The role of polydopamine films in the immobilization of aggregates of TiO2 nanoparticles on gold and ITO surfaces

In the present work, we investigated the role of polydopamine coatings in anchoring TiO2 P25 nanoparticles on gold and ITO surfaces. For this purpose, we studied the adhesion of polydopamine-coated aggregates of TiO2 nanoparticles on bare substrates and of aggregates of bare TiO2 nanoparticles on polydopamine-coated substrates. Coating with polydopamine was accomplished by oxidation in air of alkaline aqueous dopamine solutions in which the nanoparticles or the substrates were immersed. Dynamic light scattering, Fourier transform infrared spectroscopy, and transmission electron microscopy were used for the chemical and morphological characterization of aggregates of the nanoparticles. The adhesion of aggregates of the nanoparticles on the substrates was evaluated by means of AFM and XPS. The results of this study suggest that the adhesion of TiO2 P25 nanoparticles on polydopamine films, as well as of polydopamine-coated TiO2 P25 nanoparticles, is a balance of several contributions: chemical interactions, electrostatic interactions, and coating roughness. Electrostatic attraction and repulsion between nanoparticles and the substrate appear to play an important role, as indicated by the ζ-potential values of nanoparticles and substrates.