Zr(IV) basic carbonate complexes as precursors for new materials: Synthesis of the zirconium-surfactant mesophase

Article abstract of DOI:10.1016/S0025-5408(02)00886-3

The synthesis of the zirconium-surfactant mesophase was conducted by the addition of Zr(IV) salts to the excess of an alkali metal or ammonium carbonate. Zr was found to be present in the form of a salt in the inorganic precursors used for the preparations of ZrO₂-based materials. The study showed that the solutions were metastable at pH 7-10 and could be used as the precursors for the synthesis of new materials.

Full text of DOI:10.1016/S0025-5408(02)00886-3

Materials Research Bulletin 37 (2002) 1933±1940
Zr(IV) basic carbonate complexes as precursors
for new materials: synthesis of the
zirconium-surfactant mesophase
*
P. Afanasiev
Institut de Recherches sur la Catalyse, 2 Avenue A. Einstein, 69626 Villeurbanne, C e dex, France
(
Refereed)
Received 1 February 2002; accepted 19 July 2002
Abstract
Soluble anionic carbonate complexes of Zr(IV) are produced by addition of Zr(IV) salts to
the excess of an alkali metal or ammonium carbonate. The solutions are metastable at pH 7±10
and can be used as the precursors for the synthesis of new materials, as illustrated by the
example of the surfactant containing mesophase with a wormhole-like structure, prepared by
means of reaction with cetyltrimethylammonium bromide.
#
2002 Elsevier Science Ltd. All rights reserved.
Keywords: A. Oxides; B. Chemical synthesis; D. Nanostructures
1
. Introduction
Zirconium-based materials are eminently important for different ®elds of advanced
technology such as alloys, ceramics, solid-state ionics, inert bioceramics (Al O ,
2
3
ZrO ) for medical application, and others. Zirconium oxide, ZrO , is widely studied
2
2
as a catalyst and/or catalytic support [1]. Earlier, much work has been done in order to
control the morphology and surface properties of this oxide [2±4].
The inorganic precursors used for the preparations of ZrO -based materials are
2
8‡
often the salts where Zr is present in the cationic form (e.g. [Zr (OH) (H O) ] ),
2
4
8
16
such as hydrated oxychloride, ZrOCl Á8H O, oxynitrate, ZrO(NO ) , sulfate Zr(SO ) ,
2
2
3 2
4 2
or sometimes acetate [5]. The possibilities of the preparations using these precursors
*
Tel.: ‡33-4-72-44-53-39; fax: ‡33-4-72-44-53-99.
E-mail address: afanas@catalyse.univ-lyon1.fr (P. Afanasiev).
0025-5408/02/$ ± see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 2 5 - 5 4 0 8 ( 0 2 ) 0 0 8 8 6 - 3

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P. Afanasiev / Materials Research Bulletin 37 (2002) 1933±1940
are obviously limited by the chemistry of the corresponding cationic species. To
extend the synthetic possibilities, other precursors have been studied, such as
carboxylates [6] or alkoxides [7].
BasicZr(IV)saltshavebeenknownfor a longtime. The solubilityofhydrated Zr(IV)
hydroxide in a solution of ammonium carbonate was stated by Bertzelius [8], however,
the chemical identity of the species in solute was not established. Later, Zaitsev and
coworkers [9,10] characterized several carbonate complexes of Zr which are all basic
salts with various Zr to carbonate ratios. For some of them, the crystalline structures
6À
have been resolved [11,12]. Recently, the structure of [ZrOH(CO )3]2 guanidinium
3
salt has been determined [13]. However, utilization of the anionic carbonate precursors
for the materials preparation has not been reported in the literature. We believe that in
using soluble Zr(IV) carbonates, they may be useful alternative precursors for materials
synthesis. In this communication, we describe the example of a simple preparation of
the new zirconium-surfactant mesophase fromthe zirconiumbasic carbonateprecursor.
2
. Experimental
The solution of 0.01 mol of ZrOCl or ZrO(NO ) in 100 ml of distilled water was
2
3 3
added to an excess of 0.1 M solution of Na CO or (NH ) CO at room temperature.
3
2
3
4 2
The change of pH was monitored with a digital pH-meter. The obtained solution of
basic Zr carbonate was immediately used for the synthesis of surfactant containing
hybrid solids. To precipitate the surfactant containing mesophases, 0.02 mol of a
tetraalkylammonium salt (trimethylcetylpyridinium chloride or cetyltrimethylammo-
nium bromide (CTMAB)) dissolved in 100 ml of water was rapidly added to the
solution of basic Zr carbonate.
The solids were characterized using powder X-ray diffraction (XRD), FT-IR
spectroscopy, and textural measurements. The IR spectra were obtained in air in
KBr disks, pressed without grinding. Scanning electron microscopy (SEM) images
were obtained on a Hitachi S800 device, at the center of electronic microscopy of
Claude Bernard University (Lyon). High resolution transmission electron microscopy
(HREM) was done on a JEOL 2010 device, using a 200 kV accelerating voltage.
Thermogravimetric analysis with mass spectrometry of evolved gases was applied to
À1
study evolution of solids during their linear (5 K min ) heating in inert atmosphere
or in air. The gaseous products evolved upon heating of the samples were studied
using a mass-spectrometer Gas Trace A (Fison Instruments) equipped with a
quadrupole analyzer (VG analyzer) working in a Faraday mode. The ionization
was done by electron impact with an electron energy of 65 eV.
3
. Results and discussion
It was noticed that the possibility of obtaining of the soluble carbonate complexes
in the reaction of ZrOCl solution and alkali metal or ammonium carbonate depends
2

P. Afanasiev / Materials Research Bulletin 37 (2002) 1933±1940
1935
on the order of addition of reactants and the intensity of stirring. If sodium or
ammonium carbonate is added slowly to the excess of ZrOCl solution, at its own
2
pH 2, then the pH increases and formation of a white precipitate occurs at ca. pH 4; no
redissolution is noticed upon further adding of excess carbonate up to pH 11. By
contrast, if Zr salt is added to an excess of carbonate upon vigorous stirring, then
soluble species are formed. At the moment of Zr salt addition, transient formation of a
white precipitate is observed, but its redissolution occurs instantly, suggesting that the
cationic species of the Zr initial salt are ®rst transformed by the reaction with carbonate
to the neutral form (precipitation), then to the anionic form (redissolution) which
probably correspond to basic zirconium carbonates. Gradual addition of small portions
of Zr salt to the excess of Na CO allows the preparation of transparent solutions in
2
3
the pH range from 7 to 11. The lowest pH limit corresponds to the molar ratio
ZrOCl :Na CO equal to 0.5. Then, addition of more Zr salt leads to the formation of a
white precipitate. Similar results have been obtained using ZrOCl or ZrO(NO ) as
2
2
3
2
3 2
starting Zr salts, as well as Na CO or (NH ) CO as carbonate sources.
2
3
4 2
3
In the pH range from 7 to 11, the solutions of obtained complexes are stable for a
rather short time and should, therefore, be used as precursors just after their
preparation. Indeed, transparent gels are formed after several days of standing of
the solutions at ambient conditions in closed vessels. During this time, ®rst the
viscosity of the solutions drastically increases without formation of any gas, then
turbidity appears. At the same time, the pH of the solution slowly increases. Probably,
polycondensation of zirconium carbonate species occurs, with formation of hydro-
xide bridges due to the hydrolysis of aqueous carbonate complexes, as represented
schematically by the Eq. (1).
ZrÀOH ‡ ZrÀOH ! ZrÀOHÀZr ‡ H O
(1)
2
2
Fig. 1. IR spectra of hydrated Zr carbonate (a) and (CTA)ZrOOHCO sample (b).
3

1936
P. Afanasiev / Materials Research Bulletin 37 (2002) 1933±1940
Slight heating increases the rate of condensation. After 1 h of re¯ux at 373 K, a
white amorphous precipitate is formed, which according to the chemical analysis
2
À
has Zr to CO3 ratio of 1.6, and low amounts of the impurities issued from the
reaction mixture (0.6 wt.% of nitrogen and less than 0.1 wt.% of chlorine). This
solid shows in the IR spectrum (Fig. 1, spectrum a), two strong and broad lines at
À1
1
380 and 1560 cm typical for bidentate carbonate species [14]. Unfortunately,
À1
the broad line region between 1600 and 1700 cm is obscured by the strong
absorption of water, so more reliable interpretation of IR spectrum is not possible.
This solid seems to be a nonstoichiometric zirconium oxohydroxocarbonate. To
understand the details of the structure of zirconium species in the basic carbonate
solutions and/or in the amorphous precipitates, further study is necessary using
EXAFS spectroscopy.
The basic carbonate solution obtained as described earlier, might be further used
for the synthesis of materials. The new solids syntheses using these precursors might
be of several types, but the simplest possibility is evidently to make these complexes
to react with some cations in order to precipitate the corresponding salts. For the metal
cations, the syntheses of mixed oxides can be envisaged, whereas for the organic
cations hybrid organic±inorganic materials might be obtained.
Adding freshly prepared basic zirconium carbonate solution at pH 8 to the two-fold
molar excess of tetraalkylammonium halides lead to the instant precipitation of white
powders. Trimethylcetylpyridinium chloride and CTMAB give precipitates of com-
position (NR4)0.88ZrO(OH)(CO )
which suggest that reactive species have the stoichiometry close to [ZrO(OH)CO ] ,
and (NR4)0.81ZrO(OH)(CO ) , respectively,
3 0.85
3 0.91
À
3
though their nuclearity is not established. The solids also contain the impurities issued
À
from the reactants (0.8 wt.% of Br and 0.2 wt.% of Cl for CTMAB salt).
Fig. 2. Small angle diffraction of the (CTA)ZrOOHCO solid.
3

P. Afanasiev / Materials Research Bulletin 37 (2002) 1933±1940
1937
Fig. 3. SEM image of the (CTA)ZrOOHCO solid.
3
The cetyltrimethylammonium-derived solid, (C H ) ZrO(OH)(CO )
3 0.85
1
9
39 0.81
(designated further as (CTA)ZrOOHCO ), was studied in more detail. In the XRD
3
pattern of this compound, the only intense line is a small angle re¯ection correspond-
ing to the distance of 4.1 nm (Fig. 2). No peaks were observed in the higher angle
region. The IR spectrum of (CTA)ZrOOHCO registered in air (Fig. 1, spectrum b)
3
À1
consisted of a group of narrow lines at 3002, 2920, 2851, and 1480 cm , as well as
several small narrow peaks at lower frequencies, all the same as in the spectrum of the
À1
initial CTABr (not shown). Two broad bands at 1320 and 1580 cm and a weak line
À1
at 1030 cm suggest the presence of bidentate carbonate species.
SEM images of (CTA)ZrOOHCO solid show the rag-type morphology (Fig. 3)
3
consistent with its poor crystallinity. HREM shows that the sample has a so called
wormhole-like structure (Fig. 4), similar to that observed by Blin et al. [15]. The solid
consists of fairly monodisperse globular objects with the characteristic size of about
4
nm in agreement with the position of the small angle XRD peak.
Thermal decomposition of (CTA)ZrOOHCO was studied (Fig. 5). Dehydration
3
occurs at ca. 373 K with a narrow endothermal peak in the TGA curve. The most
important part of the weight loss of ca. 40 wt.% is related to an endothermal peak at
5
CH species in the mass spectra. After heating at 773 K in air, the sample loses all
20 K which is due to release of organics, since it coincides with peaks of CH and
3
2
carbonate. It still remains XRD amorphous at higher angles but loses mesoscopic
À1
2
ordering as follows from the small angle XRD. It has a BET surface area 178 m g
3
À1
and pore volume of 0.4 cm g with narrow pore size distribution having a maximum
at 2.5 nm (Fig. 5). A nitrogen adsorption±desorption hysteresis loop of the H2 type is
observed for the sample calcined at 773 K for 2 h. The H2-type hysteresis loop with a
steep desorption and smoothly sloping adsorption curve suggest that near to uniform

1938
P. Afanasiev / Materials Research Bulletin 37 (2002) 1933±1940
Fig. 4. TEM image of the wormhole-like structure of the (CTA)ZrOOHCO solid.
3
size entrances are present, typical for MCM-like and wormhole mesoporous materials
Fig. 6).
It was not our goal in this short paper to optimize the preparation of yet another
(
mesoporous zirconia, but just to illustrate the possibility of application of basic
carbonate precursor to the new materials synthesis. Earlier, many studies have been
devoted to preparation of mesoporous zirconia. In the previous works, various
combinations of precursors and surfactants have been tried. Coprecipitation of
Fig. 5. Mass spectra of gases evolved during heating of (CTA)ZrOHCO under a nitrogen ¯ow.
3

P. Afanasiev / Materials Research Bulletin 37 (2002) 1933±1940
1939
Fig. 6. Nitrogen adsorption isotherm of the sample obtained after heating (CTA)ZrOHCO in air at
3
7
73 K for 2 h.
trialkylammonium halide and zirconium oxychloride [16] or isopropoxide [17]
mixtures have been used. In the syntheses applying cationic surfactants, often no
templating (as in silica mesoporous materials) but just scaffolding by the incorporated
surfactant was observed. Using amphoteric [18] or anionic [19] surfactants and
oxychloride or propoxide Zr precursors, hexagonal and cubic mesoporous zirconia
were obtained. Hydrolysis of zirconium propoxide in the presence of the anionic
surfactant was applied to obtain hexagonal mesophases [20]. Here, using a carbonate
anionic Zr precursor and a cationic surfactant, we obtain by direct precipitation a new
zirconium-surfactant hybrid mesophase.
4
. Conclusion
We believe that the anionic carbonate complexes of Zr(IV) are the promising
alternative precursors for the materials synthesis, which are very simple to prepare,
might be applied in the pH range from 7 to 11 and beside zirconium, oxygen, and
water, contain only the carbonate moieties easily removable by heating. In this paper,
we present an example of this approach, giving an alternative way to the mesoporous
zirconia. Work is in progress on the application of these precursors to other
preparations such as mixed oxides of Zr(IV).
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