Composite Chitosan-Biochar-based sponges for the removal of Direct Blue-78 from water: Physical and chemical parameters affecting the adsorption process

A composite material made of olive pomace biochar and chitosan sponges is presented during this work as a substrate for adsorbing Direct Blue-78, an anionic azo-textile dye from water. Moreover, the removal of other pollutants in mixture is demonstrated. The aim is to show the role of different physical and chemical parameters affecting the adsorption process attributed to the synergistic action of chitosan and biochar, such as pH, ionic strength, and temperature. Both pseudo-first and second order kinetic models were also successfully applied to achieve additional information; the Weber-Morris model was implemented to explore the role of intraparticle diffusion of dyes throughout the adsorbent that did not arise as the lone kinetic relevant step. Moreover, Langmuir, Freundlich, Temkin, and Dubinin-Raduschkevich isotherms were applied to better characterize the process that occurred on heterogeneous surfaces. Finally, the Van't Hoff equation was adopted to calculate the thermodynamic parameters, showing the endothermic character and spontaneity of the adsorption process.