Mordant Yellow 3 Anions Intercalated Layered Double Hydroxides

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Mordant Yellow 3 Anions Intercalated Layered Double Hydroxides: Preparation, Thermo- and Photostability Pinggui Tang, Fuping Deng, Yongjun Feng,* and Dianqing Li State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China ABSTRACT: Mordant yellow 3 (MY3) anions have been intercalated into Zn-Al layered double hydroxides (LDH) to produce a novel intercalation compound pigment by a direct coprecipitation method. The prepared composite was characterized by various techniques such as powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry and differential thermal analysis (TGA-DTA), and UV−vis spectroscopy. The obtained results show that MY3 anions were intercalated into the interlayer spacing of LDH as observed from PXRD and FT-IR. Furthermore, the intercalation of MY3 anions into the LDH markedly enhances the thermo- and photostability of MY3, which may enlarge the practical application fields of MY3 dye.

1. INTRODUCTION Layered double hydroxides (LDH), known as one kind of anionic clays, has the general formula [M2+1−xM3+x(OH)2]x+(An−x/n)x‑·mH2O, [often abbreviated as M2+zM3+−A, z = (1 − x)/x], where M2+ and M3+ are metal cations in the brucite-like host layers and An− is interlayer anions in the hydrated interlayer galleries, x is equal to the molar ratio of M2+/(M2+ + M3+) in the range of 0.2−0.33.1 Based on the flexibility in composition and the exchangeability of interlayer anions, LDH materials have wide applications in different fields such as catalysts,2,3 adsorbents,4,5 anionic exchangers,6 pharmaceutics,7 polymer additives,8,9 and functional materials,10,11 etc. Organic dyes have attracted much attention in diverse fields, for example, textile industry, leather tanning industry, paper production, plastic, food technology. Compared to inorganic pigments, organic dyes have brighter color and less toxicity. Yet, their poor thermo- and photostability seriously limits the application fields under the outer environment such as sun light, temperature, and oxygen. Recent studies suggest that the thermo- and photostability of organic anions can be markedly improved after intercalation into the galleries of LDH because of supramolecular interactions between the host layers and the interlayer guest anions.12−16 Therefore, it is possible to effectively stabilize organic dyes by intercalating the corresponding anions into LDH to produce novel nontoxic hybrid pigments.17,18 Mordant Yellow 3 (CAS no. 6054-97-3, abbreviated as MY3), as one of the sulfonated azo compounds, is widely used as dye for textiles and in the food and cosmetics industries. Figure 1 shows its molecular structure and color of its powder. In this work, we mainly investigated the preparation of ZnAlMY3-LDH by a direct (one-step) coprecipitation method and further analyzed the structural properties and the thermo- and photostability of the synthesized product in detail.

Figure 1. The molecular structure (a) and image of the powder (b) of Mordant Yellow 3.

purchased from Tokyo Kasei Kogyo Co., LTD (Japan) with a purity of 98%. Deionized water with the conductivity of less than 10−6 S·cm−1 was freshly decarbonated by boiling before use in the synthesis and washing steps. 2.2. Synthesis of ZnAl-NO3-LDH. The ZnAl-NO3-LDH was prepared by a method involving separate nucleation and aging steps (SNAS).19 Typically, Zn(NO3)2·6H2O (35.70 g, 0.12 mols) and A1(NO3)3·9H2O (22.51 g, 0.06 mols) were dissolved in water (150 mL) to make a mixed salt solution. NaOH (14.40 g, 0.36 mols) was dissolved in water (150 mL) to make an alkali solution. The two solutions were simultaneously added to a colloid mill at a rotating speed of 3000 rpm and were mixed for 2 min. The resulting slurry was then aged at the refluxing temperature for 6 h under a N2 stream. The product cake was collected after six repetitive centrifugation and dispersion cycles in deionized water and the obtained cake was dried at 80 °C to constant weight. 2.3. Synthesis of ZnAl-MY3-LDH. ZnAl-MY3-LDH was prepared using a so-called coprecipitation method previously described.20 Typically, Zn(NO3)2·6H2O (5.95 g, 0.02 mols), A1(NO3)3·9H2O (3.75 g, 0.01 mols), and MY3 (8.33 g, 0.02 mols, [MY3]/[Al3+] = 2) were dissolved in water to make a mixed solution; NaOH (2.40 g, 0.06 mols) was dissolved in water to form an alkali solution. The alkali solution was added Received: Revised: Accepted: Published:

2. EXPERIMENTAL SECTION 2.1. Chemicals. NaOH, Zn(NO3)2·6H2O, Al(NO3)3·9H2O, HNO3, and ethanol were all A.R. grade reagents. MY3 was © 2012 American Chemical Society

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dropwise to the mixed solution under vigorous stirring, and the pH value was adjusted to 6.5 by adding 0.01 mol L−1 HNO3. The resulting slurry was then aged at 90 °C for 48 h. All the processes were under a nitrogen atmosphere. The product cake was collected after six repetitive centrifugation and dispersion cycles with water and ethanol until the solution was nearly colorless and the obtained cake was dried at 80 °C to constant weight. 2.4. Analysis and Characterization. X-ray diffraction (XRD) patterns were obtained using a Shimadzu XRD-6000 diffractometer with monochromatic Cu Kα radiation (λ = 0.15406 nm) operating at 40 kV and 30 mA, with a scanning rate of 10°·min−1 from 3° to 70°/2θ. FT-IR spectra were collected on a Bruker Vector 22 infrared spectrophotometer using the KBr disk method with a ratio of sample/KBr of 1:100 by mass. Thermogravimetry and differential thermal analysis (TGA-DTA) curves were recorded on a PCT-IA instrument in the temperature range of 30−800 °C with a heating rate of 5 °C·min−1 under air atmosphere. Diffuse reflectance UV−visible absorbance spectra were recorded using a Shimadzu UV2501PC instrument with an integrating sphere attachment in the range 200−800 nm using BaSO4 as the reference. Elemental analysis for metal elements in the LDH powder was performed using an ICPS-7500 model inductively coupled plasma emission spectrometer (ICP-ES). Carbon, nitrogen, and sulfur analyses were carried out on Elementar Analyzer vario EL cube. The color difference (ΔE) of materials after thermo- and photoaging treatment was determined in terms of CIE 1976 L*a*b* using a TC-P2A automatic colorimeter. The CIE 1976 L*a*b* is a color scale based on the opponent-colors theory, among L*, a*, and b* values indicate the level of light-dark, red-green, and yellow-blue colors.21,22

Figure 2. Powder X-ray diffraction patterns of (a) ZnAl-NO3-LDH and (b) ZnAl-MY3-LDH.

from bigger size of the MY3 anions related to the NO3− anions, suggesting successful preparation of LDH containing MY3 anions. In comparison, besides, the (110) peak remains in the same position as observed for ZnAl-NO3-LDH, indicating that the same chemical composition is in the Brucite-like layer.14 3.2. FT-IR Analysis. Figure 3 displays FT-IR spectra of (a) ZnAl-NO3-LDH, (b) MY3 and (c) ZnAl-MY3-LDH. For ZnAl-

3. RESULTS AND DISCUSSION 3.1. Chemical Composition. The chemical composition of prepared dye-LDH was determined: 23.61 wt % for Zn, 5.59 wt % for Al, 25.54 wt % for C, 3.52 wt % for N, and 4.04 wt % for S. The molar ratio of S over Al is equal to 0.608, which is lager than 0.50 for divalent dye anions ([MY3]2−) and less than 1.0 for monovalent dye anions ([MY3]−). Furthermore, no excessive N element was detected related to the S element with a ratio of 1.99, which is very close to the theoretical value of 2.0 in the molecular formula of MY3 (C13H8N2Na2O6S). Therefore, we proposed that a mixture of di- and monovalent dye anions lay in the interlayer spacing. The content of the MY3 anions was calculated by the content of the N and S. On the basis of the charge balance and the mass balance, the possible chemical formula is evaluated as Zn0.64Al0.36(OH)2(MY3−)0.08(MY32−)0.14·0.51H2O, where the amount of interlayer water is calculated from the TGA data in the range 100−200 °C (see Figure 4). 3.2. X-ray Diffraction Data. Figure 2 shows powder X-ray diffraction (PXRD) patterns of ZnAl-NO3-LDH and ZnAlMY3-LDH. The basal spacing value [(d003 + 2d006 + 3d009)/3] of ZnAl-NO3-LDH (Figure 2a) is estimated to be 0.89 nm, which agrees well with the value in the literature.23 In Figure 2b, one observes a typical layered structure of the LDH material. The new characteristic diffractions peaks (003), (006) shift to low 2θ, suggesting the expansion of the basal spacing from 0.89 nm for ZnAl-NO3-LDH to 1.54 nm for ZnAl-MY3LDH, which is close to the size along the longest direction of the MY3 anions (1.53 nm, determined by ChemBio3D Ultra 12.0 evaluation version). The expansion of d-spacing results

Figure 3. FT-IR spectra of (a) ZnAl-NO3-LDH, (b) MY3, and (c) ZnAl-MY3-LDH.

NO3-LDH, the characteristic absorption bands are observed as reported in the literature, for example, one at 1384 cm−1 is ascribed to NO3−.16 Similarly as suggested by the PXRD results, the FT-IR bands show the presence of MY3 anions in the LDH structure in the ZnAl-MY3-LDH sample, see Figure 3b. The absorption bands at 1610 and 1483 cm−1 are assigned to the vibration of phenyl groups and ones at 1178 and 1045 cm−1 are ascribed to the absorption bands of the −SO3− group. In comparison, the vibrations of the −SO3− group in ZnAl-MY3LDH shift to lower frequency related to these in pure MY3, possibly resulting from the host−guest interactions between the hydroxide layers and the dye anions. Besides, no absorption peak at 1384 cm−1 is obviously observed in the ZnAl-MY3LDH sample, which is in agreement with the determined results of element analysis. 10543

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3.3. Thermal Stability Analysis. Figure 4 demonstrates the TGA-DTA curves of MY3 and ZnAl-MY3-LDH

indicating that the thermal stability of MY3 is significantly improved by intercalation into the interlayer space of LDH. The MY3 turns black after being heated at 300 °C for 30 min (see Figure 6), while the ZnAl-MY3-LDH retains essentially its

Figure 6. Digital photographs of MY3 and ZnAl-MY3-LDH powder before and after thermal aging at 300 °C for 30 min: (a,b) MY3 and (c,d) ZnAl-MY3-LDH. Figure 4. TGA-DTA curves of MY3 in black and ZnAl-MY3-LDH in red.

original color. The darkening of the MY3 possibly results from the partial thermo-oxidative reaction, which is in agreement with the results observed on the DTA curves in Figure 4. All the results show that the ZnAl-MY3-LDH sample has a much higher thermal stability related to the MY3 sample, which may result from the strong host−guest interactions between the Brucite-like host layers and the dye anions. 4. Photostability of the Samples. The photostability of ZnAl-MY3-LDH was tested in comparison to that of the physical mixture of MY3 and ZnAl-NO3-LDH containing the same content of dye. Both of the samples were investigated using a UV accelerated photoaging instrument (power of the UV light = 1000 W and λmax = 365 nm) with a controllable temperature system as described elsewhere.24 The samples were exposed to a UV lamp and the color difference (ΔE) values of the irradiated samples (see Figure 7) were measured by automatic colorimeter every 5 min up to a total exposure time of 60 min. The ΔE values for the physical mixture sample are obviously larger than those for ZnAl-MY3-LDH after irradiation for the same times. The ΔE value of MY3 after photoaging for 60 min was 23, whereas for ZnAl-MY3-LDH it was less than 15. These values suggest that the photostability of MY3 anions is enhanced by intercalation into the interlayer space of ZnAl-LDH. The host matrix layers of the LDH afford the protections for the MY3 anions and furthermore the host−

determined in air atmosphere, suggesting that the intercalation of MY3 anions into the interlayer spacing of the LDH significantly improves the thermal stability of the MY3 species. One observes the first endothermic peak centered at 435 °C for ZnAl-MY3-LDH sample and the peak at 299 °C for the MY3 sample, which possibly corresponds to the partial thermooxidative reaction of the MY3 species. The decomposition temperature starts at ca. 350 °C for the ZnAl-MY3-LDH and at ca. 240 °C for the MY3 sample, see the DTA curves. The increase in decomposition temperature signifies enhancement of the thermal stability of the MY3. The thermal stability of ZnAl-MY3-LDH and MY3 was further evaluated using diffuse reflectance UV−vis spectroscopy and chromatic curves, which are available to monitor UV−vis absorption spectrum and color when both of the samples are heated at 100, 150, 200, 250, and 300 °C in an oven for 30 min, see Figure 5. The absorption spectrum of MY3 shows obvious change after heating at above 150 °C in the range from 450 to 600 nm. For the ZnAl-MY3-LDH sample, yet, only slight change is observed in the spectra until the heating temperature increases to 300 °C. Similarly, the color difference (ΔE) value for pristine MY3 is considerably larger than that for ZnAl-MY3LDH after thermal aging at the corresponding temperature,

Figure 5. UV−vis spectra (left) and color difference (right) of (a) MY3 and (b) ZnAl-MY3-LDH after thermal aging at different temperatures. The samples remain at each temperature for 30 min. 10544

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(7) Choy, J.-H.; Jung, J.-S.; Oh, J.-M.; Park, M.; Jeong, J.; Kang, Y.-K.; Han, O.-J. Layered Double Hydroxide as an Efficient Drug Reservoir for Folate Derivatives. Biomaterials 2004, 25, 3059. (8) Oriakhi, C. O.; Farr, I. V.; Lerner, M. M. Incorporation of Poly(acrylic acid), Poly(vinylsulfonate) and Poly(styrenesulfonate) within Layered Double Hydroxides. J. Mater. Chem. 1996, 6, 103. (9) Evans, D. G.; Duan, X. Preparation of Layered Double Hydroxides and Their Applications as Additives in Polymers, as Precursors to Magnetic Materials and in Biology and Medicine. Chem. Commun. 2006, 485. (10) Hwang, S. H.; Han, Y. S.; Choy, J. H. Intercalation of Functional Organic Molecules with Pharmaceutical. Cosmeceutical and Neutraceutical Functions into Layered Double Hydroxides and Zinc Basic Salts. Bull. Korean Chem. Soc. 2001, 22, 1019. (11) Khan, A. I.; Ragavan, A.; Fong, B.; Markland, C.; O’Brien, M.; Dunbar, T. G.; Williams, G. R.; O’Hare, D. Recent Developments in the Use of Layered Double Hydroxides as Host Materials for the Storage and Triggered Release of Functional Anions. Ind. Eng. Chem. Res. 2009, 48, 10196. (12) Tian, Y.; Wang, G.; Li, F.; Evans, D. G. Synthesis and ThermoOptical Stability of O-Methyl Red-Intercalated Ni−Fe Layered Double Hydroxide Material. Mater. Lett. 2007, 61, 1662. (13) Guo, S.; Li, D. Q.; Zhang, W. D.; Pu, M.; Evans, D. G.; Duan, X. Preparation of an Anionic Azo Pigment-Pillared Layered Double Hydroxide and the Thermo- and Photostability of the Resulting Intercalated Material. J. Solid State Chem. 2004, 177, 4597. (14) Tang, P. G.; Xu, X.; Lin, Y.; Li, D. Q. Enhancement of the Thermo- and Photostability of an Anionic Dye by Intercalation in a Zinc-Aluminum Layered Double Hydroxide Host. Ind. Eng. Chem. Res. 2008, 47, 2478. (15) Chakraborty, C.; Dana, K.; Malik, S. Intercalation of Perylenediimide Dye into LDH Clays: Enhancement of Photostability. J. Phys. Chem. C 2010, 115, 1996. (16) Tang, P.; Feng, Y. J.; Li, D. Q. Improved Thermal and Photostability of an Anthraquinone Dye by Intercalation in a Zinc− Aluminum Layered Double Hydroxides Host. Dyes Pigm. 2011, 90, 253. (17) Laguna, H.; Loera, S.; Ibarra, I. A.; Lima, E.; Vera, M. A.; Lara, V. Azoic Dyes Hosted on Hydrotalcite-like Compounds: Non-toxic Hybrid Pigments. Microporous Mesoporous Mater. 2007, 98, 234. (18) Bauer, J.; Behrens, P.; Speckbacher, M.; Langhals, H. Composites of Perylene Chromophores and Layered Double Hydroxides: Direct Synthesis, Characterization, and Photo- and Chemical Stability. Adv. Funct. Mater. 2003, 13, 241. (19) Zhao, Y.; Li, F.; Zhang, R.; Evans, D. G.; Duan, X. Preparation of Layered Double Hydroxide Nanomaterials with a Uniform Crystallite Size Using a New Method Involving Separate Nucleation and Aging Steps. Chem. Mater. 2002, 14, 4286. (20) Leroux, F.; Taviot-Gueho, C. Fine Tuning between Organic and Inorganic Host Structure: New Trends in Layered Double Hydroxide Hybrid Assemblies. J. Mater. Chem. 2005, 15, 3628. (21) M, S. Modelling of CIELAB Values in Vinyl Sulphone Dye Application Using Feed-Forward Neural Networks. Dyes Pigm. 2007, 75, 356. (22) Khan, M. A. I.; Ueno, K.; Horimoto, S.; Komai, F.; Someya, T.; Inoue, K.; Tanaka, K.; Ono, Y. CIELAB Color Variables as Indicators of Compost Stability. Waste Manage. (Oxford) 2009, 29, 2969. (23) Legrouri, A.; Badreddine, M.; Barroug, A.; De Roy, A.; Besse, J. P. Influence of pH on the Synthesis of the Zn−Al−Nitrate Layered Double Hydroxide and the Exchange of Nitrate by Phosphate Ions. J. Mater. Sci. Lett. 1999, 18, 1077. (24) Feng, Y. J.; Li, D. Q.; Wang, Y.; Evans, D. G.; Duan, X. Synthesis and Characterization of a UV Absorbent-Intercalated Zn-Al Layered Double Hydroxide. Polym. Degrad. Stab. 2006, 91, 789.

Figure 7. Color difference (ΔE) values of (a) the physical mixture of MY3 and ZnAl-NO3-LDH and (b) ZnAl-MY3-LH after UV aging for different times.

guest interaction improves the photostability of the MY3 species when they are intercalated into the interlayer spacing of the LDH.

4. CONCLUSIONS MY3 anions have been successfully intercalated into the interlayer space of ZnAl-LDH by coprecipitation to prepare a novel intercalation compound pigment. The intercalation of MY3 into the interlayer gallery of ZnAl-LDH notably enhances the thermo- and photostability of MY3 due to the host−guest interactions between the host matrix layers and the MY3 guest anions. Undoubtedly, it provides an effective way for organic anion dyes with poor thermo- and photostability to improve their stability for more practical applications in different fields.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86−10−64436992. Fax: +86−10−64425385. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China. REFERENCES

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dx.doi.org/10.1021/ie300645b | Ind. Eng. Chem. Res. 2012, 51, 10542−10545