J Solution Chem (2008) 37: 919–932DOI 10.1007/s10953-008-9286-y

Energy Storage by Poly(o-anisidine) MatrixDuring Oxidative Hydrolysis

Seddique M. Ahmed

Received: 1 October 2007 / Accepted: 9 January 2008 / Published online: 9 May 2008© Springer Science+Business Media, LLC 2008

Abstract The chromaticity of poly(o-anisidine) (POAN) doped with different acids (HA),HA-doped POAN, has been studied by the spectrophotometric technique and the resultswere substantiated by molecular mechanics (MM+) calculations. The observed absorbancedecrease (λ around 720 nm, dark green coloration) with increasing concentration of the in-organic oxidizing agent (KMnO4) can be attributed to the oxidative hydrolysis mechanism.The oxidative hydrolysis constant (Kh) is highly dependent on the strength of the acid used.The HClO4-doped POAN matrix has the ability to store about 128.878 kJ·g−1 chromogenicenergy (CE) at the wavelength 720 nm in a condensed lightweight form. MM+ calculationssuggest that the potential energy (PE) in kJ·mol−1 of the optimum molecular geometric(OMG) structure of the HClO4-doped POAN matrix is at least two (2.052) times more sta-ble than the OMG of the base form (POAN-EB) of the POAN matrix. Kinetic parametersof the oxidative hydrolysis reaction of the HA-doped POAN matrix were deduced fromabsorbance variations with time. The results of computer-oriented kinetic analysis indicatethat the rate-controlling step for HA-doped POAN oxidative hydrolysis is governed by theGinstling-Bronshein equation that represents three-dimensional diffusion (D4). Activationparameters for the oxidative hydrolysis of the HClO4-doped POAN matrix were computedand discussed.

Keywords Chromaticity · Poly(o-anisidine) · Kinetics · MM+ · Calculations

1 Introduction

Chromogenic materials have a significant part to play in future “smart windows” for ar-chitecture, vehicle, aircraft, spacecraft, and marine glazing. There are various physicalprocesses that can be used to control and modify the amount of incident daylight, solarenergy, and glare. The processes covered in this study are of the electrically activated kind,covering electrochromic, dispersed particle and dispersed liquid crystal glazing.

S.M. Ahmed (�)Chemistry Department, Faculty of Science, Assiut University, 71516 Assiut, Egypte-mail: sm_ahmed@yahoo.com

920 J Solution Chem (2008) 37: 919–932

There are other types of chromogenic materials, such as those that are thermotropic,thermochromic and photochromic. These have been covered in other studies [1–4]. Com-puter modeling of the energy efficiency of electrochromic windows in buildings has shownthat electrochromic windows can provide significant energy performance improvement com-pared to conventional double glazed windows [5]. Energy savings for specific conditions canresult in more than 30% energy savings over conventional glazing [6].

Polyaniline (PANI) and similar aryl amines such as poly(o-anisidine) (POAN), poly(o-toluidine) (POT), etc., derived polymers are probably the most intensively studied conduct-ing polymers since their discovery, especially because of their outstanding properties thatallow modified electrodes to be used as sensors, catalysis, electrochromic materials, etc.[7–13]. It is well known that the practical properties of PANI are related to its chemicalstructure of alternating -NH- and phenyl groups. Under certain conditions, PANI and simi-lar compounds show in their voltammograms a ‘middle peak’ lying between the two mainones. This additional peak has been attributed to either overoxidation, leading to degradationand/or cross-linking with phenazine insertion, or to ortho coupling [14–18]. The overoxi-dized form of polypyrrole (OPPy) films has been shown to have cation permselectivity,because of the introduction of oxygen-containing groups on the PPy backbone and the lossof the cationic charge [19–25]. As such, OPPy films have been used to reduce interferencefrom anionic redox species in glucose biosensors that are based on oxidation of immobilizedglucose. It has also been shown that the OPPy prepared in solutions of bulky anions can beused for the voltammetric determination of cationic species in the presence of a large excessof anions [23]. OPPy colloids, which can recognize enantiomers of amino acids, have beenreported [24].

Recently, we reported that the chromaticity (at λ around 840 nm) of the poly(o-toluidine)(POT) matrix was enhanced by the insertion of 9,10-anthraquinone-1,5-disulfonate (AQS2),produced by oxidative polymerization of the protonated form of the monomer or by redop-ing of the base form of POT (POT-EB) via an anion-exchange mechanism [25]. We alsocharacterized the camphor sulfonic acid CSA-doped poly(o-anisidine) (CSA-doped POAN)using various techniques [26].

In the present study, the loss of chromaticity of the doped POAN matrix (HA-dopedPOAN) via an oxidative hydrolysis mechanism was investigated. Activation parameters aswell as MM+ calculations support the proposed reaction mechanism.

2 Experimental

2.1 Chemicals and Solutions

o-Anisidine (o-AN), camphor sulfonic acid (CSA), and sodium dodecyl sulfate (SDS)(Sigma) were used as received. All of the other used reagents were of analytical reagentgrade or of chemically-pure grade, and double distilled water was used throughout.

Poly(o-anisidine) doped with hydrochloric acid (HCl-doped POAN) was prepared (in thesolid state) similar to the previously described procedure [17, 18, 25]. The chemical oxida-tion of o-AN (100 mmol·L−1) in strong acid medium (HCl, 1.0 mol·L−1) was carried out byadding 0.2 mol·L−1 ammonium peroxydisulfate, (NH4)2S2O8), solution drop by drop. Thestirring of the reaction mixture continued for 2 h to ensure the reaction was complete as in-dicated by the stabilization of the temperature of the reaction mixture. The reaction mixturewas further mixed for 2 to 3 h longer (post-polymerization) to ensure that polymerizationwas completed, then filtered and washed repeatedly with double distilled water, and finally

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equilibrated in 0.1 mol·L−1 HCl for 2 h to achieve the maximum doping. The so-obtainedpolymer was dried under vacuum at 25 °C to a constant mass. The HCl-doped POAN wasthen converted to the base form (POAN-EB) by detaching the HCl with 3% ammoniumhydroxide (NH4OH) solution for 2 h, followed by washing with double distilled water, andfinally by dimethyl ether until the washing solution becomes colorless.

2.2 Instrumentation

The absorption spectra were recorded on a Perkin-Elmer Lambda 35 apparatus (scan speed8.0 nm·sec−1) that was used for normal (zero- or first-derivative, �λ = 5.0 nm) measure-ments in the 300 to 1100 nm wavelength range. A Heto thermostat (HMT 200) was used forthe accelerated kinetic studies.

2.3 Procedure

Samples for the UV-VIS measurements were prepared by pouring 10 mL of the base formof the polymer (POAN-EB, 100 µmol·L−1), that was dissolved in water/DMF (volume ratioϕr = 3 : 2) mixtures with HClO4 (100 mmol·L−1) or other acids (HA), into a calibratedflask. To study the effect of pH on the hydrolysis reaction of H2SO4-doped POAN, differentamounts of H2SO4 were added to the base form of POAN (POAN-EB, 100 µmol·L−1). Theother acids used in this study were HCl, CH3COOH, HNO3, H3PO4, and camphor sulfonicacid (CSA). The background spectrogram of these solutions was recorded. Then, differentamounts of oxidant (KMnO4) were added into individual flasks, while the same quantity ofthe other components were added to each flask by means of a micropipette (Voaco, UK).All recorded absorption spectra were corrected for a reagent blank, which was prepared ina similar manner as for the samples but did not, however, contain the analyte. All spectralmeasurements were carried out at room temperature (24±1) °C, except those used to assessthe influence of temperature on the reaction rate for oxidative hydrolysis of the HA-dopedPOAN matrix.

2.4 Methods of Calculation

MM+ calculations, including the MM2 and MMP2 force fields [27–31], were carried outassuming that the investigated molecule was in the gas phase. The values of the potentialand geometrical energies, as well as the dipole moment, were obtained considering bothδPE = 0.42 J and the normal method [27–31]. The search for the minimum energy moleculargeometry resulted in a 3D structure. MM+ calculations iteratively change the position ofatoms towards the structure characterized by lower energy until the internal energy of themolecule has been minimized.

The energy of a molecule is influenced by the location of the atomic coordinates and canbe calculated according to the equations in [30, 35]

E(x) = Estr + Eang + Estb + Eoop + Etor + Evdw + Eele + Esol + Eres (1)

where Estr is the bond stretch, Eang is the bond angle bend, Estb is the stretch-bend, Eoop isthe out-of-plane, Etor is the torsion, Evdw is the van der Waals, Eele is the electrostatic, Esol

is the implicit solvation, and Eres is the restraint energy.

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Table 1 Results of MM+calculations of potential energy(PE) and dipole moment (μ) ofthe base (POAN-EB) and salt(HClO4-doped POAN) forms ofPOAN chain

Matrix PE (kJ·mol−1) μ (Debye)

POAN-EB (MG) 9.62 × 1079 0.00

POAN-EB (OMG) −76.74 10.17

HC1O4-doped POAN (MG) 9.62 × 1079 0.00

HC1O4-doped POAN (OMG) −157.51 10.07

Scheme 1 The MG (a) and OMG (b) calculated structures of the HClO4-doped POAN matrix

3 Results and Discussion

3.1 Molecular Mechanics Calculations

Using MM+ calculations it is possible to obtain the potential energy (PE) and dipole mo-ment (μ) for the molecular (MG) and optimum molecular (OMG) geometric structures ofthe base (POAN-EB) and the doped POAN chain with different acids HA (POAN-dopedHA) as seen in Table 1. These calculations showed that the PE of the OMG structure ofHClO4-doped POAN matrix (Scheme 1) is at least a factor of two (2.052) lower (more sta-ble) than that of the undoped (POAN-EB) polymer.

3.2 UV-VIS Spectroscopy of POAN-doped Acids

Figure 1 shows the electronic absorption spectra of POAN (140 µmol) base form (POAN-EB) and in strong acidic (H2SO4, 100 mmol·L−1) medium. The absorption maximum at λ

about 600 nm (Fig. 1 curve a) could be attributed to the emerald-base form (POAN-EB,dark blue color) [26]. While, the absorption maximum at λ of about 780 nm is due to theconducting emerald-green salt (H2SO4-doped POAN, dark green color) as shown in Fig. 1,curve b. This absorption maximum decreased rapidly with increasing concentration (0.0 to6.0 mmol·L−1) of the KMnO4 oxidant. Moreover, the spectral curves, which contain un-resolved bands, can be used to extract both qualitative and quantitative information. Foryielding additional information, first-derivative spectra (D1) are more sensitive for charac-terizing the maximum absorption at about 890 nm, as shown in Fig. 2. This observation canbe attributed to the obtained highest oxidized form of this matrix (the quinoid one), whichundergoes a hydrolysis reaction to produce ρ-hydroquinone (H2Q) by a mechanism similarto Schiff-base hydrolysis [18]. The cationic form of this matrix is a crucial feature for thehydrolysis process. A possible mechanism for the oxidation of H2SO4-doped POAN (for

J Solution Chem (2008) 37: 919–932 923

Fig. 1 Absorption spectra ofPOAN (140 µmol·L−1) in thebase form (POAN-EB) a; and(b–i) doped with H2SO4(100 mmol·L−1) after differentadditions of the oxidant(KMnO4) at concentrations of 0,40, 80, 120, 160, 2000, 4000, and6000 µmol·L−1, respectively

Fig. 2 First-derivative spectra ofcurves b, d, g, and i of Fig. 1

example) is presented in Scheme 2. The protonated forms in that Scheme are omitted forclarity. MM+ calculations showed that all transition states of the hydrolysis of this matrixhave low values for the optimal molecular geometrical (OMG) and potential (PE) energiesin kJ·mol−1 and dipole moments in Debye units (Table 1), suggesting a high possibility thatthese transition states are formed. The higher negative activation entropy is also consistentwith an SN1 or dissociative mechanism in the transition state. End group hydrolysis of thePOAN matrix is more favorable than chain-group hydrolysis [18–20, 25].

The absorbance strength of the band around 780 nm in the spectrum of POAN-dopedwith H2SO4 was decreased by increasing the concentration of the KMnO4 oxidant. The datawere analyzed using a linear-regression program [25] according the following equation

A = a + bC (2)

where A and C are the absorbance and concentration of the oxidant (KMnO4), and a and b,respectively, are the intercept and slope of the straight line. Statistical data, regression co-efficients (r) and relative standard deviations (RSD) are given in Table 2. The slope of thisstraight line corresponds to the hydrolysis constant (Kh) as given in Table 2. The detectionlimit of the oxidant (as Mn(VII)) is as low as 3.16 ppm (mg·L−1), suggesting the possibleapplication of this procedure for determining Mn(VII) in real samples, without any pretreat-ment such as analyte separation and/or preconcentration.

924 J Solution Chem (2008) 37: 919–932

Scheme 2 OMG of the possible configuration structures formed during oxidative hydrolysis of the proto-nated form of the POAN matrix. Protonated forms are omitted for clarity

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Table 2 Calibration data of theabsorbance versus oxidant(KMnO4) during oxidativehydrolysis of HClO4-dopedPOAN (100 µmol·L−1)

Matrix Kox.103 (L·mol) a r RSD.103

POAN-H2SO4 2.006 1.220 0.957 4.796

POAN-CH3COOH 2.724 0.750 0.956 3.523

POAN-CSA 2.733 1.035 0.989 3.6

POAN-HC1 2.759 1.232 0.995 3.605

POAN-HC1O4 3.223 1.316 0.979 3.036

POAN-H3PO4 3.652 1.310 0.982 2.688

POAN-CSA-SDS 3.734 1.126 0.986 3.638

POAN-universal 4.611 1.551 0.984 2.135

POAN-HNO3 5.570 0.890 0.938 16.31

Fig. 3 Values of log10 Kh

versus pH of the H2SO4-dopedPOAN matrix (a), and the firstderivative of Fig. 3a (b)

The effect of the acidity function [H+] on the oxidative hydrolysis of the POAN chainwas investigated. The hydrogen ion provided by HClO4 was found to have a remarkableeffect on the value of Kh. A good linearity (r ≥ 0.995) between log10 Kh and pH was ob-tained (Fig. 3a). Moreover, the first-derivative curve (Fig. 3b) gives a maximum log10 Kh

value within the range of pH = 1.5 to 2.0. These calculations confirmed that the protonated

926 J Solution Chem (2008) 37: 919–932

(HClO4-doped POAN) species reacts faster than the corresponding unprotonated (POAN-EB) species. Also, the increase in Kh with an increase in the concentration of [H+] in thepresent study may be due to the protonation of MnO−

4 , resulting in the formation of a morepowerful oxidant, permanganic acid (HMnO4).

3.3 Stoichiometry

The reaction mixture containing an excess of permanganate over the cationic form of POAN(H2SO4-doped POAN) was mixed in the presence of Na2SO4 (100 mmol·L−1) adjusted toa constant ionic strength. After the reaction time had elapsed, solid KI was added followingacidification by H2SO4 (10%) and then the remaining permanganate was titrated againststandard oxalic acid [32]. The results indicated that 1.2 moles of permanganate consumed 1mole of the repeating unit of the POAN matrix, as given by the following equation:

5POAN + 6KMnO4 + 9H2SO4 + 16H2O −→20H2Q + 5R-NH2 + 4NH3 + 6MnSO4 + 3K2SO4 (3)

The main products of oxidation were identified as the corresponding hydroquinone (H2Q)by a spot test and ammonia by Nessler’s reagent [33, 34].

3.4 Degradation of the Chromogenic Energy of the Doped POAN

The fundamental property of an electrically activated chromogenic material [1–5] is that itexhibits a large change in its optical properties upon a change in either the electrical fieldor the injected or ejected charge. The change in optical properties can be in the form ofabsorbance, reflectance or scattering. This optical change results in a transformation from ahighly transmitting state to a partly reflecting or absorbing state. This change can be eithertotally or partly over the visible and solar spectrum, but typically it is over just some portionof these spectral regions.

The theoretical capacity (kJ·g−1) of the chromogenic energy (CE) can be calculated ifthe weight or molecular weight (Mwt, g−1) of the chromogenic species is known

CE = NAhC

λ. (4)

Nunerical values of the constants in Eq. 4 are NA = 6.022 × 1023 mol−1, h = 6.625 ×10−34 J·s, and C = 2.997 × 108 m·s−1 where NA,h,C, and λ are the Avogadro number,Planck constant, velocity of light, and the wavelength, respectively.

If the applied wavelength (λ) during oxidative hydrolysis is known, the CE value canbe determined via integration of the peak area (Eq. 5) of the absorbance (A) versus discol-oration time according to the following:

Peak area =∫ t=00

t=0.0Adt. (5)

The CE of HClO4-doped POAN also can be calculated experimentally using the follow-ing equation:

CE = NAhC

λ

∫ t=00

t−0Adt (6)

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Fig. 4 Variation of theabsorbance λ around 720 nmwith time during the oxidativehydrolysis of POAN(100 µmol·L−1) protonated withHClO4 (100 mmol·L−1) in thepresence of the oxidant (a–e) atconcentrations of 0.0, 40, 80, 100and 120 µmol·L−1, respectively

Table 3 Results of MM+ calculations of strain [S/(kJ·mol−1)] and dipole moment [μ/(Debye)] of the pos-sible configuration structures formed during hydrolysis of POAN matrix

Matrix I II III IV V VI VII VIII IX

Strain 502.41 500.90 255.97 95.06 89.70 7.40 7.32 7.99 25.98

μ 2.44 1.15 1.73 1.65 1.14 0.97 0.83 0.90 1.26

Table 4 Collective data obtained of the chromogenic energy (CE) of HClO4-doped POAN

Oxidant (µg·L−1) Polym/Oxid Peak area (a.u.·min−1) CE (kJ·g−1·min−1)

3.16 30.26 7.725 122.627

6.32 15.129 7.340 116.507

9.48 10.086 6.938 110.126

12.64 7.564 6.481 102.872

15.80 6.052 6.244 99.110

18.96 5.043 5.718 90.761

20.54 4.655 5.559 88.248

where A is the absorbance and t is the discoloration time.A decrease in absorbance of the POAN-EB base form (compact coil), after addition of

the KMnO4 oxidant, was not observed (Fig. 1, curve a). On the contrary, after addition of theacid the dark-green color of protonated POAN was observed (Fig. 1, curve b). From theseobservations, it can be suggested that a change in the polymer conformation occurs from acompact-coil-like form (dark blue coloration at λ of about 600 nm) to an expanded-coil-likeform (dark green coloration at λ of about 780 nm). The expanded-coil-like conformationespecially facilitates the delocalization of electrons through the polymer backbone, leadingto the enhancement of the spectroactivity (chromogenic energy) of the polymer. On thecontrary, a significant decrease in the absorbance for the protonated form was recorded afteraddition of the oxidant [18] (Fig. 1, curves b–i). However, protonation of this matrix is acrucial feature for the oxidative hydrolysis process.

The degradation of the CE of HClO4-doped POAN is highly dependent on the oxidantand the time of oxidation (Fig. 4, Table 4). A good linearity was obtained (r ≈ 0.996) of

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Fig. 5 Chromogenic energy(kJ·g−1) of HClO4-doped POANversus the oxidant concentration(KMnO4, µg·mL−1)

the CE versus degradation time (min). The rate of degradation was found to be equal to1.978 kJ·g−1·min−1. Moreover, the HClO4-doped POAN matrix has the ability to store about128.878 kJ·g−1 CE at 720 nm in a condensed lightweight form. This CE storage in thepolymer may lead to new materials that are suitable for electrochromic devices [14].

3.5 Kinetic Study

Figure 4 illustrates the variation of absorbance (λ of about 720 nm) of POAN (140 µmol·L−1)protonated by HClO4 (100 mmol·L−1) with time, at different initial concentrations ofKMnO4, while keeping the other parameters constant. Computer-oriented kinetic analysiswas carried out for each absorbance versus time data set assuming various kinetic equations[17, 18, 25]. It was found that the Ginstling-Bronstein equation (D4) gives the best fit ofthe experimental data, with the correlation coefficient (r) close to unity and with a very lowrelative standard deviation. The Ginstling-Bronstein [25] equation (D4) can be expressedas: (

1 − 2

3A

)− (1 − A)

23 = kt (7)

where A is the absorbance, k is the rate constant, and t is the oxidation time.Based on fitting of experimental data obtained, e.g., when oxidative hydrolysis of POAN

(100 µmol·L−1) by KMnO4 (100 µmol·L−1) in the presence of HClO4 (100 mmol·L−1) thatwas carried out as a function of time, a reaction rate constant of k =1.882×10−4 s−1 wascomputed, where the values of statistical parameters are r =0.977 and RSD = 2.078×10−2.It is interesting to note that the k value calculated using the D4 model is about eight, four,five, twenty eight, thirty four, and fifty eight times lower than the k values obtained byapplying D1, D2, and D3 (one-, two-, or three-dimensional diffusion), or first- (F1), second-(F2), and third-order (F3) kinetics under the same conditions.

3.6 Activation Parameters

The rate constants for the oxidative hydrolysis of the POAN (100 µmol·L−1) matrix in strongacidic (HClO4, 100 mol·L−1) medium were determined over the temperature range of 283 to323 K while keeping all other conditions unaltered. The corresponding activation parameters(Table 5) were computed using the Arrhenius and Eyring equations [17, 18, 25]. Both the

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Table 5 Activation parameters of the oxidative hydrolysis of HClO4-doped POAN

Oxidant (µmol·L−1) Ea /(kJ·mol−1) �H #/(kJ·mol−1) �S#/(J·K−1·mol−1) �G#/(kJ·mol−1)

40 51.231 49.955 −489.707 197.163

60 46.069 44.736 −474.932 186.265

80 35.807 38.452 −468.491 175.082

100 33.637 37.296 −457.384 173.596

120 30.016 34.205 −446.946 167.394

140 26.228 30.856 −439.336 161.927

160 24.081 26.573 −435.395 156.321

Fig. 6 Arrhenius (solid line) andEyring (dashed line) plots of theoxidative hydrolysis of theHClO4-doped POAN matrix

Arrhenius and Eyring plots showed a close fit of the experimental data (Fig. 6). The valuesof activation parameters calculated for different experimental runs with different concentra-tions of KMnO4 are summarized in Table 5. These moderate values of the activation energysupport the proposed mechanism for the oxidative hydrolysis of POAN (Scheme 2).

The variation of �H # with �S# for the series of experiments were represented by astraight line (r ≥ 0.994) as shown in Fig. 7, suggesting that compensation of isokinetic ef-fects occurs. Several authors suggested the presence of isokinetic phenomena [17, 18, 25,37]. The most important application of the compensation and/or isokinetic effect is that suchbehaviors constitute evidence for a single dominant mechanism throughout the correlated se-ries of chemical catalysis, cooperative relaxation kinetics in thermally simulated processes,the sorption and browning of garlic, etc. [35–37]. A higher positive value of �G# indicatesthat the transition state is highly solvated. Negative values of �S# within the range of rad-ical reactions have been ascribed to the nature of electron pairing and electron unpairingprocesses, and to the loss of degrees of freedom formerly available to the reactants beforethe formation of a rigid transition state. Also, this is consistent with an SN1 or dissociativemechanism for the transition state.

On plotting �H # and �S# against the oxidant (KMnO4, µmol·L−1) concentration(Fig. 8) and extrapolating to C = 0.0,�H #0 and �S#0 values were obtained and hence�G#0 was computed at each given temperature. The values seem to be almost independentof the POAN concentration. These values at 25 °C are 55.68–0.1 and 205.91 ± 0.3 kJ·mol−1

for �H #0 and �G#0, respectively, and the value of �S#0 is equal to −504.54±0.2 J·mol−1.

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Fig. 7 Plot of �S# versus �H #

plot for the oxidative hydrolysisof the HClO4-doped POANmatrix

Fig. 8 �H # (solid line) and�S# (dashed line) plotted versusthe oxidant concentration(KMnO4, µmol·L−1)

4 Conclusions

The disappearance of the chromogenic energy (coloration efficiency) of the protonated formof the POAN matrix (HA-doped POAN), via an oxidative hydrolysis mechanism, was stud-ied experimentally using a spectrophotometric technique and was substantiated computa-tionally using Molecular Mechanics (MM+) calculations. The HClO4-doped POAN matrixhas the ability to store chromogenic energy of about 128.878 kJ·g−1 at 720 nm in a con-densed lightweight form. It was observed that the method proposed (cf., experimental) forthe study of the oxidative hydrolysis process of the protonated POAN matrix (HA-dopedPOAN) was simple, precise, inexpensive, and required neither sophisticated instrumenta-tion, such as spectroelectro-chemical equipment, nor transparent electrodes such as metaloxide anodes of the type indium-doped tin oxide coated on a glass working electrode. Theresults obtained here should encourage use of the proposed method for studying oxidationof some organic compounds in different fields such as wastewater treatment, rather than theElectro-Fenton process [38]. That method requires the addition of ferric chloride (FeCl3) tothe solution, which, in turn, requires consecutive separation steps.

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Acknowledgements The author would like to thank the faculty members of the Chemistry Department,Faculty of Science, Assiut University, Egypt, for their encouragement.

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