Interaction of Catalyst Nanoparticles and Pollutant Molecules in Photocatalytic Wastewater Treatment: Novel Characterization via Dynamic Surface Properties

In a photocatalytic wastewater treatment, the degradation reaction mostly occurs at the surface of the catalyst and nearby regions. Therefor understanding the interaction of the catalyst and pollutant in a photocatalytic degradation system is a very important issue, indicating affinity of the pollutant molecules to be attracted or repulsed from the photocatalyst particles. The aim of this experimental study is to get a better insight into the interaction of the catalyst nanoparticles and pollutant molecules via a novel characterization method based on dynamic surface phenomena analysis. Drop profile analysis tensiometry (PAT) is used for this purpose for dynamic surface tension and elasticity measurements at aqueous solution/air interface at different pH conditions. The results show that the cationic dye Malachit Green (MG) indicates low surface activity at neutral pH (about 6.5), with an equilibrium surface tension about 69. While it becomes much more surface active at pH= 9 and surface tension is decreased to 59 mN/m. Adding TiO2 nanoparticles to MG solution at pH=9 causes a significant increase in surface tension, with much slower dynamic of adsorption at water air interface, that indicates a significant attraction and attachment of MG molecules at TiO2 nanoparticles surface. This observation is in a good correlation with observed higher efficiency of MG degradation around pH 9. The capability of this novel experimental protocol is also examined for the anionic dye Eriochrom Black-T (EBT). The results show a significant interaction between TiO2 nanoparticles and EBT at pH=3, which also is in good correlation with reported higher efficiency of EBT degradation around pH 3. The elasticity measurements also are in good agreement with these results, as an important characterization parameter, for molecular interaction in adsorbed layer, discussed in this article.