Enhancing the Kinetics of Self-oscillating Chemical Reactions via Catalytic Ceria Nanomats

Abstract

Chemical reactions that exhibit self-sustained oscillations show great promise for designing multifunctional materials for biomimetic applications. Belousov−Zhabotinsky (BZ) reactions are dynamical systems that operate far from equilibrium and thus serve as model systems for such applications. Catalyzed by a metal ion that undergoes rhythmic redox cycles, the solutions of BZ reactions exhibit periodic color change that corresponds to the oxidation state of the catalyst. Here, we demonstrate that by harnessing the interactions between nano-and continuum length scales, the oscillations in BZ reactions are significantly enhanced. In particular, we show that colloidal dispersions of ceria nanosheets (CeNSs) are excellent catalysts for BZ reactions, unlike nanoparticle-decorated graphene-based composites. Further, we identify the key steps of the reaction mechanism and determine the key kinetic parameters via combination of experiments and simulations. Specifically, we elucidate that the Oregonator model can be used to simulate BZ kinetics for CeNSs. We believe that through this maiden study, where bare non-graphene-based metal nanosheets have been used to catalyze oscillatory reactions, we open up new avenues to tune characteristics of dynamical systems for biomimetic applications.

Fast-Moving Self-Propelled Droplets of a Nanocatalyzed Belousov–Zhabotinsky Reaction

“…The rate equations based on the above mechanism can be written as Here, the symbols k i ( i = 1, ..., 8) represent the rate constants of the respective forward reactions –R8; the negative subscript indicates the rate of the backward reaction. To capture the effect of the nanocatalyst concentration on the BZ kinetics, we assume that the catalyst affects step R5 only ,, and that no side/additional reactions take place in its presence. Thus, the rate constant in step R5 signifies the apparent rate constant ,, given as k 5 = k 50 [C] α e – E a / RT , where k 50 is the concentration/temperature-independent pre-exponential factor, E a is the activation energy of the nanocatalyst (Ru-GO, Ru-rGO, Ru-graphene), [C] is the concentration of Ru in the nanocatalyst, α is the order of the reaction, R is the gas constant, and T is the temperature.…”

“…To capture the effect of the nanocatalyst concentration on the BZ kinetics, we assume that the catalyst affects step R5 only ,, and that no side/additional reactions take place in its presence. Thus, the rate constant in step R5 signifies the apparent rate constant ,, given as k 5 = k 50 [C] α e – E a / RT , where k 50 is the concentration/temperature-independent pre-exponential factor, E a is the activation energy of the nanocatalyst (Ru-GO, Ru-rGO, Ru-graphene), [C] is the concentration of Ru in the nanocatalyst, α is the order of the reaction, R is the gas constant, and T is the temperature. Here, however, as the experiments are performed at a fixed concentration of nanocatalysts under isothermal conditions, the value of k 5 for Ru-GO, Ru-rGO, and Ru-graphene is used directly …”

“…In the absence of MO, the value of the rate constant in step R8-1 is taken as k 8 = 2.0 × 10 –2 s –1 . For the traditional solution-based catalyst, the value of k 5 = 1.18 M –1 s –1 , whereas the value of k 5 is taken as 2.0, 4.0, and 13.0 M –1 s –1 for Ru-GO, Ru-rGO, and Ru-graphene nanocatalysts, respectively.…”