Chelating resins VII: studies on chelating resins of formaldehyde and furfuraldehyde-condensed phenolic Schiff base derived from 4,4′-diaminodiphenylsulphone and o-hydroxyacetophenone

Reactive & Functional Polymers 42 (1999) 37–52 www.elsevier.com/ locate / react Chelating resins VII: studies on chelating resins of formaldehyde and furfuraldehyde-condensed phenolic Schiff base derived from 4,49-diaminodiphenylsulphone and o-hydroxyacetophenone *S. Samal , N.K. Mohapatra, S. Acharya, R.K. Dey Department of Chemistry, Ravenshaw College, Cuttack 753003, India Received 15 November 1997; received in revised form 6 April 1998; accepted 29 June 1998 Abstract The synthesis, characterization and capacity studies of two chelating resins having multiple functional groups capable of coordinating to several metal ions are reported. The resins were synthesized by condensing phenolic Schiff bases derived from 4,49-diaminodiphenylsulphone and o-hydroxyacetophenone with formaldehyde/ furfuraldehyde. The polymeric Schiff bases were found to form complexes readily with several transition metal ions. The resins were completely soluble in dimethyl sulphoxide, tetrahydrofuran, partially soluble in CHCl , CCl , and insoluble in water. On formation of the3 4 polychelate with transition metal ions such as Cu(II) and Ni(II), the solubility sharply decreased. The Schiff bases, resins 1 13 and the polychelates were characterized by FTIR, FT H-NMR, C-NMR and XRD studies, and thermal analyses like TGA and DSC. From FTIR studies the phenolic oxygen and the imine nitrogen of the resins were found to be the coordination 1 sites. The H-NMR data indicated the presence of bridging methylene and terminal methylol functions in the formaldehyde- condensed Schiff base. The thermal stability of the resins and the polychelates was compared by analysing TG data which provided the various kinetic parameters like activation energy, frequency factor and entropy changes associated with the thermal decomposition. The DSC and XRD data indicated that the incorporation of the metal ions significantly enhanced the degree of crystallinity. The adsorption characteristics of the resins towards Cu(II) and Ni(II) in dilute aqueous solutions were followed spectrophotometrically. Cu(II) was seen to undergo preferential adsorption in a mixture of Cu(II) and Ni(II). The effects of contact time, pH, temperature, the size of the sorbents and the concentration of the metal ions in solution on the metal uptake behavior of the resins were studied. Ó 1999 Elsevier Science B.V. All rights reserved. Keywords: Chelating resins; Phenolic Schiff bases; Formaldehyde; Furfuraldehyde 1. Introduction [1,2]. Such ligands are characterized by the presence of reactive functional groups of O, N, The chelate-forming polymeric ligands have S, and P in the polymer matrix capable of been extensively studied by several authors coordinating to different metal ions. The materi- als most often show preferential selectivity *Corresponding author. Tel.: 191-671-602-335; fax: 191-671- towards certain metal ions facilitating their use619-102. E-mail address: [email protected] (S. Samal) for preconcentration and separation of trace 1381-5148/99/$ – see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PI I : S1381-5148( 98 )00055-8 38 S. Samal et al. / Reactive & Functional Polymers 42 (1999) 37 –52 metal ions from saline and non-saline water. characteristics of the resins towards Cu(II) and The selective behavior is primarily based on the Ni(II) in their dilute aqueous solutions were stability of the polychelates at appropriate pH followed by varying contact time, pH, tempera- values. Their analytical use in conjunction with ture, size of the sorbents and concentration of atomic absorption spectroscopy (AAS) and in- the metal ions in solution spectrophotometrical- ductively-coupled plasma optical emission spec- ly. trometry (ICP-OES) studies has been well established [3,4]. 2. ExperimentalMoyers and Fritz [5] condensed m-phenyl- enediamine tetraacetic acid with resorcinol and The starting materials such as 2-hydroxy-formaldehyde to get a resin containing two acetophenone, 4,4-diaminodiphenylsulphoneiminodiacetic acid functional groups anchored (Merck, Germany), the sulphate and nitrate saltsto benzene ring and used the resin to separate of Cu(II) and Ni(II), formaldehyde, fufural-Co(II) from Ni(II) in a gravity flow column. dehyde (Merck/Qualigen, India, AnalaR grade)Several authors [6,7] studied resorcinol-form- were used as received. The solvents werealdehyde oxime polymers and found the resins distilled prior to use.to be very selective for heavy metal ions. Condensation of phenol-formaldehyde and 2.1. Preparation of Schiff basepiperazine resulted in a resin selective for Cu(II) [8,9]. The Schiff base monomer o-hydroxy- Schiff bases having multidentate coordination acetophenone-4,49-diaminodiphenylsulphone (o- sites are known to form complexes with transi- HAP-DDS) was synthesized by reacting 2.48 g tion metal ions readily [10–15]. Present in a (0.01 mol) of 4,49-diaminodiphenylsulphone polymeric matrix, they are expected to show dissolved in 10 ml of methanol with 2.72 g affinity and selectivity towards these metal ions (0.02 mol) of o-hydroxyacetophenone in the at an appropriate pH. This led us to synthesize a presence of 0.5 g of anhydrous sodium acetate. number of phenolic Schiff bases by condensing The mixture was refluxed for 1 h at 708C, and several aliphatic and aromatic diamines with allowed to stand. The solid crystals were filtered phenolic carbonyls, or conversely, dicarbonyls off, washed repeatedly in demineralized water with aminophenols. These Schiff bases were and recrystallized from ethanol. The Schiff base found to undergo condensation polymerization was isolated as a light yellow crystalline solid. readily with formaldehyde and furfuraldehyde. In the reaction conditions set for polycondensa- 2.2. Preparation of the resin tion, the C=N bond of the Schiff bases did not undergo hydrolytic cleavage. Schiff base monomer (1 g, 0.002 mol) sus- The present communication deals with the pended in 20 ml water at 408C was dissolved by resins synthesized by condensing phenolic adding a few drops of 1 M NaOH. Formalde- Schiff base derived from 4,49-diamino- hyde/ furfuraldehyde in 1:2 molar ratio was diphenylsulphone (DDS) and o-hydroxyaceto- added and the mixture was refluxed in an oil phenone (o-HAP) with formaldehyde (HCHO)/ bath at 120–1308C for 2 h. The insoluble resin furfuraldehyde (FFD). The resulting polymers was filtered off, washed repeatedly with distilled o-HAP-DDS-HCHO and o-HAP-DDS-FFD water and dried at 708C. The yield of both the were found to form polychelates with a number resins o-HAP-DDS-HCHO and o-HAP-DDS- of transition metal ions. The resins and the FFD was found to exceed 80%. The dry resin polychelates were characterized by spectral was powdered, sieved (100 mesh, ASTM) and studies and thermal analyses. The adsorption suspended over water at pH 4 overnight. It was S. Samal et al. / Reactive & Functional Polymers 42 (1999) 37 –52 39 filtered off, washed in a large excess of water Capacity (mmol /g of resin) followed by methanol and dried in vacuum at mg of metal ion adsorbed by the resin ]]]]]]]]]]]]5708C. o-Hydroxyacetophenone was also con- atomic mass of the metal 3 g of the resin densed with formaldehyde and furfuraldehyde (2)yielding o-HAP-HCHO and o-HAP-FFD resins. The spectral features of these resins were com- 2.5. Measurementspared with the Schiff base resins. The elemental analysis was carried out in a Carlo Erba 1108 elemental analyzer. The FTIR2.3. Preparation of the polychelate spectra were recorded in a Perkin Elmer spec- trometer model 1800 in the range 4000 to 400To 100 mg of the dry resin (100 mesh, 21 1 cm in KBr phase. The H-NMR spectra wereASTM) suspended over methanol, 10 ml of recorded in DMSO d solvent in a 300-MHz FTmetal salt (0.15 M) in water was added. The 6 NMR (Bruker DRX-300) instrument. Themixture was stirred for 2 h at 408C. It was 13proton decoupled C FT NMR spectra of thefiltered off, washed in distilled water followed Schiff base and the resins was run in a VXRby petroleum ether and dried in vacuum at 300-S-Varian Supercon NMR spectrometer op-708C. erating at 75 MHz. The TG and DSC of the materials were recorded in a DuPont 9900 2.4. Metal uptake thermogravimetry analyzer at a heating rate of 108C/min in nitrogen atmosphere. The XRD The resins were treated with aqueous solu- study was performed in a PW 1820 diffractome- tions of Cu(II) and Ni(II) of known concen- ter using a Cu-X-ray tube operating at 40 kV tration. The pH of the solutions was adjusted to and 30 mA in the 2u range of 4 to 358. The the desired value using either 0.1 M HCl or 0.1 estimation of the metal ion concentration in the M NaOH. A suspension of the resin on the dilute aqueous solutions was made using a metal solution of known volume and concen- Systronics Digital Spectrophotometer model tration were agitated for a definite time period 116 and the pH of the solutions were measured over a hot plate /magnetic stirrer. The resins in a Systronics Digital pH Meter model 335. were filtered off and were washed thoroughly with demineralized water. The filtrate along with the washings were collected and quantita- 3. Results and discussion tive determination of metal ion concentration was done spectrophotometrically following the 3.1. Solubility neocuproin method for Cu(II) and dimethyl The powdered resin (10 mg) was suspendedglyoxime method for Ni(II) [16]. From the data over 5 ml of the chosen solvent and thethe percentage of metal loading and capacity solubility was checked after 24 h at roomwere calculated using the following equations: temperature. Both the resins were found to be insoluble in water, partially soluble in methanol,W 2 Wi f ethanol, CHCl , and CCl but completely solu-]]]Metal uptake (%) 5 3 100 (1) 3 4Wi ble in DMSO and tetrahydrofuran (THF) (Table 1). The polychelates were found to be insoluble in most of these solvents. The decrease inwhere W 5mg of metal ion in solution initiallyi solubility of the polychelates could be due topresent; W 5mg of metal ion left in the solutionf alteration in polymer polarity and the in-after adsorption. 40 S. Samal et al. / Reactive & Functional Polymers 42 (1999) 37 –52 Table 1 Physical data aCompound Colour N (%) Solubility in different solvents Found Calc. H O CH OH C H OH CHCl CCl THF DMSO2 3 2 5 3 4 o-HAP-DDS Yellowish-white 5.75 5.78 2 1 1 1 1 1 1 o-HAP-DDS-HCHO Yellow 1.816 – 2 6 6 6 6 1 1 o-HAP-DDS-HCHO-Cu(II) Blue 0.096 – 2 2 2 2 2 6 6 o-HAP-HCHO Yellow 8.9 – 2 2 2 6 6 1 1 o-HAP-DDS-FFD Black 2.085 – 2 2 2 6 6 1 1 o-HAP-DDS-FFD-Cu(II) Grey 1.856 – 2 2 2 2 2 6 6 o-HAP-FFD Black 9.32 – 2 2 2 6 6 1 1 a(1) Soluble, (6) partially soluble, (2) insoluble. trapolymer cross-linking [9] as well as increased not observed in the Schiff base o-HAP-DDS confirming the polycondensation reaction of thecrystallinity [17]. The solubility of the resins Schiff base with formaldehyde. The C=N andstudied over a period of time was seen to Ph–O absorptions of this resin seen at 1635.7decrease steadily (Fig. 1). This could be as- 21 and 1213 cm , respectively, did not shift oncribed to curing of the resins resulting in cross- complexation with Cu(II) but their intensitylinking and the consequent increase in molecu- sharply decreased. The C=C stretch at 1485lar weight. The curing is known to be a charac- 21 21teristic of the phenol-formaldehyde resins [18]. cm in the resin appeared at 1471.6 cm in the polychelate indicating a decrease in the p-electron density in the aromatic ring. These observations could be ascribed to the coordina-3.2. Spectral studies tion of phenolic oxygen and imine nitrogen to 3.2.1. FTIR spectra the metal ion. This observation is in accordance The FTIR spectra of the Schiff base, the with the findings of Oriel et al. [19]. These resins and the polychelates are shown in Fig. 2. authors observed that incorporation of metal ion In case of the resin o-HAP-DDS-HCHO, an into the resin matrix did not result in a shift in 21 absorption at 2879.5 cm was assigned to the absorptions of the coordinating groups. symmetrical methylene C–H stretch which was The S(=O) asymmetric and symmetric stret-2 ches of the DDS moiety observed at 1294.1 and 211160 cm in the polychelate did not shift from their respective positions in the resin. Sulphate ion (from CuSO ) was seen to be present as a4 bridging group. The absorptions at 1109, 987.5, 21630, 607.5 cm are characteristics of a bridg- ing sulphate. Nakamato et al. [20] studied bridged sulphato-complexes of Co(II) and re- ported similar observations. In addition to the 21Cu(II)–O absorption at 560 cm , the Cu(II)–N 21 absorption was observed at 488 cm as a sharp singlet. Ueno and Martell [10] have made extensive band assignments for the metal che- late compounds of bis-acetylacetone-ethyl- Fig. 1. Solubilty of the resin dissolved in DMSO as a function of enediimine and bis-salicylaldehyde-ethyl-time. Sorbent size — 100 mesh, resin quantity — 10 mg, solvent — 5 ml, (m) o-HAP-DDS-FFD and ( ' ) o-HAP-DDS-HCHO. enediimine and have assigned the metal–ligand S. Samal et al. / Reactive & Functional Polymers 42 (1999) 37 –52 41 Fig. 2. (A) FTIR spectra of (a) o-HAP-DDS, (b) o-HAP-DDS-HCHO, (c) o-HAP-DDS-HCHO-Ni(II) and (d) o-HAP-DDS-HCHO-Cu(II). (B) FTIR spectra of (a) o-HAP-DDS-FFD, (b) o-HAPDDS-HCHO-Cu(II) and (c) o-HAP-DDS-HCHO-Ni(II). stretching vibrations in these Schiff base com- o-HAP-DDS-FFD, C=N stretch was noticed at 21 21plexes to the range 640–500 cm for the M– 1668.3 cm and the Ph–O stretch at 1213.1 21 21O, and 580–430 cm for the M–N bonds. cm . On complexation with Cu(II), both the For the polychelate o-HAP-DDS-HCHO- absorptions disappeared. The S=O absorptions 22Ni(II), similarly, no significant change was of the sulphone and the SO ion overlapped.4 noticed for C=N absorption. The Ph–O absorp- Characteristic absorptions at 1118.6, 1014, and 21tion was seen to shift from 1213.1 to 1217 613.3 cm were assigned to a bridging sul- 21 cm . Thamizharasi et al. [21] have observed a phate as was seen in the case of the Cu(II)- shift of Ph–O absorptions to higher polychelate of formaldehyde-condensed resin. 21wavenumber on complexation. The asymmetric The absorptions at 613.3 and 524.6 cm were 21S(=O) stretch at 1296 cm merged with the assigned to Cu(II)–O and Cu(II)–N bonds,2 21phenolic O–H bond at 1307 cm , the symmet- respectively. The polychelate o-HAP-DDS- ric S(=O) stretch remaining unaffected at FFD-Ni(II), on the other hand, registered a shift2 2121 21 in the C=N absorption from 1668.3 cm in the1141.8 cm . A sharp singlet at 1384.8 cm 212 resin to 1645 cm in the polychelate. A sharpwas due to the NO (from Ni(NO ) ) present3 3 2 21peak at 1384.8 cm was assigned to nitrateas a non-coordinating counter anion [22]. The anion present in the resin matrix. The Ni(II)–ONi(II)–O and Ni(II)–N absorptions were re- 21 21 corded at 559.3 and 478.3 cm , respectively. absorption was observed at 513 cm and In case of the furfuraldehyde condensed resin Ni(II)–N absorption was not prominent. 42 S. Samal et al. / Reactive & Functional Polymers 42 (1999) 37 –52 13.2.2. H-NMR spectra [24] also noticed the methyne proton in this The proton NMR spectra of the Schiff base, range. The appearance of this proton in the resins and the polychelates are shown in Fig. 3. relatively weak field was attributed to the higher In the Schiff base o-HAP-DDS, the methyl descreening effect associated with the triphenyl- protons of hydroxyacetophenone moiety were methane type structure. observed at 2.6 ppm. The aromatic protons in A comparison of the area of the aromatic the range 6.5–7.8 ppm were assigned as shown proton peaks of the resins and that of the Schiff in the diagram. The phenolic proton was noticed base was made which led to an empirical as a sharp singlet at 5.96 ppm. The formalde- calculation of the molecular weight of the resins hyde-condensed resins o-HAP-HCHO and o- assuming that all the ortho and para positions HAP-DDS-HCHO had a number of additional of the phenolic moiety have undergone substitu- peaks in the form of complex multiplets in the tion reaction and the results are |6000 for range 3.5 to 5 ppm. These were ascribed to the o-HAP-DDS-HCHO and |8000 for o-HAP- bridging methylene (f–CH –f) and the DDS-FFD.2 methylene groups of the terminal methylol (f– 13CH OH) functions. 3.2.3. C-NMR spectra2 13The furfuraldehyde-condensed resins o-HAP- The C-NMR spectra of o-HAP-DDS and its FFD and o-HAP-DDS-FFD did not register the resins are given in Fig. 4. Condensation with bridging methyne proton. Such a proton in the formaldehyde generated a number of additional triphenylmethane type structure is assigned in peaks between 50 to 70 ppm. These peaks could the range 5.5 to 6 ppm [23] and Dimitrov et al. be assigned to the methylene groups appearing 1 1Fig. 3. (A) H-NMR (300 MHz) spectra of (a) o-HAP-DDS and (b) its expanded aromatic region; (B) H-NMR (300 MHz) spectra of (a) o-HAP-HCHO, (b) o-HAP-DDS-HCHO, (c) o-HAP-FFD and (d) o-HAP-DDS-FFD. S .Sam al et al . / Reactive & F u n ctional P olym ers 42 (1999) 37 –52 43 13Fig. 4. C-NMR spectra of (a) o-HAP-DDS, (b) o-HAP-DDS-HCHO and (c) o-HAP-DDS-FFD. 44 S. Samal et al. / Reactive & Functional Polymers 42 (1999) 37 –52 as bridging and terminal functions. Brauman et 9.47%. Between 200 and 4008C the rate of 13 al. [25] have studied the C-NMR spectra of weight loss for the resin was 0.2861%/ 8C at a phenol /cresol-formaldehyde resin and assigned T of 229.498C, whereas the polychelate lostmax peaks in the range 30–42 ppm to ortho–ortho, at the rate of 4.268%/ 8C at a T of 288.688C.max ortho–para and para–para –CH – bridging. In In this case also the polychelate lost weight2 our case the methylene bridging was noticed in much faster than the resin. the range 45–60 ppm. The down-field shift of The thermograms could not provide a clear the methylene peak was assigned to deshielding indication of relative thermal stability. Various caused by the electron drift towards –SO – kinetic models such as Coats–Redfern, Van-2 group. These authors also assigned the ortho- Krevelen and Broido were employed fitting in and para-substituted terminal CH OH carbons 14 different mechanisms into each model:2 to peaks in the vicinity of 60 ppm. These peaks Coats–Redfern [27] in the present case appeared in the range 68 to 2ln[g(a) /T ] 5 ln[AR /bE(1 2 2RT /E)] 2 E /RT69.95 ppm. The region between 111.4 to 136.5 (3)ppm was assigned to the aromatic carbons. The phenolic C–OH carbon at 152.8 ppm in the Van Krevelen [28]Schiff base shifted to 160.7 ppm in the resin. E / RTThe o-HAP-DDS-FFD resin showed a number maxln[g(a)] 5 ln[A /b(0.368/T ) (E /RTmax m of peaks in the region between 109.9 to 158.3 21 1 1) ] 1 (E /RT 1 1) ln T (4)maxppm. The peak at 158.3 was ascribed to the phenolic C–OH carbon. A sharp peak at 71.5 Broido [29]ppm was assigned to the –CH(OH)– terminal 2function consequent upon the reaction of the ln[g(a)] 5 ln[A /b 3 (R /E)T ] 2 (E /R) 3 1/Tmaxphenolic moiety with furfuraldehyde. Zigon et (5)13 al. [26] while studying the C-NMR spectra of resorcinol-cinnamaldehyde resin observed the where a5[W 2W] / [W 2W ], W 5initial0 0 f 0 –CH(OH)– signals between 65 and 72 ppm. weight, W5weight at temperature T, W 5finalf weight, b5heating rate, T 5temperature ofmax maximum rate of weight loss (K), E5activation3.3. Thermogravimetric analyses 21 energy (kcal), A5frequency factor (s ) and The thermograms of the resins and the Cu(II) g(a)5a function of a, the various a values polychelates are shown in Fig. 5 and the depending on the mechanism of thermal de- relevant data are furnished in Table 2. Up to composition. 2008C the resin o-HAP-DDS-HCHO lost 3.8% The activation energy E and the frequency of its original weight whereas its Cu(II)-poly- factor A were computed for the different models chelate lost only 0.19%. Between 200 and from the slope and the intercept of the plot of 24008C, the materials suffered rapid weight loss. ln[g(a) /T ] vs. 1 /T for the Coats and Redfern, The loss rate was 0.2556%/ 8C for the resin at ln[g(a)] vs. ln T for the Van Krevelen and 342.318C, the temperature of maximum rate of ln[g(a)] vs. 1 /T for the Broido models after weight loss (T ); for the polychelate it was linear regression analysis of the data (Fig. 6).max 0.4121%/ 8C at T of 341.918C. Thus the The Coats–Redfern model does not involvemax polychelate was seen to lose weight at a much T in the expression. This model was used tomax faster rate than the resin above 2008C. evaluate the kinetic parameters in the entire The furfuraldehyde condensed resin, on the range (130–6008C). On the other hand, the Van other hand, lost 6.15% of its original weight Krevelen and Broido models make use of Tmax within 2008C whereas its Cu(II) polychelate lost in the expressions and hence were used to S. Samal et al. / Reactive & Functional Polymers 42 (1999) 37 –52 45 Fig. 5. TG-DTG traces of (a) o-HAP-DDS-HCHO and (b) o-HAP-DDS-HCHO-Cu(II). 21 21 calculate the kinetic parameters for different DS (cal K mol ) was calculated using the DS / Rdecomposition stages using the relevant T relation A5(kT /h)(e ) where k is themax max 223 21 value of each stage. The entropy of activation Boltzmann constant (0.32944310 cal K ), 46 S. Samal et al. / Reactive & Functional Polymers 42 (1999) 37 –52 Table 2 TG data a bSample T (K) % Weight loss in the temp. range Y (%)m c Up to 2008C 200–4008C 400–6008C o-HAP-DDS-HCHO 615.31 3.8 33.04 54.437 8.723 o-HAP-DDS-HCHO-Cu(II) 614.91 0.19 32.55 0.67 66.59 o-HAP-DDS-FFD 502.49 6.15 27.93 39.41 26.51 o-HAP-DDS-FFD-Cu(II) 563.23 9.47 49.6 1.23 39.7 aTemperature of maximum rate of decomposition. bChar yield at 6008C. of the data indicated that in case of o-HAP- DDS-HCHO, metal ion incorporation into the resin matrix enhances thermal stability; whereas the o-HAP-DDS-FFD resin and its Cu(II) poly- chelate are nearly similar in their thermal re- sponse. Biswas and co-workers [30,31] have noted that incorporation of the metal ion increases thermal stability. Chiang and Mei [32], on the other hand, observed that complexation did not bring any improvement in thermal stability. Fig. 6. Coats–Redfern plot of thermogravimetric analysis data of They attributed the results to intra-polymer o-HAP-DDS-HCHO-Cu(II). cross-linking, because if there were interchain crosslinking, a strengthened matrix and conse- 234 quently a higher thermal stability for the poly-h, the Planck’s constant (1.5836310 cal s), 21 21 chelate over that of the resin would have beenand R, the gas constant (1.9872 cal K mol ). observed.The data are furnished in Table 3. An analysis Table 3 Kinetic parameters a 21 21Sample T (K) Methods E (kcal) A (min ) DS (cal K )m 5 o-HAP-DDS-HCHO 615.31 CR 20.037 2.14310 243.721 VK 7.582 5.6 264.677 1BR 8.591 1.505310 262.713 8 o-HAP-DDS-HCHO-Cu(II) 614.91 CR 19.674 3.593310 228.961 5VK 17.274 5.156310 241.967 6BR 18.012 1.361310 240.039 4 o-HAP-DDS-FFD 502.49 CR 13.344 1.333310 248.827 VK 4.01 – – BR 5.333 1.8415 266.483 8 o-HAP-DDS-FFD-Cu(II) 563.23 CR 16.093 1.198310 230.963 VK 5.257 3.615 254.201 1BR 6.8 1.772310 262.207 aCR, Coats–Redfern; VK, Van Krevelen; BR, Broido. S. Samal et al. / Reactive & Functional Polymers 42 (1999) 37 –52 47 3.4. DSC study continued to absorb thermal energy till about 3158C, beyond which exothermic decomposition The DSC trace of the resins and the polyche- reactions set in. The Cu(II) polychelate (Tg lates are shown in Fig. 7. The data indicated endset 99.098C) furnished several endothermic that the resin o-HAP-DDS-HCHO, beyond its peaks pertaining to desorption of the solvents glass transition temperature (T , end set 508C), and melting of the different components. Theg had no exotherm indicating thermal curing of melting endotherm was prominent with a peak the resin was noticed. The material exhibited a at 257.428C. The o-HAP-DDS-FFD resin on the sharp melting temperature at 183.338C and other hand showed a small curing exotherm Fig. 7. DSC traces of (a) o-HAP-DDS-FFD and (b) o-HAP-DDS-FFD-Cu(II). 48 S. Samal et al. / Reactive & Functional Polymers 42 (1999) 37 –52 followed by a melting at 136.98C. Incorporation in Fig. 8. The resin exhibited two peaks at (2u) of the metal ion enhanced crystallinity of the 20 and 32.788. The polychelate exhibited a material seen from a very prominent endotherm number of reflection planes, the intense ones with a melting temperature at 114.378C in the appearing at 18.82, 24.73 and 33.788. This was DSC trace of o-HAP-DDS-FFD-Cu(II). assignable to a significant increase in crystallini- ty of the polymer consequent upon coordination to the metal ion. From a comparison of the peak3.5. XRD study area it was observed that the polychelate could The XRD pattern of the resin o-HAP-DDS- be nearly 24 times more crystalline than the HCHO and its Cu(II)-polychelate is presented resin. However, the observed increase in the Fig. 8. XRD pattern of (a) o-HAP-DDS-HCHO and (b) o-HAP-DDS-HCHO-Cu(II). S. Samal et al. / Reactive & Functional Polymers 42 (1999) 37 –52 49 number of reflections and intensities could be observations, a structure for o-HAP-DDS- also the result of an increase in electron density HCHO-Cu(II) was proposed (Fig. 9). due to metal ion uptake. Yang and Chen [17] reported that the polymers having p-phenylene 3.7. Metal ion uptake studies units exhibited one strong reflection at around 208 and weaker reflections at 278 and the 3.7.1. Effect of contact time authors assigned these peaks to the crystalline The saturation time for the metal uptake of nature of the resins. the resins was obtained by plotting percentage of metal uptake against contact time keeping the initial metal ion concentration (0.08 M) con-3.6. Structural features stant (Fig. 10). The equilibrium time was found The information from the foregoing studies to be 5 min in the natural pH of the salt led us to propose a structure for the resins and a solutions for Cu(II) and 15 min for Ni(II). Both Cu(II)-polychelate. It was seen from the FTIR the resins showed almost identical capacity spectra of o-HAP-DDS-HCHO-Cu(II) that the (4.07 mmol /g) for Cu(II) whereas the capacity metal ion is bound to the resin matrix via of the resins towards Ni(II) was low. Several coordination of phenolic oxygen and the imine authors [33,34] have noted higher adsorption for 22 nitrogen. The SO ion was seen to be present Cu(II) over other metal ions. It is known that4 as a bridging group. To account for these the insoluble chelating resins take up transition metal ions in high yields from aqueous media but they often adsorb metal ions very slowly due to the lower activity of the ligands placed inside the resin. The metal complexing capacity of the resin depends not only on the nature of the ligand groups but also the accessibility towards the metal ions. Thus steric hindrance by the polymeric matrix and the hydrophobic na- ture of the polymeric ligand can limit the chelating reaction [35]. Fig. 10. Effect of contact time on sorption behavior of the resins: resin quantity5100 mg, sorbent size5100 mesh, temp.5308C, 21Fig. 9. Reaction scheme showing the inter-molecular structure of pH54.1, [M ]50.08 M, extent of metal loading of the resin the polychelate o-HAP-DDS-HCHO-Cu(II) with the sulphate o-HAP-DDS-HCHO for (h) Cu(II), (n) Ni(II) and resin o-HAP- group as a bridging function. DDS-FFD for (m) Cu(II) and (j) Ni(II). 50 S. Samal et al. / Reactive & Functional Polymers 42 (1999) 37 –52 213.7.2. Effect of metal ion concentration adsorption, k 54 s and n50.6. The high kad ad The uptake of Cu(II) and Ni(II) was studied values indicated that the equilibrium for metal in the metal ion concentration range 0.04–0.32 ion adsorption was attained quickly. M. Increasing metal ion concentration enhanced metal ion loading within the range of study 3.7.3. Effect of temperature (Fig. 11) beyond which a leveling effect was The effect of temperature variation from 25 noticed because of a saturation of the available to 658C was studied for Cu(II) for both the coordinating sites. Tikhomirova et al. [36] have resins at the natural pH of the metal ion observed a similar trend. From this study the solution. The capacity of both the resins re- optimum metal ion concentration for the de- mained nearly unaffected in the range of tem- termination of the capacity of the resins was perature. This could be because of the high ascertained to be 0.08 M. Decreasing metal ion reactivity of the resins and consequent satura- concentration slows down the reaction con- tion of the available coordination sites even siderably. The adsorption coefficients, k , of under ambient conditions.ad the resins for each metal ion adsorbed was computed from the Freundlich adsorption iso- 3.7.4. Effect of pH of the reaction medium therm: The effect of pH on the extent of adsorption of Cu(II) was studied for o-HAP-DDS-FFD inlog(x /m) 5 logk 1 1/n logC (6)ad two different concentrations of the metal ion, 0.0008 and 0.08 M. Cu(OH) was precipitatedwhere C is the initial concentration of the metal 2 at pH 5.1 preventing capacity studies beyondion in mmol, m the weight of the resin in grams, pH 5. The metal uptake was seen to signifi-x the quantity of the metal ion adsorbed by the cantly increase with increasing pH (Fig. 12).resin in mmol and n a constant. The results are This was ascribed to the ease of coordination ofas follows; resin: o-HAP-DDS-HCHO, for 21 the phenoxide ion over that of the phenolic-OHCu(II) adsorption, k 55.41 s , n50.49; andad 21 group at higher pH and also the enhancedfor Ni(II) adsorption, k 54.04 s , and n5ad basicity of the C=N nitrogen which got proton-0.6; resin: o-HAP-DDS-FFD, for Cu(II) ad- 21 ated in the acidic conditions. Several workerssorption, k 54.38 s , n50.54 and for Ni(II)ad Fig. 11.Variation of metal ion concentration: resin — 100 mg, size — 100 mesh, time — 15 min, temp — 308C, pH55, adsorption of Fig. 12. Effect of pH of the reaction medium: resin: o-HAP-DDS- (j) Cu(II), (h) Ni(II) on o-HAP-DDS-HCHO and ( ' ) Cu(II) FFD, quantity — 100 mg, size — 100 mesh, time — 15 min, temp 21 and (m) Ni(II) on o-HAP-DDS-FFD. — 308C, [M ]50.08 M. (m) Ni(II), ( ' ) Cu(II). S. Samal et al. / Reactive & Functional Polymers 42 (1999) 37 –52 51 Table 4 Adsorption studies of Cu(II) and Ni(II) under competitive conditions: resin o-HAP-DDS-FFD, 100 mg, contact time 15 min, mesh 100, temperature 308C, pH 5 [Cu(II)], M [Ni(II)], M % Loading [Ni(II)], M [Cu(II)], M % Loading 0.16 0 13.877 0.16 0 2.095 0.8 0 60.137 0.8 0 38.245 1.12 0 68.36 1.12 0 47.5237 1.44 0 74.3 1.44 0 52.312 1.6 0 75.885 1.6 0 54.748 a[Cu(II)], M [Ni(II)], M % Loading Selectivity coefficient Cu(II) Ni(II) 0.16 1.44 3.3 50.903 0.0329 0.48 1.12 23.35 43.8 0.3908 0.8 0.8 58.661 32.92 2.8872 1.12 0.48 65.35 16.5 9.0246 1.44 0.16 73.753 1.8 153.345 Concentrations of the metal ions in mmol. h[Cu(II)] / [Ni(II)]jR ]]]]]Selectivity coefficient, D 5 where R represents the metal content in resin, S represents metal content in solution.h[Cu(II)] / [Ni(II)]jS 21[37] have reported the enhanced adsorption of elements like UO and Mo(IV) in the presence2 metal ions with an increase in the pH. of other anions and cations are being carried out and the results will be presented in our sub- 3.7.5. Adsorption behavior in the presence of sequent communications. both Cu(II) and Ni(II) The capacity of o-HAP-DDS-FFD resin to- Acknowledgements wards both Cu(II) and Ni(II) in a mixture was studied to determine the behavior of the resins We are thankful to the Regional Sophisticated under competitive conditions. The results are Instrumentation Centres of India located at furnished in Table 4. The concentrations of the Central Drug Research Institute, Lucknow, In- metal ions in the mixture were varied maintain- dian Institute of Technology (IIT), Chennai, ing the pH at a fixed value. At low Ni(II) IIT-Mumbai, and Punjab University, Chan- 1 13concentration, the capacity of the resin towards digarh for providing FTIR, FT H/ C-NMR, Cu(II) remained nearly unaffected. With in- TG-DTG, DSC and XRD results. creasing Ni(II) concentration, the capacity of the resin towards Cu(II) progressively de- Referencescreased. The extent of adsorption of Ni(II) as compared to Cu(II) was significantly low. 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