Eucalyptus sawdust as an alternative adsorbent for rhodamine B dye removal

This paper describes the decoloration potential of a low-cost natural adsorbent, eucalyptus sawdust (ES), for rhodamine B (RhB) removal. Fourier-transform infrared spectroscopy analysis of the adsorbent revealed the presence of characteristic groups of cellulose, hemicellulose, and lignin. Scanning electron microscopy images showed that the surface of ES is heterogeneous and irregular. Point of zero charge studies revealed a negatively charged surface, which is favorable for RhB adsorption. A 23 full factorial central composite rotatable design was used to optimize dye removal. The optimal conditions were found to be biomass dosage of 0.49%, particle size of 0.44 mm, and unadjusted pH (4.0), providing high adsorption capacity and removal percentage. Adsorption studies were conducted using RhB concentrations of 50 and 100 mg L-1; under these conditions, the maximum adsorption was 90.1% and 92.8%, respectively, and the equilibrium was established in 420 min. Isothermal data were fitted to the Langmuir model, revealing a maximum adsorption capacity of 29.94 mg g(-1). The rate of adsorption followed second-order kinetics, indicating the occurrence of a chemical phenomenon and diffusion as the rate-governing step. Thermodynamic parameters showed that RhB adsorption is endothermic, spontaneous, and favorable.