The Role of the Relative Dye/Photocatalyst Concentration in TiO 2 Assisted Photodegradation Process

Despite photocatalytic degradation is studied generally focusing the catalyst, its interaction with the contaminant molecule plays a fundamental role in the efficiency of that process. Then, we proposed a comparative study about the photodegradation of two well‐known dyes, with different acidity/basicity – Methylene Blue ( MB ) and Rhodamine B ( RhB ), catalyzed by TiO 2 nanoparticles, varying both dye and photocatalyst concentrations. The results showed that the amphoteric character of MB molecules, even in a range of concentration of 5.0–10.0 mg L −1 , did not imply in pH variation in solution. Therefore, it did not affect the colloidal behavior of TiO 2 nanoparticles, independent of the relative dye/catalyst concentration. The acid–base character of RhB influenced the resultant pH of the solution, implicating in different colloidal behavior of the nanoparticles and consequently, in different degradation conditions according to dye concentration. As the isoelectric point of TiO 2 is between the pH range of the RhB solutions used in this study, from 1.0 to 7.5 mg L −1 , the resultant pH was the key factor for degradation conditions, from a well dispersed to an agglomerated suspension.