A novel core-shell magnetic Prussian blue-coated Fe3O4 composites (Fe3O4@PB) were designed and synthesized by in-situ replication and controlled etching of iron oxide (Fe3O4) to eliminate Cd (II) from micro-polluted water. The core-shell structure was confirmed by TEM, and the composites were characterized by XRD and FTIR. The pore diameter distribution from BET measurement revealed the micropore-dominated structure of Fe3O4@PB. The effects of adsorbents dosage, pH, and co-existing ions were investigated. Batch results revealed that the Cd (II) adsorption was very fast initially and reached equilibrium after 4 h. A pH of 6 was favorable for Cd (II) adsorption on Fe3O4@PB. The adsorption rate reached 98.78% at an initial Cd (II) concentration of 100 μg/L. The adsorption kinetics indicated that the pseudo-first-order and Elovich models could best describe the Cd (II) adsorption onto Fe3O4@PB, indicating that the sorption of Cd (II) ions on the binding sites of Fe3O4@PB was the main rate-limiting step of adsorption. The adsorption isotherm well fitted the Freundlich model with a maximum capacity of 9.25 mg·g−1 of Cd (II). The adsorption of Cd (II) on the Fe3O4@PB was affected by co-existing ions, including Cu (II), Ni (II), and Zn (II), due to the competitive effect of the co-adsorption of Cd (II) with other co-existing ions.
Different mole ratios (n Cu : n Ni ¼ x : y) of hybrid copper-nickel metal hexacyanoferrates (Cu x Ni y HCFs) were prepared to explore their morphologies, structure, electrochemical properties and the feasibility of electrochemical adsorption of cobalt ions. Cyclic voltammetry (CV), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) indicated that the x : y ratio of Cu x Ni y HCF nanoparticles can be easily controlled as designed using a wet chemical coprecipitation method. The crystallite size and formal potential of Cu x Ni y HCF films showed an insignificant change when 0 # x : y < 0.3. Given the shape of the CV curves, this might be due to Cu 2+ ions being inserted into the NiHCF framework as countercations to maintain the electrical neutrality of the structure. On the other hand, crystallite size depended linearly on the x : y ratio when x : y > 0.3. This is because Cu tended to replace Ni sites in the lattice structure at higher molar ratios of x : y. Cu x Ni y HCF films inherited good electrochemical reversibility from the CuHCFs, in view of the cyclic voltammograms; in particular, Cu 1 Ni 2 HCF exhibited long-term cycling stability and high surface coverage. The adsorption of Co 2+ fitted the Langmuir isotherm model well, and the kinetic data can be well described by a pseudo-second order model, which may imply that Co 2+ adsorption is controlled by chemical adsorption. The diffusion process was dominated by both intraparticle diffusion and surface diffusion. Fig. 7 (a, b and c) CV of Cu x Ni y HCF films in 0.5 M Co 2+ solutions at different scan rates (v ¼ 0.005, 0.025, 0.05, 0.1, 0.15 V s À1 ); insets show the logarithmic values of reduction peak current (i pc ) as a function of the logarithmic values of scan rate; (d) Nyquist plots of Cu x Ni y HCF films from 100 Hz to 1000 kHz.This journal is
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