Electrophoretic deposition of TiO2 and composite TiO2–MnO2 films using benzoic acid and phenolic molecules as charging additives
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Electrophoretic deposition (EPD) method has been developed for the fabrication of TiO(2) and MnO(2) films. Benzoic acid and phenolic molecules, such as 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid, gallic acid, salicylic acid and salicylic acid sodium salt were investigated as charging additives for the EPD of TiO(2) and MnO(2) particles. The deposition yield has been studied as a function of the additive concentration and deposition time for cathodic deposits obtained from the suspensions, containing benzoic acid, 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid and anodic deposits prepared from the suspensions, containing gallic acid and salicylic acid sodium salt. The results obtained for the phenolic molecules with different number of OH groups were analyzed and compared with corresponding experimental data for benzoic acid without OH groups. The adjacent OH groups, as well as adjacent OH and COOH groups bonded to the aromatic ring of the phenolic molecules were beneficial for adsorption of the molecules on oxide particles. The adsorption mechanisms involved the interaction of COOH groups and OH groups of the organic molecules with metal ions on the particle surfaces and complexation. Gallic acid was shown to be an effective charging additive, which provided stabilization of TiO(2) and MnO(2) particles in the suspensions and enabled their deposition. It was shown that composite TiO(2)-MnO(2) films can be obtained using gallic acid as a common dispersing agent for TiO(2) and MnO(2). The Ti/Mn ratio in the composite films was varied in the range of 0-1.3. The thickness of the films was varied in the range of 0-10 μm. The mechanisms of particle charging and deposition were discussed.