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CHAPTER 5 MECHANOCHEMICAL SYNTHESIS AND

CHARACTERISATION OF POLY (o-PHENYLENE DIAMINE)

Poly(o-phenylene diamaine) (PoPD) was prepared in solvent-free condition by

utilizing two different oxidants namely ammonium peroxydisulfate (APS) and ferric

chloride (FC) in the presence of different doping acids viz., HCl, H2SO4 and H3PO4

through mechanochemical treatment of o-phenylene diamaine (oPD). The effect of

oxidants and doping agents on the physicochemical properties of mechanochemically

prepared PoPDs is presented vividly in this chapter.

5.1. INTRODUCTION

One of the latest advances in conducting polymers is the creation of aromatic

diamine polymers by oxidative polymerizations. The polymers of aromatic diamines

including phenylene diamines (PDs), diamino naphthalenes (DANs), diamino

anthraquinones (DAAQs), benzidine, naphthidine, and diaminopyridine have received

increasing attention. These monomers are very susceptible to oxidative

polymerization via oxidation of one or both amino groups to give linear

polyaminoaniline, linear polyaminonaphthylamine, ladder polyphenazine, and

phenazine unit containing polymers. It is believed that investigations on the aromatic

diamine polymers are more attractive since they exhibit more novel multi-

functionality than PANI and polypyrrole (PPy). These polymers have shown

apparently different characteristics versus widely researched conducting polymers

such as PANI and PPy in the application of electrocatalysis, electrochromics, sensors,

electrode materials, heavy metal ion complex, and detection [1,2] although the

polymerization mechanism and properties of the polymers have not been definitely

reported. It should be appreciated that the aromatic diamine polymers possess good

multifunctionality partially due to one free amino group per repetitive unit on the

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polymers. Most of the polymers of the aromatic diamines have been prepared by

electrochemical polymerization, but only a small number of polymers were obtained

through chemically oxidative polymerization. Investigations on enzyme- and

photocatalyzed oxidative polymerizations are very few.

The earliest investigation was in 1911, when it was predicted that the

univalent oxidation products of the pPD and its derivatives are free radicals that may

polymerize in a sufficiently concentrated solution at low temperature or in the solid

state [3,4]. In 1943, Michaelis and Granick discussed the formation of polymers of the

pPD and its derivatives oxidized by halogen and perchlorate in acidic aqueous

solution. Polarographic investigations of oPD were reported with gold, graphite, and

platinum electrodes in HCl and buffer (pH 1-4) solutions, and the oxidation potential,

critical oxidation potential, and polarographic half-wave potential of oPD were given

first by Lord and Rogers in 1954 [5]. Porker and Adams examined the anodic

polarography of three PDs on a rotating Pt electrode using a current-scanning

technique in 1956 [6]. They observed a linear relationship between limiting current

and pPD concentration. The electropolymerization mechanism of three PDs was first

suggested by Elving and Krivis in 1958 [7]. They proposed that the oxidation

mechanism of three PDs depends on the PD monomer structure and solution pH value

[8].The electrochemical characteristics including capacities and electrode efficiencies

of PDs and their derivatives such as methyl-pPD, chloro-pPD, 2,6-dichloro-pPD, 4-

hydroxy-mPD, amino-pPD, and 1,2-DAN in basic electrolyte (1.44 M NaOH

solution) were systematically studied for the first time by Glicksman in 1961 [9]. In

1963, Mark and Anson first reported the effect of acid strength on the electrooxidation

of PDs and their N-substituted derivatives including N,N-dimethyl-pPD and N-phenyl-

pPD on Pt electrode by chronopotentiometry [10]. The electrode filming phenomenon

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of PDs was first found by Prater in 1973. A polarogram for 3-methyl-oPD solution

was studied for the polarographic reduction of Ni2+ in 2001 [11]. However, PoPD was

first prepared as a stable film on an electrode by electropolymerization of oPD in

acidic solution by Yacynych and Mark in 1976 [12].The electrical conductivity of the

PoPD film prepared by electro-oxidation was reported for the first time by Yano et al.

in 1985 [13]. Since 1986, increasing investigations on the electropolymerization of

aromatic diamines have appeared. As compared with the electropolymerization of

aromatic diamines, studies on the chemically oxidative polymerization of the aromatic

diamines occurred later and were of decreased intensity. Bach pioneered the chemicall

oxidative polymerization of pPD with metal chelate and oxygen as oxidant in 1966

[14]. The chemical oxidative polymerization of pPD was first reported as an additive

of aniline polymerization in order to increase the rate and yield of polymerization

[15]. Chemical oxidative polymerization of four aromatic diamines with persulfate as

the oxidant in acidic aqueous solution from 0 °C to room temperature was developed

for the first time by Chan, Rawat, and coworkers in 1991 [16]. The enzymatic

oxidative polymerization of oPD was first carried out by using Horsh Radish

Peroxidase and H2O2 as catalyst and oxidant, respectively, at room temperature by

Kobayashi et al. in 1992 [17]. In 1995, the chemically oxidative polymerization of

oPD was found to form ladder-like poly(aminophenazine) if the polymerization was

performed in glacial acetic acid at 118°C. From then on, the oxidative polymerization

and polymers from aromatic diamines have been being extensively investigated

because the polymers exhibit a number of advantages including the choice of

monomer, diversity and facility of polymerization, variety of macromolecular

structure, variability of electro-conductivity, multi-functionality, and potentially wide

applicability. In recent years the oxidative polymers of the aromatic diamines have

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undergone a very rapid development in academic research and industrial application.

Significant progress has been made in the successful synthetic techniques, the

characterization of structure and properties, and the design of functional materials of

these polymers.

5.2. MECHANOCHEMICAL POLYMERIZATION OF oPD

5.2.1. Synthesis of doped/undoped PoPD 1.09 g of solid oPD was taken in a glass mortar and was hand-ground for 5

minutes using a pestle. To this finely grounded oPD, 2.2 g of solid APS or 2.7 g of

solid FC was added. After the addition of the oxidant, the solid phase mixture was

further hand-ground immediately for 20 minutes until the colour of the product turned

dark brown. The formed polymeric product was washed thoroughly with water,

methanol and diethyl ether. After repetitive washings, the polymer was dried in

vacuum oven at 40ºC for 12 h. The purified dry PoPD powders prepared in the

presence of APS and FC individually was used for further characterization.

The preparation of doped PoPD involves the addition of 0.5 ml of doping

agent (37 wt.% HCl / 96 wt.% H2SO4 / 87 wt.% H3PO4) to 1.09 g of solid oPD in a

glass mortar. This monomer-doping agent reactant mixture was thoroughly hand-

ground for 30 minutes in order to achieve homogeneity. The rest of the

polymerization procedure was followed as given above. The purified PoPD salts

obtained employing APS or FC as oxidants were used for performing further studies.

Herein, undoped PoPD is termed as PoPD, PoPD doped with HCl as PoPD-HCl,

PoPD doped with H2SO4 as PoPD-H2SO4 and PoPD doped with H3PO4 as PoPD-

H3PO4.

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5.2.2. Elemental analysis, yield and processability

Table 5.1 shows the elemental make-up of PoPD and its salts prepared using

APS or FC. The undoped counterpart of PoPD indicates the presence of small amount

of sulphur or chlorine that has resulted from the self-doping process from the

corresponding oxidants. However S/N or Cl/N ratio indicates that the doping that has

take place is almost negligible. The C, H, and N composition of PoPDs prepared from

APS or FC is consistent with molecular composition of oPD revealing the presence of

oPD repeating units in the polymeric framework. PoPD-HCl is found to be the highly

doped polymeric sample irrespective of the oxidants used. The doping level amongst

PoPD salts follows the order PoPD-HCl > PoPD-H2SO4 > PoPD-H3PO4 in both cases

of APS and FC. The extent of doping is more when HCl is used as a doping agent

because of the favourable factors like molecular size, oxidizing ability and pH value

of the reaction medium. From table 5.2, it can be observed that PoPD-HCl is found to

be produced in better quantity than the other PoPDs in both APS and FC. On the

whole, the adopted synthetic methodology for preparing PoPDs has yielded good

quantity of polymeric powders. The solubility of PoPDs was tested in water and some

organic solvents. PoPDs were found to be highly soluble in dimethyl formamide

(DMF), dimethyl sulfoxide (DMSO), N-methyl pyrrolidine (NMP), acetone and

ethanol. It was found to be more dispersible in water, chloroform and acetonitrile.

5.2.3. FTIR spectra

Figure 5.1A (a-d) shows the FTIR spectra of PoPDs synthesized by solid-state

method using APS as oxidant. In all the spectrum of PoPD and its salts, the band at

3373 cm−1 is due to the characteristic N–H stretching due to NH2 moieties, can be

correlated to open phenazine rings or terminal NH2 groups present in the structure of

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the polymers. The broad peak at around 3217 cm−1 can be assigned to the N–H

stretching vibration of the NH3+ moieties. The two bands at around 1535 and 1631

cm−1 are assigned to the stretching vibration of the C-C and C-N in the phenazine

ring, respectively. The peaks appearing at 756 and 621 cm−1 is characteristic of the C-

H out-of-plane bending vibrations of benzene nuclei in the phenazine skeleton. The

peaks at 1242 and 1371 cm−1 are associated with the C-N stretching in the benzenoid

and quinoid imine units, respectively. The vibrational bands located in the range of

625, 569 and 496 cm-1 is associated with (PO4)3- and (SO4)2- groups.All of these data

are similar to the previous report on PoPD [18], which confirm that the obtained

sample is unambiguously found to be doped forms of PoPD.

Fig 5.1B (a-d) displays the FTIR spectrum of PoPD and its salts prepared using

FC. All the bands obtained were similar to that of the PoPD spectra prepared in the

presence of APS except for a small shift in the characteristic frequencies. From this

observation, it is concluded that the chemical structures of synthesized polymer do not

change when the oxidizing agent was changed from APS to FC.

5.2.4. UV–Vis absorption spectra

Fig. 5.2A (a-d) presents the UV–Vis spectra of the PoPD and its salts prepared by

employing APS and dispersed in NMP solution. Two major absorption peaks are

located around 279-289 and 418-431 nm. The former peak is assigned to the π-π*

transitions of the benzenoid and quinoid structures [19]. The latter peak is due to

polaronic transition associated with the phenazine ring conjugated to two lone pairs of

nitrogen of the NH2 groups. The intensity of the polaronic band is relatively higher in

the case of PoPD-HCl when compared with other acids. If the size of the doping acid

is large, the diffusion of doping acid into the polymer matrix will be hindered due to

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steric factor. In line with this observation the doping degree among POPD salts

follows the order PoPD-HCl > PoPD-H2SO4 > PoPD-H3PO4.

Fig. 5.2B (a-d) shows the UV-Vis spectra of the PoPD and its salts prepared by

using FC and dispersed in NMP solution. Here too, a small shift in the characteristic

peak values is noticed. The π -π* transition band of the benzenoid and quinoid

structures is found to appear at 276-284 nm and the polaronic band appears at 421-

423 nm. The intensity of polaronic band is higher for PoPD-HCl indicating that the

presence of relatively more polaronic chains its backbone compared to other PoPDs.

5.2.5. XRD pattern

The X-ray diffraction pattern of PoPDs obtained through mechanochemical

route by using APS is shown in 5.3A (a-d). The peaks at ~12-13.5°, ~16.7-16.9°, ~18-

18.4°, ~25.9-26.2° are seen in the diffractograms. This diffraction patterns show all

the prepared POPD and its salts are crystalline. The peaks at lowest angle are

considered to be the distance between two in the polymer chain with dopant ions

situated between the two stacks. In view of this fact, one could notice no peak at

2θ = 12-13.5° for PoPD [fig.5.3A (a)] rather than its salts indicating the presence of

very little dopant anions. However, this peak is comparatively strong for all the PoPD

salts. The peaks at ~18-18.4° can be attributed to the periodicity parallel to the

polymer chain and the peak at ~25.9-26.2° may be due to the periodicity

perpendicular to the polymer chain. The former peak is sharper in all PoPDs and is

sharper and more intense in PoPD-HCl. This observation further proves the highly

doped state of PoPD-HCl than its other salts.

The X-ray diffraction pattern for the PoPD powders obtained using FC as

oxidiser is shown in 5.3B (a-d). The Bragg’s peak at 2θ = ~10.78º is more visible only

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for PoPD-HCl [fig.5.3B (b)] clearly suggesting the presence of dopants in between the

PoPD stacks. These observations indicate that PoPD-HCl is in highly ordered and

doped state. The intense peaks at around ~26° and ~27° is present in all the PoPD

salts as in PoPDs prepared by using APS. This observation us to believe that there is a

high degree of periodicity in the respective polymer backbone. It should be probably

concluded that increase in PoPD crystallinity in the case of FC used for

polymerization is the consequence of the effect of coordination ability of excessive

ferric ions at the surface of the whole crystal with the NH2 groups in oPD and

enhanced interfacial diffusion of the products formed during the course of

mechanochemical reaction [20].

5.2.6. Morphology

FESEM picture of PoPD and its salts prepared by using APS is presented in fig

5.4A (a-d). PoPD-HCl is found to have sub-micron sized particles (fig. 5.4A (a))

along with few agglomerated structures. The morphology of PoPD-H2SO4 (fig. 5.4A

(b)) is non-uniform and has larger aggregates. Hard crystalline lumps is found in the

surface of PoPD-H3PO4 (fig. 5.4A (c)). PoPD has greater degree of aggregation and

hence the particle appears as bigger mass [fig. 5.4A (d)].

Fig 5.4B (a-d) shows the FESEM pictures of PoPD and its salts prepared by

employing FC as oxidizer. The surface morphology of PoPD-HCl prepared through

mechanochemical polymerization indicates the formation of shorter one dimensional

nanorods wth size around 100 nm [fig. 5.4B (a)]. Fig.5.4B (b) displaying the image of

PoPD-H2SO4 show similar polymeric nanorods with some fused structures. The

morphology of PoPD-H3PO4 (fig. 5.4B (c)) shows uniform granular structures with

the size ranging from 80-100 nm. FESEM image of PoPD [fig.5.4B (d)] showed the

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formation of bigger sized aggregated particulates. We suppose that both the oxidizing

agent and doping agent greatly influences the morphological features of PoPDs.

5.2.7. Electrochemical activity

Fig 5.5A (a-e) shows the cyclic voltammograms of the PoPDs (synthesized by

using APS) film on GCE in 0.5 mol/l H2SO4. One redox couple is noticed for PoPD

and its salts. The anodic and cathodic peak potential values are listed in table 5.5. The

peak at 0.002 to -0.020 V in all the PoPD based polymers is related to redox

transitions of the polymer. In the CV of PoPD-HCl [fig 5.5A (c)], the difference in the

anodic and cathodic peak potential value is least (~ 78 mV) in comparison to other

PoPDs and hence this leads us to presume that the same polymer has better redox

property. This also indicates the presence of negligible amount of oligomeric fractions

or degradation products in the selected experimental conditions for PoPD-HCl. This

inference is in complete agreement with the observations made earlier.

Fig 5.5B (a-e) shows the cyclic voltammograms of the PoPD (prepared by using

FC) film on GCE in 0.5 mol/L H2SO4. The CV without characteristic peaks

[fig. 5.5B (a)] showed the absence of polymeric film on GCE. One oxidation peak at

0.01 and -0.02 V along with a reduction peak at -0.14 V and -0.12 V appearing in the

CVs of PoPD and PoPD-H3PO4 respectively [fig. 5.5B (b) & (e)] can be assigned to

the redox transitions happening in the polymeric film. The CVs of PoPD-HCl and

PoPD-H2SO4 [fig. 5.5B (c) & (d)] displays these peaks at -0.006 V, -0.026 V (anodic

peaks) and at -0.130 V, -0.114 V (cathodic peaks). These results suggest the

formation of electroactive PoPD salts both in the case of APS and FC.

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5.2.8. Conductivity

The conductivity of PoPD salts obtained by solid-state route is listed in table 5.6.

To compare with others, the conductivity of PoPD synthesized by using HCl as

protonating agent in both of the oxidants has resulted in higher value. The lowest

value among PoPD salts was observed for PoPD-H3PO4. As discussed in previous

chapters, the conductivity of PANI and its derivatives depends on the degree of

doping, oxidation state, particle morphology, crystallinity, inter or intrachain

interactions, molecular weight etc i.e., the conductivity of PANI and its derivatives

increase with increase in doping degree, crystallinity. Based on these considerations,

the differences in conductivity of these PoPD salts can be explained by the results of

FTIR spectra, UV-Vis spectra, X-ray diffraction peaks and CV studies. All these

results show that PoPD-HCl has higher doping level, crystallinity and good

electrochemical activity. The nanostructured morphology of PoPD-HCl obtained by

using APS and FC may have also contributed to higher conductivity.

5.2.9. Thermal stability

The thermograms of the PoPDs prepared by reacting APS and FC individually are

presented fig.5.6A (a-d) and 5.6B (a-d) respectively. There are two weight losses in

the TG curve of PoPD salts (fig. 5.6A (b-d) & 5.6B(b-d)), which are clearly shown by

the two DTG peaks at ~280°C and 505°C. The weight loss at lower temperatures is

associated with the DTG peak at 280°C, which is 15% of the initial sample weight,

may be due to a loss of the respective dopants in PoPD (e.g. HCl or H2SO4 or H3PO4).

The weight loss at higher temperatures is associated with the DTG peak at 505°C may

be due to an occurrence of oxidative decomposition of PoPDs in air. Indeed, it was

seen that the PoPDs were destroyed after calcination in air at 280°C. The DTG curve

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of undoped polymer samples in both cases of APS and FC shows a single weight loss

above 200°C (fig. 5.6A (a) and 5.6B (a)) indicating the absence of dopants in its

backbone. It can be seen from the TG and DTG curves that PoPDs are thermally

stable upto 210°C. All these results imply that the PoPD salts are in the doped state.

5.3. CONCLUSIONS

A simple solid phase reaction method for the synthesis of PoPD and its salts at

room temperature was demonstrated without using any organic solvent by employing

two oxidants namely APS and FC individually. Elemental analysis proved the

presence of corresponding dopant anions (Cl, S, P) in the polymeric backbone of

PoPD prepared using APS or FC. The yield obtained from this reaction route was

found to be satisfactory. All of the prepared PoPD salts were found to be form

dispersions with common solvents like DMF, DMSO, NMP, acetone and ethanol.

Spectroscopic profile of the PoPDs shows the presence of quinoid and benzenoid

units and formation of conducting emeraldine state in all PoPD salts. More crystalline

PoPD salt was obtained by doping with HCl in comparison with other doping acids

used in both the cases of APS and FC. FESEM picture shows the formation of

agglomerated nanostructures in the case of POPD salts prepared using APS as oxidant

and more uniform nanostructured PoPDs prepared using FC. PoPD-HCl was found to

be more conductive and electroactive. All the as-prepared PoPD salts are found to be

thermally stable up to 400ºC. Among these inorganic acids used as doping agents,

HCl was found to be more suitable to prepare PoPDs with high conductivity,

crystallinity and electroactivity through this mechanochemical route irrespective of

the oxidants (APS or FC) employed for the polymerization. These differences mainly

depended on the characteristics of inorganic acids (e.g., HCl, H2SO4 and H3PO4):

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small amount of water in the acids; strong and weak oxidizability of the acids. All

these lead to PoPD salts with different physicochemical properties. The unique

structure and good processability of the PoPDs makes it potentially suitable for use as

electrode materials in energy storage devices.

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3. J. Piccard, Ann, J. Electroanal. Chem 381(1911) 351.

4. J. Piccard, Ber, J. Electroanal. Chem 59 (1926) 1438.

5. L. Michaelis, S. Granick, J. Am. Chem. Soc, 65 (1943) 1747.

6. S. S. Lord Jr, L.B. Rogers, Anal. Chem, 26 (1954) 284.

7. R.E. Porker, R.N. Adams, Anal. Chem, 28 (1956) 828.

8. P. J. Elving, A.F. Krivis, Anal. Chem, 30 (1958) 1645.

9. P. J. Elving, A.F. Krivis, Anal. Chem, 30 (1958) 1648.

10. R. Glicksman, J. Electrochem. Soc, 108 (1961) 1.

11. H.B. Mark Jr, F.C. Anson, Anal. Chem, 35 (1963) 722.

12. K.B. Prater, J. Electrochem. Soc, 120 (1973) 365.

13. H.B. Mark Jr, D. Koran, L. Gierst, J. Electroanal. Chem, 498 (2001) 228.

14. M. Yacynych, H.B. Mark Jr, J. Electrochem. Soc, 123 (1976) 1346.

15. J.Yano, A. Kitani, R.E. Vasquez, K. Sasaki, Nippon Kagaku Kaishi (1985)

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Phys. Chem, 94 (1990) 7716.

18. H.Q. Jiang, X.P. Sun, M.H. Huang, Y.L.Wang, D. Li, S.J. Dong, Langmuir 22

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1302.

Table 5.1. Elemental composition of PoPD and its salts

Table 5.2. Yield of PoPD and its salts

Table 5.3. Assignment of bands found in FTIR spectra of PoPD and its salts

PoPDs prepared using APS Polymer %C %H % N % O % Cl % S % P Cl/N or S/N or

P/N ratio PoPD 55.20 3.50 17.20 23.66 -- 0.44 -- 0.02 PoPD-HCl 53.78 3.34 16.88 23.72 2.28 -- -- 0.13 PoPD-H2SO4 53.81 3.38 16.92 23.90 -- 1.99 -- 0.11 PoPD-H3PO4 53.83 3.41 16.96 24.02 -- -- 1.78 0.10

PoPDs prepared using FC PoPD 54.26 3.23 17.05 24.97 0.49 -- -- 0.02PoPD-HCl 53.80 3.36 16.90 23.32 2.62 -- -- 0.15 PoPD-H2SO4 53.82 3.39 16.94 23.94 -- 1.91 -- 0.11 PoPD-H3PO4 53.85 3.43 16.98 23.95 -- -- 1.79 0.10

PoPDs prepared using APS Polymer Yield in % PoPD 68 PoPD-HCl 83 PoPD-H2SO4 80 PoPD-H3PO4 75

PoPDs prepared using FC PoPD 70 PoPD-HCl 86 PoPD-H2SO4 82 PoPD-H3PO4 76

PoPDs prepared using APS Polymer (NH2)s (N-H)s (C=N)s (C=C)s (C-N-C)s PoPD 3370 3215 1630 1535 1240 PoPD-HCl 3373 3217 1631 1535 1242 PoPD-H2SO4 3372 3216 1633 1536 1243 PoPD-H3PO4 3375 3219 1630 1537 1241

PoPDs prepared using FC PoPD 3351 3196 1632 1536 1242 PoPD-HCl 3354 3194 1635 1537 1246 PoPD-H2SO4 3352 3195 1633 1535 1240 PoPD-H3PO4 3355 3194 1635 1537 1243

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Table 5.4. Assignment of UV-Vis absorption peaks of PoPD and its salts

Table 5.5. Redox potentials of PoPD and its salts

PoPDs prepared using APS Polymer Epa/V Epc/V

PoPD 0.013 -0.141 PoPD-HCl 0.002 -0.080 PoPD-H2SO4 -0.020 -0.160 PoPD-H3PO4 -0.020 -0.120

PoPDs prepared using FC PoPD -0.015 -0.170 PoPD-HCl -0.006 -0.130 PoPD-H2SO4 -0.026 -0.114 PoPD-H3PO4 -0.023 -0.159

Table 5.6. Conductivity values of PoPD and its salts

PoPDs prepared using APS Polymer π–π* band (nm) polaron–π* band (nm) PoPD 289 419 PoPD-HCl 274 431 PoPD-H2SO4 273 427 PoPD-H3PO4 279 418

PoPDs prepared using FCPoPD 284 421 PoPD-HCl 278 421 PoPD-H2SO4 273 421 PoPD-H3PO4 276 423

PoPDs prepared using APS Polymer Conductivity (S/cm) PoPD 1.38 x 10-3 PoPD-HCl 2.46 x 10-1 PoPD-H2SO4 1.56 x 10-2 PoPD-H3PO4 0.23 x 10-2

PoPDs prepared using FC PoPD 1.86 x 10-3 PoPD-HCl 8.23 x 10-1 PoPD-H2SO4 2.06 x 10-2 PoPD-H3PO4 0.32 x 10-2

127

Fig.5.1A. FTIR spectra of PoPD and its salts prepared using APS: (a) PoPD (b) PoPD-HCl (c) PoPD-H2SO4 and (d) PoPD-H3PO4

128

Fig.5.1B. FTIR spectra of PoPD and its salts prepared using FC: (a) PoPD

(b) PoPD-HCl (c) PoPD-H2SO4 and (d) PoPD-H3PO4

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Fig.5.2A. UV-Vis spectra of PoPD and its salts prepared using APS: (a) PoPD (b) PoPD-HCl (c) PoPD-H2SO4 and (d) PoPD-H3PO4

130

Fig.5.2B. UV-Vis spectra of PoPD and its salts prepared using FC: (a) PoPD (b) PoPD-HCl (c) PoPD-H2SO4 and (d) PoPD-H3PO4

131

Fig.5.3A. XRD pattern of PoPD and its salts prepared using APS: (a) PoPD

(b) PoPD-HCl (c) PoPD-H2SO4 and (d) PoPD-H3PO4

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Fig.5.3B. XRD pattern of PoPD and its salts prepared using FC: (a) PoPD

(b) PoPD-HCl (c) PoPD-H2SO4 and (d) PoPD-H3PO4

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Fig.5.4A. FESEM image of PoPD and its salts prepared using APS: (a) PoPD-HCl (b) PoPD-H2SO4 (c) PoPD-H3PO4 and (d) PoPD

134

Fig.5.4B. FESEM image of PoPD and its salts prepared using FC: (a) PoPD-HCl

(b) PoPD-H2SO4 (c) PoPD-H3PO4 and (d) PoPD

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Fig.5.5A. Cyclic voltammograms of PoPD and its salts prepared using APS: (a) Plain

GCE (b) PoPD/GCE (c) PoPD-HCl/GCE (d) PoPD-H2SO4/GCE and (d) PoPD-H3PO4/GCE

136

Fig.5.5B. Cyclic voltammograms of PoPD and its salts prepared using FC: (a) Plain

GCE (b) PoPD/GCE (c) PoPD-HCl/GCE (d) PoPD-H2SO4/GCE and (d) PoPD-H3PO4/GCE

137

A

Fig.5.6A. TG/DTA curves of PoPD prepared using APS: (a) PoPD (b) PoPD-HCl

(c) PoPD-H2SO4 and (d) PoPD-H3PO4

138

B

Fig.5.6B. TG/DTA curves of PoPD prepared using FC: (a) PoPD (b) PoPD-HCl

(c) PoPD-H2SO4 and (d) PoPD-H3PO4