Estudo do efeito da modificação da fibra de sisal usando plasma frio reativo e seu impacto na remoção do azul de metileno

Abstract

Many industrial processes use toxic substances, such as some dyes. Sectors that require coloration in their production and in turn generate contaminated effluents include the textile and cosmetics industries, among others. Inappropriate disposal of these particulates often causes contamination of rivers, streams and even groundwater. Therefore, as a solution for the control of toxic substances from effluents, adsorption is widely used and is considered an efficient process. In this study, the methylene blue dye was used as adsorbate in solution for its adsorption analysis by the sisal fiber, comparing the removal of the fiber in natura (without treatment) and treated using reactive plasma. As an alternative form of surface treatment of sisal fiber, the reactive plasma technique is attractive because it presents a high index of surface modification since it presents a highly reactive atmosphere, low treatment time, non-generation of waste and low cost. Plasma treatment was performed through the gas mixture of argon and carbon dioxide at a pressure of of 6x10-1 Torr. The treatment resulted in an increase in the surface roughness of the fibers, amorphization of the lignin layers and a slight decrease in the fibers crystallinity index (79% to in natura fiber and 75% to the treated). A higher mechanical strength in modulus and tension was also observed, resulting in 12.223 MPa and 392 MPa, respectively, while the in natura fiber showed a worse performance compared to treated fiber resulting in 5.999 and 175 MPa for the module and tension. Plasma treatment induced changes in sisal fibers resulted in major removal of the methylene blue dye reaching a 96% removal rate. The adsorption studies showed that there was a better fit to the pseudo-second order model for both fibers (in natura and treated), demonstrating that there is a chemical nature in the adsorption of these fibers. The models of adsorption isotherms adjusted to the in natura and treated fiber, being the best fit for RedlichPeterson and Langmuir models, respectively. This adjustment indicates that in the treated fiber the adsorption occurred in monolayer, which does not happen in the in natura fiber. All these parameters were adjusted according to the determination coefficient (R2). It was observed that the plasma treatment did not cause the loss of the original properties and plays a fundamental role in increasing the adsorption and resistance of the fiber and can be used for the process of removing particulate pollutants in effluents at a low cost.