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Multiscale modelling of stimuli-responsive nanoreactors

Periodic Reporting for period 4 - NANOREACTOR (Multiscale modelling of stimuli-responsive nanoreactors)

Reporting period: 2020-02-01 to 2020-07-31

The catalysis by metal nanoparticles is one of the fastest growing areas in nanoscience due to our society's exploding need for fuels, drugs, and environmental remediation. However, the optimal control of catalytic activity and selectivity remains one of the grand challenges in the 21st century. This project 'Nanoreactor' aimed to theoretically and numerically derive design rules for the optimization of nanoparticle catalysis by nanoreactors constituted of thermosensitive yolk-shell carrier systems. In the latter, the nanoparticle is stabilized in solution by an encapsulating, thermosensitive hydrogel shell. Responsive nanoreactors permit catalytic reaction to be switched and tuned, e.g. by the temperature or the pH. The novel hybrid character of these emerging 'nanoreactors' opens up unprecedented ways for the control of nanocatalysis due to new designable degrees of freedom. The complex mechanisms behind stimuli-responsive nanocatalysis were here addressed by a concerted, interdisciplinary modelling approach, based on multiscale computer simulations of solvated polymers and the statistical and continuum mechanics of soft matter structures and dynamics. We aimed to integrate the molecular solvation effects and our growing knowledge of hydrogel mechanics and thermodynamics into advanced reaction-diffusion equations for a quantitative rate prediction. One key objective was to derive predictive theories for reactant transport through the polymer shell, that is, the hydrogel permeability and include those in useful rate equations to describe the experiments. The expected results and design principles shall help experimentalists to synthesize tailor-made, superior nanocatalysts for the increasing demand of our society for energy materials, fine chemicals and enviromental remediation.
In summary, as main results we have achieved unprecedented microscopic insights how important molecules (reactants) permeate responsive and selective hydrogels for a wide range of conditions and therefore could formulate analytical equations as input for macroscopic rate laws. In particular, our study on the partitioning of charged reactants in hydrogels provides a completely new view on how complex ions and salt penetrate polymer membranes. We have in addition formulated novel macroscopic rate laws for catalyzed bimolecular reactions that consider the action of the responsive, switchable hydrogel and its permeability for various, application-relevant nanoreactor geometries (core-shell, yolk-shell, multi-sink) and catalyzed processes (unimolecular, bimolecular, photogenerated-bimolecular). These results and design principles will help experimentalists and engineers to synthesize tailor-made, superior nanocatalysts, e.g. for the production of green energy. So far the results were disseminated on over 20 conferences/workshops and published in more than 30 peer-reviewed publications.
The main progress beyond the state-of-the art can be separated into 2 parts: 1) we have achieved unprecedented microscopic insights how important molecules (reactants) permeate responsive hydrogels and could formulate analytical scaling laws as input for macroscopic rate laws. 2) we have formulated novel macroscopic rate laws that consider the action of the responsive hydrogel and its permeability for various, application-relevant nanoreactor geometries (core-shell, yolk-shell, multi-sink) and catalyzed processes (unimolecular, bimolecular, photogenerated-bimolecular).
Multi-scale modeling of stimuli-responsive nanoreactors