Evaluation of Sorption Behavior of Polymeric Resin [poly 4, 4'-(naphthyl bis(oxy))bisbenzaldehyde ethylenediamine] for Cu (II) and Ni (II) ions.
: Summary: The synthesis of a new polymeric resin [poly 4,4'-(naphthyl bis(oxy))bisbenzaldehyde ethylenediimine] (PNBOBen) by polymerization from dialdehyde 4,4'-naphthylbis(oxy) bisbenzaldehyde with ethylenediamine in m-cresol is described The synthesized Schiff base polymer (PNBOBen) was characterized by elemental microanalysis, FT-IR and 1H-NMR spectroscopy. The thermal degradation pattern of PNBOBen resin was also measured at higher temperature. The dialdehyde (NBOB) and Schiff base polymer (PNBOBen) were soluble in various common organic solvents including tetrahydrofuran (THF), dimethylformamide (DMF), dimethylacetamide (DMAc) and dimethylsulphoxide (DMSO). The metal uptake behavior of PNBOBen was investigated for Cu (II) and Ni (II) ions and optimized with respect to the sorptive medium (pH), shaking rate and equilibration time. The resin exhibited lower swelling ratios in an acidic medium because of the protonation in the imine group of polymer. The sorption of Cu (II) and Ni (II) by PNBOBen, followed Langmuir, Freundlich, and DubininRadushkevich (DR) isotherms. Thus in both metal ions, Cu (II) was sorbed slightly better than Ni (II) ions onto the polymeric resin (PNBOBen).Key words: Polymeric resin, Synthesis, FTIR, 1H-NMR, Batch adsorption.
Schiff base polymers are important class of polymers due to their high thermally stability , chelating property [2, 3], high mechanical strength [4, 5] and semi conducting property [6, 7]. The presence of heteroatoms in the structure of polymer, reduced reactivity due to their lower solubility in organic solvents and their high melting points.
Banerjee et al [8, 9] synthesized hetero atom containing Schiff base polymers from 4,4-[1,4- phenylenebis(oxy)]bisbenzaldehyde as well as 4,4- arylbis(oxy)bisacetophenone. Schiff base polymerscontained an ether linkage in the polymer structures Some Schiff base polymers formed from 4,4- (hexafluoroisopropylidine)bis(p-phenoxy)dianilinewith benzidine [10, 11], and oligosalicyaldehyde and diamines have high thermal stabilities at 1000C . The solubility of these polymers was observed in polar and non-polar solvents in acidic and basic media [13, 14].
The present work is aimed at the synthesis of Schiff base polymer (PNBOBen), its characterization by FT-IR, NMR, thermogravimetry (TG) and differential thermal analysis (DTA). This resin was used as an adsorbent toward Cu and Ni metal ions with preconcentration , followed by desorption and determination by atomic absorption spectrophotometer.Results and Discussions
Characterization of PNBOBenAfter the valuable result of elemental analysis of dialdehyde (NBOB), was used to prepare a new Schiff base polymer (PNBOBen) with ethylenediamine by polycondensation having 84% yield in m-cresol. The effect of solvent of reaction medium, heating time, temperature of reaction and solubility of Schiff base polymer were examined individually. Better yield was obtained with DMAc, after treating with a number of organic solvents. In order to estimate the optimal heating time, reactionswere performed for 2, 4, 6, 8 hrs at 100heating time was estimated as optimal.
C and 4 hr
The 4,4'-[naphthylbis(oxy)]bisbenzaldehyde (NBOB) indicated very clear band in the IR spectrum at 1743 cm-1 because of the aldehydic CO vibrations. The derived Schiff base polymer gave rise to a characterized peak around 1616-1644 cm-1 due to CN vibrational frequencies (Fig. 1). The 1H-NMR spectrum of dialdehyde showed a peak of aldehydegroup at and 9.1 due to a proton attached to the aldehyde group. In the 1H-NMR spectrum of Schiff base polymer, the ratios of peaks area are in agreement with the reported assignments  no peak attributed to aldehyde group is observed. But newpeak was observed at 2.9 and due to N-CH formation in respecting polymer Fig. 2 (a and b).The TGA plot of polymeric resin showed a two-step mass loss up to 550 oC in (Fig. 3). The loss of 14 % of resin in mass up to 165 oC in the first step may be due to the elimination of sorbed water and CO2. This suggests the presence of approximately one water molecule, the second loss started after 165 oC with maximum weight loss of 71 % up to 512 oC which indicated the high thermal stability of modified resin.Sorption Optimization
Various buffers were used to examine the pH of metal ions, with the range of pH 2- 10. The resin showed pH-dependent swelling-deswelling behaviors. The % sorption of metal ions increased by increasing in pH of aqueous solutions and maximum% sorption was achieved at pH 6 for Cu (II), and pH8 for Ni (II) metal ions, which were selected as optimal pH values for both metal ions. Increasing pH beyond the range resulted in the precipitation of metal ion as hydroxides. The amount of sorption increased by shaking rate and achieved a maximum value at about 80 rpm for both Cu (II) and Ni (II) metal ions which was selected as optimal shaking rate. The shaking time was studied for the maximum sorption of metal ions and 10 min were selected with Cu (II) as well as Ni (II) metal ions for further studies.
Kinetics of Resin
The kinetics of resin metal interface at optimum pH, was calculated by the variation of sorption with time from kinetic equations i.e. Morris- Weber and Lagergren.  is given as under:where sorbed concentration of metal ions on resin(molg-1) at time 't' was plotted verses (t)1/2, andgave 9.1 min for Ni (II) and 10.6 min for Cu (II) withthe co-efficient of correlation 0.979 and 0.994 for these metal ions, but deviated when the agitation timebecame some higher (Fig. 4).The lagergren equation  is as follows:
log (qe- qt) log qe kt/ 2.303 (Eq 2)
when a graph was plotting by log(qe- qt) verses, 't', where qe is the sorbed concentration of metal ion at equilibrium, qt is the sorbed concentration of metal ion on to resin (PNBOBen) (molg-1) and k is Lagergren constant (Fig. 5).Sorption IsothermsThe sorption of Cu (II) and Ni (II) metal ions were determined by varying concentration from2.7 x 10-7
to 5.2 x 10-4
on 100 mg sorbent(resin) / 10 mL sorbate for 10 min (optimized shakingtime) as well as with 80 rpm (optimized shakingrate), at 30 1
C, and gave 90% maximum sorption,which explained by equations are shown as below:
(log Cads log A + (1/n) log Ce. (Eq 3) Langmuir Equation:((Ce/Cads) (1/ Qb) + (Ce/Q), (Eq 4) Dubinin Radushkevich Equation:(ln Cads ln Xm Be2 ) (Eq 5)
where e is calculated by RT ln [1 + (1/Ce)] equation, Ce is the amount of metal ions in the liquid phase at equilibrium and Cads is a amount of metal ions adsorbed/ mass of adsorbent. The Freundlich (A) (n), Langmuir (Q) (b) and D-R (Xm) (B) constants were calculated from intercept and slope of linear plot at room temperature. The results are listed in (Table-1) which concluded that % sorption decreased at low temperature. The result of E calculated from slope of D-R plot using the equation  as below:The energy for Cu (II) and Ni (II) ions wasfound to be 14.84 and 15.21, which are within the range of 9- 16 k J mol-1, estimated for ion exchange or chemisorption. Thus both metal ions were well sorbed onto the polymeric resin (PNBOBen), but Cu (II) was sorbed slightly better than Ni (II) ions.
Desorption of metal ions were determined by shaking the 0.5 g of resin with metal solutions, at optimized circumstances. The insoluble resin was filtered and washed with various concentration (0.1-2.0 M) and volumes (1- 10 mL) of mineral acid. Each washings were collected and analyzed by flame AAS. It was observed that these metals could be desorbed very well with 5- 6 mL HCl (2M).
Table-1: Sorption parameters of Cu (II) and Ni (II) ions (7 x 10-7 to 5.2 x 10-4 mol L-1) on modified resin
(PNBOBen)n (100 mg) at 30 oC.
ReagentsAnalaR grade chemicals: 4- Florobenzaldehyde, 1,4-naphthquinone, ethylenediamine, m-creosol, n-hexane, tetrahydro- furan (THF), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethylsulphoxide (DMSO), NiCl2 and CuCl2 were obtained from Fluka, Switerzerland). Buffer solutions of pH 1-2, 3-6, 7-9were prepared by mixing appropriate ratios of 0.1M HCl and KCl, 0.05 M acetic acid and sodium acetate,0.05 M ammonia and NH4Cl solutions, respectively.Instrumentations
The elemental micro-analysis was carried out by Elemental Micro-Analysis Ltd, Deven, U.K. Infrared spectra were recorded on a Nicolet Avatar330 FT- IR (Thermo Nicolet Electron Corporation, USA) with attenuated total reflectance (ATR) accessory (Smart partner) within 4000- 600 cm-1. UV-Vis Spectrophotometric studies were carried out on double beam Hitachi 220 spectrophotometer, (Hitachi (Pvt) Tokyo, (Japan) within 185 to -700 nm. The proton nuclear magnetic resonance (1H-NMR) spectra were recorded on a Bruker ACF300 spectrometer, using (TMS) as an internal reference. TG and DTA analysis were recorded on Shimadzu TG- 30 thermal analyzer (Japan) from room temperature to 700 oC with a nitrogen flow rate 50 mL/ min. The heating rate was programmed at 10 oC/ min.
Synthesis of Polymeric Resin (PNBOBen)
Dialdehyde 4, 4'- [naphthylbis(oxy)]bisbenzaldehyde (NBOB) was prepared from reported method  and then polymerized as following way:
(2mmol) Ethylenediamine was dissolved in15 mL m-creosol at room temperature. (2 mmol) dialdehyde (NBOB) was added in clear reaction mixture and contents were heated at 100 oC for 4 hrs with constant stirring under nitrogen atmosphere. The reaction mixture was cooled at room temperature and poured in 100 mL methanol. Precipitates wereseparated by filtration. Crude products were recrystallized from DMAc and n- hexane. The decomposition point was found to be greater than 330 oC . The structural formulas of dialdehyde (NBOB) and Schiffbase polymer (PNBOBen) are given in (Fig. 6a and b).Poly[4, 4'-(naphthylbis(oxy)]bisbenzaldehyde)ethylenediimine] (PNBOBen)
Analysis of (C26H20N2O2)n, calculated: C,79.6 %; H, 5.102 %; N, 7.14 % .
Found: C, 78.9 %; H, 5.22 %; N, 7.09 %.
Sorption of Metal Ions on Resin (PNBOBen)
In the batch technique, 100 mg of resin was treated with 10 mL aqueous solution of (0.05 M) Cu (II) and Ni (II) metal ions solutions at 25 1 oC. The pH of solution was adjusted using suitable buffers. Suspensions of resins were agitated for an exact time period over magnetic stirrer for 10 min. The insoluble resins were filtered off and washed carefully with chilled demineralized water. The filtrates were collected and determined by flame atomic spectrophotometer, using air acetylene flame. Lamp current was 3 mA with slit width 0.5 mm for Cu (II) and Ni (II) ions. The following equation was used to calculate the metal uptake or % sorption and thedistribution co-efficient (Kd) :
% Sorption (Ci- Cf / Ci) x 100 (Eq 7) Ci Initial concentration of metal ions in solution (mg/L) Cf Final concentration of metal ions in solution (mg/L). equationConclusions
This research work represents the synthesis of degradable pH-sensitive polymer (PNBOBen) from dialdehyde 4,4'- [naphthylbis(oxy)]bisbenzaldehyde with ethylenediamine by polycondensation and characterized by various spectroscopic techniques. The thermal analysis of polymers indicated better stability than dialdehyde, with 71 % weight loss around 550oC. Under the optimum conditions, approximately quantitative sorption was successively achieved 89% and 78% on resin for both of Cu(II) and Ni(II) metal ions, respectively. The Langmuir, Freundlich and D-R sorption isotherms were alsomeasured for both metals ions. It was observed that these metals could be desorbed very well with 5-6 mL HCl (2M). Therefore, this resin may be used as preconcentration as well as to remove for trace metal ions from waste materials.
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|Publication:||Journal of the Chemical Society of Pakistan|
|Date:||Apr 30, 2014|
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