Complex formation processes at the surface of Cu–O composite nanoparticles with and without external magnetic field

Abstract

Effects of preliminary magnetization on Cu–O nanoparticles (CNPs) and their electronic structures were examined in conjunction with their near-surface reactivity. CNPs were exposed to the external magnetic field, H (≤4 kOe), in a glove box of Ar atmosphere at room temperature. The absorption intensity of UV/vis diffuse reflectance spectra of CNPs at the wavelength between 500 nm and 800 nm increased with magnetization. In order to elucidate the chemical consequences from magnetization, the reaction processes of CNPs at the boundary to the cyclohexane solution of acetyl pyridine (Apy) were examined by monitoring the decrease in the UV absorption band intensity at 279.5 nm due to π–π * transition using a flow cell. The decrease in the UV absorption intensity is correlated with the increase in the extent of the reaction. We observed the two-step reaction process with a faster initial decay and a slower later one. We found the application of the magnetic field creates new active centers for the present coordination reaction. These magnetically acquired active centers are associated with the latter, more sluggish step of the two-step reaction. All these magnetic effects are consistently explained by the delocalization of the 3d electrons of Cu due to the partial change from antiferromagnetic to ferromagnetic states.