3.2. Preparation and Characterization of LaCoO3

LaCoO₃ was synthesized by a sol-gel process. Briefly, the mixtures of metal nitrates and citric acid were stirred for 12 h and then heated at 100 °C to remove water in the oil bath. The resultant sticky gel was subsequently oven-dried at 100 °C overnight. The obtained spongy material was then grinded into fine powders and calcined for 7 h in a muffle furnace to form the desired perovskite structure. After cooling, the sample was washed and dried overnight.

Transmission electron microscope (TEM) and selected-area electron diffraction (SAED) patterns were conducted on the field emission transmission electron microscope (Tecnai G2 F30, Eindhoven, Holland). The X-ray powder diffraction (XRD) analysis was characterized by Cu Kα irradiation (λ = 1.5406 Å) (Bruker D8-Advance, Karlsruhe, Germany). The surface area of LaCoO₃ was analyzed by a Brunauer–Emmett–Teller (BET) analyzer (Micrometrics ASAP 2020, Norcross, GA, USA). The zeta potential analysis was acquired through a Malvern Zetasizer with a Zetasizer (Nano ZS90, Malvern, UK) at 25 °C.