Two-step one-pot electrosynthesis and catalytic activity of xCoO–yCo(OH)2-supported silver nanoparticles

Abstract

Efficient two-step electrosynthesis of xCoO–yCo(OH)2 (CoOxHy)-supported silver nanoparticles (AgNPs) is carried out in N,N-dimethylformamide (DMF) using atmospheric oxygen as a reagent and mediator at the potentials of its reduction to the superoxide ion. In the first step, the reduction of oxygen in the presence of Co (II) ions added to the solution as a salt or generated upon dissolution of a Co anode by means of electrolysis results in a mixture of amorphous cobalt oxide CoO and its hydrated form Co (OH)2. The addition of Ag+ ions to the resulting solution of CoOxHy by similar methods results in two parallel reactions of Ag+ reduction to give AgNPs: reversible reduction by CoO and irreversible reduction by DMF. In the second step, oxygen-mediated electroreduction of CoO+ and residual quantities of Ag+ occurs, as well as regeneration of CoOxHy. The resulting spherical AgNPs are bound and stabilized by the CoOxHy matrix. Both steps occur quantitatively and consume the theoretical amount of electricity (2 F with respect to Co2+ in the first step and 1 F with respect to Ag+ in the second step). Depending on the production method, the size of the AgNPs varies in a range from 7±2 to 27±10 nm. The Ag/CoOxHy nanocomposites obtained exhibit catalytic activity in the p-nitrophenol reduction with sodium borohydride in an aqueous medium. Their activity caused by AgNPs significantly increases in the presence of cetyltrimethylammonium chloride (CTAC), a micelle-forming cationic surfactant.