27Al NMR study of the effect of aqueous and methanolic media on the distribution of tetraphenylammonium aluminosilicate species

Article abstract of DOI:10.1134/S0022476615020079

The effects of tetraphenylammonium (TPhA) on the equilibrium distribution of aluminosilicate oligomers in aqueous and methanolic alkaline aluminosilicate solutions are investigated using ²⁷Al NMR spectroscopy. Alkaline solutions containing both silicate and aluminate ions are of considerable research interest inter alia because of their involvement in the synthesis of zeolites. In the present work, we use ²⁷Al NMR to characterize alkaline aqueous and methanolic tetraphenylammonium (TPhA) aluminosilicate solutions with different Al/Si ratios. Tetraphenylammonium (TPhA) is used as a cation template and no alkalie metals are used for the preparation of aluminosilicate solutions. The distribution of aluminosilicate species is affected by the presence of the alcohol such as methanol and the method of mixing the silicate and aluminosilicate solutions. To understand the reaction between silicate and aluminate ions in this system, the evolutions of ²⁷Al NMR spectra with time are investigated.

Full text of DOI:10.1134/S0022476615020079

Journal of Structural Chemistry. Vol. 56, No. 2, pp. 250-258, 2015.
Original Russian Text © 2015 N. Goudarzi.
27Al NMR STUDY OF THE EFFECT OF AQUEOUS
AND METHANOLIC MEDIA ON THE DISTRIBUTION OF
TETRAPHENYLAMMONIUM ALUMINOSILICATE SPECIES
N. Goudarzi
UDC 541.67:546.621:546.21
The effects of tetraphenylammonium (TPhA) on the equilibrium distribution of aluminosilicate oligomers
in aqueous and methanolic alkaline aluminosilicate solutions are investigated using 27Al NMR
spectroscopy. Alkaline solutions containing both silicate and aluminate ions are of considerable research
interest inter alia because of their involvement in the synthesis of zeolites. In the present work, we use 27Al
NMR to characterize alkaline aqueous and methanolic tetraphenylammonium (TPhA) aluminosilicate
solutions with different Al/Si ratios. Tetraphenylammonium (TPhA) is used as a cation template and no
alkalie metals are used for the preparation of aluminosilicate solutions. The distribution of aluminosilicate
species is affected by the presence of the alcohol such as methanol and the method of mixing the silicate
and aluminosilicate solutions. To understand the reaction between silicate and aluminate ions in this
system, the evolutions of 27Al NMR spectra with time are investigated.
DOI: 10.1134/S0022476615020079
Keywords: 27Al NMR spectroscopy, tetraphenylammonium hydroxide, evolution with time, methanolic
aluminosilicate solutions.
INTRODUCTION
The cation of the organic or inorganic base is considered to play a structure directing role in the synthesis of zeolites,
an interesting but as yet poorly understood phenomenon. This role is commonly discussed in terms of the cation having
a templating function during the formation of the aluminosilicate framework from mixing of silicate and aluminate solutions.
However, the importance of the initial solution chemistry for the preparation of a specific zeolite structure has long been
recognized [1, 2]. It is clear that for zeolite formation and crystal growth nucleation occurs through the co-polymerization of
aluminate and silicate ions in a solution mixture. The question of whether dissolved aluminosilicate species are involved as
precursors in the hydrothermal formation of natural or synthetic zeolites has been investigated by a number of authors for
some years [3-7]. In principle, NMR spectroscopy is powerful tool for detecting and characterizing aluminum and silicon
containing species in aqueous solution. Accordingly, a number of investigations have been carried out to address the structure
of ions present in silicate, aluminate and aluminosilicate solutions [8-27]. Kinrade and Swaddle identified 29Si NMR peaks
due to low molecular weight aluminosilicate anions of sodium aluminate solutions by 29Si NMR spectroscopy [18]. Using
similar methods, Mortlock et al., investigated tetrapropylammonium (TPA) aluminosilicate solutions [17, 21]. They also
reported the correlation between the partial charge on Si atoms and chemical shift was used to confirm the assignment of 29Si
Faculty of Chemistry, Shahrood University of Technology, Shahrood, Iran; goudarzi@shahroodut.ac.ir;
goudarzi10@gmail.com. The text was submitted by the authors in English. Zhurnal Strukturnoi Khimii, Vol. 56, No. 2,
pp. 266-274, March-April, 2015. Original article submitted August 27, 2013.
250
0022-4766/15/5602-0250 © 2015 by Pleiades Publishing, Ltd.

NMR peaks due to cage species containing double-rings, such as a prismatic hexamer and a cubic octamer, with some
replacement by aluminum [28].
Evidence of dissolved aluminosilicate anions has come from both 29Si and 27Al NMR spectroscopies [29-35]. The
notation Qn for silicate solutions, where n refers to the number of siloxane bridges, is well established [10-15]. In the case of
individual aluminum sites in aluminosilicate anions there is a special similar notation. An aluminum site is presented as “q”
with the number of oxygen bridges to silicon indicated by a superscript. Thus, if aluminum has no silioxane bridges, as for
5−
4
the AlO aluminate anion (or its protonated congeners up to Al(OH)−), it is represented as q0, where q1, q2, q3 and q4 indicate
Al(1OSi), Al(2OSi), Al(3OSi), and Al(4OSi), respectively. It is generally assumed that Loewenstein′s [36] rule is obeyed,
3+
i.e., there are no Al–O–Al bridges. Muller et al. assigned chemical shifts (from the signal for Al[H2O] ) of 79.5 ppm,
6
74.3 ppm, 68.5 ppm, and 64.2 ppm to q0, q1, q2, and q3 respectively, using TBMA aluminosilicate solutions [34]. Dent
Glasser and Harvey, using potassium aluminosilicate solutions, found several bonds in the 27Al-NMR spectra lying at shifts
of 80 ppm, 70-72 ppm, 66 ppm, 61 ppm, and 58 ppm and assigned them to q0, q1, q2, and q3 respectively [35].
Interest in the physicochemical processes occurring during zeolite synthesis has stimulated the study of dissolved
silicate oligomers in aqueous alkaline solutions and their possible link to zeolite nucleation and crystal growth. Although
laboratory and industrial syntheses typically involve only aqueous precursor solutions, several authors have noted the effects
of adding organic solvents to silicate solutions [36, 37]. This work represents some insight into interactions between the
aluminate and silicate species in aqueous and methanolic tetraphenylammonium (TPhA) aluminosilicate solutions and
compares and contrasts the interaction between aluminate and silicate species after mixing of these solutions with and
without alcohol. Also, in the present work, we have used 27Al NMR to characterize aluminosilicate solutions with different
Al/Si mole ratios using tetraphenylammonium as a template. No alkali metals such as sodium or potassium were used for the
preparation of silicate or aluminate solutions. For more information and understanding of the reaction between aluminate and
silicate ions, the evolution of 27Al NMR spectra with time was also investigated.
EXPERIMENTAL
Tetraphenylammonium (TPhA) was used as a template. Firstly, tetraphenylammonium bromide (TPhABr) was
converted to hydroxide by dissolving it in a minimum of water and passing it down a column of Aldrich amberlite resin IRA-
400(OH). Elution with double distilled water was carried out until the solution was at pH 7. The water was then removed
under reduced pressure. Pure silica was produced by hydrolysis of silicon tetrachloride (99.8 % purity) using doubly distilled
water. The precipitate was filtered off and washed many times with doubly distilled water to remove all the acid. It was then
dried at ca. 105 °C for 48 h. Aqueous silicate solutions were prepared in polyethylene bottles by dissolving SiO2 in
appropriate amounts of tetraphenylammonium hydroxide. Dissolution of silica required ca. one week at a temperature of
70 °C, yielding a clear solution. Aluminate solutions were made by dissolving a suitable amount of aluminum powder in
0.6 mol TPhAOH solutions. The aluminate ion concentration in the solution was 0.1 mol. The same procedure was performed
for the preparation of methanolic silicate solutions, except methanol was used instead of water. For the preparation of
methanolic aluminate solutions, an appropriate amount of aluminum powder was dissolved in an alcoholic TPhAOH solution.
The fresh aluminate solution was added to the silicate solution at ambient temperature (ca. 25 °C) to achieve the desired Si/Al
molar ratios. After mixing, the solutions were allowed to reach a steady state for at least one week at room temperature (ca.
22 °C), except when the temporal evolution of the spectra was being studied. Data on the composition of aluminosilicate
solutions are listed in Table 1. All solutions contained ca. %5 v/v D2O (Aldrich Chemical Company) to provide
field/frequency lock for the NMR spectroscopy.
To investigate the degree of solute-solvent interaction, the aluminosilicate solution was modified by addition of
alcohol such as methanol. To understand the distribution of aluminosilicate species in methanolic media, four possible ways
of mixing silicate and aluminate solutions with and without alcohol have been investigated. 27Al NMR spectroscopy was
therefore used to investigate the difference between these aluminosilicate solutions. We found that although the final
251

TABLE 1. Data on the Composition of Aluminosilicate Solutions
Sample No.
Al/Si molar ratio
Si, %w/w
Al, %w/w
MeOH, %w/w
H2O, %w/w
1
2
3
4
7.5
7.5
7.5
7.5
0.301
0.341
0.344
0.391
0.125
0.137
0.136
0.154
0.0
91.90
51.09
51.02
2.78
38.12
39.31
88.27
concentrations of Si, Al, OH and TPhA in the methanolic aluminosilicate solutions were the same, nevertheless, the
distribution of aluminosilicate species, which were prepared by mixing methanolic silicate and aqueous aluminate, is
significantly different from aluminosilicate solutions prepared by mixing aqueous silicate and alcoholic aluminate solutions.
In addition, the influence of alcohol (methanol) on the distribution of aluminosilicate anions was investigated at different
Si:Al ratios. Furthermore, variation of different aluminosilicate species during evolution with time was monitored by 27Al
NMR spectroscopy.
Spectra were measured using a Bruker AMX 500 spectrometer, operating at 130.3 MHz for 27Al NMR. Aluminum-
27 NMR spectra were obtained by applying 90° pulses (14 ms pulse duration), a recycle delay of 0.2 s was sufficient to allow
a complete return of the magnetization to equilibrium. The 27Al chemical shifts were measured by substitution with
a 1.0 molar aqueous sample of AlCl3 and are thus considered to be referenced with respect to the octahedral [Al(H2O)6]3+
cation. All solutions were clear to the eye at the time of recording the spectra (i.e. no gel had been formed).
RESULTS AND DISCUSSION
The effect of Al/Si molar ratio on the TPhA aluminosilicate solution. To study the effect of the Al/Si molar ratio
on the distribution of aluminosilicate species, a series of aluminosilicate solutions with Al/Si molar ratios of 1.0, 5.0, 7.5,
10.0, and 12.5 were prepared by mixing aqueous TPhA aluminate and aqueous TPhA silicate solutions with a constant silicon
concentration (0.12 M Si for all solutions), with various aluminium concentrations. All solutions were allowed to reach
steady state for one week before spectra were obtained. It was reported [35, 36] that aluminosilicate solutions with high
concentrations of Si show improved signal-to-noise ratios as the molar percent of Al increases, but the features of the spectra
do not change substantially. However, the results obtained from our work indicate that with low concentrations of Si and high
Al/Si molar ratios, the molar percent of Al increases as the intensity of some species such as q0 and q1 are increased, but some
of them, like q3, decrease; it should be mentioned that the pH of the solutions was the same (i.e. ca. pH = 13).
Fig. 1a shows the 27Al NMR spectrum of the aluminosilicate solution with an Al/Si molar ratio of 1.0. The spectrum
illustrates four separated bands located at chemical shifts of ca. 80 ppm, 75.1 ppm, 69.9 ppm, and 65.1 ppm, which are
associated with q1, q2, q3, and q4 respectively. The 27AlNMR peak assignments of TPhA aluminosilicate solution species are
based on the assignment of similar peaks that appear in tetramethylammonium (TMA) aluminosilicate by Muller et al. [30].
The following assignment for the 27AlNMR spectrum of Fig. 1a has been tentatively suggested in this work. The peak at the
chemical shift of 65.1 ppm is possibly due to the Q83 (1Al) octameric species and the signal at ca. 69.9 ppm might be assigned
to the Q36 (1Al), prismatic species. However, it should be noted some other aluminosilicate species which are created through
replacing Si with Al in the related prismatic regions. Fig. 2 illustrates some proposed structures of aluminosilicate species.
Also, the peaks located at ca. 80 ppm and 75 ppm are assigned to the q0 and q1, respectively. Fig. 1b-e reveals that by
increasing the Al/Si molar ratio some new peaks can be observed from the corresponding spectra. Fig. 1b shows the 27Al
NMR spectrum for an aluminosilicate solution with an Al/Si molar ratio of 5. The band located at the chemical shift of 68-
73 ppm is well resolved in two peaks at δAl = 70.1 ppm and δAl = 71.6 ppm associated to aluminum with two siloxane bridges
(i.e. q2). The band positioned at ca. 63-68 ppm is resolved in at least four peaks at the chemical shifts of 64.4 ppm, 65.3 ppm,
65.9 ppm, and 66.1 ppm, where all peaks belong to aluminum with q3 site. Fig. 3 illustrates the horizontal expansion of the
band in this region. The assignment of the peaks in the spectra is difficult in spite of the high
252

Fig. 1. 27Al NMR spectra at 130.32 MHz of TPhA aluminosilicate solutions (aqueous TBMA
silicate and ethanolic TBMA aluminate) with different Al/Si molar ratios: 1.0 (a), 5.0 (b), 7.5 (c),
10.0 (d) and 12.5 (e), and 0.12 mol silica concentrations at 22 °C. Spectral width, 15576.3 Hz;
acquisition time, 0.1 s; recycle delay, 0.20 s; pulse angle, 90° (14 μs); number of repetitions, 2048.
Fig. 2. Some proposed structures of silicate species.
natural abundance of 27Al since no coupling information is available. Thus, it is not easy to say exactly which kind of
aluminosilicate species belongs to the observed signal. Nevertheless assignments can come by analogy with 29Si spectra of
aqueous alkaline silicate solutions, which have been studied under a variety of conditions (including 29Si enrichment) [11].
As a result, on the basis of shielding arguments and referring to the previous reports, we tentatively assigned the peaks at
δAl = 70.2 ppm and δAl = 71.7 ppm to cyclic tetramer (I) and doubly bridged cyclic tetramer (II), respectively (cubic octamer
253

Fig. 3. Horizontal expansion of the 27Al NMR spectrum in the region of q3.
silicate species can be present in these, Fig. 3). The peak at δAl = 67.6 ppm can be denoted as the prismatic hexamer (q3) and
δAl = 65.3 ppm is ascribed to the substituted cubic octamer aluminosilicate species (IV) (Fig. 3), the latter suggested by
Samadi-Maybodi et al. [22]. The results obtained from these experiments specify that by increasing the Al/Si molar ratio the
intensity of peaks at δAl = 70.1 ppm and δAl = 71.6 ppm are increased, while the intensity of the peak at δAl = 65.3 ppm is
decreased. It is supposed that the silicate species, such as bridged cyclic and doubly bridged cyclic tetramers may act as
precursors for the formation of the cubic octamer, Q83 . Since the aluminosilicate species can be more stable than the
corresponding silicate species, once bridged cyclic tetramer (I) and doubly bridged cyclic tetramer (II) species are formed, the
formation of the silicate species of the cubic octamer “Q83 ” is decreased, and as a result the concentration of the
corresponding aluminosilicate (i.e. structure IV) is diminished. By considering the above results, it can be concluded that the
production and distribution of aluminosilicate species are influenced by the aluminum concentration.
The effect of methanol. In order to investigate the effect of alcohol such as methanol on the reaction of aluminate
anions with silicate species, the following aluminosilicate solutions have been prepared by mixing: (a) an aqueous silicate
solution with an aqueous aluminate solution (Sample No. 1); (b) an alcoholic silicate solution with an aqueous aluminate
solution (Sample No. 2); (c) an aqueous silicate solution with an alcoholic aluminate solution (Sample No. 3); and
(d) an alcoholic silicate solution and an alcoholic aluminate solution (Sample No. 4). Data on the chemical composition of the
solutions and their characterizations are shown in Table 1.
Aluminum-27 NMR spectra were recorded at ambient NMR probe temperature (ca. 22 °C) under the same spectral
conditions and are shown in Fig. 4a-d. Fig. 4a represents a 27Al NMR spectrum of sample No. 1 that shows five separate
bands, indicating the existence of at least five kinds of aluminosilicate species. In this figure, q0 (AlO 54− ) and q1
(aluminosilicate species with one siloxane bridge) should be present at 80 ppm and 75 ppm, respectively [38-40]. However,
the first band at the highest frequency appears at 80 ppm that is related to q0 species and the second bond in the NMR
spectrum illustrates the aluminosilicate species with one siloxane bridge (q1). The other bands located at ca. 70.5 ppm,
64.2 ppm, and 59.5 ppm represent q2 (Al2OSi), q3 (Al3OSi), and q4 (Al4OSi), respectively. The intensity of the peak at ca.
59.5 ppm is very small, which means that the probability of the formation of q4 species in the aluminosilicate solution is
weak. The 27Al NMR spectrum indicates that the concentrations of these species are not equivalent, so that
q0 >> q1 ∼ q2 > q3 >> q4. Indeed, there are different kinds of aluminosilicate species which contain aluminum with the same
siloxane bridges, i.e., with the similar qn sites, for instance, there are different aluminosilicate species, which all contain q2
254

Fig. 4. 27Al NMR spectra at 130.32 MHz of TPhA aluminosilicate
solutions contain: (a) an aqueous silicate solution with an aqueous
aluminate solution (Sample No. 1); (b) a methanolic silicate solution
with an aqueous aluminate solution (Sample No. 2); (c) an aqueous
silicate solution with a methanolic aluminate solution (Sample No. 3);
and (d) a methanolic silicate solution and a methanolic aluminate
solution (Sample No. 4) at 22 °C. Spectral width, 15576.3 Hz;
acquisition time, 0.1 s; recycle delay, 0.20 s; pulse angle, 90° (14 μs);
number of repetitions, 2048.
sites (Fig. 2). Such structures have been proposed by Engelhard et al. [41] for silicate anions and subsequently by other
authors for silicate and aluminosilicate species [11-13]. 27Al NMR spectra of these four solutions indicate that when we mix
an aqueous silicate solution with an ethanolic aluminate solution (Sample No. 3), the number of aluminosilicate species
increase in comparison with other solutions (samples Nos. 1, 2, and 4). Fig. 4c shows a decrease in low order aluminosilicate
species (q0 and q1) and an increase in the amount of high order of aluminosilicate species (q3 and q4). Fig. 4b shows the 27Al
NMR spectrum of sample No. 2 with four bands at chemical shifts of 79.5 ppm, 74.5 ppm, 70 ppm, and 65 ppm.
A methanolic silicate solution was used for the preparation of the aluminosilicate solution; however, there are no significant
differences between Fig. 4a and b (Samples No. 1 and 2, respectively). The 27AlNMR spectrum of the aluminosilicate
solution prepared with methanolic aluminate and an aqueous silicate solution (Sample No. 3) is presented in Fig. 1c. The
spectrum shows several resolved bands located at chemical shifts of ca. 80 ppm, 75 ppm, 70 ppm, 64 ppm, and 58 ppm,
assigned to q0, q1, q2, and q3, respectively. It is pertinent to mention that the band located at a chemical shift of 64 ppm is
significantly sharper than the others, presumably indicating that the electric field gradient at aluminum is significantly smaller
for some environments giving rise to the sharp peaks. Harris and co-workers [40] assigned this signal to the substituted cubic
octameric aluminosilicate species. It should be noted that signals at chemical shifts of 80 ppm and 75 ppm are well separated
revealing that the exchange rate between q0 and q1 is slow on the NMR time scale. Results obtained from this experiment
reveal that at the same concentration of silicon and aluminum, the formation and distribution of aluminosilicate species are
strongly dependent on the solvent in the silicate and aluminate solutions. Comparison of Fig. 4b (sample No. 2) and Fig. 4c
(sample No. 3) indicates that although the final compositions of the aluminosilicate solutions are the same, the features of the
spectra are totally different. As a result, the solvent plays an important role in the reaction between the silicate and aluminate
ions. In both aqueous and methanolic silicate solutions, there are a number of silicate species, such as the monomer (Q0),
255

dimer (Q12 ), cyclic trimer (Q32 ), cyclic tetramer (Q24 ), prismatic hexamer (Q36 ), and cubic octamer (Q83 ). It is proposed [40]
that the formation of aluminosilicate species is accomplished by the interaction of aluminate anions with silicate species in
different ways such as, addition (the addition of the aluminate ion to any silicate species to produce aluminosilicate species
with one aluminum q1 site); substitution (replacement of silicon by aluminum to create qn with any value of n) and chelation
(this would imply the ring or cage formation). Fig. 4c shows that a number of aluminosilicate species were produced by
mixing aqueous silicate and methanolic aluminate solutions, indicating that this mixing condition favors the interaction of
silicate species with aluminate ions. As Fig. 4c shows, one can deduce that the replacement of silicon by aluminum through
substitution and chelating is highly efficient, and hence the creation of aluminosilicate species such as q3 and q4 is favored
(Table 2). It can be said that in methanolic aluminate solutions there are aluminate species such as, Al(CH3CH2OH)34+
,
AlOH(CH3CH2OH)32+ or Al(OH)2(CH3CH2OH)+2 which have a positive charge. The formation of these species from the
reaction of aluminate and methanol was approved in our previous work [40]. On the other hand, silicate species such as the
prismatic hexamer (Q36 ) and cubic octamer (Q83 ) carry negative charges (6- and 8-, respectively). Consequently, the
interaction between aluminate and silicate species should be more efficient.
Fig. 4d displays a 27Al NMR spectrum of the methanolic aluminosilicate solution prepared by mixing both
methanolic silicate and aluminate solutions (sample No. 4) with three separate signals observed at chemical shifts of 79 ppm,
70 ppm, and 65 ppm. The signal at the highest frequency located at a chemical shift of 79 ppm reveals that the q0 species is
more concentrated than the others (Table 2). Results obtained from this experiment establish that the interaction between the
aluminate ion and the silicate species in the methanolic solution is unfavorable and, therefore, the formation of the
aluminosilicate species is less feasible.
Evolution of 27Al NMR spectra with time. The aim of this part of the experiment was to provide some insight into
the effects that aluminate/silicate replacement processes have on the appearance of 27Al NMR spectra, and to show how these
effects may be exploited in assigning structures and determining reaction mechanisms. The aluminosilicate solution was
made by adding an aqueous TPhA silicate solution to the methanolic TPhA aluminate solution to achieve an Al/Si ratio of 10
without using any alkali metals. To study the evolution of the 27Al NMR spectra with time, four different protocols were used
at a temperature of 22 °C.
(1) Recording 27Al NMR spectrum soon after mixing the solution, (2) a spectrum after 0.5 h, (3) a spectrum after
8 h, and (4) a spectrum after 18 h.
Fig. 5a displays the 27Al NMR spectrum immediately following the mixing of aqueous TPhA silicate and methanolic
TPhA aluminate solutions with an Al/Si ratio of 10 and 0.12 at 22 °C. The major peak, ca. 80.0 ppm, may be assigned
primarily to free aluminate (q0). However, peaks at ca. 75.1 ppm, 70.2 ppm, and 65.1 ppm represent q1, q2, and q3
environments, respectively, which are clearly present very quickly after mixing.
Fig. 5b-d represents the 27Al NMR spectra, the mixing of aluminate and silicate solutions after 0.5 h, 8 h and 18 h
respectively. The signal intensities corresponding to the different aluminosilicate environments vary with time, so that the
signal at the highest frequency is highly dominant during the first hour after mixing, whereas the signals assigned to q1, q2, q3,
and q4 are substantial at the end of the evolution time (i.e., after 12 h). This suggests that the aluminate anions react with the
silicate anions in different ways depending on the individual silicate species involved. As explained elsewhere [23]
TABLE 2. Peak Area (relative intensity) of Different Aluminosilicate Species in Different Aluminosilicate Solutions
Sample No.
Figure
q0, %
q1, %
q2, %
q3, %
q4, %
1
2
3
4
1a
1b
1c
1d
0.323
0.336
0.341
0.374
0.119
0.131
0.130
0.146
0.0
90.90
52.04
51.02
2.78
0.43
0.0
39.12
39.06
87.27
9.85
0.0
256

Fig. 5. 27Al NMR spectra at 130.32 MHz of the TPhA aluminosilicate
solution with the Al/Si molar ratio of 10, taken at 22 °C, at the
following times after mixing the aqueous silicate and aluminate solution
with 0.15 mol SiO2, (a) after mixing; (b) 1 h; (c) 8 h; (d) 16 h. Spectral
conditions: spectral width, 15576.3 Hz; acquisition time, 0.1 s; recycle
delay, 0.20 s; pulse angle, 9090 °C (14 μs).
formation of the aluminosilicate linkages is not necessarily step by step, i.e., building up the aluminum environments q1, q2,
q3, and q4 might occur simultaneously. Indeed, this process can be expected because when the aluminate ions are introduced
to the silicate solutions they are exposed to a number of preexisting silicate species [11-12], e.g., monomer, dimer, cyclic
trimer, linear trimer, prismatic hexamer, and cubic octamer. The silicate solution used for this particular experiment was
made one week before it was utilized. Therefore, it is likely that the aluminate ions could react with a number of silicate
species at the same time, though the mode of reaction is a matter of speculation. Considering the results obtained from this
experiment, it can be deduced that there are two different steps. At the first stage the aluminate ions attack the silicate species
simultaneously and the replacement of Si by Al occurs rather quickly. In the second step (i.e., 1-8 h) the reaction between
silicate and aluminosilicate is slow and therefore the feature of the spectra do not vary with time quickly. It can be said that
the system undergoes a re-equilibrium process; aluminosilicate species are formed slowly during this time.
CONCLUSIONS
The present work shows the formation of aluminosilicate anions through the reaction of aluminate and silicate
anions using tetraphenyl ammonium hydroxide (TPhAOH) as a base without any alkali metal. The results obtained from this
study specify that there are two stages of the aluminosiliacte formation. Also, in this study methanol plays an important role
in the formation of aluminosilicate species from aqueous silicate and methanolic aluminate solutions. The results also
indicate that at a constant silicate concentration, the production and distribution of aluminosilicate species are influenced by
the aluminum concentration.
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