We developed a liquid-phase synthesis method for Pd-based nanostructure, in which Pd dissolved in dimethyl sulfoxide (DMSO) solutions was precipitated using acid aqueous solution. In the development of the method, in situ monitoring using atmospheric scanning electron microscopy (ASEM) revealed that three-dimensional (3D) Pd-based nanonetworks were deformed to micrometer-size particles possibly by the surface tension of the solutions during the drying process. To avoid surface tension, critical point drying was employed to dry the Pd-based precipitates. By combining ASEM monitoring with critical point drying, the synthesis parameters were optimized, resulting in the formation of lacelike delicate nanonetworks using citric acid aqueous solutions. Precipitation using HCl acid aqueous solutions allowed formation of 500-nm diameter nanorings connected by nanowires. The 3D nanostructure formation was controllable and modifiable into various shapes using different concentrations of the Pd and Cl ions as the parameters.
A novel method to produce palladium micrometer-sized particles is presented. This method consists of the leaching of palladium using dimethyl sulfoxide (DMSO) solution containing CuCl 2 and NaCl followed by the precipitation with citric acid aqueous solution. Precisely, palladium was dissolved in a DMSO solution containing 0.1-0.2 M of CuCl 2 and 0-0.2 M of NaCl at 343 K. The dissolved palladium was precipitated by the addition of a citric acid aqueous solution, and the dried precipitates were imaged using standard SEM. We obtained micrometer-sized particles: angular particles were formed by the addition of 0.1-0.5 M citric acid aqueous solution while spherical particles by 1.0-2.0 M citric acid solution. The maximum recovery efficiency of palladium was 76.1% and purity of palladium was 92.5 mass%. To investigate the mechanism of particle formation, in-situ monitoring of the formations of palladium particles in the liquid phase was conducted using atmospheric scanning electron microscopy (ASEM). The monitoring revealed that palladium particles form coral-like branching strings in the liquid phase. Comparison with dried spherical particles suggests that the stings were changed into spherical shapes during drying.
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