I ndi an Journal of Chemi stry Vol. 4 1A, May 2002, pp. 934-941

Heavy metal ion uptake by homo and copolymers-A comparative study

K Hussain Reddy* & A Ravikumar Reddy

Department of Chemi stry, Sri Kri shnadevaraya Uni versity, Anantapur 5 15 003, India

Received 8 Jalluary 2002; revised 26 February 2002

Homo and copolymers of 2-hydroxy ethyl methacryl ate and chloromethylated styrene-an thranilic ac id have been prepared by free radical polymeri za tion technique. The che lating pol ymers have been characteri zed by IR and solid state 13C NMR spectroscopic techniques. Thermal stabilities of these polymers are investiga ted using thermogravimetric and differential thermal analy ses. Heavy metal ions viz. , Pb(II ), Hg(II ), Cd(lI ) and Cr(V I) have been removed by employ ing the present che lating po lymers. Metal ion uptake e ffi c iency, e ffec t of pH and time on the metal removal have also been studi ed. The metal removal properties are also tested under competitive conditions and found to depend strongly on pH. The polymers possess apprec iable selectivity for Pb(lI) and Hg(lI ) over Cd(I1) and Cr(VI). The amount of metal uptake by the polymer has been determined using a to mic absorption spec trophotometer. The po lymers have been reused a fter desorbing the metal ion from the polymer metal complex by HCI.

In recent years, there has been growing attention to the removal of toxic materials from industrial waste waters, not only for pollution control but also to enable to reuse the water l

-, . Most of the waste water results from cooling, rinsing, finishing , tanning, plating operations in the industry and is contaminated with heavy metal s4. Heavy metals are not biodegradable, hence their concentration continuously increases in the environment. These metal s besides being carcinogenic, pose serious threat to aquatic biota and environment.

Adsorption techniques employing activated carbon5

, starch xanthate6, fly ash 7, surpentine

minerals8 have been used for the treatment of industrial waste water. Alkaline precipitation9 and ion exchange lO methods have also been used for the removal of toxic metals. Recently bioprecipitation of some toxic metal ions by sewage bacteria has been reported II . However, conventional methods are generally non-selective and less efficient.

The use of complexing agents for the separation of metal ions are well established. An alternative mode of application of complex formation is however, the use of chelating resins in which various chelating groups have been incorporated and are attached to the resin matrix . Syntheses of che lating polymers have been accomplished using either polymerization or simple functionalization principles 12. The former involves the polymerization of monomers containing the desired ligands.

The functi onalized polymers have been recently used 13. 14 for the removal of heavy metal ions. In the li ght of the above, we report herein , the synthes is and

characterization of the chelating homo and copolymers of 2-hydroxy ethyl methacrylate and chloromethylated styrene - anthranilic acid and their applications in the removal of heavy metal ions.

Materials and Methods Chloromethylated styrene (Fluka) and 2-hydroxy

ethylmethacrylate (Merck) were freed from inhibitor by washing with 5% NaOH solution . Anthranilic acid (Merck) was purified before use. The polymerizations were initiated with benzoyl peroxide (BPO, 97% active compound; BDH Chemical s, Limited). Stock solutions of metal ions were prepared using AR grade lead nitrate, mercuric chloride, cadmium nitrate and dichromate salts.

Elemental analyses of the chelating polymers were carried out on an Hareaus Carlo Erba DP-200; CDR] , Lucknow. Fourier transform infrared (FTIR) spectra were recorded on a Brucker IFS 66 V model using potass ium bromide pellets . Solid state 13C NMR spectra of the samples were recorded on a Brucker DSX 300 MHz instrument. NETZSCH-Geratebau­GmbH thermal analysing system(T AS) was used to evaluate the thermal stability, decomposition temperature and kinetic parameters of the polymers at a heating rate of 10°C min- I. The metal removal was determined using a UNICAM UK Model 839 atomic absorption spectrophotometer.

Preparation of poly(2-hydroxy ethyl methacrylate) (PHEM)

2-hydroxy ethyl methacrylate( 12 ml , 0.095 mol) , methylethylketone (ME K) (30 111 1) and benzoyl

REDDY et al.: METAL rON UPTAKE BY HOMO & COPOLYM ERS 935

peroxide(BPO) (0.2g) were taken in a polymerization tube (l00 ml) and deaerated by pass ing oxygen free nitrogen gas for half an hour. The reaction tube was closed and kept ina thermostat at 70± 1 DC for 17 h. At the end, contents were added to large excess of methanol. The precipitated po ly(2-hydroxy ethyl methacrylate) (PHEM) was filtered, washed with methanol and purified by disso lving in DMF and reprecipitating by the addition of excess methano l. The purified polymer was dried under reduced pressure at 60DC for constant weight.

Preparation of chloromethylated polystyrene-anthranilic acid (CMPS-AA)

Chloromethylated polys tyrene (CMPS) was achieved by subj ecting chloromethylated styrene to solution polymeri zati on technique using free radical initiator (BPO). Chloromethylated styrene (7.25 g, 0.0475 mol), BPO (0.2 g) and EMK (30 ml ) were taken into a polymeri zation tube and purged with nitrogen gas for 30 min . The reaction tube was closed, kept in a thermostat at 70 ± I DC for 17 h. The contents were poured to excess methanol. The precipitated chloromethylated polystyrene was filtered, washed with methanol, purified by dissolving in DMF and reprecipitating by the additi on of excess methanol. The CMPS was dried under reduced pressure at 60DC fo r constant weight. The CMPS obtained was used fo r the preparation of CMPS-AA. 1.0 g of CMPS was allowed to swell in DMF ( 15 ml) for 45 min . The anthranilic acid (0.0036 mol) was di ssolved in hot DM F (30 ml ) and was added to the polymer suspension. Ethylacetate ( 100 ml) and triethylamine (0.015 mol, 1.5 g) were added to the above mixture, while stin·ing magnetically . The reaction mixture was reflu xed for 8 h. On cooling to room temperature, the res in was collec ted by filtration, washed several times with DMF, ethylacetate and absolu te alcohol and dried in a vacuum desiccator.

Preparation of copoly( chloromethylated styrelle­anthranilic acid-2 -hydroxy ethyl methacrylate) P(CMS-AA-HEM)

The copoly(chloromethylatd styrene-2-hydroxy ethyl methacrylate) P(C MS-HEM ) was prepared by soluti on polymeri zati on technique using free radi cal initiator (BPO). Chloromethylated styrene (7 .25 g, 0.0475 mol), 2-hydroxy ethyl methacrylate (6 ml , 0.0475 mol) and BPO (0.2 g) were taken into a polymeri zation tube. The contents were di ssolved in (40 ml) ethyl methyl ketone and purged with nitrogen

gas for 30 min . The reaction tube was closed and kept in a thermostat at 70 ± I DC for 17 h. At the end, contents were added to large excess of methanol. The precipitated copoly(chloromethylated styrene-2-hydroxy ethyl methacrylate) was filtered, washed with methanol purified by di ssolving in DMF and reprecipitating by the addition of excess methano l. The purified polymer was washed with chloroform to remove the traces of CMPS and PHEM formed duri ng the reaction and finally with methanol. The pure copolymer was dried under reduced pressure at 60DC fo r constant weight. The procedure involved in the preparation of P(CMS-AA-H EM) is simil ar to that of (CMPS-AA). 1.0 g of copoly(chloromethylated styrene-2-hydroxy ethyl methac rylate) was allowed to swell in DMF ( 15 ml) for 45 min . Anthranilic acid (0.0036 mol , 0 .5g) was dissolved in DMF (30 ml ) and was added to the polymer suspension. Ethylacetate (l00 ml ) and triethylamine (0 .015 mol, 1.5 g) were added to the above mi xture, while st1IT1I1g magnetically. The reaction mixture was reflu xed for 8 h. The P(CMS-AA-HEM) obtained was filtered after cooling to room temperature, washed several times with DMF, ethyl acetate and absolute alcohol and dried in a vacuum dess icator at room temperature.

Recommended procedure f or the removal of metal ion at different pH values

A 2.5 ml of 1 x 10.2 M metal ion (Pb(II), Hg(TI ), Cd(II ) or Cr(Y I) } solution, 7.5 ml of buffer (PH 2- 10) soluti on and resin (0.2 g) were combined in a 100 ml beaker and maintained under stirring for I h. The metall ated res in was filtered and washed thoroughl y with di stilled water. The filtrate was collected quantitatively into a 25 ml standard fl as k and diluted to the mark . The amount of metal ion present in the fi ltrate was estimated using atomi c absorption spectroscopy [Pb, 283 .3 ; Cd, 228 .8 and Cr, 357 .9 nm] and Hg(II) was determined (470 nm) spectrophoto­metrically using 1, IO-phenanthroline I5

. The amoun t of metal ion was deduced from the predetermined calibration curve.

Recommended procedure f or the removal of Hg( II) at different time intervals

A 2.5 ml of I x 10.2 M Hg(U) solution, 7.5 ml of bu ffer (PH 10) solution and res in (0.2 g) were mi xed in a 100 ml beaker, the mixture was maintained under stirring for di ffe rent periods of time (1 5, 30, 45, 60 and 120 min). The metallated res in was filtered and washed thoroughly with distilled water. The filtrate

936 INDIAN J CHEM, SEC A, MA Y 2002

was collected quantitatively into a 25 ml standard flask and diluted to the mark . The amount of Hg(II) present in the fil trate was estimated usi ng 1,10-phenanthroline spectrophotometrically. The amount of Hg(lI ) was estimated from the predetermined calibrati on plot.

Recoil/mended procedure 10 determine the metal iOIl selectivity on various chelating polymers

An aliquot [containing 0.1 M Pb(ll) (0.5 ml), Hg(lI) (0.5 ml) , Cd(lI ) ( I ml) and Cr(VI) (2 ml)] was taken in a 100 ml beaker containing I g of the resin and 7.5 ml of buffer (pH 10) sol ution. The mixture was maintained under sti rring for I h. The metallated resin was filtered and washed thoroughly with di stilled water. The filtrate was collected quantitatively in 100 ml standard flask and diluted to vol ume. The amounts of metal ions were determined by AAS and spectrophotometric [for Hg( II )] methods.

Results and Discussion 2-Hydroxy ethyl methacrylate, chloromethylated

styrene and anthranil ic ac id were used to get the homo and copolymers. The preparative scheme for the chelating polymers is given in Scheme I. The reactions were carried out in DMF, which causes considerable swelling of the polymer. The CMPS was colourless, however CMPS-AA and P(CMS-AA­HEM) are yellow and pale yellow in colour. The analytical data are given. PHEM: 80% yield. Anal. Found: C, 54.5%; H, 7.9%. Calcd: C, 55 .3%; H, 7.89%. CMPS-AA: 70% yield. Anal. Found: C, 73.2%; H, 6.0 1 %; N, 5.50%. Calcd : C, 75.8%; H, 5.92%; N, 5.53%. P(CMS-AA-HEM): 63% yield. Anal. Found : C, 63 .9%; H, 7.4%; N, 3.01 %. Calcd: C, 65.5 %; H, 7.5%; N, 3.2%. The data suggest that yields of the resins are moderate to high. The analytical data are in agreement with the calculated va lues.

The chelating polymers are insoluble in organic solvents. The typical CP/MAS solid state 13C NMR spectrum was recorded . The backbone of methylene carbon appeared as a sharp peak at 48.33, 47.52 and 48.05 ppm respectively for PHEM , CMPS-AA and P(CMS-AA-HEM). 40.48 ppm peak was also observed in P(C MS-AA-HEM), it is due to the (-CHr ) methylene group of HEM. Ester carbony l carbon (C=O) appeared at 180.50, 170.72 and 179.28 ppm respectively for PHEM, CMPS-AA and P(CMS-AA­HEM). 164.3 1 peak observed in case of P(CMS-AA­HEM), thi s is due to the carbonyl carbon of HEM .

TH]

H2c=T o=c

I

H:) BPO, ME".,

70± I'C

'rH] - H,C-C-

- I 0=0

I o

1-10)

Ca) Polymerizat ion of2-hydroxy ethyl methacry;ate (HEM)

rcOl!'( 811. . DM!'

Ethyiacctate TIOP.

(b) Preparat ion of po ly (chloromethylntcd styrene-ant hranil ic acid) P(CMS-AA)

Ti l] T il]

. " '~~) "",:;;~~'. -"'c¢- "'~=\

TH]

-H'C¢-H'~r

0-CH2 HO) I

o~C)QJ H2N

112CCI 110

reOlD<811. DMF [ thyiacc tate. TEA

Ce) Preparation of polYCchloromcthyla tcd styrene - anth ranilic ilcid - 2.hydrox\, ethyl methacryla te) P(CMS-A A-1-1 EM) .

Scheme I

The lower value when compared to PHEM may be due to the presence of adjacent (CMS-AA) group. The assignment of the peaks are given in Table I.

Infrared spectra of the chelati ng polymers were recorded in the range 4000-500 em- I, using KBr discs . A comparison of IR spectra or CMPS to that of CMPS-AA and P(CMS-AA-HEM) ~ hows the absence of VC-CI (672 em - I) and the presence of C-O-C (- 1095 cm- I). IR: CMPS ; v 2958 (C-H), 672 (C-Cl) cm- I. PHEM : v 3600 (O-H), 2992 (C-H), 1740 (C=O), 11 20 (C-O-C) cm- I. CMPS-AA : v 3320 (N-H), 2902 (C­H) , 1690 (C=O), 1085 (C-O-C) em- I. P(CMS-AA­HEM): v 3500 (O-H), 3250 (N-H), 2950 (C-H), 1730 (C=O), 11 33 (C-O-C) cm- I. The lower OH and NH stretching frequencies (-3300 em- I) were due to hydrogen bonding in polymeric assoc iation. Thus the above data support the formatio n of the chelat ing polymers.

REDDY el al.: METAL ION UPTAKE BY HOMO & COPOLYMERS 937

Thermograms of the chelating polymers are shown in Fig. I. A mathematical interpretation of thermo­gravimetric curves enables one to determine kinetic parameters of pyrolysis reactions . Horowitz and Metger l 6 have demonstrated the method of calcul ation of energy of activation of polymeric substances. The equation used for the calculation of energy of activation (£) was,

I I [Wo]_ £8 n n - ---W RT 2

t - s

... ( I )

where 8 = T - T,. Wo is the initi a l weight, WI is the weight at any time

t, 1~ is the peak temperature and T is the temperature

at panicul" weight loss. A plot of In In [ : : ] ve"us

Table I - So lid state IJC-CP/MAS NMR spectral data of the chelating polymers

Oppm of Oppm or oppm of A' sS lgnmenl PH EM CMPS-AA P(CMS-AA-HEM )

23.23

48.33 47.52

62.87 68.47

128.27

180.50 170.72

20.65

48 .05

66.05

132.65

179.28 164.3 1

H,C group present in the polymer back­bone

Methylene (-CH2-) backbone

(-C-) of the main chai n and 68.47 is chain CH of the main chain

Aromatic carbons

Ester carbon y I

o - .-----::::--=--=-~~

O~----~--------------200 400 600 800

Temp. (oe)

Fi g_ I - Thermogra ms of the polymers PH EM(-). CMPS-AA (_._._) and P(CMS-AA-HEM) (- + - + - )

8 gives an excellent approximation to a straight line. The slope is related to the acti vation energy , i. e.,

£ Slope = --2

RTs ... (2)

Representative plots are shown in Fig. 2. The calcul ated values for the act ivation energy of decomposition are li sted in Table 2. The activation energy associated with each stage of decompositi on was a lso evaluated by the well known Bro ido method l 7

. The equation used for the calcu lat ion of activation energy (£) was,

In In(-' I = (~I ~ Y" j R j T + Constant ... (3)

where W -W Y" = t 00

W -W ° ~

that is , Y' is the fraction of the number of initi al mo lecules not yet decomposed ; WI the weight at any

0.5 ,-------------------,-------,

o . PHEM

- 0.5

.-,. - 1 ;;-<. -1 .5

~ -2

-2.5

-3

-3.5

-4

• CM"S-AA

• p(CMS-AA-HEM)

• •

- 4.5 +------,------,-------,----,--__ -, __ -1

-300 -200 -100 o 100 200

O(K)

Fi g. 2 - Representative Horowitz and Metger plots

0.5.,------,-----

o -0.5

-1

?:: -1 .5

S -2 c C -2.5

-3

-3.5

-4

. PHEM

• Ctv'PS-AA

.t. p(CMS-AA -HEM)

-4.5 +--.--~--~_-__ --_ ------'

1.5 2 2.5 3 3.5

Fig. 3 - Representati ve Broido pl ots

300

938 INDIAN J CHEM, SEC A, MA Y 2002

Table 2-Activation energy of decompos iti on for various chelating polymers by thermograv imetric analyses

Polymer samples Peak Decomposition Weight loss Method Activation energy

PHEM

CMPS-AA

P(CMS-AA- HEM )

HM Horow itz & Metger BR Broido

OJ E o

o

ClJ u c ClJ

0.0

~ -2.0

Q.

E ~

, -. \

temperatu re temperature range (%) (kJ morl ) (TsOC) (O°C)

244 200-380 76 HM 42 .05 BR 65.32

418 380-600 12 HM 57.35 BR 44 .8

180 11 5-335 2 1 HM 34.52 BR 39.55

430 335-500 42 HM 44 .82 BR 50.64

580 500-700 20 HM 66.75 BR 78.3 1

220 200-274 8 HM 4 .2 BR 50.05

343 274-400 32 HM 48.90 BR 75 .82

565 400-780 40 HM 78.60 BR 108.95

-4 .01+-----------__ ------------------------~--------------~ a 200 400

Temp (oe)

600 800

Fi g. 4 - DTA plots of the polymers PH EM(- ), CMPS-AA (_._._) and P(CMS- AA-HEM) (- + - + -)

d In~ 2

Till £ =

d( ~ ) R ... (4)

time ' t', W= the weight at infinite time (= zero); and

Wo the initi al weight. A plot of In In (1 IY') versus l iT gives an excellent approximation to a straight line

over a range of 0 .999 > Y" > 0.00 I. The slope is re lated to the acti vation energy . Representative plots are shown in Fig. 3 . The calculated values for the ac tivation energy of decomposition are li sted in Table 2.

The DTA plots of the po lymers are g iven in Fig. 4.

where <», a constant rate of temperatu re rise , Till the te mperature at which the peak di fferenti al thermal analyses deflection occurs; and T, the temperature .

Ki ss inger ls.19 method was used for the determination

of acti vation energy. The eq uation used for the calcul at ion of ac ti vation energy (£) was,

The plot of [ In ~lagainst the reciprocal of the Till

REDDY el al. : METAL ION UPTAKE BY HOMO & COPOLYMERS 939

absolute temperature (lID gives the energy of activation (E) of the decomposition using the equat ion,

Slope = E

R ... (5)

Representative plots are shown in Fig. 5. The calculated values for the activation energy of decomposition are 9.21, 10.23 and 11.46 kJ mort for PHEM , CMPS-AA and P(CMS-AA-HEM) respectively . It has been found that all the chelating polymers are stable and shows maximum peak differential thermal analyses deflection In the temperature range 350-580°C.

Removal of heavy metal ions effect of pH all the removal of metal ions

The effect of pH on metal ion uptake was studied at different pH values by following the recommended procedure. The effect of pH on the removal of heavy metal ion by the present chelating polymers are given in Fig. 6. Uptake efficiencies of the polymers depended strongly on the pH. It increased from pH 2 to pH 10. As the pH increases, uptake of metal ion by polymer also increases . As the uptake of metal ions is maximum at pH 10, an NH4CI-NH40H buffer solution of this pH is se lected for further studies. At higher pH values (-10), the alcoholic OH [present in PHEM, P(CMS-AA-HEM)] is presumably deproto­nated and binds with metal ions to give metal chelate. The time required for full metal ion uptake is found to be about I h. Affinity order at pH lOis Pb(II) ~ Hg(IJ) > Cr(YI) > Cd(lI) for CMPS AA and P(CMS-AA­HEM) and Pb(lI) ~ Hg(Il ) > Cd(II) > Cr(VI) for

- 9 ,4 ..-------------------,

- 9.6

-9.8

-1 0

-10.2

~-10.4

~-10,6 i:i: -10.8

E -11

-11,2

-11 .4

.PHEM

• CrvPS-AA

• p( CMS-AA-HEM)

_lUi +---=-t-----r----.,.-----r--l 0,5 1,5 2.5

1ITx 1O-3(K-1)

Fi g. :=; - Representati ve Ki ssinger plots

PHEM . At pH 6, Hg(II) > Pb(IJ) > Cd(II) > Cr(YI) for PHEM, Hg(Il) > Cr(YI) > Pb(II) > Cd(II) for CMPS­AA and Hg(II) > Cr(YI) > Cd(II) > Pb(II) for P(CMS­AA-HEM) , At pH 2 appreciable metal ion removal was not observed. Therefore, the present chelating polymers are Pb(II) selective at pH 10 and Hg(II) selective at pH 6. Thus, selectivity of chelating polymers depends on pH.

Effect of time on the metal ion uptake The effect of time on metal ion uptake was studied

at pH 10 by following the recommended procedure . It was found that Ih time was required for maximum and constant metal ion uptake, The data are presented in Fig. 7.

Selectivity studies The selectivity studies were carried out by

following the recommended procedure, In this case, 100 ppm of each metal ion in the solution was

(ij > 0 E QJ 0:: ::!'! 0

(ij > 0 E QJ 0::

~

11 Fb(II)

120 C']t-Jg(U)

o Cd(II)

100 ~ Cr(VQ L--

80

60

40

:111 I

12 6 L....-___ 1-.JOj 12 Rl

6 10 I <-I 2 __ 6 __ 1-.JQ

R2 pH

R3

Fig. 6 - Effect of pH on the removal of metal ions by R I [PHEM); R2[CMPS-AA) and R3 P[CMS-AA-HEM)

120 --

100

80 . ,

60

40

20

0 I I I 115 30 45 60 1201 ~5 30 45 60 1201115 30 45 60 1201

RI R2 RJ Time (min)

Fig. 7 - Effect of time on the removal of Hg( lI ) by R I [PHEM) ; R2[CM PS-AA) and R3 P[CMS-AA-HEMl

940 INDIAN J CHEM, SEC A, MA Y 2002

allowed to react with the polymer at pH 10. The overall metal uptake capacity of the polymers at pH 10 under competitive conditions are In good agreement with the results obtained In the noncompetitive experiments. The chelating efficiencies of the present polymers increased from PHEM , CMPS-AA and P(CMS-AA-HEM). Thi s is probably due to the increase in the stabi lity of the complex in the above order. The selec tivity order is P(CMS-AA-HEM) > CMPS-AA > PHEM and the data are presented in Fig. 8.

Effect of recyclability Oil the removal of metal iOlls The most importan t advantage of chelating

polymers is their reuse after a parti cul ar process. The desorb ing the metal from metallated polymers using 6M HCI in tctrahydrofuran. The metal free polymers

I1!l RJ(II)

120 o Hg(II)

(ZJ Cd(II)

100

_ 80 ro > 0 E60 OJ c:: *' 40

20

0 R1 R2 R3

Selectivity

Fig. 8 - Selectivity studies on the removal of meta l ions by R I [PHEMJ; R2[CMPS-AA] and R3 P[CMS-AA-HEM J

can be reused after neutrali zation . in acidic medium, the metallated chelating resins are protonated and re leases the metal into the solution . The metal io n uptake was found to be al most same even after 4 cyc les. For every cycle, the % metal ion desorption and uptake was estimated. The data are given in Table 3.

Conclusion Heavy metal ions [vi z., Pb(J/ ), Hg(rI) and Cd(lI )]

are known inorganic pollutants. The presence of these metal ions in aquatic sys tems pose heavy risk to human health . Therefore, removal of metal ion from water bodies may be considered as an interesting research acti vi ty .

Chelating polymers have been sy nthesized by empl oy ing free radical po lymeri zation and subsequent modifications. These res ins have been characterized based o n elemental analyses, infrared and so li d state 13C NMR spec tra. Kinetic data suggest that the resins are highly stable and may be used for the removal of metal ions at room temperature. The metal uptake effi ciency increases with p H and reaches plateau value around pH 10. The favourab le characteristic of present chelating po lymers is the time required for the maximum and constan t uptake of metal ion from aq ueous media. Just I h time is sufficient in the present methods, while recently reported methods20

.2

1.22 require longer period of time. The metal ion selectivi ty of present chelating polymers (at p H 10) is found to be in the order Pb(Jl) > H(II) > C r(VI) > Cd(II ). The metal ion upt ake efficiency of the resin is not a ltered much even after four cycles .

Table 3 - Recyclability of the res ins on the uptake of meta l ions at recommended pH from 207 .2 ppm of Pb( ll ), 200.6 ppm of Hg( ll ), 112.4 ppm of Cd(l l) and 52.0 ppm of Cr(Vl)

Cycle Polymer Pb(ll ) Hg(ll) Cd(ll ) Cr(Vl) No. Uptake desorp- Uptake desorp- Uptake desor- Uptake desorp-

(ppm) ti on (%) (ppm) lion(%) (ppm) ption (%) (ppm ) ti on (o/c)

PHEM 175.2 98.5 179 .7 97.5 56.7 98.0 19.2 95.8

2 174.8 97.4 175.4 96.4 56.3 96.5 19.0 98.5

3 174 .1 96.5 174.5 95 .5 55.8 97.8 18.5 97.5

4 173 .5 97.5 173 .8 98.5 55.6 97.5 17.2 97.4

I CMPS-AA 189.2 99.0 182.35 95.8 69. 1 98.3 44. 98.6

2 189.0 98.2 182.0 97.4 68.5 98.5 43.2 95.8

3 188.5 98.5 178.4 96.5 98.3 97.8 42 .8 97.4

4 188. 1 98.6 177.6 97.8 67.5 97.7 42.3 96.4

I P(CMS-AA-HEM) 203 .5 97 .6 194.85 99.4 79.5 96.5 47.1 98.3

2 203.2 98.5 192.4 98.5 77.5 . 97.3 46.8 98.2

3 202 .8 97.5 190.3 97.4 76.4 98.5 46.4 97.4

4 202.5 97.4 189.2 96 .5 76 .1 97.5 45.1 96.8

REDDY et ai.: METAL ION UPTAKE BY HOMO & COPOLYMERS 941

The metal ion uptake efficiency of the polymers is in the order P(CMS-AA-HEM) > CMPS-AA > PHEM. Thus, the copolymer containing functional groups of both the homo polymers is more efficient in the removal of metal ions.

Acknowledgement The authors thank the CSIR, New Delhi, India

(Grant No. 01 (1 558)/98/EMR-I1) for financial support. Further, we acknowledge RSIC Chennai ; SIF, Bangalore and NMDC, Hyderabad for providing thermal and solid state J3C NMR and AAS data respectively.

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