Two-step electrosynthesis and catalytic activity of CoO−CoO • xH2O-supported Ag, Au, and Pd nanoparticles

• Published in: Russian chemical bulletin 2020-02, Vol.69 (2), p.241-254
• Main Authors: Fazleeva, R. R., Nasretdinova, G. R., Osin, Yu. N., Ziganshina, A. Yu, Yanilkin, V. V.
• Format: Article
• Language: English
• Subjects: Agglomerates; Anodic dissolution; Aqueous solutions; Catalytic activity; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Cobalt oxides; Dissolution; Electrolysis; Full Article; Gold; Inorganic Chemistry; Nanocomposites; Nanoparticles; Nitrophenol; Organic Chemistry; Oxygen; Palladium; Reagents; Silver
• ISSN: 1066-5285; 1573-9171
• DOI: 10.1007/s11172-020-2752-4

Two-step electrosynthesis of CoO-CoO• x H 2 O-supported metal nanoparticles (MNPs, M = Au, Ag, Pd) was carried out in N , N -dimethylformamide in the absence and in presence of poly( N -vinylpyrrolidone) (PVP) using atmospheric oxygen as both a reagent and a mediator at potentials of its reduction to a superoxide radical anion. In the first step, oxygen reduction in the presence of Co 2+ ions added to the solution as a salt or generated by dissolving the Co-anode during electrolysis produces a mixture of cobalt oxide CoO and its hydrated form CoO-CoO • x H 2 O (CoO x H y ). When Ag + , Au + , Pd 2+ ions are added to the obtained solution of CoO x H y , a redox reaction between CoO and the metal ion gives the MNPs and CoO + . In the second step, oxygen-mediated electroreduction of CoO + serving as the second mediator is carried out, and the redox reaction is completely shifted towards the formation of MNPs. In the absence of PVP, AgNPs (18±4 nm) bind and stabilize completely in the CoO x H y matrix, PdNPs (6±1 nm) stabilize only partially, and AuNPs (21±10 nm) do not bind and, therefore, only their agglomerates are obtained (~200 nm). In the presence of PVP, individual AgNPs (5±2 nm), AuNPs (13±5 nm), PdNPs (3±1 nm) are stabilized in the PVP shell and are bound by the matrix. The obtained nanocomposites M/CoO x H y and M@PVP/CoO x H y catalyze the reduction of p -nitrophenol with sodium borohydride in an aqueous medium. Their catalytic activity is due to MNPs; CoO x H y acts as an inert matrix.