Novel biocide multifunctional materials based on mesoporous silicas modified by treatment with...

Novel biocide multifunctional materials basedon mesoporous silicas modified by treatmentwith guanidine polymersor mercaptopropyltrimethoxysilane: synthesis,characterization, and applications

Alexander Timin • Evgeniy Rumyantsev

Received: 10 May 2013 / Accepted: 30 July 2013

� Springer Science+Business Media Dordrecht 2013

Abstract Mesoporous thiol and guanidine-modified silicas with narrow pore size

distribution have been prepared by the sol–gel technique. The surface area of the

silicas was modified by treatment with 3-mercaptopropyltrimethoxysilane (MPT-

MS) and the guanidine polymers polyacrylate guanidine (PAG) and polymethac-

rylate guanidine (PMAG). The mesoporous silicas were characterized by nitrogen

adsorption–desorption analysis, Fourier transform infrared spectroscopy, and laser

diffraction. The materials obtained were used as adsorbents for removing heavy

metal ions (Cu2?) from water. It was found that modification of the silica surface by

treatment with MPTMS and guanidine polymers provides new sorbents with high

adsorption capacity compared with unmodified silica. The equilibrium adsorption

capacity for Cu2? ions on the surface of silicas modified by PAG and PMAG was 65

and 99.8 mg/g, respectively. Moreover, the modified silicas were tested for anti-

microbial activity, in vitro, against the Gram-positive prokaryote Staphylococcus

aureus and the Gram-negative prokaryote Escherichia coli. The results showed that

only silica modified with guanidine polymers had high antimicrobial activity. To

summarize, silica modified by treatment with guanidine polymers is more effective

than thiol-modified silica for removing heavy metal ions from aqueous solution and

can also be used as a biocide for surface sterilization.

Keywords Sol–gel � Mesoporous silicas � Adsorbent � Heavy metals �Surface area � Biocide � Antimicrobial activity

A. Timin (&) � E. Rumyantsev

Department of Inorganic Chemistry, Ivanovo State University of Chemistry

and Technology (ISUCT), 7, Sheremetevsky prosp., Ivanovo, Russian Federation

e-mail: [email protected]

123

Res Chem Intermed

DOI 10.1007/s11164-013-1358-y

Introduction

Mesoporous materials based on silicas have been used as adsorbents, catalysts, and

catalyst supports [1]. Many different adsorbents are used to solve different

environmental and pollution problems. However, many are not very effective

because they suffer from low removal capacity, low specific surface area, low

porosity, long equilibration time, and low selectivity [2].

Nanotechnology, because of its simplicity and efficiency, especially using sol–

gel methods, has been successfully applied to the synthesis of many different

adsorbents based on silica [3–6]. It is well known that active silica with a large

specific surface area is of the great importance for adsorption and ion exchange.

These properties are well studied, even though the shape of the silica surface is

basically unknown [7]. Template methods have been used to synthesize the silicas

with large pore size and pore volume [4]. Surfactants are usually used to produce the

pore size needed [4], but there are many problems after this synthetic procedure

because of the need to remove the template molecules. For this reason, modification

of the silica surface is one of the most promising ways of improving adsorption

(removal capacity, equilibration time, selectivity), structural, and morphological

(specific surface area, pore size, pore volume) properties. Two well-known

techniques are used to modify the silica surface:

– use of organosilanes with different functional groups, for example –NH2, –SH,

–COOH etc. [8, 9]; and

– immobilization of bioorganic molecules in the silica matrix during the sol–gel

process.

Such modification can change the morphology and physical properties of the

materials (specific surface area, pore, and volume size) [10, 11]. The most

convenient way of chemically modifying the surface is by simple immobilization

(or fixing) of the group on the surface by adsorption, electrostatic interaction,

hydrogen bond formation, or use of another type of interaction [12].

Biocide polymers are among the most interesting because they are harmless and

are highly selective compared with many other compounds. Moreover, they can be

used as templates and for surface modification, and in medicine for creation of

antimicrobial surfaces [13]. In fact, modification of the silica surface by these

polymers provides new highly effective materials with new physicochemical and

biological properties [6]. Examples of such biocide polymers are the guanidine

polymers polyacrylate guanidine (PAG) and polymethacrylate guanidine (PMAG)

(Fig. 1). These guanidine polymers can react with different compounds via

chemical and electrostatic interactions.

Sol–gel technology is used to synthesize hybrid materials modified with different

organo-chelating molecules. These materials have been successfully used for water

purification by removal of heavy metals [14]. There are, however, no studies on

application of silicas modified by guanidine polymers for selective removal of

copper ions from water and the effect of these polymers on the physical, chemical,

and antimicrobial properties of the modified silicas.

A. Timin, E. Rumyantsev

123

The purpose of the work discussed in this paper was to investigate the effect of

modification of silica on its structural and morphological properties, then

application of the materials for selective removal of Cu2? ions from water. The

antimicrobial activity of the silicas against Staphylococcus aureus and Escherichia

coli was also investigated. We focused on ways of modifying the silica surface and

compared the adsorption capacity of guanidine-modified silicas with that of

unmodified silica and thiol-modified silica. We present results from chemical,

physical, and biological study of materials prepared by use of the sol–gel technique.

Experimental

Materials and methods

3-Mercaptopropyltrimethoxysilane (MPTMS, 95 %) and tetraethyl orthosilicate

(TEOS, 99 %) were purchased from closed-company ‘‘Ecos-1’’. Cetyltrimethylam-

monium bromide (CTAB, 99 %) was purchased from Sigma–Aldrich. These

materials were used without further purification. Copper nitrate (ChemMed, Russia)

was used to prepare the metal ion solutions. Deionized water was used throughout

this work. The guanidine polymers PGA (M = 400,000) and PMAG (M = 500,000)

were synthesized at the department of macromolecular compounds of the

Kabardino-Balkar State University by N.M. Berbekova. They were recrystallized

from a water–acetone mixture then dried under vacuum at 60 �C.

Escherichia coli (E. coli) (ATTC 25922), Staphylococcus aureus (S. aureus), and

nutrient agar were provided by the Laboratory for Microbiology, Ivanovo State

Medical Academy, Russia.

H2C C

R

CO O

H HN

CH2N NH2 n

+

-

a

H2C C

R

CO O

H2N NH2C

NH2

n

+

-

b

H2C C

R

CO O

NH2

CH2N NH2

_

+

nc

R = H - polyacrylate guanidine (PAG)R = CH3 - polymethacrylate guanidine (PMAG)

Fig. 1 Structural formulas of guanidine polymers

Novel biocide multifunctional materials

123

Synthesis of unmodified silica

A typical procedure for synthesis of unmodified silica used TEOS and water in the

molar ratio 1:4 [15]. In a typical synthesis, 4 g TEOS was mixed with 1.668 g water

and vigorously stirred for 2 h. Aqueous ammonia solution (NH4OH, 5 %; 0.05 ml)

was then added every 25 min as basic catalyst. The final product was transferred to

a Petri dish for evaporation of the solvent at room temperature. The powder sample

obtained was dried under vacuum at 100 �C for 2 days.

Synthesis of silicas modified by guanidine polymers

Synthesis of silicas modified by PAG and PMAG was similar to the synthesis

described above. The molar ratio of TEOS/H2O used was the same as in the

synthesis described above. In a typical synthesis, 0.2 g PAG was dissolved in

1.667 g water during the sol–gel process to prepare solutions with the necessary

concentration of PAG. These solutions were then mixed with TEOS and vigorously

stirred for 2 h. The same synthetic route was used for silica modified by PMAG

(0.2 g). Aqueous ammonia solution (NH4OH, 5 %; 0.05 ml) was then added every

25 min as basic catalyst. The final product was transferred to a Petri dish for

evaporation of the solvent at room temperature. The powder samples obtained were

dried under vacuum at 100 �C for 2 days. The synthetic route is shown in Fig. 2.

Synthesis of thiol-modified silica

TEOS and MPTMS were used in 4:1 molar ratio. For this procedure 1.667 g water,

0.95 g MPTMS, and 10 g ethanol were mixed and stirred for 20 min. TEOS (4 g)

and CTAB (1 g) were then slowly added dropwise to the mixture. After addition of

TEOS was complete, the mixture was stirred for 2 h. Aqueous ammonia solution

(NH4OH, 5 %; 0.05 ml) was then added every 25 min as basic catalyst. CTAB was

used as surfactant to form the pore size needed inside the silica matrix. The final

product was transferred to a Petri dish for evaporation of the solvent at room

temperature. The powder sample obtained was extensively washed with hot water–

ethanol solution at 70 �C to remove CTAB from silica matrix then dried under

vacuum at 100 �C for 2 days.

Characterization of mesoporous adsorbents

The materials were characterized by use of conventional analytical techniques.

Nitrogen adsorption measurements were performed out at 78 K by use of a

Micromeritics ASAP 2020 analyzer (Norcross, GA, USA). The specific surface area

was calculated by use of the Brunauer–Emmett–Teller (BET) method [16] in the

range of relative pressure from 0.05 to 0.25. Before the experiment all samples were

degassed at 100 �C under vacuum. The pore volume and pore size distributions

were calculated by use of the Barrett–Joyner–Halenda (BJH) model [17] on the

desorption branch. Fourier-transform infrared (FTIR) spectra were obtained on a

Avatar 360 FTIR spectrometer (Thermo Nicolet, USA) by the KBr pellet method.


123

The particle sizes of the materials were measured by laser diffraction on an

Analysette 22 Compaq (Fritch, Germany).

Antimicrobial tests

Antimicrobial activity of the prepared silicas containing PMAG and PAG was

evaluated by use of cultures of the Gram-positive prokaryote Staphylococcus aureus

(associated with skin and mucous membranes) and the Gram-negative prokaryote

Escherichia coli (associated with the gastrointestinal mucosa). The experiments were

performed in the solid nutrient media. Pure cultures of all experimental bacteria and

fungi were obtained from the Microbial Type Culture Collection (Ivanovo State

Medical Academy). Agar plates were prepared by adding 0.9% lonagar to SAAM

(synthetic amino acid medium) to give a plate volume of 20 ml in 100- by 15-mm

plastic petri dishes. Plates were used within 24 h of preparation.

Adsorption isotherms of unmodified and modified silicas

To measure the adsorption isotherms, approximately, 50 mg adsorbents and 10 ml

Cu2? solution of different concentrations (0.01, 0.02, 0.04, 0.06, 0.08, 0.1 mol/l) were

added to a 20-ml flask and shaken for 60 min at 293 K. The initial pH was adjusted to

Si

OC2H5

OC2H5

OC2H5C2H5O + 4xH2O Si O Si O Si

O

Si

O

Si

OH

OH

HO

OH

OHHO

OH

OH

OH

OH

OHHOH2C C

R

CO O

H HN

CH2N NH2 z

+

-

HydrolysisPolycondensation

x

y

+

Immobilization

NCO

O

H

HC

NH2

NH2

C

R

CH2 - +

NC

O

O

H

H CNH2

NH2

C

RCH2

N

CO O

H H

CH2N NH2

CR

H2C

Si O Si OSi O

Si O

Si

O

Si

OSiO

SiO

SiO Si O

Si O Si O

OH

SiOH

OH

Si OH

OHOH

OH Si

HOHO

O

SiO

HO+

-

n

- +

Fig. 2 Synthetic route to silicas modified by PAG and PMAG (n = y ? z)


123

5 with dilute nitric acid and sodium hydroxide solution. pH was measured by use of a

pH-meter U-500 (Aquilon, Russia). The effect of the solution pH on adsorption of

Cu2? was studied by Shengju et al. [2]. It was proved that at pH 5, adsorption of Cu2?

from water is maximum. This pH was therefore chosen as the optimum for maximum

removal of Cu2? ions from aqueous solution. The concentration of copper ions (Cu2?)

in the solution was determined by UV–visible spectroscopy and use of optical density

values. The UV–visible spectra of solutions and suspensions were recorded by use of

an SF-104 spectrophotometer (Aquilon, Russia).

The magnitude of Cu2? adsorption on the surface of unmodified and modified

silicas was determined as the difference between its initial and equilibrium

concentrations in the aqueous solution (pH 5) after contact with a sorbent, by use of

the formula

Q ¼ ðCo � CadsÞ � Vm

ð1Þ

where Q is the magnitude of Cu2? adsorption, mmol/g; Co and Cads are the initial

and equilibrium concentrations of Cu2? in the aqueous solution, mmol/l; V is the

volume of the solution, l; and m is the mass of the sorbent sample, g.

Results and discussion

Characterization of the materials

The adsorbents were examined by FTIR to characterize the effect on the structure and

morphology of the adsorbents of adding the guanidine polymers and MPTMS during

the sol–gel process. The FTIR spectra of unmodified silica and silicas modified by

guanidine polymers are presented in Fig. 3. The FTIR spectrum of unmodified silica

contains the important bands: 3,470–3,420, 1,630, 1,390, 1,060–1,220, 960 and

798 cm-1. The features around 960 and 1,060 cm-1 are assigned to the Si–O–Si

stretching vibrations [18, 19]. The vibrations of Si–OH appeared around 1,630 and

3,470 cm-1 [20].

The FTIR spectra of silicas containing PAG and PMAG contain the same peaks,

which correspond to Si–O–Si and Si–OH vibrations. However, the peak at 860 cm-1

corresponds to CH2=C non-planar bending vibrations. The bands around 1,680 and

1,656 cm-1 correspond to the N=C stretching vibrations and NH2 bending vibrations

[13]. The bands in the range from 3,650 to 3,200 cm-1 characterize –OH groups of

intermolecular hydrogen bonds. These results prove that the guanidine polymers have

been successfully immobilized on the silica surface and inside the silica skeleton via

the sol–gel process.

The FTIR spectrum of thiol-modified silica is represented in Fig. 4. The FTIR

spectrum of thiol-modified silica also contains peaks which are typical of unmodified

silica. However, the spectrum of thiol-modified silica contains characteristic bands

for mercapto groups around 2,551 cm-1 [3, 21], so we conclude that mercapto groups

have been successfully grafted on to the silica surface by hydrolysis and

polycondensation.


123

We used the laser diffraction method to determine particle size distribution. The

results obtained are presented in Fig. 5. The unmodified silica is characterized by

the most narrow particle size distribution (range from 0.22 to 6 lm). This synthesis

of unmodified silica results in an average particle size of 6 lm. However, it also

contained nanoparticles (\0.68 lm). It is clear that addition of guanidine polymers

and MPTMS leads to an increase of particle size. The most intense peak for silica

500 1000 1500 2000 2500 3000 3500 4000

Si-O

H

C=

NN

3

2

T, %

v, cm-1

1

Si-O

-Si

Fig. 3 FTIR spectra: unmodified silica (1), PAG-modified silica with a PMAG content of 0.2 g (2),PAG-modified silica with a PMAG content of 0.2 g (3)

500 1000 1500 2000 2500 3000 3500 4000

Si-O

H

1

v, cm-1

T,%

2

SHSi-O

-Si

Fig. 4 FTIR spectra: unmodified silica (1), thiol-modified silica (2)


123

modified by PAG ranges from 2 to 6 lm. For silica modified by PMAG it ranged

from 5 to 12 lm. The silica modified by MPTMS is characterized by the widest

particle size distribution and the biggest particle size (from 0.09 to 8 lm).

According to the polycondensation process, MPTMS is more reactive than TEOS

and can easily form large particle agglomerates.

The mesoporous structure of the modified silicas was confirmed by nitrogen

adsorption by use of BET analysis. The isotherms of silicas containing PAG and

PMAG are identical so only the isotherm for silica modified with PAG (c) is

presented in Fig. 6. Isotherms b and c (thiol-modified silica and silica modified by

PAG) correspond to the type IV isotherm which is typical for mesoporous materials

(Fig. 6). Isotherm b is characterized by a more intense hysteresis loop. Isotherm a

(unmodified silica) shows this adsorbent is not porous.

The specific surface area of the adsorbents was determined by use of multipoint

BET measurement. Pore volume and average pore diameter of the adsorbents were

determined by the BJH method [16]. The structural properties of the adsorbent

samples are shown in Table 1.

It is clear that the pore size of the silica increased after modification. The surface

area, pore volume, and pore size of the modified adsorbents were all higher than

those for unmodified silica. The unmodified silica is not porous whereas the thiol-

modified silica is characterized by the highest surface area. The pore diameter of

silica modified by PAG varies over a range of 8–13 nm and the average pore

diameter is 11 nm. This can be explained by the fact that molecules of the guanidine

polymers serve as templates to form the necessary pore size for obtaining

Freq, %

size, μm

Freq, %

Freq,% Freq,%

(a) (b)

(c) (d)

size, μm

size, μm

size, μm

Fig. 5 Particle size distribution: unmodified silica (a), silica modified by PAG (b), silica modified byPMAG (c), silica modified by MPTMS (d)


123

mesoporous materials. The pore diameter of thiol-modified silica varies over the

range 5–7 nm and the average pore diameter is 6.31 nm (Fig. 7).

In sol–gel synthesis CTAB is used as a surfactant template to form the pore size

needed. The thiol-modified silica is characterized by a narrower pore size

distribution than silica modified by PAG (Fig. 7).

Antimicrobial properties of the materials

The antimicrobial activity of the materials was investigated against E. coli and S.

aureus in solid nutrient media. Before the experiment all tested samples were grafted

on paper discs. Pure silica, a paper disc, and piece of textile fabric were used as control

samples. The experimental activity results were evident after 300 min. It is clear that

only silicon oxides containing PAG and PMAG had high antimicrobial activity

0

5

10

15

20

25

0.00 0.20 0.40 0.60 0.80 1.00

Vol

ume

adso

rbed

cm

3 /g

Relative Pressure(P/Po)

0

50

100

150

200

250

300

350

400

450

0.00 0.20 0.40 0.60 0.80 1.00

Vol

ume

adso

rbed

cm

3 /g


0

20

40

60

80

100

120

140

160

180

0.00 0.20 0.40 0.60 0.80 1.00

Vol

ume

adso

rbed

cm

3 /g


(a) (b)

(c)

Fig. 6 Nitrogen adsorption–desorption isotherms: unmodified silica (a), thiol-modified silica (b), silicamodified by PAG (c)

Table 1 Physical properties of the adsorbents

No. Sample Specific area (m2/g) Pore volume (cm3/g) Pore size (nm)

1 SiO2 40 0.015 3.21

2 SiO2/PAG (0.2 g) 160 0.217 8–13

3 MPTMS/SiO2 345 0.312 5–7


123

suppressing test culture growth. The zone of growth retardation of S. aureus on the

solid nutrient medium was more 35 mm (Fig. 8). The experiment was repeated and

the same results were obtained. Figure 8 is indicative of high antimicrobial activity of

silica containing guanidine polymers against E. coli and S. aureus bacteria. This was

indicative of a potential application of silica containing guanidine polymers in the

textile industry and for formation of an antimicrobial surface.

Adsorption isotherms of the modified and unmodified silicas

The Langmuir (Eq. 2), Freundlich (Eq. 3), and Redlish–Peterson (Eq. 4) equations

were used to analyze the experimental adsorption isotherms in Fig. 9.

Qe ¼QbCe

1þ bCe

ð2Þ

Qe ¼ KFC1=ne ð3Þ

Qe ¼KRCe

1þ ARCbe

ð4Þ

where b is the Langmuir isotherm constant. The ratio of Qe (mmol/g) gives the

theoretical monolayer saturation capacity of the adsorbent, Ce is the equilibrium

concentration (mmol/l) of Cu2? ions.

In the Freundlich model (Eq. 3), KF and n are constants specific to the adsorbent.

In the Redlish–Peterson model (Eq. 4), KR and AR are the specific isotherm

constants, and b is the exponent, which ranges from 0 to 1 (when b equals to 1, the

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

d,nm

cm3/nm/g,d

V

∂∂

1

2

3

Fig. 7 Pore size distribution: unmodified silica (1), thiol-modified silica (2), silica modified by PAG (3)


123

Redlich–Peterson equation becomes the Langmuir isotherm). The adsorption

isotherms of Cu2? are presented in Fig. 9. The adsorption values of Cu2? ions

increased rapidly in the initial phase and then the increasing trend decreased as the

initial concentration increased. The equilibrium adsorption capacity of Cu2? on

unmodified silica, thiol-modified silica, silica modified by PMAG, and silica

modified by PAG was 21.3, 38, 65, and 99.8 mg/g, respectively, at 298 K.

Modification by MPTMS and guanidine polymers leads to increased adsorption of

Cu2? because of chemical and electrostatic interactions between amino and

mercapto groups of the modified silica and Cu2? ions. Although thiol-modified

silica has a larger surface area, the adsorption capacity of silica modified by

guanidine polymers is higher. This might be because guanidine polymers are more

reactive than mercapto groups of thiol-modified silica. The adsorption capacity of

silica modified by PAG is higher than the adsorption capacity of silica modified by

Solid medium agarStaphylococcus

results of test-tubes growth-free seedingStaphylococcus

Solid medium agarE. Coli

results of test-tubes growth-free seedingE. Coli

Fig. 8 Results of antimicrobial tests: 1 silica modified by PMAG (0.2 g), 2 thiol-modified silica (0.2 g),3 silica modified by PAG (0.2 g), 4 pure silica, 5 paper disc, 6 piece of textile fabric


123

PMAG. This might be because of structural factors: CH3 groups in PMAG may

prevent interactions between Cu2? ions and functional groups of polymers.

The adsorption equilibrium data of Cu2? were analyzed with the above

Langmuir, Freundlich, and Redlich–Peterson adsorption equations. The corre-

sponding data are listed in Tables 2, 3, and 4. According to the correlation

coefficient, the adsorption isotherm for unmodified silica fits the Langmuir equation,

which characterizes formation of a surface monolayer. According to the correlation

coefficients of the adsorption isotherms of Cu2? for modified silicas, the Redlich–

Peterson model is the most suitable. Adsorption of Cu2? on to the surface of

modified silica is more complicated because of chemosorption. It can be supposed

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0.1 20.1 40.1 60.1 80.1 100.1

C, mmol/L

Q, mmol/gRedlich-PetersonmodelLangmuir model

MPTMS/SiO2

SiO2/PMAG(0.2 g)

SiO2/PAG(0.2 g)

SiO2

1

2

3

4

Fig. 9 Isotherms of Cu2? adsorption on the surface of: unmodified silica (1), thiol-modified silica (2),PMAG-modified silica with a PMAG content of 0.2 g (3), PAG-modified silica with a PAG content of0.2 g (4)

Table 2 Nonlinear fitting data and equations of the Langmuir model

Sample Average value of fitting data Equations

b Qe r2

SiO2 9.38 0.3333 0.993 Qe = 3.09Ce/(1 ? 9.38Ce)

MPTMS/SiO2 18.58 0.5920 0.986 Qe = 10.99Ce/(1 ? 18.58Ce)

SiO2/PMAG(0.2 g) 14.84 0.9267 0.988 Qe = 13.75Ce/(1 ? 14.84Ce)

SiO2/PAG(0.2 g) 12.89 1.5649 0.994 Qe = 20.17Ce/(1 ? 12.89Ce)

pH 5, weight of adsorbent 50 mg, sample volume 10 ml, equilibration time = 60 min


123

that the chemosorption process is caused by electrostatic interactions between

positively charged metal ions and the negatively charged silica matrix of thiol-

modified silica [2] and silica modified by guanidine polymers [13]. Also the

increased adsorption capacity for Cu2? may be associated with chelation (formation

of co-ordinate bonds between functional groups of guanidine polymers and metal

ions) (Fig. 10).

Moreover, a large specific surface area of the modified silicas can also lead to

increased adsorption capacity for Cu2?. To summarize, it was shown that

modification of the silica surface by MPTMS and guanidine polymers increased

the specific surface area and adsorption capacity for Cu2? compared with

unmodified silica.

Conclusions

Multifunctional mesoporous modified silicas with high adsorption capacity for Cu2?

ions were synthesized by use of the sol–gel process. It was found that modification

of the silica surface by guanidine polymers and MPTMS led to an increase of

specific surface area, pore volume, and pore size of the adsorbents and greater

adsorption capacity for Cu2? ions. The particle sizes of the materials were

determined. According to the correlation coefficient (r2), the adsorption isotherms

for the modified silicas fit the Redlich–Peterson nonlinear model. Silicas modified

by guanidine polymers were more effective than silica modified by MPTMS for

Table 3 Nonlinear fitting data and equations of the Frendlich model


KF n r2

SiO2 14.48 1.439 0.870 Qe = 14.48Ce0.695

MPTMS/SiO2 11.79 1.491 0.981 Qe = 11.79Ce0.670

SiO2/PMAG (0.2 g) 5.99 1.424 0.988 Qe = 5.99Ce0.702

SiO2/PAG (0.2 g) 3.06 1.386 0.992 Qe = 3.06Ce0.721


Table 4 Nonlinear fitting data and equations of the Redlich–Peterson model


KR AR b r2

SiO2 3.43 49.69 0.635 0.953 Qe = 3.43Ce/(1 ? 49.69Ce0.635)

MPTMS/SiO2 4.53 50.40 0.602 0.995 Qe = 4.53Ce/(1 ? 50.40Ce0.602)

SiO2/PMAG (0.2 g) 18.34 53.09 0.645 0.996 Qe = 18.34Ce/(1 ? 53.09Ce0.645)

SiO2/PAG (0.2 g) 18.30 55.58 0.674 0.998 Qe = 18.30Ce/(1 ? 55.58Ce0.674)



123

removal heavy ions. Addition of polymers and MPTMS to the sol–gel matrix led to

increased particle size distribution. Moreover, the materials obtained were tested for

antimicrobial activity against the bacteria Staphylococcus aureus and Escherichia

coli and only silicas containing guanidine polymers had excellent antimicrobial

properties in solid agar medium. The results obtained are indicative of potential

application of the materials in different branches of science and technology: as

effective adsorbents for removal of heavy metals from water and as biocide

materials.

Acknowledgments We thank Dr Khashirova S. Yu., Department of Macromolecular Compounds, The

Kabardino-Balkar State University by N. M. Berbekova, for synthesis of guanidine polymers. The work is

supported by the Grant of the RFBR (Project No. 12-03-31309).

References

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2. W. Shengju, F. Li, X. Ran, S. Wei, G. Li, J Nanopart Res 12, 2111 (2010)

3. D. Liu, J.H. Lei, L.P. Guo, X.D. Du, K. Zeng, Microporous Mesoporous Mater 117, 67 (2009)

4. B. Thomas, N. Baccile, S. Masse, C. Rondel, I. Alric, J Sol-Gel Sci Technol 58, 170 (2011)

5. L.K. Neudachina, A.Y. Golub, Y.G. Yatluk, V.A. Osipova, Y.A. Berdyugin, E.M. Gorbunova,

L.V. Adamova, Inorg Mater 47, 435 (2011)

OH O

Si

SH

OH O

Si

OOH

Si

O

Si

SHSH SH

Cu2+

NCO

O

H

HC

NH

NHC

R

CH2

H

H

OH O

Si

OH

OH O

Si

OOH

Si

O

Si

OHHO HO

- + Cu2+

OH O

Si

SH

OH O

Si

OOH

Si

O

Si

SHSH SH

Cu2+

-+N CO

O

H

HC

HN

HNC

R

CH2

H

H H

OH O

Si

OH

OH O

Si

OOH

Si

O

Si

OHHO HO

Fig. 10 Possible mechanism of interaction between Cu2? and functional groups of guanidine polymersand MPTMS


123

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