Simultaneous removal of cadmium and lead ions from aqueous solutions by nickel oxide-decorated reduced graphene oxides

Herein, we report nickel oxide-decorated reduced graphene oxide synthesis through hydrothermal routes and their adsorption behavior in single and binary metal ion-containing aqueous media. The formation of the hybrid was verified through microscopic and spectroscopic characterizations. Generally, wastewater contains multiple metal ions, and the presence of other ions may affect the adsorption process. Hence, adsorption studies in a multicomponent system are essential to understand the adsorbent’s potential for real-life application. Systematic adsorption studied in single metal ion-containing solutions indicated that the hybrids’ adsorption capacities were ~ 725 mg g−1 and ~ 890 mg g−1 for cadmium and lead ion, respectively. Simultaneous metal ion removal experiments in binary metal ion systems indicated an increase in adsorption capacity with a maximum value of ~ 1000 mg g−1 for lead ion adsorption and a decrease in adsorption capacity with a maximum value of ~ 580 mg g−1 for cadmium ion adsorption. This observation suggested that the lead and cadmium ion adsorption process is affected by the synergistic and antagonistic effects, respectively. Experimental results indicate that the process followed the Langmuir isotherm and pseudo-second-order kinetics irrespective of the systems when the adsorption experiments were done in single and binary metal ion-containing systems. Thermodynamic studies indicated endothermicity and spontaneity of the process. The kinetic experiments showed that the film diffusion dominates the metal ion adsorption process.