Abstract
Different mole ratios (nCu : nNi = x : y) of hybrid copper–nickel metal hexacyanoferrates (CuxNiyHCFs) 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 CuxNiyHCF nanoparticles can be easily controlled as designed using a wet chemical coprecipitation method. The crystallite size and formal potential of CuxNiyHCF films showed an insignificant change when 0 ≤ x : y < 0.3. Given the shape of the CV curves, this might be due to Cu2+ 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. CuxNiyHCF films inherited good electrochemical reversibility from the CuHCFs, in view of the cyclic voltammograms; in particular, Cu1Ni2HCF exhibited long-term cycling stability and high surface coverage. The adsorption of Co2+ fitted the Langmuir isotherm model well, and the kinetic data can be well described by a pseudo-second order model, which may imply that Co2+ adsorption is controlled by chemical adsorption. The diffusion process was dominated by both intraparticle diffusion and surface diffusion.
Highlights
Iron hexacyanoferrate (PB, Prussian blue) and its analogues (PBAs) are collectively referred to as transition metal hexacyanoferrates (MHCFs, M 1⁄4 Fe, Cu, Co, Ni, etc.) Due to the electrochromism, magnetism, redox activity, and electrochemical stability associated with their unique cubic structure, MHCFs have been applied in a number of elds, including catalysis,[1] electrochromics,[2] electrocatalysis,[3,4] detection,[5] chemical sensors,[6] capacitors,[7] secondary batteries,[8] photocatalysis,[9] photochromics,[10] biosensors,[11,12] and metal ion sieving or capture,[13,14] making great contributions to environmental technology and new-generation energy development
Ghasemi et al.[22] found that NiCoHCF has a higher capacitance than nickel hexacyanoferrate (NiHCF) or cobalt hexacyanoferrate (CoHCF); Li et al.[23] revealed that CuNiHCF has a higher capacity retention than CuHCF as a cathode for sodium-ion batteries; it was reported that the mixed MHCF showed an enhanced catalytic efficiency to H2O2 as compared to that of FeHCF.[24]
Cu2+ inset in NiHCF lattice instead of K+ as countercations to maintain the electrical neutrality of the structure in a situation such as that exhibited by Fig. 4b
Summary
Iron hexacyanoferrate (PB, Prussian blue) and its analogues (PBAs) are collectively referred to as transition metal hexacyanoferrates (MHCFs, M 1⁄4 Fe, Cu, Co, Ni, etc.) Due to the electrochromism, magnetism, redox activity, and electrochemical stability associated with their unique cubic structure, MHCFs have been applied in a number of elds, including catalysis,[1] electrochromics,[2] electrocatalysis,[3,4] detection,[5] chemical sensors,[6] capacitors,[7] secondary batteries,[8] photocatalysis,[9] photochromics,[10] biosensors,[11,12] and metal ion sieving or capture,[13,14] making great contributions to environmental technology and new-generation energy development. Chen et al.[31] prepared exact ratios of CuHCF nanoparticle ink by a wet chemical coprecipitation method, and printed them onto the electrode surface to remove cesium electrochemically; the cesium removal was comparable in magnitude to that by an electrodeposited lm. Wang et al.[25] prepared h-MHCF lms by the same method; the surface coverage of redox-active sites of the CuCoHCF lms was 35 nmol cmÀ2, which was much higher than the 9.02 nmol cmÀ2 of electrodeposited lms;[32] and the Co/Ni atomic ratio in CoNiHCF compounds had been proved to be controlled by the reactant ratio in the reaction mixture. We prepared a series of CuxNiyHCF nanoparticle lms with different molar ratios (nCu : nNi 1⁄4 x : y) by using a wet chemical coprecipitation method, and explored the characteristics of each ratio and the variations among them by multiple characterization methods. The feasibility of electrochemical adsorption of cobalt ions onto hybrid copper–nickel hexacyanoferrate lms is discussed, as well as the adsorption isotherms and kinetics properties
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