Effects of aging temperature on the size and morphology of Cu(OH)2 and CuO nanoparticles

By using Y-shaped tubular reactor, Cu(OH)2 nanoparticles in the form of nanostrands or nanowires were synthesized from copper nitrate and sodium hydroxide aqueous solutions by varying aging temperature between 5 and 40 °C. Phase pure Cu(OH)2 was obtained after aging below 20 °C, while CuO appeared at 30 °C and became a sole crystalline phase at 40 °C. The average representative particle size and its distribution breadth of CuO, obtained after dehydration at 160 °C, were reduced from 58 ± 30 to 17 ± 7 nm, respectively, by decreasing the aging temperature of the precedent Cu(OH)2 from 20 to 5 °C. The effects of aging temperature of Cu(OH)2 on the crystalline phase and particle morphology of as-aged Cu(OH)2 and of CuO after thermal dehydration were discussed in terms of the polar component of the solvation free energy for the nuclei-growth processes of Cu(OH)2. The latter is associated with the ionic charge of the aqueous phase, and predominated by the increasing dielectric constant of the solvent, i.e., water with decreasing temperature. After dip coating the dialyzed Cu(OH)2 colloidal dispersion on a Ni substrate and heated at 160 °C under reduced pressure, deposition of the equiaxed CuO particles of 150 ± 20 nm was observed. The effects of drying condition on the morphology of the nanoparticle deposition were also discussed.