Preparation and characterization of an AC–Fe3O4–Au hybrid for the simultaneous removal of Cd2+, Pb2+, Cr3+ and Ni2+ ions from aqueous solution via complexation with 2-((2,4-dichloro-benzylidene)-amino)-benzenethiol: Taguchi optimization
Activated carbon (AC) was magnetized with Fe3O4 nanoparticles (AC–Fe3O4-NPs) and loaded with Au nanoparticles (AC–Fe3O4–Au-NPs), and was fully characterized using different techniques such as XRD, XPS, VSM, TEM and SEM. 2-((2,4-Dichloro-benzylidene)-amino)-benzenethiol (DBABT), a complexing agent, was synthesized and characterized using 1H-NMR, ES-MS and FT-IR analysis. Subsequently, AC–Fe3O4-NPs was modified with DBABT and applied for the ultrasound-assisted removal of Cd2+, Pb2+, Cr3+ and Ni2+ ions via complexation with DBABT. The influences of variables such as reaction time and adsorbent mass (equilibrium) were optimized simultaneously. The method under optimum conditions was set at pH 5, concentrations of 5, 15, 25 and 25 mg L−1 for the Cd2+, Pb2+, Cr3+ and Ni2+ ions, respectively, 0.02 g for the adsorbent mass, 5 min sonication time and 6 mg L−1 for the concentration of DBABT, producing removal percentages of 80.59, 93.85, 68.52 and 81.68 for Cd2+, Pb2+, Cr3+ and Ni2+ ions, respectively. Analysis of real experimental equilibrium data at various concentrations of analytes reveals the efficiency of the Langmuir model for good representation of experimental data, with maximum mono-layer adsorption capacities of 185.22, 135.14, 188.70 and 133.34 mg g−1 for Cd2+, Pb2+, Cr3+ and Ni2+ ions respectively. The experimental data at various real times reveal that in most situations the systems reach equilibrium at contact times lower than 20 min, while the data fitted well to a combination of a pseudo second order kinetic model and intraparticle diffusion.