Highly efficient simultaneous adsorption of Cd(ii), Hg(ii) and As(iii) ions from aqueous solutions by modification of graphene oxide with 3-aminopyrazole: central composite design optimization

Abstract

In this work, graphene oxide (GO) chemically modified with 3-aminopyrazole (GO-f) was synthesized for the simultaneous adsorption of three heavy metals, Cd(II), Hg(II), and As(III), from aqueous solutions. The 3-aminopyrazole functionalized GO adsorbent acts as a good host for welcoming the incoming guest and the abundant nitrogen-containing functional groups on the adsorbent surfaces play an important role in heavy metal adsorption. The synthesized adsorbent was characterized by FT-IR, EDX, SEM and TGA measurements. In order to study the influence of pH, adsorbent dose, and initial ion concentration on the adsorption process, the central composite design (CCD) was employed. The quadratic model was used for analysis of variance and indicated that adsorption of metal ions strongly depends on pH. Time-dependent adsorption can be demonstrated by the pseudo-second-order kinetic model, and the adsorption process was modeled by the Langmuir isotherm for the adsorbent. Owing to the large specific surface area, hydrophilic behavior, and functional moieties, the adsorbent showed excellent removal ability with a maximum adsorption capacity of 285.714, 227.273, and 131.579 mg g⁻¹ for cadmium, mercury and arsenic ions, respectively. Thermodynamic analysis revealed that the adsorption of Cd(II), Hg(II) and As(III) ions was spontaneous and endothermic. Moreover, the competitive adsorption capacities of the heavy metal ions were lower than the noncompetitive ones. Also, the same affinity order was observed for noncompetitive and competitive adsorption: Cd(II) > Hg(II) > As(III). A desorption study revealed the favorable regeneration ability of the adsorbent powder, even after three adsorption–desorption cycles.