Indian Journ al or Chemistry Vol. 45A, September 2006. pp. 2045-2047

Cellulose acer. .• te based thorium(IV) phosphate as a new and novel hybrid fibrous cati on exchanger: Synthesis, characteri zati on

and thermal anal ys is

K G Varsh ncy"·''', M Drab ik" & Arun Agrawal "

" Depa rt ment o f Appl ied Chem istry. Facu lty o f' Engineeri ng and Techno logy, A l igarh Musli m Un iversity. ;\l igarh 202 002. India

" Institute o f Inorganic Chemistry, Slovak Academy of Sc iences. X-12 36 !3rati sl•tva. Slovak Republi c

Email : roma_gopa l @n.: dillmail.com

Receit •et! -1 Febnwrr 2006: ret•ised 24 .l1111 l' 2006

Cel lulose acetate based thorium(IV ) phospha te (CAThP) has been synthes ized as a new phase of hybrid fibrous cation ex­changer by mixing thori um nit rate. phosphoric acid and cell ulose ace ta te in dif'f'crent pro porti ons to obta in a material o f optimum ion exchange propert ies. I t has been charac terized by using JR. TGA. XRD and SEM stud ies in additi on to i ts ion exchange ca­p•tcity . elution. concentration and pH titration. Extensive thermo­gravimetr ic studies have been performed to evalu•t tc the behaviour o f the materia l and it s tentati ve structure.

IPC Code: Int. Ci s 1301139/00

Fibrous inorgan ic ion exchangers arc quite interes ting from the practica l poi nt of view because or their po­tent ial appli ca ti ons 1

• They can be used to prepare in­organic ion exchange papers or thin layers suitable fo r chromatographi c cati on separati ons and as ion ex­change membranes wi thout a binder wi th good elec­trochemica l behav iour. Because of th ei r high se lec­ti vi ty and stabi l ity they can also be used as ion selec­ti ve membranes. A lbe rti et e l . ~ sy nthesized th orium phosphate as f ibrous ion exchanger suitab le for mak­ing (support free) inorgan ic sheets. Hi s main empha­sis has been on ly on its chem ica l analys is. th erma l stab ility and ion exchange properti es wi th alkali metal ions without explorin g its analyti cal potential. Our efforts have been to synthes ize new f ibrous hybri d materi als and to ex plore their ana ly tica l appli ca ti ons with a view to use them in environmental studi es.

We have observed ea rli er that the introducti on o f po lymeri c species into inorganic f ibrous materi al greatly enhances its mechanica l strength , making it potentially more use ful in industrial and environ­mental appli cati ons'-x . Acry lonitri le, acry lamide,

po lys tyrene and pectin have been used in our labora­tori es to prepare some hybri d f ibrous materia ls in­vo lv ing cerium(IV) and thorium(IV). They have shown good ion exchange behav iour, and chemica l and mechanica l stabi I i ty along w ith selec ti vity fo r certain metal ions use ful for environmental poll ution control. The present study is an ex tension of our ef­fo rts to prepare new and novel ion exchange material s based on polymeri c spec ies. Synthes is, ion exchange charac teri sti cs and thermal behav iour of ce ll ulose acetate based thorium (IV) phosphate (CATh P) arc described here.

Experimental A nu mber of samples were prepared by adding one

vo lume of 0 .1 M Th (N0,)~. 5 H 20 so luti on in two vo l­umes o f ( I : I ) mi xture o f 2 M H 3 PO~ and ce ll ulose acetate (0-1 8%) dropw ise w i th constant sti rri ng usi ng

a magneti c sti rrer at a temperature of 90±5°C. The resulting slurry was stirred !'or 4 h at thi s temperature. l'ilterecl and washed w ith deminerali zed water (p H-6). On dry ing at room temperature, the prec ipitate re­sulted into a sheet, which was crushed into small pieces and converted into the H+-form by treating with I M HN0.1 for 24 h w ith occasional shaki ng and intermittentl y replacing the supern atant liquid wi th fresh acid . T he materi al obtained was then washed w ith deminerali zed water to remove th e excess ac id

be fore dry ing fi na ll y at 45°C and sieved to obta in parti cles o f 50-70 mesh size. Vari ous samples were prepared by th is method vary ing the amoun t of cellu­lose acetate. T he sample obtained w ith a 5% cell ulose acetate was found to have a maximum Na+ ion ex ­change capacity (i .e.c.). The sample ( 1.70 meq/dry g) was selected for all subsequent studi es.

T he i .e.c. of the sample was determined by the co l­umn process taking I g of the materi al (H+ form) in a glass tube o f intern al diameter - I em, fitted w ith glass woo l at its bottom. A 250 mL porti on of I M al 0 1 so lution was used as eluant mainta inin ~ slow fl ow rate (-0.5 mL min-1

). The effluent was tit7-a tecl against a standard alkali so luti on to determine the tota l H+-ions released. T he i.e.c. in meq/d ry g fo r Li+ . Na+ , K+ , Mg~+ , Ca2+ , Sr2+ and Ba2+ were found

to be 1.53, 1.70, 1.93, 2. 1 0, 2.74, 2.95 and 3. 16. respccti ve ly.

2046 INDIAN J CII EM , SEC A. SEPTEM BER 2006

0.3

1J 0.25 .---

f-.-

Cll (/) 1----<ll Cll

0.2 ~ 1--

1--(/)

c: 0.1 5 0

+ 1----:r: 0 0.1 1----_

-C" Cll

E 0.05

0

10 20 30 40 50 60 70 80 90 100 110

Volume of NaN03 (ml)

Fig. 1- lli stog ram showing the eluti on behaviour o f ce llulose ace tate based thoriulll ( IV ) phosphate.

Table !- Concentrati on behav iour o r cellu lose ace t:lte based thor iu111 (IV) phosphate

Concentration or NaNO, (M )

0.2 0.4

0.6 0.8 1.0 1.2

Ion exchange capacit y ( 111eq/dry g)

0.75 1.03 1.2 1 1. 25 1.70 I. 70

The extent of elution was found to depend on the concentrati on of the eluant. Hence, a fixed volume (250 mL) or the NaNO, so luti on or vary ing concen­tration s (0.2-1.2 M) was passed through the co lumn containing I g o f the exchanger and the effluent was titrated against a standard alkali so lution for the H+-i ons eluted out. Table I shows concentration behaviour o f CA ThP.

Optimum concen trati on of the elu an t for a com­plete elution of H+-i ons in 250 mL or NaN0.1 so lution was found to be I M. A similar co lumn containing I g or exchanger was then eluted w ith a aNO, so lution or I M concen trati on in eli fferent I 0 mL fract ions w ith a minimum fl ow rate as described above. Studies were made to find out the minimum vo lume necessary for a complete elution of H+-i ons, which refl ect effi­ciency or the CAThP co lumn. The results arc shown in Fig. I .

Results and discussion CATh P is a new fibrous ion exchanger obtained in

the form or shee t. The surface morphology o f the hy-

brid material was observed by the SEM photograph taken at 2000x magnifi cati on. It wa~ found to be similar to that o f the inorganic paren t 1aterial , tho­rium phosphate, which is fibrous in nature.

The eluti on behav iour reveals that till~ exchange is fast on CAThP. A lmos t all the H+-i ons are el uted out in the first II 0 mL of the effluent fro m a col umn or 1.0 g m aterial. The optimum concentration for the eluant was found to be I M (Table I ) fo r a complete remova l of H+-ions from a CAThP column. M oreo­ver, the exchange takes place in one step as indicated by the pH titrati on curves obtained unccr equ i librium conditions for LiOH/LiCI , NaOH/NaCI and KOH/ KCI exchanges, which may be clue to the fact that the first ionization or phosphori c ac id is much faster as compared to the other two (pK" values or I-I :~ P0-1 being 2.1 2, 7.2 1 and 12.30) . A fast release or H+-ions in aqueous media is al so suppon d by the low pH (-2) of the sa lt soluti on w ith which the material is kept in contact for somet ime. It s how~; strong ca ti on exchange behaviour or the material.

The thermal studi es on CAThP ind icate that the hybrid materi al is very stab le retaini ng an ion ex­

change capacity o f -93% on heating up to I 00°C. Even on heating up to 400°C, about 44% of the i .e .c. is retained. However, when the material is heated up to 600°C, it shows a sharp decrease in its ion ex­change capacity re taining only - 13%.

Assuming the basic structure of thori um phosphate as proposed by A lberti and appl y ing the A lberti for­mula'! for the evaluati on o f the ex ternal water mole­cule in our materia l, a tentati ve formula can be sug­ges ted as:

NOTES 2047

where X stands for the cellulose acetate monomer unit.

The evaluation of the cellulose acetate part in our material is based on the elemental analysis (carbon content 8.96%). The TG A data on the mass losses of the composites during heating were compared with one another and it is found that the rati o of phosphate to cellulose acetate is shifted towards much hi gher concentration of cellulose acetate in the co mposites ( -20-40%) agai nst the ori ginal mt xt ng amount (3-8%). This di screpancy may be explained on the basis of the fact that a polymerization process has oc­curred in the material.

In the reaction mi xture containing I% cellulose acetate, the co mposition of the material was found to be close to the pure thorium phosphate. The X-ray diffracti on pattern of CAThP indicates it s semi crys­talline nature as it exh ibit s so me weak peaks. The IR spectrum confirms the presence of metal ox ide and metal hydroxide bands in the material. The metal oxygen and metal hydrox ide bands are observed at 622.2 and 669.4 cm·1

. The bands at 107 1.2 cm·1 indi­cate the presence of phosphate groups while the ab­sorpti on bands at 1595.8, 1630.8, 3433.8, 3656.9, 3694.7 and 3779.6 cm·1 correspond to the water or crysta lli zati on. The band at 2364.2 cm·1 indicates the C-H stretching of carbon. The C=O stretc hin g of ester was observed at 1722.6, 1758.2 , 18 12.4 and 1854. 1 cm·1

• The absorp tion ba nd at 1353.2 cm·1 indicate C- 0 stretching of alcohol.

The cellulose acetate based thorium (IV ) phosphate is a hybrid fibrous material possess ing an improved ion exchange capacity as compared to the parent tho­rium phosphate prepared under similar conditi ons. It appears to be a promising ion exchanger having good thermal stability poss ibly due to a mutual interaction of thorium phosphate and cellulose acetate, resu lting into the chemical bonds formation between the atoms originated from both phases.

Acknowledgement Thanks are due to the Chairman, Department of

Applied Chemi stry, Aligarh Muslim University. for research facilities and to The Mini stry of Environment and Forests, and All India Council for Technical Ed u­cation, New Delhi for financial assistance. One of the authors (M.D. ) acknowledges the support of VEGA grant, project No. 2/5011 /25.

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