Adsorptive removal of cadmium from aqueous solutions using NiFe2O4/hydroxyapatite/graphene quantum dots as a novel nano-adsorbent

Abstract

In this study, NiFe2O4/hydroxyapatite/graphene quantum dots (NiFe2O4/HAP/GQDs) as nano-adsorbent to remove cadmium (Cd2+) from aqueous solution were synthesized. This nano-adsorbent was depicted by some techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). Adsorption studies were conducted to investigate the effect of contact time, pH, adsorbent dosage and initial cadmium ion concentration on removal efficiency. To determine the most fitting kinetic model, the suitability of pseudo-first-order and pseudo-second-order models was compared. The adsorption isotherm was described well by the Langmuir isotherm and maximum equilibrium uptake capacity (qe) was 344.83 mg g−1. Studies revealed that adsorption process is not a physical process and formation of complexes (bidentate and monodentate complexes) between—COO− and—OH functional groups on the surface of NiFe2O4/HAP/GQDs and Cd2+ ions may occur. In addition, the adsorbent can simply be removed by an ordinary filtration process.