Three-dimensional photon transport in spinodal photocatalytic aerogels: how bicontinuous morphology controls kinetic rate constants

TL;DR

This study uses advanced 3D photon transport modeling to quantify how bicontinuous pore structures in photocatalytic aerogels influence light absorption and kinetic rate measurements, providing correction methods for better catalyst design.

Contribution

It introduces a GPU Monte Carlo photon transport approach combined with 3D spinodal masks to accurately quantify light distribution in photocatalytic aerogels, surpassing traditional 1D approximations.

Findings

Solid-phase receives 50% more photons than volume averages at porosity 0.70.

Photon channelling causes preferential illumination in pore channels.

Kinetic descriptors differ by 34% between Monte Carlo and diffusion models.

Abstract

Porous monolithic photocatalysts based on anatase TiO2 in silica aerogels are promising for air purification. Their bicontinuous spinodal architecture offers high surface area and strong light scattering. However, extracting intrinsic kinetic rates requires accurate optical models. Current methods replace the complex 3D pore network with a homogeneous 1D slab, an approximation whose error is unknown for spinodal geometries. We combine 3D spinodal masks from Cahn-Hilliard simulations with GPU Monte Carlo photon transport to quantify this. We introduce a solid-phase fluence estimator that accounts for catalytic site distribution, comparing it to volume averages and diffusion approximations. The solid phase receives 50% more photons than volume averages at porosity 0.70, rising to 70% at 0.90. This preferential illumination stems from quasi-ballistic paths through pore channels, termed photon channelling. The extracted kinetic descriptor differs by 34% between 3D Monte Carlo and diffusion models. Homogeneous controls show that roughly 50% of the total 73% discrepancy is intrinsic to the bicontinuous structure and cannot be fixed by effective medium theories. These results provide the first quantitative correction for kinetic extraction in such photocatalysts and establish design rules linking synthesis coarsening, pore size, and light efficiency.