Fabrication of size-controlled Co nanoparticles via mediation of H-adatoms on pyridine-like nitrogen of carbon nitride nanotubes and their superior catalytic performance for hydrogen generation

Abstract

We report a new route to fabricate size-controlled Co nanoparticles (NPs) on carbon nitride nanotubes (CNNTs). The size of the Co nanoparticles is controlled down to 2 nm. Our density functional theory calculations provide the clue for the formation mechanism of these size-controllable Co NPs in the presence of sodium hypophosphite, water, Co(2+) ions and OH(-) ions on the pyridine-like nitrogen of CNNTs. First, two H-adatoms from water are bonded onto the pyridine-like nitrogen while sodium hypophosphite is bonded with the oxygen of water. Next, the reduction of Co(2+) ions occurs via combination with two electrons donated from these two H-adatoms. The Co NPs-CNNT fabricated via this method shows the highest hydrogen generation rate of 19.6 kg h(-1) per kg of catalyst from aqueous metal hydride solution. This superior catalytic activity (about 82 times higher than that for the Co powder in the bulk state) is attributed to the increased surface area, as well as the approx. 1.5 times larger number of Co nanoparticle catalysts with about 2 nm sizes formed via mediation of the two H-adatoms bonded to the pyridine-like nitrogen.