Production of magnetic photocatalysts and their application in photocatalytic reactions

Abstract

Many studies have been carried out to assess the efficient degradation of recalcitrant organic contaminants present in industrial effluents. Heterogeneous photocatalysis appears as a good alternative for the treatment of these effluents. The most used semiconductor in photocatalysis is TiO2 P25, due to its high efficiency and other advantages. However, one of its limitations is the small size of its particles, making difficult its separation from the treated effluent. To overcome this problem, an alternative is to associate this semiconductor with a magnetic phase, where the photocatalyst can be easily separated from the treated effluent by the action of a magnetic field. Several authors reported that a layer is needed to avoid the physical contact of TiO2 and iron, since the contact of these can reduce the photocatalytic activity. In this study, Ti/Fe/AC and Ti/C/Fe, where TiO2-P25 (Ti) was immobilized on the surface of two different substrates: (i) Fe/AC - Fe3O4 particles dispersed on the surface of commercial activated carbon (AC) and ii) Fe/C - Fe3O4 and Fe3C particles coated with charcoal (C) (core-shell configuration), which was obtained from thermal decomposition of sucrose. These photocatalysts were obtained with the following TiO2 contents: 20, 40, and 60%, characterized and used for the degradation of remazol black 5 (RB5), acetaminophen, and phenol in the presence of UV radiation. The results obtained were divided into two articles. The first one presents the results obtained with the photocatalysts 20, 40, and 60Ti/Fe/AC (the numbers indicate the TiO2 content) for the degradation of black remazol dye (RB5). The characterization results showed that TiO2 particles are present on the surface of the Fe/AC support, and that it consists of magnetite, amorphous carbon, and graphite. BET surface area reduced from 283 to 165 m 2 g -1 , with the increase of TiO2 supported. The sedimentation tests showed that after 30 minutes in the presence of magnetic field, the turbidity of the photocatalyst/water mixture reduced up to 93%. The photocatalytic efficiency of the obtained materials increased with the TiO2 content, reducing 95% of its coloration and 90% of the total organic carbon. In the second article, the characterization results of the photocatalysts 20, 40, and 60Ti/C/Fe proved the formation of the magnetic phases, Fe3C and Fe3O4, which are coated with amorphous and graphitic charcoal. Scanning electron microscopy images showed that TiO2 particles are also present on the C/Fe surface. The sedimentation kinetics of the photocatalysts showed efficiency of 76 to 89% in only 30 minutes in the presence of magnetic field, while the TiO2 tests were not significant. The photocatalysts showed high capacity for degradation of RB5, acetaminophen, and phenol in aqueous solution, and the 60Ti/Fe/C sample degraded 99, 77, and 90% of these three contaminants, respectively. Comparing the 60Ti/Fe/AC and 60Ti/C/Fe photocatalysts, they discolored 95 and 99% of the BR5 dye, respectively, proving that both materials showed good photocatalytic efficiency. Thus, it can be concluded that all materials prepared in this work presented excellent photocatalytic efficiency and great ease in the separation of the reaction medium, which simplifies its application and reduces operational costs. These factors indicate the high potential of these materials for large-scale applications.