Glycine-Assisted Hydrothermal Synthesis of NiAl-Layered Double

Glycine-Assisted Hydrothermal Synthesis of NiAl-Layered Double Hydroxide Nanostructures Vanessa Prevot,* Nathalie Caperaa, Christine Taviot-Gue´ho, and Claude Forano Clermont UniVersite´, Laboratory of Inorganic Materials, UMR CNRS 6002, 24 AVenue des Landais 63177 Aubiere cedex, France

CRYSTAL GROWTH & DESIGN 2009 VOL. 9, NO. 8 3646–3654

ReceiVed April 7, 2009; ReVised Manuscript ReceiVed May 5, 2009

ABSTRACT: Flower-like NiAl-layered double hydroxides (LDH) were successfully synthesized by a straightforward one-pot hydrothermal method using Ni(II) glycinate complex as a chemical precursor under extremely high basic conditions and soft hydrothermal conditions. Systematic screening of synthesis parameters such as reaction time and hydrothermal process temperature was carried out. The materials have been thoroughly characterized via a set of techniques including X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, chemical analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermal gravimetric analysis (TG). The results demonstrate that a too long reaction time value disrupts the flower-like microspheres and a too high temperature value is deleterious for the LDH structure. Transition mixed oxides with the same flowerlike morphology were readily obtained by thermal treatment at a moderate temperature of the above LDH precursors. Introduction In recent years, a lot of attention has been paid to the design of nanotextured inorganic materials of hierarchical complex morphology which tend to exhibit significantly improved exploitable properties in comparison with the bulk forms.1 Consequently, considerable efforts have focused on developing materials synthesis for controlling crystal structure particle, size, and morphology often leading to the use of organic medium,2 surfactants,3 or polymer template.4,5 In this context, nanostructured layered double hydroxides6 (LDH) have received increased interest because of their versatile composition, anionicsexchange properties, and potential applications in domains such as catalysis,7 environmental remediation processes,8 (bio)-nanocomposites,9 and biosensors.10 LDH are two-dimensional (2D) layered materials, described by the general formula [MII1-xMIIIx(OH)2][Am-x/m · nH2O] with MII ) Mg2+, Zn2+, Ni2+, Co2+, Cu2+..., MIII ) Al3+, Cr3+, Fe3+, Ga3+...) and Am- ) inorganic or organic anions. The great variety of metal and interlayer species combinations allows tailoring of their physical (magnetic, optical, electrochemical) and chemical properties (redox and acido-basic properties). LDH can be conveniently synthesized from metal salt solution by coprecipitation11 with either strong or retardant base.12 Yet, the synthesis of nanostructured LDH is still a big challenge for chemists. Recently, various synthetic methods such as sonochemistry,13 microwave using synthesis,14 hydrothermal treatment,15 and sol-gel techniques16 have been developed to direct the crystal growth. The use of organic solvents,17 surfactants, marcomolecules, and biomolecules18 has also been reported to generate LDH with new morphologies. For instance, in a nonaqueous system of ethylene glycol, methanol, and dodecyl sulfate under solvothermal conditions, an unusual coral-like LDH microsphere was prepared.19 Original belt-like LDH structures have also been obtained in reverse microemulsion medium (dodecyl sulfate, water, and isooctane) with subsequent modifications by nonionic triblock copolymer surfactant addition.20 In a different approach, polymeric template was used to nanostructure the LDH. Li et al.21 reported the synthesis of hollow LDH via layer-by-layer deposition on a polystyrene bead * Corresponding author. E-mail: [email protected].

surface. Moreover, we recently succeeded in preparing three dimensionally ordered macroporous LDH22 using the opal inverse method.5,23 It is well-known in biomineralization that the presence of amino acid inducing specific adsorptions and metal cation complexation may modify the inorganic crystal growth.24 Recently, different works have reported amino acid assisted inorganic solid synthesis.25-27 High order shell ornamented dendritic nanoarchitectures of copper hydroxide were fabricated using glycine as organic additives,27 whereas glycine was also involved in the preparation of hollow Ni(OH)2 and NiO spheres under hydrothermal treatment in which Oswald ripening is the underlying process in the hollowing process.26 Wu and colleagues28 reported the bioinspired synthesis of ZnO complex hierarchical architectures with controllable morphologies using the amino acid histidine as the directing and assembling agent. Concerning LDH, many publications have been published on the preparation of hybrid amino acid intercalated LDH by different methods, namely, the direct coprecipitation,29 that is, the fabrication of the inorganic phase in presence of organic anion, anionic exchange,30 and the calcination-reconstruction process.31 Nevertheless, none of these studies has underlined a specific influence of the amino acid on the materials morphology. In this paper, a simple chemical method in the presence of glycine is described to fabricate the hierarchical structure of NiAl-based LDH in which Ni glycine complex acts as a chemical precursor showing effectiveness in controlling the nucleation and growth of inorganic solids. Experimental Section Preparation. All the reagents were analytical grade and used without further purification. In a typical experiment, 26 mmol of glycine (NH2CH2COOH pKa1 ) 2.3, pKa2 ) 9.6) and 15 mmol of sodium sulfate were dissolved in 25 mL of 0.2 M solution of Ni(NO3)2 · 6H2O and Al(NO3)3 · 6H2O (Ni/Al molar ratio of 2). A clear green solution was obtained after stirring for 5 min. Then 10 mL of 5 M NaOH (OH-/(Σ Ni2+ + Al3+) ) 10) was added all at once under stirring inducing a pH increase from 3.1 to 13.5, leading to a clear blue solution. Afterward, the solution was transferred into a 40 mL capacity Teflon-lined stainless steel autoclave (autogenous pressure) and heated at different temperatures (60-200 °C) during different periods of time ranging from 1 h to 14 days. After the hydrothermal treatment, the autoclave was allowed to cool down to room temperature, the resulting green precipitate was

10.1021/cg900384n CCC: $40.75  2009 American Chemical Society Published on Web 06/15/2009

Synthesis of NiAl-LDH Nanostructures recovered by centrifugation, and the clear colorless supernatant was removed showing the complete precipitation of the nickel species. There was no change in the solution pH before and after the hydrothermal treatment. The precipitate was washed three times with deionized water and dried at room temperature. Characterization. Chemical analyses (Ni, Al, C, S, H) were performed by inductively coupled plasma atom emission spectroscopy at the Vernaison Analysis Center of CNRS (France). Powder X-ray diffraction (XRD) experiments patterns were carried out with a Panalytical X’pert pro diffractometer in θ/θ geometry equipped with a real-time multistrip X’celerator detector using Cu KR1/2 radiation. Diffractograms were recorded in the range of 2-100° 2θ (continuous mode, step 0.013°). The cell parameters, structure, and microstructure refinements were conducted with the program Maud (Materials Analysis Using Diffraction, http://www.ing.unitn.it/∼maud). In order to minimize preferred orientation effects, the samples were collected with the side loading mode. Instrumental broadening was measured using Y2O3 data collected in the same conditions as used for the samples. The Rietveld structure refinement was performed considering the R3jm space group and taking as initial values for the atomic positions and the isotropic atomic displacement parameters those reported elsewhere.32 The metal atom occupancies were set at fixed values according to the stoichiometry calculated from the chemical analysis and were not refined. The refined parameters were the sample displacement, the zero shift, the cell parameter, the scale factor, the atomic positions, the water-site occupancy, and microstructure parameters. In-situ high temperature measurements were carried out using an Anton Paar HTK-16 high temperature chamber. The powder was deposited on Pt. The patterns were recorded in an air atmosphere in the temperature range 25-1200 °C with a heating rate of 5 °C/min and an equilibration time of 15 min before measurement at each temperature. The measurement conditions were in the range 5-70° in (continuous mode, step 0.0334°). Attenuated total reflectance Fourier transform infrared (FT-IR) spectra were measured in the range 400-4000 cm-1 on a FTIR Nicolet 5700 spectrometer (Thermo Electon Corporation) equipped with a Smart Orbit accessory. UV-visible spectra were obtained with a Nicolet evolution 500 diode Array spectrophotometer. SEM characteristics of the samples were imaged by either a JEOL 5190 microscope operated at 15 keV or a Zeiss supra 55 FEG-VP operating at 3 keV. Specimens were mounted on conductive carbon adhesive tabs and imaged after carbon sputter coating to make them conductive. Transmission electron microscopy (TEM) images were taken using a Hitachi 7650 microscope at an acceleration voltage of 80 kV. Samples were dispersed in ethanol, and then one droplet of the suspension was applied to a 400 mesh holey carbon-coated copper grid and left to dry in air. Nitrogen adsorption-desorption were performed at -196 °C with a Micromeritics ASAP 2020. Before analysis, samples were pretreated at 80 °C under a vacuum for 12 h. The surface areas were estimated by using the Brunauer-Emmett-Teller method. Thermogravimetric analyses (TGA) were recorded on a Setaram TGDTA 92 instrument in the temperature range of 25-1000 °C, with a heating rate of 5 °C/min. Gases evolving from the TG apparatus were analyzed using a mass spectrometer Thermostar 300 from Balzers Instruments.

Results and Discussion Structure, Microstructure, and Morphologies of the LDH Phases. The powder X-ray diffraction pattern of the powder collected after hydrothermal treatment at 120 °C after a reaction time of 24 h (Figure 1) shows the formation of pure NiAl-CO3 LDH phase. Indeed, all the reflection lines for NiAl-CO3 can be indexed in a hexagonal cell (a ) 0.30407(1) nm, c ) 2.3133(2) nm) with the rhombohedral symmetry R3jm as expected. The interlayer spacing d003 ) 0.771 nm, derived from the c parameter value or obtained from the position of the first diffraction line, is characteristic of carbonate anion intercalated LDH. Carbonate anion intercalation is further confirmed by IR spectroscopy with the ν3 vibrational band of carbonate anions observed at 1364 cm-1 (See Supporting Information). The presence of this anion may be due to the strong basic conditions

Crystal Growth & Design, Vol. 9, No. 8, 2009 3647

Figure 1. Results of the structural refinement for NiAl-CO3 sample obtained at 120 °C after a reaction time of 24 h: experimental X-ray diffraction (cross), calculated (line), Bragg reflections (ticks), and difference profiles (reliability factors: sig ) 4.577499, Rw (%) ) 1.8, Rnw (%) ) 0.02, Rb (%) ) 1.2, Rexp (%) ) 0.4).

used, which are in favor of atmospheric CO2 dissolution during the precursor solution preparation. It is worth noting that the bands corresponding to glycinate anions are not detected on the FTIR spectrum indicating that intercalation of glycinate anions in LDH29 does not occur during this process. The morphology of the sample was examined by fieldemission scanning microscopy (FE-SEM). As can be seen in Figure 2a, a unique flower-like morphology with an average diameter of around 10 µm ((2 µm) was observed, consisting of a large thin disk shape central particle supporting smaller aggregated particles. Higher magnification reveals that the disk is composed by the association of smaller particles which were able to stick and merge together (indicated by the arrows Figure 2b). Further insight into the morphology of the NiAl-CO3 flowerlike microsphere was gained using TEM. The image (Figure 3) confirms the formation of thin and large interconnected particles. The corresponding selected area of the electron diffraction (SAED) pattern shows that LDH platelets are monocrystalline and can be indexed in a R3jm space group in agreement with XRD refinement results. Influence of the Synthetic Parameters. To better understand LDH formation under such hydrothermal conditions and the growth of the flower-like structures, different reaction times and reaction temperatures were applied and the effect on the resulting powders was observed. The XRD patterns (Figure 4) indicate that in the early stage of the precipitation (∼1 h), the pure LDH structure is already formed. It must be remarked that XRD patterns of the samples collected after 2 and 3 h show the presence of a second series of 00l harmonics at lower angles. These diffraction lines correspond to the formation of an additional LDH phase displaying a larger interlayer basal spacing (0.8476 nm) which has been attributed to sulfate containing LDH,33 sulfate ions being present in the precursor solution. The corresponding FTIR spectra agree well with the presence of sulfate anions showing the ν3 split band of sulfate at 1107 cm-1 on the side of the ν3 carbonate anion band at 1371 cm-1. After a 3 h reaction time, the PXRD patterns display only the reflection lines corresponding to pure carbonate intercalated LDH confirming the high affinity of LDH for carbonate anions. In parallel, the progressive disappearance of the sulfate species

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Figure 2. (a, b) FESEM images of the as-obtained NiAl-CO3 LDH at different magnifications.

Figure 3. TEM image of the flower-like structure and the SAED pattern corresponding.

Figure 4. PXRD pattern of the samples prepared at 120 °C for (a) 1 h, (b) 2 h, (c) 3 h, (d) 5 h, (e) 12 h, and (f) 14 days and in the inset the variation of the a cell parameter with x the molar fraction of aluminum.

has been quantified by infrared analysis (see Supporting Information), indicating that surface adsorbed sulfate species remains for a reaction time up to 24 h. To get more information about the LDH growth process under hydrothermal conditions as a function of the reaction time and the temperature applied, the average size of the coherent domain along the 00l (L00l) and 110 (L110) directions were calculated from peak profile

analysis of the X-ray diffraction pattern, using the approach developed by Popa and Balzar34 implemented in MAUD program. The refined microstructural parameters together with the refined cell parameters are presented in Table 1. These mean values obtained from 110 and 00l reflections can be employed to calculate the average apparent diameter and thickness of the crystalline domains. As shown in Figure 5, in both 110 and 00l directions, we observe an increase of the average apparent sizes with the reaction time and with reaction temperature, probably as a result of Ostwald ripening. Furthermore, the rapid increase along the 110 direction (Figure 5) indicates that the nucleation and early growth took place mainly in the hk0 crystal planes. Scanning electron microscopy (SEM) images show different morphologies depending on the reaction time (Figure 6). A control of the morphology can thus be achieved by adjusting the time of the hydrothermal reaction. One hour after the beginning of the reaction, LDH exhibits pompon-like morphology with diameter less than 1 µm (Figure 6a,b), which then evolves into larger spherical sponge-like structures for aging time less than 4 h. Recently, LDH spherical aggregations have also been obtained by He et al.35 using urea hydrolysis in the presence of surfactant, typically sodium dodecanesulfonate or sodium dodecylsulfate. However, in that study, the process involved first the formation of spherical amorphous aluminum hydroxide precursor which was subsequently converted into LDH. For aging times between 5 h and 48 h, we observed a flower-like morphology. Yet, upon prolonged hydrothermal reaction at 120 °C, this flower-like nanotexture is lost in favor of large interconnected particles with heterogeneous shapes and sizes (Figure 6f). In a second step, similar reactions were performed but without sulfate anions in the medium while keeping other parameters constant. In these conditions, pure NiAl-CO3 was systematically obtained in all cases, displaying the same structural and morphological features; however, the homogeneity of the morphology was lower. This is likely to be

Synthesis of NiAl-LDH Nanostructures


Table 1. Phase Composition, Coherent Domain Size, Interlayer Distance, Specific Surface Area and Pore Volume for Samples Obtained at Different Reaction Times and Temperatures samples 1 h 120 °C 5 h 120 °C 12 h 120 °C 24 h 120 °C 14 days 120 °C 24 h 80 °C 24 h 100 °C 24 h 150 °C a

compositiona x molar fraction of aluminum

L00l (nm)

L110 (nm)

c (nm) d003

a (nm)

SBET (m2/g)

Vpores (cm3/g)

Ni2.1Al(OH)6(CO3)0.50 1.7H2O x ) 0.322 Ni2.2Al(OH)6(CO3)0.50 2.4H2O x ) 0.312 Ni2.25Al(OH)6(CO3)0.50 1.6H2O x ) 0.307 Ni2.5Al(OH)6(CO3)0.51 1.8H2O x ) 0.286 Ni2.6Al(OH)6(CO3)0.50 2.1H2O x ) 0.278 Ni2.3Al(OH)6(CO3)0.51 1.8H2O x ) 0.303 Ni2.3Al(OH)6(CO3)0.51 2.0H2O x ) 0.303 Ni2.8Al(OH)6(CO3)0.50 2.0H2O x ) 0.263

6

9

0.30309(2)

20

0.10

15

26

0.303326(9)

35

0.11

17

46

0.30349(1)

38

0.12

17

40

0.30407(1)

39

0.11

31

70

0.304416(8)

31

0.06

11

23

0.30307(1)

37

0.12

14

27

0.303664(8)

41

0.15

22

34

2.2853(2) 0.762 2.2960(2) 0.765 2.3046(3) 0.768 2.3133(2) 0.771 2.30738(8) 0.769 2.2871(2) 0.762 2.3021(2) 0.767 2.3407(2) 0.780

0.30522(1)

7

0.03

Calculated from chemical analysis.

Figure 5. Variation of the size of the coherent domains along [110] and [00l] against (a) reaction time and (b) reaction temperature.

due to the ionic strength effects (controlled here mainly by sulfate, nitrate, sodium, and hydroxide ions) and inducing specific adsorption as confirmed by infrared spectroscopy and already indicated elsewhere.24,36 Indeed, the ionic strength of the mother solution (calculated from I ) (1/2)∑Cizi2 where Ci and zi are respectively the concentration and the charge number of the various ions in the solution) was found high with a value of 4.4 M. It appears that the synthesis temperature has also a great influence on both the structure and morphology of the solid products. Figures 7 and 8 show respectively the X-ray diffractograms and the morphology images of NiAl-LDH obtained at different temperatures ranging from 60 to 200 °C and for a reaction time of 24 h. Experiments performed at temperatures above 180 °C reveal the formation of β-Ni(OH)2 platelets conjointly with the NiAl-CO3 LDH structure (Figure 7d), whereas above 200 °C only pure β-Ni(OH)2 was precipitated (Figure 7e). The application of higher temperature proved to be deleterious for the formation of LDH structure. On the other hand, the morphology of the samples (Figure 8) goes from sponge-like microspheres at low temperatures (60-80 °C) to large polydispersed stacked particles (200 nm - 3 µm) at high temperature (150 °C). A minimal temperature of 60 °C is needed to collect a powder from the solution. According to the chemical analysis (Table 1), an increase of the reaction time results in a higher Ni/Al ratio (R ) (1 - x)/x with x the mole fraction of aluminum) in the solid, respectively, 2.1 and 2.6 for 1 h and 24 h of treatment. This evolution is confirmed by the linear increase of the a cell parameter with the x value in agreement with the Vegard’s law (inset of Figure 4). The data point noted with an asterisk is out of the linear variation owing to the presence of the

NiAl-SO4 phase. While the first LDH nucleus precipitates nearly in the expected ratio 2.0 with regard to the precursor solution, upon reaction time and crystal growth, the Ni/Al ratio of precipitated LDH increases and reaches a value of 2.5 after 24 h. A similar trend is observed upon temperature increase: the Ni/Al ratio increases from 2.3 at 80 °C to 2.8 at 150 °C and aluminum is totally absent from the layered structure at 200 °C. These composition modifications suggest that the longer the aging time and the reaction temperature, higher the amount of Ni-rich hydroxide phases, the pure β-Ni(OH)2 formation being favored rather than LDH precipitation for the highest temperature, that is, 200 °C. Probably changes in Ni/Al chemical composition occurring during the reaction process involve a dissolution-precipitation phenomenon leading to an increase of the molecular Al species stability in solution.37 The more thermodynamically stable and less soluble Ni-rich LDH phases are obtained in more extreme reaction conditions, β-Ni(OH)2 displaying a lower solubility value than the Ni1-xAlx(OH)2(CO3)x/2 · nH2O phase. Nitrogen adsorption-desorption isotherms were measured to determine the surface area and the porosity properties of the samples (Table 1). As commonly observed for LDH materials, all the samples prepared in this study exhibit a type IV isotherm with H4 hysteresis loop according to BDDT classification,38 showing an open-slit type mesoporous structure. Only slight modifications of the surface area are observed according to the preparation conditions. These results show no significant modification of the textural properties (surface area and porous volume) link to the original morphologies obtained. Note that thermal treatment carried out at 150 °C induces a net decrease of the surface area (7 m2/g) which might be ascribed to the

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Figure 6. FE-SEM images of NiAl-CO3 LDH obtained of the samples prepared at 120 °C for (a) and (b) 1 h, (c) 3 h, (d) 5 h, (e) 12 h, and (f) 14 days.

Formation Mechanism of Flower-Like LDH. Characterization of the Precursor Solution. Before the hydrothermal treatment, that is, during the mixing of the various reactants, several reactions may occur such as precipitation, hydrolysis, dissolution, and metal cation complexation. Dissolution of Ni2+ and Al3+ nitrate salts leads to an acidic pH value of 3.1. At such a pH, glycine (pKa1 ) 2.34, pKa2 ) 9.60 and pHi ) 5.97) is present in both its acidic (Gly+: +H3NCH2-COOH) and zwitterionic (Gly ( : +H3N-CH2-COO-) forms, but its dissolution does not affect the pH of the solution even though the molar ratio of glycine over metal cations is high (Gly/(Σ Ni2+ + Al3+) ) 5.2). The addition of sodium sulfate does not affect the pH value. On the other hand, the subsequent addition of the concentrated sodium hydroxide (5 M) causes a pH increase of the reaction medium to a final value of 13.5 and simultaneously the color of the translucent solution turns from green to dark blue. At intermediate pH values, a white solid is precipitated whose XRD pattern resembles that of boehmite. With a further increase of the pH above 11.5, the solution becomes blue translucent (Figure 9) as a result of boehmite conversion into soluble tetrahydroxoaluminate ion according to the following chemical reaction:39 Figure 7. PXRD pattern of the samples prepared for 24 h at (a) 80 °C, (b) 100 °C, (c) 150 °C, (d) 180 °C, and (e) 200 °C.

formation of well-crystallized large stacked particles as observed in SEM pictures (Figure 8c).

AlOOH(s) + H2O + OH- ) Al(OH)4-(aq)

(1)

Figure 9 displays the UV-vis spectra of the precursor solution before and after its complete titration by sodium hydroxide. At low pH, the UV-vis absorption property of the solution



Figure 8. FE-SEM images of the samples prepared for 24 h at (a) 80 °C, (b) 100 °C, (c) 150 °C, and (d) 180 °C.

tation. However, the complex stability decreases under hydrothermal treatment leading to the release of nickel cations in solution. The speciation diagram of aluminum ions indicates that Al(OH)4- complex ion is the prominent species at high pH value (pH > 13) (eq 1). Then, nickel ions liberated in solution and aluminum species coprecipitate conjointly to form the NiAlLDH phase following eq 2. 2 Ni(Gly)3 + Al(OH)4 + 3 OH + 0.5 CO2 + (n-0.5)H2O f Ni2Al(OH)6(CO3)0.5 · nH2O

Figure 9. UV-visible spectra before (green) and after (blue) concentrated NaOH addition.

indicates that metal cations exist as aquo complexes, Ni(H2O)62+ and Al(H2O)63+. At high pH value, a shift of Ni2+ complex bands to higher energies is observed showing the replacement of all six aquo ligands with other Lewis bases. It is well-known that amino acid anions are strong chelating agents which may coordinate to a transition metal ion through either or both the amino and the carboxylate groups.40 Glycine may effectively form stable complexes with divalent and trivalent metallic cations, depending on its ionic forms Gly+, Gly (, Gly-. For example, the constants of stability of the NiGly and AlGly are, respectively, 6.1 and 0.77 M.41 Addition of concentrated NaOH to the aqueous solution of glycine results in the deprotonation of the ammonium group, yielding the anion H2NCH2CO2(Gly-). This latter species acts as a bidentate ligand toward Ni2+ transition metal cations forming a five-membered heterocyclic ring through the oxygen atoms of the carboxylate group and the nitrogen atom of the amino group. Then, the titration of the precursor solution leads to the formation of the trisglycinatoNi(II) complex,42 Ni(Gly)3-, which is further used as a molecular precursor during the following hydrothermal treatment. LDH Precipitation. Scheme 1 illustrates the formation process of NiAl-CO3 LDH. The presence of glycine induces the formation of glycinato Ni(II) complexes which are stable at room temperature and hampered NiAl-CO3 LDH coprecipi-

(2)

Samples prepared under the same experimental conditions as above but without glycine in the synthetic medium do not give the peculiar flower-like morphology. In this synthetic process, the LDH nucleation is delayed due to the glycinato nickel complex formation and the subsequent crystal growth is modified. According to crystal growth theory, the small particles formed at the earlier stages of the reaction (see Scheme 1) displaying high surface energy grow in size upon a dissolutioncrystallization process. These larger particles formed undergo further growth and merge together to form bigger particles, a phenomenon that may be favored by the hydrothermal conditions and the basic medium used. The influence of various chelating agents on LDH preparation and on the shape of resulting particles has already been described. For instance, trisodium citrate was used in a variable pH process involving urea decomposition to prepare well-crystallized NiFe-LDH with platelets size in the micrometer range.43 In the same manner, Zeng et al.44 employed ethylenediamine in a solution-based chemical approach to lower the precipitation rate of β-Ni(OH)2 and prepare hollow spheres. Finally, the solvatation effects of ethylene glycol and methanol by reducing the ion activities permitted delay of the nucleation and the crystallization processes of MgAlLDH.19 Thermal Behavior. The TGA and DTG curves of all the samples prepared whatever the synthesis parameters displayed the same features. Figure 10 shows the TG/DTG curves and the corresponding thermodesorption of gases (H2O and CO2) of the solid obtained using hydrothermal treatment at 120

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Scheme 1. Illustration of the Formation Process of Flower-like NiAl-CO3 LDH

°C for 24 h. The thermal behavior of LDH compound is generally characterized by the following three main steps:45 the first one at low temperature corresponds to the removal of interlamellar water, namely, the dehydration step; the second one which occurs at higher temperature is linked to

the dehydroxylation of the LDH layers; and the third one is due to the loss/decomposition of interlayer anions. Note that the two last steps can arise at the same temperature range (249-500 °C) which is the case here. A total mass loss amounting to 35% was obtained comprising mainly two successive mass losses of 11.5% and 23.5%. The gases evolved confirmed the scheme of decomposition with a water departure in the temperature range of 100 to 450 °C resulting from dehydration and dehydroxylation steps. In the temperature range 250-450 °C, CO2 thermodesorption is also observed corresponding to carbonate anion decomposition. The in situ high temperature XRD patterns of NiAl-CO3 (120 °C, 24 h) displayed in Figure 11 can be divided in three main parts: (1) up to 150 °C, no significant change is observed in the diffraction pattern, then (2) a decrease of the interlamellar distance (0.65 nm) was observed between 150-325 °C corresponding to the grafting of carbonate anions to the hydroxyl layer,46 and finally (3) above 325 °C, the LDH structure was converted into amorphous mixed oxides which crystallize at higher temperature. Interestingly, the flower-like nanostructures were maintained (Figure 11) up to 1200 °C leading to corresponding nanotextured NiO and NiAl2O4 mixed oxides. Such a conservation of LDH precursor morphology has already been underlined during the calcination-reconstruction process on LDH hollow capsules21 and 3D ordered macroporous structures,22 permitting then the removal of the polymeric template and the maintanence of the LDH nanostructuration. The FE-SEM image at higher magnification clearly shows the craterization at the surface of the platelets already observed for the LDH particles submitted to a thermal treatment.47 Conclusion

Figure 10. (Top) TGA/DTG curves of NiAl-CO3 obtained at 120 °C for 24 h and (bottom) the corresponding H2O and CO2 thermodesorption signal.

In summary, a simple route based on hydrothermal thermolysis of Ni(II) complex was adapted to prepare a nanotextured 3D flower-like NiAl-CO3 LDH structure. The formation of Ni glycinate complex permits the delay of and reduction of the rate of the NiAl-CO3 coprecipitation. It has been proven that the obtained materials and morphology depend on synthesis time



References

Figure 11. (Top) PXRD pattern of the NiAl-CO3 obtained at 120 °C for 24 h versus temperature (°C) from bottom to top: 25 °C, 50 °C, 75 °C, 100 °C, 125 °C, 150 °C, 175 °C, 200 °C, 225 °C, 250 °C, 275 °C, 300 °C, 325 °C, 350 °C, 400 °C, 450 °C, 500 °C, 600 °C, 700 °C, 800 °C, 900 °C, 1000 and 1200 °C and (bottom) the FESEM image of the sample calcined at 1200 °C.

and temperature used in the hydrothermal treatment. The sizes of the coherent domain determined by PXRD pattern refinements clearly indicate that a longer reaction time induces a better crystallinity of the samples. Throughout the reaction, NiAl-CO3 particles went through a “pompon-like” intermediate phase which is further transformed into flower-like morphology. In this latter nanostructure, interconnected particles are associated on large thin disk-shaped particles. By increasing the reaction temperature up to 200 °C, the LDH structure is no more stabilized and pure β-Ni(OH)2 precipitates. Interestingly, the assynthesized LDH flower-like morphology can be converted by calcination into mixed oxides displaying the same nanotextured morphology. Supporting Information Available: SEM image of NiAl-CO3 phase obtained without addition of glycine, FTIR spectra of NiAlCO3 phase obtained versus reaction time. This information is available free of charge via the Internet http://pubs.acs.org.

(1) (a) Co¨lfen, H.; Antonietti, M. Angew. Chem., Int. Ed. 2005, 44, 5576. (b) Hyeon, T.; Lee, S. S.; Park, J.; Chung, Y.; Na, H. B. J. Am. Chem. Soc. 2001, 123, 12798. (c) Patzke, G. R.; Krumeich, F.; Nesper, R. Angew. Chem., Int. Ed. 2002, 41, 2446. (d) Portehault, D.; Sophie, C.; Nassif, N.; Baudrin, E.; Jolivet, J.-P. Angew. Chem., Int. Ed. 2008, 47, 6441. (2) (a) Bu¨hler, G.; Feldman, C. Angew. Chem., Int. Ed. 2006, 45, 4864. (b) Garnweitner, G.; Goldengerg, L. M.; Sakhno, O. V.; Antonietti, M.; Niederberger, M.; Stumpe, J. Small 2007, 3, 1626. (c) Toneguzzo, P.; Viau, G.; Acher, O.; Fievet-Vincent, F.; Fievet, F. AdV. Mater. 1998, 10, 1032. (3) (a) Casavola, M.; Buonsanti, R.; Caputo, G.; Cozzoli, P. D. Eur. J. Inorg. Chem. 2008, 6, 837. (b) Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. S. Nature 1992, 359, 710. (4) Caruso, F. Chem.sEur. J. 2000, 6, 413. (5) Yan, H.; Blanford, C. F.; Holland, B. T.; Smyrl, W. H.; Stein, A. Chem. Mater. 2000, 12, 1134. (6) (a) Wypych, F.; Satyanarayana, K. G. Clay Surfaces - Fundamentals and Applications. Interface Science and Techology; Elsevier: Amsterdam, 2004; Vol. 41, p 533. (b) Rives, V. Layered Doubles Hydroxides: Present and Future; Nova Science Publisher: New York, 2001. (c) Duan, X., Evans, D. G., Eds.; Structure and Bonding: Layered Double Hydroxides; Springer: Berlin/Heidelberg, 2006; Vol. 119. (7) (a) Tichit, D.; Gerardin, C.; Durand, R.; Coq, B. Top. Catal. 2006, 39, 89. (b) Vaccari, A. Catal. Today 1998, 41, 53. (8) Forano, C. Environmental Remediation Involving Layered Double Hydroxides. In Clays Surfaces: Fundamentals and Applications; Wypych, F.; Satyanarayana, K. G., Eds.; Elsevier: New York, 2004; Vol. 1, p 425. (9) (a) Darder, M.; Lopez-Blanco, M.; Aranda, P.; Leroux, F.; Ruiz-Hitzky, E. Chem. Mater. 2005, 17, 1969. (b) Evans, D. G.; Duan, X. Chem. Commun. 2006, 485. (c) Leroux, F.; Besse, J.-P. Chem. Mater. 2001, 13, 3507. (10) Forano, C.; Vial, S.; Mousty, C. Curr. Nanosci. 2006, 2, 283. (11) Geraud, E.; Bouhent, M.; Derriche, Z.; Leroux, F.; Prevot, V.; Forano, C. J. Phys. Chem. Solids 2007, 68, 818. (12) Costantino, U.; Marmottini, F.; Nocchetti, M.; Vivani, R. Eur. J. Inorg. Chem. 1998, 1439. (13) Seida, Y.; Nakano, Y.; Nakamura, Y. Clays Clay Miner. 2002, 50, 525. (14) Rivera, J. A.; Fetter, G.; Bosch, P. Microporous Mesoporous Mater. 2006, 89, 306. (15) (a) Xu, Z. P.; Stevenson, G.; Lu, C.; Lu, G. Q. J. Phys. Chem. B. 2006, 110, 16923. (b) Xu, Z. P.; Stevenson, G.; Lu, C.-Q.; Lu, G. Q.; Bartlett, P.; Gray, P. J. Am. Chem. Soc. 2006, 128, 36. (16) He, J.; Wei, M.; Li, B.; Kang, Y.; Evans, D. G.; Duan, X. Preparation of Layered Double Hydroxides. In Structure and Bonding: Layered Double Hydroxide; Springer: Berlin, Germany, 2006; Vol. 119, p 89. (17) Malherbe, F.; Forano, C.; Besse, J.-P. Microporous Mater. 1997, 10, 67. (18) (a) Li, B.; He, J.; Evans, D. G.; Duan, X. J. Phys. Chem. Solids 2006, 67, 1067. (b) Sun, Y.; Zhou, Y.; Wang, Z.; Ye, X. Appl. Surf. Sci. 2009, 255, 4497. (c) Vial, S.; Ghanbaja, J.; Forano, C. Chem. Commun. 2006, 290. (19) Gunawan, P.; Xu, R. J. Mater. Chem. 2008, 18, 2112. (20) Hu, G.; O’Hare, D. J. Am. Chem. Soc. 2005, 127, 17808. (21) Li, L.; Ma, R.; Iyi, N.; Ebina, Y.; Takada, K.; Sasaki, T. Chem. Commun. 2006, 3125. (22) Ge´raud, E.; Rafqah, S.; Sarakha, M.; Forano, C.; Prevot, V.; Leroux, F. Chem. Mater. 2008, 20, 1116. (23) Schroden, R. C.; Stein, A. 3D Ordered Macroporous Materials. In Colloids and Colloid Assemblies; Caruso, F., Ed.; Wiley-VCH: New York, 2004; p 465. (24) Mann, S. Biomineralization; Oxford University Press: U.K., 2001. (25) (a) Chen, Z.; Shen, Y.; Xie, A.; Zhu, J.; Wu, Z.; Huang, F. Cryst. Growth Des. 2009, in press. (b) Diaz, I.; Perez-Pariente, J. Chem. Mater. 2002, 14, 4641. (26) Wang, Y.; Zhu, Q.; Zhang, H. Chem. Commun. 2005, 5231. (27) Zhang, Z.; Shao, X.; Yu, H.; Wang, Y.; Han, M. Chem. Mater. 2005, 17, 332. (28) Wu, Q.; Chen, X.; Zhang, P.; Han, Y.; Chen, X.; Yan, Y.; Li, S. Cryst. Growth Des. 2008, 8, 3010. (29) (a) Aisawa, S.; Takahashi, S.; Ogasawara, W.; Umetsu, Y.; Narita, E. J. Solid State Chem. 2001, 162, 52. (b) Hibino, T. Chem. Mater. 2004, 16, 5482. ´ .; Pa´linko´, I.; Kiricsi, I. Inorg. Chem. 1999, 38, 4653. (30) Fudala, A

3654


(31) (a) Nakayama, H.; Wada, N.; Tsuhako, M. Int. J. Pharm. 2004, 269, 469. (b) Aisawa, S.; Kudo, H.; Hoshi, T.; Takahashi, S.; Hirahara, H.; Umetsu, Y.; Narita, E. J. Solid State Chem. 2004, 177, 3987. (32) Bellotto, M.; Rebours, B.; Clause, O.; Lynch, J.; Bazin, D.; Elkaı¨m, E. J. Phys. Chem. C 1996, 8527. (33) Bookin, A. S.; Cherkashin, V. I.; Drits, V. A. Clays Clay Miner. 1993, 41, 558. (34) Popa, N. C.; Balzar, D. J. Appl. Crystallogr. 2002, 35, 338. (35) (a) Li, B.; He, J. J. Phys. Chem. C 2008, 112, 10909. (b) Li, B.; He, J.; Evans, D. G. Chem. Eng. J. 2008, 144, 124. (36) Hu, Z.; Deng, Y. J. Colloid Interface Sci. 2003, 266, 359. (37) Benezeth, P.; Palmer, D. A.; Wesolowski, D. J. Geothermics 1997, 26, 465. (38) Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscou, L.; Pierotti, R. A.; Rouquerol, J.; Siemieniewska, T. Pure Appl. Chem. 1985, 57, 63.

Prevot et al. (39) Panias, D.; Asimidis, P.; Paspaliaris, I. Hydrometallurgy 2001, 56, 15. (40) Casale, A.; De Robertis, A.; De Stefano, C.; Gianguzza, A.; Patane, G.; Rigano, C.; Sammartano, S. Thermochim. Acta 1995, 255, 109. (41) Furia, T. E. CRC Handbook of Food AdditiVes; CRC Press Inc.: Boca Raton, FL, 2006. (42) Ozutsumi, K.; Ohtaki, H. Bull. Chem. Soc. Jpn. 1983, 56, 3635. (43) Han, Y.; Liu, Z. H.; Yang, Z.; Wang, Z.; Tang, X.; Wang, T.; Fan, L.; Ooi, K. Chem. Mater. 2008, 20, 360. (44) Zhang, S.; Zeng, H. C. Chem. Mater. 2009, 21, 871. (45) Lebedeva, O.; Tichit, D.; Coq, B. Appl. Catal. A: Gen. 1999, 183, 61. (46) Vaysse, C.; Guerlou-Demourgues, L.; Delmas, C. Inorg. Chem. 2002, 41, 6905. (47) Prinetto, F.; Ghiotto, G.; Graffin, P.; Tichit, D. Microporous Mesoporous Mater. 2000, 39, 229.

CG900384N

Glycine-Assisted Hydrothermal Synthesis of NiAl-Layered Double

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