TiO2 thick films supported on stainless steel foams and their photoactivity in the nonylphenol ethoxylate mineralization

Abstract

The main interest in employing a structured catalyst for water treatment processes is to avoid an extra recovering-step of the powder catalyst after concluding the treatment. For this purpose, TiO2 powder (Degussa P25) was immobilized onto metallic foam walls (TiO2-foam) through the washcoating method and its photocatalytic activity was evaluated in the degradation of nonylphenol ethoxylate (NP4EO), which is considered an endocrine disrupter. The morphological and physicochemical characteristics of TiO2 films were studied by X-ray Diffraction, Laser Raman Spectroscopy and Scanning Electron Microscopy. The fast and easy washcoating method used in this work allowed the immobilization of the TiO2 powder onto a relatively inexpensive metallic substrate. The TiO2 layer was uniformly distributed, having a high adherence to the metallic foam walls, which were previously submitted to a passivation treatment. This pre-treatment hindered a further migration of cations from the foam core to the titania film and favored the subsequent film anchorage. Moreover, the catalytic film so obtained maintained the anatase and rutile phases with their original proportions, preserving the properties of the TiO2 powder. The photocatalytic activity of the TiO2-foam was similar to that of a commercial catalyst (TiO2–Ti mesh), i.e. both reduced the TOC of the NP4EO solution by about 91%, showing similar reaction kinetics and overall quantum yield (Фoverall). These results demonstrate that by means of the method under study, TiO2 can be successfully immobilized without decreasing its photocatalytic activity. These catalysts may be applied in water/wastewater treatment, reducing the process stages and the overall cost of the procedure.