Solvothermal synthesis of size-tunable ZnFe₂O₄ colloidal nanocrystal assemblies and their electrocatalytic activity towards hydrogen peroxide

Three ZnFe₂O₄ colloidal nanocrystal assemblies (CNAs), namely CNA1, CNA2 and CNA3, have been synthesized solvothermally with the size of 560 nm, 460 nm and 330 nm and are formed by the self-assembly of primary nanocrystals with the crystallite sizes of 19.2 nm, 15.5 nm and 21.8 nm, respectively. It was found that CNA2 performed superparamagnetic behavior with a saturation magnetization value of 36.9 emu g⁻¹ while either CNA1 or CNA3 exhibited weak ferromagnetic with a small hysteresis loop and large saturation magnetization. Electrochemical sensing measurements toward the reduction of hydrogen peroxide showed that the peak currents of the CNAs in cyclic voltammograms showed a linear relationship with the concentration of hydrogen peroxide in the experimental conditions and the peak potentials were increased with the order of CNA3, CNA2 and CNA1. The formation mechanism of ZnFe₂O₄ CNAs had been discussed based on the experimental data. The magnetism and electrocatalysis of the ZnFe₂O₄ CNAs were supposed to be dependent on the size of primary nanoparticles and the structure of the CNAs. - Highlights: • Size-tunable ZnFe₂O₄ colloidal nanocrystal assemblies were synthesized solvothermally. • Magnetic properties of ZnFe₂O₄ assemblies are depended on the size and self-assembly of primary nanoparticles. • Electrocatalytic activity of ZnFe₂O₄ assemblies is determined by their structure.