Interfacial Characterization of the Electrochemical Adsorption of Caffeine on Poly(pyrrole) Nanotubes/Silica.

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In this work, a polypyrrole nanotube/silica (PPyNT/SiO₂)-modified electrode was prepared by an all-electrochemical route and characterized by electrochemical, spectroscopic, and microscopy analyses; scanning electron microscopy confirmed the superimposition of a particulate silica on the PPyNTs without any loss of electroactivity of conducting polypyrrole. The PPyNTs/SiO₂ electrode was employed for the electroadsorption of caffeine, where it was found that in its less oxidized form, the PPyNTs boosted the adsorption capability of intrinsic silica. Electrochemical impedance spectroscopy (EIS) modeling was employed and modeled with equivalent circuit methodology, and all the results were compared with the Sips isotherm model, showing that the PPyNTs/SiO₂ electrode presented a more heterogeneous surface (n _S = 1.25) and a nearly 2-fold increase in maximum adsorption capacity (q _ms) compared to pristine PPyNTs.