**3.1 Electrosynthesis and characterization of polyANS**

The electrosynthesis of a film of polyANS was tested by chronopotenciometry and cyclic voltametry in five different electrodes: Au, Pt, glassy carbon, carbon paste and Au modified with PANI. No deposition of a polymer onto the Au, Pt and glassy carbon electrodes was observed, in agreement to reported for aminonaphtalen disulfonics acids (Mažeikienė & Malinauskas, 2004) probably because the products formed during the oxidation are very solubles. On the contrary film growth was presented onto carbon paste and Au/PANI electrodes, the syntheses and properties obtained in each electrode are presented to continuation.

Electrochemical Preparation and Properties of Novel Conducting Polymers

Montes-Rojas, 2008):

only was assumed of Sauerbrey equation that:

Derived from 5-Amino-2naphtalensulfonic Acid, Luminol and from Mixtures of Them 101

From the perspectives of electrochemical applications, arguably the most important underlying process of conducting polymers is the exchange between the films and ions molecules that accompany film redox switching. In case of sulfonated polyanilines is accepted that the charge compensation is accomplished mainly by the ejection of cations (Mello et al., 2000; Varela et al., 2000a, 2000b, 2001; Cano-Márquez et al.; 2007) in contrast with the behavior of PANI, which is carried out by the incorporation of anions (Hillman & Mohamud, 2006). In order to define as is realized the charge compensation of polyANS electrochemical quartz crystal microbalance (EQCM) measurements were carried out in monomer free solution, the curves obtained were analyzed considering that the change of frequency is correlated to change of mass for the Sauerbrey equation (Donjuan-Medrano &

∆� � � ���∆� � � � � ���

Where Δf and Δm are the change of frequency and the change of mass respectively, Cf is the proportionality constant which depend of the base frequency (f0); density of quartz (ρq) and the wave velocity within the quartz crystal (υq). The negative sign in the equation indicate that when the frequency increase the mass diminishes and when the frequency decreases the mass augment. In order to use the Sauerbrey equation it is necessary probe that the film deposited in the quartz is "rigid", it is the mass loading of the quartz crystal microbalance show ideal acoustic coupling to the crystal surface (Buttry & Ward, 1992) and determinate experimentally the value of Cf (Donjuan-Medrano & Montes-Rojas, 2008). In raison that in this work only a qualitative analysis was carried out, it was not required to validate the Souerbrey equation, neither it was indispensable determinate experimentally the value of Cf,

It is that the change of mass is proportional to -Δf. The obtained results for H2SO4 are shown in Figure 4, in a first time the potentiodinamic profile of I and -Δf was analyzed over the range - 200-900 mV (Figure 4a), it was observed that when the scan begin there are not redox process, so the frequency remain constant, to 300 mV appear the oxidation peak this indicate that the polyANS is oxidate and positives charges in the polymer chain are generated, simultaneously a decrease of mass is presented, this mean that for maintain the electrical neutrality of the doped polyANS the charge compensation is carried out predominantly for ejection of cations from the polymer phase to the solution as is attaint for a self-doped polymer, when it was reach the potentials for the full oxidation of polymer an increase of mass was observed, contrary to decrease of mass observed for PANI in similar conditions (Orata & Buttry, 1987). During the reverse sweep the mass decrease until finalized the reduction, it is the anion incorporated during the oxidation are ejected when the film back to netral condition, to end of scan the mass augment to until reach nearly the initial value. For the reason that the two peak of oxido-reduction of film are before 500 mV, the same experiment was repeated fixing the upper limit potential to 500 mV, as can be been in Figure 4b, the behavior is similar to those obtained for the extended range, in fact the mass of polyANS remains constant until the film commence the oxidation process in this moment the mass descend, this behavior indicate that the electroneutralization of film is achieved principally by expulsion of protons containing in the -SO3H group of polyANS, to higher potentials the mass increase, a similar behavior has

� ����

� ∆� (1)

∆� � � ���∆ (2)

#### **3.1.1 Electrosynthesis and electrogravimetric study of polyANS synthesized onto Au/PANI electrodes**

The syntheses electrochemical of film of PolyANS onto the Au/PANI electrode was carried out by cyclic voltametry, this modified electrode was used as working electrode for the reason that in earlier work it was demonstrated that contrary to the metallic electrodes a film of sulfonated PANI is obtained onto Au/PANI electrodes since, during electroxidation of PANI positive charges are generated at the polymer chain, which are compensated by incorporation of anions from the solution. Consequently, the –SO3 group of sulfonated PANI is incorporated to the PANI film as a dopant anion, anchoring sulfonated monomers on the PANI surface. Then, when the oxidation potential of monomers is attained the monomer is polymerized on PANI. During the reduction the anion cannot be ejected of PANI because the polymer synthetised is trapped within the PANI chains. (Cano-Márquez et al., 2007). Figure 3 shows curves obtained in diverse stages of growth of polyANS. At the very beginning of the electrodeposition the curve obtained is very similar to those of PANI (Shin-Jung & Su-Moon, 2002), in fact, in this stage the polyANS produced is small in comparison to those of PANI as a result the response obtained is those of PANI, which is characterized by three well redox centered pair centered at around 250, 780 and 500 mV corresponding to leucoemeraldine to emeraldine, emeraldine to pernigraniline redox transitions and sobreoxidation products respectively. When the cycle increase the response change gradually until become in those of polyANS, in fact the peaks attributed to oxidoreduction of film shift until overlapping (Figure 3). The reduced separation of the two peaks for sulfonated polyaniline has been associated with steric effects caused by the bulky sulfonic acid substituent (Wei et al., 1996; Yue et al., 1991). Additionally to the two oxidoreduction process of polyANS situated between 200 and 500 mV, the cyclic voltammogram of polyANS present a redox pair centered at around 540 mV, at present time no clear assignation can be proposed for this peak, however it can be speculated that have as origin the oxido-reduction of degradation products because is located of same potential of degradation products of PANI.

Fig. 3. Cyclic voltammograms of the 14th (a), 28th (b) 42th (c) and 56th (d) cycle of the electropolymerization of 1 mM ANS in 0.5 M H2SO4, obtained onto Au/PANI electrode. The potential was scanned from -200 to 1090 mV at 100 mVs-1.

The syntheses electrochemical of film of PolyANS onto the Au/PANI electrode was carried out by cyclic voltametry, this modified electrode was used as working electrode for the reason that in earlier work it was demonstrated that contrary to the metallic electrodes a film of sulfonated PANI is obtained onto Au/PANI electrodes since, during electroxidation of PANI positive charges are generated at the polymer chain, which are compensated by incorporation of anions from the solution. Consequently, the –SO3 group of sulfonated PANI is incorporated to the PANI film as a dopant anion, anchoring sulfonated monomers on the PANI surface. Then, when the oxidation potential of monomers is attained the monomer is polymerized on PANI. During the reduction the anion cannot be ejected of PANI because the polymer synthetised is trapped within the PANI chains. (Cano-Márquez et al., 2007). Figure 3 shows curves obtained in diverse stages of growth of polyANS. At the very beginning of the electrodeposition the curve obtained is very similar to those of PANI (Shin-Jung & Su-Moon, 2002), in fact, in this stage the polyANS produced is small in comparison to those of PANI as a result the response obtained is those of PANI, which is characterized by three well redox centered pair centered at around 250, 780 and 500 mV corresponding to leucoemeraldine to emeraldine, emeraldine to pernigraniline redox transitions and sobreoxidation products respectively. When the cycle increase the response change gradually until become in those of polyANS, in fact the peaks attributed to oxidoreduction of film shift until overlapping (Figure 3). The reduced separation of the two peaks for sulfonated polyaniline has been associated with steric effects caused by the bulky sulfonic acid substituent (Wei et al., 1996; Yue et al., 1991). Additionally to the two oxidoreduction process of polyANS situated between 200 and 500 mV, the cyclic voltammogram of polyANS present a redox pair centered at around 540 mV, at present time no clear assignation can be proposed for this peak, however it can be speculated that have as origin the oxido-reduction of degradation products because is located of same potential of

**3.1.1 Electrosynthesis and electrogravimetric study of polyANS synthesized onto** 

Fig. 3. Cyclic voltammograms of the 14th (a), 28th (b) 42th (c) and 56th (d) cycle of the electropolymerization of 1 mM ANS in 0.5 M H2SO4, obtained onto Au/PANI electrode. The

potential was scanned from -200 to 1090 mV at 100 mVs-1.

**Au/PANI electrodes** 

degradation products of PANI.

From the perspectives of electrochemical applications, arguably the most important underlying process of conducting polymers is the exchange between the films and ions molecules that accompany film redox switching. In case of sulfonated polyanilines is accepted that the charge compensation is accomplished mainly by the ejection of cations (Mello et al., 2000; Varela et al., 2000a, 2000b, 2001; Cano-Márquez et al.; 2007) in contrast with the behavior of PANI, which is carried out by the incorporation of anions (Hillman & Mohamud, 2006). In order to define as is realized the charge compensation of polyANS electrochemical quartz crystal microbalance (EQCM) measurements were carried out in monomer free solution, the curves obtained were analyzed considering that the change of frequency is correlated to change of mass for the Sauerbrey equation (Donjuan-Medrano & Montes-Rojas, 2008):

$$
\Delta f = -\mathcal{C}\_{\text{f}} \Delta m = -\left(\frac{2f\_o^2}{\rho\_q \vartheta\_q}\right) \Delta m \tag{1}
$$

Where Δf and Δm are the change of frequency and the change of mass respectively, Cf is the proportionality constant which depend of the base frequency (f0); density of quartz (ρq) and the wave velocity within the quartz crystal (υq). The negative sign in the equation indicate that when the frequency increase the mass diminishes and when the frequency decreases the mass augment. In order to use the Sauerbrey equation it is necessary probe that the film deposited in the quartz is "rigid", it is the mass loading of the quartz crystal microbalance show ideal acoustic coupling to the crystal surface (Buttry & Ward, 1992) and determinate experimentally the value of Cf (Donjuan-Medrano & Montes-Rojas, 2008). In raison that in this work only a qualitative analysis was carried out, it was not required to validate the Souerbrey equation, neither it was indispensable determinate experimentally the value of Cf, only was assumed of Sauerbrey equation that:

$$
\Delta m = -\mathcal{C}\_{\text{f}} \Delta \tag{2}
$$

It is that the change of mass is proportional to -Δf. The obtained results for H2SO4 are shown in Figure 4, in a first time the potentiodinamic profile of I and -Δf was analyzed over the range - 200-900 mV (Figure 4a), it was observed that when the scan begin there are not redox process, so the frequency remain constant, to 300 mV appear the oxidation peak this indicate that the polyANS is oxidate and positives charges in the polymer chain are generated, simultaneously a decrease of mass is presented, this mean that for maintain the electrical neutrality of the doped polyANS the charge compensation is carried out predominantly for ejection of cations from the polymer phase to the solution as is attaint for a self-doped polymer, when it was reach the potentials for the full oxidation of polymer an increase of mass was observed, contrary to decrease of mass observed for PANI in similar conditions (Orata & Buttry, 1987). During the reverse sweep the mass decrease until finalized the reduction, it is the anion incorporated during the oxidation are ejected when the film back to netral condition, to end of scan the mass augment to until reach nearly the initial value. For the reason that the two peak of oxido-reduction of film are before 500 mV, the same experiment was repeated fixing the upper limit potential to 500 mV, as can be been in Figure 4b, the behavior is similar to those obtained for the extended range, in fact the mass of polyANS remains constant until the film commence the oxidation process in this moment the mass descend, this behavior indicate that the electroneutralization of film is achieved principally by expulsion of protons containing in the -SO3H group of polyANS, to higher potentials the mass increase, a similar behavior has

Electrochemical Preparation and Properties of Novel Conducting Polymers

Derived from 5-Amino-2naphtalensulfonic Acid, Luminol and from Mixtures of Them 103

In order to determinate whether there are or not anion participation in the electroneutralization of PolyANS, EQCM measurements were carried out in solutions for acids with anions of different molar mass: H2SO4 (96 gmol-1) (Figure 4), HCl (35.45 gmol-1), HClO4 (99.4 gmol-1), HNO3 (62 gmol-1) and camphorsulfonic acid (HCS) which molar mass of anion is 231.1 gmol-1 (Figure 5). A decrease of mass is presented during the oxidation in H2SO4, HCl, HClO4 and HNO3 showed that during the electroneutralization, protons are ejected to polyANS. However, a participation of anion can be proposed in reason of the marked dependence of frequency profile and cyclic voltammogram of anion of acids as is showed in Figure 4 and 5. The decrease of mass (-Δf) change with the acid used and not relation between the anion molar mass and the variation of frequency was present. These results show that the charge compensation of polyANS is carried out by both expulsion of protons and additions of anions, but the predominant process is the cation expulsion. In the HCS case also the electroneutralization is realized principally by proton expulsion despite the fact that the mass remain constant during the oxidation, in fact the change of mass registered are the sum of two contribution incorporation of anions and ejection of protons, as the frequency remains constant during the oxidation this mean that the augmentation of mass by incorporation of anions has the same value that the diminution of mass by expulsion of cations, this resultant is due to the molar mass of CS is more grand that those of the anions of other acids. Finally, it is important to note that the process of electroneutralization of polyANS is different of those of homopolymer of ortanilic acid, in

Fig. 5. Cyclic voltammograms and frequency responses recorded simultaneously of a polyANS film in dfferents 0. 5 M acids solutions. The scan rate was 100 mVs-1.

been presented for sulfonated PANI (Varela et al., 2000). After the reverse of the scan direction the mass continue increase until the process of reduction begin, in this point the mass decrease, finally the mass increase attaint the value original. The experimental evidence presented above demonstrates that the charge process during the charge compensation is carried out principally by expulsion of cations of polyANS, however is not possible establish whether or not anion participation. In addition the evolution of frequency in the direct scan is completely different to those obtained in the inverted scan, it is the change of mass obtained is not reversible resulting in a broad frequency curve. This behavior is different to those obtained for sulfonated PANI (Mello et al, 2000; Varela et al. 2001) where the curves of frequency were more reversible. This behavior suggest that the electroneutralization is more complexes for the polyANS that for the films synthesized to anilines ring substituted by sulfonic groups, probably due the distance of the sulfonic group and nitrogen is much longer in polyANS that the anilines substituted directly in the ring for sulfonic groups, so in this case the electroneutralization is more easy.

Fig. 4. Plot I/E (full line) and -Δf/E (doted line) potentiodinamic profil for polyANS obtained for two upper limit (a) 900 and (b) 500 mV in H2SO4 0.5 M electrolyte solution at 100 mVs-1.

been presented for sulfonated PANI (Varela et al., 2000). After the reverse of the scan direction the mass continue increase until the process of reduction begin, in this point the mass decrease, finally the mass increase attaint the value original. The experimental evidence presented above demonstrates that the charge process during the charge compensation is carried out principally by expulsion of cations of polyANS, however is not possible establish whether or not anion participation. In addition the evolution of frequency in the direct scan is completely different to those obtained in the inverted scan, it is the change of mass obtained is not reversible resulting in a broad frequency curve. This behavior is different to those obtained for sulfonated PANI (Mello et al, 2000; Varela et al. 2001) where the curves of frequency were more reversible. This behavior suggest that the electroneutralization is more complexes for the polyANS that for the films synthesized to anilines ring substituted by sulfonic groups, probably due the distance of the sulfonic group and nitrogen is much longer in polyANS that the anilines substituted directly in the ring for sulfonic groups, so in this case the

Fig. 4. Plot I/E (full line) and -Δf/E (doted line) potentiodinamic profil for polyANS obtained for two upper limit (a) 900 and (b) 500 mV in H2SO4 0.5 M electrolyte solution at

electroneutralization is more easy.

100 mVs-1.

In order to determinate whether there are or not anion participation in the electroneutralization of PolyANS, EQCM measurements were carried out in solutions for acids with anions of different molar mass: H2SO4 (96 gmol-1) (Figure 4), HCl (35.45 gmol-1), HClO4 (99.4 gmol-1), HNO3 (62 gmol-1) and camphorsulfonic acid (HCS) which molar mass of anion is 231.1 gmol-1 (Figure 5). A decrease of mass is presented during the oxidation in H2SO4, HCl, HClO4 and HNO3 showed that during the electroneutralization, protons are ejected to polyANS. However, a participation of anion can be proposed in reason of the marked dependence of frequency profile and cyclic voltammogram of anion of acids as is showed in Figure 4 and 5. The decrease of mass (-Δf) change with the acid used and not relation between the anion molar mass and the variation of frequency was present. These results show that the charge compensation of polyANS is carried out by both expulsion of protons and additions of anions, but the predominant process is the cation expulsion. In the HCS case also the electroneutralization is realized principally by proton expulsion despite the fact that the mass remain constant during the oxidation, in fact the change of mass registered are the sum of two contribution incorporation of anions and ejection of protons, as the frequency remains constant during the oxidation this mean that the augmentation of mass by incorporation of anions has the same value that the diminution of mass by expulsion of cations, this resultant is due to the molar mass of CS is more grand that those of the anions of other acids. Finally, it is important to note that the process of electroneutralization of polyANS is different of those of homopolymer of ortanilic acid, in

Fig. 5. Cyclic voltammograms and frequency responses recorded simultaneously of a polyANS film in dfferents 0. 5 M acids solutions. The scan rate was 100 mVs-1.

Electrochemical Preparation and Properties of Novel Conducting Polymers

sweep rate as is expected for a surface bound species.

Derived from 5-Amino-2naphtalensulfonic Acid, Luminol and from Mixtures of Them 105

the response of polyANS. The polymers which dissolve very slowly, it is when are cycled repeatedly diminish slightly the current intensity. The peak heights scale linearly with the

The electropolymerization of ANS in carbon paste electrodes not modified with this monomer in solution were carried out by chronoamperometry and cyclic voltammeter. The results obtained with potentiodinamic methods are presented in the copolymer section, in the case of chronoamperometry the electroxidation was achieved with a solution formed only by ANS, since the monomer was used itself as an electrolyte, the potential was stepped in 1250 mV during 60 s. After the growth was terminated, the film was studied by recording cyclic voltamograms; the curves obtained are show in figure 7. We note that the locations of the redox peak and the general appearance of the voltammogram are similar to sulfonated polyanilines o (Royappa et al., 2001; Nguyen et al., 1994) and the polyANS synthetised with Au/PANI and carbon paste modified with ANS. The cyclic voltamogram obtained exhibit two broad and overlapping oxidation peak between 200 and 600 mV. The oxidation peak correspond to the oxidation of the neutral nitrogen atoms in the polymer backbone to form the radical carbon and dication ant they compare well with the peaks for PANI films (Buttry & Ward, 1992). A process centered in 100, similar to those obtained with the monomer contain in the bulk paste electrode also appear when the electrodeposition is realized with the monomer in solution. A linear relationship was found between the peak current and scan rate, indicating that the elecroactive polymer film is well adhered to electrode. To investigate the influence of the pH on the redox behavior of the film, cyclic voltammograms of electrochemically synthesized films prepared under the same conditions as above, were recorded in solutions of different pH values. The voltammograms obtained are shown in Figure 7. One of the most obvious changes in the voltammetric behaviour of polymer in neutral and alkaline media in comparison to pH acid is the diminution in current, which is produced by the haut solubility of sulfonated polymer in pH neuter. In addition the peak attributed to polyANS shift not much to negative potentials. Thus the electroactivity of

polyANS is practically independent of pH as is attaint for a self-doped polymer.

adsorption of monomers and oligomers in the paste carbone, it may be speculated

The same experiments were made with glassy carbon, Au and Pt as working electrode, the chronoamperograms obtained showed no rising transients, and no evidence of a film was obtained by cyclic voltammetry, in agreement with Mažeikienė et al, 2004. These results show that the polymerization of sulfonated monomers only can be carried out in carbon paste electrodes. The reasons for this positive deposition are unknown. However physic

In this part of work was showed that the ANS can be polymerized in carbon paste and Au/PANI electrodes, this result is contrary to those obtained for other amino naphtalensulfonic, in fact in this study is proved that is not possible the electrochemical homopolymerization of these type of compounds (Mažeikienė & Malinauskas, 2004). Additionally is well established that Sulphonated anilines are difficult to polymerise under conventional conditions, in fact the haut solubility of film in aqueous milieu made difficult the synthesis of a film, the strategies employed for the electrodepositon of sulfonated homopolymer has been oriented to the diminution of solubility of oligomer, for this , the electropolymerization has carried out to bass temperatures and the combination of organic and aqueous solvents (Krishnamoorthy et al., 2002). In other works is reported the formation of sulfonated polymers using metallic electrodes however the polymerization rate is very bass (Zhang, L; 2006). The advantages of the use of Au/PANI and carbon paste

fact for this polymer the compensation of charge is carried out exclusively by ejection of protons and the profiles of change of frequency are very reversible (Cano-Márquez et al, 2007), which suggest that the process is more simple. The differences between these sulfonated homopolymers proved that the distance between the sulfonic group and the nitrogen impact in the electroneutralization process, when these groups are closer the cation participation is more important.

#### **3.1.2 Electrosyntheses of polyANS using carbon paste electrodes**

The electrodeposition of polyANS was also evaluated using carbon paste electrodes, the electrosynthesis was carried out by two methods with the monomer in solution and incorporated onto the carbon paste electrode. The results found employed the first methodology are presented in a subsequent section, in the case of the second mode the electrodeposition was realized potenciodinamic in a solution containing only H2SO4 1 M and the working electrode was carbon paste modified with ANS, the curve registered during the successive scans are presented in the Figure 6, this cyclic voltammogram is similar to those obtained with Au/PANI electrodes, in fact the curve can be show a shoulder and a broad peak situated around 309 and 424 mV correspondingly, in the counterpart cathodic are two overlapping peak centered in 269 and 319 mV. Following an analogy to the parent polyaniline these peaks can be assigned to the leucoemeraldine to emeraldine transition and the emeraldine to perigraniline transition, respectively. Additionally a redox process appear around 100 mV, it not was possible the assignation of these peaks to an specific reaction, however it is possible that the peak correspond to the oxido-reduction of oligomers accumulate in the electrode, in fact these peaks not are observed when the response is analyzed in solutions basic. Subsequent cycles show anodic and cathodic current maxima with increasing currents, indicating progressive film formation. The electrochemical behavior of films synthetised was examined by cyclic voltametry, for this experience was necessary shift the upper limit potential to 600 mV, with the finality of avoid the oxidation of monomer and more film synthesis, it is examine only

Fig. 6. Succesive cyclic voltammograms of a paste carbone electrode modified with ANS (0.1452 cm2) in H2SO4 (1 M). The composition of electrode was graphite powder, nujol and ANS in percentages of mass of 80, 18.5 and 1.5 respectively. Scan rate: 100 mVs-1.

fact for this polymer the compensation of charge is carried out exclusively by ejection of protons and the profiles of change of frequency are very reversible (Cano-Márquez et al, 2007), which suggest that the process is more simple. The differences between these sulfonated homopolymers proved that the distance between the sulfonic group and the nitrogen impact in the electroneutralization process, when these groups are closer the cation

The electrodeposition of polyANS was also evaluated using carbon paste electrodes, the electrosynthesis was carried out by two methods with the monomer in solution and incorporated onto the carbon paste electrode. The results found employed the first methodology are presented in a subsequent section, in the case of the second mode the electrodeposition was realized potenciodinamic in a solution containing only H2SO4 1 M and the working electrode was carbon paste modified with ANS, the curve registered during the successive scans are presented in the Figure 6, this cyclic voltammogram is similar to those obtained with Au/PANI electrodes, in fact the curve can be show a shoulder and a broad peak situated around 309 and 424 mV correspondingly, in the counterpart cathodic are two overlapping peak centered in 269 and 319 mV. Following an analogy to the parent polyaniline these peaks can be assigned to the leucoemeraldine to emeraldine transition and the emeraldine to perigraniline transition, respectively. Additionally a redox process appear around 100 mV, it not was possible the assignation of these peaks to an specific reaction, however it is possible that the peak correspond to the oxido-reduction of oligomers accumulate in the electrode, in fact these peaks not are observed when the response is analyzed in solutions basic. Subsequent cycles show anodic and cathodic current maxima with increasing currents, indicating progressive film formation. The electrochemical behavior of films synthetised was examined by cyclic voltametry, for this experience was necessary shift the upper limit potential to 600 mV, with the finality of avoid the oxidation of monomer and more film synthesis, it is examine only

Fig. 6. Succesive cyclic voltammograms of a paste carbone electrode modified with ANS (0.1452 cm2) in H2SO4 (1 M). The composition of electrode was graphite powder, nujol and

ANS in percentages of mass of 80, 18.5 and 1.5 respectively. Scan rate: 100 mVs-1.

**3.1.2 Electrosyntheses of polyANS using carbon paste electrodes** 

participation is more important.

the response of polyANS. The polymers which dissolve very slowly, it is when are cycled repeatedly diminish slightly the current intensity. The peak heights scale linearly with the sweep rate as is expected for a surface bound species.

The electropolymerization of ANS in carbon paste electrodes not modified with this monomer in solution were carried out by chronoamperometry and cyclic voltammeter. The results obtained with potentiodinamic methods are presented in the copolymer section, in the case of chronoamperometry the electroxidation was achieved with a solution formed only by ANS, since the monomer was used itself as an electrolyte, the potential was stepped in 1250 mV during 60 s. After the growth was terminated, the film was studied by recording cyclic voltamograms; the curves obtained are show in figure 7. We note that the locations of the redox peak and the general appearance of the voltammogram are similar to sulfonated polyanilines o (Royappa et al., 2001; Nguyen et al., 1994) and the polyANS synthetised with Au/PANI and carbon paste modified with ANS. The cyclic voltamogram obtained exhibit two broad and overlapping oxidation peak between 200 and 600 mV. The oxidation peak correspond to the oxidation of the neutral nitrogen atoms in the polymer backbone to form the radical carbon and dication ant they compare well with the peaks for PANI films (Buttry & Ward, 1992). A process centered in 100, similar to those obtained with the monomer contain in the bulk paste electrode also appear when the electrodeposition is realized with the monomer in solution. A linear relationship was found between the peak current and scan rate, indicating that the elecroactive polymer film is well adhered to electrode. To investigate the influence of the pH on the redox behavior of the film, cyclic voltammograms of electrochemically synthesized films prepared under the same conditions as above, were recorded in solutions of different pH values. The voltammograms obtained are shown in Figure 7. One of the most obvious changes in the voltammetric behaviour of polymer in neutral and alkaline media in comparison to pH acid is the diminution in current, which is produced by the haut solubility of sulfonated polymer in pH neuter. In addition the peak attributed to polyANS shift not much to negative potentials. Thus the electroactivity of polyANS is practically independent of pH as is attaint for a self-doped polymer.

The same experiments were made with glassy carbon, Au and Pt as working electrode, the chronoamperograms obtained showed no rising transients, and no evidence of a film was obtained by cyclic voltammetry, in agreement with Mažeikienė et al, 2004. These results show that the polymerization of sulfonated monomers only can be carried out in carbon paste electrodes. The reasons for this positive deposition are unknown. However physic adsorption of monomers and oligomers in the paste carbone, it may be speculated

In this part of work was showed that the ANS can be polymerized in carbon paste and Au/PANI electrodes, this result is contrary to those obtained for other amino naphtalensulfonic, in fact in this study is proved that is not possible the electrochemical homopolymerization of these type of compounds (Mažeikienė & Malinauskas, 2004). Additionally is well established that Sulphonated anilines are difficult to polymerise under conventional conditions, in fact the haut solubility of film in aqueous milieu made difficult the synthesis of a film, the strategies employed for the electrodepositon of sulfonated homopolymer has been oriented to the diminution of solubility of oligomer, for this , the electropolymerization has carried out to bass temperatures and the combination of organic and aqueous solvents (Krishnamoorthy et al., 2002). In other works is reported the formation of sulfonated polymers using metallic electrodes however the polymerization rate is very bass (Zhang, L; 2006). The advantages of the use of Au/PANI and carbon paste

Electrochemical Preparation and Properties of Novel Conducting Polymers

formed by aniline and luminol and those of sulfonated polyanilines.

constant as it is attaint for an electroactive specie fix to surface electrode.

Derived from 5-Amino-2naphtalensulfonic Acid, Luminol and from Mixtures of Them 107

current of B1/B1' is only environ three fold more grand that B2/B2'. This dependence show that product correspondent to peaks B1/B1' are produced in more quantity when E<sup>λ</sup> is more higher. Two difference important were observed in voltammogramas obtain using two differents Eλ, first, the evolution of the intensity of current, For E<sup>λ</sup> = 0.9 V the current of peaks B1 and B1' increase significantly the first cycles, after remain almost constant, while that for E<sup>λ</sup> = 0.8V, the current augment slowly but continually, this last evolution of current is more congruent with a polymerization. The second is relationated with the peak B1/B1', for Eλ = 0.8 V, the peak is more broader that for Eλ = 0.9 V in addition in some cycles is possible to observe that the peak is the resultant of the overlap of two peaks, probably those of the dimmer or degradation oxidation and those of the bipolaron state of polymer. It is we propose that the peak B1/B1' and B2/B2' can be assigned to polaron and bipolaron states of polymer respectively; because the voltammograms are very similar to those of copolymer

Finally the film were analysed in H2SO4 solution by cyclic voltammetry, for this Eλ was shifted to more negatives potentials in order to avoid the oxidation of monomer in the bulk electrode paste. Voltamograms were carried out for different scan rates, the peak heights scale linearly with the sweep rate and the cathodic and anodic peak separation remains

Fig. 8. Subsequent multisweep cyclic voltammograms obtained in a H2SO4 (0.5M), the upper limit were: (a) 0.9 and (b) 0.8 V. The working electrode was paste carbon electrodes formed

In order to determinate weather the monomer concentration affect the electrosyntheses of film of polyluminol, electrodeposition were carried out employing carbon paste electrodes modified with different percentages of luminol, the results are presented in Figure 9, the voltamogramms have the same aspect, only they are differenced by the intensity in current which increase with the quantity of monomer in the bulk carbon paste electrode. This means that only the quantity of film is affected by the quantity of momomer. A similar experiment was achieved using a carbon paste electrode not modified and a solution with luminol, the curve obtained has an aspect equal to those obtained with modified electrode. It can be speculated that the curve not change with luminol concentration in the interface electrode/electrolyte, since when the monomer is in solution, the luminol is adsorbed in the electrode surface and the concentration in the interface is increase by preconcentration, so

by: graphite (60 %), nujol (26%) and luminol (14%). The scan rate was 100 mVs-1.

the concentration of luminol is more elevated than the metallic electrodes.

electrodes for the electrosynthesis of sulfonated polymers in relation to other strategies is the facility to obtain thick films rapidly in working to room temperatures and with aqueous solutions.

Fig. 7. Cyclic voltammograms of polyANS in: (a) H2SO4 0.1 M and (b) Na2SO4 0.1 M. Synthesis of the films was performed by potential step at 1240 mV using as working solution ANS 8 mM. Scan rate: 100 mV/s.

#### **3.2 Electrodeposition and characterization of polyluminol 3.2.1 Electrosyntheses of polyluminol**

The films obtained of electrooxidation of luminol have been denominated polyluminol. However, different works have showed that the product obtained are dimmers and no polymers (Ferreira et al., 2008; Robertis et al., 2008), the chemical composition of film has been attributed to the bass solubility of monomer in solution. In order to obtain a polymer of luminol we propose increase the monomer concentration in the interface electrode/electrolyte using paste carbon electrodes bulk modified with luminol. The curves obtained during successive scan for two different upper limit potential (Eλ) are presented in figure 8, in both cases the peaks due to the oxidation and reduction increase in intensity for each cycles as it is characteristic of growth of a film. The voltammogram acquired are different of those obtained with metallic electrodes in similar conditions, for the reason that additionally to process B1/B1' presented in metallic electrodes (Chang et al., 2005; Kumar et al., 2009), a second process B2/B2' is presented. A similar process to B2/B2' is obtained for the copolymers of aniline and luminol synthesised using solutions with more concentration of luminol that aniline (Roberti et al., 2008; Ferreira et al., 2008) and during the oxidation of luminiol in higher potentials 1.2 V (Zhang & Chen, 2000). Additionally the aspect of voltammogram presented in Figure 8 is very similar to those of copolymer therefore probably this peak are associated to polymer formation. The current of process B2/B2' by rapport to B1/B1' is strongly dependent of upper limit potential, for Eλ= 0.9 V the intensity of current B2/B2' is very small in comparaison with those B1/B1', while that when Eλ= 0.8 the

electrodes for the electrosynthesis of sulfonated polymers in relation to other strategies is the facility to obtain thick films rapidly in working to room temperatures and with aqueous

Fig. 7. Cyclic voltammograms of polyANS in: (a) H2SO4 0.1 M and (b) Na2SO4 0.1 M. Synthesis of the films was performed by potential step at 1240 mV using as working

The films obtained of electrooxidation of luminol have been denominated polyluminol. However, different works have showed that the product obtained are dimmers and no polymers (Ferreira et al., 2008; Robertis et al., 2008), the chemical composition of film has been attributed to the bass solubility of monomer in solution. In order to obtain a polymer of luminol we propose increase the monomer concentration in the interface electrode/electrolyte using paste carbon electrodes bulk modified with luminol. The curves obtained during successive scan for two different upper limit potential (Eλ) are presented in figure 8, in both cases the peaks due to the oxidation and reduction increase in intensity for each cycles as it is characteristic of growth of a film. The voltammogram acquired are different of those obtained with metallic electrodes in similar conditions, for the reason that additionally to process B1/B1' presented in metallic electrodes (Chang et al., 2005; Kumar et al., 2009), a second process B2/B2' is presented. A similar process to B2/B2' is obtained for the copolymers of aniline and luminol synthesised using solutions with more concentration of luminol that aniline (Roberti et al., 2008; Ferreira et al., 2008) and during the oxidation of luminiol in higher potentials 1.2 V (Zhang & Chen, 2000). Additionally the aspect of voltammogram presented in Figure 8 is very similar to those of copolymer therefore probably this peak are associated to polymer formation. The current of process B2/B2' by rapport to B1/B1' is strongly dependent of upper limit potential, for Eλ= 0.9 V the intensity of current B2/B2' is very small in comparaison with those B1/B1', while that when Eλ= 0.8 the

solution ANS 8 mM. Scan rate: 100 mV/s.

**3.2.1 Electrosyntheses of polyluminol** 

**3.2 Electrodeposition and characterization of polyluminol** 

solutions.

current of B1/B1' is only environ three fold more grand that B2/B2'. This dependence show that product correspondent to peaks B1/B1' are produced in more quantity when E<sup>λ</sup> is more higher. Two difference important were observed in voltammogramas obtain using two differents Eλ, first, the evolution of the intensity of current, For E<sup>λ</sup> = 0.9 V the current of peaks B1 and B1' increase significantly the first cycles, after remain almost constant, while that for E<sup>λ</sup> = 0.8V, the current augment slowly but continually, this last evolution of current is more congruent with a polymerization. The second is relationated with the peak B1/B1', for Eλ = 0.8 V, the peak is more broader that for Eλ = 0.9 V in addition in some cycles is possible to observe that the peak is the resultant of the overlap of two peaks, probably those of the dimmer or degradation oxidation and those of the bipolaron state of polymer. It is we propose that the peak B1/B1' and B2/B2' can be assigned to polaron and bipolaron states of polymer respectively; because the voltammograms are very similar to those of copolymer formed by aniline and luminol and those of sulfonated polyanilines.

Finally the film were analysed in H2SO4 solution by cyclic voltammetry, for this Eλ was shifted to more negatives potentials in order to avoid the oxidation of monomer in the bulk electrode paste. Voltamograms were carried out for different scan rates, the peak heights scale linearly with the sweep rate and the cathodic and anodic peak separation remains constant as it is attaint for an electroactive specie fix to surface electrode.

Fig. 8. Subsequent multisweep cyclic voltammograms obtained in a H2SO4 (0.5M), the upper limit were: (a) 0.9 and (b) 0.8 V. The working electrode was paste carbon electrodes formed by: graphite (60 %), nujol (26%) and luminol (14%). The scan rate was 100 mVs-1.

In order to determinate weather the monomer concentration affect the electrosyntheses of film of polyluminol, electrodeposition were carried out employing carbon paste electrodes modified with different percentages of luminol, the results are presented in Figure 9, the voltamogramms have the same aspect, only they are differenced by the intensity in current which increase with the quantity of monomer in the bulk carbon paste electrode. This means that only the quantity of film is affected by the quantity of momomer. A similar experiment was achieved using a carbon paste electrode not modified and a solution with luminol, the curve obtained has an aspect equal to those obtained with modified electrode. It can be speculated that the curve not change with luminol concentration in the interface electrode/electrolyte, since when the monomer is in solution, the luminol is adsorbed in the electrode surface and the concentration in the interface is increase by preconcentration, so the concentration of luminol is more elevated than the metallic electrodes.

Electrochemical Preparation and Properties of Novel Conducting Polymers

Derived from 5-Amino-2naphtalensulfonic Acid, Luminol and from Mixtures of Them 109

Fig. 10. Cyclic voltammograms for polyluminol synthesised using Eλ = 0.8 V and carbon paste electrode graphite (60 %), luminol (7 %) and nujol (33 %) at differents electrolytes. Scan rate = 100mVs-1. Inset complete cyclic voltammogram for polyluminol at PBS.

Fig. 11. Cyclic voltammetry of polyluminol, obtained in different supporting electrolytes containing: H2SO4 (0.5 M), Na2SO4 (1 M) and phosphate buffer solution (pH = 7). Synthesis of the films was performed as indicate in Figure 8a, using: (a) luminol (1 Mm) in H2SO4 (0.5

A more extended applications of polyluminol films and its derivatives is the electrocatalysis of ascorbic acid (Chen & Lin, 2002; Ashok et al., 2009; Ma et al., 2010; Kumar et al., 2009a; Kumar et al., 2009b). As the potentiodinamic response of films obtained using carbon paste electrodes are different to those synthesised with metallic electrodes; in fact the cyclic voltammogram is more similar to those of copolymers of aniline and luminol, we think that

M) and (b) a modified carbon paste electrode (14%).

**3.2.3 Electrochemical oxidation of ascorbic acid** 

Fig. 9. Cyclic voltammograms (50 mVs-1) of electrochemically synthesised polyluminol in 0.5 M aqueous H2SO4. The films were synthetised with the conditions of Figure 8 with (a) Eλ = 0.9 and (b) Eλ = 0.8 V. The composition of carbon paste was graphite (60 %), luminol (indicated in the Figure) and nujol (the necessary to reach the 100%). El 0 % indicate the film synthesised with the luminol in solution (1 mM).

#### **3.2.2 Electrochemical activity of polyluminol to pH neutral**

It is proved that the films obtained to oxidation of luminol are self-doped (Ferreira et al., 2008), this implicate that they are electroactive to 4 < pH. Figure 10 shows the voltammograms for polyluminol synthesised with Eλ = 0.8 V at acid and neutral pH. It can be observed that the peaks shift slightly to lower potentials in a Na2SO4 aqueous solution (1 M), when the same experiment is carried out with posphate buffers solution, pH = 7, (PBS) the peaks of polyluminol overlap into only one, while the current of this process remain in similar values. The difference between the voltamperometric responses at two electrolytes of a similar pH, probably is due to the charge/discharge process because the anion and cations are different. This behaviour in neutral milieu is similar to those observed in sulfonated polyanilines (Sanchís et at., 2008; Kariakin et al., 1994), and as a consequence congruent with the behaviour of a polymer. It is important note that an irreversible oxidation is observed in buffer solution (inset Figure 10), correspondent to the oxidation of monomer in the bulk electrode.

To compare the properties of polyluminol synthesized to monomer in solution and in the bulk carbon paste, cyclic voltammogramms in supporting electrolyte solutions acid and neutral pH were investigated. Figure 11 shows voltammograms for polyluminol films obtained in acid and neutral electrolytes. The films are quite electrochemicaly active in both neutral solutions Na2SO4 and PBS, in Na2SO4 a shift to more positives potentials was observed and in PBS an overlap of the two peak was presented. However we note that the more defined and reversible peak in the case of films synthesised with the monomer in the bulk paste carbon electrode, in addition the relation between the anodic current peak in acid solution (I0) respect to those obtained in milieu neuter PBS (IPBS) or Na2SO4 (Is), were IPBS/I0 = 0.579 and IPBS/I0 =1.249, while that when the films were made to monomer in solution IPBS/I0 = 0.487 and IPBS/I0 =0.412. A comparable tendance was showed for films obtained with other percentages of luminol in carbon paste 1.5, 3 and 7 %. These result demonstrate that in terms of extension of its electrochemical properties to high pH, are better the films elaborated to modified carbon paste electrodes than those carried out the monomer in solution.

Fig. 9. Cyclic voltammograms (50 mVs-1) of electrochemically synthesised polyluminol in 0.5

(a) Eλ = 0.9 and (b) Eλ = 0.8 V. The composition of carbon paste was graphite (60 %), luminol (indicated in the Figure) and nujol (the necessary to reach the 100%). El 0 % indicate the film

It is proved that the films obtained to oxidation of luminol are self-doped (Ferreira et al., 2008), this implicate that they are electroactive to 4 < pH. Figure 10 shows the voltammograms for polyluminol synthesised with Eλ = 0.8 V at acid and neutral pH. It can be observed that the peaks shift slightly to lower potentials in a Na2SO4 aqueous solution (1 M), when the same experiment is carried out with posphate buffers solution, pH = 7, (PBS) the peaks of polyluminol overlap into only one, while the current of this process remain in similar values. The difference between the voltamperometric responses at two electrolytes of a similar pH, probably is due to the charge/discharge process because the anion and cations are different. This behaviour in neutral milieu is similar to those observed in sulfonated polyanilines (Sanchís et at., 2008; Kariakin et al., 1994), and as a consequence congruent with the behaviour of a polymer. It is important note that an irreversible oxidation is observed in buffer solution (inset Figure 10), correspondent to the oxidation of monomer in the bulk

To compare the properties of polyluminol synthesized to monomer in solution and in the bulk carbon paste, cyclic voltammogramms in supporting electrolyte solutions acid and neutral pH were investigated. Figure 11 shows voltammograms for polyluminol films obtained in acid and neutral electrolytes. The films are quite electrochemicaly active in both neutral solutions Na2SO4 and PBS, in Na2SO4 a shift to more positives potentials was observed and in PBS an overlap of the two peak was presented. However we note that the more defined and reversible peak in the case of films synthesised with the monomer in the bulk paste carbon electrode, in addition the relation between the anodic current peak in acid solution (I0) respect to those obtained in milieu neuter PBS (IPBS) or Na2SO4 (Is), were IPBS/I0 = 0.579 and IPBS/I0 =1.249, while that when the films were made to monomer in solution IPBS/I0 = 0.487 and IPBS/I0 =0.412. A comparable tendance was showed for films obtained with other percentages of luminol in carbon paste 1.5, 3 and 7 %. These result demonstrate that in terms of extension of its electrochemical properties to high pH, are better the films elaborated to modified carbon paste electrodes than those carried out the monomer in

M aqueous H2SO4. The films were synthetised with the conditions of Figure 8 with

synthesised with the luminol in solution (1 mM).

electrode.

solution.

**3.2.2 Electrochemical activity of polyluminol to pH neutral** 

Fig. 10. Cyclic voltammograms for polyluminol synthesised using Eλ = 0.8 V and carbon paste electrode graphite (60 %), luminol (7 %) and nujol (33 %) at differents electrolytes. Scan rate = 100mVs-1. Inset complete cyclic voltammogram for polyluminol at PBS.

Fig. 11. Cyclic voltammetry of polyluminol, obtained in different supporting electrolytes containing: H2SO4 (0.5 M), Na2SO4 (1 M) and phosphate buffer solution (pH = 7). Synthesis of the films was performed as indicate in Figure 8a, using: (a) luminol (1 Mm) in H2SO4 (0.5 M) and (b) a modified carbon paste electrode (14%).
