Aplicação do óxido de grafeno reduzido derivado de biomassa como adsorvente para diferentes efluentes industriais

Abstract

Wastewater contamination by organic compounds, such as phenols, textile dyes, and pharmaceuticals, represents a significant environmental challenge. Carbon-based adsorbents, such as reduced graphene oxide (rGO), have gained prominence due to their high surface area and pollutant removal capacity. In this study, a cellulosic biomass-derived rGO (CB-rGO) was sustainably synthesized and applied as an adsorbent in four distinct systems: phenol, methylene blue (MB), synthetic textile dyeing effluent, and the pharmaceutical rifampicin. In this context, the present study synthesized biomass-derived rGO and characterized it by techniques such as HRTEM, XRD, Raman, FTIR, and Zeta potential analysis, in addition to determining the specific surface area from the N2 adsorption isotherms at 77 K, using the BET model. The material demonstrated high efficiency in all tested scenarios: in the first system, using phenol as a contaminant, it achieved 98% removal and a maximum adsorption capacity of 240 mg/g, using only 10 mg of CB-rGO in a solution with an initial concentration of 200 mg/L. In the second system, with methylene blue (AM), 99% dye removal was obtained, using 50 mg of adsorbent in a solution of 80 mg/L. The third system, involving a synthetic dyeing effluent, showed 98% efficiency in pollutant removal, with 0.3 g of CB-rGO at a concentration of 40 mg/L. Finally, in the fourth system, with the drug rifampicin (20 mg/L), 96% removal was recorded using 0.2 g of the material. In addition to its high efficiency, CB-rGO stood out for its reuse in more than five consecutive cycles, maintaining efficiency above 80% in all cases, proving its robustness and economic viability. In all systems evaluated in this study, the Freundlich isotherm presented the best fit to the experimental data, with an average R2 of 0.99, indicating that the adsorption occurred in multilayers and on a heterogeneous surface. The kinetic study of the three systems demonstrated that the pseudo-first-order model was the most appropriate to describe the behavior of Systems 2, 3 and 4, while the pseudo-second-order model best fitted System 1. In the thermodynamic study, all systems presented positive enthalpy values (∆H°), confirming the endothermic nature of the process. The decreasing values of the Gibbs free energy (∆G°) indicate that increasing the temperature favors the removal efficiency. Furthermore, the positive entropy values (∆S°) suggest an increase in randomness at the solid/liquid interface during the adsorption process. The results highlight the potential of this sustainable adsorbent, derived from waste, as a promising alternative for the treatment of water contaminated with various pollutants, combining high performance, low cost and reusability.