Removal of Cu²⁺, Zn²⁺ and Pb²⁺ ions using a graphene-containing nanocomposite: A kinetic study

In the present paper, the urgent issue of removing heavy metal ions from aqueous solutions is considered by the example of extraction of Cu²⁺, Zn²⁺ and Pb²⁺ ions using an innovative sorbent-polyhydroquinone/graphene nanocomposite. Kinetics of the metal sorption on this material was studied. Moreover, the effect of solution pH on the sorption capacity of the nanocomposite was estimated. Besides, to elucidate mechanisms of kinetic removal and determine process parameters, experimental data were fitted to kinetic (pseudo-first- A nd pseudo-second-order, and Elovich) and diffusion (intraparticle and Boyd) models. The kinetic experiments showed that equilibrium is reached within 60 min. The effective diffusion coefficient values calculated according to the Boyd model were found to increase in the following sequence: Pb²+ (1.26 10^-13 m² s^-1) < Zn²+ (3.74 10^-13m² s^-1) < Cu²⁺ (4.24 10^-13 m² s^-1). Finally, it was established that the metal sorption process is controlled by the internal diffusion of the sorbate into the bulk (volume) of the sorbent.