Silver/silver bromide/polypyrrole nanoparticles obtained by microemulsion photopolymerization in the presence of a cationic surfactant

Abstract

Conductive silver/silver bromide/polypyrrole nanoparticles were obtained by photopolymerization in o/w microemulsions of pyrrole monomer in the presence of silver nitrate as electron acceptor and dopant under UV light irradiation. The microemulsions were prepared using cetyltrimethylammonium bromide (CTAB) as cationic surfactant. The particles were analyzed by scanning electron microscopy (SEM), UV/Vis, Fourier transform infrared spectroscopy, cyclic voltammetry, and X-ray diffraction (XRD). It was observed from SEM analysis that spherical particles can be obtained by this procedure with relatively narrow particles sizes distributions and average particle diameters of the silver cores (Dp) between 39 and 46 nm, which decreases as the surfactant concentration is increased. The conductivities of the resulting materials were between 0.12 and 0.40 S/m. Formation of cores of Ag and AgBr were observed from the XRD analysis, which was ascribed to the reduction of Ag⁺ to Ag⁰ and to reaction of Ag⁺ with the counterion of CTAB surfactant, respectively.

Appendices

Appendix 1

The following equations were used for the theoretical calculation of PPy shell thickness (Fig. 8):

Fig. 8

Geometry of Ag/AgBr/PPy nanoparticle

$$ \in ={r_2}-{r_1} $$

(6)

$$ {V_{\mathrm{core}}}=\frac{\pi }{6}\mathrm{Dp}_{\mathrm{core}}^3 $$

(7)

$$ {N_{\mathrm{p}}}=\frac{{{}^{6m}\mathrm{A}{{\mathrm{g}}^x}\mathrm{A}{{\mathrm{g}}^{+}}\to \mathrm{A}{{\mathrm{g}}^0}}}{{\pi \mathrm{Dp}_{\mathrm{core}}^3{\rho_{\mathrm{Ag}}}}} $$

(8)

$$ {V_{\mathrm{shell}}}=\frac{{{m_{\mathrm{p}\mathrm{y}}}{x_{\mathrm{p}\mathrm{y}}}}}{{{\rho_{\mathrm{p}\mathrm{py}}}{N_{\mathrm{p}}}}} $$

(9)

$$ {V_{\mathrm{T}}}={V_{\mathrm{core}}}+{V_{\mathrm{shell}}}=\frac{{4\pi }}{3}r_2^3 $$

(10)

$$ {r_2}={{\left[ {\frac{3}{{4\pi }}\left( {{V_{\mathrm{core}}}+{V_{\mathrm{shell}}}} \right)} \right]}^{{\frac{1}{3}}}} $$

(11)

where ε is PPy shell thickness, V _core volume of Ag/AgBr core, Dp_core average diameter of Ag/AgBr cores, N _p particles number, m _Ag mass of silver used, x _Ag+→Ag0 fraction of Ag⁺ reduced to Ag⁰ or forming AgBr (set equal to 0.1), ρ _Ag average density of Ag (1.049 × 10⁷ g/m³), V _shell volume of PPy shell, m _py mass of pyrrole monomer used, x _py conversion of monomer (experimentally determined equal to 0.1), and ρ _ppy density of polypyrrole (1.48 × 10⁶ g/m³).

Appendix 2

Fig. 9

XRD spectrum of nanoparticles corresponding to run 1