Estudo da aplicação de nanofios de óxido de zinco modificados em sistema de fotoeletrocatálise heterogênea

Abstract

The Chemical industry’s growth forced a change of scenario for industrial wastewater treatment, on which the as-called persistent organic pollutants (POP’s), a series of chemically resistant, highly harmful and bioaccumulative substances, suddenly make up a significant fraction of the output flows from industrial processes, generating effluents with high chemical oxygen demand (COD) and incompatible with traditional treatment techniques. In this context, the so called advanced oxidative processes become an attractive alternative to reduce the content of these compounds to tolerable levels without inducing secondary pollution. In particular, photocatalytic processes are highly targeted for their ability to reduce high COD loads. The present work explores the application of carbon dots modified ZnO nanowires as a low-cost catalyst to act in a photoelectrocatalysis process, an improvement on traditional photocatalytic processes, aiming at the degradation of rhodamine B, a widely used industrial dye. The proposed objectives were to synthesize the nanomaterials that make up the catalyst composite in the laboratory, build a bench scale reactor to carry out batch photoelectrocatalysis tests and characterize the degradation kinetics of rhodamine B using the prepared photoanodes. The constructed reactor proved to be suitable for conducting kinetic tests on a bench scale and could be used in the future by students at the State University of Amazonas to carry out experiments focused on photoelectrochemistry. The photoelectrocatalytic treatment process proved to be significantly more effective than the photochemical and electrochemical oxidation processes under similar conditions, achieving a reduction of 95.7% of rhodamine B concentration in 250 mL of 1 mg.L-1 solution using a ZnO based photoanode. The kinetics of the reaction showed satisfactory compatibility with the pseudo first order model in relation to the concentration of rhodamine in solution, thus it was possible to determine the specific speed of the reaction catalyzed by the ZnO nanowires, finding a value of 0,048 ± 0.004 min-1 . The modification of the ZnO nanowire film with the addition of the synthesized carbon dots resulted in a notable reduction in its catalytic activity, reducing the degree of removal to 45,6% and the specific speed to 0,0058 ± 0,0005 min-1 , against the initial expectations.