Yolk-Shell Nanoparticles with CO2-Responsive Outer Shells for Gas- Controlled Catalysis

Yolk-shell nanoparticles (YSNPs) consisting of a gold nanoparticle core, a CO2-responsive crosslinked poly(N,N- diethylaminoethyl methacrylate) shell, and a void in between, denoted as Au@void@PDEAEMA, were synthesized, characterized, and utilized as a catalyst for the gas-controllable reduction of 4-nitrophenol (4-NP) and nitrobenzene (NB). We show that the rate of the catalytic reaction can be regulated by controlling the diffusion of reactant molecules through the polymer shell by switching the latter between a hydrophilic state upon CO2 bubbling and a hydrophobic state by bubbling N2 to remove CO2. While for the reduction of 4-NP, it is possible to turn on and turn off the reaction through alternating bubbling of the two gases, with a mixture of 4-NP and NB, the respective reactions of either reactant can be selectively favored using the gases (CO2 for the relatively faster reaction of 4-NP and N2 for the faster reaction of NB). Moreover, the gas-controlled reversible dispersion and the agglomeration state of Au@void@PDEAEMA were explored for in situ recovery of the nanoparticle catalyst and their reuse for catalytic reactions without using ultracentrifugation. Finally, the effect of structural parameters of such YSNPs on the catalytic activity was investigated by either varying the thickness of the polymer shell at the same void space or changing the void while keeping the same polymer shell thickness.