Article pubs.acs.org/IECR
Facile Preparation of Nanocryptomelane and Its Application in the Treatment of Aqueous Solutions Containing Basic Fuchsin Wei Xu,† Zifeng Deng,‡ and Guangming Li*,† †
State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, and Department of Chemistry, Tongji University, 1239 Siping Road, Shanghai 200092, China
‡
ABSTRACT: Cryptomelane nanomaterials were synthesized by a facile redox−reflux method. The physicochemical properties of these composites were studied in detail using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, laser Raman spectroscopy, thermogravimetric analysis (TGA), and N2 adsorption− desorption techniques. The catalytic activities of nanocryptomelane were evaluated through treatment of aqueous solutions that contained basic fuchsin. In the case of basic fuchsin, the catalytic activity of synthetic nanocryptomelane was much higher than that of natural cryptomelane. Moreover, synthetic nanocryptomelane shows high stability and recyclability, has a high specific surface area, and is rich in mesopores. It could be anticipated that the specific surface area of the material had an obvious effect on the degradation of basic fuchsin. Kinetic studies indicated that the reaction follows the Langmuir−Hinshelwood model. The catalytic activities were found to be primarily correlated with the specific surface area. Overall, cryptomelane nanomaterials have great potential in the treatment of dye-containing wastewater.
1. INTRODUCTION Triphenylmethane dyes are the most stable among synthetic coloring agents,1 which are extensively used in the textile industry for the dying of nylon, wool, silk, and cotton, as well as in the paper and leather industries.2,3 Industrial wastewater containing these dyes not only brings environmental pollution concerns4,5 but can also cause the extinction of some aquatic life through the enrichment of mutagenic and carcinogenic materials in the food chain.1,6,7 Currently, several physicochemical8−11 and biodegradable12,13 methods have been used to remove dye from wastewater. However, these methods require the use of expensive chemicals, which, in turn, cause secondary pollution. Thus, it is important to find new materials or applicable technologies to address the widely used and structurally different dyes. Cryptomelane is a type of manganese oxide composed of 2 × 2 edge-shared [MnO6] octahedral chains14 that form onedimensional tunnel (0.46 nm × 0.46 nm) structures.15 The manganese ions in octahedral sites exist in both the Mn4+ and Mn3+ oxidation states, and the potassium ions located in the tunnels provide charge balance and a stable structure.16 Natural cryptomelane contains many impurities, including trace amounts of harmful elements (Cu, Cr, etc.). Although better results can be achieved by increasing the reaction time and the amount of natural cryptomelane, this approach leads to an increase in secondary pollution in the treatment of the dye wastewater.17 In recent years, several different processes have been proposed to prepare cryptomelane-type materials, as well as a variety of other manganese oxides. The synthetic counterpart to cryptomelane is known as octahedral molecular sieve, OMS-2.14,16,18 Because of its porous structure and mixedvalence manganese species, cryptomelane has been extensively explored as a potential material for ion exchange,19 batteries,20 waste immobilization,21,22 and catalysts.23−25 Synthetic nanocryptomelane has the environmental advantages of natural cryptomelane26 but also exhibits other excellent characteristics, © 2012 American Chemical Society
including high storage stability, high purity, and lower cost. Compared with other water-scavenging agents,10,12 synthetic cryptomelane has a higher treatment efficiency and, thus, a greater economic benefit, because of its ability to use a lower dosage in a shorter reaction time. Thus, synthetic cryptomelane has great potential in the field of wastewater treatment. In this article, a simple and low-cost method is proposed to synthesize nanocryptomelane. Studies of its physical and chemical adsorptive properties, porosity, and recycling of synthetic cryptomelane were performed. As a difficult-tobiodegrade triphenylmethane dye, basic fuchsin was selected as a simulated wastewater containing the corresponding dye. Studies with or without the addition of gaseous oxygen were performed to elucidate the mechanism, especially to distinguish the roles of pure oxygen and atmospheric oxygen in the oxidation process. The correlation between catalytic performance and catalyst structure was also investigated. These results will provide a new opportunity for the use of nanomaterials in industrial wastewater treatment.
2. EXPERIMENTAL SECTION 2.1. Materials. Nanocryptomelane was prepared by an improved method25,27−29 involving the oxidation of Mn2+ by KMnO4. A typical synthesis was as follows: First, 5.6 g of KMnO4 in 80 mL of deionized water was added to a solution of 8.5 g of MnSO4·H2O in 70 mL of deionized water; a certain volume of concentrated HNO3 was then added to maintain the pH value near 0.6−1.0. The solution was then refluxed, with stirring, at 100 °C for 24 h. The precipitate was wet-aged for 12 h. Next, the products were separated in a centrifuge at 2500 Received: Revised: Accepted: Published: 16188
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Figure 1. (A) XRD pattern, (B) FT-IR spectrum, (C) Raman spectrum, and (D) TGA−DSC profile of the prepared nanocryptomelane.
Corporation, Madison, WI). The experiments were conducted with a TA Instruments model 2950 instrument under a N2 atmosphere. The temperature was increased from 30 to 980 °C at a rate of 10 °C/min, and the final temperature was held for 10 min during the experiments. 2.3. Catalytic Activity Evaluation. Complete oxidations of basic fuchsin (BF) were performed in a solid−liquid reaction under atmospheric pressure and room temperature. The catalytic activities of nanocryptomelane were evaluated in terms of the degradation of 200 mg/L BF. A certain amount of cryptomelane was added to 50 mL of a solution of BF in a tapered bottle. The suspensions were magnetically stirred for 24 h, and the catalyst particles were obtained by centrifugal separation. The filtrates (543 nm for BF) were analyzed by UV−vis spectroscopy (Agilent 8453, Palo Alto, CA). The effects of parameters on the removal efficiency of BF were studied with the same procedure. The Mn2+ contents of the filtrates were measured by atomic absorption spectrometry (Agilent 3510, Palo Alto, CA). 2.4. Kinetic Experiments. Kinetic studies were conducted in a temperature-controlled bath shaker. Fifty millliliters of a dye solution (concentration 200 mg/L) and a fixed dosage of 0.15 g of synthetic cryptomelane were used in the process. Samples were shifted and filtered at different time intervals (0− 5 h). The concentrations of the samples were analyzed by UV− vis spectroscopy.
rpm for 20 min, after which they were washed with deionized water several times to remove unreacted materials. The products were then washed with deionized water until the pH value reached 7.0. The washed products were then collected and dried in a desiccator, and the final product was obtained after grinding. Natural cryptomelane was obtained from the Xialei Manganese Deposit, Guangxi, China. In a natural setting, the sample was washed with distilled water, exposed to the sun and air, dried, and crumbled. 2.2. Catalyst Characterization. SEM images of the samples were collected on a Philips XL-30 transmission electron microscope (Philips Company, Eindhoven, The Netherlands). XRD patterns were obtained on a D8-Advance diffractometer (Bruker Optik GmbH, Ettlingen, Germany) with Cu Kα radiation. Nitrogen sorption measurements were performed using a Tristar3000 nitrogen adsorption apparatus (Micromeritics Instrument Corporation, Norcross, GA). Adsorption and desorption experiments were studied at 77 K after initial pretreatment of the samples by degassing at 403 K for 2 h. The specific surface areas of the samples were determined by the Brunauer−Emmett−Teller (BET) method, and the micropore size distribution was reported using the Horvath−Kawazoe (HK) model. The mesopore/macropore size distribution was calculated by the Barrett−Joyner−Halenda (BJH) method using the desorption data. Raman spectra were recorded at room temperature in the range of 100−3200 cm−1 with a Renishaw inVia Raman microscope setup (Renishaw PLC, Gloucestershire, U.K.). A 514-nm argon ion laser was used to record the spectra for the conventional cryptomelane. Infrared spectra of the materials were obtained on a Nicolet NEXUS-912A FT-IR spectrometer (Thermo Nicolet Corporation, Madison, WI). The thermal stability of the samples was studied by thermogravimetric analysis (Thermo Electron
3. RESULTS AND DISCUSSION 3.1. Characteristics of Catalysts. The XRD patterns of the as-synthesized hybrid materials are shown in Figure 1A. Different reflections of the cryptomelane compounds were present with characteristic peaks at 2θ = 12.7°, 18.1°, 28.9°, 37.5°, 42°, and 50°. Comparatively, the peak (211) at 2θ = 37.5° was very sharp for all samples, implying that the α-MnO2 16189
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Figure 2. SEM images of synthetic cryptomelane.
particles were highly oriented.28 These patterns demonstrate that a well-ordered layered structure resulted from the rapid redox reaction between Mn2+ and Mn7+. The intense and sharp peaks were attributed to the tetragonal structure of cryptomelane30 (JCPDS card 29-1020). Notably, the results indicate that the framework of synthetic cryptomelane is quite stable. A broad absorption peak in the FT-IR spectrum is shown in Figure 1B. The sharp absorption peaks near 717, 521, and 467 cm−1 were caused by the characteristic vibrations of the Mn−O bonds within the nanomaterials.31 The broad absorption observed at 3399 cm−1 for the nanostructures of MnO2 was assigned to the stretching vibrations of the −OH groups of adsorbed water, whereas the peak at 1622 cm−1 was due to the bending vibrations of the −OH groups. Therefore, the surface of the product was rich in −OH groups.32 To investigate the properties of nanocryptomelane, the crystal structure of synthetic cryptomelane was determined by laser Raman spectrometry. These results showed that there were five characteristic peaks. The peaks at 636 and 572 cm−1 were strong Raman peaks, and the peaks at 502, 383, and 182 cm−1 were weak Raman peaks (Figure 1C). Bands at 500−510, 570−580, and 630−640 cm−1 were attributed to MnO2. The peak at 650 cm−1 was associated with Mn3O4, and the peaks at 572 and 650 cm−1 were characteristic of Mn−O lattice vibrations.33 The Raman spectrum suggested that the synthetic product obtained was a mixture of different manganese oxides with oxidizing Mn4+ sites.34,35 This finding is in good agreement with the XRD results mentioned previously. The results of the TGA and DSC experiments are shown in Figure 1D. Three major weight losses appeared between 50 and 900 °C. The first weight loss, which occurred at 294 °C and represented approximately 4%, was attributed to physisorbed or chemisorbed water. The second weight loss of 4%, observed at 516−642 °C, was due to oxygen evolution from the materials, as reported previously. The third weight loss, of approximately 2%, was due to the second lattice oxygen release at 713−758 °C. 28,36 Corresponding with these weight losses, two prominent endothermic peaks at 565 and 756 °C were observed in the DSC curve. Referring to the TGA data, the endothermic peak at 565 °C, which was associated with a 4% weight loss, was assigned to the desorption/decomposition of oxygen on the surface of the nanocryptomelane. The regeneration temperature was determined for nanocryptomelane after wastewater treatment. The peak at 756 °C was attributed to the release of lattice oxygen from the framework of the tunnels.36 The materials decomposed to hausmannite (Mn3O4) during the XRD analyses. Thus, the synthesized samples showed better thermal stability.
The SEM images of synthetic cryptomelane are shown in Figure 2. From the low-magnification images (Figure 2A,B), it can be observed that the synthetic crystals combined to form in the shape of a “bird’s nest”. The high-magnification image (Figure 2C) displays fibrous morphologies typical of cryptomelane, regardless of the type of hydrothermal treatment. The fibers, which were a few hundred nanometers long, exhibited one-dimensional nanoscale morphologies with diameters of approximately 50 nm.28,37 Uniform holes, with an average diameter of 40 nm, were observed on the acicular cryptomelane, which showed a large surface area. Such a structure is beneficial to adsorption and catalytic oxidation. 3.2. Blank and Comparative Experiments. The experimental conditions used to study the roles of pure oxygen and atmospheric oxygen in the oxidation reaction were as follows: pH 3.60, 3 g/L synthetic cryptomelane, 120−160 mesh grain size, 1-h reaction time, and room temperature. The degradation rate of BF did not show significant difference between the pure oxygen environment (85.86%) and the atmospheric environment (84.75%). These results indicate that gaseous oxygen cannot promote the catalytic oxidation reaction and that oxygen does not produce oxygen-free radicals on the surface of the synthetic cryptomelane. The catalytic activities of synthetic and natural cryptomelane were analyzed in terms of the degradation of 200 mg/L BF through the comparative experimental method. The degradations of BF by synthetic and natural cryptomelane are shown in Figure 3. The catalytic activity of the synthetic cryptomelane was higher than that of natural cryptomelane. Furthermore, the degradation of BF reached 85% after 1 h through the use of synthetic cryptomelane, but it reached only 70% after 3 h using
Figure 3. Comparison of the degradation rates of BF using synthetic and natural cryptomelane. 16190
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Figure 4. Effects of (A) dosage, (B) particle size of synthetic cryptomelane, (C) reaction time and (D) pH of aqueous medium on the catalytic degradation of basic fuchsin. (Conditions: CBF = 200 mg/L, VBF = 50 mL, T = 25 ± 2 °C. For A, particle size = 120−160 mesh, pH = 3.6, t = 3 h; for B, m = 0.15 g, pH = 3.6, t = 3 h; for C, particle size = 120−160 mesh, pH = 3.6, m = 0.15 g; and for D, particle size = 120−160 mesh, m = 0.15 g, t = 3 h.)
aqueous medium. Figure 4B shows the degradation rate as a function of particle size. The relative amount of active surface sites of cryptomelane was expected to increase when the grain size was relatively smaller. Consequently, the contact surface area should be expanded, and the reaction rate should be increased. Nevertheless, the reaction activity did not increase as the size of the cryptomelane decreased. When the particle size of the nanomaterial decreased to a certain extent, the decomposition rate of the dye in the wastewater also decreased. This effect was attributed to the decrease of the active surface area when the particle size was reduced to a certain extent.39 Therefore, 120−160 mesh nanomaterial was selected as the optimum grain size in the subsequent experiments. 3.3.2. Effects of Reaction Time and pH of the Aqueous Medium. It was found that BF was completely degraded within 5 h by cryptomelane with a low amount of 3 g/L (Figure 4C). This result showed a better degradation rate using synthetic cryptomelane than natural cryptomelane. In fact, longer reaction times were favorable for the reaction between synthetic cryptomelane and BF, which contributed to a higher degradation. Based on the results, 3 h was identified as the optimal reaction time. Furthermore, during the degradation process, the initial solution acidity played a significant role in the degradation of BF; this effect was greater than those of any other factors. The degradation rate increased with decreasing pH (Figure 4D), which might explain why reactions were observed only at lower pH. At higher pH, the amount of adsorbed BF might be significantly lower, resulting in lower degradation rates. The reason for this difference might be that
natural cryptomelane. The cause of this discrepancy might be that the specific surface area of synthetic cryptomelane (60.26 m2/g) is higher than that of natural cryptomelane (26.99 m2/g) using the same particle size.28 In the remainder of this article, the effects of the reaction conditions, including the dosage and particle size, the reaction time, and the pH of the aqueous medium, on the catalytic activity of cryptomelane are primarily discussed with respect to synthetic cryptomelane. 3.3. Removal of Basic Fuchsin from Aqueous Solutions by Oxidation on Nanocryptomelane. The results reported in the preceding section show that synthetic nanocryptomelane is an excellent catalytic oxidation material with a well-crystallized structure and a large specific surface area. The synthetic nanomaterial was then applied to the redox reaction of basic fuchsin, which was used as a model for dye in wastewater, to investigate the activity of nanocryptomelane. The effects of the amount of sample, particle size, reaction time, and initial solution acidity were studied. All experiments were performed at room temperature. 3.3.1. Effects of Dosage and Particle Size of Synthetic Cryptomelane. The influence of the dosage of synthetic cryptomelane on the degradation of BF is shown in Figure 4A. The removal efficiency of BF was nearly 100% at a dosage of 3 g/L. When the dosage exceeded this threshold, the effect was no longer evident. Accordingly, the surface structure of cryptomelane had abundant holes and was conducive to adsorbing BF on its surface. Notably, the degradation efficiency of BF improved at higher dosages of mineral.35 Different particle sizes of cryptomelane were used to remove BF from 16191
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the surface of the nanocryptomelane was covered by a precipitate that was generated between Mn2+ and OH− in the reaction. Hence, the pH value must be strictly controlled during the reaction. In summary, these results show that the degradation rate could reach greater than 95% using the following conditions: pH 3.6, 3 g/L synthetic cryptomelane with a grain size of 120− 160 mesh, and a reaction time of 3 h at room temperature. The chroma of the effluent was decreased by a factor of 5−10, which could meet the first grade discharge standard (40 times) for wastewater from the textile industry.40 3.3.3. Repeated Use of Synthetic Cryptomelane. The catalyst was washed after the reactions, calcined for 12 h at 300 °C, and reused for the same oxidation reaction. The results of recycling synthetic cryptomelane are shown in Table 1. The
−
a
sample amount (g/L)
degradation rate (%)
1 2 3
3 3 3
99.54 95.78 90.58
(1)
where r and θ are the reaction rate and the surface coverage, respectively. C is the concentration of reactant, k (g/m3·min) is the reaction rate constant, and K (g/m) is the Langmuir− Hinshelwood adsorption equilibrium constant. This approach assumes that the rate-limiting step is the reaction between the adsorbed species (organic molecules, etc.) and that their coverage can be calculated using the Langmuir equation.41 Assuming that C0 is the initial concentration of the reactants, so that, at time t = 0, C = C0, integration of eq 1 gives ln(C0/C) t = kK −K C0 − C C0 − C
(2)
The Langmuir−Hinshelwood model has been applied to the kinetic data to consider the adsorption equilibria. A linear form was obtained by plotting the change of [ln(C0/C)]/(C0 − C) with respect to t/(C0 − C) (Figure 6). This observation
Table 1. Repeated Use of Synthetic Cryptomelanea number of times used
dC kKC = r = kθ = dt 1 + KC
CBF = 200 mg/L, VBF = 50 mL, pH = 3.6, t = 3 h, T = 25 ± 2 °C.
cycle test showed that the degradation rate of an aqueous solution containing BF was kept stable using recycled cryptomelane. It was concluded that the synthetic cryptomelane did not cause secondary pollution and could be used repeatedly in the treatment of wastewater. The effect of the treatment of wastewater by cryptomelane material demonstrated excellent performance that was far better than that of other sewage treatment materials.10 3.4. Kinetic Analysis. UV−vis spectra were recorded during the degradation of BF by synthetic cryptomelane, and the results are summarized in Figure 5. As Figure 5 illustrates,
Figure 6. Kinetic model for basic fuchsin at different times (continuous line). (Conditions: particle size = 120−160 mesh, m = 0.15 g, t = 0−5 h, T = 25 ± 2 °C.)
indicates that the degradation of BF by synthetic cryptomelane is consistent with the L−H model, in which the reaction can occur both on the surface of the material and in the bulk solution. The reaction rate constant and the adsorption equilibrium constant were calculated to be k = 1.41 g/m3·min and K = 6.9 × 10−3 m3/g, respectively. The degradation of BF in aqueous solution conformed to pseudo-first-order reaction kinetics.43 Thus, the reaction of the cryptomelane material with adsorbed organic molecules was also considered to be a singlemolecule adsorption reaction.42 K could be used as a parameter to compare the degradation rates of different catalysts. The value of K and adsorption capacity show a linear relationship.44 Thus, organic molecules of BF were first adsorbed on the surface of cryptomelane and then oxidized on the surface of the material. 3.5. Mechanisms of Removing Basic Fuchsin by Nanocryptomelane. It is important to elucidate the mechanism of the removal of BF from wastewater using nanocryptomelane, which could later play a basic theoretical role in the application of nanomaterials in other environmental areas. Furthermore, much additional work is required to solve this problem. The BET specific surface areas (SBET) of the powders were analyzed by nitrogen adsorption to describe the surface properties of the synthetic material. Figure 7 depicts the
Figure 5. UV−vis spectra of BF treated for different times. (Conditions: CBF = 200 mg/L, VBF = 50 mL, T = 25 ± 2 °C, particle size = 120−160 mesh, pH = 3.6, t = 0−4.5 h, m = 0.15 g.)
the consumption of BF was reduced at the maximum wavelength (λmax = 543 nm) of BF. It was found that high concentrations of BF dye in aqueous solutions were completely degraded over various times. After 180 min, the degradation rate of BF reached greater than 95%. From these data, it is important to understand the reaction kinetics.5,7 Hypothetically, the degradation of BF by synthetic cryptomelane could be an interfacial process41 that follows the Langmuir−Hinshelwood (L−H) model42,43 16192
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Table 2. Solubility of Mn(II) from Synthetic Cryptomelanea
a
sample
pH
Mn(II) concentration (mg/L)
scan blank wastewater 1 wastewater 2
7.0 6.2 3.6
4.67 19.51 25.90
CBF = 200 mg/L, VBF = 50 mL, m = 0.15 g, t = 3 h, T = 25 ± 2 °C.
that Mn(III) and Mn(IV) centers were incorporated within an oxide surface when the reaction occurred. BF was oxidized through the flux of Mn(III) and Mn(IV) from the surface to Mn(II) in solution, given the exceedingly high solubility of oxides formed from the Mn2+ oxidation state.30 As the reaction proceeded, Mn(III) and Mn(IV) were released from the crystal lattice. Meanwhile, Mn2+ was also adsorbed in the inside channel of the material, thus preventing the release of high-valence-state manganese ions and occupying the active site of cryptomelane. The BET tests showed that the surface area (43.11 m2/g) of cryptomelane had decreased by 28.5% after the reaction compared to that of the original cryptomelane. It was assumed that a pure adsorption reaction had occurred between the dye solution and cryptomelane. Furthermore, the more effective the material was, the higher the surface bonding capability was. Specific interactions between the reductant molecules and oxide surface sites were considered to be necessary for the reaction.45 It is generally accepted that the mechanism of removing BF is influenced by both the adsorption site at the crystal surface and the extent of chemical bonding with the surface. Thus, the degradation of BF is a surface oxidation reaction. The present study could help further distinguish and understand the possible reaction mechanisms.24
Figure 7. Nitrogen adsorption−desorption isotherm of the synthetic cryptomelane. Inset: Corresponding pore size distribution obtained from the adsorption curve.
isotherm and pore-size distribution plots of the synthesized nanorods. The cryptomelane showed a very wide pore size distribution, and the BET surface areas were within the same range. The nanomaterial exhibited a relatively spacious pore size, with an average pore diameter of 42.10 nm (Figure 7, inset). The BET surface area of the material was 60.26 m2/g, which was higher than the maximum value reported for natural cryptomelane (38.45 m2/g).17 This large surface area is conducive to the adsorption of organic matter. Along with the increase in surface area using synthetic cryptomelane, the catalytic activity of synthetic cryptomelane also gradually improved. Therefore, its surface-binding capability was stronger, and it exhibited higher degradation rates under identical conditions. Basic fuchsin in aqueous solution was first adsorbed onto the surface of the cryptomelane. Then, the chemical reaction occurred on the surface, and the generated product was separated from the surface of cryptomelane. From this analysis, one can see that the relatively weak adsorption capacity of cryptomelane can bring a higher degradation rate. The K value of the reaction was not large, BF in aqueous solution was easily adsorbed onto the surface, and the substances produced were also easily desorbed from the surface.1,42 If the reactants were not adsorbed, the catalytic reaction would not happen.41 In contrast, if the reactants were firmly adsorbed on the surface, the catalytic reaction would be relatively difficult.41,43 The particular performance of cryptomelane is very conducive to the catalytic reaction, and the kinetic data confirm that the catalyst exhibits a beneficial effect on the catalytic oxidation of BF. The mechanisms for the oxidation of organic compounds by metal complexes in homogeneous solutions have been conjectured. Reaction by a bonded mechanism involves direct bonding between the nanomaterial and BF. These concepts can then be extended to describe the reactions at material surfaces and used to explain the relative reactivities of organic compounds with Mn(III) and Mn(IV) sites of cryptomelane. In nature, manganese exists as Mn(II), Mn(III), and Mn(IV). Among these states, Mn(III) and Mn(IV) mainly exist in the form of insoluble manganese oxides and hydroxides, and only Mn(II) is soluble.26 The release of Mn2+ at oxide sites was determined at different pH values for the reaction. These results are reported in Table 2. However, at a lower pH value, the amount of dissolved manganese was much higher than that of the blank solution in the reaction process. It was assumed
4. CONCLUSIONS In conclusion, synthetic nanocryptomelane, with stronger oxidability than natural cryptomelane, was prepared by a facile and simple reflux method. Moreover, this cryptomelane exhibited a higher catalytic activity because of its larger specific surface area. A lower pH value was favorable for the dissolution of the basic fuchsin on the surface of nanocryptomelane and enhanced the removal efficiency of basic fuchsin. The synthetic cryptomelane exhibited good surface oxidation for the degradation of basic fuchsin under ambient conditions. In addition, the costs were lower when using synthetic cryptomelane than when using natural cryptomelane. Therefore, synthetic cryptomelane should also be applied in other environmental fields, such as soil remediation, catalytic materials, and heavy-metal adsorption.
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AUTHOR INFORMATION
Corresponding Author
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[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We are grateful to Prof. Anhai Lu of Central South University and Dr. Huiqin Zhang of Peking University for their help in providing natural cryptomelane samples. 16193
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(22) Li, L. Y.; King, D. L. Cryptomelane as High-Capacity Sulfur Dioxide Absorbent for Diesel Emission Control: A Stability Study. Ind. Eng. Chem. Res. 2005, 44, 7388. (23) Wang, J. Y.; Xia, G. G.; Yin, Y. G.; Suib, S. L.; O’Young, C. L. Cyclohexane Functionalization Catalyzed by Octahedral Molecular Sieve (OMS-1) Materials. J. Catal. 1998, 176, 275. (24) Yoshizawa, K.; Shiyota, Y.; Yamabe, T. Methane-Methanol Conversion by MnO+, FeO+, and CoO+: A Theoretical Study of Catalytic Selectivity. J. Am. Chem. Soc. 1998, 120, 564. (25) Luo, J.; Zhang, Q. H.; Martinez, J. G.; Suib, S. L. Adsorptive and Acidic Properties, Reversible Lattice Oxygen Evolution, and Catalytic Mechanism of Cryptomelane-Type Manganese Oxides as Oxidation Catalysts. J. Am. Chem. Soc. 2008, 130, 3198. (26) Gao, X.; Lu, A. H.; Qin, S.; Zheng, D. S.; Zheng, X. S.; Zheng, Z. A Study of Crystal Structural Characteristics and Environmental Properties of Natural Cryptomelane. Acta Petrol. Mineral. 2001, 20, 477. (27) McKenzie, R. M. The Surface Charge on Manganese Dioxides. Aust. J. Soil Res.. 1981, 19, 41. (28) Nyutu, E. K.; Chen, C. H.; Sithambaram, S.; Crisostomo, V. M. B.; Suib, S. L. Systematic Control of Particle Size in Rapid OpenVessel Microwave Synthesis of K-OMS-2 Nanofibers. J. Phys. Chem. C 2008, 112, 6786. (29) Cheney, M. A.; Birkner, N. R.; Ma, L. Z.; Hartmann, T.; Bhowmik, P. K.; Hodge, V. F.; Steinberg, S. M. Synthesis and Characterization of Inorganic Double Helices of Cryptomelane Nanomaterials. Colloids Surf. A 2006, 289, 185. (30) Tang, X. F.; Li, Y. G.; Chen, J. L.; Xu, Y. D.; Shen, W. J. Synthesis, Characterization, and Catalytic Application of TitaniumCryptomelane Nanorods/Fibers. Microporous Mesoporous Mater. 2007, 103, 250. (31) Farmer, V. C., Ed.; The Infrared Spectra of Minerals; Science Press: Beijing, 1982. (32) Yadav, G. D.; Manyar, H. G. Synthesis of a Novel Redox Material UDCaT-3: An Efficient and Versatile Catalyst for Selective Oxidation, Hydroxylation and Hydrogenation Reactions. Adv. Synth. Catal. 2008, 350, 2286. (33) Buciuman, F.; Patcas, F.; Craciun, R.; Zahn, D. Vibrational Spectroscopy of Bulk and Supported Manganese Oxides. Phys. Chem. Chem. Phys. 1999, 1, 185. (34) Gao, T.; Glerup, M.; Krumeich, F.; Nesper, R.; Fjellvåg, H.; Norby, P. Microstructures and Spectroscopic Properties of Cryptomelane-Type Manganese Dioxide Nanofibers. J. Phys. Chem. C 2008, 112, 13134. (35) Liu, Z. X.; Xing, Y.; Chen, C. H.; Zhao, L. L.; Suib, S. L. Framework Doping of Indium in Manganese Oxide Materials: Synthesis, Characterization, and Electrocatalytic Reduction of Oxygen. Chem. Mater. 2008, 20, 2069. (36) Villegas, J. C.; Garces, L. J.; Gomez, S.; Durand, J. P.; Suib, S. L. Particle Size Control of Cryptomelane Nanomaterials by Use of H2O2 in Acidic Conditions. Chem. Mater. 2005, 17, 1910. (37) Shen, X. F.; Ding, Y. S.; Liu, J.; Cai, J.; Laubernds, K.; Zerger, R. P.; Vasiliev, A.; Aindow, M.; Suib, S. L. Control of Nanometer-Scale Tunnel Sizes of Porous Manganese Oxide Octahedral Molecular Sieve Nanomaterials. Adv. Mater. 2005, 17, 805. (38) Liu, Z. Y.; Zhang, X. T.; Nishimoto, S.; Jin, M.; Tryk, Donald, A.; Murakami, T.; Fujishima, A. Highly Ordered TiO2 Nanotube Arrays with Controllable Length for Photoelectrocatalytic Degradation of Phenol. J. Phys. Chem. C 2008, 112, 253. (39) Kanungo, S. B.; Parida, K. M.; Sant, B. R. The Kinetics and the Mechanism for the Catalytic Decomposition of H2O2 Over Different Crystalline Modifications of MnO2. Electrochim. Acta 1981, 26, 1157. (40) Chinese National Standard GB 4287-1992. Discharge Standard of water pollutants for dyeing and finishing of textile industry. (41) Yang, L. Y.; Dong, S. Y.; Sun, J. H.; Feng, J. L.; Wu, Q. H.; Sun, S. P. Microwave-Assisted Preparation, Characterization and Photocatalytic Properties of a Dumbbell-Shaped ZnO Photocatalyst. J. Hazard. Mater. 2010, 179, 438.
REFERENCES
(1) Wawrzkiewicz, M. Application of Weak Base Anion Exchanger in Sorption of Tartrazine from Aqueous Medium. Solvent Extr. Ion Exch. 2010, 28, 845. (2) Gregory, P. Dyes and dyes intermediates. In Kirk-Othmer Encyclopedia of Chemical Technology; Kroschwitz, J. I., Ed.; John Wiley & Sons: New York, 1993; Vol. 8, p 544. (3) Wawrzkiewicz, M.; Hubicki, Z. Remazol Black B Removal from Aqueous Solutions and Wastewaters Using Weakly Basic Anion Exchange Resins. Cent. Eur. J. Chem. 2011, 9, 867. (4) Wawrzkiewicz, M. Comparison of Gel Anion Exchangers of Various Basicity in Direct Dye Removal from Aqueous Solutions and Wastewaters. Chem. Eng. J. 2011, 173, 773. (5) Wawrzkiewicz, M. Sorption of Sunset Yellow Dye by Weak Base Anion ExchangerKinetic and Equilibrium Studies. Environ. Technol. 2011, 32, 455. (6) Wawrzkiewicz, M.; Hubicki, Z. Removal of Tartrazine from Aqueous Solutions by Strongly Basic Polystyrene Anion Exchange Resins. J. Hazard. Mater. 2009, 164, 502. (7) Wawrzkiewicz, M.; Hubicki, Z. Kinetics of Adsorption of Sulphonated Azo Dyes on Strong Basic Anion Exchangers. Environ. Technol. 2009, 30, 1059. (8) Seredych, M.; Bandosz, T. J. Removal of Cationic and Ionic Dyes on Industrial−Municipal Sludge Based Composite Adsorbents. Ind. Eng. Chem. Res. 2007, 46, 1786. (9) Chen, L.; Yin, S. F.; Luo, S. L.; Huang, R.; Zhang, Q.; Hong, T.; Au, P. C. T. Bi2O2CO3/BiOI Photocatalysts with Heterojunctions Highly Efficient for Visible-Light Treatment of Dye-Containing Wastewater. Ind. Eng. Chem. Res. 2012, 51, 6760. (10) Huang, L. H.; Kong, J. J.; Wang, W. L.; Zhang, C. L.; Niu, S. F.; Gao, B. Y. Study on Fe(III) and Mn(II) Modified Activated Carbons Derived from Zizania Latifolia to Removal Basic Fuchsin. Desalination 2012, 286, 268. (11) Wawrzkiewicz, M. Comparison of the Efficiency of Amberlite IRA 478RF for Acid, Reactive, and Direct Dyes Removal from Aqueous Media and Wastewaters. Ind. Eng. Chem. Res. 2012, 51, 8069. (12) An, S. Y.; Min, S. K.; Cha, I. H.; Choi, Y. L.; Choi, Y. S.; Kim, C. H.; Lee, Y. C. Decolorization of Triphenylmethane and Azo Dyes by Citrobacter sp. Biotechnol. Lett. 2002, 24, 1037. (13) Reife, A. Dyes, Environmental Chemistry. In Kirk-Othmer Encyclopedia of Chemical Technology; Kroschwitz, J. I., Ed.; John Wiley & Sons: New York, 1993; Vol. 8, p 754. (14) Roberto, N. D.; Shen, Y. F.; Neth, E. J.; Suib, S. L.; O’Young, C. L.; Levine, S.; Newsam, J. M. Synthesis and Characterization of Octahedral Molecular Sieves (OMS-2) Having the Hollandite Structure. Chem. Mater. 1994, 6, 815. (15) Giraldo, O.; Brock, S. L.; Marquez, M.; Suib, S. L.; Hillhouse, H.; Tsapatsis, M. Materials: Spontaneous Formation of Inorganic Helices. Nature 2000, 405, 38. (16) Liu, J.; Makwana, V.; Cai, J.; Suib, S. L.; Aindow, M. Effects of Alkali Metal and Ammonium Cation Templates on Nanofibrous Cryptomelane-Type Manganese Oxide Octahedral Molecular Sieves (OMS-2). J. Phys. Chem. B 2003, 107, 9185. (17) Zhao, D. J.; Lu, A. H.; Wang, L. J.; Zheng, X. S.; Liu, R.; Guo, Y. J. Mineralogical Characteristics Study of Natural Cryptomelane in the Xialei Manganese Deposit, Guangxi. Acta Sci. Nat. Univ. Pekin. 2005, 41, 859. (18) Suib, S. L. Structure, Porosity and Redox in Porous Manganese Oxide Octahedral Molecular Sieve Materials. J. Mater. Chem. 2008, 18, 1623. (19) Feng, Q.; Kanoh, H.; Ooi, K. Manganese Oxide Porous Crystals. J. Mater. Chem. 1999, 9, 319. (20) Dai, J. X.; Li, S. Y.; Siow, K. S.; Gao, Z. Q. Synthesis and Characterization of the Hollandite-Type MnO2 as a Cathode Material in Lithium Batteries. Electrochim. Acta 2000, 45, 2211. (21) Hettiarachchi, G. M.; Pierzynski, G. M.; Ransom, M. D. In Situ Stabilization of Soil Lead Using Phosphorus and Manganese Oxide. Environ. Sci. Technol. 2000, 34, 4614. 16194
dx.doi.org/10.1021/ie302202r | Ind. Eng. Chem. Res. 2012, 51, 16188−16195
Industrial & Engineering Chemistry Research
Article
(42) Kim, S. B.; Hong, S. C. Kinetic Study for Photocatalytic Degradation of Volatile Organic Compounds in Air Using Thin Film TiO2 Photocatalyst. Appl. Catal. B 2002, 35, 305. (43) Sapawe, N.; Jalil, A. A.; Triwahyono, S.; Adam, S. H.; Jaafar, N. F.; Satar, M. A. H. Isomorphous Substitution of Zr in the Framework of Aluminosilicate HY by an Electrochemical Method: Evaluation by Methylene Blue Decolorization. Appl. Catal. B: Environ. 2012, 125, 311. (44) Nguyen, T.; Ollis, D. F. Complete Heterogeneously Photocatalysed Transformation of 1,1-and 1,2-Dibromothane to Carbon Dioxide and Hydrogen Bromide. J. Phys. Chem. 1984, 88, 3386. (45) Stone, A. T.; Morgan, J. J. Reduction and Dissolution of Manganese(III) and Manganese(IV) Oxides by Organics: 2. Survey of the Reactivity of Organics. Environ. Sci. Technol. 1984, 18, 617.
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