Journal of Environmental Protection, 2010, 1, 302-313
doi:10.4236/jep.2010.13036 Published Online September 2010 (http://www.SciRP.org/journal/jep)
Sol-Gel Materials with Pesticide Delivery
Properties
Malina Raileanu1*, Ligia Todan1, Maria Crisan1, Ana Braileanu1, Adriana Rusu1, Corina Bradu2,
Adrian Carpov3, Maria Zaharescu1
1Ilie Murgulescu Institute of Physical Chemistry, Romanian Academy, Bucharest, Romania; 2Faculty of Chemistry, Organic Chemis-
try Department, University of Bucharest, Bucharest, Romania; 3Petru Poni Institute of Macromolecular Chemistry, Iasi, Romania.
Received March 26th, 2010; revised April 20th, 2010; accepted April 25th, 2010.
ABSTRACT
Pesticides are widely used in agricu lture, although they may create haza rds both to humans and to the environment. In
order to reduce the harmful effects of their administration, there has been made a great effort to find solutions. The
porous sol-gel silica materials which are able to entrap different organic molecules represent new studied controlled
release carriers. The aim of the present work was to prepare and characterize sol-gel composites based on trichlorfon
as organophosp horous pesticide embedded in silica matrices generated from three differen t SiO2 sources : tetraethylor-
thosilicate (TEO S ), colloida l silica (CS), and sodium silicate (SS). Similar samples to those containing only trichlorfon
have also been synthesised, in which α-, β-, and γ-cyclodextrin have been included in order to study the possibility of
improving the release of the pesticide from the silica matrices. The porous sol-gel silica materials generated from
TEOS and CS are able to entrap the trichlorfon and ensure an efficient delivery of the pesticide. In the absence of
cyclodextrins, better results are obtained in the case of TEOS precursor, compared to colloidal silica. The addition of
cyclodextrins in order to improve the release of the pesticide from the silica matrices was successful only in the case of
CS as SiO2 precursor. The best release of the pesticide was obtained with β-CD.
Keywords: Sol-Gel, Tetraethylorthosilicate, Colloidal Silica, Trichlorfon, Cyclodextrin
1. Introduction
Nowadays, agrochemicals play an important role in
making possible the continuous increase of food produc-
tion. On the other hand, a high level of chemicals could
become a da nger for humanity. Pesticides represent one of
the most im por tant ty pes of c h em ical s used i n a gric ulture.
They include a wide di versity of substances. Am ong them ,
the class of organophosphorous compounds (OPs) has
gained an enormous commercial success, due to their
properties of controlling moths, ants, cockroaches, ter-
mites, fruit flies and similar insects, fleas, locusts, cater-
pillars and ticks [1]. They are th e most frequently used in
many cultures, at various stages of cultivation, as common
insecticides, in order to control insect and arthropod pests
on vegetable crops together with the increase of crop
yields [2-8]. Among the organophosphorous pesticides,
trichlorfon [O,O-dimethyl-(2, 2, 2-trichloro-1-hydroxy
ethyl)-phosphonate] is one of the most popular, being ex-
tensively used in agriculture since 1952 as a broad spec-
trum insecticide [2,9-16]. One of the major problems of
agriculture which must be solved refers to the controlled
use of pesticides. The presence of the used pesticides in
the surface and ground waters [4,6,17,18] emphasises this
environmental issue. As a result of the increased aware-
ness and worry regarding the potential of pesticides to
have detrimental impacts on both human and ecosystem
health, there is a great interest in developing less persis-
tent but more selective pesticides. However, their use can
be too expensive because they require more frequent
application. Because of the high costs and the limitations
in what the design of new pesticides is concerned, the
industry and the researchers have decided not to fabricate
new pesticides, but to improve the delivery systems of the
current ones. An effective way is using the controlled
release alternative. The controlled release systems have
become more a nd more im portant d ue to their adva ntages:
they minimize pesticide residues available to the envi-

Sol-Gel Materials with Pesticide Delivery Properties 303
ronment, thus reducing the environmental hazards and
human toxicity, they increase the efficacy and the lon-
gevity of the pesticide and decrease the application costs,
allowing less frequent uses [17,19-22]. Hussain [21] di-
vides the controlled release formulations of pesticides into
four main types: polymer membrane reservoirs, matrices
containing physically-trapped pesticides, covalently-
bounded pesticides and coated pesticide granule systems.
Some examples are already mentioned in the literature
[8,22-25]. A s the property of t he sol-gel process to pre pare
inorganic-organic hybrids by embedding organic mole-
cules in the inorganic oxide matrix is a well known fact
[26-35], Böttcher et al. [20] have used the sol-gel matrix
as an alternative to biocide encapsulation. They prepared
sol-gel composite films with controlled release properties.
The aim of the present work was to prepare and char-
acterize sol-gel composites powders based on trichlorfon
as organophosphorous pesticide embedded in silica ma-
trices generated from three different SiO2 sources: tetra-
ethylorthosilicate-TEOS, colloidal silica-CS, and sodium
silicate-SS. Both routes of the sol-gel method (the al koxide
and the aqueous one) have been used. The aqueous route
selection was based both on economical and ecological
reasons: the aqueous SiO2 precursors are less expensive
than TEOS and the soil attack is almost inexistent in a
system in which the pesticide proceeds from an aqueous
medium. Because the ability of cyclodextrins to form
inclusion complexes with a wide variety of agricultural
chemicals is well known [36-42], the possibility of using
them in order to improve the release of the pesticide from
the silica matrices has been studied. A comparison be-
tween the performances of the prepared materials has
been made, in order to establish the most propitious re-
agents (e.g. silica precursor and type of cyclodextrin) and
synthesis conditions which could lead to the best results
from the point of view of the applicability.
2. Materials and Methods
2.1. Preparation of Samples
Composite samples, consisting of pesticide embedded in
silica gels (pest icide/SiO2 = 1/3 in weight), have been pre-
pared using both routes of the sol-gel method: the alkoxide
and the colloidal one. The pesticide was an organophos-
phorous one, trichlorfon respectively: O,O-dimethyl-(2, 2,
2-trichloro-1-hydroxy ethyl)-phosphonate (T), from Ji-
angsu Hongze Chemical and Industry Co., Ltd. The SiO2
precursors were: tetraethylorthosilicate (TEOS) from
Merck, colloidal silica Ludox SM-30 type (CS) from
Aldrich, and a sod ium silicate solution 26 wt.% SiO2 (SS)
from Merck, respectively. In the case of TEOS, the
ethanol (from Riedel de Haën) has been used as solvent.
The gelation of all prepared sol-gel materials was ac-
complished at neutral pH, which is also totally harmless
for the soil in case of application. The pH adjustment was
realized with a 25 wt.% HNO3 solution. The experiments
were made at the room temperature. All samples have
been prepared under continuous stirring, in a few steps.
First, the alkoxide was solv ed in the correspo nding quan-
tity of alcohol (the molar ratio of SiO2/ROH = 0.075/
0.515), respectively the colloidal silica and the sodium
silicate solutions have been diluted with water, in order
to ensure the same SiO2 concentration in all samples
(solutions “a”). Then, the aqueous solution of trichlorfon
(solution “b”) was added drop by drop to solution “a”,
resulting solution “c”. Its pH was checked and adjusted
to the value of 6. For each of the obtained composite
samples the corresponding SiO2 matrices have been pre-
pared, in the same experimental conditions but in the
absence of trichlorfon. In order to study the influence of
the presence of cyclodextrins over the release of th e pes-
ticide from the prepared materials, similar samples to
those containing only trichlorfon have been synthesised
at the same time, in which α-, β-, and γ-cyclodextrin (CD)
from Wacker-Chemie GMBH have been included. All
cyclodextrin types have been introduced in the reaction
mixture as aqueous solutions, simultaneously with the
trichlorfon, in the quantity imposed by the solubility limit.
The composition of the corresponding samples was: 19
wt.% T, 24 wt.% CD and 57 wt.% SiO2, respectively.
In the present work, a number of 15 gels have been
prepared. Their names were established depending on the
used SiO2 precursor, as follows: TEOS, CS, and SS (for
the silica matrices); TEOS + T, CS + T, and SS + T (for
the silica/trichlorfon composites); TEOS + T + CD (α-,
β-, or γ-), CS + T + CD (α-, β-, or γ-) and SS + T + CD
(α-, β-, or γ-), respectively (for those composites in
which both trichlorfon and cyclodextrin have been in-
cluded in the silica matrices).
2.2. Methods of Characterization
The structural characterization of the prepared samples
was accomplished by IR spectroscopy, using a FT-IR
NICOLET 6700 (400-4000 cm-1) spectrophotometer.
Their thermal behaviour was studied up to 800℃, usin g a
Mettler Toledo Star System TGA/SDTA851/LF 1600℃,
with a heating rate of 10 K min-1, dynamic air atmos-
phere, and a flow rate of 50 mL min-1.
The release of trichlorfon from the silica matrix was
investigated during a series of batch experiments. In
these tests, a quantity of sample corresponding to 100.0
mg trichlorfon (between 0.3863 g and 0.8803 g sample)
was contacted with 100 mL ultrapure water and continu-
ously mixed (150 rpm.) in a closed glass vessel at the
temperature of 21  1℃ using a thermostated shaker
(GFL 3033). Trichlorfon concentrations from the aque-

Sol-Gel Materials with Pesticide Delivery Properties 304
ous solutions were determined by High Performance
Liquid Chromatography (HPLC) technique, using a Var-
ian Pro Star chromatograph equipped with an UV-Vis
detector (λ = 200 nm). A column Inertsil ODS2 (25 cm ×
4.6 cm × 1/4") was used as stationary phase. The mobile
phase was a mixture of acetonitrile/water (1:1, v/v) with
a flow rate of 1 mL min-1.
3. Results and Discussion
In the experimental conditions mentioned above, 15 gels
have been obtained after gelation times of hours (for the
samples synthesized from TEOS as silica precursor),
days (for the samples obtained from CS), and minutes
(for the samples proceeding from SS), respectively. They
have been dried at room temperature and subjected to
characterization, as follows:
3.1. IR Spectroscopy
All the prepared samples, and the organic compounds
included in the sol-gel silica matrices (trichlorfon , α-, β-,
and γ-cyclodextrin) have been structurally characterized
using the IR spectroscopy. Figure 1 presents the IR spec-
tra of the sol-gel prepared pesticide-silica composites in
the absence of cyclodextrins in comparison with the cor-
responding spectra of the silica matrices that proceed
from three different precursors and with the trichlorfon
IR spectrum.
The IR spectra of the prepared samples were compared
to the trichlorfon IR spectrum in order to emphasize the
fact that, regardless of the SiO2 precursor, the pesticide
was embedded inside the sol-gel matrix. Some of its
characteristic vibration bands are absent from the spectra
of the composite samples. The assignments of the wave
number values from Figure 1 which refer to the silica
matrices proceeding from different precursors are pre-
sented in Table 1.
The characteristic vibration bands for a SiO2 gel could
be observed, no m at t e r of the used precursor.
Regarding the IR band frequencies of trichlorfon pre-
sented in Figure 1, they correspond to the following vi-
brations: OH stretching at 3384 cm-1, CH stretching be-
tween 2800 and 3000 cm-1, OH bending at 1638 cm-1,
CH deformation vibrations at 1461 and 1380 cm-1, PO
stretching at 1240 and 1203 cm-1, CO stretching at 1085
and 1041 cm-1, and C-Cl vibration between 850 and 550
cm-1.
From Figure 1 it can be concluded that the silica ma-
trix, no matter of its provenience, could be an excellent
carrier for trichlorfon as embedded organophosphorous
pesticide. Subsequent investigations (e.g. release tests)
will prove that these matrices are also able to release the
incorporated pesticide from their pores.
Figure 2 presents the comparison between the IR spec -
4000 3500 3000 2500 2000 1500 1000500
0.0
0.2
0.4
0.6
0.8
1.0
1.2
TEOS + T
2898
2860
2964 1380
1461
1638
12401041
1203
1085
3384
621
724
813 533
1638
1085
2353
3458
798 467
T
TEOS
Absorbance (a.u.)
Wavenumbers (cm-1)
4000 3500 3000 2500 2000 1500 1000500
0.2
0.4
0.6
0.8
1.0
1.2
2345
3458
1646
1381
1108
798
474
T
CS+T
CS
Absorbance (a.u.)
Wavenumbers (cm-1)
4000 35003000 25002000 15001000500
0.0
0.4
0.8
1.2
1.6
2.0
2.4
2360 1638 813
1093
1387
3472 474
T
SS+T
SS
Absorbance (a.u.)
Wavenumbers (cm-1)
Figure 1. IR spectra of trichlorfon, of the sol-gel pesticide-
silica composite samples and of the corresponding silica
matrices obtained from different precursors: TEOS, CS,
and SS, respectively.
tra of the pesticide-silica composites and those of the
corresponding samples in which cyclodextrins have also
been included. For the same silica matrix, all the spectra
of the samples with cyclodextrins are similar. For this

Sol-Gel Materials with Pesticide Delivery Properties 305
Table 1. IR band frequencies and their assignments for the
silica gels issued from different precursors (TEOS, CS and
SS, respectively).
SiO2 precursor Wavenumber [cm-1] Assignment
TEOS, CS 3458
SS 3472
Structural OH-
SS 2360
TEOS 2353
CS 2345
CO2 vib.
CS 1646
TEOS, SS 1638 δ HOH
SS 1387
CS 1381 NO3- vib.
CS 1108
SS 1093
TEOS 1085
νas Si-O-Si
SS 813
TEOS, CS 798 νsym Si-O-Si
CS, SS 474
TEOS 467 δ O-Si-O
reason only those containing γ-CD have been presented.
The IR spectrum of the γ-CD has also been included.
A very good correspondence between our data refer-
ring to the IR spectra of cyclodextrins and the literature
ones [43-46] has been obtained. The following IR vibra-
tion bands have been registered: OH stretching at 3370
cm-1, CH stretching at 2945 cm-1, the H bond vibration
band at 2366 cm-1, OH bending at 1660 cm-1, CH defor-
mation at 1478 and 1351 cm-1, CO stretching and OH
bending at 1190 cm-1, CO/CC stretching at 1115 and
1015 cm-1, and the pyranose ring vibration at 739 and
584 cm-1.
The literature data [47-49] recognize the limits of the
IR spectroscopy method regarding the structural investi-
gation of the inclusion compounds of the cyclodextrins.
The explanation is simple: the characteristic b ands of the
cyclodextrins represent an overwhelming part of the
complex. Therefore, they are hardly influenced by the
complex formation. Only slight alterations of the spec-
trum of the host could be observed due to the guest mole-
cules, expressed by shifted bands or altered intensities of
the IR signals. However, there are some situations in
which the cyclodextrins inclusion complexes formation
may be proved by the IR spectroscopy analysis [50]. In
the present study the identification of the inclusion com-
pounds eventually formed between trichlorfon and cyclo-
Figure 2. IR spectra of the sol-gel pesticide-silica composites
prepared from different SiO2 precursors, of the corre-
sponding samples in which γ-CD has be en add ed, and of the
γ-CD.
dextrins has become more difficult because of the silica
matrix presence.

Sol-Gel Materials with Pesticide Delivery Properties 306
3.2. Thermal Analysis
The use of the thermoanalytical techniques in order to
investigate the formation of the cyclodextrins inclusion
compounds is well recognized for three decades [41,42,
50,51].
All the prepared samples and the organic compounds
included in the sol-gel silica matrices: trichlorfon, α-, β-,
and γ-cyclodextrin, respectively, have been characterized
by thermal analysis. Table 2 and Figures 3-5 present the
obtained re sults.
In what the three types of cyclodextrins are concerned,
the obtained results presented in Table 1 are in agreement
with the literature data [41,47,50,52-54].
Because the registered derivatograms of the sol-gel
samples obtained with different cyclodextrins (α-, β-, and
γ-CD, respectively) are similar, Figures 3-5(c) present
only the experimental results obtained using γ-CD.
As seen in Figures 3-5, the nature of the silica matrix
has a significant influence over the thermal behavior of
the material. The trichlorfon elimination (which starts in
the pure co mpound at 196℃) is modified in the presence
of the matrix: in the case of the organic precursor TEOS,
it takes place at 409℃, in the case of the inorganic pre-
cursors, the corresponding temperatures are lower: 182℃
for the colloidal silica and 245℃, respectively, for the
sodium silicate. Regarding the elimination of trichlorfon
in the presence of cyclodextrins (α-, β-, and γ-CD), only
in the case of the matrix proceeded from TEOS, the
process takes place at temperatures (195-202℃) compa-
rable with those of the pure trichlorfon (196-258℃). In
the case of the inorganic SiO2 precursors (CS and SS,
respectively), the trichlorfon elimination starts at modi-
fied temperatures (156-164℃ for CS and 155-196℃ for
SS). The influence of the silica matrix on the thermal
behavior of the sol-gel prepared materials can also be
seen in the major modification of the temperatures cor-
responding to the combustion of cyclodextrins. No mat-
ter the type (α-, β-, or γ-CD), they are eliminated by
combustion from the samples at much lower tempera-
tures (α-CD: 305-330℃, β-CD: 295-311℃, and γ-CD:
310-335℃), compared to the temperatures of combustion
of the pure cyclodextrins which are around 500℃ (α-CD:
499℃, β-CD: 48 0℃, and γ-CD: 498℃).
It can be assumed that the shift of the decomposition
temperatures is due not only to the silica matrices but
also to the inclusion compounds formation. The supposi-
tion could be correct for all the sol-gel prepared samples
containing both trichlorfon and cyclodextrin, because the
melting step corresponding to the trichlorfon could not
be observed. In fact, the lack of the melting step of the
guest molecule from the derivatograms is considered to
be the proof of the inclusion compound formation [41,42,
Temperature/℃
Mass/%
(a)
Temperature/℃
Mass/%
(b)
Temperature/℃
Mass/%
(c)
Figure 3. Thermal behavior of the silica matrix obtained
from TEOS (a) and of the sol-gel samples prepared from
TEOS in the presence of T (b) and of both T and γ-CD (c).
50]. Therefore, it can be concluded that the thermal
analysis indicates that the pesticide molecules have in-

Sol-Gel Materials with Pesticide Delivery Properties 307
Temperature/℃
Mass/%
(a)
Temperature/℃
Mass/%
(b)
Temperature/℃
Mass/%
(c)
Figure 4. Thermal behavior of the silica matrix obtained
from CS (a) and of the sol-gel samples prepared from CS in
the presence of T (b) and of both T and γ-CD (c).
teracted with the cavity of the cyclodextrins host mole-
cules, forming the inclusion complexes. Some doubts still
Temperature/℃
Mass/%
(a)
Temperature/℃
Mass/%
(b)
Temperature/℃
Mass/%
(c)
Figure 5. Thermal behavior of the silica matrix obtained
from SS (a) and of the sol-gel samples prepared from SS in
the presence of T (b) and of both T and γ-CD (c).
exist, taking into account the fact that in the samples
prepared without cyclodextrins, the silica matrix (no

Sol-Gel Materials with Pesticide Delivery Properties 308
Table 2. Thermal behavior of the organic compounds used in the sol-gel materials preparation.
Included organic
compound (O C )
Range of
temperature
[℃]
Temperature of the
thermal effect [℃]Thermal effect Mass loss [%]
partial total Assignment
20-120 76 endothermic - Melting
T 120-230 196 endothermic 73.49 94.16 Decomposition
230-280 258 endothermic 10.27 Decomposition
280-800 10.40 Decomposition
20-140 73, 107 endothermic 9.94 Water elimination
α-CD 140-390 274 endothermic 68.24 99.28 Decomposition
390-800 499 exothermic 21.10 Combustion
20-130 102 endothermic 13.33 Water elimination
β-CD 130-250 endothermic - 100.18 Melting
250-390 268 endothermic 64.46 Decomposition
390-800 480, 532 exothermic 22.39 Combustion
20-130 88 endothermic 10.33 Water elimination
γ-CD 130-390 287 endothermic 70.55 101.10 Decomposition
390-800 362, 498 exothermic 20.22 Combustion
matter its provenience) seems to be a protection medium
for the trichlorfon which doesn’t melt when it is included.
In order to clarify this aspect and to evidence the
presence of the organic compounds (trichlorfon and cy-
clodextrins) inside the prepared sol-gel silica matrices,
even after their heating up to 800℃, the mass losses cor-
responding to each of the samples have been calculated
from the thermal analysis results. They are presented in
Tables 3-5 for each of the silica precursors used for the
preparation of the silica matrix, in order to accomplish a
comparative study.
As it can be seen, except for the samples obtained from
sodium silicate as precursor of the silica matrix, in all
cases the values of “included organic compound” (IOC)
were higher than those corresponding to the “total mass
loss of the sample” (TML). This fact indicates that the
SiO2 matrices proceeded from TEOS and colloidal silica
respectively, are better hosts for the organic materials,
compared to that obtained from sodium silicate.
In order to establish both the role of the silica matrix
and of the presence of cyclodextrins on the release prop-
erties of the materials, the thermal analysis results need
supplementary information to elucidate the formation of
the inclusion compounds and the properties of the pre-
pared sol-gel samples. Thus, trichlorfon release tests have
been accomplished.
3.3. Trichlorfon Release Tests
The release of trichlorfon from the sol-gel silica matrices
in the absence and in the presence of cyclodextrins has
been assessed by high-performance liquid chromatogra-
phy (HPLC) measurements.
Relatively recent literature data [7] evidence the fact
that although the organophosphorous pesticides (OPPs)
are among the most widely employed world-wide, only a
limited number of representative compounds has been
separated by high-performance liquid chromatography
(HPLC). Regarding the gas chromatography (GC), the
number of publications is even much smaller. The ex-
planation could consist in the fact that the analyses are
still based on an empirical selection of the stationary
phase, and they depend practically on the experience
obtained on a case by case basis. Poor recoveries of
compounds such as trichlorfon and dichlorvos (a possible
trichlorfon transformation product) have been reported
[55]. Despite these informations, in our work trichlorfon
release tests have been accomplished, in order to estab-
lish that the sol-gel silica matrices could represent new
and relatively cheap pesticide carriers with delivery
properties. The trichlorfon concentrations have been de-
termined at intervals of 1, 2, 3, 6, 12 and 24 hours, re-
spectively. The experimental results are presented in
Figures 6-8.
Figure 6 refers to the sol-gel samples in which the
pesticide was embedded in the silica matrices obtained
from TEOS and from colloidal silica (CS) in the absence
of cyclodextrins. It can be seen that both silica matrices

Sol-Gel Materials with Pesticide Delivery Properties 309
Table 3. The mass loss referring to the included organic compounds of the sol-gel prepared materials, using TEOS as SiO2
precursor.
Type of included
organic compound
Quantity of included organic compound [m g ]
T CD IOC
*
Registered mass loss [mg]
TML** per stage
Range of
temperature [℃]
T 13.94 - 13.94 12.38 12.38 140-800
11.16 140-280
9.55 12.23 21.78 20.51 4.58 280-420
T + α-CD
4.77 420-800
4.63 130-280
6.40 8.19 14.59 9.13 2.49 280-420
T + β-CD
2.01 420-800
8.05 140-280
7.64 9.78 17.42 14.79 3.53 280-420
T + γ-CD
3.21 420-800
* IOC - The “included organic compound” refers only to the trichlorfon and cyclodextrin introduced in the sample by means of the chemical synthesis. It ex-
cludes the organic precursor (TEOS) and the alcohol used in the synthesis as solvent. **TML - The “total mass lo ss of the sample” is composed from: ( a) the
mass loss of trichlorfon and cyclodextrin, (b) the organic matter eliminated both from solvent and from the organic silica precursor (TEOS), (c) the mass loss of
the water p roceeded f rom the mois tures of t richlorfo n and cyclod extrins, (d ) the mass l oss of th e water proceed ed from th e inorganic s ilica pr ecursors (CS and
SS), and (e) the nitrate eliminated from the samples proceeded from SS.
Table 4. The mass loss referring to the included organic compounds of the sol-gel prepared materials, using CS as SiO2 pre-
cursor.
Type of included
organic compound
Quantity of included organic compound [m g ]
T CD IOC
Registered mass loss [mg]
TML per stage Range of temperature [℃]
10.92 - 10.92 8.44 5.97 120-220
T 2.47 220-800
5.28 120-190
10.86 13.89 24.75 20.91 7.04 190-260
3.62 260-370
T + α-CD
4.97 370-800
2.80 100-180
6.12 7.83 13.95 11.12 5.98 180-380
T + β-CD
2.34 380-800
4.89 120-190
9.87 12.64 22.51 19.53 6.34 190-260
3.46 260-370
T + γ-CD
4.84 370-800
obtained from different SiO2 precursors have included
the pesticide inside their pores, having the property to
release it in time. But the release properties in the case of
the sample obtained from TEOS precursor were better
than in the case of CS.
The corresponding release profile for the sample ob-
tained from sodium silicate as SiO2 precursor is absent
because the trichlorfon was not detected in this case.
Studying the degradation and the half-lives of some
organophosphorous pesticides (including trichlorfon and
dichlorvos) in water samples, Molina et al. [55] show
that in many cases transformation products form which

Sol-Gel Materials with Pesticide Delivery Properties 310
Table 5. The mass loss referring to the included organic compounds of the sol-gel prepared materials, using SS as SiO2 pre-
cursor.
Type of included
organic compound
Quantity of included organic compound [m g ]
T CD IOC
Registered mass loss [mg]
TML per stage Range of temperature [℃]
4.41 - 4.41 7.14 2.91 150-520
T 4.23 520-800
4.31 5.51 9.82 11.91 9.73 150-540
T + α-CD 2.18 540-800
2.70 3.46 6.16 7.59 5.90 100-370
T + β-CD 1.69 370-800
4.45 5.70 10.15 13.09 11.02 150-550
T + γ-CD 2.07 550-800
Figure 6. The release profiles of trichlorfon for the sol-gel
samples proceeding from TEOS and from CS as SiO2 pre-
cursors.
are more stable than the parent compounds. This could
explain the lack of the trichlorfon detection in the case of
the sol-gel samples proceeding from the sodium silicate
precursor. These samples have involved the greatest
water quantity for the synthesis. Moreover, the mentioned
samples were the only ones which presented the syneresis
phenomenon after their gelation. Shchipunov [34] men-
tions that the volume shrinkage (syneresis) of th e synthe-
sized gel after its preparation is of great importance. He
considers that the decrease in volume results in the dete-
rioration of the functional characteristics of the embed-
ded organic molecule. Th is deterioration is attributable to
the poor accessibility of substances owing to the diffu-
sion restriction in small pores and could also explain the
experimental chromatographic results obtained for the
samples proceeding from sodium silicate.
Figure 7. The release profiles of trichlorfon for the sol-gel
samples proceeding from TEOS in the absence of cyclodex-
trins and in the presence of α-, β-, and γ-CD, re spectively.
The addition of the cyclodextrins in the sol-gel mate-
rial formulations modifies their release properties, as it
can be seen in Figures 7 and 8.
Figure 7 shows that the addition of cyclodextrins (α-,
β-, and γ-CD) in the sol-gel composite formulation pro-
ceeding from TEOS as silica precursor hasn’t got a ben-
efic effect, because the released trichlorfon concentration
decreases in all cases.
Regarding the materials ob tained from colloidal silica,
the chromatographic results are presented in Figure 8.
Figure 8 shows another way of how cyclodextrin ad-
dition influences the release properties of the prepared
materials: no matter the type (α-, β- or γ-CD), their pres-
ence improves the release of the pesticide, increasing the
trichlorfon concentration. The best results have been ob-
tained in the case of β-CD addition.
From the presented data it can be concluded that the

Sol-Gel Materials with Pesticide Delivery Properties 311
Figure 8. The release profiles of trichlorfon for the sol-gel
samples proceeding from CS in the absence of cyclodextrins
and in the presence of α-, β-, and γ-CD, respectively.
porous sol-gel silica materials generated from different
SiO2 sources (except the sodium silicate) are able to en-
trap the organophosphorous pesticide (e.g. trichlorfon) in
order to create new controlled release carriers. In all
cases (except sample CS + T) the release of trichlorfo n in
time is slow and continuous during the studied interval of
time (1-24 hours). In the absence of cyclod extrins, better
results are obtained in the case of the materials obtained
from TEOS, compared to those proceeding from colloid-
dal silica as SiO2 precursor. The use of cyclodextrins in
order to improve the controlled release of the pesticide
from the silica matrices showed that only in the case of
CS precursor, the addition was successful.
4. Conclusions
Two series of sol-gel composite samples have been pre-
pared, using proper recipes. The first consists in trichlor-
fon as pesticide, embedded in silica gels generated from
different silica sources (TEOS, CS, and SS). The second
series is likewise synthesized with the first one. The only
difference between them is the presence of cyclodextrins
in the reaction mixtures.
The release properties of the prepared materials de-
pend both on the nature of the silica matrix and on the
presence or absence of cyclodextrin in the reaction mix-
ture. Thus, best results have been obtained for the sam-
ples proceeding from TEOS in the absence of cyclodex-
trins and for those obtained from CS, in the presence of
cyclodextrins.
The delivery properties of the sol-gel silica matrices
being confirmed, it can be concluded that they can be
considered as a new, ecological type of pesticides carri-
ers.
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