Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides as proxies for the Antarctic atmospheric mineral aerosols
The aim of the study is to determine the effects of structure and content of X, CX in the oxides X/SiO₂ (X = Al₂O₃, TiO₂, Al₂O₃/TiO₂) on the surface characteristics. The low-temperature nitrogen adsorption isotherms on the surface of 12 individual and mixed fumed oxides of Si, Ti and Al, as proxies...
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| Zitieren: | Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides as proxies for the Antarctic atmospheric mineral aerosols / M.S. Bazylevska, V.I. Bogillo // Український антарктичний журнал. — 2019. — № 1 (18). — С. 3-17. — Бібліогр.: 40 назв. — англ. |
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irk-123456789-1682922020-04-30T01:26:29Z Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides as proxies for the Antarctic atmospheric mineral aerosols Bazylevska, M.S. Bogillo, V.I. Геолого-геофізичні дослідження The aim of the study is to determine the effects of structure and content of X, CX in the oxides X/SiO₂ (X = Al₂O₃, TiO₂, Al₂O₃/TiO₂) on the surface characteristics. The low-temperature nitrogen adsorption isotherms on the surface of 12 individual and mixed fumed oxides of Si, Ti and Al, as proxies for the Antarctic atmospheric mineral aerosols, were measured by volumetric method. Метою роботи було визначення впливу природи та вмісту X, CX в оксидах X/SiO₂ (X = Al₂O₃, TiO₂, Al₂O₃/ TiO₂) на характеристики їх поверхні. Методом волюметрії виміряні низькотемпературні ізотерми адсорбції азоту на поверхні 12 індивідуальних і змішаних пірогених оксидів Si, Ti та Al, як компонентів мінеральних аерозолів в атмосфері Антарктики. 2019 Article Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides as proxies for the Antarctic atmospheric mineral aerosols / M.S. Bazylevska, V.I. Bogillo // Український антарктичний журнал. — 2019. — № 1 (18). — С. 3-17. — Бібліогр.: 40 назв. — англ. 1727-7485 http://dspace.nbuv.gov.ua/handle/123456789/168292 504.3.054: 544.723.23: 544.772: 547-302 en Український антарктичний журнал Національний антарктичний науковий центр МОН України |
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Геолого-геофізичні дослідження Геолого-геофізичні дослідження |
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Геолого-геофізичні дослідження Геолого-геофізичні дослідження Bazylevska, M.S. Bogillo, V.I. Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides as proxies for the Antarctic atmospheric mineral aerosols Український антарктичний журнал |
| description |
The aim of the study is to determine the effects of structure and content of X, CX in the oxides X/SiO₂ (X = Al₂O₃, TiO₂, Al₂O₃/TiO₂) on the surface characteristics. The low-temperature nitrogen adsorption isotherms on the surface of 12 individual and mixed fumed oxides of Si, Ti and Al, as proxies for the Antarctic atmospheric mineral aerosols, were measured by volumetric method. |
| format |
Article |
| author |
Bazylevska, M.S. Bogillo, V.I. |
| author_facet |
Bazylevska, M.S. Bogillo, V.I. |
| author_sort |
Bazylevska, M.S. |
| title |
Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides as proxies for the Antarctic atmospheric mineral aerosols |
| title_short |
Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides as proxies for the Antarctic atmospheric mineral aerosols |
| title_full |
Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides as proxies for the Antarctic atmospheric mineral aerosols |
| title_fullStr |
Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides as proxies for the Antarctic atmospheric mineral aerosols |
| title_full_unstemmed |
Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides as proxies for the Antarctic atmospheric mineral aerosols |
| title_sort |
adsorption properties of the fumed individual and mixed si, ti and al oxides as proxies for the antarctic atmospheric mineral aerosols |
| publisher |
Національний антарктичний науковий центр МОН України |
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2019 |
| topic_facet |
Геолого-геофізичні дослідження |
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http://dspace.nbuv.gov.ua/handle/123456789/168292 |
| citation_txt |
Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides as proxies for the Antarctic atmospheric mineral aerosols / M.S. Bazylevska, V.I. Bogillo // Український антарктичний журнал. — 2019. — № 1 (18). — С. 3-17. — Бібліогр.: 40 назв. — англ. |
| series |
Український антарктичний журнал |
| work_keys_str_mv |
AT bazylevskams adsorptionpropertiesofthefumedindividualandmixedsitiandaloxidesasproxiesfortheantarcticatmosphericmineralaerosols AT bogillovi adsorptionpropertiesofthefumedindividualandmixedsitiandaloxidesasproxiesfortheantarcticatmosphericmineralaerosols |
| first_indexed |
2025-07-15T03:05:08Z |
| last_indexed |
2025-07-15T03:05:08Z |
| _version_ |
1837680515620012032 |
| fulltext |
3
Cite: Bazylevska M. S., BogilloV. I. Adsorption properties of the fu-
med individual and mixed Si, Ti and Al oxides as proxies for the An-
tarctic atmospheric mineral aerosols. Ukrainian Antarctic Journal,
2019. № 1(18), 3—17.
UDC: 504.3.054: 544.723.23: 544.772: 547-302
M. S. Bazylevska*, V. I. Bogillo
Institute of Geological Sciences, National Academy of Sciences of Ukraine,
55B O. Gonchara Str., Kyiv, 01054, Ukraine
* Corresponding author: bazilevskaya1955@gmail.com
ADSORPTION PROPERTIES OF THE FUMED INDIVIDUAL AND MIXED SI,
TI AND AL OXIDES AS PROXIES FOR THE ANTARCTIC ATMOSPHERIC
MINERAL AEROSOLS
ABSTRACT. The aim of the study is to determine the effects of structure and content of X, C
X
in the oxides X/SiO
2
(X = Al
2
O
3
,
TiO
2
, Al
2
O
3
/TiO
2
) on the surface characteristics. The low-temperature nitrogen adsorption isotherms on the surface of 12 indi-
vidual and mixed fumed oxides of Si, Ti and Al, as proxies for the Antarctic atmospheric mineral aerosols, were measured by
volumetric method. The specific surface areas of the oxides, S
BET
were calculated by using the Brunauer–Emmett–Teller (BET)
theory. The dependence between C
X
and S
BET
is not obeyed for the mixed oxides, which can be caused by effects of the reaction
temperature of MCl
n
(M = Si, Ti and Al) hydrolysis in the oxygen/hydrogen flame and by different concentration ratios of O
2
,
H
2
and MCl
n
on the structural characteristics of the primary particles and their aggregates. The N
2
adsorption energy distribu-
tions of the oxides surface were calculated by the regularization procedure. It was demonstrated that the surfaces are character-
ized by high energetic heterogeneity. Result. The Zero-Adsorption Isotherm (ZAI) approach was applied to describe the N
2
adsorption in the whole range of its pressures. The ZAI derived in approximation of adsorbed vapor as a set of molecular clusters.
The specific surface areas for the oxides, A
s
, maximal numbers of the molecules in the adsorbed clusters, thicknesses of the ad-
sorbed liquid film and the free surface energies of the oxides in the absence of adsorption, γS0, were calculated using the ZAI
equations. The A
s
correlates well with SBET and it measures 77.5% of the S
BET
. The γS0 increases as the N
2
average adsorption
energy grows. The dependence between γS0 and C
X
(taking into account γS0 for X) is not obeyed for the mixed oxides. The γS0 for
SiO
2
, Al
2
O
3
and TiO
2
rises as the permittivity and the index of refraction increase. The γS0 is within the range of dispersive com-
ponents of free surface energy, which is determined by other experimental methods and calculated using the Lifshitz’ theory. The
obtained parameters allow estimate the activity of the oxide surface with respect to trace gases in the Antarctic atmosphere that
is necessary for calculating their partition coefficients between particles and the atmosphere and the kinetics of their removal.
Keywords: mineral aerosols, Antarctic atmosphere, fumed individual and mixed Si, Ti and Al oxides, nitrogen adsorption.
Геолого-геофізичні дослідження
Geological and Geophysical Research
ISSN 1727-7485. Український антарктичний журнал. 2019, № 1 (18)
INTRODUCTION
Atmospheric aerosols play a major role in Earth’s
cu rrent climate due to their impact on the global
radiation balance (Seinfeld and Pandis, 2006). Aero-
sols also lead to formation of cloud droplets and ice
crystals by serving as cloud condensation nuclei
(CCN) and ice nuclei particles (INP). Aerosols affect
the life time of clouds, size distributions of cloud
droplets, glaciation rates and the distribution of water
mass in different atmospheric layers. Unfortunately,
aerosols are still the least understood and constrained
aspects of the climate system. The uncertainty of
aerosols’ climate impacts arise from the fact that how
an aerosol affects the radiative balance is a function
of both an aerosol’s chemical composition and phy-
si cal properties (e.g. size, shape). Both chemical and
physical properties of aerosols are functions of emi-
ssion sources, atmospheric processing pathways, and
lifetime in the atmosphere.
4 ISSN 1727-7485. Ukrainian Antarctic Journal. 2019, № 1 (18)
M. S. Bazylevska, V. I. Bogillo
The atmosphere above Antarctica constitutes the
cleanest part of the Earth's troposphere which allows
here to study the composition and temporal change
of the background atmosphere without any direct
impact of civilization. Furthermore, with the exception
of very few rocky terrains, the Antarctic continent is
largely free of aerosol sources, so that the main part of
the particles must be advected by long-range transport
to Antarctica or has its source region in the surroun-
ding Southern Ocean. Due to this unique position,
Antarctica is an outstanding place to document long-
term changes of the composition of our atmosphere
in the industrial period. The Antarctic climate system
can be linked with aerosol particles by complex feed-
back processes that involve aerosol-cloud inter actions.
In addition, because there are less anthropogenic
emission sources in Antarctica, it is a suitable place
to study the formation and growth processes of the
natural aerosol particles. Mineral dust is extremely
important in the nucleation processes, as sites for
heterogeneous chemistry. Particles are for med from a
large numbers of minerals, e.g. alumina, silica and
iron oxides, coated with sulfates, nitrates and organic
species as small particles in the atmosphere. Mineral
dust always acts like solid core for trace gases con-
densation on their surface.
Another important aspect of studying mineral
aero sols in Antarctica is the need to interpret records
of particulates observed in firn and ice cores. Mineral
dust is one of the more studied paleoclimatic and
paleo-environmental proxies among those that can
be recovered from the ice cores. Dust particles arrive
in the remote polar area after long-range transport
from deserted and semi-deserted continental areas
located at lower latitudes. Many characters of dust in
the ice are measured, because of their potential to
provide paleo-climatic information on the location
and aridity at the dust sources, the scavenging and
transport processes, and the atmospheric pathways.
Although global dust sources are absent, Antarctica
is the largest polar desert in the world, where appro-
ximately 2% of its surface area is ice-free and contains
active High Latitude Dust sources (HLD, Bullard et
al., 2016). The best-known local dust sources are
located in West Antarctica, with the McMurdo Dry
Valleys being the largest ice free area (approximately
4,800 km2) with frequent dust suspension (Lancaster,
2002; Ayling and McGowan, 2006; Atkins and Dunbar,
2009; Bullard et al., 2016). As it follows from dust
samples collected in snow pits on Berkner Island, the
dust sources are located also in the ice-free areas of
East Antarctica (Bory et al. 2010). Coastal ice-free
areas have also been identified as active dust sources
around the Maitri Station, Larsemann Hills, and
Neumayer Station in East Antarctica (Weller et al.,
2008; Chaubey et al., 2011; Bud havant et al., 2015),
as well as in the Antarctic Peninsula region (Artaxo
and Rabello, 1992; Kavan et al., 2017; Asmi et al.,
2018). Alternately, the mineral particles can be re-
sus pended from the surface of ablating glaciers (At-
kins and Dunbar, 2009). Long-range transport of dust
from other HLD sources, such as South America
(Patagonia), New Zealand, and deserts in Australia
and Africa, contribute to the dust depositions in
Antarctica (Ne and Bertler, 2015; Bullard et al., 2016;
Asmi et al., 2018). The main non-Antarctic dust source
for the Antarctic Peninsula region is in Patagonia
(Bullard et al., 2016). Patagonian dust was found in
ice cores and snow samples in the Antarctic Peninsula
and in East Antarctica (Basile et al., 1997; Pereira et
al., 2004; McConnell et al., 2007; Bory et al., 2010;
Delmonte et al., 2017).
The dust deposition rates of > 100 g m–2 year–1
were reported from Patagonia (Bullard, 2016). The
rates measured in McMurdo Dry Valleys (< 8 g m–2
year–1) are lower than other HLD sources (Lancaster,
2002). Nevertheless, the dust fluxes of 7.8—24.5 g m–2
year–1 (Atkins and Dunbar, 2009) and 0.2—55 g m–2
year–1 (Chewings et al. 2014) are reported in this
source. The mass concentrations of PM
10
(particles
with a diameter of < 10 μm) and PM
2.5
(with a
diameter of < 2.5 μm) in boundary atmospheric layer
were 5.1 and 4.3 mg m–3, respectively in the Larsemann
Hills during summer (Budhavant et al., 2015), and
8.3 and 6.03 mg m–3 at the Maitri station (Chaubey et
al., 2011). PM
10
concentrations from McMurdo
station during two summers in 1995—1997 were 3.4
and 4.1 mg m–3 on average (Mazzera et al., 2001).
Mean PM
10
and PM
2.5
concentrations of 4.4 mg m–3
and 2.4 mg m–3, respec tively were measured in the
5ISSN 1727-7485. Український антарктичний журнал. 2019, № 1 (18)
Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides
Antarctic Peninsula during the late 1980s (Artaxo
and Rabello, 1992). Seasonal variations in aerosol
loadings showed increased concentrations in January
and a decrease in February and March in Terra Nova
Bay, West Antarctica in 2000—2001 (Truzzi et al.,
2005). PM
10
concentrations of 2.1—5 mg m–3 on
average were reported from the Antarctic Peninsula,
with higher concentration in summer (October to
March) in 2013—2015 (Asmi et al., 2018). The con-
centrations of the particles near ly doubled in summer
when winds were high (Asmi et al. 2018).
Because mineral dust may undergo processing as it
is transported in the atmosphere, its impact on global
processes may change over the course of its “life
story”. Therefore, knowledge of its physicochemical
pro perties, especially its adsorption characteristics, is
very important for predicting its effects in atmospheric
chemistry and biogeochemical cycles in Antarctica.
Most of the experiments on the interaction of trace
gases with mineral dust were performed with oxides
such as SiO
2
, Al
2
O
3
, and CaO (Pokrovskiy et al.,
1999; Al-Abadleh and Grassian, 2003).
The surface of mineral dust particles acts as a sink
for many gases, such as sulfur dioxide (SO
2
), with the
formation of sulfite ion (SO
3
2–) associated with it,
which is oxidized to sulfate ion (SO
4
2–) in the presence
of ozone or other oxidizing agents. However, an evi-
dence has recently been obtained of an alternative
way of generating these ions for a series of reactions:
in the presence of water vapor, titanium oxides, iron or
mineral dust containing these oxides, exposure to the
UV part of solar radiation produces gaseous sulfuric
acid (H
2
SO
4
), which then reacts with the surface of
the particles (Dupart et al, 2012). Metal oxides in
mineral dust act as atmospheric photocatalysts, pro-
moting the formation of gaseous OH radicals, which
initiate the conversion of SO
2
to H
2
SO
4
in the vicinity
of the particle. At a low concentration of dust in the
atmosphere characteristic over Antarctica, this process
can lead to the nucleation phenomena and the for-
mation of the CCN.
In the present work, highly dispersed fumed silica,
alumina, titania, and mixed X/SiO
2
oxides (X =
= Al
2
O
3
, TiO
2
and Al
2
O
3
/TiO
2
) are used as proxies of
mineral aerosols. These oxides produced by conden-
sa tion processes are often of more theoretical interest
because it is easier to control their nucleation and
growth rate, particle size and size distribution, and
rate of disappearance. They can therefore be used
more readily to study the various theories of aerosol
formation and destruction. The choice of oxides SiO
2
and Al
2
O
3
is due to their dominance in the earth’s
crust and in the composition of the mineral dust as
ice nucleating particles, while TiO
2
has semiconductor
properties and can serve as a natural photocatalyst for
the formation of H
2
SO
4
, which is the main component
of CCN that have a significant impact on the Antarctic
climate. Natural analogues of these oxides can be
mineral particles formed during volcanic eruptions,
for example, Mt. Erebus in Antarctica, as a result of
high-temperature hydrolysis of metal halides, MHal
n
(M = Si, Al, Ti; Hal = Cl, Br, I) in presence of water
vapor. Nitrogen was used as an adsorbed substance.
The main goal of the work was to determine the
influence of the oxides composition on the adsorption
characteristics of their surface.
MATERIALS AND METHODS
Highly dispersed fumed individual silica, alumina,
titania and mixed oxides X/SiO
2
(X = Al
2
O
3
, TiO
2
,
Al
2
O
3
/TiO
2
) (synthesized at the experimental plant of
the Institute of Surface Chemistry of the National
Academy of Sciences of Ukraine, Kalush, Ukraine)
were studied at various concentrations (C
X
) phase X
oxide (Table 1). Titania, titania/silica and alumina/
titania/silica contain a mixture of anatase (particle
shell, main part) and rutile (core of particles). Alumina
includes ≈ 20% (by weight) of the crystalline γ-phase
and ≈ 80% of the amorphous phase, whereas in alu-
mina/silica and alumina/titania/silica it is completely
amorphous. Silica is completely amorphous in all
fumed oxides. Alumina/titania/silica includes ≈ 22%
Al
2
O
3
, ≈ 28% SiO
2
and ≈ 50% TiO
2
(a mixture of 88%
anatase and 12% rutile). The phase composition and
other properties of these mixed oxides are reported in
(Gun’ko et al. 2007).
The nitrogen adsorption/desorption isotherms on
the oxide surfaces were measured at 77.35 K and
relative pressure x = P/P
S
(P and P
S
are the equilibrium
6 ISSN 1727-7485. Ukrainian Antarctic Journal. 2019, № 1 (18)
M. S. Bazylevska, V. I. Bogillo
vapor pressure of nitrogen and its saturated vapor
pressure, respectively) in the range from ≈ 5 × 10–7 to
≈ 0.99 by using an ASAP 2010 V-3.00 volumetric
multigas sorption analyzer (Micromeritics, Norcross,
GA). Before measurements, the samples were sub-
jected to treating in vacuum at 393 K for 6 hours to
remove physically adsorbed water and other volatile
impurities from the surface of the oxides. The total
pore volume was estimated by converting the volume
adsor bed at the relative pressure of 0.985 to the
volume of liquid nitrogen.
Methods for the calculation
of adsorption parameters
BET theory
The specific surface area of the samples was calculated
in accordance with standard Brunauer – Emmett –
Teller (BET) procedure based on adsorption data in
the x = P/P
S
range from 0.06 to 0.25 (Brunauer et al.,
1938; Gregg et al, 1982)
(1)
S
BET
= a
m
σ
m
N
A
(2)
, (3)
where a is the number of moles of adsorbed substan-
ce per unit weight of adsorbent (mol g–1), a
m
is the
capacity of the monolayer of adsorbed substance per
unit weight of adsorbent, σ
m
is the average area
occupied by the adsorbed molecule in the monolayer
(for N
2
it is assumed to be 16.2 Å2), N
A
is the Avogadro
number, ΔQ
A
is the average differential heat of ad-
sorption, ΔQ
V
is the heat of vaporization of the ad-
sorbed substance, R is the universal gas constant, T is
the adsorption temperature in K.
Regularization procedure
The nitrogen adsorption in the monolayer taking into
account the energetic heterogeneity of the oxide
surface was studied using the modified regularization
procedure proposed in (Pyziy et al., 1997; Bogillo and
Shkilev, 1999). Using the capacities of the monolayer
obtained by the BET method, a
m
, for those values of
a for which a
m
≥ a, we can determine the overall
surface coverage with adsorbed substance within the
monolayer, Θ(P,T) = a/a
m
. Adsorption within these
limits is generally described by the Fredholm integral
equation of the first kind
, (4)
where θ(P, T, E
A
) is the coverage of the local surface
area with the adsorption energy E
A
, ρ(E
A
) is the
normalized differential surface distribution on E
A
,
E
A(min)
and E
A(max)
are the lower and upper limits of this
distribution.
In the simplest case, the local coverage, θ(P, T,
E
A
), is described by the Langmuir isotherm:
, (5)
where K
L, 0
is a preexponential factor depending on the
rotational, vibrational, and translational degrees of free-
dom of a polyatomic molecule adsorbed on the sur face
and in the gas phase. This value can be approximately
estimated using the ratio (Bogillo et al., 1998)
K
L, 0
≈ P
s
exp(ΔQ
V
/ RT). (6)
One of the important problems in describing ad sor-
ption equilibria on a heterogeneous surface remains
the choice of the minimum information necessary for
a stable calculation of the distribution ρ(E
A
). The main
idea of the numerical regularization is to replace the
ill-posed problem of minimizing the selected function
by a well-posed problem which smoothes the calcu-
la ted distribution and distorts the origin problem
insignificantly. Thus, the solution of equation (4) is
replaced by minimizing the functional:
(7)
.
7ISSN 1727-7485. Український антарктичний журнал. 2019, № 1 (18)
Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides
where α (1 ≥ α > 0) is the regularization parameter
depending on the relative errors in determining the
adsorption isotherm.
To obtain the optimal α, we proposed a two-step
procedure. First, the functional Φ[ρ(E
A
)] is minimized
at α = 0. Thus, this minimum can serve as an measure
of the accuracy of experimental data for m points on
the adsorption isotherm:
( )
2/1
1
20 )(),,(),(1min ⎥
⎦
⎤
⎢
⎣
⎡
−Θ= ∑
=
m
j
AA EETPTP
m
ρθξ .
In the second step, the value of α is calculated at
which the distribution ρ1(E
A
), which minimizes the
func tional Φ[ρ(E
A
)], satisfies the following condition:
(9)
.
A feature of this modified method is the possibili ty
of improving the solution by varying the free parame-
ter η. The calculations showed that none of the
methods for estimating α proposed in the literature
leads to stable solutions of equation (4) in the absence
of η. The distributions ρ(E
A
) were calculated on the
basis of part of the nitrogen adsorption isotherms
corresponding to the monolayer surface coverage.
ZAI theory
A new isotherm, so-called Zeta Adsorption Isotherm
(ZAI) was recently derived to describe accurately the
adsorption in the full range of P up to P
S
(Zandavi
et al., 2014). This isotherm is obtained in the app-
roximation of adsorbed vapor as a set of molecular
clusters, of which at least one is adsorbed by one of
the M adsorption sites. Each adsorbed cluster is
approximated as a quantum-mechanical harmonic
oscillator with a binding energy that depends on the
number of molecules in the cluster. The maximum
number of molecules which cluster can consist of is
ζ
m
. Using the canonical ensemble, the dependence of
the amount of adsorbed matter on the solid/vapor
interface per unit surface on the vapor pressure ratio
is described as
. (10)
Parameters c
Z
and α
Z
are related to distribution of
the clusters with different number of molecules and
to the chemical potential of the adsorbed liquid at
standard pressure, respectively.
In ZAI, the number of adsorption sites per unit of
mass of a solid, M
g
is related to the specific surface
area, A
s
, as
M
g
= A
s
M. (11)
In the derivation of ZAI, it is assumed that one
molecular cluster occupies one adsorption site. The
average cross-sectional area of the adsorption site or
the molecular cluster of a given vapor (I) is denoted
as σ(I). Then the specific adsorption surface area of
the solid, A
s
is given as
σ(I) M
g
(I) = A
s
. (12)
When the specific volume of the adsorbed liquid
film is equal to that for a pure liquid in the volume,
v
f
, the thickness of the adsorbed liquid film, τ
af
, is
defined as
. (13)
Equation 10 together with the Gibbs adsorption
equation for this surface allows to derive the ratio for
surface tension or free surface energy of a solid in the
absence of adsorption, γS0 (Ghasemi et al., 2009):
, (14)
where γLV is the surface tension or free surface energy
of the adsorbed substance in the liquid/vapor system
and k
B
is the Boltzmann constant.
Lifshitz theory
The value of γ S0, in the general case, is the sum of the
dispersive, γ
S
D and polar, γ
S
p components of the free
surface energy:
8 ISSN 1727-7485. Ukrainian Antarctic Journal. 2019, № 1 (18)
M. S. Bazylevska, V. I. Bogillo
γS0 = γ
S
D + γ
S
p. (15)
The dispersive component, γ
S
D is related to the
Ha maker constant of the material, A
H
(Israelachvili,
1992):
A
H
= 24πD
0
2γ
S
D, (16)
where D
0
is the smallest equilibrium distance between
two identical materials in a vacuum. Given the Born
repulsion, this distance is 1.6 A.
On the other hand, the approximate expression
from the Lifshitz’ theory for A
H
in vacuum or in air
can be written as (Dzyaloshinskii et al., 1961):
, (17)
where n
0
is the refractive index, ε
k
is the permitti-
vity of the material, ν
c
is the main frequency of
electron absorption in the UV range (ν
c
= (3÷5) ×
× 1015 s–1), and h is the Planck constant (h = 6.626 ×
× 10–34 J s).
RESULTS AND DISCUSSION
Fumed oxides, such as silica, titania, alumina, silica/
alumina, titania/silica, alumina/titania/silica are wi-
de ly used in industry as adsorbents, pigments,
catalysts, fillers and additives in polymers. There is a
multistage hierarchy of the oxides structure related to
the features of their synthesis when using MCl
n
(M =
= Si, Ti, and Al) in an oxygen/hydrogen flame at T >
1300 K. Variations in the reaction temperature and
the ratio between the O
2
/H
2
and MCl
n
concentrations
affect the structural characteristics of the primary
particles and the concentration of hydroxyl groups on
the surface of the oxides. Nonporous spherical primary
particles with a diameter of 5—100 nm, depending
on the synthesis conditions and the composition of
the oxides, form aggregates with a diameter of 100—
500 nm, and then loose agglomerates (>1 μm). These
structural levels differ significantly in apparent density,
ρ
ap
. For example, for fumed silica, ρap is 1—3% for
agglomerates, ∼30% for aggregates, and ∼100% of the
specific density of primary particles (Gun’ko et al.,
Table 1. The specific adsorption area of the oxides surface, S
BET
, the С constant of the BET equation,
the nitrogen average isosteric adsorption heat, ΔQ
A
, the apparent pore volume, v
p
, the nitrogen average
adsorption energy in the monolayer, E
A(av)
and its standard deviation, σ
Ea
Sample Composition
S
BET
v
p
C
ΔQ
A
E
A(av)
σ
Ea
m2g–1 cm3g–1 kJ mole–1
T
100
100% TiO
2
60 0.17 98 8.53 7.9 2.9
ST
29
SiO
2
-29%TiO
2
73 0.16 93 8.49 7.3 4.2
ST
20
SiO
2
-20%TiO
2
65 0.13 263 9.16 7.6 6.5
ST
14
SiO
2
-14%TiO
2
217 0.49 117 8.64 6.6 3.1
ST
9
SiO
2
-9%TiO
2
198 0.47 116 8.63 7.1 2.2
S
100
100%SiO
2
267 0.62 126 8.69 7.1 2.5
SA
1..3
SiO
2
-1.3%Al
2
O
3
294 0.68 129 8.70 7.7 1.6
SA
3
SiO
2
-3%Al
2
O
3
156 0.35 165 8.86 7.6 4.7
SA
23
SiO
2
-23%Al
2
O
3
311 0.74 106 8.58 7.4 1.6
SA
30
SiO
2
-30%Al
2
O
3
239 0.57 106 8.58 7.5 1.8
A
100
100%Al
2
O
3
159 0.42 133 8.72 7.3 1.5
SAT SiO
2
-22%Al
2
O
3
-50%TiO
2
32 0.08 97 8.52 6.9 8.3
9ISSN 1727-7485. Український антарктичний журнал. 2019, № 1 (18)
Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides
2007). The smaller these particles, the stronger they
are bound in the aggregates and the narrower is the
particle size distribution.
Roughness and amorphisms of the particle surface,
variations in the types and concentration of hydroxyl
groups on the surface can be the main reasons for the
structural and energetic heterogeneity of the oxides
surface with respect to various adsorbates. Since some
phases in mixed oxides are amorphous (SiO
2
, Al
2
O
3
),
while others, for example, TiO
2
, can be crystalline,
their surface heterogeneity can increase. The
interfaces between the amorphous and crystalline
phases in such oxides include strained bonds,
incompletely coordinated metal atoms (Lewis acid
centers), single and bridged hydroxyl groups
(Bronsted acid centers), strongly bonded water
molecules, and other adsorption centers that cause
high surface heterogeneity.
One of the main characteristics of the adsorption
capacity of materials is the specific adsorption surface
area, S
BET
. The higher it is, the greater the substance
amount is held by a unit weight of the adsorbent, i.e.,
the more efficient the adsorption. These S
BET
for the
studied oxides are given in Table 1. It also presents
the pore volumes of materials, v
p
, corresponding to
the effective volume, since nitrogen adsorption
occurs not only in the internal free volume of the
aggregates, but also in the free volume of agglomerates,
that is, on the outer surface of the aggregates.
Fig. 1 shows the experimental isotherm of nitro-
gen adsorption on the surface of mixed SAT oxide
(Table 1) in the P/P
S
range from 0 to 1.0 (a) and up to
0.35 (b). Its shape corresponds to the type II adsorp-
tion isotherm according to the Brunauer classification
(Gregg et al., 1982), which is characteristic of vapor
adsorption on the surface of non-porous materials.
The absence of a plateau on the adsorption isotherms
observed at P/P
S
> 0.9 (Fig. 1, a) and the lack of
hysteresis, i. e. coincidence of the adsorption and
desorption isotherms, testifies that mesopores con-
tri bution in the total pore volume of the studied ma-
terials is negligible.
Fumed TiO
2
includes primary crystalline particles
of anatase (70÷85%) and rutile (15÷30%), while fumed
Al
2
O
3
≈ 20% of its crystalline γ-form. Fumed SiO
2
is
completely amorphous. Obviously, the observed dec-
rea se in S
BET
during the transition from silica to tita nia/
silica and titania, as well as close S
BET
values for silica,
silica/alumina and alumina are due to the contribution
of crystalline forms of TiO
2
and Al
2
O
3
to S
BET
for
mixed oxides. Low v
p
indicate the con den sation of
adsorbed nitrogen in the secondary pores formed due
to the interparticle space of the aggregates upon
contact of the primary non-porous oxide particles.
Fig. 1. Experimental and calculated according to the theories of ZAI and BET nitrogen adsorption isotherms on the surface of
alumina/titania/silica (SAT) at 77.35 K in the P/P
S
range from 0 to 1.0 (a) and up to 0.35 (b)
a b
10 ISSN 1727-7485. Ukrainian Antarctic Journal. 2019, № 1 (18)
M. S. Bazylevska, V. I. Bogillo
The average differential heats of nitrogen ad sorp-
tion calculated on the basis of the C constant of the
BET equation are given in Table 1. All of them are in
a rather narrow range (8.52÷9.16 kJ mol–1), but ex-
ce ed the heat of vaporization of nitrogen (5.58 kJ
mol–1), which is usually equated to the non-specific
contribution (dispersion interaction) to the adsorption
energy. Such a difference may indicate a significant
con tribution of the specific (quadrupole – dipole
and/or quadrupole – ion) interaction of a quadrupole
nitrogen molecule with polar single or bridging OH–
surface groups or with coordination-unsaturated
metal ions at the oxide phase boundary.
Some distributions of the oxides surface on the N
2
adsorption energy in the monolayer range, which
com puted by using the regularization procedure, are
shown in Fig. 2, a, b.
It is seen that the oxides surface is characterized by
a high degree of heterogeneity with respect to N
2
adsorption, which manifests itself in the presence of
several peaks in the distribution curves and their
considerable width. Since the distributions allow only
a qualitative comparison of them for the surface of
various oxides, we approximated them with a Gaussian
distribution. The average N
2
adsorption energies and
their standard deviations are given in Table. 1. Note
that ΔQ
V
for N
2
, which characterizes the ability of
the dispersion interaction of N
2
with surface sites, is
5.4 kJ mol–1. The upper limits of the distributions
significantly exceed this value, which may be due to
the contribution of the electrostatic interaction of the
quadrupole of N
2
molecule with OH group dipoles
and ions of the oxide surface sites. The highest E
A
at Θ(p.T) → 0 (Fig. 2, a) and E
A(av)
+ σ
Ea
(Table 1)
are typical for TiO
2
, ST
29
, and SAT, in which the
content of crystalline phases is maximum.
As follows from Fig. 1, the BET isotherm is close
to the experimental one at P/P
S
< 0.3, but deviates
significantly from it at large P/P
S
. It is well known
that the BET isotherm describes adsorption on the
surface of non-porous materials only in a limited
pressure range corresponding to the filling of the
monolayer (Gregg et al., 1982). At P → P
S
, the BET
equation predicts infinite adsorption and negative
adsorption at P > P
S
. Other adsorption isotherms
(Frenkel – Halsey – Hill or Aranovich – Donahue)
more accurately describe adsorption at high P, but
they also predict infinite adsorption at P ≈ P
S
. Then
the Zeta Adsorption Isotherm (ZAI) used here to
describe accurately the adsorption in the full range of
P up to P
S
. Table 2 shows the specific surface areas of
oxides, A
s
, their monolayer capacitances, M
V
and M
g
,
Fig. 2. Distributions of surface of SiO
2
, TiO
2
, TiO
2
/SiO
2
, TiO
2
/Al
2
O
3
/SiO
2
(a) and SiO
2
, Al
2
O
3
, Al
2
O
3
/SiO
2
(b) on the N
2
adsorp-
tion energy
11ISSN 1727-7485. Український антарктичний журнал. 2019, № 1 (18)
Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides
Table 2. The specific adsorption area of the oxides surface. A
s
, the monolayer capacities. M
V
and M
g
,
the α
Z
, c
Z
and ζ
m
parameters of Eq. 10, and the square of the correlation coefficient for the Eq. 10, R2
Sample A
s
, m2 g–1 M
V
, cm3 g–1 M
g
× 106, mole g–1 α
Z
с
Z
ζ
m R2
T
100
43 9,98 445 0,916 6137 70 0,955
ST
29
60 13,76 614 0,862 1167 72 0,947
ST
20
51 11,68 521 0,862 3096 62 0,946
ST
14
176 40,36 1801 0,874 1239 58 0,966
ST
9
159 36,43 1625 0,881 1059 54 0,970
S
100
204 46,86 2091 0,885 1650 71 0,963
SA
1..3
225 51,69 2306 0,887 1833 56 0,959
SA
3
116 26,60 1187 0,882 2053 61 0,956
SA
23
240 55,17 2461 0,887 1305 72 0,959
SA
30
184 42,23 1884 0,886 1205 59 0,962
A
100
123 28,13 1255 0,901 3483 59 0,963
SAT 223 5,24 234 0,897 1954 112 0,933
Table 3. The thickness of adsorbed N
2
film on the oxides surface, τ
af
, the free surface energy of the oxides
in the absence of adsorption, γS0, this energy, estimated for mixed oxides, γS0
(calc)
, the dispersive component
of free surface energy of the oxides determined by immersion calorimetry, γD
(exp)
, by method of inverse gas
chromatography at finite concentrations, γD
(IGC)
, and calculated by the Lifshitz’ theory, γD
(calc)
, the refractive
indices, n
0
and permittivity, ε
k
of individual oxides
Sample
τ
af
γ S0 γ S0
(сalс)
aγD
(expp)
bγD
(calc)
cγD
(IGC)
n
0
ε
k
nm mJ m–2
T
100
25 81,8 72 79 35,2 2,8 21,3
ST
29
26 67,3 74
ST
20
22 73,7 73 44,9
ST
14
21 68,3 73
ST
9
19 67,7 72
S
100
25 70,9 32 34 28,6 1,5 4,6
SA
1..3
20 71,7 71
SA
3
22 72,1 71
SA
23
26 69,5 72
SA
30
21 68,9 73 32,5
A
100
21 76,9 85 80 51,8 1,8 10,4
SAT 40 72,8 78
a from the calorimetric data of the immersion of oxides in n-heptane (Medout-Marere, 2000). b based on the Hamaker constants
calculated by the Lifshitz theory (Bergstrom, 1997). c from data of inverse gas chromatography at finite concentrations (Bogillo
et al., 1996).
12 ISSN 1727-7485. Ukrainian Antarctic Journal. 2019, № 1 (18)
M. S. Bazylevska, V. I. Bogillo
the parameters of Eq. 10, and the squares of the co-
rrelation coefficients.
As follows from Fig. 1, a, the isotherm calculated
by the ZAI equation deviates noticeably from expe-
rimental one in the range 0 < x < 0.35, but it is close
to the experimental one in the range 0.35 < x < 0.99,
while the isotherm calculated by the BET equation
deviates significantly from it and a → ∞ as x → 1.0.
Using the σ(N
2
) = 16.2 Å2 for the surfaces of all
oxides, the M equals to M
g
/A
s
= 1.0244 × 10–5 mole
m–2. A comparison of the A
s
values with the S
BET
from
Table 1 indicates a close relationship between them:
A
s
= (0.775 ± 0.012) · S
BET
; R2 = 0.999. The lower
surface areas obtained using ZAI compared to BET
may be due to variations in the orientation of nitro-
gen molecules (e.g., orthogonal) in clusters (ZAI), in
contrast to the strictly parallel orientation of mo le cu-
les in the adsorbed layer, as is assumed in the classical
BET theory.
The Table 3 shows the thicknesses of the adsorbed
nitrogen film on the oxide surface, the free surface
energies of these oxides in the absence of adsorption,
these energies estimated for mixed oxides based on
γ S0 for component X in the oxide, γ S0
(calc)
, dispersive
components of the free surface energy of individual
oxides, determined by the calorimetric method, γD
(exp)
and by the method of inverse gas chromatography at
final concentrations, γD
(IGC)
, calculated using Lifshitz’
theory, γD
(calc)
, as well as refractive indices, n
0
and
permittivity, ε
k
of individual oxides. In the calculations
for nitrogen at 71.1 K, γLV = 10.3 mJ m–2 was used
(Prausnitz, 1966).
We estimated γ S0 for mixed oxides based on these
values for individual oxides and the fraction of
component X. As can be seen from the data in Table
3, for most mixed oxides, the calculated γ S0 exceed
the experimental ones by 2.5–6.7 mJ m–2. Only for
samples ST
20
, SA
1,3
, and SA
3
there is a slight excess
(by 0.7÷1.1 mJ m–2) of experimental values over the
calculated ones.
The assumed additivity of γ S0 for mixed oxides is
valid for an external mixture of oxides forming par ti-
cles, while for an internal mixture that is inhomo ge-
neous in volume of a particle, it will be violated.
Among the studied individual oxides, silica has a
mi ni mum γ S0 and is part of all mixed oxides. There-
fore, we can assume a higher SiO
2
content in the
upper shell of mixed oxide particles compared to its
bulk content, while Al
2
O
3
and crystalline TiO
2
pha-
ses form mainly the core of these particles. This
assumption is consistent with the conclusions about
the particle structure of fumed mixed oxides in
(Gun’ko et al., 2007).
Square root of free surface energy of oxides as a
function of the average nitrogen adsorption energy
within the monolayer is shown in Fig. 3.
An increase in E
A(av)
leads to an increase in (γS0)1/2,
and a linear relationship is observed between these
parameters:
; R = 0.523.
Thus, using Eqs 16 and 17, we can estimate γ
S
D
of the material. The values of n
0
and ε
k
for indivi-
dual oxides are given in the Table 3. The calculated
γ
S
D
(calc)
values (in mJ m–2) are varied in sequence: TiO
2
(216) > Al
2
O
3
(70) > SiO
2
(33), which qualitatively
coincides with the sequence of changes in γ S0 of these
oxides (TiO
2
(82) > Al
2
O
3
(77) > SiO
2
(71)). Using
A
H
calculated ta king into account various spectral
corrections from (Bergstrom, 1997), lower γ
S
D values
for TiO
2
(77÷82 mJ m–2) are obtained, which are
Fig. 3. The surface free energy of the individual and mixed Si,
Ti and Al oxides as a function of their average N
2
adsorption
energy within the monolayer
13ISSN 1727-7485. Український антарктичний журнал. 2019, № 1 (18)
Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides
close to those found for Al
2
O
3
(69÷72 mJ m–2),
however for SiO
2
in all cases, the calculation leads
to lower γ
S
D (27÷31 mJ m–2).
Plots of A
H
for inorganic materials from (Bergst-
rom, 1997) and γS0 for the oxides on n
0
and (ε
k
)1/2
values are shown in Fig. 4. It can be seen that in all
cases there is a tendency for A
H
and γS0 to increase
as the n
0
and (ε
k
)1/2 rise. The relations (A
H
× 10–20 =
= (14.1 ± 1.6)n
0
– (13.5 ± 3.1), N = 30, R = 0.854
and A
H
× 10–20 = (7.2 ± 1.8) (ε
k
)1/2 – (8.3 ± 5.1), N =
= 30, R = 0.636) allow to estimate easy the A
H
values
of materials.
The γ
S
D value based on A
H
determined by ca lo ri-
metric immersion of metal oxides in n-hexane
(Me dout-Marere, 2000) is shown in Table 3. It is
seen that, in contrast to the calculated γ
S
D and
experimental γS0, the reverse sequence of oxide
activity (Al
2
O
3
> TiO
2
) is observed, however, lower
γ
S
D is obtained for SiO
2
, which is close to that
calculated using the equations of the Lifshitz
theory.
The Table 3 shows also γ
S
D determined from data
of inverse gas chromatography at finite concentrations
at 403 K (Bogillo et al., 1996). As in previous case, γ
S
D
Fig. 4. The dependence of Hamaker constant for inorganic materials (a, b) and free surface energy of the metal oxides in the
absence of adsorption (c, d) on the index of refraction (a, c) and on the square root of permittivity of the materials (b, d)
14 ISSN 1727-7485. Ukrainian Antarctic Journal. 2019, № 1 (18)
M. S. Bazylevska, V. I. Bogillo
for SiO
2
is lower than for other oxides and for Al
2
O
3
γ
S
D is higher than for TiO
2
. If for SA
30
, γ
S
D is between
γ
S
D of individual SiO
2
and Al
2
O
3
, then γ
S
D for ST
20
is
significantly higher than that obtained for indi vidual
Si and Ti oxides. For the same oxide, the highest
constant С of the BET equation (263) is observed
(Table 1) compared with other oxides (93÷165) and,
accordingly, the highest isosteric heat of adsorption,
ΔQ
A
(9.2 kJ mole–1) in compared with the rest oxides
(8.5÷8.9 kJ mole–1).
The comparison of γ
S
D and γS0 values for various
silicas (Bilinski et al., 1999; Pokrovskiy et al., 1999)
shows that these values depend on the method used,
the temperature of preliminary sample preparation,
the nature of the adsorbed substance, the adsorption
temperature, and γ
S
D varies from 28.6 to 71 mJ m–2
(Bilinski et al., 1999), which coincides with γ
S
D
(IGC)
and γS0 values from the Table 3. Even greater
variations are observed for γ
S
p (11.9÷160 mJ m–2),
which is associated with a significant influence of
the choice of a polar adsorbed substance for de-
termining this parameter (Bilinski et al., 1999). Si-
milar significant variations in γ
S
D
(IGC)
and γS0 were
also noted for other oxides, minerals, carbon and
solid organic materials (Pokrovskiy et al., 1999).
Slight variations of γS0 for the studied oxides, in
contrast to the calculated and ex perimental γ
S
D and
the dependencies shown in Fig. 4, c, d suggest that
the main contribution to γS0 is made by its dispersive
component.
The obtained parameters for the metal oxides
allow evaluating the adsorption activity of their
surface with respect to other trace gases in the
Antarctic atmosphere. For these parameters it is
necessary to calculate the partition coefficients of
these gases between particles and the atmosphere,
K
SA
, and the kinetics of their removal from the
atmosphere (Bogillo et al., 2008). The K
SA
value for
the adsorbed substance/material surface pair can be
calculated by knowing the specific surface area of the
material, its free surface energy, or the Hamaker’
constant, as well as the γLV value (Bogillo et al., 1998;
Pokrovskiy et al., 1999), or the critical temperatu -
re and critical pressure of the adsorbed substance
(Mauer et al., 2001).
CONCLUSIONS
Using the volumetric method, low-temperature nit-
rogen adsorption isotherms on the surface of 12
fumed individual and mixed oxides of Si, Ti, and Al,
as components of mineral aerosols in the Antarctic
atmosphere, were measured. The aim of the work was
to determine the effect of the origin and concentration
of X, C
X
in oxides of the X/SiO
2
type (X = Al
2
O
3
,
TiO
2
, Al
2
O
3
/TiO
2
) on the structural and energetic
characteristics of their surface.
Using the BET theory, the specific surface areas of
the oxides, S
BET
, were calculated. The relationship
between C
X
and S
BET
for mixed oxides does not exist.
Since the synthesis of oxides is carried out by hyd-
rolysis of metal chlorides MCl
n
(M = Si, Ti, and Al)
in an oxygen/hydrogen flame at T > 1300 K, variations
in T and the concentrations of O
2
, H
2
, and MCl
n
, as
well as the degree of crystallinity, probably significantly
affect structural characteristics of primary par ticles
and aggregates formed from them.
Using the regularization method, the surface dis-
tri butions of the oxides on the N
2
adsorption energies
were computed. It was found that their surface is
cha racterized by a high degree of heterogeneity,
manifested in the presence of several peaks in the
distribution curves and their significant width. Since
the upper limits of the distributions significantly
exceed the heat of vaporization of N
2
, this may be
due to the significant contribution of the electrostatic
interaction between the quadrupole molecule N
2
and
dipoles of surface OH groups and ions in the overall
adsorption energy.
Since the BET isotherm describes adsorption only
in a limited narrow pressure range, the Zeta Adsorp-
tion Isotherm (ZAI) derived in the approximation of
adsorbed vapor as a set of molecular clusters was used
for its full range. ZAI describes isotherms well, and
the specific surface areas of oxides, A
s
, the maxi mum
number of molecules in adsorbed clusters, the thick-
ness of an adsorbed liquid film, and the free surface
energies of oxides in the absence of adsorption, γS0,
are calculated using the ZAI equations.
The A
s
correlates well with S
BET
and account for
77.5% of one, which may be due to the contribution
15ISSN 1727-7485. Український антарктичний журнал. 2019, № 1 (18)
Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides
of the orthogonal orientation of N
2
molecules in
clusters (ZAI), in contrast to their parallel orientation
in the BET theory.
It was shown that γS0 increase with rise of average
adsorption energies of N
2
. There is no dependence
between γS0 and C
X
(taking into account γS0 for X) for
mixed oxides, which may be due to a higher content
of SiO
2
in the shell of their particles, while Al
2
O
3
and
TiO
2
form mainly their core.
The γS0 value of individual oxides increases with rise
of their permittivity and refractive index. The γS0 is in
the range of dispersive components of the free surface
energy determined by other experimental methods
and calculated according to the Lifshitz theory.
These parameters for oxides make it possible to
estimate the adsorption activity of their surface in
relation to other trace gases in the Antarctic atmo-
sphere, which is necessary to evaluate their partition
coefficients between particles and the atmosphere
and their removal kinetics.
Acknowledgements. Adsorption measurements were
performed at the Adsorption and Chromatography
Laboratory (Head is Prof. M. Jaroniec) of the Che-
mistry Department, Kent State University, Ohio, USA
with financial support from the US National Science
Foundation (COBASE program).
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17ISSN 1727-7485. Український антарктичний журнал. 2019, № 1 (18)
Adsorption properties of the fumed individual and mixed Si, Ti and Al oxides
М. С. Базилевська*, В. Й. Богилло
Інститут геологічних наук, Національна академія наук України,
вул. Олеся Гончара, 55Б, м. Київ, 01054, Україна
* Автор для кореспонденції: bazilevskaya1955@gmail.com
АДСОРБЦІЙНІ ВЛАСТИВОСТІ ПІРОГЕННИХ ІНДИВІДУАЛЬНИХ І ЗМІШАНИХ ОКСИДІВ
SI, TI ТА AL ЯК МОДЕЛЕЙ МІНЕРАЛЬНИХ АЕРОЗОЛІВ В АТМОСФЕРІ АНТАРКТИКИ
РЕФЕРАТ. Метою роботи було визначення впливу природи та вмісту X, C
X
в оксидах X/SiO
2
(X = Al
2
O
3
, TiO
2
, Al
2
O
3
/
TiO
2
) на характеристики їх поверхні. Методом волюметрії виміряні низькотемпературні ізотерми адсорбції азоту на
поверхні 12 індивідуальних і змішаних пірогених оксидів Si, Ti та Al, як компонентів мінеральних аерозолів в атмосфері
Антарктики. Згідно теорії БЕТ розраховано питомі площі поверхні оксидів, S
BET
. Залежності між C
X
і S
BET
для змішаних
оксидів не виявлено, що пов’язано з впливом температури реакції гідролізу MCl
n
(M = Si, Ti та Al) у кисень/водневому
полум’ї та відношень концентрацій O
2
, H
2
і MCl
n
на структурні характеристики первинних частинок та агрегатів.
Методом регуляризації розраховано розподіли поверхні оксидів за енергіями адсорбції N
2
та показано, що вона
характеризується високою мірою енергетичної неоднорідності. Для опису адсорбції N
2
у повному діапазоні його
тисків застосовано Зета – ізотерму адсорбції (ZAI), яку отримано в наближенні адсорбованого пару, як набору
кластерів молекул. За рівняннями ZAI розраховано питомі площі поверхні оксидів, A
s
, максимальні кількості молекул
в адсорбованих кластерах, товщини адсорбованої рідкої плівки та вільні поверхневі енергії оксидів за відсутності
адсорбції, γS0. A
s
гарно корелює з S
BET
та складає 77,5% від неї. Величина γS0 зростає при збільшенні середньої енергії
адсорбції N
2
. Залежності між γS0 та C
X
(з урахуванням γS0 для X) для змішаних оксидів не виявлено. Для SiO
2
, Al
2
O
3
і TiO
2
γS0 зростає при збільшенні діелектричної проникності оксидів та показника заломлення і знаходяться в діапазоні їх
дисперсійних компонент вільної поверхневої енергії, які визначено іншими експериментальними методами та
розраховано згідно теорії Ліфшиця. Знайдені параметри для оксидів дозволяють оцінити активність їх поверхонь по
відношенню до домішок в атмосфері Антарктики, що необхідно для розрахунку їх коефіцієнтів розподілу між
частинками та атмосферою і кінетики їх видалення.
Ключові слова: мінеральні аерозолі, атмосфера Антарктики, пірогенні індивідуальні та змішані оксиди Si, Ti та Al,
адсорбція азоту.
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