Unraveling the Adsorption Process of Cd2+ on Bio-Adsorbents: Experimental and Theoretical Points of View

In this chapter, we concentrate on the study of Cd2+ adsorption from both experimental and computational sides. The adsorption mechanisms of Cd2+ on biochar remain an enigmatic aspect in the current research field. While numerous studies have explored the adsorption capacities of different materials, a comprehensive understanding of the underlying adsorption mechanisms is still lacking. Kinetics models such as pseudo-first-order, pseudo-second-order, and intraparticle diffusion offer valuable insights into kinetics and rate constants but may fall short in predicting the complex adsorption mechanisms, owing to certain assumptions that may not hold in real-world systems. Isotherm studies serve as an essential approach for predicting the adsorption mechanisms in various systems, providing information about the nature of adsorption through different isotherm curves. However, a single equation cannot satisfactorily explain all the mechanisms. In the context of heavy metal adsorption on carbonaceous materials, experimental techniques have proposed interactions, i.e., electrostatic, π–π interaction, precipitation, ion exchange, and complexation. Computational approaches, however, have predominantly relied on adsorption energies to define interactions, with a limited focus on the kinetics and thermodynamics aspects of the adsorption process using molecular modeling. Indeed, several studies are limited to small models, and some of them lack complete and systematic methodologies. The absence of studies exploring computationally dynamic systems further restricts a comprehensive understanding. Bridging these gaps through experimental and computational efforts is crucial to unravel the intricate adsorption mechanisms and optimize the adsorption process for environmental remediation and industrial applications.