Desenvolvimento e avaliação de catalisadores híbridos para aplicação em processos de fenton heterogêneo e processos de oxidação com persulfato

Abstract

The growing number of industries that appear every year has resulted in a large generation of effluents that are toxic to the environment and difficult to degrade. These effluents cannot be disposed of in water bodies without prior treatment, so it is important to develop technologies that will minimize these impacts efficiently. In this context, Fenton processes as well as oxidative processes based on sulfate radicals, which occur through persulfate activation, are promising techniques in the treatment of industrial effluents, however, when catalyzed by metals, these processes present limitations such as the need to a low operating pH and the difficulty in recovering and recycling the catalyst. To remedy these limitations, the development of stable heterogeneous catalysts is a great alternative. Therefore, this work aimed to develop heterogeneous, stable hybrid catalysts with good catalytic activity, for application in Fenton reactions and persulfate activation in the treatment of synthetic effluents containing reactive blue dye 19 (AR19). The magnetite-based catalysts (Mag-SC and Mag-SH) were obtained via coprecipitation and hydrothermal method and later characterized by DRX, FTIR, DLS, MEV, MO, MET, EDX and BET techniques. Mag-SC showed better performance in the Fenton reaction for the oxidation of the dye, with smaller particle size (12 nm) and greater surface area (148 m2 / g), but with unviable recyclability. After choosing the co-precipitation method that provided the best catalyst for the oxidation of the effluent, it was synthetically combined with Black Clay, forming the Mag-AP and then it was coated with polyaniline through chemical polymerization Mag-AP- PANI. The clay increased the catalytic activity of magnetite from 89 to 95%, with less interference from the adsorption process, and still guaranteed greater catalytic stability for up to 3 cycles in Fenton processes and 6 cycles in photo-Fenton, with low leaching of the catalyst. Mag-AP-PANI showed low performance in Fenton processes (64%) but was better used in the photo-Fenton process (92%), in which it showed stability for up to 3 cycles with less leaching than Mag-AP. The three catalysts were compared in the persulfate activation, and showed a good performance both at pH = 3 (75, 80 and 95%) and pH = 6 (71, 70 and 92%), for Mag, Mag-AP and Mag- AP-PANI, respectively. At pH = 3 only Mag-AP showed stability for up to 3 cycles, with no leaching observed at the detection limit of the analysis and Mag-APPANI with at least 6 cycles, with low leaching. At pH = 6, only Mag-AP-PANI remained stable for 2 cycles. The results obtained proved the viability of co-precipitation synthesis as a simple method of magnetite nanoparticles, the black clay support showed great efficiency to improve the catalytic properties of magnetite, making the catalyst more stable, with greater recyclability and efficiency for the Fenton's processes, the polyaniline-containing catalyst proved to be very promising for activation of persulfate in conditions close to neutrality and with good catalytic performance, besides presenting an excellent recyclability, it also reduced the leaching of the catalyst.