**7. Conclusion**

72 Electropolymerization

al., 2009). To check this explanation, the electropolymerization with 5,15-ZnOEP(py)22+ has also been performed by iterative scans limited to the anodic part (cyclic voltammograms performed between 0 and +1.80 V/SCE) in order to avoid the reduction of the pyridinium

As previously said, this porphyrin–POM copolymer has been prepared in order to use it as photocatalyst for the reduction of metal cations. For this purpose, we have chosen silver

To carry out this experiment, the copolymer has previously been removed from the electrode by dissolution in DMF, and then, a drop of the copolymer solution has been deposited on a slide of quartz and the solvent evaporated in air. Then, the covered slide has been plunged in an aqueous solution of Ag2SO4 (80 µM) containing 0.13 M of propan-2-ol used as sacrificial electron donor. Finally, the sample has been exposed during 8 hours to visible light. The reaction has been followed by UV-visible absorption spectroscopy (Fig. 21.a): during light irradiation, a very large plasmon band appeared progressively, suggesting the formation of silver aggregates. Transmission electron micrographs and electron diffraction patterns have confirmed this result: silver triangular nanosheets were principally obtained (Fig. 21.b and c). The mechanism explaining the reaction has been

Fig. 21. (a) Change in the UV-visible absorption spectrum of a porphyrin–POM copolymer deposited on quartz in aerated aqueous solution containing 80 µM of Ag2SO4 and 0.13 M of propan-2-ol under visible illumination. (b) Transmission electron micrograph of a silver triangular nanosheet obtained. (c) Selected-area electron diffraction pattern of the previous silver nanostructure. The first spots (circled) correspond to the formally forbidden ⅓{422}

For this study, silver has been chosen as a model system for metal reduction, but this copolymer could be used in water depollution for reduction or recovery of valuable or toxic metals that could also be combined with degradation of organic pollutants (used instead of

It can be noticed that hybrid {porphyrin–POM} systems can be obtained for similar application purposes by plunging an ITO electrode coated with a cationic polymer of porphyrins, as described in the first parts of this chapter, into an aqueous solution of POMs. The aim of this

– further to the

reflections and the second spots (squared) correspond to the {220} reflections.

process is to replace the counteranions of the polycationic polymers (PF6

sacrificial donor) as already proposed (Troupis et al., 2006).

**6.2.5 Electrostatic {porphyrin–POM} systems** 

substituents. As expected, the coils appear non-agglomerated in this case (Fig. 19.c).

cations as a model system to perform photocatalytic tests (Schaming et al., 2010b).

discussed in detail in our previous works (Schaming et al., 2010a, 2011c).

**6.2.4 Photocatalytic tests** 

In this chapter, we have shown that electropolymerization of porphyrins can be easily performed by nucleophilic attacks of di-pyridyl compounds directly onto electrogenerated dications of octaethylporphyrins, by an ECEC-type mechanism.

The first tests have been performed with porphyrins substituted with bipyridinium(s). According to the degree of substitution of the monomer (which is linked to its charge), different morphologies of the polymers can be observed, which seem to be induced by the electric field imposed during the electropolymerization process.

We have further shown that it is also possible to use non-substituted β-octaethylporphyrins in the presence of free Lewis bases having two nucleophilic sites. This second way of electropolymerization allows to avoid the somewhat complicated synthesis of the monomeric substituted porphyrin, and consequently allows to modulate easily the nature of the bridging spacers between the macrocycles. Thus, original organic or inorganic compounds, with specific interesting properties, can be used, on condition that two pyridyl groups have beforehand been grafted. Consequently, this new easy way of electropolymerization of porphyrins appears as a promising approach to elaborate new functional materials, for example with catalytic properties if polyoxometalates are used as spacers. Other applications can be envisaged according to the spacer chosen.

Finally, it is interesting to note that as all the electropolymerization methods, it is easy to control the thickness of the polymers, according to the number of scans performed, which is also a great advantage compared to the classical chemical methods of polymerization.
