Organic-inorganic hybrid materials prepared by sol-gel approach have attracted a great deal of attention in material science. Organic polymeric part of the composite provides mechanical and chemical stability whereas the inorganic part supports the ion-exchange behaviour and thermal stability and also increases the electrical conductivity. Such modified composite materials can be applied as an electrochemically switchable ion exchanger for water treatment, especially water softening. Polyaniline zirconium(IV) tungstoiodophosphate nanocomposite ion exchanger is prepared by sol-gel method. Polyaniline zirconium(IV) tungstoiodophosphate nanocomposite ion exchanger is synthesized and characterized by Fourier transform-infrared spectra, ultraviolet-visible spectra, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, ion exchange, conductivity, and antimicrobial studies. A mechanism for the formation of the polyaniline zirconium(IV) tungstoiodophosphate nanocomposite ion exchanger was discussed. The route reported here may be used for the preparation of other nanocomposite ion exchangers.
Organic-inorganic hybrid materials prepared by sol-gel approach have attracted a great deal of attention in material science. Organic polymeric part of the composite provides mechanical and chemical stability whereas the inorganic part supports the ion-exchange behaviour, thermal stability and also increases the electrical conductivity. Such modified composite materials can be applied as electrochemically switchable ion exchanger [
A few such excellent ion exchange materials have been developed and are successfully being used in chromatographic techniques [
Zirconium(IV) tungstoiodophosphate ion exchanger was prepared by mixing 1.61 g of zirconium oxychloride octahydrate (0.1 M) in 50 mL of 4 N hydrochloric acid solution. This was added to a solution containing 5.4 g of potassium iodate (0.5 M) and 8.3 g of sodium tungstate (0.5 M) in 100 mL of water at the flow rate of 0.5 mL min−1. To the resulting mixture, 50 mL of 1 M orthophosphoric acid was added by maintaining the pH as 1 with constant stirring using a magnetic stirrer at room temperature. The white gel obtained was filtered off, washed thoroughly with distilled water to remove excess acid and was dried in an air oven at 60°C.
Polyaniline was prepared from aniline by
The composite ion exchanger was prepared by the sol-gel mixing of polyaniline, an organic conducting polymer with the inorganic precipitate of zirconium(IV) tungstoiodophosphate [
Polyaniline Zr(IV) tungstoiodophosphate nanocomposite ion exchanger and H+ form of conducting polymeric-inorganic hybrid ion exchanger were characterized by FT-IR spectra, UV-visible spectra, X-ray diffraction, SEM, TGA, and conductivity studies. AC electrical conductivity measurement was done on the pelletized samples by using Digital LCR meter (Pacific, Model: PLCR 8C) at different temperatures. UV-visible spectra of the synthesized samples were recorded at room temperature in different solvents, namely, NMP, chloroform, o-cresol, and DMSO in 300–900 nm range with Elico model SL-164 Double Beam UV-visible spectrophotometer. FT-IR spectra of conducting organic polymer, inorganic ion exchanger, and conducting polymer-inorganic hybrid ion exchanger were taken by KBr disc method at room temperature performed on NEXUS-670 FT-IR spectrophotometer. The powder X-ray diffraction technique has been employed to identify the crystalline phases of the samples using monochromatized Cu-
For the determination of ion-exchange capacity, one gram of the dry cation exchanger in H+ form was taken into a glass column. The bed length was approximately 1.5 cm long. 1 M alkali metal chlorides (LiCl, NaCl, and KCl) were used to elute the H+ ions completely from the cation exchange columns maintaining a very slow flow rate of ~0.5 mL min−1. The effluents were titrated against standard 0.1 M NaOH solution for the total ions liberated in the solutions using phenolphthalein indicator.
To find out the optimum concentration of eluent for complete elution of H+ ions, a fixed volume (250 mL) of LiCl, NaCl, and KCl solutions of varying concentrations (0.2–1.8 M) was passed through a column containing 1 g of the exchanger in H+ form with a flow rate of ~0.5 mL min−1. The effluent was titrated against standard alkali solution of 0.1 M NaOH for the H+ ions eluted out for the determination of eluent concentration using phenolphthalein as an indicator.
A column containing 1 g of the exchanger in H+ form was eluted with 1.4 M of LiCl, 1.4 M of NaCl and 1.2 M of KCl solutions of different 10 mL fractions with minimum flow rate of 0.5 mL min−1. Each fraction of 10 mL effluent was titrated against standard NaOH (0.1 M) solution to determine the strength of H+ ions eluted out.
The optimum shaking time of ion exchanger with LiCl, NaCl, and KCl solutions for complete elution of H+ ions was also determined. 0.25 g of the ion exchanger was shaken with 25 mL of alkali metal chloride solutions (LiCl, NaCl, and KCl), and the amount of liberated H+ ions was titrated against the standard NaOH solution after every half an hour interval.
The pH titration studies of PANI Zr(IV) tungstoiodophosphate was performed by the method of Topp and Pepper [
The distribution behaviour of metal ions plays an important role in the determination of the selectivity of the material. The distribution coefficient (
In the present study, new and novel organic-inorganic electrically conducting nanocomposite cation exchanger was chemically prepared by sol-gel mixing of organic conducting polymer, polymer (polyaniline) into the matrix of inorganic ion exchanger, Zr(IV) tungstoiodophosphate. The different steps involved in the mechanism for the formation of conducting polymeric-inorganic nanocomposite ion exchanger are shown in Scheme
Polymerisation reaction with the ion exchanger as the dopant.
From the capacitance obtained from the instrument and thickness as well as the diameter of the pellet, the AC electrical conductivity of the polyaniline Zr(IV) tungstoiodophosphate sample was calculated using the following equation:
The capacitance and conductance of the material over a range of temperature and frequency are then calculated from the relationship between the applied voltage and measured current and are related to relative permittivity (
The conductivity of chemically synthesized PANI and its samples presented in Table
AC conductivity of various polyaniline samples at room temperature.
Sample |
|
|
|
|
|
---|---|---|---|---|---|
PANI salt | 15.30 (n.f) | 4.90 | 6.69 | 1.78 |
|
Dedoped PANI | 9.2 (p.f) | 0.96 | 6.73 | 1.42 |
|
PANI ZrTIP | 16.10 (n.f) | 4.40 | 6.67 | 2.66 |
|
Dedoped PANI ZTIP | 8.9 (p.f) | 0.57 | 6.67 | 0.84 |
|
H+ form of PANI ZTIP | 17.16 (n.f) | 4.74 | 6.66 | 1.53 |
|
The conductivity for this organic-inorganic hybrid ion exchanger shows semiconductor behaviour. The linear portion of the graph
Conductivity of polyaniline Zr(IV) tungstoiodophosphate ion exchanger at different temperatures.
Temp. (°C) |
|
|
|
1000/ |
|
---|---|---|---|---|---|
100 | 0.95 | 41.9 | 4.76 | 2.681 | −5.3475 |
95 | 0.68 | 35.2 | 2.86 | 2.717 | −5.8569 |
90 | 0.54 | 30.9 | 2.00 | 2.755 | −6.2146 |
85 | 0.49 | 28.0 | 1.64 | 2.793 | −6.4131 |
80 | 0.45 | 25.1 | 1.32 | 2.833 | −6.6301 |
75 | 0.44 | 18.9 | 1.02 | 2.874 | −6.8879 |
70 | 0.41 | 16.3 | 0.80 | 2.916 | −7.1309 |
65 | 0.37 | 14.5 | 0.64 | 2.959 | −7.354 |
60 | 0.33 | 12.1 | 0.49 | 3.003 | −7.6211 |
55 | 0.29 | 10.8 | 0.37 | 3.049 | −7.9020 |
50 | 0.26 | 9.2 | 0.29 | 3.096 | −8.1456 |
45 | 0.21 | 7.1 | 0.18 | 3.145 | −8.6226 |
40 | 0.18 | 5.3 | 0.11 | 3.195 | −9.1150 |
35 | 0.16 | 4.4 | 0.08 | 3.247 | −9.4335 |
Arrhenius plot for polyaniline Zr(IV) tungstoiodophosphate ion exchanger.
In order to determine the conductivity parameters, the temperature dependence of conductivity (linear portion) is fit to the following equation:
The activation energy of conductivity for this hybrid ion exchanger was found to be 0.086 eV. Actually, the mobility of charge carriers under the influence of an external field up to 100°C increases with doping level. The value of activation energy is indicating that the charge carrier has to overcome the same energy barrier while conducting. Thus, the polarons act as charge carrier hopping from state in all the polymer samples.
FT-IR spectra are used as a tool to characterize the molecular structures of organic-inorganic hybrid ion exchanger. The FT-IR spectrum of PANI-Cl− (a), polyaniline Zr(IV) tungstoiodophosphate ion exchanger (b), and H+ form of polyaniline Zr(IV) tungstoiodophosphate ion exchanger (c) are given in Figure
The peaks at 1565 cm−1 and 1495 cm−1 are attributed to C=N and C=C stretching modes for the quinoid and benzenoid rings, the peaks at about 1300 cm−1 and 1231 cm−1 are attributed to C–N stretching mode for benzenoid ring, and the peak at 1121 cm−1 is assigned to the plane bending vibration of C–H (modes of N=Q=N, Q=NH+–B, and B–NH+–B), and out-plane bending vibrations of PANI are reported to occur at about 801 cm−1.
In the present study also, all the peaks represented above are observed in PANI ZTIP nanocomposite ion exchanger (Table
FT-IR spectral data of the polymer samples.
Characterisation | PANI-Cl− (cm−1) | PANI ZTIP (cm−1) | H+ form of PANI ZTIP (cm−1) |
---|---|---|---|
C=N and C=C stretching modes for the quinoid and benzenoid rings | 1565, 1495 | 1595, 1493 | 1560, 1472 |
C–N stretching mode for benzenoid ring | 1300, 1231 | 1309, 1216 | 1383, 1240 |
In-plane C–H bending mode | 1121 | 1152 | 1117 |
Out of plane C–H bending mode | 801 | 811 | 798 |
Due to |
1010 | 1000 | |
M–O bond and presence of iodate | 523, 450 | 590, 506 |
UV-visible spectra of all the polyaniline samples were recorded at room temperature in solvents like N-methyl pyrrolidone, chloroform, and m-cresol and the peak positions are given in Table
UV-visible absorption data of polyaniline samples in different solvents.
Sample | Peak position (nm) | ||
---|---|---|---|
NMP | CHCl3 | m-Cresol | |
PANI-HCl | 312, 575, 620 | 224, 428, 651 | 314, 556 |
PANI ZTIP | 308, 558 | 226, 326, 554 | 312, 534 |
H+ form of PANI ZTIP | 319, 617 | 243, 328, 554 | 330, 366, 963 |
In m-cresol, the polymer chains of PANI have an extended conformation in which the twist defects between aromatic rings are removed, and hence the interaction between the adjacent polarons becomes stronger. The absorption peak at 550 nm is associated with the replacement of random coil conformation by intraband transitions within the half filled polaron band. At the same time, between
The powder X-ray diffraction technique has been employed to identify the crystalline phases of the samples using monochromatized Cu-
Average crystallite size of polymer samples.
Sample | Crystallite size (nm) |
---|---|
PANI emeraldine salt | 64 |
H+ form of PANI ZTIP | 78 |
PANI ZTIP | 75 |
Scanning electron microscopy was performed on ground materials at various magnifications. SEM images for the polyaniline Zr(IV) tungstoiodophosphate ion exchanger at various magnifications are shown in Figure
It has been revealed that, after binding of polyaniline with Zr(IV) tungstoiodophosphate, the morphology has been changed, and the average crystallite size of the composite material was found to be ~75 nm. The X-ray powder diffraction pattern of this ion exchanger suggests an amorphous nature of the composite material. Thus, it was confirmed from both XRD and SEM that the crystallite size shows the nanorange.
TGA and DTG (first derivative of TGA) curves for polyaniline emeraldine salt (a) and polyaniline Zr(IV) tungstoiodophosphate nanocomposite ion exchanger (b) in nitrogen atmosphere are shown in Figure
TGA studies of the composite cation exchange material in the original form were carried out by an automatic thermobalance on heating the material from 40°C to 1000°C at a constant rate of 10°C min−1 in the nitrogen atmosphere. The thermogravimetric analysis curves, TGA and DTG, reveal a considerable weight loss of about 15.8% from 40°C to 120°C in polyaniline Zr(IV) tungstoiodophosphate nanocomposite ion exchanger, and this can be explained due to the removal of external water molecules. Slow weight loss of the material from 120°C to about 440°C may be due to the removal of dopant as well as conversion of phosphate group to pyrophosphate group [
The ion-exchange capacity of the hybrid ion exchanger for alkali metal ions increases according to the decrease in the hydrated ionic radii [
IEC of various ions on polyaniline Zr(IV) tungstoiodophosphate ion exchanger.
Exchanging ions | pH of the metal solution | Ionic radii ( |
Hydrated ionic radii ( |
Ion-exchange capacity (meq·dry g−1) |
---|---|---|---|---|
Li+ | 3.3 | 0.68 | 3.40 | 4.2 |
Na+ | 5.0 | 0.97 | 2.76 | 5.3 |
K+ | 6.8 | 1.33 | 2.32 | 5.9 |
Effect of alkali metal chloride concentration on ion exchange capacity of PANI ZTIP nanocomposite ion exchanger is presented in Figure
Effect of the concentration of eluent on IEC.
Concentration of eluent (M) | Ion-exchange capacity (meq·dry/g) | ||
---|---|---|---|
Li+ ion | Na+ ion | K+ ion | |
0.2 | 2.5 | 2.9 | 3.5 |
0.4 | 2.7 | 3.2 | 3.9 |
0.6 | 3.0 | 3.6 | 4.3 |
0.8 | 3.3 | 4.1 | 4.8 |
1.0 | 3.7 | 4.4 | 5.1 |
1.2 | 3.9 | 4.8 | 5.9 |
1.4 | 4.2 | 5.3 | 5.9 |
1.6 | 4.2 | 5.3 | 5.9 |
1.8 | 4.2 | 5.3 | 5.9 |
Effect of concentration of eluent on IEC.
The elution behaviour (Figure
Elution behavior of polyaniline Zr(IV) tungstoiodophosphate ion exchanger.
Volume of eluent (mL) | Strength of H+ released (M) | ||
---|---|---|---|
LiCl | NaCl | KCl | |
10 | 0.0650 | 0.0740 | 0.0830 |
20 | 0.0450 | 0.0470 | 0.0440 |
30 | 0.0380 | 0.0422 | 0.0395 |
40 | 0.0370 | 0.0390 | 0.0392 |
50 | 0.0340 | 0.0370 | 0.0228 |
60 | 0.0330 | 0.0292 | 0.0197 |
70 | 0.0320 | 0.0289 | 0.0186 |
80 | 0.0290 | 0.0267 | 0.0175 |
90 | 0.0290 | 0.0250 | 0.0173 |
100 | 0.0280 | 0.0240 | 0.0160 |
110 | 0.0250 | 0.0200 | 0.0150 |
120 | 0.0240 | 0.0160 | 0.0149 |
130 | 0.0200 | 0.0156 | 0.0145 |
140 | 0.0200 | 0.0153 | 0.0140 |
150 | 0.0180 | 0.015 | 0.0140 |
160 | 0.0170 | 0.015 | 0.0140 |
170 | 0.0150 | 0.015 | 0.0140 |
180 | 0.0150 | 0.015 | 0.0140 |
190 | 0.0150 | 0.015 | 0.0140 |
200 | 0.0150 | 0.015 | 0.0140 |
Elution behavior of polyaniline Zr(IV) tungstoiodophosphate ion exchanger.
The effect of elution time on IEC of the hybrid exchanger is shown in Table
Effect of elution time on IEC of polyaniline Zr(IV) tungstoiodophosphate ion exchanger using LiCl, NaCl, and KCl eluents.
Equilibrium time (Hours) | Ion-exchange capacity of ion exchanger (meq·dry g−1) | ||
---|---|---|---|
Li+ ion | Na+ ion | K+ ion | |
0 | 1.28 | 2.12 | 3.92 |
0.5 | 1.92 | 3.40 | 5.60 |
1.0 | 2.00 | 4.00 | 6.30 |
1.5 | 2.14 | 5.40 | 7.80 |
2.0 | 4.12 | 6.20 | 9.60 |
2.5 | 5.32 | 7.00 | 15.20 |
3.0 | 5.80 | 7.40 | 15.20 |
3.5 | 6.32 | 7.40 | 15.20 |
4.0 | 6.32 | 7.40 | 15.20 |
4.5 | 6.32 | 7.40 | 15.20 |
5.0 | 6.32 | 7.40 | 15.20 |
Effect of elution time on IEC of polyaniline Zr(IV) tungstoiodophosphate ion exchanger using (a) LiCl (b) NaCl (c) KCl eluents.
The pH titration curves for polyaniline Zr(IV) tungstoiodophosphate nanocomposite ion exchanger were obtained under equilibrium conditions with LiOH/LiCl, NaOH/NaCl, and KOH/KCl systems indicating bifunctional behaviour of the material as shown in Figure
pH value of polyaniline Zr(IV) tungstoiodophosphate nanocomposite ion exchanger with various alkali metal hydroxides.
At low pH, the weak acidic groups remain undissociated. The addition of LiOH, NaOH, and KOH neutralized the solution, and the weak acidic group dissociates; thus, the ion exchange starts toward completion. The pH titration curves showed a gradual rise in pH initially and a steep rise at the end because strong acidic groups were completely exchanged with Li+, Na+ and K+ ions at the end. The rate of H+-K+ exchange was faster than those of H+-Na+, and H+-Li+ exchanges.
In order to find out the potentiality of polyaniline Zr(IV) tungstoiodophosphate nanocomposite ion exchanger in the separation of metal ions, distribution studies for three metal ions were performed in four solvent systems. The results of distribution studies (Table
Distribution coefficient values of some metal ions on polyaniline Zr(IV) tungstoiodophosphate in different solvent systems.
Metal ions |
|
|||
---|---|---|---|---|
DMW | 10% ethanol | 10% acetone | 1 M H2SO4 | |
Pb2+ | 265 | 172 | 251 | 51 |
Cu2+ | 96 | 115 | 122 | 13 |
Co2+ | 59 | 86 | 37 | 90 |
The antimicrobial activity studies of the PANI and polyaniline Zr(IV) tungstoiodophosphate nanocomposite ion exchanger were carried out using the Kirby-Bauer antimicrobial susceptibility test procedure [
Antimicrobial activity studies of polymer samples.
Organisms | Media | Zone of inhibition in (mm) | ||
---|---|---|---|---|
Control | PANI | Polyaniline Zr(IV) tungstoiodophosphate ion exchanger | ||
|
Muller |
18 |
15 |
20 |
|
Histon Agar | 20 | 20 | 16 |
Zone formation against (a)
From the table, polymer and the conducting polymeric-inorganic nanocomposite ion exchanger showed higher antimicrobial activity against
The characterization of polyaniline Zr(IV) tungstoiodophosphate ion exchanger is justified on the basis of FT-IR, UV-visible, XRD, SEM, and TGA. The principle characteristic peaks of quinoid-benzenoid N-moieties, C–N stretching, and C–H aromatic in-plane and out-plane bending vibrations of PANI are reported to occur at about 1600, 1500, 1350, 1130, and 820 cm−1, respectively. In the present study also all the peaks are observed in prepared polyaniline Zr(IV) tungstoiodophosphate nanocomposite ion exchanger using potassium perdisulphate as the oxidant, but they are modified both in intensity and peak position when the ion exchanger is incorporated into the conducting polymeric matrix PANI. XRD pattern of this cation exchanger shows that the composite material is in a semicrystalline form. The SEM images and XRD studies show that the average crystallite size of the H+ form of composite material was found to be 78 nm. The thermal analysis points out the inference that prepared polyaniline Zr(IV) tungstoiodophosphate nanocomposite ion exchanger is thermally stable. The three different absorption peaks are observed in the UV-visible spectra of the polymer samples due to the transition from
The intrinsic multifunctional character of organic/inorganic hybrid materials makes them potentially useful in multiple fields. Illustrative examples of this versatility are their high added value applications as coating for corrosion production and abrasion resistance, artificial membranes for ultra- and nanofiltration adsorbents for toxic compounds, and so forth. Most of the organic/inorganic hybrid materials are nanocomposite materials in which the inorganic part and the organic entities interact at the molecular level in the nanoscopic domain. The most obvious advantage of organic and inorganic hybrids is that they have good ion-exchange properties, high stability, reproducibility, and selectivity for heavy toxic metal ions. In the present work, polyaniline Zr(IV) tungstoiodophosphate is a newly synthesised organic-inorganic nanocomposite ion exchanger, which possess all such characteristics and is highly selective for lead, a hazardous toxic metal in the environment. Thus, the material can be used in making Pb(II) ion selective membrane electrode.
This study was not supported by any grant. K. Jacinth Mispa, P. Subramaniam, and R. Murugesan report that they have not received any financial support for the research from organizations that may either gain or lose from the publication of this paper.
The authors are grateful to ICP section of CECRI, Karaikudi for allowing the use of XRD measurements. The authors would also like to acknowledge the STIC, Cochin University, and the Department of Physics, Aditanar College of Arts and Science, Tiruchendur, for SEM and conductivity studies, respectively.