Sol–gel catalysts immobilized on stainless steel meshes for Ba2+ removal in a continuous flow process: an experimental design

Abstract This study describes the use of a continuous flow system for photocatalytic reactions employing a TiO2 sol–gel structured catalyst. The catalyst was immobilized on various stainless steel meshes to investigate the barium(II) removal. To verify its photocatalytic activity, batch tests were carried out and the results were compared to the commercial catalyst P25. Effects of thermal treatment on the structured catalyst were investigated. The continuous flow photocatalytic tests were conducted under different experimental conditions through an experimental design to verify the effect of the parameters (pH and volume flow). The results of the batch tests indicated that the TiO2 sol–gel catalyst showed very similar activity to the TiO2 P25 when used in powder suspension (32% reduction of Ba2+). In the continuous flow process, maximum adhesion of catalysts on meshes was found at a calcination temperature of 623 K. The experimental design indicated the pH as a significant parameter in the studied conditions. It was observed that at pH levels close to 7, also indicated by the study of the zero charge point and lower flow rates, it was possible to obtain ∼20% removal of Ba2+ ions, in a continuous flow reactor with a residence time of 83 min.