Application of Box-Behnken design and desirability function in the optimization of Cd(II) removal from aqueous solution using poly(o-phenylenediamine)/hydrous zirconium oxide composite: equilibrium modeling, kinetic and thermodynamic studies.

In this research work, poly(o-phenylenediamine) was incorporated into the hydrous zirconium oxide matrix to form poly(o-phenylenediamine)/hydrous zirconium oxide composite which is used for the removal of Cd(II) from aqueous solution. The characterization of the material was done based on FTIR, XRD, SEM, and TGA-DTA. The effects of contact time, pH, adsorbent dose, and initial concentration of Cd(II) on the removal of Cd(II) were studied by performing 29 sets of sorption runs using Box-Behnken design combined with response surface methodology (RSM). Various isotherm models were tested to describe the adsorption equilibrium. The adsorption equilibrium data fitted well with Freundlich isotherm model. The maximum adsorption capacity of 66.66 mg g-1 was obtained from Langmuir isotherm. The pseudo-second-order kinetic model described the adsorption kinetics more accurately. Diffusion-based kinetics such as intraparticle diffusion and Bangham's model suggested that both film and intraparticle pore diffusion were involved in the adsorption process. The Elovich model pointed towards the chemisorption. The investigation of desorption and regeneration suggested that the material can be used as an effective sorbent for removal of Cd(II) from aqueous system.