Desenvolvimento de catalisadores magnéticos verdes para degradação de compostos orgânicos e geração de hidrogênio

Abstract

The development of sustainable catalysts represents a strategic advance towards cleaner and more efficient industrial processes. This work proposed the synthesis of green magnetic catalysts based on spinel-type ferrites (CoFe2O4, CuFe2O4, MnFe2O4 and Fe3O4) obtained by coprecipitation in a deep eutectic solvent, which were evaluated using green chemistry metrics. The nanoparticles synthesized ranged in size from 9.42-18.2 nm, with spherical and nanocube morphologies, exhibiting magnetic properties with saturation magnetization between 32.0-51.8 emu g-1 and remnant magnetization of 12.4-25.0 emu g-1 . Evaluation of the catalytic activity revealed high efficiency in the reduction of 4- nitrophenol, methyl orange and methyl red, under a molar ratio of 2000 between the amount of sodium borohydride and pollutant, and only 10 mg of catalyst, with reaction times between 10-540 s. At the same time, hydrogen was generated by hydrolysis, which reached 196 mL in 10 min, with a gas generation rate of 19600 mL min-1 g -1 and activation energy of 1909 kJ mol-1 . The leaching tests showed low metal ion release, demonstrating the stability of the catalysts. Electrochemical oxidation via electro-Fenton achieved complete degradation of 4-nitrophenol under optimized conditions (pH 6, 50 mg L-1 of catalyst, 70 mA cm2 , 20 min), with successful application in real river water samples from the Aracaju metropolitan region (91.2-99.6%). The system can also be used to generate hydrogen peroxide, which reached 74.5 mg L-1 at pH 3. The joint action of hydroxyl and sulfate radicals indicated a complex degradation mechanism, with the formation of higher molar mass by-products. Computational toxicity and germination tests revealed low mutagenicity and toxicity of the final products. It is concluded that the catalysts developed have high performance, stability and low environmental impact, and are promising for integrated environmental and energy applications. As a prospect, the operationalization of an electrochemical reactor with deposition of the catalysts on the electrodes is proposed, with a view to the simultaneous degradation of organic pollutants and co-production of hydrogen.