1 23

Journal of Radioanalytical andNuclear ChemistryAn International Journal Dealing withAll Aspects and Applications of NuclearChemistry ISSN 0236-5731 J Radioanal Nucl ChemDOI 10.1007/s10967-014-3249-0

Mechanism of sorption of pertechnetateonto ordered mesoporous carbon

Đ. Petrović, A. Đukić, K. Kumrić,B. Babić, M. Momčilović, N. Ivanović &Lj. Matović

1 23

Your article is protected by copyright and

all rights are held exclusively by Akadémiai

Kiadó, Budapest, Hungary. This e-offprint is

for personal use only and shall not be self-

archived in electronic repositories. If you wish

to self-archive your article, please use the

accepted manuscript version for posting on

your own website. You may further deposit

the accepted manuscript version in any

repository, provided it is only made publicly

available 12 months after official publication

or later and provided acknowledgement is

given to the original source of publication

and a link is inserted to the published article

on Springer's website. The link must be

accompanied by the following text: "The final

publication is available at link.springer.com”.

Mechanism of sorption of pertechnetate onto ordered mesoporouscarbon

Ð. Petrovic • A. Ðukic • K. Kumric •

B. Babic • M. Momcilovic • N. Ivanovic •

Lj. Matovic

Received: 14 February 2014

� Akademiai Kiado, Budapest, Hungary 2014

Abstract Ordered mesoporous carbon (OMC) was used

as an adsorbent for the removal of pertechnetate (TcO4-)

anion. The maximum uptake (93 %) of TcO4- was

obtained after 60 min of contact. The adsorption of TcO4-

is almost pH-independent in very wide pH region (from 4.0

to 10.0). Maximum Kd of 6.6 9 103 cm3 g-1 was found at

pH 2.0. TcO4- interacts with carboxylic functional groups

present at the surface of the OMC by displacing the OH-

ions with TcO4- via ion exchange mechanism.

Keywords Technetium-99 � Adsorption � Ordered

mesoporous carbon � Surface functional groups

Introduction

The presence of the radionuclide 99Tc in the environment

comes from anthropogenic nuclear activities such as nuclear

power plants, nuclear weapons testing facilities, reprocess-

ing of spent nuclear fuel, nuclear accidents and medical

application of 99mTc. The predominant chemical form of the

long-lived radionuclide 99Tc (t1/2 = 2.1 9 105 year) is the

highly soluble and environmentally mobile pertechnetate

anion (TcO4-), that easily penetrates the ecosystems [1]. The

control of environment pollution by 99Tc is therefore con-

sidered a primary task. Many investigations are orientated

toward the immobilization of 99Tc, as well as its adsorption

from contaminated groundwaters using various adsorbent

materials.

In recent years, many synthetic and natural materials,

including clay minerals [2–4], inorganic compounds [5, 6],

strongly magnetic iron-sulfide materials [7], organic poly-

mers [8], activated carbons [9–13], various synthetic resins

and sponges [14–17] have been evaluated for use in long-

term immobilization of 99Tc and its removal from con-

taminated groundwaters. Compared to other materials,

removal of TcO4- by activated carbons is one of the most

efficient processes, because of large specific surface area,

porous structure and variety of surface functional groups of

activated carbons. Gu et al. [10] used commercial activated

carbon (Nuchar WV-G) for adsorbing TcO4- from syn-

thetic groundwater over a wide range of pH values. The

distribution coefficient (Kd) of TcO4- was determined to

range from 2.1 9 103 to 2.7 9 104 cm3 g-1. In contrast to

this material, the activated carbon (Merck KGaA/Merk-

Schuchart) used by Holm et al. [11] has Kd in the order of

106 at pH 2–4. Wang et al. [12] grouped commercial acti-

vated carbon materials into two distinct types: (i) type I

materials that have high sorption capabilities with the Kd

varying from 9.5 9 105 to 3.2 9 103 cm3 g-1 (in the pH

range from 4.5 to 9.5) and (ii) type II materials that have

relatively low sorption capabilities with Kd remaining more

or less constant (1.1 9 103–1.8 9 103 cm3 g-1) over a

similar pH range. The difference in sorption behavior

between the two types of materials was attributed to the

different distribution of surface functional groups (carbox-

ylic and phenolic). The presence of a large fraction of more

acidic carboxylic subgroups is found to be responsible for

the high sorption capabilities observed for type I materials.

The ordered mesoporous carbon (OMC) belongs to a

family of porous materials which attracted great attention

in recent years because of its unique features, such as high

surface area and uniform, large and tunable pore channels.

These features make OMC more attractive for use in the

Ð. Petrovic � A. Ðukic � K. Kumric � B. Babic �M. Momcilovic � N. Ivanovic � Lj. Matovic (&)

Vinca Institute of Nuclear Sciences, University of Belgrade,

P.O. Box 522, 11001 Belgrade, Serbia

e-mail: ljiljam@vinca.rs

123

J Radioanal Nucl Chem

DOI 10.1007/s10967-014-3249-0

Author's personal copy

adsorption processes and thus, we found interesting to

investigate sorption properties and mechanism of sorption

of TcO4- onto the OMC which, to our knowledge, has not

been investigated previously. Recently, the OMC has been

investigated for the removal of bromate [18], uranium(VI)

[19] and dye molecules [20] from the aqueous solutions.

Experimental part

Material characterization

The OMC was synthesized under acidic conditions as

previously described by Momcilovic et al [21]. The

structure of the ordered mesoporous material has been

investigated using various characterization techniques:

X-ray diffraction (XRD), laser scattering particle size

analysis system, Fourier transform infrared spectroscopy

(FT-IR), Boehm method and batch equilibrium method for

determination of point of zero charge (pHPZC).

XRD pattern of the sample was recorded using a Sie-

mens D5000 diffractometer with filtered Cu Ka radiation

(k = 1.5406 A). The scanning range was 2h = 2�–80�,

with the scanning rate of 0.02�/s.

A Malvern 2000SM Mastersizer laser scattering particle

size analysis system was used to obtain quantitative parti-

cle size distributions (PSD) of the sample. The specified

resolution range of the system was from 0.02 to 2,000 lm.

Approximately 0.05 g of the OMC powder was dispersed

in 10 cm3 of water with a sonication in a water bath for

3 min. Particle and dispersant reflection indexes were

1.590 and 1.330, respectively.

The functional groups of the sample were determinate

by PerkinElmer Spectrum Two FT-IR spectrometer using

the pressed KBr pellets (1:100) technique.

The acidic and basic surface groups of the studied OMC

were determined by the Boehm method. The acidic sites were

determined by mixing 0.15 g of the OMC with 20 cm3 of

different bases (0.1 mol dm-3 NaOH, 0.05 mol dm-3

NaHCO3 or 0.05 mol dm-3 Na2CO3) in 25 cm3 beakers. The

beakers were sealed and shaken for 24 h. The solutions were

then filtered and titrated with 0.1 mol dm-3 HCl. Similarly,

the basic sites were determined by mixing 0.15 g of the OMC

with 20 cm3 of 0.1 mol dm-3 HCl. The obtained solution was

titrated with 0.1 mol dm-3 NaOH. The equation for deter-

mining the number of moles of surface acidic and basic func-

tional groups on the surface of OMC (nCSF, mmol g-1) is [22]:

nCSF ¼ cNaOH � VNaOHð Þinitial� cHCl � Vekv:HClð Þtitrant

� �

� V

Valiquot

� 1; 000 ð1Þ

where cNaOH and VNaOH are the concentration and volume

of the reaction base (NaOH) mixed with the OMC, cHCl

and Vekv.HCl are the concentration and equivalent volume of

titrant (HCl) added to the aliquot (Valiquot) taken from the

original sample (V).

The point of zero charge of the OMC sample was

determined by batch equilibration method using KNO3

(0.01 and 0.1 mol dm-3) as a background electrolyte.

Batch experiments were carried out at room temperature by

mixing 0.125 g of the OMC and 25 cm3 of the working

KNO3 solution with different initial pH values in PVC

bottles. Initial pH values of solution were adjusted with

0.1 mol dm-3 HNO3 and 0.1 mol dm-3 KOH. The solu-

tion with different initial pH values (pHi) were shaken on

mechanical shaker (Promax 2020, Heidolph, Schwabach,

Germany) for 24 h. After that, the liquid phases were

separated by filtration through a 0.45 lm microporous

membrane filter (Membrane Solutions LLC, Plano, TX)

and the final pH values of solutions (pHf) were measured.

Adsorption studies

Radioactive technetium (in the form of pertechnetate) was

obtained from a 99Mo/99mTc generator (Vinca Institute of

Nuclear Sciences, Belgrade, Serbia) and its radioactive

concentration was determined by a Capintec CRC-15 dose

calibrator (Capintec, Inc. Ramsey, NJ, United States).

CRC-15 dose calibrator has 6 cm diameter and 25 cm deep

ionization chamber well that allows convenient measure-

ments of virtually any radioisotope geometry. Ionization

chamber is filled with high pressure Argon gas. The effects

of the sample container, sample volume and activity con-

centration are minimized by optimizing the counting

geometries. Assays may be made reliably in the chamber

from as low as 1 lCi for most radioisotopes to as high as

8 Ci of 99mTc. The resolution of the instrument is

0.001 MBq, i.e. 0.01 lCi. The measurements of 99mTc

activity in aliquots were made using vial geometry.

Batch experiments were performed at room temperature

by mixing 0.04 g of well powdered OMC adsorbent and

10 cm3 of working 99mTcO4- solution in closed glass vials.

Experimental set-up is presented in Fig. 1. The total99mTcO4

- radioactive concentration in the working solu-

tion was 1.4 MBq cm-3 (37.8 lCi cm-3) at pH 4.0. The

initial pH was adjusted by adding 0.1 mol dm-3 HCl. The

samples were shaken on a laboratory shaker for 60 min at a

stirring speed 200 rpm for better mass transport with high

interfacial area of contact. After that, the liquid phases

were separated from the solid phases by filtration through a

0.45 lm microporous membrane filter. The residual

radioactive concentration of 99mTcO4- in each aliquot was

determined with a Capintec CRC-15 dose calibrator.

The effects of different experimental parameters, such

as contact time (1–180 min), solution pH (2.0–12.0), ionic

strength (0.01 and 0.1 M NaCl) and initial 99mTcO4-

J Radioanal Nucl Chem

123

Author's personal copy

radioactive concentration (0.07–2.89 mCi cm-3) were

investigated with respect to the removal efficiency of

TcO4-. All experiments were carried out in duplicate, and

the data obtained were used for analysis.

Calculations

The removal efficiency (E, %), the distribution coefficient

(Kd, cm3 g-1) and the adsorption capacity (qe, mCi g-1) of99mTcO4

- were calculated using the following equations:

E ¼ Ai � Afð ÞAi

� 100 ð2Þ

Kd ¼Ai � Afð Þ

Af

� V

mð3Þ

qe ¼Ai � Aeð Þ

m� V ð4Þ

where Ai, Af and Ae are the initial, the final and the equi-

librium 99mTcO4- radioactive concentrations in the liquid

phase (MBq cm-3), V the volume of the solution (cm3) and

m the mass of adsorbent (g).

Results and discussion

Microstructural characterization

XRD pattern of the synthesized OMC is presented on

Fig. 2. Broad peaks located at the positions 2h = 22.5� and

2h = 43.6�, respectively, correspond to the amorphous

carbon and demonstrate that OMC has an amorphous

structure. Two resolved diffraction peaks attributed to the

(002) and (100) reflections are typical for the OMC [23,

24].

Figure 3 shows a PSD curve of the synthesized OMC.

The sample has a bimodal distribution of particles in the

range from 4.4 to 1905.5 lm, with the mean particle size of

7.5 and 447.2 lm. The percentage of the smaller particles

is about 1.5 % which indicates that the larger particles with

mean size of 447.2 lm are dominant in the sample. As

previously described by Momcilovic et al. [21], specific

surface area calculated by BET equation, SBET, is

712 m2 g-1. Also, calculated porosity parameters con-

firmed that OMC is mesoporous with certain amount of

micropores.

Distribution of positive and negative charge on the

surface of the particles of the adsorbent is one of the major

factors that influence the sorption uptake. In order to

understand the sorption mechanism, it is necessary to

determine the pH at which the surface has net neutral

charge (pHPZC). In the state when the sorbent surface has

zero point of charge, adsorption of target solute is carried

Fig. 1 Experimental set-up for the sorption of TcO4- onto the OMC

Fig. 2 XRD pattern of the ordered mesoporous carbon

Fig. 3 PSD curve of the ordered mesoporous carbon

J Radioanal Nucl Chem

123

Author's personal copy

out by diffusion into micropores and mesopores. If the pH

of the solution is greater than values of the pHPZC, the

surface will have a negative charge and sorption of positive

ions will be favored due to the electrostatic attraction. The

sorption of negatively ions will be favored at pH values

lower than pHPZC [25]. In order to determine the pHPZC of

the OMC, the batch equilibration method was used. The

experimental results are represented in Fig. 4 as a function

of final pH values, pHf, from initial pH values, pHi, of the

solutions. The plateau obtained at pH 8.1 ± 0.2 correspond

to the pHPZC of the OMC. The same results of the values of

the pHPZC for all electrolyte concentrations (0.01 and

0.1 mol dm-3) indicate that the pHPZC of the OMC is

independent of the ionic strength of inert electrolyte

(KNO3). The high pHPZC value of the OMC of 8.1 ± 0.2 is

due to the basic oxygen groups (chromene and pyrone) and

the p-electron system of the basal planes of carbons [26].

The type and concentration of functional groups give the

amphoteric characteristics to activated carbons in aqueous

solution. Since infrared spectroscopy provides information

on the chemical structure of the adsorbent material, FT-IR

analysis was performed in order to identify surface func-

tional groups responsible for TcO4- sorption. The FT-IR

spectra is showed in Fig. 5, while the corresponding

assignments of FT-IR bands to the specific chemical bonds

are presented in Table 1.

The FT-IR spectra of the OMC shows absorption bands

due to aliphatic (bands at 2,974 and 2,886 cm-1 originate

from C–H stretching in –CH2– [27, 28], 1,450 cm-1

originate from –CH2– deformation [28]) and aromatic

structures (bands at 818, 756 and 700 cm-1 that originate

from the in-plane and out-of-plane aromatic ring defor-

mation vibrations of C–H in variously substituted benzene

rings [28, 29]). Bands at 1,111, 1,613 and 1,717 cm-1 are

vibrational modes assigned to stretching vibrations of C–O

and C=O, and indicate the significant presence of oxygen-

containing functional groups: carboxylic and phenolic

groups. Weak sharp absorption bands at 3,594 and

3,733 cm-1 present in spectra may be ascribed to isolated

O–H groups [27, 28]. However, the relative portions of

these groups cannot be determined from these spectra

because of the qualitative nature of FT-IR measurements.

It is well known that the most common functional

groups (containing oxygen) on the activated carbon sur-

faces are carboxyl, lactonic, carbonyl and phenolic groups.

The chemical titration method, such as proposed by Boehm

[22], determines the amount of acidic (carboxyl, lactonic

and phenol) and basic groups on the surface of carbon

materials. This method is especially useful when it is used

in combination with other techniques such as FT-IR ana-

lysis. The number of acidic and basic groups is presented in

the Table 2.

Fig. 4 Determination of the pHPZC of the ordered mesoporous carbonFig. 5 FT-IR spectra of the ordered mesoporous carbon

Table 1 FT-IR spectra band assignments for the ordered mesoporous

carbon

Band

number

(cm-1)

Assignment References

\820 C–H deformation modes in in-plane and

out-of-plane aromatic ring

[28, 29]

*1,115 C–O stretching vibration in phenolic and

carboxylic group

[26–28,

30]

*1,450 –CH2– deformation [28]

*1,613 C=O stretching vibration [27, 30]

*1,717 C=O in the carboxylic group [26–28]

*2,886,

2,974

C–H stretching vibration in methylene

and methyl group

[27, 28]

*3,594,

3,733

O–H stretching vibration in free O–H in

phenolic and carboxylic groups

[26–28]

J Radioanal Nucl Chem

123

Author's personal copy

As can be seen from the Table 2, on the surface of the

OMC dominates acidic groups, among which the most

prominent are phenolic groups. This is expected since the

resorcinol (1,3-isomer of benzenediol with the formula

C6H4(OH)2) was used as a precursor for the synthesis of the

OMC.

Adsorption studies

Effect of contact time

The effect of contact time on the sorption of TcO4- onto

the OMC was investigated at different contact times

ranging from 1 to 180 min (Fig. 6). As can be seen in

Fig. 6, the equilibrium adsorption was established after

60 min of contact and the maximum uptake (93 %) of

TcO4- was reached. Also, it is evident that the adsorption

rate increased rapidly in the first 5 min of adsorption, and

87 % of the TcO4- was adsorbed during this period of

time. This means that, after only 5 min of adsorption, the

removal efficiency of TcO4- exceeded 94 % of its value at

equilibrium. Such a rapid process indicates that the sorp-

tion is primarily a surface phenomenon, and the OMC

surface adsorbing sites (functional groups) are readily

available for TcO4- ions from the solution.

After equilibrium was reached, the contact time no

longer had an influence on the TcO4- sorption, and the

removal efficiency remained constant over the time period

observed (180 min). In addition, the distribution coeffi-

cient, Kd, as shown in the insert in Fig. 6, remained con-

stant at equilibrium state with the mean value of 3.5 9 103.

Therefore, the adsorption time of 60 min was selected as a

fixed parameter for the rest of the study.

Effect of initial pH and ionic strength

The effect of the solution pH and ionic strength, I, on the

adsorption of TcO4- using the OMC was investigated at

varying pH values from 2.0 to 12.0. The obtained results

are presented in Fig. 7. It is evident that the adsorption of

TcO4- was pH-dependent, with maximum removal effi-

ciency of 99 % at the pH value 2.0. Then, the removal

efficiency slightly decrease and reach the value of 93 % at

the pH values between 4.0 and 10.0. At the pH values

beyond 10.0, the adsorption of TcO4- decreased sharply

and the removal efficiency of TcO4- fell to 72 %. The

distribution coefficients, presented in the insert in Fig. 7,

behaved in a similar manner as a function of solution pH,

with the maximum Kd value of 6.6 9 103 at the pH 2.0,

plateau with the mean Kd of 2.9 9 103 at the pH range

from 4.0 to 10.0, and the Kd value less than 1 9 103 at the

pH [ 10.0. Under the investigated experimental condi-

tions, E and Kd values are insensitive to ionic strength

changes, indicating that the sorption of TcO4- was not

affected by the presence of competing Cl- ions. Xu et al.

[18] also found that the bromat removal from water using

OMC was independent on the presence of competing

anions.

As can be seen from Fig. 7, high removal efficiency of

TcO4- is achieved at pH B 10.0. Since the adsorption of

anions is favored at pH \ pHPZC, and having in mind that

pHPZC for the OMC is 8.1 ± 0.2, high removal efficiency

of TcO4- was expected to be achieved at pH \ 8.1 ± 0.2.

However, as known from the literature [31], the specific

adsorption of cations, shifts pHPZC toward lower values,

and the specific adsorption of anions shifts pHPZC to the

opposite direction. This enables the high yield of removal

efficiencies of anions, like TcO4- ions on the OMC, in

wider range of pH values (from 2.0 to 10.0).

Effect of initial radioactive concentration

The effect of the initial radioactive concentration on the

adsorption of TcO4- onto the OMC was studied by varying the

Table 2 Functional groups on

the OMC determined by Boehm

method

Adsorbent Basic groups

(mmol g-1)

Acidic groups

(mmol g-1)

Carboxylic groups

(mmol g-1)

Phenolic groups

(mmol g-1)

Lactonic groups

(mmol g-1)

OMC 0.1325 1.3367 0.0200 1.3033 0.0134

Fig. 6 Effect of contact time on the adsorption of TcO4- by the

OMC (at an initial radioactive concentration 1.3 MBq cm-3). Insert

variation of Kd values with contact time. Conditions: pH 4.0; stirring

speed, 200 rpm; concentration of adsorbent, 4 g dm-3. Vertical error

bars represent standard errors

J Radioanal Nucl Chem

123

Author's personal copy

99mTcO4- concentration from 0.07 to 2.89 mCi cm-3 in the

solution at pH 4.0. The obtained results are presented in

Table 3. As can be seen, the adsorption capacity of TcO4-

increased with increasing in the initial radioactive concen-

tration, whereas the removal efficiency remained more or less

constant (94.0–91.3 %) over the same concentration range.

Adsorption of TcO4- onto the OMC yielded linear adsorption

isotherm (Fig. 8), with an estimated Kd = 2.6 9 103 cm3 g-1

and the correlation coefficient R2 = 0.9961. The plateau was

not reached due to the fact that the TcO4- concentration in the

simulated groundwater was extremely low (in the order of

1.3 9 10-10 to 5.6 9 10-9mol dm-3, which is comparable

with the 99Tc activity found in the environment [1, 10, 11]),

and under the investigated experimental conditions the sur-

face of the OMC was far from being saturated with TcO4-.

Mechanism of TcO4- sorption onto OMC

Comparison of Kd value(s) obtained in this study with those

of other researchers [10–12] indicate that the TcO4-

adsorption by the OMC is well classed compared to other

carbon materials (adsorbents). Depending on the influence

of pH on the Kd values of the investigated activated car-

bons, Wang et al. [12] grouped them into two distinct

types. Type I materials have high sorption capabilities with

the Kd varying from 9.5 9 105 to 3.2 9 103 cm3 g-1 (in

the pH range from 4.5 to 9.5). Type II materials have

relatively low sorption capabilities with the Kd remaining

more or less constant (1.1 9 103–1.8 9 103 cm3 g-1) over

a similar pH range. In the same pH region (from 4.0 to

10.0) OMC exhibits plateau with the mean Kd of 2.9 9 103

as presented in Fig. 7. According to the value of Kd

(2.9 9 103 cm3 g-1) obtained for the OMC, it is clear that

the OMC cannot be classified into any of these two groups,

but somewhere in between, much more closely to the

materials of type II. Different sorption behavior between

the two types of materials was attributed to the different

distribution of surface functional groups (carboxylic and

phenolic) and, in the order of increasing acidity, the car-

boxylic groups were divided into three subgroups. The

presence of a large fraction of acidic carboxylic subgroups

was found to be responsible for the high sorption capa-

bilities observed for type I materials, where direct

involvement of C–TcO4 bonding occurs:

R� C� OH þ TcO�4 ! R� C� OTcO3 þ OH� ð5Þ

The low sorption capabilities of type II materials were

attributed to the exclusive presence of phenolic and car-

boxylic groups with lower acidity. The proposed main

mechanism of attaching the TcO4- to these functional

Fig. 7 Effect of pH and ionic strength (0.01 and 0.1 M NaCl) on the

adsorption of TcO4- by the OMC (at an initial radioactive concen-

tration 1.3 MBq cm-3). Insert variation of Kd values with pH and

ionic strength. Conditions: contact time, 60 min; stirring speed,

200 rpm; concentration of adsorbent, 4 g dm-3. Vertical error bars

represent standard errors

Table 3 Effect of the initial 99mTcO4- radioactive concentration, Ai,

on the removal efficiency, E, and equilibrium radioactivity adsorbed

per unit mass, qe, of the OMC

Ai, mCi cm-3 Ae, mCi cm-3 qe, mCi g-1 E, %

0.07 4.1 9 10-3 16.5 ± 0.3 94.0 ± 1.4

0.48 0.03 112.5 ± 1.8 93.8 ± 1.4

0.98 0.07 226.8 ± 2.8 92.6 ± 1.2

1.43 0.12 326.5 ± 4.6 91.3 ± 1.3

1.92 0.16 440.3 ± 6.2 91.7 ± 1.3

2.41 0.21 551.3 ± 7.1 91.5 ± 1.2

2.89 0.25 659.8 ± 9.8 91.3 ± 1.4

Fig. 8 Effect of the initial radioactive concentration on the adsorp-

tion of TcO4- by the OMC. Conditions: contact time, 60 min; pH,

4.0; stirring speed, 200 rpm; concentration of adsorbent, 4 g dm-3.

Vertical error bars represent standard errors

J Radioanal Nucl Chem

123

Author's personal copy

groups was through either hydrogen bonding or electro-

static attraction (Eq. 6), where no consumption or release

of H? or OH- ions occurs:

R� OH�2 þ TcO�4 ! R� OH2 � OTcO3 ð6Þ

In order to verify the exact mechanism of TcO4- sorp-

tion onto the OMC, pH value of the TcO4- solution after

adsorption (pHf) was examined as a function of the initial

pH of the TcO4- solution (pHi). The obtained results are

presented in Fig. 9. A release of OH- induces a sharp

increase of pHf values. Also, as can be seen from the insert

in Fig. 7, surface chemistry of OMC is insensitive to ionic

strength indicating that the surface chemistry is controlled

by inner sphere chemical complexation rather than by

electrostatic interactions. This implies that the main

mechanism of TcO4- sorption onto OMC is displacement

of OH- with TcO4- as presented in Eq. (5), rather than

hydrogen bonding, which is equivalent to an outer sphere

complexation. Attaching of TcO4- to carboxylic or phe-

nolic functional groups through hydrogen bonding or

electrostatic attraction is unlikely because: (1) Kd value is

independent of pH in the pH region from 4.0 to 10.0, and

(2) the sorption has not been changed with the increase of

ionic strength of the medium. As a result, the direct C–

OTcO3 bonding in carboxylic groups (Eq. (5)) is expected

to be the main mechanism of sorption of pertechnetate ion

onto the OMC. Relatively low Kd value of 2.9 9 103 for

the OMC can be explained by the substantially smaller

number of carboxylic groups compared to the number of

phenolic groups present on the surface of OMC (Table 2).

The reaction occurs very rapidly indicating the sorption is

primarily a surface phenomenon.

Conclusions

Ordered mesoporous carbon has been investigated for its

sorption capability to remove pertechnetate (TcO4-) from

water. The mechanism of TcO4- sorption was proposed

and conclusions are summarized as follows:

– OMC has amorphous structure characteristic for carbon

materials with well defined pore sizes (mesoporous

with certain amount of micropores) and bimodal

distribution of particles with the mean particle size of

7.5 and 447.2 lm;

– Maximum Kd value of 6.6 9 103 cm3 g-1 was

obtained at pH 2.0;

– The adsorption of TcO4- is almost pH-independent in

very wide pH region (from 4.0 to 10.0);

– The sorption equilibrium was established after 60 min

of contact and the maximum uptake (93 %) of TcO4-

was reached. Such a rapid process indicates that the

sorption is primarily a surface phenomenon, and the

OMC surface adsorbing sites (functional groups) are

readily available for TcO4- ions from the solution;

– TcO4- interacts with carboxyl functional groups pres-

ent at the surface of the OMC by displacing the OH-

with TcO4- via ion exchange mechanism.

The obtained results indicate that the TcO4- adsorption

by the OMC is well classed compared to other carbon

materials (adsorbents). As a material resistant to aging (to

the oxidizing conditions and the presence of water), as well

as its good sorption properties, the OMC appears to be an

efficient adsorbent for the TcO4- removal from aqueous

solutions.

Acknowledgments We acknowledge the support to this work pro-

vided by the Ministry of Education and Science of Serbia through the

project No. III 45012.

References

1. Shi K, Hou X, Roos P, Wu W (2012) Determination of techne-

tium-99 in environmental samples: a review. Anal Chim Acta

709:1–20

2. Vinsova H, Konirova R, Koudelkova M, Jedinakova-Krizova V

(2004) Sorption of technetium and rhenium on natural sorbents

under aerobic conditions. J Radioanal Nucl Chem

261(2):407–413

3. Jaisi DP, Dong H, Plymale AE, Fredrickson JK, Zachara JM,

Heald S, Liu C (2009) Reduction and long-term immobilization

of technetium by Fe(II) associated with clay mineral nontronite.

Chem Geol 264:127–138

4. Jedinakova-Krızova V, Zeman J, Vinsova H, Hanslık E (2010)

Bentonite stability, speciation and migration behaviour of some

critical radionuclides. J Radioanal Nucl Chem 286:719–727

5. Zhang F, Parker JC, Brooks SC, Watson DB, Jardine PM, Gu B

(2010) Prediction of uranium and technetium sorption during

Fig. 9 pH change of the solution at the adsorption equilibrium of

TcO4-

J Radioanal Nucl Chem

123

Author's personal copy

titration of contaminated acidic groundwater. J Hazard Mater

178:42–48

6. Kumar S, Rawat N, Kar AS, Tomar BS, Manchanda VK (2011)

Effect of humic acid on sorption of technetium by alumina.

J Hazard Mater 192:1040–1045

7. Watson JHP, Ellwood DC (2003) The removal of the pertech-

netate ion and actinides from radioactive waste streams at Han-

ford, Washington, USA and Sellafield, Cumbria, UK: the role of

iron-sulfide-containing adsorbent materials. Nucl Eng Des

226:375–385

8. Chen J, Veltkamp A (2002) Pertechnetate removal by macropo-

rous polymer impregnated with 2-nitrophenyl octyl ether

(NPOE). Solvent Extr Ion Exch 20:515–524

9. Ito K, Akiba K (1991) Adsorption of pertechnetate ion on active

carbon from acids and their salt solutions. J Radioanal Nucl

Chem 152(2):381–390

10. Gu B, Dowlen EK, Liang L, Clausen LJ (1996) Efficient sepa-

ration and recovery of technetium-99 from contaminated

groundwater. Sep Technol 6:123–132

11. Holm E, Gafvert T, Lindahl P, Roos P (2000) In situ sorption of

technetium using activated carbon. Appl Radiat Isot 53:153–157

12. Wang Y, Gao H, Yeredla R, Xu H, Abrecht M (2007) Control of

pertechnetate sorption on activated carbon by surface functional

groups. J Colloid Interface Sci 305:209–217

13. Popova NN, Bykov LG, Petukhova AG, Tananaev GI, Ershov GB

(2013) Sorption of Tc(VII) and Am(III) by carbon materials:

effect of oxidation. J Radioanal Nucl Chem 298:1463–1468

14. Liang L, Gu B, Yin X (1996) Removal of technetium-99 from

contaminated groundwater with sorbents and reductive materials.

Sep Technol 6:111–122

15. Suzuki T, Fujii Y, Yan W, Mimura H, Koyama S, Ozawa M

(2009) Adsorption behavior of VII group elements on tertiary

pyridine resin in hydrochloric acid solution. J Radioanal Nucl

Chem 282:641–644

16. Chen Q, Dahlgaard H, Hansen HJM, Aarkrog A (1990) Deter-

mination of 99Tc in environmental samples by anion exchange

and liquid–liquid extraction at controlled valency. Anal Chim

Acta 228:163–167

17. Hughes DL, DeVol AT (2006) Characterization of a Teflon�

coated semiconductor detector flow cell for monitoring of per-

technetate in groundwater. J Radioanal Nucl Chem 267:287–295

18. Xu C, Wang X, Shi X, Lin S, Zhu L, Chen Y (2014) Bromate

removal from aqueous solutions by ordered mesoporous carbon.

Environ Technol 35(8):984–992

19. Liu Y, Li Q, Cao X, Wang Y, Jiang X, Li M, Hua M, Zhang Z

(2013) Removal of uranium(VI) from aqueous solutions by

CMK-3 and its polymer composite. Appl Surf Sci 285P:258–266

20. Zhuang X, Wan Y, Feng C, Shen Y, Zhao D (2009) Highly

efficient adsorption of bulky dye molecules in wastewater on

ordered mesoporous carbons. Chem Mater 21:706–716

21. Momcilovic M, Stojmenovic M, Gavrilov N, Pasti I, Mentus S,

Babic B (2014) Complex electrochemical investigation of

ordered mesoporous carbon synthesized by soft-templating

method: charge storage and electrocatalytical or Pt-electrocata-

lyst supporting behavior. Electrochim Acta 125:606–614

22. Goertzen LS, Theriault DK, Oickle MA, Tarasuk CA, Andreas

AH (2010) Standardization of the Boehm titration. Part I. CO2

expulsion and endpoint determination. Carbon 48:1252–1261

23. Wu F, Huang R, Mu D, Shen X, Wu B (2014) A novel composite

with highly dispersed Fe3O4 nanocrystals on ordered mesoporous

carbon as an anode for lithium ion batteries. J Alloys Compd

585:783–789

24. Zhu Z, Hu Y, Jiang H, Li C (2014) A three-dimensional ordered

mesoporous carbon/carbon nanotubes nanocomposites for sup-

ercapacitors. J Power Sources 246:402–408

25. Kandah MI, Shawabkeh R, Al-Zboon MA (2006) Synthesis and

characterization of activated carbon from asphalt. Appl Surf Sci

253:821–826

26. Xiao B, Thomas MK (2005) Adsorption of aqueous metal ions on

oxygen and nitrogen functionalized nanoporous activated car-

bons. Langmuir 21(9):3892–3902

27. Boonamnuayvitaya V, Sae-ung S, Tanthapanichakoon W (2005)

Preparation of activated carbons from coffee residue for the

adsorption of formaldehyde. Sep Purif Technol 42:159–168

28. Puziy M, Poddubnaya IO, Martinez-Alonso A, Suarez-Garcia F,

Tascon MDJ (2002) Synthetic carbons activated with phosphoric

acid: i. Surface chemistry and ion binding properties. Carbon

40:1493–1505

29. Al-Qodah Z, Shawabkah R (2009) Production and characteriza-

tion of granular activated carbon from activated sludge. Braz J

Chem Eng 26(1):127–136

30. Wang Y, Gao H, Yeredla R, Xu H, Abrecht M (2007) Control of

pertechnetate sorption on activated carbon by surface functional

groups. J Colloid Interface Sci 305(2):209–217

31. Babic BM, Milonjic SK, Polovina MJ, Cupic S, Kaludjerovic BV

(2002) Adsorption of zinc, cadmium and mercury ions from aqueous

solutions on an activated carbon cloth. Carbon 40:1109–1115

J Radioanal Nucl Chem

123

Author's personal copy