Application of DFT and Response Surface Models to analyze the adsorption process of basic blue 3 and reactive blue 19 dyes on sugarcane bagasse and coconut endocarp biomass

In this study, the biomass wastes of sugarcane bagasse and coconut endocarp were used for the adsorption of basic blue 3 and reactive blue 19 dyes from aqueous solutions. DFT calculations and Response Surface Models (RSM) were used to analyze the adsorbent-adsorbate interactions and to propose an adsorption mechanism. These adsorbents were characterized by FTIR, DRX, SEM and EDX. RSM allowed the evaluation of the effects of temperature and pH on the dye adsorption. DFT modeling was used to analyze the dye - biomass interactions using six representative model molecules for the composition of lignocellulosic biomass. The experimental and modeling results showed that the best experimental conditions to remove BB3 dye were 40 degrees C and pH 4, while the best conditions for RB19 dye adsorption were 40 degrees C and pH 6. RSM models satisfactorily correlated the experimental data with R2 values of 0.90 - 0.98 and modeling errors of 0.30- 1.53%. The adsorption of these dye molecules was endothermic and governed by physical interaction forces. The adsorption capacity for BB3 increased with increasing pH, whereas that of RB19 showed the opposite trend. DFT calculations indicated that BB3 and RB19 molecules interact via the nitrogen located in the phenoxazine and the sulfonate group, respec-tively, with the hydroxyl and oxygenated groups of monomers that compose the natural polymers of these lignocellulosic materials.