Radiolysis of water confined in porous silica: A simulation study of the physicochemical yields

TL;DR

This study uses Monte Carlo simulations to analyze how water confined in porous silica affects the initial chemical yields during radiolysis, highlighting the influence of pore size and electronic properties on radical distribution and electron yields.

Contribution

It provides new insights into the physicochemical effects of water confinement in silica pores on radiolytic yields, emphasizing the role of electronic band alignment.

Findings

Enhanced solvated electron yields for pore radii ≤ 100 nm

Radicals become spatially isolated in smaller pores

The conduction band edge position significantly influences radiolysis outcomes

Abstract

We investigate the radiolysis of liquid water confined in a porous silica matrix by means of an event-by-event Monte Carlo simulation of electron penetration in this composite system. We focus on the physical and physicochemical effects that take place in the picosecond range, before the radicals start to diffuse and react. We determine the radiolytic yields of the primary species for a system made of cylindrical pores filled with water over a wide range of pore radii $R_{\rm C}$. We show that the relative position of the conduction band edge $V_0$ in both materials plays a major role in the radiolysis of composite systems. Due to its lower $V_0$ as compared to that of silica, water acts as a collector of low-energy electrons, which leads to a huge enhancement of the solvated electron yields for $R_{\rm C} \leq$ 100 nm. The confinement has also a marked effect on the spatial distribution of the radicals, which become isolated in a very large number of pores as $R_{\rm C}$ decreases.