Kinetic and thermodynamic studies on the removal of Zn2+ and Ni2+ from their aqueous solution using poly(phenylthiourea)imine

Novel poly(phenylthiourea)imine (PPTUI) was synthesized by the polycondensation of 4,4′-bis(thiourea)biphenylmethane in the presence of terephthaldehyde, using p-tolunesulfonic acid as the catalyst and dimethyformamide (DMF) as the solvent. The chemical, structural and textural characteristics of the adsorbent were determined by the FT-IR, 1H NMR, BET, SEM and EDAX analysis. The adsorption capacity of the PPTUI for the removal Ni2+ and Zn2+ ions from the aqueous solution was investigated. The adsorption parameters, such as pH, adsorbent dose, contact time, initial metal ion concentration and temperature were optimized. Batch adsorption kinetics have been mathematically described, and it has been found that the adsorption of Ni2+ and Zn2+ ions onto the PPTUI follow the pseudo-second order kinetic model. Adsorption isotherms have also been investigated, and the data fitted well in the order of the Sips > Redlich–Peterson > Freundlich > Langmuir isotherm models. The thermodynamic parameters of adsorption ΔH° and ΔG° suggest that the adsorption of Ni2+ and Zn2+ ions onto the PPTUI is endothermic and spontaneous in nature. Competitive adsorption decreases the amount of individual metal ions adsorbed, and the adsorption of the Ni2+ ion is higher than that of the Zn2+ ion. Desorption experiments show that the adsorption of Ni2+ and Zn2+ ions is reversible, and the adsorbent was easily regenerated with 90% adsorption capacity, even after four cycles. The PPTUI has good adsorption efficiency for the removal of Ni2+ and Zn2+ ions compared to other adsorbents.

► PPTUI has great efficiency for the removal of Zn2+ and Ni2+ ions.
► Maximum adsorption capacity of PPTUI for Zn2+ and Ni2+ ions were found to be 212.8 and 226.32 mg/g respectively.
► The adsorption of PPTUI follows pseudo-second-order kinetics.
► PPTUI seems to be better adsorbent for the removal of Zn2+ and Ni2+ ions.