Synthesis and characterization of halloysite/graphene quantum dots magnetic nanocomposite as a new adsorbent for Pb(II) removal from water

Abstract

Graphene quantum dots (GQDs) were covalently immobilized onto the NiFe2O4-halloysite nanotubes (NiFe2O4-HNTs) surface to fabricate a nanocomposite material utilized as an active adsorbent to eliminate Pb(II) ions from water. NiFe2O4 nanoparticles were synthesized and simultaneously deposited on HNTs. Then, the material surface was coated by APTES (aminopropyltriethoxysilane) to cause GQDs be connected to the external layer via an amide bond. The prepared nanomaterial structure was identified by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Brunauer-Emmet-Teller (BET) isotherm, energy dispersive X-ray spectroscopy (EDS) analysis and VSM (vibrating sample magnetometry). Box-Behnken design incorporated with response surface method (RSM) was utilized to find out the impact of pH, time, initial concentration of Pb(II) and adsorbent dose on lead removal. Study discovered that adsorption operation is the quasi-second-order kinetic model and adapted more precisely with Langmuir adsorption model. The Langmuir highest uptake capacity of 42.02 mg/g at 298 K was acquired. The Elovich model recommended that the process is a kind of chemisorption. The calculated thermodynamic variables verified that the uptake process is endothermic and spontaneous. Additionally, the adsorbent can be simply separated with the aid of a magnet.