Síntese de filmes compósitos de TiO2 e quitosana para aplicação em processos de fotodegradação

Abstract

Some photodegradative reactions, which are proposed as an alternative to conventional processes for the reduction of dyes, may be more efficient in so-called hybrid processes, such as photoelectrocatalysis. When the photocatalyst is immobilized in the form of fixed film on a conductive surface (substrate), forming the working electrode, dispenses separation steps, which facilitates its removal and reuse. Titania (TiO2) is one of the most used semiconductors for photodegradation of textile dyes, due to its physicochemical properties and catalytic efficiency. On the other hand, chitosan has adequate characteristics for preparation of composite films, besides being obtained from the reject, which adds environmental interest and low cost to its qualities. Thus, in the present work, composite films of TiO2 and chitosan with different proportions were prepared and immobilized in steel and glass plates for use in photodegradative processes of the textile dye Reactive Black 5 (RB5). The photocatalysis reactions were conducted for 2 h at 25 °C under UV radiation, agitation and air bubbling. The film with the best performance was tested in photoelectrocatalysis, under the same conditions, but under a potential of 0.75 V. The efficiency of the processes was evaluated by removal of color (by UV/Vis spectrophotometry) and organic matter content (by total organic carbon, TOC). The films were characterized to the morphology, by scanning electron microscopy (SEM), to the thermal behavior by TG/DTG, to the absorption of UV/Vis radiation for determination of band gap, by DRS, regarding the structure, by absorption spectroscopy of Infrared radiation and for the study of electrochemical behavior by cyclic voltammetry. The results showed that the films are well adhered to the glass, as substrate, but on stainless steel it is necessary to apply primer. A crosslinking of chitosan with glutaraldehyde was performed before obtaining the films, because partial solubilization with increase of TOC occurred. The composite films have good conductivity on the steel, are electrically reproducible and have high photocatalytic activity in the conditions studied. Under same conditions, the application of the potential to the system did not cause a significant change in the degradation of RB5 dye for 2 h of reaction, but opens possibilities for further investigations of the synergism of this photodegradative process, since from the proposed system, the dye was degraded, even making use of a small mass of catalyst and a relatively low potential. The best bleaching results were 41 and 35% for photocatalysis and photoelectrocatalysis, respectively.