Radioanalytical separation and size-dependent ion exchangeproperty of micelle-directed titanium phosphate nanocomposites

Rajesh Chakraborty • Sriparna Chatterjee •

Pabitra Chattopadhyay

Received: 9 September 2013 / Published online: 8 November 2013

� Akademiai Kiado, Budapest, Hungary 2013

Abstract Nanocomposite titanium-phosphate (TiP) of

different sizes was synthesized using Triton X-100 (poly-

ethylene glycol-p-isooctylphenyl ether) surfactant. The

materials were characterized by FTIR and powdered X-ray

diffraction (XRD). The structural and morphological

details of the material were obtained by scanning electron

microscopy (SEM) and transmission electron microscopy.

The SEM study was followed by energy dispersive spec-

troscopic analysis for elemental analysis of the sample. The

important peaks of the XRD spectra were analyzed to

determine the probable composition of the material. The

average size distribution of the particles was determined by

dynamic light scattering method. Ion exchange capacity

was measured for different metal ions with sizes of the TiP

nanocomposite and size-dependent ion exchange property

of the material was investigated thoroughly. The nanoma-

terial of the smallest size of around 43 nm was employed to

separate carrier-free 137mBa from 137Cs in column chro-

matographic technique using 1.0 M HNO3 as eluting agent

at pH 5.

Keywords Nanocomposite � Triton X-100 � Ion

exchange capacity � Radioanalytical separation

Introduction

The salts of multivalent metalloacids are a class of widely

studied inorganic ion exchangers because of their excellent

stability, insolubility in common solvent within very wide

limits of pH, subsequent utilization in column separation

and of course selective sorption behavior towards different

metal ions. Metalloacid salts of such type are a large group

of ion exchangers, amongst which tetravalent cations Zr,

Th, Ti, Sn are most studied, followed by some trivalent

cations such as Al and Cr. The anions most extensively

employed include phosphate, arsenate, antimonate, vana-

date and molybdate [1–3]. Acid salts of these types have

gel or microcrystalline structure and their composition and

properties are easily modified by the conditions of syn-

thesis. Their composition is most likely non-stoichiometric

and the proportion of cations, anionic groups and water

vary widely affecting the ion exchange properties of the

material. The hydrogen atoms bound to the anionic groups

create the ion exchange properties, and the selectivity

depends on the size of the exchanging cations and cavities

and the distances between layers of the material. In par-

ticular, the hydration size and energy of the exchanging

cations has a great effect on the selectivity of tunnel- and

layer-structured materials. If the material has high charge

density it can strip or partly strip away the hydration shell

of cations, decreasing their size and enabling their access to

the inner structure of the material. Among all the metal-

loacids discussed so far Phosphate-based molecular sieves

[4–6] of Zr and Ti with mostly a neutral framework have

also attracted considerable attention of the academia and

industry. Titanium phosphates (TiPs) have been exten-

sively studied with respect to their diverse structures and

wide applications in some areas such as ion exchange [6, 7]

intercalation [8] proton conduction [9, 10] catalysis

Electronic supplementary material The online version of thisarticle (doi:10.1007/s10967-013-2815-1) contains supplementarymaterial, which is available to authorized users.

R. Chakraborty � P. Chattopadhyay (&)

Department of Chemistry, The University Burdwan, Golapbag,

Burdwan 713104, India

e-mail: pabitracc@yahoo.com

S. Chatterjee

Department of Colloids and Material Chemistry, IMMT,

Bhubaneswar 751013, India

123

J Radioanal Nucl Chem (2014) 299:1565–1570

DOI 10.1007/s10967-013-2815-1

[11, 12] and so forth [13, 14]. TiPs with layered [14, 15]

and mesoporous [16] structures have already been prepared

by different methods. Furthermore, attempts have been

made to synthesize nanostructured-TiPs apart from that of

porous materials. Such as TiP nanotubes were successfully

synthesized via a microemulsion-based solvothermal route

by an amine extraction [17]. Core–shell TiP nanospheres

were synthesized by using docusate sodium salt as the

structure-directing agent [18]. Hollow TiP spheres were

successfully obtained using polystyrene particles as tem-

plates [19]. Thus, due to their potential applications in ion-

exchange and catalysis the design of novel porous TiP

nanocomposite with well-defined morphology and uniform

size distribution is a matter of great interest.

The present work deals with the synthesis, characteriza-

tion and successful employment of nanocomposite TiP in

radioanalytical separation of the carrier-free 137mBa from137Cs. 137mBa is a short-lived radionuclide 62 (t1/2 = 2.55 min)

and is in secular equilibrium with the long-lived parent, 137Cs

[T1/2 = 30.07 years, 63 b-decay to 137mBa (94.4 %) with

single photon emission (662 keV). Radiochemical analysis

is required not only for processing radioactive waste samples

in the laboratory, but also for at-site or in situ applications of

carrier-free radioactive nuclides produced in the nuclear

reactions for radio-labeling of the pharmaceuticals in view of

getting potent radiopharmaceuticals. Monitors for nuclear

waste processing operations represent an at-site application

where continuous unattended monitoring is required to

assure effective process radiochemical separations produc-

ing waste streams that qualify for conversion to stable waste

forms. In connection with the present work, 137Cs/137mBa

generator has great advantage because of fast growth of

radioactive 137mBa, safe and frequent in-site elution, better

image quality, applications in teletherapy and irradiation or

sterilization of materials and plants [12, 20, 21].

Experimental

Reagent and apparatus

The powder X-ray diffraction (XRD) data were recorded

from a PANalytical X’pert Pro diffractometer with Cu Karadiation. The morphology of the nanosized materials was

studied by using of a JEOL-2003 analstation scanning

electron microscope (SEM). IR spectra were obtained by

JASCO FT-IR model 420 using KBr disc. Radioactivity was

measured with a scintillation counter equipped with a well

type NaI(Tl) detector. Size distribution measurements of the

nanoparticles were made by dynamic light scattering

(Model DLS-nanoZS, Zetasizer, Nanoseries, Malvern

Instruments). Samples were filtered several times through a

0.22 mm millipore membrane filter prior to measurements.

The radiotracer 137Cs in equilibrium mixture of daughter137mBa was obtained from Board of Radiation Isotope and

Technology (BRIT), India. TiCl4 (AR grade) was purchased

from Merck (Mumbai, India). Triton X-100 was purchased

from Himedia (Mumbai, India). The reagents for the syn-

thesis of the ion-exchange material were obtained from

commercial sources and used without further purification.

Synthesis of TiP nanocomposites using TX-100

Nanocomposite TiP were prepared by adding one volume of

0.05 M TiCl4 solution to two volumes of a (1:1) mixture of

6.0 M H3PO4 and TX-100 solutions drop-wise with constant

stirring [22]. Solutions of TiCl4 were prepared in 0.5 M

Fig. 1 a SEM image of TiP1and b STEM image of TiP1 for

EDS analysis

1566 J Radioanal Nucl Chem (2014) 299:1565–1570

123

H2SO4 and those of Triton X-100 and 6.0 M solution of

phosphoric acid was prepared in demineralized water. The

resulting slurry, was stirred for 3 h at this temperature, fil-

tered and then washed with demineralized water for removal

of the adhering ions (chloride and sulphate) till pH \ 4

before drying at room temperature. It was then treated with

1 M HNO3 for 24 h and was finally washed with deminer-

alized water, dried inside oven at 50 �C. The size of the core

of the material has been controlled by changing water to

surfactant ratio [23]. The ratio metric variation of water and

Triton X-100 has been utilized to produce nanocomposite

TiP of different sizes. TiP1, TiP2, TiP3, TiP4 and TiP5

were prepared using 10-1, 10-2, 10-3, 10-4 and 10-5 M of

Triton X-100 as a micelle, respectively.

Determination of size-dependent ion exchange capacity

(IEC) of TiPs

Previously reported batch method [24] was followed to

determine the hydrogen ion capacity. An accurately

weighed (0.5 g) portion of the ion exchange materials, TiP

were treated with 2.0 M HCl and then filtered off, washed

with distilled water, and dried at 50 �C for 2–3 h to remove

free HCl. The acidic form of the material was equilibrated

with 20.0 mL of 0.1 M NaOH solution for 1 h at room

temperature with stirring, and then the excess alkali was

titrated with 0.1 M HCl solution to determine the total acidic

hydrogen content. The IEC of the ion exchangers for dif-

ferent alkali and alkaline-earth metal ions was determined

by the batch method. To a glass-stoppered centrifuge tube

(diameter 2.0 cm) containing 0.5 g of the dry solid ion

exchangers, 50.0 mL of 2.0 M solutions of different alkali

and alkaline-earth metal ions were added to the tube in each

case; then the mixture was shaken for 1 h. The ion

exchangers were subsequently filtered off and washed with

bi-distilled water to remove the adhering H? ions. The

exchange capacities for the metal ions were determined by

measuring the liberated acid by titration with a standard

alkali solution. The IEC of each metal ion was determined

repeatedly for each concentration of Triton X-100 and the

effect size on IEC was observed.

Fig. 2 EDS spectrum of TiP1

Fig. 3 a TEM of TiP 4 with 100 nm scale. b SAED pattern of TiP

J Radioanal Nucl Chem (2014) 299:1565–1570 1567

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Studies on radio analytical separation by the TiP1

Separation of 137mBa from 137Cs radionuclide was per-

formed by column chromatographic technique following

the earlier reports [25–28]. In the column method, a glass

column of 5.0 cm length and 1.0 cm inner diameter was

packed with the 1.0 g of the material. The column bed was

preconditioned with a 10-5 M (pH 5) HCl solution. A

2.0 mL solution sample containing the measured amount of

cesium and barium radionuclides, where 137Cs is in secular

equilibrium with its daughter nuclide 137mBa was passed

through the column at a flow rate of 1.0 mL min-1. After

absorption of the mixture, 10.0 mL of a 10-5 M HCl

solution was passed through the column to ensure the total

absorption of the mixture. Finally, the daughter fraction

was eluted with 2 mL 1 M nitric acid, which was followed

40 60 80 100 120 1400

5

10

15

20

25

30

35

TIP 1N

umbe

r de

nsity

Particle size (nm)

40 60 80 100 120 1400

5

10

15

20

25

30

35

TIP 2

Num

ber

dens

ity

Particle size (nm)

40 60 80 100 120 1400

5

10

15

20

25

30

35

TIP 3

Num

ber

dens

ity

Particle size (nm)40 60 80 100 120 140

0

5

10

15

20

25

30

35TIP 4

Num

ber

dens

ity

Particle size (nm)

40 60 80 100 120 1400

5

10

15

20

25

30

35

TIP 5

Num

ber

dens

ity

Particle size (nm)

Fig. 4 DLS study for the

measurement of average size

distribution of nanoparticles of

TiP1, TiP2, TiP3, TiP4 and

TiP5 using 10-1, 10-2, 10-3,

10-4 and 10-5 M of Triton

X-100 as a micelle, respectively

1568 J Radioanal Nucl Chem (2014) 299:1565–1570

123

by collecting the effluent in ten successive counting tubes

(1.0 mL each). The c-activity in each tube was measured

with a NaI (Tl) c-ray spectrometer several times with a

time gap of 30 s.

Results and discussion

Characacterization of TiPs

The FTIR spectrum of TiP (Fig. S1) exhibits a broad band

in the region *3,410 cm-1 which is attributed to asym-

metric and symmetric hydroxy –OH stretches. A sharp

medium band at *1,640 cm-1 is attributed to aqua (H–O–

H) bending. A band in the region *1,050 cm-1 is attrib-

uted to P=O stretching. All the prominent peaks in the

XRD spectra (Fig. S2) for the materials have been analyzed

to determine the composition and probable molecular for-

mula of the material. The analyses of the prominent peaks

at 41.26, 58.04 and 73.20 (in 2h unit) confirm the material

as titanium phosphate with molecular formula TiP2O7

(Card no. JCPDF 38-1468).

Figure 1a, b show the SEM and STEM images of the

nanostructured material. Sample does not have unique

morphology. Magnified image shown in Fig. 1a clearly

indicates the size range of the individual flakes in nano-

meter region. EDS analysis (viz. Fig. 2) ensures the pre-

sence of P, Ti and O as dominant chemical elements in the

samples. The transmission electron microscopy (TEM)

image of TiP4 in Fig. 3a in 100 nm scale bar indicates the

flake-like morphology of the material. Further the SAED

pattern corresponding to this TEM image turns out to be

several partial rings, as shown in the Fig. 3b. The texture of

TiPs featured by diffraction pattern can be regarded as

polycrystalline with D spacing to be 3.2, 2.7 and 1.6 nm.

DLS measurement of TiP and sorption behavior

of the metal ions

The DLS study for measurement of average size distribu-

tion of TiP is shown in the Fig. 4. Variation of size of the

nanomaterial with varying water to surfactant (different

concentration of TX-100) ratio is listed in Table 1.

Exchange capacity for different metal ions increases with

decreasing size of TiP. This is simply because of the fact

that as the size of the particles becomes smaller, the

number of atoms on the surface of the exchanger increases.

Consequently small-sized particles show better sorption

behavior than the larger ones. Again the alkali metals show

a decreasing trend of the IEC (Cs? [ K? [ Na?) while the

alkaline earth metal ions follow the order Ba2? [ Ca2?.

The size and charge of the exchanging ions affect the IEC

of exchanger. This sequence is in accordance with the

hydrated radii of the exchanging ions. Ions with the smaller

hydrated radii easily enter the pores of the exchanger,

which results in higher adsorption.

Radio analytical separation

Separation of 137mBa from 137Cs radionuclide is ensured by

elution with a 1 M nitric acid solution. In presence of nitric

acid solution, Ba(II) forms very stable water-soluble

compound Ba(NO3)2 and hence it is eluted out of the

column matrix, whereas Cs(I) remains absorbed on the

column. The eluted sample was collected and counts of the

same fraction were taken at different time intervals to plot

the decay curve (Fig. 5). From the decay curve it is found

that the half-life of the daughter is 2.63 min which in very

much proximity to the actual the half-life of 137mBa (T1/

2 = 2.55 min). The radioactivity measured 1 h later is

equal to the background level which indicates that the

eluate does not contain observable amounts of the parent137Cs. As Ba(II) forms a stable and water soluble

Table 1 Exchange capacities of ZTPs of different particle sizes

towards metal ions

IEC in meq/g onto TiPs of different particle sizesa

Ions TiP 1 TiP 2 TiP 3 TiP 4 TiP 5

Na? 1.906 1.880 1.857 1.832 1.811

K? 2.116 2.09 2.067 2.046 2.021

Cs? 2.285 2.264 2.240 2.196 2.171

Ca2? 3.072 3.048 3.025 3.001 2.976

Ba2? 3.326 3.305 3.284 3.259 3.234

a Average size of TiPs (in nm):TiP1, 43.82; TiP2, 68.06; TiP3,

91.28; TiP4, 122.4; TiP5, 141.8

0 1 2 3 4 5 6 7 8 9

7.0

7.5

8.0

8.5

9.0

ln (

coun

ts)

Time (min)

Fig. 5 Decay curve of 137mBa eluted from TiP1 ion exchanger

(R = 0.99876 for eight points)

J Radioanal Nucl Chem (2014) 299:1565–1570 1569

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compound with HNO3, only 2.0 mL of 1 M HNO3 solution

was sufficient to remove 137mBa completely at a given

moment. When all the 137mBa was eluted from the 137Cs-

loaded generator, the 137mBa was allowed to grow until

secular equilibrium was established, so that the subsequent

fractions of the daughter nuclide could be recovered from

the parent nuclide adsorbed on the column by repeated

elution with a 1 M HNO3 solution. Thus the overall system

can be considered as a radionuclide generator. Fig. 5 shows

the decay curve of 137mBa eluted from TiP1 ion exchanger.

Conclusion

The designing of the conventional exchanger in nanoscale

range and its characterization has demonstrated its appli-

cability towards attaining a novel separation and confine-

ment of long-lived 137mBa from the long lived 137Cs of137Cs-137mBa radioactive equilibrated mixtures with

enhanced efficiency. It is of interest and importance to

fulfill the increasing demand for the radioactive waste

management for environmental protection and studies

related to nuclear medicines. The synthesis of the TiP

nanomaterial was attempted in a green chemical approach

without using any hazardous solvent or chemical.

Acknowledgments Financial assistance from UGC-DAE Center for

Scientific Research, Kolkata is gratefully acknowledged. The authors

are obliged to Dr. Suresh Valiyaveettil, Associate Professor, Materials

Research Laboratory (S5-01-03), Department of Chemistry, National

University of Singapore for his technical support in performing SEM

and EDS experiments. The authors are indented to Dr. P. Mitra,

Department of Physics, and B.U. for his cooperation in XRD analysis

and Dr. K. Bhattacharaya, BARC, Mumbai for TEM experiments.

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