Residual biomass of Fraxinus americana as a resource to remove aniline blue dye from environmental samples

Abstract

This study reports for the first time the use of Fraxinus americana seeds (FAS) as biosorbent for the removal of aniline blue (AB) dye from natural water and textile effluents, demonstrating its potential as a cost-effective and sustainable alternative for water treatment. An experimental design was used to identify the optimal variables for AB removal. These variables were a biosorbent dose of 2.5 g L−1 , and solution pH=3. These conditions resulted in an experimental biosorption capacity of 18.4 mg g−1 and a removal efficiency of 91.8%. To understand the biosorption mechanism of AB on FAS, different characterization techniques were used, including scanning electron microscopy, Fourier transform spectroscopy using the attenuated total reflectance technique, Boehm titration, and the determination of pH at point of zero charge. Biosorption kinetics showed that FAS saturation was reached at 30 min using initial AB concentration of 50 mg L−1 , while 60 min were necessary for initial AB concentrations of 100 and 200 mg L−1 . Pseudo first order, pseudo second order, Elovich, and intraparticle diffusion models were used to fit the biosorption kinetic data, while the Langmuir, Freundlich, and Sips models were applied to correlate the biosorption isotherms. The experimental values were best fitted to the pseudo-second order model. The results obtained from the biosorption isotherms fit better to the Langmuir isotherm model, indicating a maximum theoretical biosorption capacity of 40.3 mg L−1 . This value represents the model-predicted capacity under monolayer adsorption conditions. Dye biosorption was thermodynamically spontaneous and an exothermic monolayer process where hydrogen bonding and electrostatic interactions played a relevant role. The application of the biosorbent to real samples showed a removal efficiency of up to 93.6%. These results are promising because the biosorbent was obtained from waste that is widely available in nature and does not require physical or chemical treatment for effective AB removal. This study contributes to the valorization of FAS residues for water and wastewater treatment within the framework of a circular economic model.