Highly efficient remediation of Cu (II) from water by novel poly(o-phenylenediamine)/zinc oxide nanohybrids: Kinetic, equilibrium, and thermodynamic studies

Herein, novel nanohybrids of poly(o-phenylenediamine)/zinc oxide (POPD/ZnO) were synthesized using an ultrasound-assisted technique via a facile in situ polymerization method for the removal of Cu (II) ions from water. These nanohybrids were characterized using infrared spectra (FTIR), UV–Visible spectra, scanning electron microscopy (SEM), X-ray scattering (XRD), thermogravimetric analysis (TGA), and BET (Brunauer-Emmett-Teller surface area). Numerous parameters were optimized to see the performance of the adsorption process like effect of POPD loading, adsorbent dose, initial Cu (II) ion concentration, pH, contact time, and temperature. POPD/ZnO-13/87 was found the best adsorbent based on above analysis. Non-linear equilibrium isotherm (Langmuir and Freundlich), kinetics (pseudo-first and second order, intraparticle diffusion model), and thermodynamic studies were performed to analyze the adsorption process. Langmuir isotherm and pseudo-second-order kinetic model were found appropriate while thermodynamic parameters Gibbs free energy change (ΔG°), entropy change (ΔS°) (166.32 J mol−1 K−1), and enthalpy change (ΔH°) (34.03 kJ mol−1) were calculated showing an endothermic and spontaneous process for adsorption of Cu (II) ions. According to Langmuir isotherm, the maximum adsorption capacity was found at 2485 mg g−1 while experimental adsorption capacity was found 2360 mg g−1 at adsorbent doses = 0.4 g L−1, Cu (II) ion concentration = 1000 mg L−1, pH = 6.5, temperature = 25 °C in 90 min that was higher than that of other reported materials till date to the best of our knowledge. Mechanism studies suggested that the electrostatic interaction and cation-π interaction between nanohybrids and Cu (II) ions was the main driving force for the adsorption of Cu (II) ions.