Effect of drying step on layered double hydroxides properties: Application in reactive dye intercalation

Applied Clay Science 182 (2019) 105246

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Research paper

Effect of drying step on layered double hydroxides properties: Application in reactive dye intercalation

T

Kaoutar El Hassania, , Hajar Jabkhiroa, Daina Kalninab, Buscotin Horax Beakoua, Abdellah Anouara ⁎

a

University Hassan First, Faculty of Science and Technology, Laboratory of Applied Chemistry and Environment, BP. 577, Route de Casa, 26000 Settat, Morocco Rudolfs Cimdins Riga Biomaterials Innovations and Development Centre of RTU, Institute of General Chemical Engineering, Faculty of Materials Science and Applied Chemistry, Riga Technical University, Pulka 3, LV-1007 Riga, Latvia

b

ARTICLE INFO

ABSTRACT

Keywords: Layered double hydroxide Freeze-drying Reactive dye Partial intercalation Preferential orientation

Freeze-dried sulfate intercalated layered double hydroxides (LDH) phase was synthetized by coprecipitation method via direct intercalation of sulfate anion. The effect of freeze-drying process on LDH properties was investigated. The resulting phase was evaluated for its efficiency in the intercalation of the reactive azo dye, Remazol Brilliant Red F3B (RR-F3B). The freeze-dried phase exhibited a low crystallinity and narrow particle size distribution compared to conventional LDH phases. The freezing step led to highly aggregated nanoparticles with a characteristic distance d003 of 8.12 Å. The preferential arrangement of the intercalated dye species was examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. The results showed that RR-F3B molecules were partially accommodated between the LDH layers as single-layer with horizontal orientation. The effect of drying on morphological and structural properties can be attributed to several stresses during freezing and drying steps.

1. Introduction Reactive dyes are the most used dye class in textile industry, especially in dyeing cotton fabrics which make up about half of the world's fiber consumption (Schramm et al., 1988; Khatri et al., 2015). This dye class has a weak fixation efficiency (Weber and Stickney, 1993; Gouvêa et al., 2000), which means that the loss in the dyeing process lead to a serious environmental crisis. The unfixed dyes generate a highly colored effluent with high levels of dissolved solids that require an efficient removal process from aqueous media. Many attempts have been made using variety of materials for reactive dyes disposal such as nanoparticles (Kale and Kane, 2019; Tony and Mansour, 2019), activated carbon (Saroyan et al., 2019; Streit et al., 2019), clays (Kim et al., 2019; Queiroga et al., 2019), sludge (Shiva Shankar et al., 2019), modified chitosan (Li et al., 2019; Tanhaei et al., 2019), and polymers (Tayebi et al., 2019). Layered double hydroxides (LDH)/dye represent suitable inorganic/ organic assemblies for stabilizing various contaminants in solutions including organic macromolecules (El Hassani et al., 2017; Dai et al., 2019; Gao et al., 2019). The interest in incorporating organic compounds onto LDH as inorganic host structures is still drawing attention. LDH are 2D layered nanomaterials with general formula [M1−x2+ ⁎

Mx3+(OH)2]Ax/mm−. nH2O, where M2+ and M3+ are divalent and trivalent metal cations constituting the positively charged host layers with exchangeable balancing anions Am- in the interlayer space (Miyata and Kumura, 1973). Owing to their structure, they are known for their exceptional property which is anionic exchange capacity (Meyn et al., 1990, 1993). Nevertheless, the nature of that space is highly influenced by the forces that compose it. That is to say, the higher the affinity of the interposed anion, the more the exchange process is complicated. In fact, the carbonate ion has the highest affinity towards LDH structure, making its presence a challenging situation (Iyi et al., 2004). Generally, the contamination by carbonate ion happens during the separation of the wet LDH originating from atmospheric CO2 whether throughout filtration or drying; thus, the effect of drying step is crucial. Indeed, drying process is a critical step in nanoparticles preparation and can affect their physiochemical properties (Rahman et al., 2008; Wang et al., 2010; Bastan et al., 2017; Olusegun et al., 2019). Various drying techniques were applied to discard water from wet nanoparticles such as conventional oven-drying, spray drying (Bastan et al., 2017; Olusegun et al., 2019), freeze-drying (Eggenhuisen et al., 2013; Ge et al., 2018), and supercritical drying (Balakhonov et al., 2018; Pakowski, 2007). In many cases, to obtain a final dry product with the expected properties, choosing a specific drying process is crucial. That

Corresponding author. E-mail address: [email protected] (K. El Hassani).

https://doi.org/10.1016/j.clay.2019.105246 Received 15 May 2019; Received in revised form 22 June 2019; Accepted 30 July 2019 0169-1317/ © 2019 Elsevier B.V. All rights reserved.

Applied Clay Science 182 (2019) 105246

K. El Hassani, et al.

is why, not all drying methods could prevent carbonate contamination for wet LDH compounds. For example, Hibino (2015) investigated the effect of three drying methods regarding the prevention of carbonate contamination. He found that carbonate content in air-dried LDH was greater than those in vacuum or oven-dried LDH powder, subsequently affecting their adsorption capacity. Still, very few studies have been devoted to studying the effect of drying methods on the preparation of powdered LDH nanomaterial. This work focused on preparing magnesium-aluminum containing LDH intercalated by sulfate anion (MgAl/SO4) using common coprecipitation followed by freeze-drying process. Freeze-drying, known as lyophilization, is a low-thermal method for water elimination from a frozen material by sublimation and desorption of ice crystals. This technique represents a key process in the production of nanoscaled materials for various industries (Chen and Wang, 2007; Hua et al., 2010; Ratti, 2013). Besides, freeze-drying commonly involves three steps: freezing, primary drying, and secondary drying (Flosdorf, 1949). Although, freeze-drying is an efficient process to obtain a fine and homogeneous dry powder with an excellent control over impurity levels and composition (Abdelwahed et al., 2006a), the frozen-materials are exposed to several stresses during freezing and drying steps. Consequently, further undesirable effects may rise (Wang et al., 2005; Chung et al., 2012). The aim of this study is to obtain insight into drying effect on physical and morphological properties of MgAl/SO4 phase was discussed. Assays for the intercalation of RR-F3B dye onto MgAl/SO4 were carried out and the possible LDH/dye interactions were discussed.

transform infrared spectrometer (FT-IR, Varian 800 Scimitar Series, Australia) through attenuated total reflectance (ATR, GladiATRTM) mode. Spectrawere recorded in the range of 400–4000 cm−1 with spectral resolution 4 cm−1 and 50 times scanning. The average particle size and size distribution were measured by dynamic light scattering (DLS, Zetasizer Nano Series, Malvern Ltd). 2.4. Intercalation experiments The intercalation assays of RR-F3B dye in aqueous solution onto MgAl/SO4 were carried out, at room temperature, in a batch experiment. The effect of pH was studied in the range 3.5–11. 30 mg of LDH were dispersed in 30 mL of dye solution at initial dye concentration of 50 mg/L. The initial pH was adjusted with H2SO4 and NaOH (0.1 N or 1 N). For kinetic studies, three kinetics models were applied to fit the experimental data: Lagergren-pseudo-first order Eq. (1) (Lagergren, 1898), pseudo-second order Eq. (2) (HO, 2006), and Weber's intraparticle diffusion Eq. (3) (Weber and Morris, 1963).

Log(q e

qt) = logq e

K1. t 2.303

(1)

t 1 t = + qt k2q 2e qe

(2) (3)

qt = kit1/2 + C −1

where, qe and qt are the amounts of RR-F3B dye adsorbed (mg·g ) at equilibrium and at time t (min), respectively; k1 (min−1) and k2 (g. (mg·min)−1) are the pseudo-first order and pseudo-second order rate constants, respectively. ki (mg.(g·min0.5)−1) is the intra-particle diffusion rate constant, and C is the intercept. For deintercalation experiments, 50 mg of MgAl/SO4 was added to 50 mL of RR-F3B dye solution (20 mg·L−1, pH = 4). The mixture was stirred at room temperature to reach equilibrium. Then, the saturated solid was separated by centrifugation, washed and oven-dried. The dyeloaded samples were dispersed in three types of solution: distilled water, NaOH (0.1 mol·L−1) and Na2CO3 (0.1 mol·L−1). The mixture was stirred for 300 min on a thermostatic shaker and then separated by centrifugation. The concentration of the solutions was measured by UV–vis spectrophotometer.

2. Experimental section 2.1. Materials C.I. Remazol Brilliant Red F3B or reactive red 120 is an azo-reactive dye of the chemical formula C29H19N3Na4O17S5, noted as RR-F3B. The maximum absorption (λmax) in the UV–Vis spectra was obtained at a wavelength of 466 nm. All the reagents were used without further purification. 2.2. Preparation of MgAl-SO4 LDH 2.2.1. Coprecipitation MgAl/SO4 phase was synthetized by coprecipitation method with direct intercalation of sulfate anions at room temperature. Mixed salt solution containing Mg(NO3)2.6H2O (0.75 mol·L−1) and Al (NO3)3.9H2O (0.25 mol·L−1) with a molar ratio of 3, was gradually added to a reaction medium initially containing 50 mL of Na2SO4 (5.10−1 mol·L−1) as sulfate anion source. The pH of the reaction mixture was adjusted at 9 using NaOH solution of (2 mol·L−1). In order to avoid the insertion of carbonate anions, the synthesis was carried out under an inert atmosphere N2. The resulted white gel was washed several times with decarbonized distilled water and then centrifuged.

3. Results and discussion 3.1. Characterization of freeze-dried MgAl/SO4 XRD patterns of as prepared MgAl/SO4 and MgAl/RR-F3B after intercalation of RR-F3B dye are presented in Fig. 1A. Freeze-dried MgAl/ SO4 exhibited diffraction peaks at 2θ = 10.88°, 21.72°, 34.82°, 38.49°, 45.43°, 60.77°, 60.91°, sharing the same characteristic reflections of the hydrotalcite-like structure (Cavani et al., 1991). Thus, the diffraction peaks could be assigned to MgAl-LDH planes (Fig. 1A). However, the freeze-drying conditions influenced the intensity of the peaks providing low crystalline phase with many stacking defects. In Contrast to the conventional oven-dried MgAl-LDH phases that show, generally, sharp and symmetrical diffraction peaks illustrating a well-ordered structure (high crystallinity) (Paikaray and Hendry, 2012; Khitous et al., 2016). Also, Julklang et al. (2017) prepared spray-dried MgAl-LDH phases and the drying process conditions showed no effect on the LDH crystallinity or structural arrangement of functional groups in the interlayer space. That is to say, the freeze-drying step produced fewer crystals, which is in agreement with the findings of different studies (Abdelwahed et al., 2006a; Moriyama et al., 2016). The basal spacing d003 was calculated to be 8.12 Å, which is close to other studies findings (Constantino and Pinnavaia, 1995; Theiss et al., 2012; Radha and Kamath, 2013), indicating the successful intercalation of the sulfate anion in the Mg–Al

2.2.2. Freeze-drying The white gel was frozen and the resulting solid was freeze-dried using Alpha 1-4 LDplus Freezer Dryer under vacuum at −30 °C overnight. 2.3. Characterization methods X-ray diffraction (XRD) was performed at room temperature under ambient air conditions on a Phaser D2 diffractometer, using Cu Kα1 radiation (λ = 1.54060 Å) at 10 mA, 30 kV and a 2θ angle ranging from 5° to 90°. Scanning electron microscopy (SEM) analysis was performed on a Phenom XL scanning electron microscope with an accelerating voltage of 10 kV. The sample was spread on carbon tape adhered to a SEM stage and coated with a thin gold layer before imaging. Surface functional groups of the sample were determined using Fourier 2

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Fig. 1. (A) X-ray diffraction patterns of freeze-dried MgAl/SO4 and MgAl/RR-F3B (after dye intercalation); (B) ATR-FTIR spectra of freeze-dried MgAl/SO4.

phase. However, different d003 values for the same anion were reported by other studies; this suggests that several modes of stacking of interlayer sulfate anion and water molecules are possible. For instance, Mostarih and de Roy (2006) found that the intercalation of sulfate anion in LDH compounds gives two types of phases, LDH-SO4/11 Å and LDH-SO4/8.9 Å. This was explained by the presence of sodium sulfate [(2Na+)aq + SO42−] in the interlayer space, which is easily removable by washing. While, Li et al. (2006) obtained two types of arrangements for sulfate intercalated-LDH phase, characterized by different distances d003, depending on the amount of water molecules present in the interlayer space. Experimentally, by varying the relative humidity in which the LDH sample was stored, the orientation of the interlayer anion changes. Consequently, in this study, the freeze-drying step influenced the orientation of sulfate ions between the positive layers during the sublimation of ice crystals. ATR-FTIR spectra analysis confirmed the presence of sulfate anion in the interlayer space of MgAl/SO4 phase and the result is shown in Fig. 1B. A broad band at ~3445 cm−1 corresponds to (i) hydroxyl group deformation mode water molecules and (ii) stretching modes of OH groups associated with the interlayer water molecules and the hydrogen bonding. The bands observed in the region of lower frequencies (~ 400–600 cm−1) correspond to LDH lattice vibrations MgeO, AleO and metal-oxygen-metal fragments vibrational modes (Saiah et al., 2009). A weak band at ~ 981 cm−1 and an intense band at ~1116 cm−1 can be assigned to the vibration mode of SO42− anions in the interlayer space (Paikaray and Hendry, 2014; Davantès et al., 2015), confirming that the sample was sulfate type LDH. However, despite all the precautions taken during the synthesis, there is still weak absorption band at 1355 cm−1, which belongs to CO32− ions (Duan et al., 2016). Carbonate contamination might have many reasons and, in this work, it was likely captured from air during the washing-centrifugation cycles. It was believed that no contamination occurred during the freeze-drying process or could be very low as the process is performed under vacuum, while conventional drying is generally carried out in open-recipients to the atmosphere. According to the authors knowledge, there is no information in the literature concerning carbonate contamination during freeze-drying that could support the previous assumptions. Moriyama et al. (2016) studied the effect of freeze-drying on Cl- and NO3-type LDH, but carbonate contamination was not investigated since the syntheses were conducted in air. The morphological features and particle size distribution of freezedried MgAl/SO4 phase were examined and the results are shown in Fig. 2A–B. As observed in Fig. 2A, a rough and non-homogeneous surface with multiple-pores was observed in the freeze-dried phase. This structure is composed of highly agglomerated nanoparticles with a fluffy texture. In fact, during the opted drying method, freezing is the aggressive step that causes stresses inducing severe aggregation or

fusion of nanoparticles (Wang et al., 2005; Abdelwahed et al., 2006b; Chung et al., 2012). Niu and Panyam (2017) confirmed the relationship between aggregation phenomena and freezing step using real-time dynamic visualization and super-resolution imaging techniques for frozen systems. Furthermore, the freeze-dried LDH phases are less dense than the oven-dried LDH phases. From Fig. 2B, the resulting phase displayed a narrow particle size distribution ranging from 200 to 300 nm with average particle size of 220 nm. In contrast to the conventional drying process, the particle size usually exhibits bimodal distribution and aggregates with size ranging from 1 μm to 10 μm (He et al., 2006). 3.2. Dye intercalation via anion exchange 3.2.1. Effect of initial pH RR-F3B intercalation experiments were examined within a large interval of pH values, from 3.5 to 11. The discoloration rate (%) was determined from the difference between the initial concentration C0 (mg/L) and equilibrium concentration Ce (mg/L) of dye: [(C0 − Ce)/ C0]·100%. The results illustrated in Fig. 3 indicate maximum discoloration (98%) at acidic pH 4. When increasing the initial solution pH, the discoloration rate decreases slightly to a value of 91% corresponding to pH 11. These results implied that the pH did not have a significant impact. This could be explained in two different ways: (1) based on the structure of RR-F3B dye molecule, which has four sulfonate groups, the dye exhibits a permanent anionic charge over a wide pH range, while the MgAl layers are positively charged enhancing the fixation of the dye on the surface through electrostatic forces. (2) On the other hand, the removal of RR-F3B was not totally controlled by the fixation mechanism on the external surface of MgAl/SO4, however a further anion exchange of interlayer SO42− with dye species occurred. 3.2.2. Kinetics study To get more insights into the mechanism of RR-F3B dye removal, the order of dye-MgAl interactions was studied using three kinetic models. The results are shown in Fig. 4 and the calculated parameters of each model are listed in Table 1. In case the removal of RR-F3B dye was conducted totally by adsorption on the external surface preceded by diffusion through a boundary, the kinetics would generally follow the pseudo-first-order equation of Lagergren. However, the plot of log (qe − qt) versus time was not linear as shown in Fig. 4A, which indicates that it is not the appropriate model to describe these results. The second-order model was then tested by plotting t qt versus time. From Fig. 4B, a linear regression was obtained with high value of correlation coefficient (Table 1). In addition, the theoretical value of qe is consistent with the experimental data. That is to say, the second-order model could describe better the RR-F3B dye removal that is monitored 3

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Fig. 2. (A) SEM images at low (left) and high magnification (right); (B) Particle size distribution of freeze-dried MgAl/SO4.

saturated, the dye penetrates progressively into the internal surface of the particles through the pores that constitutes the intra-particle diffusion step, thus the ion exchange occurs. 3.2.3. Identification and preferential arrangement of the intercalated RRF3B dye The estimated dimensions of geometry-optimized RR-F3B dye were obtained using ChemDraw software, and they are illustrated in Fig. 5. The intercalation of RR-F3B dye was confirmed by XRD analysis (Fig. 1B). XRD pattern of MgAl/RR-F3B demonstrated an increase in the peaks intensity, which could be explained by drying the sample in oven. Besides, the intercalation of RR-F3B resulted in a weak displacement of the peaks and basal distance of 7.91 Å was obtained. The latter value was lower than sulfate characteristic distance (8.12 Å), suggesting that the interlayer space was not expanded despite the size of RR-F3B molecule. In fact, the value of the interlayer distance is the difference between the basal distance and the thickness of the layers. Taking into account that the thickness of the LDH single layer is 4.8 Å, the interlayer distance, which is the size of the intercalated molecule, should be approximately 3.11 Å. Although the RR-F3B molecule long axis length is about 21.26 Å, the calculated distance between the layers would be 16.46 Å, resulting in a basal distance of 26 Å for single-layer of vertically intercalated RR-F3B. Now, considering the short axis length of about 3.7 Å in Fig. 5B (calculating from the right part of the molecule), a theoretical basal distance of 8.5 Å would be expected. This value does not match with the experimental value; however, the FTIR data reveal no presence of other anions having the characteristic distance of 7.9 Å. This leads us to suggest that the dye was partially intercalated in the inner structure with a flat orientation of RR-F3B molecules (parallel to MgAl layers) as single-layer. This arrangement would result in a basal distance value similar or close to the experimental data. ATR-FTIR analysis was performed to gain further proofs for the intercalation of RR-F3B (Fig. 6). Comparing the FTIR spectrums before and after the intercalation with the dye spectra, the appearance of several new bands was observed (Fig. 6A). From Fig. 6B, the

Fig. 3. Effect of initial pH of RR-F3B solution (T = room temperature; Cdye = 50 mg·L−1; MgAl/SO4 dosage = 1 g·L−1). Inset: photograph of RR-F3B solution before (left) and after treatment at pH = 4 (right).

by a chemisorption process, confirming the assumption (2) in the section of initial pH effect. None of the tested kinetics models could identify the diffusion mechanism. Thus, investigating the intra-particle diffusion model was further considered. From Fig. 4C, the plot of qt versus t1/2 is consisted of two segments and do not pass through the origin. In fact, according to this model, if the adsorption process is entirely controlled by intra-particle diffusion, a linear relation should be obtained (Khenifi et al., 2010). Also, if the line does not pass through the origin then the diffusion phenomena is not the only rate-controlling step. Accordingly, the first segment presents the step that controls the diffusion at the external surface of MgAl/SO4. Once the latter is

Fig. 4. Fitting plots of RR-F3B dye intercalation onto freeze-dried MgAl phase. 4

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Table 1 Kinetic parameters of RR-F3B intercalation onto freeze-dried MgAl phase. Pseudo first order −1

qexp (mg·g 85

)

Pseudo second order K1 (min 0.03

−1

)

qe (mg·g 27.62

−1

)

R

2

0.725

K2·10

−3

(g·(mg·min)

Intra-particle diffusion

−1

)

6.91

−1

qe (mg·g

)

85.03

R

2

0.999

Kp (mg·(g·min1/2)−1)

C (mg·g−1)

R2

1.72

65.8

0.804

3.3. Deintercalation of RR-F3B loaded MgAl-LDH Assays of RR-F3B deintercalation were carried out using three types of solutions: distilled water, NaOH and Na2CO3. The deintercalation rate (%) was determined by the ratio of the concentration of the released dye Ce′ (mg/L) to the initial intercalated concentration Ce (mg/ L) of dye: [Ce′/Ce]·100%. The results are shown in Fig. 7. At the end of each experiment, the solids were recuperated, washed and oven-dried at 80 °C for XRD and ATR-FTIR characterizations. At room temperature, distilled water and NaOH solutions were not suitable for removing the dye from MgAl-SO4 interlayer space, where the deintercalation reached only 3% (Fig. 7A). However, the use of Na2CO3, under the same operating conditions, generates a recovery rate of ~32%, which is more interesting than the other solutions. In order to recover high amount of intercalated dye, the deintercalation of RR-F3B dye, using Na2CO3, at different operating temperatures was investigated (Fig. 7B). The deintercalation rate increased rapidly from 22 °C to 40 °C, then slowly achieving complete recovery of RR-F3B dye at 80 °C. These results confirm that RR-F3B dye was not physically adsorbed on MgAl-LDH surface; however, the interaction dye-MgAl- SO4 was strong. Furthermore, the deintercalation of RR-F3B dye from MgAl-LDH under the effect of Na2CO3 was confirmed by comparing the FTIR spectrums of different LDH phases: freeze-dried “MgAl/SO4”, dye loaded “MgAl/RRF3B” and after deintercalation at 80 °C “MgAl/CO3-80”. The results are shown in Fig. 8. The FTIR data indicate that the characteristic vibrations of RR-F3B dye disappeared after deintercalation. In addition, the bands corresponding to the vibrations of the sulfate ions disappeared completely while a very intense band attributed to the carbonate anion appeared (striped zone). This confirms that the carbonate anion, originating from Na2CO3 solution and owning a high affinity for the LDH phases, was completely substituted the RR-F3B dye.

Fig. 5. The optimized geometrical structure and estimated dimensions of RRF3B dye – illustrating the side view (A and B). Red atoms are O, white atoms are H, blue atoms are N, yellow atoms are S and gray atoms are C. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

characteristic band of sulfate anion (striped zone) disappeared, whereas characteristic vibration of sulfonate groups of RR-F3B, around 1043 cm−1, appeared. Asserting that the predominant interactions are established between the positively charged MgAl layers and the sulfonate groups of RR-F3B. Additionally, the OeH peak of MgAl/RR-F3B did not change compared to the virgin material, suggesting that hydrogen bonding did not participate in RR-F3B fixation. Changes in LDH lattice vibrations (MgeO, AleO and metal-oxygen-metal), located in the fingerprint region, are observed. The peaks were more distinguished; this is probably due to the drying process changing and is not related to the fixation of RR-F3B dye.

4. Conclusion In summary, the synthesis of freeze-dried MgAl/SO4 phase was presented. The freeze-drying process has influenced the structural and morphological properties of the resulted phase compared to the conventionally dried LDH nanomaterial. MgAl/SO4 phase exhibited a low

Fig. 6. ATR-FTIR spectrums of freeze-dried MgAl/SO4, MgAl/RR-F3B after dye intercalation an RR-F3B dye; (B) close-up view of the fingerprint region (1400–500 cm−1). 5

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Fig. 7. (A) Deintercalation of RR-F3B using distilled water, NaOH and Na2CO3 (T = Room temperature; Csolution = 0.1 mol·L−1; MgAl/RR-F3B dosage = 1 g·L−1; time = 300 min); (B) Temperature effect on RR-F3B deintercalation in presence of Na2CO3. 1688–1713. https://doi.org/10.1016/j.addr.2006.09.017. Abdelwahed, W., Degobert, G., Fessi, H., 2006b. A pilot study of freeze drying of poly (epsilon-caprolactone) nanocapsules stabilized by poly(vinyl alcohol): formulation and process optimization. Int. J. Pharm. 309, 178–188. https://doi.org/10.1016/j. ijpharm.2005.10.003. Balakhonov, S.V., Teben'kov, P.V., Brylev, O.A., Churagulov, B.R., 2018. Comparison of the physicochemical and electrochemical properties of vanadium oxide-based nanomaterials prepared by cryochemical synthesis and supercritical drying technique. Inorg. Mater. 54, 60–65. https://doi.org/10.1134/S0020168518010016. Bastan, F.E., Erdogan, G., Moskalewicz, T., Ustel, F., 2017. Spray drying of hydroxyapatite powders: the effect of spray drying parameters and heat treatment on the particle size and morphology. J. Alloys Compd. 724, 586–596. https://doi.org/10. 1016/j.jallcom.2017.07.116. Cavani, F., Trifiro, F., Vaccari, A., Trifirò, F., Vaccari, A., 1991. Hydrotalcite-type anionic clays: preparation, properties and applications. Catal. Today 11, 173–301. https:// doi.org/10.1016/0920-5861(91)80068-K. Chen, G., Wang, W., 2007. Role of freeze drying in nanotechnology. Dry. Technol. 25, 29–35. https://doi.org/10.1080/07373930601161179. Chung, N.-O., Lee, M.K., Lee, J., 2012. Mechanism of freeze-drying drug nanosuspensions. Int. J. Pharm. 437, 42–50. https://doi.org/10.1016/j.ijpharm.2012.07.068. 3+ layered double Constantino, V.R.L., Pinnavaia, T.J., 1995. Basic properties of Mg2+ 1-x Alx hydroxides intercalated by carbonate, hydroxide, chloride, and sulfate anions. Inorg. Chem. 34, 883–892. https://doi.org/10.1021/ic00108a020. Dai, X., Zhang, S., Waterhouse, G.I.N., Fan, H., Ai, S., 2019. Recyclable polyvinyl alcohol sponge containing flower-like layered double hydroxide microspheres for efficient removal of As(V) anions and anionic dyes from water. J. Hazard. Mater. 367, 286–292. https://doi.org/10.1016/j.jhazmat.2018.12.092. Davantès, A., Costa, D., Lefèvre, G., 2015. Infrared study of (poly)tungstate ions in solution and sorbed into layered double hydroxides: vibrational calculations and in situ analysis. J. Phys. Chem. C 119, 12356–12364. https://doi.org/10.1021/acs.jpcc. 5b01578. Duan, S., Ma, W., Cheng, Z., Zong, P., Sha, X., Meng, F., 2016. Preparation of modified Mg/Al layered double hydroxide in saccharide system and its application to remove As(V) from glucose solution. Colloids Surf. A Physicochem. Eng. Asp. 490, 250–257. https://doi.org/10.1016/j.colsurfa.2015.11.060 0927-7757/©. Eggenhuisen, T.M., Munnik, P., Talsma, H., de Jongh, P.E., de Jong, K.P., 2013. Freezedrying for controlled nanoparticle distribution in Co/SiO2 Fischer–Tropsch catalysts. J. Catal. 297, 306–313. https://doi.org/10.1016/j.jcat.2012.10.024. El Hassani, K., Beakou, B.H., Kalnina, D., Oukani, E., Anouar, A., 2017. Effect of morphological properties of layered double hydroxides on adsorption of azo dye methyl orange: a comparative study. Appl. Clay Sci. 140, 124–131. https://doi.org/10.1016/ j.clay.2017.02.010. Flosdorf, E.W. (Ed.), 1949. Freeze-Drying, Drying by Sublimation. Reinhold Publishing Corporation, New York. Gao, H., Cao, R., Xu, X., Xue, J., Zhang, S., Hayat, T., Alharbi, N.S., Li, J., 2019. Surface area- and structure-dependent effects of LDH for highly efficient dye removal. ACS Sustain. Chem. Eng. 7, 905–915. https://doi.org/10.1021/acssuschemeng.8b04476. Ge, Y., Jin, R., Tian, Z., 2018. V2O5 nano-sheets derived from bulk via a freeze-drying method. Superlattice. Microst. 123, 469–472. https://doi.org/10.1016/j.spmi.2018. 06.011. Gouvêa, C.A.K., Wypych, F., Moraes, S.G., Durán, N., Nagata, N., Peralta-Zamora, P., 2000. Semiconductor-assisted photocatalytic degradation of reactive dyes in aqueous solution. Chemosphere 40, 433–440. https://doi.org/10.1016/S0045-6535(99) 00313-6. He, J., Wei, M., Li, B., Kang, Y., Evans, D.G., Duan, X., 2006. Preparation of Layered double Hydroxides. In: Layered Double Hydroxides. Springer-Verlag, Berlin/ Heidelberg, pp. 89–119. https://doi.org/10.1007/430_006. Hibino, T., 2015. Layered double hydroxide–agarose composites for water treatment: carbonate contamination during the drying process. Appl. Clay Sci. 116–117, 93–101. https://doi.org/10.1016/j.clay.2015.08.020. HO, Y., 2006. Review of second-order models for adsorption systems. J. Hazard. Mater.

Fig. 8. Comparison of ATR-FTIR spectrums after RR-F3B deintercalation in presence of Na2CO3 at 80 °C.

crystallinity, highly aggregated particles and a narrow size distribution ranging from 200 to 300 nm. A weak characteristic band of carbonate anion was detected by FTIR analysis, suggesting that the contamination has occurred during the washing step and not in the drying step. Intercalation of RR-F3B reactive dye has occurred via anion exchange with sulfate ions. Except that, the dye species were partially intercalated with horizontal orientation. The deintercalation was achieved in the presence of Na2CO3 at high temperature 80 °C with a recovery rate of 95%. Declaration of Competing Interest None. Acknowledgements This work was supported by BATTUTA project, financed by the EU Commission within the framework of the Erasmus Mundus Programme [20132445, 2016]. References Abdelwahed, W., Degobert, G., Stainmesse, S., Fessi, H., 2006a. Freeze-drying of nanoparticles: formulation, process and storage considerations. Adv. Drug Deliv. Rev. 58,

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