Thermodynamics and kinetics of bivalent cadmium biosorption onto nanoparticles of chitosan-based biopolymers

• Kinetics and thermodynamics of Cd2+ biosorption onto CPG nanoparticles are studied.
• Adsorption kinetic data are best modeled using second-order rate equations.
• The Cd2 adsorption onto CPG was physical diffusion controlled reaction.
• The experimental equilibrium results well fit the Langmuir model.
• The thermodynamics show endothermic, favorable and spontaneous adsorption processes.

Ternary nanoparticles of chitosan, non-living biomass (Pseudomonas sp.) and gelatin, CPG were prepared by emulsion crosslinking method and applied as a new efficient adsorbent for Cd(II) removal from aqueous solution with removal capacity above 90%. The Cd(II) removal capacity was dependent on the composition of CPG, intial Cd(II) concentration, medium pH and temperature. The fabricated CPG was characterized by TEM and FTIR. Among four different adsorption models Langmuir model best-predicted the biosorption data, where two adsorption sites, A and B with variable site capacities, v were distinguished. The values of v were stoichiometric and temperature independent. The thermodynamic data showed the physical, spontaneous and endothermic nature of the adsorption processes. The pseudo-second-order equation was best describing the adsorption rates compared to other investigated kinetic models and the temperature effect on biosorption kinetics was further studied. The aforementioned results suggest that the CPG nanoparticles can be applied effectively for the elimination of Cd(II) pollution from wastewater.