Catalyzed bimolecular reactions in responsive nanoreactors

TL;DR

This paper develops a comprehensive theory for surface-catalyzed bimolecular reactions within stimuli-responsive nanoreactors, revealing how shell permeability influences reaction rates and reactant limiting behavior, supported by experimental data analysis.

Contribution

It introduces a unified mathematical framework for bimolecular reactions in nanoreactors with gating shells, highlighting the role of permeability and coupling of reactant fluxes, which was not previously understood.

Findings

Reaction rates depend on shell permeability, not just bulk concentrations.

Diffusional fluxes of reactants are strongly coupled in nanoreactors.

Experimental data on hydrogel nanoreactors supports the theory.

Abstract

We describe a general theory for surface-catalyzed bimolecular reactions in responsive nanoreactors, catalytically active nanoparticles coated by a stimuli-responsive 'gating' shell, whose permeability controls the activity of the process. We address two archetypal scenarios encountered in this system: The first, where two species diffusing from a bulk solution react at the catalyst's surface; the second where only one of the reactants diffuses from the bulk while the other one is produced at the nanoparticle surface, e.g., by light conversion. We find that in both scenarios the total catalytic rate has the same mathematical structure, once diffusion rates are properly redefined. Moreover, the diffusional fluxes of the different reactants are strongly coupled, providing a richer behavior than that arising in unimolecular reactions. We also show that in stark contrast to bulk reactions, the identification of a limiting reactant is not simply determined by the relative bulk concentrations but controlled by the nanoreactor shell permeability. Finally, we describe an application of our theory by analyzing experimental data on the reaction between hexacyanoferrate (III) and borohydride ions in responsive hydrogel-based core-shell nanoreactors.