Investigation the adsorption properties of graphene oxide and polyaniline nano/micro structures for efficient removal of toxic Cr(VI) contaminants from aqueous solutions; kinetic and equilibrium studies

Graphene oxide (GO) and polyaniline (PANI) were synthesized and characterized by different techniques to be used as efficient adsorbents for hexavalent chromium Cr(VI) from aqueous solutions. The adsorption behavior of both GO and PANI is controlled mainly by the solution pH achieving the best uptake capacity at the acidic conditions. The uptake equilibrium was attained after 120 and 180 min for the adsorption of Cr(VI) by GO and PANI, respectively. Pseudo-second order, Intraparticle diffusion, and Elovich kinetic models were evaluated to understand the adsorption mechanism. The obtained results represented mainly by pseudo-second-order kinetic model rather than by the other models. The adsorption equilibrium studies well described using three traditional isotherm models (Langmuir, Freundlich and Temkin models). The theoretical estimation of the maximum uptake capacity of Cr(VI) ions (q(max)) using Go and PANI are 49 and 59 mg/g, respectively. Monolayer model with one energy site was used as advanced isotherm model for more interpretation of the adsorption behavior of the studied adsorbents. The calculated parameters of studied model give more information about the number of receptor adsorption sites, the number of adsorbed Cr(VI) ions per site, average occupation sites and monolayer adsorption quantity and total saturation adsorption quantity.