of 3.8 Å. At the very beginning, the solution quickly transfers to the surface of CHA. However, the hydrated cesium ions with a radius of 3.29 Å must remove their bound water to diffuse into the pore systems, during which a certain amount of energy (or heat) related to the hydration enthalpy is consumed. We believe that the energy feeds insufficiently at ambient temperature (293 K) but amply because of the increase in the sorption temperature, contributing to the shorter equilibrium time at higher temperatures, i.e., 323 and 353 K. Conversely, the dramatic process brings challenges in sorbent regeneration. Most sorbents can be recovered by alkali washing or acid washing at present, but none of them operates perfectly as a result of their low efficiency and reproduced Cs effluent. The reclamation of cesium sorbents, especially those containing radioactive Cs137, is still an unavoidable issue that we must cope with in the future.
■
REFERENCES
(1) Van Tendeloo, L.; Wangermez, W.; Kurttepeli, M.; et al. Environ. Sci. Technol. 2015, 49, 2358−2365. (2) Barrer, R. M. Zeolite and Clay Minerals; Academic Press: New York, 1978; pp 829−830. (3) Wu, L.; Degirmenci, V.; Magusin, P.; et al. J. Catal. 2013, 298, 27−40. (4) Wang, J.; Peng, Z.; Chen, Y.; et al. Chem. Eng. J. 2015, 263, 9−19. (5) Zones, S. I. Zeolite SSZ-13 and its method of preparation. U.S. Patent 4,544,538 A, Oct 1, 1985. (6) Goto, I.; Itakura, M.; Shibata, S.; et al. Microporous Mesoporous Mater. 2012, 158, 117−122. (7) Zhu, X.; Kosinov, N.; Hofmann, J. P.; et al. Chem. Commun. 2016, 52, 3227−3230. (8) Eilertsen, E. A.; Arstad, B.; Svelle, S.; et al. Microporous Mesoporous Mater. 2012, 153, 94−99. (9) Wu, L.; Hensen, E. J. M. Catal. Today 2014, 235, 160−168. (10) Dai, W. L.; Wang, X.; Wu, G. J.; et al. ChemCatChem 2012, 4, 1428−1435. (11) Ferretti, G.; Faccini, B.; Vittori, A. L.; et al. Proceedings of the European Geosciences Union (EGU) General Assembly 2015; Vienna, Austria, April 12−17, 2015; Vol. 17, EGU2015-10790. (12) Bukhari, S. S.; Behin, J.; Kazemian, H.; et al. Fuel 2015, 140, 250−266. (13) Volli, V.; Purkait, M. K. J. Hazard. Mater. 2015, 297, 101−111. (14) Zhao, X. S.; Lu, G. Q.; Zhu, H. Y. J. Porous Mater. 1997, 4, 245− 251. (15) Ojumu, T. V.; Du Plessis, P. W.; Petrik, L. F. Ultrason. Sonochem. 2016, 31, 342−349. F
DOI: 10.1021/acs.energyfuels.6b03429 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels (16) Kim, M. Y.; Choi, J. S.; Crocker, M. Catal. Today 2014, 231, 90−98. (17) Brookshear, D. W.; Nam, J. G.; Nguyen, K.; et al. Catal. Today 2015, 258, 359−366. (18) Shang, J.; Li, G.; Singh, R.; et al. J. Am. Chem. Soc. 2012, 134, 19246−19253. (19) Shang, J.; Li, G.; Singh, R.; et al. J. Chem. Phys. 2014, 140, 084705. (20) Shang, J.; Li, G.; Singh, R.; et al. J. Phys. Chem. C 2010, 114, 22025−22031. (21) Shang, J.; Li, G.; Gu, Q.; et al. Chem. Commun. 2014, 50, 4544− 4546. (22) Lee, E. H.; Lim, J. G.; Chung, D. Y.; et al. J. Radioanal. Nucl. Chem. 2010, 284, 387−395. (23) Singh, S.; Thorat, V.; Kaushik, C. P.; et al. J. Hazard. Mater. 2009, 162, 743−745. (24) Ngwenya, N.; Chirwa, E. M. N. Miner. Eng. 2010, 23, 463−470. (25) Catalfamo, P.; Corigliano, F.; Primerano, P.; et al. J. Chem. Soc., Faraday Trans. 1993, 89, 171−175. (26) Liu, B.; Zheng, Y.; Hu, N.; et al. Microporous Mesoporous Mater. 2014, 196, 270−276. (27) Ridha, F. N.; Webley, P. A. Sep. Purif. Technol. 2009, 67, 336− 343. (28) Sakthivel, T.; Reid, D. L.; Goldstein, I.; et al. Environ. Sci. Technol. 2013, 47, 5843−5850. (29) Franus, W.; Wdowin, M.; Franus, M. Environ. Monit. Assess. 2014, 186, 5721−5729. (30) Zhang, M.; Zhang, H.; Xu, D.; et al. Sep. Sci. Technol. 2011, 46, 2260−2274. (31) Torad, N. L.; Naito, M.; Tatami, J.; et al. Chem. - Asian J. 2014, 9, 759−763. (32) Yang, H.; Luo, M.; Luo, L.; et al. Chem. Mater. 2016, 28, 8774− 8780. (33) Ahmaruzzaman, M. Prog. Energy Combust. Sci. 2010, 36, 327− 363.
G
DOI: 10.1021/acs.energyfuels.6b03429 Energy Fuels XXXX, XXX, XXX−XXX
