Preparação, caracterização e aplicação de filmes finos nanoestruturados de PAH/PAA/TiO2 na fotoxidação de ibuprofeno

Abstract

Ibuprofen is an anti-inflammatory with an annual production of more than 15 thousand tons, whose concentration in aquatic ecosystems reaches the order of tens of μg L-1. The degradation of this emerging pollutant and other pharmaceuticals by photocatalysis, using solar energy and TiO2 nanoparticles, is a cheap and promising option, compared to conventional water treatments. However, nano-TiO2 is toxic and causes disturbances in the redox cycles of the micro-systems, causing several impacts to the local microbiota. An effective way to avoid this problem is the immobilization of the photocatalysts in thin films, avoiding the leaching of this material to the environment. In this context, the objective of the present work was the preparation, characterization and application of nanostructured self-assembled thin films (SATFs) of poly (acrylic acid), polyallylamine hydrochloride and TiO2 by the layer-by-layer technique. For that, the surface response methodology and design of experiments were used to evaluate which deposition parameters would lead to the best properties for the application in the photodegradation of ibuprofen in aqueous medium. The SATFs were extensively characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), infrared absorption spectroscopy (FTIR), among others. The degradation solution was evaluated by molecular absorption spectroscopy (UV-Vis) optical emission spectroscopy (ICP-OES) and mass spectrometry (MS). In general, the SATF with the best properties was able to degrade 50% of IBU. This SATF presented high stability in aqueous medium, besides maintaining its photocatalytic activity for at least three cycles, and the TiO2 leaching was less than 0.5% in mass after the accomplishment of these tests. It was also possible to demonstrate that the degradation measurement made by MS resulted in IBU reduction rates higher than those measured by UV-Vis, reaching 95%. MS measures only the IBU molecule, while the UV-Vis response refers to the aromatic chromophore, which may be present in by-products of the degradation. In addition, photosensitization of SATFs with copper increased the degradation of the drug tested to 76%. From these results, it was possible to conclude that SATFs prevent photocatalyst leaching while maintaining the efficiency of the IBU degradation, with removal rates similar to those of other advanced treatment processes. These SATFs can also be reused, without the need for separation processes.