Physicochemical analysis of multilayer adsorption mechanism of anionic dyes on lignocellulosic biomasses via statistical physics and density functional theory

Abstract This paper reports the physicochemical analysis of the multilayer adsorption of anionic dyes on lignocellulosic biomasses. Experimental studies, statistical physics modeling and density functional theory (DFT) calculations were carried out to understand and characterize the adsorption mechanism of dyes Acid Blue 29, Acid Blue 113 and Reactive Blue 4 using coconut shells, cauliflower cores and broccoli stalks as low-cost adsorbents. Steric parameters and adsorption energies were estimated from an advanced multilayer statistical physics model and these parameters were associated with the biomass composition and dye molecular properties. DFT calculations were also performed to characterize the atomic interactions of dye molecules and surface functionalities from the main biopolymers contained in the lignocellulosic biomasses. Results showed that the multilayer adsorption of these anionic dyes was related to the cellulose contained in these biomasses where the best adsorption capacities were obtained for cauliflower cores with a cellulose composition of 11.2%. It was also confirmed that the dye aggregation played an important role for the removal of these adsorbates where cluster formation was significantly affected by adsorption temperature. Hydrogen bonding was the main interaction for the endothermic dye adsorption using these biomasses. Results reported in this paper contribute to understand the dye adsorption mechanism using low-cost adsorbents like lignocellulosic materials with the aim of improving the performance of treatment technologies for water decolorization.