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# The influence of hydrothermal synthesis conditions on gyrolite texture and specific surface area

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Influence of hydrothermal synthesis conditions on the gyrolite specific surface area, dominant pore size and their differential distribution by the radius were determined. The synthesis of gyrolite has been carried out in unstirred suspensions within 32, 48, 72, 120, 168 h at 200°C temperature from a stoichiometric composition (the molar ratio of CaO/SiO2 was equal to 0.66 where water/solid ratio of the suspension was equal to 10.0) of the initial CaO and SiO2·nH2O mixture. It was found that the structure of gyrolite and the shape of dominated pores (from pores between parallel plates to cylindrical pores) changes prolonging the duration of hydrothermal synthesis. The stable gyrolite crystal lattice was formed only after 120 h of isothermal curing. Its specific surface area S BET = 38.28 m2/g, the radius of dominant plate pores r p = 30–40 Å, the cumulative pore volume ΣV p = 0.08 cm3/g. It was determined that the pores with 4.0–5.0 nm radius were dominated in gyrolite structure after 168 h of synthesis. It was estimated that the ion exchange between gyrolite with less orderly structure in Zn(NO3)2 + NH4OH alkaline solution ($${c_{{{\text{Zn}}^{2+}}}}$$—0.3 g/dm3) proceeds more faster and effectively.
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1 23
Materials and Structures
ISSN 1359-5997
Volume 44
Number 9
Mater Struct (2011) 44:1687-1701
DOI 10.1617/s11527-011-9727-8
The influence of hydrothermal synthesis
conditions on gyrolite texture and specific
surface area
K.Baltakys, A.Eisinas, T.Dizhbite,
L.Jasina, R.Siauciunas & S.Kitrys
1 23
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ORIGINAL ARTICLE
The inﬂuence of hydrothermal synthesis conditions
on gyrolite texture and speciﬁc surface area
K. Baltakys
A. Eisinas
T. Dizhbite
L. Jasina
R. Siauciunas
S. Kitrys
Received: 23 June 2010 / Accepted: 15 March 2011 / Published online: 25 March 2011
RILEM 2011
Abstract Inﬂuence of hydrothermal synthesis con-
ditions on the gyrolite speciﬁc surface area, dominant
pore size and their differential distribution by the
radius were determined. The synthesis of gyrolite has
been carried out in unstirred suspensions within 32,
48, 72, 120, 168 h at 200C temperature from a
stoichiometric composition (the molar ratio of CaO/
SiO
2
was equal to 0.66 where water/solid ratio of the
suspension was equal to 10.0) of the initial CaO and
SiO
2
nH
2
O mixture. It was found that the structure of
gyrolite and the shape of dominated pores (from pores
between parallel plates to cylindrical pores) changes
prolonging the duration of hydrothermal synthesis.
The stable gyrolite crystal lattice was formed only
after 120 h of isothermal curing. Its speciﬁc surface
area S
BET
= 38.28 m
2
/g, the radius of dominant plate
pores r
p
= 30–40 A
˚
, the cumulative pore volume
RV
p
= 0.08 cm
3
/g. It was determined that the pores
with 4.0–5.0 nm radius were dominated in gyrolite
structure after 168 h of synthesis. It was estimated that
the ion exchange between gyrolite with less orderly
structure in Zn(NO
3
)
2
? NH
4
OH alkaline solution
(c
Zn
2þ
—0.3 g/dm
3
) proceeds more faster and
effectively.
Keywords Gyrolite Ion exchange reactions
Calcium silicate hydrate BET analysis
1 Introduction
Calcium silicate hydrates are highly multiplex system
with over 30 stable phases. Most of them occurring in
nature as hydrothermal alteration products of calcium
carbonate rocks and as vesicle ﬁllings in basalts,
include many chemically and structurally distinct
phases [17]. From a theoretical and practical point of
view, the synthesis, properties and structure of the
main calcium silicate hydrates—C–S–H(I), 1.13 nm
tobermorite, xonotlite, a-C
2
S hydrate have been
analyzed in detail [13, 15, 18, 24, 25, 27, 29, 33].
Majority of these compounds are occurring naturally
or may be synthesized in the laboratory.
Recently, the interest of gyrolite group compounds
(gyrolite, Z-phase, truscottite, reyerite) increases
because the new possibilities of application were
found: it may be used to educe heavy metal ions and
remove them from wastewaters [5, 12, 19]. It was
show that gyrolite sorption properties is greater than
K. Baltakys (&) A. Eisinas (&) R. Siauciunas
Department of Silicate Technology, Kaunas University of
Technology, Radvilenu 19, LT-50270 Kaunas, Lithuania
e-mail: kestutis.baltakys@ktu.lt
A. Eisinas
e-mail: anatolijus.eisinas@ktu.lt
T. Dizhbite L. Jasina
Latvian State Institute of Wood Chemistry, Dzerbenes 27,
Riga LV-1006, Latvia
S. Kitrys
Department of Physical Chemistry, Kaunas University of
Technology, Radvilenu 19, LT-50270 Kaunas, Lithuania
Materials and Structures (2011) 44:1687–1701
DOI 10.1617/s11527-011-9727-8
Author's personal copy
tobermorite group minerals [7, 8, 28]. Of speciﬁc
interest is the purported ability of gyrolite to separate
supercoiled plasmid, open circular plasmid, and
genomic DNA [34].
Gyrolite can be synthesized from CaO and various
forms of SiO
2
with the molar ration CaO/SiO
2
(C/
S = 0.66) in aqueous suspension at temperatures of
about 200C. Kalousek and Nelson [11], and also
Stevula and Petrovic [29] found that gyrolite could
likewise be prepared by interacting dicalcium silicate
(2CaOSiO
2
)withSiO
2
in aqueous suspension under
hydrothermal conditions. Stevula et al. were found that
over the temperature range of 200–300C under hydro-
thermal conditions, both the natural and synthetic
gyrolite behave analogously. Above this temperature,
both natural and synthetic gyrolite decompose, forming
the stable phases truscottite and xonotlite [30].
Okada et al. using lime and amorphous silica as
the starting materials, hydrothermally prepared gyr-
olite with the C/S molar ratio of 0.66 and 0.50 at
200C for 0.5–128 h [22, 23].
Jauberthie et al. determined that the tobermorite gel,
formed by hydrothermal reaction of silica and lime, is
transformed either into Z-phase if the quantity of lime
is less than 37% or into 1.0 nm tobermorite if the
quantity of lime is between 37 and 42%. The 1.0 nm
tobermorite is stable in the presence of gyrolite,
whereas Z-phase is metastable [10].
Baltakys and Siauciunas [3, 27] were determined
the inﬂuence of SiO
2
modiﬁcation on crystallization
process of gyrolite. Authors showed that gyrolite does
not form even during a week in the mixtures of CaO
and amorphous SiO
2
at 150C under the saturated
steam pressure. The temperature increase positively
affects synthesis of this compound—pure gyrolite is
produced at 175C after 72 h, and after 32 h—at
200C. It should be underlined that in the mixtures
with quartz the mechanism of compound formation is
quite different. Due to a low quartz solubility rate
at temperature range from 150 to 200C, neither
Z-phase, nor gyrolite is formed even after 72 h of
hydrothermal curing. a-C
2
S hydrate and C–S–H(II)
prevail in the beginning of the synthesis and gradu-
ally recrystallizes into 1.13 nm tobermorite and
xonotlite.
Shaw et al. [26] having used the synchrotron X-ray
radiation source of high energy have explored the
mechanical, kinetic, and energetic processes that are
proceeding during the formation of gyrolite. The
formation of gyrolite in the temperature range from
190 to 240C in the pure calcic system involves a three
stage process: amorphous gel ? C–S–H gel ?
Z-phase ? gyrolite.
Although often it is stated that the crystal lattice
of the gyrolite found in nature always has both sodium
and aluminium ions [9, 16]. There is a little data in the
references about the inﬂuence of Al
2
O
3
and Na
2
O
additives on the synthesis of low base calcium sili-
cate hydrates (in contrast to 1.13 nm tobermorite)
[1921, 32].
It should be noticed that Miyake et al. [19]
successfully synthesized (Al ? Na)-substituted gyr-
olite (Ca
8
Si
11.32
Al
0.68
Na
0.44
O
30
(OH)
4
6.6H
2
O) and
used it for the ions exchange reactions (K
?
and
Cs
?
) in aqueous solutions.
Stumm et al. [31] have indicated that zinc
incorporation into synthetic gyrolite is also possible
up to Zn/(Zn ? Ca) = 1/6, corresponding to approx-
imately 6 wt%. Increasing zinc content led to a
gradual diminishing of the basal reﬂection (001) of
gyrolite, as for the nanocrystalline phases.
Baltakys andSiauciunas [1] proved that the formation
of gyrolite is accelerated by mixing suspension because
pure gyrolite forms after 16 h of isothermal curing at
200C. Stirring affects the sequence of intermediate
compounds: gyrolite crystallizes together with Z-phase.
Also, 5% Na
2
O additive in the stirred suspensions
signiﬁcantly accelerates the synthesis of gyrolite: this
compound dominates already after 6 h at 200C.
The structure, optical properties and chemistry of
natural gyrolite were studied by many scientists [2, 4,
16, 26]. However, their opinions differ. A full struc-
tural solution for gyrolite was proposed by Merlino.
However, some properties (like sorption capacity)
depend not only on the crystal lattice of a porous body
but also on that of the surface microstructure and
speciﬁc surface area, as well as on the dominant pore
size and their differential distribution in the compound
according to the radius. In the case of gyrolite crystal
lattice, these properties usually depend on the propor-
tion of crystalline S
1
; S
2
;
S
2
; S
2
ðÞand amorphous (X
sheet) parts. However, no data were found in references
about the inﬂuence of synthesis conditions on gyrolite
crystal lattice.
The aim of this work was to determine the
inﬂuence of hydrothermal synthesis conditions on
1688 Materials and Structures (2011) 44:1687–1701
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the gyrolite speciﬁc surface area, as well as dominant
pore size and their differential distribution according
to the radius in this compound. Also, the application
of gyrolite in the ion exchange reaction is discussed.
2 Materials and methods
2.1 Materials and manufacture of synthetic
gyrolite
In this work the following reagents were used as
starting materials: ﬁne-grained SiO
2
nH
2
O (Reachim,
Russia, ignition losses 21.43%, speciﬁc surface area
S
a
= 1,560 m
2
/kg by Blaine’s); CaO (97.6% Reachim,
Russia) additionally was burned at 950C for 0.5 h.
The synthesis of gyrolite has been carried out in
unstirred suspensions in the vessels of stainless steel.
Pure gyrolite was synthesized within 32, 48, 72, 120,
168 h at 200C temperature from a stoichiometric
composition (the molar ratio of CaO/SiO
2
was equal
to 0.66 where water/solid ratio of the suspension was
equal to 10.0) of the initial CaO and SiO
2
nH
2
O
mixture. These synthesis conditions were chosen
according to previously published data [3, 27].
The products of the synthesis have been ﬁltered,
rinsed with ethyl alcohol to prevent carbonization of
materials, dried at the temperature of 50 ± 5C and
sieved through a sieve with a mesh width of 50 lm.
2.2 Analytical techniques
The X-ray powder diffraction data were collected
with a DRON-6 X-ray diffractometer with Bragg–
Brentano geometry using Cu Ka radiation and
graphite monochromator, operating with the voltage
of 30 kV and emission current of 20 mA. The step-
scan covered the angular range 2–60 (2h) in steps of
2h = 0.02. The computer program X-ﬁt was used
for calculation of crystallite size and for diffraction
proﬁle reﬁnement under the pseudoVoid function and
for a description of the diffractional background
under the third degree of Tchebyshev polynom, we
have used fundamental parameters peak proﬁling (a
computer program X-ﬁt) [6].
The surface area, total pore volume and pore size
distribution of the synthesis products were performed
by a BET surface area analyzer ‘KELVIN 1042
Sorptometer’ (Costech Instruments).
2.3 Methodology
2.3.1 Speciﬁc surface area from the BET equation
The speciﬁc surface area of gyrolite was calculated
by the BET equation using the data of the lower part
of N
2
0
\ 0.35):
1
X
p
0
p
1

¼
C 1
X
m
C
p
p
0
þ
1
X
m
C
;
ð1Þ
sample at relative pressure p/p
0
, p the partial pressure
0
the saturated vapor pressure of
m
coverage of one monolayer, C is a constant which is a
function of the heat of the adsorbate condensation
BET
is a constant).
BET equation yields a straight line when 1/X[(p
0
/
p) - 1] is plotted versus p/p
0
. The slope of (C - 1)/
X
m
C and the intercept of 1/X
m
C was used to
determine X
m
and C: S = slope = (C - 1)/X
m
C and
I = intercept = 1/X
m
C. Solving for X
m
yields
X
m
= 1/(S ? I). BET plot is usually found to be
linear in the range p/p
0
= 0.05–0.35. The total surface
area of the sample S
t
was determined by the equation
S
t
= X
m
NA
cs
/M, where M is the molecular mass of the
cs
the cross-
sectional area occupied by each nitrogen molecule
(16.2 9 10
-20
m
2
). The speciﬁc surface area was
given by the equation S
BET
= S
t
/m, where m is the
mass of gyrolite sample.
2.3.2 Classiﬁcation of hysteresis loops
It is widely accepted that there is a correlation
between the shape of the hysteresis loop and the
texture (e.g., pore size distribution, pore geometry,
connectivity) of a mesoporous materials. An empir-
ical classiﬁcation of hysteresis loops was given by the
IUPAC [14], which is based on an earlier classiﬁca-
tion by de Boer. The IUPAC classiﬁcation is shown
in Fig. 1. According to the IUPAC classiﬁcation type
H1 is often associated with porous materials consist-
ing of well-deﬁned cylindrical-like pore agglomerates
of compacts of approximately uniform spheres. It was
found that give rise to H2 hysteresis are often
disordered and the distribution of pore size and shape
is not well deﬁned. Isotherms revealing type H3
Materials and Structures (2011) 44:1687–1701 1689
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hysteresis do not exhibit any limiting adsorption at
high p/p
0
, which is observed with non-rigid aggre-
gates of plate-like particles giving rise to slit-shaped
pores. The desorption branch for type H3 hysteresis
contains also a steep region associated with a forced
closure of the hysteresis loop, due to the so-called
tensile strength effect. Similarly, type H4 loops are
also often associated with narrow slit pores.
2.3.3 Pore volumes and size distributions
Vapors in equilibrium with liquid contained in ﬁne
capillaries or pores will have depressed vapor pressures.
In fact, if the pore is adequately small in diameter, the
vapor will condense at pressures far below normal. As
indicated by the Kelvin equation, nitrogen gas will
condense into all pores with radius less than 150 nm at a
relative pressure of 0.99. By measuring the volume of
nitrogen adsorbed at a relative pressure of 0.99 and with
prior knowledge of the surface area, the average pore
The total pore volume and pore size distribution
were calculated according to the corrected Kelvin
equation and Orr et al. scheme using entire N
2
desorption isotherm at 77 K [14]. The Kelvin equa-
tion relates the adsorbate vapor pressure depression to
the radius of a capillary which has been ﬁlled with
ln
p
p
0
¼2
cV
m
cosh
RTr
k
; ð2Þ
where p is the saturated vapor pressure in equilibrium
with the adsorbate condensed in a capillary or pore,
p
0
the normal adsorbate saturated vapor pressure, c
the surface tension of nitrogen at its boiling point
(c = 8.85 ergs/cm
2
at (-195.8C)) the molar volume
of liquid nitrogen (V
m
= 34.7 cm
3
), h the wetting
angle (usually taken 0 and cosh = 1), R the gas
constant (R = 8.134 9 10
7
ergs deg
-1
mol
-1
), T the
absolute temperature (T = 77 K) and r
K
the Kelvin
Kelvin equation can be rearranged:
r
k
¼
4:146
lg
p
0
p
: ð3Þ
K
is not the actual pore radius
because some adsorption takes place on the wall of
the pore prior to the occurrence of condensation in
the pore. During desorption an adsorbed layer
remains on the wall when evaporation takes place.
Therefore, the true pore radius r
p
was calculated by
the equation r
p
= r
K
? t.
Theoretically t value is, by assuming that for
any value of relative pressure the thickness of
the adsorbed ﬁlm on pore walls is the same as the
thickness of the adsorbed layer on a plane surface, the
thickness of the adsorbed layer is given by equation:
t ¼
V
a
V
m
s; ð4Þ
where t is the thickness of the adsorbed layer on the
pore wall (mm), V
a
is the volume of adsorbed gas
(mm
3
thickness of a monomolecular layer of adsorbent
(mm). t was calculated according to the Halsey
equation [14], which for nitrogen can be written as:
t ¼ 3:54
5
2:303 lg
p
0
p
"#
1
=
3
: ð5Þ
The values of 5 and 3.54 in equation are empirical,
where 3.54 is the thickness of one adsorbed nitrogen
layer. This value of 3.54 A
˚
is somewhat less that the
diameter of a nitrogen molecule based on the cross-
sectional area of 16.2 A
˚
2
.
If the pores are assumed to be cylindrical and if the
relative pressure is changed from (p/p
0
)
2
to (p/p
0
)
1
,
2
and r
1
will empty (p
2
\ p
1
,
Fig. 1 IUPAC classiﬁcations of hysteresis loops
1690 Materials and Structures (2011) 44:1687–1701
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r
2
\ r
1
). When p
2
is lowered to p
1
the thickness of the
adsorbed ﬁlm on previously emptied pores changes
from t
2
to t
1
. The volume of liquid (V
L
) evaporated due
to emptying of pores and the decrease in thickness of
adsorbed layers in previously empty pores was calcu-
lated by the following equation:
V
L
¼ p r
p
t
2

2
L þ t
2
t
1
ðÞ
X
A; ð6Þ
where
r
p
is the average pore radius in the interval r
2
to r
1
, L the total length of all pores in the range r
2
to
r
1
, A the area of adsorbed ﬁlm remaining in the pores
after evaporation out of the pores has occurred. The
mean volume of pores with
r
p
is V
p
¼ pr
2
p
L:
Then
V
p
¼
r
p
r
p
t
2

2
V
L
r
p
r
p
t
2

2
t
2
t
1
ðÞ
X
A:
ð7Þ
Cylindrical using r
p
= r
K
? t:
V
p
¼
r
p
r
K

2
V
L
Dt
X
A

: ð8Þ
The volume of liquid desorbed in any interval of
desorption isotherm is related to the volume of gas by
the equation: DV
L
(cm
3
) = DV
gas
(1.54 9 10
-3
). For
cylinders A was given by
A
c
m
2

¼
2DV
p
r
p
10
4
; ð9Þ
with V
p
in cm
3
and r
p
in A
˚
.
For the calculations of pores between parallel
plates we used the following equation: d
p
= r
k
? 2t;
r
k
= l, where l is a distance between plates:
d
p
¼ r
K
þ 2t; ð10Þ
d
p
—distance between two plates, A
˚
.
V
p
¼
d
p
r
K
DV
L
2Dt
X
A

; ð11Þ
A
p
m
2

¼
2V
p
d
p
: ð12Þ
The analysis of desorption isotherms was ﬁnished
when (DtRA) exceeded DV
L
, because the desorbed
gas is coming from an adsorbed layer rather than
from evaporation of the liquid out of the pore center.
RA is the cummulative surface area and is obtained
by summing A in each radius interval.
3 Results and discussion
It was determined that a stable monolayer of
absorbed N
2
was formed on the surface of gyrolite.
The BET equation gives a linear plot in the range
of relative pressures 0.05 B p/p
0
B 0.30 (Figs. 1, 2).
Straight lines were obtained for all gyrolite samples
in BET coordination 1= Xp
0
=pðÞ1½ðÞðÞp
0
=pðÞ:
A straight line correlation coefﬁcient R
2
of synthe-
sized after 32 h hydrothermal treatment gyrolite was
equal to 0.9986 (Fig. 2a), the same as after 48 h
(Fig. 2b).
A straight lines correlation coefﬁcients R
2
remains
very close to the unit, i.e. 0.9991, when hydrothermal
synthesis was prolonged up to 168 h (Fig. 3).
It was noted that duration of hydrothermal syn-
thesis has inﬂuence on both gyrolite structure and
speciﬁc surface area (Table 1). It was determined that
S
BET
was equal to 82.07 m
2
/g after 32 h of isothermal
curing of gyrolite. Prolonging the hydrothermal
synthesis duration to 48 h, S
BET
of the product also
increased to 91.52 m
2
/g. It should be noted that S
BET
characteristic for gyrolite decreased more than two
times to 43.54 m
2
/g already after 72 h of synthesis.
Besides, this tendency was observed also after 120 h
because S
BET
was equal to 38.28 m
2
/g. Meanwhile,
after 168 h of isothermal curing S
BET
value of
gyrolite slightly increased (46.00 m
2
/g). It is likely
that one of the reasons was gyrolite crystal structure,
where water content can varies from 12 to 20%
weight [2, 26, 31]. Also, depending on the synthesis
conditions crystallite size of this compound varies
from 1,066 to 2,156 A
˚
(Fig. 4).
Calculated C
BET
constant values showed the
structural changes of gyrolite during hydrothermal
synthesis. Certainly, C
BET
values varied in the range
from 50 to 250 when experimental conditions were
ideal, while lower constant values meant that adsor-
bate was condensed into pores and calculated S
BET
should be higher than the real one. In contrarily,
when C
BET
[ 250 chemical reaction between adsor-
bent surface and adsorbate might occur without
formation of adsorbate monolayer. Obtained results
conﬁrmed Merlino [16] suggested gyrolite lattice
structure which is consisted of octahedral Ca–O
layers, interlayers (Ca
2?
and H
2
O) and silicate
layers.
Based on the ‘OD’ theory, Merlino determined
that gyrolite is consisted of different layers (Fig. 5):
Materials and Structures (2011) 44:1687–1701 1691
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A centrosymmetric layer S
1
, which composition is
(Si
8
O
20
)
8-
, consists of two types of six-mem-
bered rings;
Double tetrahedra layer S
2
, which composition is
(Si
14
Al
2
O
38
)
14-
. There are the other two types of
six-membered rings in the layer;
Octahedral layer (O), which composition is
[Ca
7
O
10
(OH)
4
]
4-
, consists calcium octahedra
combined by the edge;
X interlayers which are consisted of H
2
O and
O
2-
, coordinated Ca and Na octahedra (coordi-
nate bond).
It was proved that structural elements of gyrolite
lattice after 32 and 48 h of synthesis were combined
with undeﬁned composition (Ca
2?
,H
2
O) of X inter-
layer. Due to this it isn’t coincidentally that C
BET
constant values are equal to 827.08 and 1678.06
y = 1635.3x - 1.9796
R
2
= 0.9986
0
100
200
300
400
500
0.00 0.06 0.12 0.18 0.24 0.30
tg
α
1
p
p
X
1
0
0
p
p
y = 1188.7x - 0.7088
R
2
= 0.9986
0
100
200
300
400
0.00 0.06 0.12 0.18 0.24 0.30
tg
α
1
p
p
X
1
0
0
p
p
b
a
Fig. 2 The isotherm of N
2
77 K in BET plot. Duration
of hydrothermal synthesis at
200C temperature, h: a 32,
b 48
y = 1789.2x + 11.426
R
2
= 0.9994
0
100
200
300
400
500
600
0.00 0.06 0.12 0.18 0.24 0.30
tg
α
1
p
p
X
1
0
0
p
p
y = 1867.3x + 4.9717
R
2
= 0.9992
0
100
200
300
400
500
600
0.00 0.06 0.12 0.18 0.24 0.30
tg
α
1
p
p
X
1
0
0
p
p
y = 2095.7x + 7.4048
R
2
= 0.9991
0
100
200
300
400
500
600
700
0.00 0.06 0.12 0.18 0.24 0.30
tg
α
1
p
p
X
1
0
0
p
p
a
b
c
Fig. 3 The isotherm of N
2
77 K in BET plot. Duration
of hydrothermal synthesis at
200C temperature, h: a 72,
b 120, and c 168
1692 Materials and Structures (2011) 44:1687–1701
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(Table 1). Meanwhile C
BET
constant values of the
product after 72, 120 and 168 h synthesis decreased
4–5 times. This allows to state that after sufﬁciently
long synthesis duration the structural elements of
gyrolite lattice were connected to more orderly
structure of the interlayer X. This assumption is
600
1000
1400
1800
2200
24 48 72 96 120 144 168
Duration of synthesis, h
Crystallite size, Å
Fig. 4 Dependence of gyrolite crystallite size on duration of
hydrothermal synthesis
Octahedral Ca-O layers
Interlayers (Ca
2+
and H
2
O)
Sicate layers
Fig. 5 The crystal lattice structure of gyrolite (by Merlino
[16])
23456
2
θ
, deg.
1
2
3
4
5
Intensity, a. u.
Fig. 6 X-ray diffraction curves of gyrolite. Duration of
hydrothermal synthesis at 200C temperature, h: 1 32, 2 48,
3 72, 4 120, and 5 168
Table 1 Calculated parameters of gyrolite speciﬁc surface area (S
BET
)
Duration of
synthesis (h)
Sample
mass, m (g)
BET equation constants Capacity of monolayer
X
m
¼
1
SþI
gðÞ
S
BET
(m
2
/g)
C
BET
¼
1
IX
m
Reliability
coefﬁcient R
2
Slope S = tga Intercept I
123 45 678
32 0.0262 1635.30 1.9796 0.000611 82.07 827.08 0.9986
48 0.0323 1188.70 0.7088 0.000841 91.52 1678.06 0.9986
72 0.0448 1789.20 11.4260 0.000555 43.54 157.59 0.9994
120 0.0490 1867.30 4.9717 0.000534 38.28 376.59 0.9992
168 0.0363 2095.70 7.4048 0.000475 46.00 284.02 0.9991
Materials and Structures (2011) 44:1687–1701 1693
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conﬁrmed by XRD analysis: prolonging the isother-
mal curing duration the basic diffraction maximum
intensity and area increases (Fig. 6).
The results showed that all samples were charac-
terized by gyrolite hysteresis phenomenon: adsorp-
tion and desorption isotherms do not coincide,
desorption isotherm was more in the left than
adsorption isotherm (Figs. 7, 8). It is characteristic
to mesoporous solids when the radius of pores was in
a range from 15 to 500 A
˚
. Besides, it has a clear bend
in a lower p/p
0
area (point A). Microporous sorbents
do not have point A in the interval 0.05 B p/
p
0
B 0.30. Thus, it should be stated that during all
experimental conditions formed gyrolite is mesopor-
ous compound (Figs. 7, 8).
the basis of nature of N
2
isotherm (hysteresis) and taking into account the
abundant information on the structure of the gyrolite.
Right side of the hysteresis loop would correspond to
the isotherms that are obtained in the case of materials
with pores formed between parallel crystal planes.
However, the isotherms of adsorption and desorption
must coincide in the range of relative pressures
p/p
0
& 0.30, moreover the curve of desorption iso-
therm falls very steeply (Fig. 7). This indicates that in
the product structure was dominated by disordered, the
plate form pores. Meanwhile, prolonging synthesis
duration to 1 week, the isotherms were much narrower
and overlap in a slightly higher pressure p/p
0
. The
relative pressure p/p
0
& 0.70, which seems to be more
typical to the cylindrical slits (Fig. 8). It allows to state
that during the isothermal curing changes both the
structure of synthesized products and the form of pores,
i.e. cylindrical pores started to dominate.
Before calculation of distribution of pores to diam-
eters it is necessary to identify the common model of a
dominating form of pores. These models are selected
according to the form of hysteresis loop (Figs. 1, 7,and
8). Theoretically, S
BET
value is equal to the value of
RA when the form of pore is uniform. Meanwhile,
during hydrothermal synthesis the particles of various
diameters are formed in the products. For this reason, in
polydisperse systems are determined only dominant
pores. The most suitable modelof pore distribution is the
one whose experimentally deﬁned S
BET
value is the
closest to the value of the calculated speciﬁc surface
RA. Later on, according to model of dominate pores is
calculated the dominant pore volume, size and their
differential distribution according to the radius.
Therefore, the distribution of pores to the diameters
was calculated according to two models (cylinder
pores and pores between parallel plates) (Tables 2, 3).
The obtained results showed that none of the selected
models suits for a description of the pores of the
product which was synthesized after 32 h of isother-
mal curing. These data show that the structure of pores
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0
p/p
o
V
, cm
3
/g
A
0
40
80
120
160
200
240
280
320
0.0 0.2 0.4 0.6 0.8 1.0
p/p
o
V
, cm
3
/g
A
a
b
Fig. 7 The isotherm of N
2
gyrolite at 77 K. Duration
of hydrothermal synthesis at
200C temperature, h: a 32,
b 48
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is not well formed. For this reason, we performed
calculations of products after 48–168 h of synthesis.
It was determined that the pores of gyrolite after 48 h
of synthesis were formed between parallel planes,
because S
BET
= 91.52 m
2
/g and RA = 99.33 m
2
/g.
Meanwhile, by using a cylindrical model the error
between S
BET
and RA exceeds higher value (S
BET
=
91.52 m
2
/g and RA = 150.72 m
2
/g) (Table 2). Pro-
longing the synthesis duration (168 h) pores shape
was better described by a cylindrical model, because
calculated RA values was closer (Table 3). This
phenomenon was conﬁrmed also by the shape of
isotherm which narrowed (Fig. 8).
It was determined that the pore volume of the
gyrolite samples with characteristic orderly crystal
structure decreased from 110 to 80 mm
3
/g (Fig. 9).
Also, the obtained results showed that the stable
gyrolite crystal lattice was formed only after 120 h of
isothermal curing because cumulative pore volume is
not inﬂuenced by synthesis conditions.
0
10
20
30
40
50
60
70
80
p/p
o
V
, cm
3
/g
A
0
10
20
30
40
50
0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0
0.0 0.2 0.4 0.6 0.8 1.0
p/p
o
V, cm
3
/g
A
0
10
20
30
40
50
60
p/p
o
V
, cm
3
/g
A
a
b
c
Fig. 8 The isotherm of N
2
gyrolite at 77 K. Duration
of hydrothermal synthesis at
200C temperature, h: a 72,
b 120, and c 168
Materials and Structures (2011) 44:1687–1701 1695
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Table 2 The data of RA calculations and pore size distribution of gyrolite (48 h)
No. Relative
pressure,
p/p
0
N
2
volume
the V
(ncm
3
/g)
Kelvin
the pores,
r
K
(A
˚
)
Thickness
of N
2
layer, t (A
˚
)
True
pore
(A
˚
)
Average
Kelvin
pores, r
K
(A
˚
)
Average
true pore
p
(A
˚
)
Change,
Dt (A
˚
)
Change,
DV
(ncm
3
/g)
Change of
evaporated liquid
DV
L
(910
3
cm
3
/g)
DtRA
(910
3
cm
3
/g)
True
volume of
the pores,
V
p
(910
3
cm
3
/g)
Surface
of pore
walls,
A
(m
2
/g)
Total
surface,
RA
(m
2
/g)
Calculations using between parallel plates pores model
1 0.91 226.96 98.25 13.17 124.58 76.88 100.93 2.28 80.04 123.26 0.00 161.81 32.06 0.17
2 0.84 146.92 55.51 10.88 77.28 50.67 71.77 0.67 23.29 35.86 0.01 50.76 14.15 14.32
3 0.81 123.64 45.83 10.21 66.26 42.33 62.21 0.55 17.12 26.36 0.79 36.43 11.71 26.03
4 0.78 106.52 38.84 9.66 58.18 36.21 55.08 0.46 11.31 17.42 1.19 22.87 8.31 34.33
5 0.75 95.21 33.58 9.21 51.99 30.32 48.09 0.64 15.42 23.75 2.19 30.70 12.77 47.10
6 0.70 79.79 27.06 8.57 44.19 24.73 41.34 0.52 12.27 18.90 2.46 23.36 11.30 58.40
7 0.65 67.51 22.40 8.04 38.49 20.64 36.28 0.44 8.11 12.49 2.60 12.82 7.06 65.47
8 0.60 59.41 18.89 7.60 34.08 17.51 32.32 0.39 7.11 10.95 2.54 10.85 6.71 72.18
9 0.55 52.29 16.14 7.21 30.56 15.02 29.09 0.35 5.60 8.63 2.53 6.92 4.76 76.94
10 0.50 46.69 13.90 6.86 27.62 12.98 26.39 0.32 11.86 18.27 2.43 27.25 20.65 97.59
11 0.45 34.83 12.07 6.54 25.16 11.75 24.72 0.12 2.17 3.34 1.16 2.15 1.74 99.33
12 0.43 32.66 11.42 6.43 24.27 10.97 23.64 0.18 0.82 1.27 1.75
13 0.40 31.84 10.51 6.25 23.01
Calculations using cylindrical pore model
1 0.91 226.96 98.25 13.17 111.42 76.88 88.91 2.28 80.04 123.26 0.00 164.83 37.08 0.17
2 0.84 146.92 55.51 10.88 66.40 50.67 61.22 0.67 23.29 35.86 0.01 52.33 17.10 17.27
3 0.81 123.64 45.83 10.21 56.04 42.33 52.27 0.55 17.12 26.36 0.95 38.74 14.82 32.09
4 0.78 106.52 38.84 9.66 48.50 36.21 45.64 0.46 11.31 17.42 1.47 25.35 11.11 43.20
5 0.75 95.21 33.58 9.21 42.79 30.32 39.21 0.64 15.42 23.75 2.76 35.09 17.90 61.09
6 0.70 79.79 27.06 8.57 35.63 24.73 33.03 0.52 12.27 18.90 3.20 28.03 16.97 78.06
7 0.65 67.51 22.40 8.04 30.44 20.64 28.46 0.44 8.11 12.49 3.47 17.14 12.04 90.11
8 0.60 59.41 18.89 7.60 26.48 17.51 24.92 0.39 7.11 10.95 3.49 15.11 12.12 102.23
9 0.55 52.29 16.14 7.21 23.35 15.02 22.06 0.35 5.60 8.63 3.58 10.88 9.87 112.10
10 0.50 46.69 13.90 6.86 20.76 12.98 19.69 0.32 11.86 18.27 3.54 33.86 34.40 146.49
11 0.45 34.83 12.07 6.54 18.61 11.75 18.23 0.12 2.17 3.34 1.74 3.86 4.23 150.72
12 0.43 32.66 11.42 6.43 17.85 10.97 17.30 0.18 0.82 1.27 2.65
13 0.40 31.84 10.51 6.25 16.76
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Table 3 The data of RA calculations and pore size distribution of gyrolite (168 h)
No. Relative
pressure,
p/p
0
N
2
volume
the V
(ncm
3
/g)
Kelvin
the pores,
r
K
(A
˚
)
Thickness
of N
2
layer, t (A
˚
)
True
pore
(A
˚
)
Average
of the pores,
r
K
(A
˚
)
Average
true pore
p
(A
˚
)
Change,
Dt (A
˚
)
Change,
DV
(ncm
3
/g)
Change of
evaporated
liquid
volume, DV
L
(910
3
cm
3
/g)
DtRA
(910
3
cm
3
/g)
True volume
of the pores,
V
p
(910
3
cm
3
/g)
Surface of
pore
walls,
A (m
2
/g)
Total
surface,
RA
(m
2
/g)
Calculations using between parallel plates pores model
1 0.93 55.49 134.53 14.62 163.77 113.60 141.14 1.71 10.01 15.42 0.00 19.16 2.71 0.17
2 0.90 45.48 92.68 12.91 118.51 81.25 105.91 1.16 6.06 9.34 0.02 12.12 2.29 2.46
3 0.87 39.42 69.81 11.75 93.31 62.71 85.35 0.86 4.38 6.75 0.21 8.61 2.02 4.48
4 0.84 35.04 55.61 10.89 77.40 50.80 71.91 0.67 3.28 5.05 0.30 6.30 1.75 6.23
5 0.81 31.76 45.99 10.22 66.43 42.45 62.34 0.55 2.63 4.05 0.34 4.94 1.59 7.81
6 0.78 29.13 38.91 9.67 58.25 36.27 55.15 0.46 2.25 3.46 0.36 4.17 1.51 9.33
7 0.75 26.88 33.64 9.21 52.06 30.38 48.16 0.64 2.53 3.90 0.60 4.29 1.78 11.11
8 0.70 24.35 27.12 8.57 44.26 24.77 41.39 0.53 1.77 2.73 0.58 2.61 1.26 13.37
9 0.65 22.58 22.42 8.05 38.52 21.66 37.56 0.19 0.60 0.92 0.23 0.79 0.42 12.79
10 0.63 21.98 20.90 7.86 36.61 19.90 35.36 0.26 0.86 1.32 0.33 1.18 0.67 13.46
11 0.60 21.12 18.91 7.60 34.11 17.53 32.35 0.39 0.49 0.76 0.52
12 0.55 20.63 16.16 7.21 30.59
Calculations using cylindrical pore model
1 0.93 55.49 134.53 14.62 149.15 113.60 127.37 1.71 10.01 15.42 0.00 19.38 3.04 0.17
2 0.90 45.48 92.68 12.91 105.60 81.25 93.58 1.16 6.06 9.34 0.02 12.36 2.64 2.81
3 0.87 39.42 69.81 11.75 81.56 62.71 74.03 0.86 4.38 6.75 0.24 9.07 2.45 5.26
4 0.84 35.04 55.61 10.89 66.51 50.80 61.36 0.67 3.28 5.05 0.35 6.85 2.23 7.49
5 0.81 31.76 45.99 10.22 56.21 42.45 52.39 0.55 2.63 4.05 0.42 5.54 2.12 9.61
6 0.78 29.13 38.91 9.67 48.58 36.27 45.71 0.46 2.25 3.46 0.44 4.80 2.10 11.71
7 0.75 26.88 33.64 9.21 42.85 30.38 39.27 0.64 2.53 3.90 0.75 5.26 2.68 14.39
8 0.70 24.35 27.12 8.57 35.69 24.77 33.08 0.53 1.77 2.73 0.76 3.52 2.13 16.52
9 0.65 22.58 22.42 8.05 30.47 21.66 29.61 0.19 0.60 0.92 0.31 1.14 0.77 17.28
10 0.63 21.98 20.90 7.86 28.75 19.90 27.63 0.26 0.86 1.32 0.45 1.69 1.23 18.51
11 0.60 21.12 18.91 7.60 26.51 17.53 24.94 0.39 0.49 0.76 0.72 0.09 0.07 18.58
12 0.55 20.63 16.16 7.21 23.38 15.05 22.09 0.35 2.41 3.72 0.65 6.62 5.99 24.57
13 0.50 18.21 13.94 6.87 20.80 13.01 19.72 0.32 1.19 1.83 0.78 2.40 2.43 27.01
14 0.45 17.03 12.08 6.55 18.63 11.31 17.71 0.29 1.24 1.91 0.79 2.73 3.09 30.10
Materials and Structures (2011) 44:1687–1701 1697
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It was determined that the pores with 2.0–3.0 nm
radius were dominated in the gyrolite structure after
72 h of synthesis (Fig. 10). Meanwhile, the pores
with 3.0–4.0 nm and even bigger radius started to
form after 120 h of hydrothermal treatment. This
tendency of pores growth remains by continuing
isothermal curing (up to 168 h), because the pores
with 3.0–5.0 nm radius is dominated in the pore
distribution by radius curve (Fig. 10c).
In the next stage of experiment there was done
Zn
2?
ion adsorption by using gyrolite samples with
characteristic different structural properties (speciﬁc
surface area, crystal size, pore shapes, etc.).
tion more than half zinc ions were intercalated to
gyrolite structure, i.e. *71% (21.36 mg Zn
2?
/g),
when the initial solution concentration was 0.3 g/dm
3
(Fig. 11a). It should be noted that ion exchange
reaction ended after 15 min when adsorbent was
substituted by *99% (28.63 mg Zn
2?
/g) of zinc ions.
Meanwhile, the rapidity of these ions intercalation to
orderly structure of gyrolite was much slower (synthe-
sis duration—168 h) because only *55% (16.67 mg
Zn
2?
/g) of zinc ions were intercalated after 30 s
of reaction. Besides, the equilibrium was reached
after 5 min of adsorption—91% (27.25 mg Zn
2?
/g),
because the concentration of zinc ions remains almost
the same continuing the reaction (Fig. 11a).
Thus, the ion exchange between gyrolite with less
orderly structure and Zn(NO
3
)
2
? NH
4
OH alkaline
solution (c
Zn
2þ
—0.3 g/dm
3
) proceeds more faster and
effectively.
The exchange reaction mechanism (Ca
2?
\$ Zn
2?
)
in gyrolite may take place from edge and planar
surface sites as well as from interlayer Ca
2?
sites
(Fig. 5).
10
30
50
70
90
110
130
100101
Pore diameter, D
p
[nm]
Cumulative pore volume, V
p
[mm
3
/g]
1
3
2
Fig. 9 Gyrolite total pore volume. Duration of hydrothermal
synthesis at 200C temperature, h: 1 72, 2 120, and 3 168
Table 3 continued
No. Relative
pressure,
p/p
0
N
2
volume
the V
(ncm
3
/g)
Kelvin
the pores,
r
K
(A
˚
)
Thickness
of N
2
layer, t (A
˚
)
True
pore
(A
˚
)
Average
of the pores,
r
K
(A
˚
)
Average
true pore
p
(A
˚
)
Change,
Dt (A
˚
)
Change,
DV
(ncm
3
/g)
Change of
evaporated
liquid
volume, DV
L
(910
3
cm
3
/g)
DtRA
(910
3
cm
3
/g)
True volume
of the pores,
V
p
(910
3
cm
3
/g)
Surface of
pore
walls,
A (m
2
/g)
Total
surface,
RA
(m
2
/g)
15 0.40 15.79 10.53 6.25 16.78 9.27 15.25 0.55 1.29 1.98 1.64 0.92 1.20 31.30
16 0.30 15.50 8.01 5.71 13.72 7.48 13.06 0.26 0.52 0.80 0.82
17 0.25 13.99 6.95 5.45 12.40
1698 Materials and Structures (2011) 44:1687–1701
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The results presented here show that the gyrolite
cation exchangers are interesting family of exchang-
ers and further research is needed to understand better
their exchange and selectivity properties.
4 Conclusions
It was determined that the structure of gyrolite and the
shape of dominated pores (from pores between parallel
plates to cylindrical pores) changes prolonging the
duration of hydrothermal synthesis. It should be
underlined that the stable gyrolite crystal structure
was formed only after 120 h of isothermal curing. Its
speciﬁc surface area S
BET
= 38.28 m
2
dominant plate pores r
p
= 30–40 A
˚
, the calculated
total pore volume RV
p
= 0.08 cm
3
/g. Calculated C
BET
constant values conﬁrmed the structural changes of
gyrolite during hydrothermal synthesis. After sufﬁ-
ciently long synthesis duration the structural elements
of gyrolite structure were connected to more orderly
structure of the interlayer X. This phenomenon is
0.0
5.0
10.0
15.0
20.0
25.0
Pore diameter, D
p
[nm]
First derivative, dV
p
/dD
p
[mm
3
/
g*nm]
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
Pore diameter, D
p
[nm]
First derivative, dV
p
/dD
p
[mm
3
/g*nm]
0.0
2.0
4.0
6.0
8.0
10.0
12.0
110100
110100
110100
Pore diameter, D
p
[nm]
First derivative, dV
p
/dD
p
[mm
3
/
g*nm]
a
b
c
Fig. 10 Gyrolite
differential pore volume
plot when duration of
hydrothermal synthesis at
200C temperature, h: a 72,
b 120, and c 168
27.5
28
28.5
29
29.5
30
τ
, min
1
4
3
5
2
Σ
X, mg/g
R
2
= 0.9716
27.5
28
28.5
29
29.5
30
0 7.5 15 22.5 30 37.5 45
32 52 72 92 112 132 152
τ
, h
Σ
X, mg/g
ab
Fig. 11 Integral kinetic curves (a) and total amount (b)ofZn
2?
3
)
2
solution when the initial
concentration of Zn
2?
ions is 0.3 g/dm
3
at 25C. Duration of hydrotermal synthesis, h: 1 32, 2 48, 3 72, 4 120, and 5 168
Materials and Structures (2011) 44:1687–1701 1699
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conﬁrmed by X-ray diffraction analysis too: prolong-
ing the duration of isothermal curing crystallite size of
this compound varies from 1,066 to 2,156 A
˚
. It was
estimated that the ion exchange between gyrolite with
less orderly structure in Zn(NO
3
)
2
? NH
4
OH alkaline
solution (c
Zn
2þ
—0.3 g/dm
3
) proceeds more faster and
more than half zinc ions were intercalated to gyrolite
structure, i.e. *71% (21.36 mg Zn
2?
/g).
Acknowledgments This work was supported by the partners
of Action COST MP0701 ‘Composites with novel functional
and structural properties by nanoscale materials’ and ﬁnancially
by the Agency for International Science and Technology
Development Programmes in Lithuania.
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... where ΔVp is volume of gas emitted, cm 3 . Parallel plate type pairs are calculated using the following Equations (9)-(11) [37]: ...
... Additionally, the sharp increase of isotherms at p/p0 ~0.05 shows that some micropores can be presented in the structure of the synthesis products compounds. It is worth mentioning that the same tendency can be observed in most calcium silicate hydrates [37]. ...
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We have investigated the incorporation of zinc into both nanocrystalline and crystalline calcium silicate hydrates with starting C/S ratios of 2/3 (0.66). Zinc was added replacing calcium in the starting mixtures [Zn/(Zn+Ca)=0–1/4; 0–10 wt.% Zn], and the resultant phases were characterised using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), differential thermal analysis–thermogravimetry (DTA–TG) and environmental scanning electron microscopy (ESEM).In both groups of samples, increasing zinc content led to gradual structural changes, until eventually a second phase was formed. Zinc was incorporated to similar limits in both sets of samples. The thermal stability of the structures increased to a certain zinc content, beyond which there was structural destabilisation. Zinc incorporation is possible up to ∼6 wt.%. Our observations strongly indicate similar zinc incorporation mechanisms in both sample series, namely incorporation of zinc into the interlayer of C-S-H(I) and the X-sheet of gyrolite for nanocrystalline and crystalline samples, respectively.
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