Removal of rhodamine B and methylene blue using residual Onecarpus bacaba Mart fibers as biosorbent: kinetic and thermodynamic parameters

Among the most common water contaminants, dyes are responsible for polluting rivers and other water bodies as well as contributing to other environmental problems, thus posing serious health hazards to humans and animals. In order to minimize these environmental impacts, this study proposes the use of Onecarpus bacaba Mart fiber residues, in natura (OBMi) and NaOH-modified (OBMm), to bioadsorb rhodamine b (RhB) and methylene blue (MB) dyes. The biosorbents OBMi and OBMm were characterized by means of infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, Boehm titration, PZC, and scanning electron microscopy. This study also analyzed the influence of pH, contact time, absorbent mass, temperature, and contaminant concentrations by means of batch equilibrium assays. It was observed that the OBMi absorbent showed a low dye removal capacity. Maximum OBMm adsorption capacity for RhB and MB at 25 °C was 26.60 mg g−1 and 407.98 mg g−1, respectively. In both systems, OBMm:RhB and OBMm:MB, adsorption kinetics followed a pseudo-second-order model, and the Langmuir and Freundlich models constituted the best fit for isothermal curves. Lastly, thermodynamic parameters indicated that adsorption of both RhB and MB onto OBMm is spontaneous.