Ultrasound-assisted green synthesis of poly(o-phenylenediamine)/zinc oxide nanohybrids for enhanced adsorption of Cu (II) from water: Kinetic, equilibrium, and thermodynamic studies

Abstract

Fabricating novel eco-friendly adsorbents with excellent stability, outstanding adsorption capacity, facile separation, brilliant recyclability, and extensive Cu (II) ion removal capability remains challenging. To solve the pollution of Cu (II) ions from water resources, herein, novel nanohybrids of poly(o-phenylenediamine)/zinc oxide (POPD/ZnO) were synthesized using ultrasound-assisted technique via a facile in situ polymerization method following green chemistry principles. As prepared nanohybrids were characterized using infrared spectra (FTIR), UV-Visible spectra, scanning electron microscopy (SEM), X-ray scattering (XRD), and thermogravimetric analysis (TGA). The results revealed that ZnO nanoparticles were successfully incorporated into the POPD matrix and the stability of nanohybrids was found better than the POPD alone. Optimization of numerous parameters was done to see the performance of the adsorption process such as the effect of loading of OPD in nanohybrids, adsorbent dose, initial Cu (II) ion concentration, pH of the solution, contact time, and temperature. The nanohybrids POPD/ZnO-13/87 was found the best adsorbent according to the above analysis and used for the isotherm studies. The adsorption process was analyzed using a Non-linear equilibrium isotherm (Langmuir and Freundlich), kinetics (pseudo-first and second order, along with intraparticle diffusion model) and thermodynamic models. Langmuir isotherm and pseudo-second-order kinetic model were found appropriate for the adsorption process. Thermodynamic parameters (Gibbs free energy change (ΔG°), entropy change (ΔS°), and enthalpy change (ΔH°)) were calculated showing endothermic and spontaneous t process for adsorption of Cu (II) ions. According to Langmuir isotherm, the maximum adsorption capacity was found 2485 mg·g-1 that was higher than that of other reported materials till date. Mechanism studies suggested that the electrostatic interaction and cation-π interaction in between nanohybrids and Cu (II) ions was the main driving force for the adsorption of Cu (II) ions. The adsorption capability was enhanced using the nanohybridization of POPD/ZnO via ultrasonication technique in comparison to POPD and ZnO alone. These nanohybrids are efficient adsorbents to remove the maximum pollution of Cu (II) ions in a sustainable way by using the green synthesized POPD/ZnO nanohybrids.