_Artículo 1 _PhysicochemicalAndPhotocatalyt

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Vol.:(0123456789)1 3
Journal of Thermal Analysis and Calorimetry (2020) 140:2131–2142 
https://doi.org/10.1007/s10973-019-08896-0
Physicochemical and photocatalytic properties of tin dioxide 
supported onto silica gel
S. Khalameida1 · V. Sydorchuk1 · S. Levytska1 · N. Shcherban2
Received: 27 March 2019 / Accepted: 6 October 2019 / Published online: 15 November 2019 
© Akadémiai Kiadó, Budapest, Hungary 2019
Abstract
The samples containing 1–10% tin dioxide supported onto silica gel have been synthesized via precipitation or thermolysis 
of tin tetrachloride. The prepared samples have been characterized using DTA–TG, XRD, Raman and UV–Vis spectroscopy, 
TPD of ammonia, and low-temperature nitrogen adsorption–desorption. The supported samples have been tested as photo-
catalysts in the process of rhodamine B degradation under visible irradiation. It has been established that the deposited phase 
is uniformly dispersed on the surface. Redshift of band gap is observed for the supported samples. Unlike a bulk SnO2, the 
supported samples exhibit photocatalytic activity under visible irradiation.
Keywords Tin dioxide · Silica gel · Photocatalysis · DTA–TG · UV–Vis spectroscopy
Introduction
Tin dioxide SnO2 is a versatile material since it has wide 
numerous applications in a bulk and deposited state as cata-
lyst, ion-exchanger, and material for gas sensors [1–3]. Being 
a semiconductor by its nature, it is a promising photocatalyst 
for processes of organic pollutants degradation [4–6]. The 
efficiency of these applications is determined by crystal and 
porous structure, surface design, and electronic character-
istics of SnO2. The main disadvantages of tin dioxide as a 
photocatalyst are (i) large band gap (3.4–4.0 eV [1, 4, 6]); 
as a result, this material is active only under UV irradia-
tion; (ii) preferably, a microporous structure, whereby a large 
portion of the surface is inaccessible for large molecules 
of organic substrates and diffusion difficulties slow down 
the photocatalytic transformations. There are several ways 
to overcome these shortcomings. Among them, introduc-
tion of intrinsic (structural) and extrinsic (dopant) defects in 
“white” oxides results in the band gap narrowing and mani-
festation of activity under visible irradiation [7]. The use of 
mechano- and sonochemical processes for these purposes 
simultaneously optimizes the porosity, creating a meso-
macroporous structure (the most suitable structure for most 
adsorption and catalytic processes) as it was demonstrated 
for different perovskites and SnO2 [4, 5]. Another approach 
can be the deposition of an active phase onto the surface 
of mesoporous supports as it was shown for TiO2 [8–10], 
 BaTiO3 [11], and heteropolycompounds [12, 13]. However, 
this method practically was not investigated for the prepara-
tion of supported photocatalysts based on tin dioxide. The 
exceptions are the papers on photodegradation of rhodamine 
B (RhB) under UV irradiation using tin dioxide supported 
on porcine bone and SBA-15 [14, 15]. In the first case, it 
has been showed that about 97.3% of RhB can be decom-
posed (based on bleaching of RhB solution degree) when the 
composition SnO2/porcine bone as a photocatalyst was used, 
while only 51.5% of RhB can be degraded using pure SnO2 
nanoparticles. In the second case, the rate constant of RhB 
photocatalytic degradation is 3.8 × 10−5 s−1; in the third case, 
the rate constant achieves value of 1.5 × 10−4 s−1. Therefore, 
the possibility of pollutants photodegradation under visible 
irradiation using SnO2 embedded into structure of support, 
as it was done for titania [8–10] and mixed oxides [11, 16], 
was not studied.
At the same time, it is known that deposition of tin diox-
ide onto silica promotes to improvement of its catalytic per-
formance in acid-catalyzed and oxidation processes [17–21]. 
Several methods for deposition of SnO2 on porous supports 
are known from the literature: sol–gel [22], polymeric [20], 
 * S. Khalameida 
 svkhal@ukr.net
1 Institute for Sorption and Problems of Endoecology, NAS 
of Ukraine, Naumova Street 13, Kiev 03164, Ukraine
2 L.V. Pysarzhevsky Institute of Physical Chemistry, NAS 
of Ukraine, Nauky Ave. 31, Kiev 03028, Ukraine
http://crossmark.crossref.org/dialog/?doi=10.1007/s10973-019-08896-0&domain=pdf
2132 S. Khalameida et al.
1 3
template [21], and impregnation [17]. We used the simplest 
of them, namely impregnation of commercial silica gel and 
subsequent precipitation or thermolysis of prepared precur-
sors. Silica being a dielectric was chosen as a support.
The aim of this work is the study of crystal and porous 
structure, electronic characteristics of the supported SnO2/
SiO2 compositions of different SnO2 content and influence 
of these physicochemical properties on their photocatalytic 
activity under visible irradiation.
Experimental
Reagents and materials
Silica gel KSKG (China) was used as a support. In order to 
increase the mesopore size, it was also subjected to hydro-
thermal treatment (HTT) in a vapor phase at 150 °C for 3 h 
[23, 24]. Tin tetrachloride SnCl4·5H2O was used as a source 
of tin, aqueous ammonia solution—as a precipitant.
Preparation of supported SnO2/SiO2 compositions
Samples of SnO2/SiO2-supported compositions with differ-
ent tin dioxide content, designated as XSn, where X = 1, 3, 5, 
7 and 10, (the number in the sample designation corresponds 
to SnO2 content in mass%), were synthesized by deposition 
of tin dioxide on silica gel granules using incipient wetness 
impregnation. For this purpose, a fraction (0.5–2 mm) of 
silica gel was impregnated with an appropriate amount of 
 SnCl4·5H2O aqueous solution, held for 1 h, then treated 
with 1 M NH4OH solution to form an insoluble SnO2, then 
dried at 110 °C and calcined in air at 450 and 550 °C (2 h). 
This is precipitation method (designation of samples − XSn-
prec). In another procedure, the stage of precipitation using 
 NH4OH was absent. This is thermolysis method (designation 
of samples − XSn-therm). For the purpose of activation, a 
precipitated sample containing 5% SnO2 was also milled in 
air for 0.5 h at 300 rpm (sample 5Sn-mill). For comparison, 
the supported sample was also prepared by direct dry milling 
of mixture of 5% SnO2 and silica gel under the same condi-
tions (sample 5Sn-mill-mix). Milling was carried out using 
a planetary ball mill Pulverisette-7, premium line (Fritsch 
Gmbh) with a vessel of silicon nitride. Twenty-five balls 
from S3N4 with a 10 mm diameter (total ball mass − 40 g) 
were used as working bodies.
Physicochemical measurements
The crystal structure of the supported samples was studied 
by means of X-ray powder diffraction (XRD) using Philips 
PW 1830 diffractometer with CuKα radiation. The curves 
of DTA and TG were recorded using the Derivatograph-C 
apparatus (F. Paulik, J. Paulik, L. Erdey) in the temperature 
range of 20–1000 °C at a heating rate of 10° min−1. The ini-
tial sample mass was about 200 mg, and the sensitivity was 
50 mg. Raman spectra were recorded using spectrograph 
of Renishaw system (Ar laser, 514 nm). Strength (H0) and 
acid sites concentration in SnO2/SiO2 catalysts were deter-
mined using an indicator method and the back titration of 
n-butylamine by hydrochloric acid in the presence of bro-
mothymol blue, respectively, as well as using temperature-
programmed desorption (TPD) of ammonia [19]. The porous 
structure of the initial silica gel and supported samples was 
studied using nitrogen adsorption–desorption technique. The 
isotherms were obtained using an automatic gas adsorption 
analyzer ASAP 2405 N (“Micromeritics Instrument Corp”) 
after outgassing the catalysts at 150 °C for 2 h. The specific 
surface area S, mesopore volume Vme, and micropore vol-
ume Vmi were calculated from these isotherms using BET, 
BJH, and t-plot methods, respectively. The total pore volume 
VΣ was determined by impregnation of the samples, which 
were preliminarily driedat 150 °C, with liquid water (so-
called incipient wetness method [25]). Macropore volume 
Vma was calculated as the difference between VΣ and sorp-
tion pore volume Vs. The latter one was determined from 
the isotherms at nitrogen relative pressure close to 1.0. 
The mesopore size dme was calculated from the curves of 
pore size distribution (PSD) plotted using the desorption 
branches of isotherms. Diffuse reflectance UV–Vis spec-
tra of the powders were registered on Lambda 35 UV–Vis 
spectrometer (PerkinElmer Instruments). The band gap was 
determined using Planks formula.
Photocatalytic testing
Photocatalytic degradation was performed in a glass reac-
tor under visible irradiation. LED Cool daylight lamp, 
Philips (100 W) possessing emission spectra exclusively 
in the visible range with a broad maximum in the region 
of 500–700 nm and a local maximum around 440 nm, 
was used as an irradiation source. The dye rhodamine 
B (RhB) in the form of 1.5 × 10−5 mol L−1 solution was 
used as a pollutant [16]. The main absorption bands λmax 
in the spectra of substrate is 553 nm. The catalyst dose 
was 1 g L−1 (80 mg of catalysts and 80 mL of solution). 
Duration of dark adsorption to establish of equilibrium 
was 60 min. The initial solution and solutions after dye 
adsorption and degradation for 30–600 min were analyzed 
spectrophotometrically at λmax (Lambda 35, Perkin Elmer 
Instruments) after centrifugation of the reaction mixture 
(10 min at 8000 rpm). The calculation of photodegrada-
tion rate Kd was based on the temporal changes of the dye 
concentration after reaching the adsorption equilibrium. 
The total organic carbon (TOC), which is a measure of dye 
2133Physicochemical and photocatalytic properties of tin dioxide supported onto silica gel 
1 3
mineralization [26], for selected solutions, was determined 
using a Shimadzu TOC analyzer (model 5050A).
Results and discussion
Thermogravimetric measurements
In order to determine the temperature of thermodestruc-
tion of SnCl4·5H2O resulting in tin dioxide formation, 
the DTA–TG curves for bulk salt as well as for compo-
sitions precursors prepared on its basis were registered. 
Obviously, SnCl4·5H2O is decomposed in air according 
to Eq. (1):
Theoretical mass loss for this process is 54.1% w/w. 
Experimental value of mass loss calculated from DTA–TG 
curves of bulk SnCl4·5H2O is 55.5% w/w. At the same 
time, this process takes place in a wide temperature 
range—from 100 to 450 °C (Fig. 1a). It can be divided into 
two stages: (i) sharp stage at 100–200 °C with an intensive 
endoeffect at about 150 °C when mass loss is 47.9% w/w 
(crystallization water) and (ii) slow stage at 200–450 °C 
when mass loss is 7.6% w/w. It should be noted that simi-
lar curves were obtained for hydrous copper, cobalt, and 
manganese chlorides [27].
On the other hand, there is an endoeffect at 20–200 °C 
with a maximum at 115  °C, which is accompanied by 
release of water from the pores, for the initial porous silica 
and supported samples, namely their precursors (Fig. 1b, c, 
respectively). These endoeffects are characteristic for porous 
materials including supported compositions based on porous 
carriers [11–13, 16, 28, 29]. Therefore, the first stage of 
 SnCl4·5H2O decomposition for supported precursors is over-
lapped with removal of this physically bound water from 
the pores of silica gel. At the same time, removal of surface 
OH groups additionally occurs on the second stage which 
is the characteristic for silica [23]. This value is 0.72% w/w 
(Table 1).
Therefore, mass loss in the range of 200–450 °C for 
precursors is determined by the tin chloride decomposi-
tion process and the removal of hydroxyl groups. The first 
component depends on the precursor composition, i.e., 
content of SnCl4, and the second one is approximately 
constant—about 0.72% w/w:
where X—SnO2 content in composition.
It can be seen that Δm200–450_therm values, determined 
from the experimental data (Table  1, column 6), are 
(1)SnCl4 ⋅ 5H2O = SnO2 + 4HCl + 3H2O
(2)
Δm200−450_therm = X ⋅ 7.6∕100 + (1 − X) ⋅ 0.72∕100 (%w/w),
well-consistent with those ones calculated by the formula 
(2).
Precursors, prepared with a precipitation stage, contain 
tin dioxide and ammonium chloride which are formed in the 
pores of silica gel according to the equation:
In line with it, mass loss in the range of 200–450 °C for 
these precursors is determined by the ammonium chloride 
sublimation [30] and the removal of hydroxyl groups both 
for silica gel and precipitated tin dioxide [1, 4, 5]. The 
 NH4Cl content in the products of the reaction (3) is about 
58.6% w/w and mass loss in the range of 200–450 °C for 
precipitated SnO2 is 4.86% [4]. Therefore, total mass loss 
in the range of 200–450 °C for the precursors prepared via 
precipitation can be calculated as follows:
The experimental data presented in column 7 of Table 1 
are in a good agreement with those ones calculated by 
the formulas (2) and (4).
Based on the results of thermogravimetric measure-
ments, the first calcination temperature of precursors was 
determined as 450 °C. The second calcination temperature 
of 550 °C was chosen since content of surface OH groups 
was reduced by 11% compared with the samples calcined at 
450 °C for silica gel as shown in [21] and by 8% for tin diox-
ide xerogel [4] according to the data of DTA–TG. Therefore, 
use of the samples calcined at these temperatures makes 
it possible to establish the influence of the content of OH 
groups on the photocatalytic activity. It should also be noted 
that the indicated values of temperature (450 and 550 °C) 
correspond to optimal conditions for regeneration of oxide 
catalysts using oxygen and air, respectively [31].
Crystal structure
Crystal structure of tin dioxide in composition is formed 
during calcinations of precursors. XRD patterns for some 
supported samples as well as for pure SnO2 calcined at 
550 °C are depicted in Fig. 2. As can be seen, positions 
of the diffraction peaks corresponding to the planes (110), 
(101), (200), and (211) are attributed to tetragonal modifica-
tion of cassiterite/rutile (JCPDS N 41-1445). The intensity 
of all the peaks is predictably increased with an increase in 
the content of tin dioxide. The reflexes also differ in width, 
which is a measure of crystallinity (crystallite size Dhkl), 
and I110/I101 ratio. Since reflex with maximal intensity (110) 
is overlapped with halo characteristic for amorphous silica, 
calculation of crystallites size was performed using reflex 
attributed to the plane (101) (D101). These parameters are 
determined by SnO2 content in composition and calcinations 
(3)SnCl4 + 4NH3 + 2H2O = SnO2 + 4NH4Cl
(4)
Δm200−450_prec = X ⋅ 58.6∕100 + X ⋅ 4.86∕100 + (1 − X) ⋅ 0.72∕100
2134 S. Khalameida et al.
1 3
Fig. 1 a DTA, TG, DTG curves 
for SnCl4·5H2O. b DTA, TG, 
DTG curves for the initial silica 
gel. c DTA, TG, DTG curves 
for a precursor containing 10% 
 SnCl4
Mass loss/%
0
12
24
36
48
60
200 400
Temperature/°C
600 800
TG
DTG
DTG/mg min–1
DTG/mg min–1
DTG/mg min–1
DTA/µV mg–1
DTA/µV mg–1
DTA/µV mg–1
DTA
0.20.6
0.5
0.4
0.3
0.2
0.1
0.0
– 0.1
0.0
– 0.2
– 0.4
– 0.6
– 0.8
– 1.0
– 1.2
Mass loss/%
Temperature/°C
Mass loss/%
Temperature/°C
0.0
– 0.1
– 0.2
0
1
2
3
4
5
6
200 400 600 800
0.0
– 0.1
– 0.2
0
1
2
3
4
5
6
7
200 400 600 800
TG
DTG
DTA
TG
DTG
DTA
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.50
(a)
(b)
(c)
2135Physicochemical and photocatalytic properties of tin dioxide supported onto silica gel 
1 3
temperature which is also quite expected (Table 2). Thereby, 
 D101 value is increased as a result of enrichment of the com-
position with tin dioxide and an elevation in the calcinations 
temperature. On the other hand, calculated crystallite size 
for the supported samples is 2–3 times smaller than for bulk 
 SnO2 calcined at 450–550°C. It indicates well-dispersion 
of the deposited phase on the support surface as it was pre-
viously observed for supported titania [8–10] as well as for 
mixed oxide compositions [11, 32]. 
A feature of the supported samples also is an increase 
in I110/I101 value (Table 2, column 5) compared to that for 
pure SnO2 prepared under the same conditions as well as 
described in the literature [1, 6, 33]. It can also be seen that 
this value is larger for the samples prepared via precipitation 
and decreases when calcinations temperature is elevated. 
This parameter characterizes the surface orientation of 
defined planes which can be very important for catalytic 
processes [34, 35] including photocatalytic transformation 
[36]. Particularly, the  ratio of different crystallographic 
planes (surface content) and, as a result, catalytic proper-
ties, could be changed by various types of treatment for 
vanadium–molybdenum oxides [35, 37]. These are so-called 
structural-sensitive reactions [1, 36].
Raman spectra confirm low crystallinity for deposited 
 SnO2 phase which can be seen from the comparison of the 
spectra registered for bulk and supported tin dioxide (Fig. 3) 
As can be seen (Fig. 3, spectra b, c), there are low-inten-
sity bands centered at 795 and 590 cm−1 which attributed 
to SnO2 nanoparticles with a size less than 10 nm [17, 38, 
39]. Besides, broad bands at 300–550 cm−1, which can be a 
Table 1 Results of 
thermogravimetric 
measurements for some SnO2/
SiO2 samples
N Synthesis conditions Temperature of effect 
from DTG curve/°C
Δm20–200/% w/w Δm200–450/% 
w/w
Δm450–550/% 
w/w
1 Initial silica gel 113 3.71 0.72 0.19
2 3Sn without precipitation 110 3.88 0.93 0.20
3 5Sn without precipitation 115 3.60 1.13 0.21
4 5Sn with precipitation 118 4.11 3.94 0.26
5 7Sn without precipitation 113 3.69 1.31 0.22
6 10Sn without precipitation 118 3.53 1.48 0.24
7 10Sn with precipitation 121 4.55 6.88 0.29
8 Precipitated SnO2 128 13.01 4.86 0.48
1200
900
600
300
0
3300
2200
1100
0
3300
2200
1100
0
3300
2200
1100
0
17700
11800
5900
0
10 15 20 25 30 35 40 45 50 55 60
a
b
c
d
e
110
2θ/°
101
In
te
ns
ity
/a
.u
.
Fig. 2 XRD patterns for the supported samples after calcinations at 
450 °C: 3Sn_prec (a), 5Sn_therm (b), 5Sn_prec (c), 10 Sn_prec (d), 
bulk precipitated SnO2 (e)
Table 2 Some parameters of crystal structure
Sample Method of prepara-
tion
Temperature/°C D101/nm I110/I101
3Sn Precipitation 450 5.0 1.69
550 5.8 1.55
5Sn Precipitation 450 6.0 1.88
550 7.1 1.70
Thermolysis 450 7.3 1.58
550 10.0 1.50
7Sn Precipitation 450 7.5 1.55
550 8.8 1.45
10Sn Precipitation 450 10.4 1.52
550 11.0 1.40
Thermolysis 550 11.2 1.34
100Sn Precipitation 450 12.0 1.05
550 15.6 1.11
2136 S. Khalameida et al.
1 3
superposition of several bands characteristic for tin dioxide 
[39], are presented in Fig. 3 (spectra b and c). Similar spectra 
were also obtained for samples containing 5–10% of SnO2 
incorporated into structure of dealuminated zeolite ß [18]. It 
should be noted that there are no bands for amorphous silica 
in this range [40].
Porous structure
Parameters of porous structure for initial silica gel and 
supported samples were calculated from nitrogen adsorp-
tion–desorption isotherms, examples of which are shown in 
Fig. 4. All of them belong to type IV according to IUPAC 
classification which is characteristic for mesoporous materi-
als. The curves of pore size distribution PSD (inset of Fig. 4) 
also indicate it.
Thus, initial silica gel contains mesopores with a size 
in the range of 2–14  nm and maximum on PSD curve 
about 7.8 nm but does not contain micro- and macropores 
(Table 3). Deposition of tin dioxide on siliceous surface 
predictably leads to some decrease in the specific surface 
area, total pore volume and mesopore volume but their size 
remains almost the same (inset of Fig. 4, Table 3, columns 
7). Silica gel subjected to HTT has a smaller specific sur-
face area but larger mesopores, namely 9.8 nm. Therefore, 
the supported sample based on the hydrothermally treated 
silica gel also has a smaller specific surface area and larger 
mesopores. Maximum reduction in the specific surface area 
4000
3000
2000
1000
0
750
500
250
0
1000
750
500
250
0 500 1000
Raman shift/cm–1
1500 2000
0
a
In
te
ns
ity
/a
.u
.
b
c
Fig. 3 Raman spectra for bulk tin dioxide (a) and supported samples 
containing 5 (b) and 10% (c) of SnO2
Fig. 4 Nitrogen adsorption–
desorption isotherms and PSD 
curves for the initial silica gel 
and some supported samples 700
a/
cc
 g
–1
dv
/d
r
600
500
400
300
200
100
0
0.0 0.2 0.4 0.6 0.8
P/P0
1.0
0 5 10 15
r /nm
20
0.035
0.030
0.025
0.020
0.015
0.010
0.005
0.000
Initial silica gel
1Sn-prec
5Sn-prec
5Sn-mill
2137Physicochemical and photocatalytic properties of tin dioxide supported onto silica gel 
1 3
and pore volume is observed for the milled sample 5Sn-
mill (Fig. 4, Table 3, column 4) which is consistent with the 
results obtained for a milled silica gel of different porous 
structure [23, 41].
UV–Vis spectra
Diffuse reflectance UV–Vis spectra for some supported 
samples with different SnO2 content are presented in Fig. 5. 
One can see that they differ in the position of the absorp-
tion edge λ and the magnitude of absorption in the visible 
region. It is important that significant redshift of absorption 
Table 3 Parameters of porous 
structure of supported samples
Sample Method of preparation Temperature/°C S/m2 g−1 VΣ/cm3 g−1 Vme/cm3 g−1 dme/nm
SiO2 – – 371 0.97 0.98 7.8
1Sn Precipitation 450 365 0.92 0.92 7.8
Thermolysis 450 367 0.93 0.92 7.8
3Sn Thermolysis 450 362 0.90 0.90 7.8
550 359 0.91 0.90 7.8
5Sn Thermolysis 450 357 0.93 0.92 7.9
550 355 0.94 0.93 7.9
Precipitation 450 360 0.91 0.91 7.8
Precipitation 550 354 0.90 0.89 7.8
5Sn-HTT Precipitation 450 320 0.90 0.89 9.5
5Sn-mill Precipitation – 198 0.50 0.48 7.9
5Sn-mill-mix Precipitation – 301 0.74 0.73 7.8
7Sn Thermolysis 450 350 0.90 0.89 8.1
550 345 0.89 0.89 8.0
10Sn Thermolysis 450 344 0.88 0.87 8.1
550 340 0.87 0.87 8.1
Fig. 5 UV–Vis spectra for some 
supported samples 1.0
0.5
0.4
1Sn-prec
10Sn-prec
5Sn-prec
5Sn-therm
0.3
0.2
350 400 450
K
 –
 M
 in
de
x
K
 –
 M
 in
de
x
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
200 300 400 500
Wavenumber/nm
Wavenumber/nm
2138 S. Khalameida et al.
1 3
edge is observed for the supported samples compared with 
bulk SnO2.
Thus, λ is 364–341 nm for bulk tin dioxide [4, 5], while 
its value is shifted toward 407–356 nm for the precipi-
tated samples containing 1–10% SnO2 (Table 4). It cor-
responds to narrowing the band gap Eg from 3.64 eV for 
bulk SnO2 [4, 5] to 3.05–3.48 eV for the supported sam-
ples (Table 4, columns 4, 5). Such an effect was earlier 
described for silica supported TiO2 photocatalysts [8, 9] 
and for SnO2–TiO2 solid solution embedded into SBA-15 
structure [42]. But it was not observed for deposited SnO2, 
as a rule [15, 21, 42]. Similar spectrum is given only in the 
paper [18] for sample containing 10% SnO2 incorporated 
into the structure of dealuminated ß zeolite. However, the 
authors do not discuss it. Moreover, co-precipitated (but 
not supported) SnO2–SiO2 samples prepared by a sol–gel 
method and additionally calcined at 800 °C showed red-
shift in UV–Vis spectra with an increase in SnO2 content 
from 1 to 10% [43].
It is noteworthy that observed redshift of absorption 
edge for the precipitated samples is significantly larger 
than for the samples prepared via thermolysis (Fig. 5, 
Table 4). An observed redshift effect can be associated 
with different surface orientations of deposited crystallites 
compared to crystallites in bulk SnO2 (Table 2, increase in 
I110/I101 ratio from 1.05–1.10 to 1.34–1.88). It is in a good 
agreement with the results described for TiO2 in [30]; 
UV–Vis spectroscopy measurements of anatase crystals 
with different surface orientations have revealed differ-ences in the band gap indicating the upward shift in the 
conduction band minimum for anatase (101) and (100) 
compared to (001) surfaces.
A feature of the spectrum for 5Sn-prec-450 is the pres-
ence of another absorption edge in the long-wavelength 
region—about 540 nm (selected fragment in Fig. 5). As a 
result, the occurrence of an additional level in the forbidden 
zone of SnO2 is possible. Similarly, a new metastable surface 
phase exhibits with much reduced band gap from that one of 
bulk TiO2 (about 2 eV) on the rutile TiO2 (011) surface [36].
Photocatalytic tests
It is well-known that the photocatalytic properties of semi-
conductors depend on their electronic characteristics, crystal 
and porous structure, specific surface area and degree of 
hydroxylation, and therefore, adsorption capacity toward 
the substrate [7, 26]. It is also natural that the first stage of 
Table 4 Electronic and photocatalytic properties of the supported samples
*n.d not done
N SnO2 content/% Preparation conditions λ/nm Eg/eV a/% Kd 105/s−1 Bleaching 
degree/%
1 1Sn Precipitation, 450 °C 392 3.16 40 5.6 84
2 3Sn Precipitation, 450 °C 399 3.11 45 7.2 88
3 5Sn Precipitation, 450 °C 407 3.05 56 9.1 92
4 5Sn Precipitation, 550 °C 388 3.20 40 7.0 84
5 5Sn Thermolysis, 450 °C 375 3.31 44 6.1 80
6 5Sn Thermolysis, 550 °C 365 3.40 37 5.1 76
7 5Sn Precipitation, 450 °C, SiO2 treated via HTT *n.d – 33 3.9 63
8 5Sn Precipitation, 450 °C MChT *n.d – 32 3.1 68
9 5Sn Precipitation, 450 °C + SiO2 MChT *n.d – 37 0.1 11
10 7Sn Precipitation, 450 °C 367 3.38 41 5.8 82
11 10Sn Precipitation, 450 °C 364 3.41 25 3.1 59
12 10Sn Thermolysis, 450 °C 356 3.48 36 2.0 44
13 100Sn Precipitation, 450 °C 341 3.64 30 – –
0.30
dV
H
C
l/d
T
0.25
0.20
0.15
0.10
0.05
0.00
0 100 200 300 400 500 600 700
1.0
T
C
D
 s
ig
na
l/a
.u
.
0.8
0.6
0.4
0.2
0.0
Temperature/°C
Fig. 6 NH3-TPD profile for the sample 5Sn_prec-450
2139Physicochemical and photocatalytic properties of tin dioxide supported onto silica gel 
1 3
catalysis is the adsorption of reagents on the catalyst surface. 
Based on the fact that the tested dye has a basic nature, it was 
important to evaluate the acidic properties of the photocata-
lyst surface. Using the indicator method, it was established 
that the supported samples have concentration of acid sites 
within 1.58–1.68 mmol g−1 or 4.3–4.6 μmol m−2. The value 
of Gammet function H0 is about − 3, i.e., acid sites are weak.
At the same time, ammonia TPD profile obtained for the 
sample 5Sn_prec-450 (Fig. 6) shows the value of acid sites 
concentration equal to 1.51 mmol g−1 which is close to the 
above indicated range. Temperature of the maximum is at 
172 °C which also corresponds to weak acid sites. It should 
be noted that similar results were obtained for SnO2–SiO2 
xerogels containing 3–9% w/w of tin dioxide [44], while 
content of acid sites for bulk SiO2 and SnO2 is 1.10 and 
0.38 mmol g−1 or 3.0 and 6.5 μmol m−2, respectively. As 
can be seen, the supported samples have close acidity val-
ues, but higher than the values based on the additivity rule. 
Therefore, the difference in RhB adsorption during dark 
stage a (%), determined as the ratio of optical density of 
RhB solution before and after dark stage, depends primarily 
on the value of the specific surface area and, possibly, on the 
surface content of (110) plane (I110/I101 ratio).
At the same time, band gap (namely < 3.26  eV) and 
absorption value in the region with wavelength > 380 nm for 
the photocatalyst determine its activity under visible irradia-
tion [7]. As shown in Table 4, some of the prepared samples 
(namely NN 1-4) meet these conditions. Consequently, the 
appearance of an electron–hole pair on the catalyst surface 
due to the action of photons of visible light is possible in this 
case. It results in initiation of a conventional photocatalytic 
process. As a result, these samples showed high activity in 
the process of RhB degradation. The latter is evidenced by 
the character of the changes in the RhB spectrum during 
its degradation in the presence of the samples of different 
activity (Fig. 7a, b). The similar spectra were also obtained 
for other photocatalysts. It should be noted that bulk pre-
cipitated SnO2 prepared under the same conditions does not 
show noticeable activity when it is exposed to visible light 
[4] which is associated with a high band gap value (3.41 eV) 
and minimal absorption in visible region for this sample. 
It is well-known that RhB photodegradation in the pres-
ence of tin dioxide can occur by two pathways [4–6]: as de-
ethylation process in a stepwise manner (with the formation 
of three intermediates from RhB to Rh110) or as a direct 
cleavage of the chromophore rings. A gradual blueshift of 
the band at 553 nm on the spectrum of the RhB solution is 
observed in the first case and the reduction in its intensity 
without shift takes place in the second case. As shown in 
Fig. 7a, b, mixed mechanism is realized in this case as it 
was described earlier for doped and milled SnO2 [4, 5]: (i) 
decrease of the intensity band at 553 nm occurs for 60 min 
which corresponds to direct degradation of RhB [16]; (ii) 
shift of this band toward 498–500 nm for 180 min which is 
accompanied by complete de-ethylation of RhB to Rh110; 
(iii) decrease in intensity of the band at 498–500 nm which 
is associated with degradation of Rh110 with cleavage of the 
chromophore rings (for duration > 180 min).
The photocatalytic tests showed that the degradation 
of RhB under visible irradiation (as dye bleaching) using 
the supported samples proceeds according to first-order 
kinetic equation (Fig.  8) with a correlation coefficient 
R2 = 0.93–0.99, which is agreed with literature data [4–6, 
16]. The photodegradation rate constants Kd were calculated 
from the slopes of the plots ln(D/D0) − τ (where D and D0 
are values of optical density of RhB solution after time τ 
and dark adsorption, respectively). One can see (Table 4) 
that photocatalytic activity, the measure of which is the Kd 
magnitude, for the precipitated samples is increased with 
an increase in SnO2 content up to 5% and decreased with a 
further increase in its content up to 10%. In general, it corre-
lates with the electronic characteristics of the photocatalysts: 
0.3
D
0.2
0.1
0.0
400 500 600
0.30
0.25
0.20
0.15
0.10
0.05
0.00
200 300 400 500
Wavenumber/nm
600 700
0
1800 s
3600 s
7200 s
10,800 s
18,000 s
27,000 s
36,000 s
0
1800 s
3600 s
7200 s
10,800 s
18,000 s
27,000 s
36,000 s
RhB initial
D
Wavenumber/nm
(a)
(b)
Fig. 7 a Spectra of RhB depending on degradation time in the pres-
ence of 5Sn_prec_450. b Spectra of RhB depending on degradation 
time in the presence of 3Sn_prec_450
2140 S. Khalameida et al.
1 3
the samples containing 1–5% SnO2 have Eg = 3.05–3.20 eV, 
i.e., less than 3.26 eV and absorption in visible region for 
them is 25–40%, while these parameters are 3.35–3.41 eV 
and 15–20%, respectively, for samples containing 7–10% 
 SnO2 (Table 4). Therefore, generation of an electron–hole 
pair is possible in the first case. Moreover, the number of 
active sites should be increased with an increase in SnO2 
content. In the second case, the samples also exhibit suffi-
cient photocatalytic activity. The latter can be explained as 
follows. The spectrum of RhB absorption is overlapped in a 
wide region with the emission spectrum of a lamp—illumi-
nation source; the maxima are located at 553 and 565 nm, 
respectively. Therefore, the absorption of visible light and 
the direct excitation of RhB molecules are very likely. Sub-
sequent injection of an electron from the excited RhB mol-
ecules into the conduction band of a photocatalyst occurs. It 
is so-called photosensitization contributing the initiation of 
photocatalytic process [26, 45]. Obviously, this mechanism 
determines the photocatalytic activity of the samples pos-
sessing Eg > 3.26 eV, although it can also contribute to the 
activityof the samples with Eg < 3.26 eV.
For the most active sample, namely containing 5% SnO2, 
the influence of preparation conditions on the photocatalytic 
activity was studied. One can see that the samples prepared 
via thermolysis have lower activity, and it is directly related 
to the larger Eg value and lower absorption for visible irra-
diation (Table 4). An increase in calcinations temperature 
for the samples prepared via precipitation and thermolysis 
from 450 to 550 °C results in a slight decrease in activity. It 
can be explained by a decrease in concentration of the sur-
face OH groups which influence on photocatalytic processes. 
As mentioned above, their content according to TG data is 
reduced by approximately 10% in this temperature range.
It is also important to evaluate the effect of other phys-
icochemical characteristics on photocatalytic properties. 
Particularly, it is difficult to associate an increase in crys-
tallite size D101, which is observed with increasing SnO2 
content (Tables 2, 4), with activity. Here, it is important to 
have an actual increase in the content of the active phase, 
as established for 5.8–17.7% of SnO2 embedded into SBA-
15 under UV irradiation [15]. At the same time, surface 
exposition of certain crystallographic planes can affect the 
dye adsorption and through it on photocatalytic activity. On 
the contrary, the dependence of the activity on the specific 
surface area was precisely established earlier [1, 7]. At the 
same time, the tested samples have close S values (Table 3). 
In order to reduce the specific surface area of the support, 
and therefore the supported sample, silica gel was subjected 
to HTT. Photocatalyst prepared on the basis of a hydrother-
mally treated support showed significantly lower activity 
(Table 4, sample 7).
Finally, an attempt to activate the most effective cata-
lyst (sample 3) by milling, as was done for bulk SnO2 [5], 
was made. As shown in Table 4 (sample 8), positive effect 
was not achieved. Furthermore, the samples prepared via 
milling of tin dioxide and silica gel mixture (without pre-
liminary deposition of SnO2 on silica gel) was practically 
inactive, although the adsorption of RhB was quite large 
(sample 9). It can be explained as follows. Under milling, 
 SnO2 (semiconductor) is partially (sample 8) or completely 
(sample 9) coated by a silica layer (dielectric). As a result, 
the active sites of SnO2 are blocked. Taking into account a 
large excess of silica in relation to SnO2, as well as the dif-
ference in the hardness of the components (Mohs hardness 
of amorphous silica and SnO2 is 5 and 6.5, respectively) 
[46, 47], “smearing” of amorphous silica on SnO2 nano-
crystallites is possible. Similar results were described when 
“core–shell” particles were formed during dry milling of 
cerium and molybdenum oxides mixtures [48].
As shown in Table 4 (column 8) bleaching degree of RhB 
under visible irradiation for the most active sample reaches 
88–92% which is comparable with ones obtained in [14] 
for the same dye using the SnO2/porcine bone photocatalyst 
but under UV irradiation. At the same time, the mineraliza-
tion degree of a dye is even more important indicator for 
evaluating of the photocatalyst efficiency [26]. This param-
eter, calculated as the degree of total organic carbon (TOC) 
reduction, is 40 and 75% for sample containing 5% SnO2 
calcined at 450 °C and prepared via thermolysis and pre-
cipitation, respectively.
Conclusions
Using thermogravimetric analysis, it has been established 
that hydrous tin tetrachloride is transformed into tin dioxide 
in silica gel pores at 450 °C. The choice of the temperature 
of the precursor transformation into the oxide composition 
0.5
In
/D
/D
0
0.0
– 0.5
– 1.0
– 1.5
– 2.0
– 2.5
– 3.0
– 3.5
– 4.0
0 5000 10000
τ /s
15,000 20,000 25,000 30,000 35,000 40,000
SnO2 bulk
1Sn/SiO2
5Sn/SiO2
10Sn/SiO2
Fig. 8 Kinetic curves of RhB degradation for some tested samples
2141Physicochemical and photocatalytic properties of tin dioxide supported onto silica gel 
1 3
is based on these results. Also, it has been estimated the 
degree of surface dehydroxylation within the range of 
450–550 °C. Deposition of 1–10% tin dioxide onto silica 
gel contributes to its dispersion on the surface; crystallite 
size of SnO2 is decreased from 12 nm for a bulk sample to 
5–10 nm (depending on SnO2 content) for the supported 
samples. Besides, surface re-orientation of the crystallites 
occurs: content of (110) plane, expressed as I110/I101 ratio, 
is increased by 45–80%. Moreover, narrowing the band gap 
from 3.64 eV for bulk SnO2 to 3.05–3.48 eV for the samples 
containing 1–10% SnO2 is observed. As a result, the sup-
ported samples, in contrast to the bulk SnO2, exhibit photo-
catalytic activity under visible irradiation. The precipitated 
samples are more effective compared with the samples pre-
pared by thermolysis. An increase in calcinations tempera-
ture decreases the photocatalytic activity due to a reduction 
in the specific surface area and surface dehydroxylation. 
The precipitated sample with 5% of tin dioxide calcined at 
450 °C, which has I110/I101 = 1.88 and band gap 3.05 eV, 
possesses maximal activity.
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https://doi.org/10.1002/masy.200850519
	Physicochemical and photocatalytic properties of tin dioxide supported onto silica gel
	Abstract
	Introduction
	Experimental
	Reagents and materials
	Preparation of supported SnO2SiO2 compositions
	Physicochemical measurements
	Photocatalytic testing
	Results and discussion
	Thermogravimetric measurements
	Crystal structure
	Porous structure
	UV–Vis spectra
	Photocatalytic tests
	Conclusions
	References