05. Micro- and Nano-Scale Transport, MEMS

Polyacrylamide (PAM) hydrogels loaded with the photocatalyst ZnIn2S4 (ZIS) are promising for photocatalytic hydrogen production. However, there is a lack of microscopic studies comparing the distribution and transport of water in the network structure of hydrogels with or without the loading of photocatalysts. In this study, the distribution of bound, intermediate and free water in hydrogels without photocatalysts as well as in hydrogels loaded with photocatalysts were probed using molecular dynamics (MD) and their diffusion coefficients were calculated. The water diffusion inside the hydrogels was improved with increasing water content. With the addition of ZIS, the ductility of the polymer was enhanced, which increased the hydrophilicity of the hydrogel. This leads to an increase in the content of bound water in the hydrogel and slower diffusion of water. In addition, more water existed in the form of free water as ZIS occupied a certain space near the PAM, which hindered the formation of the intermediate water layer. The analysis of water distribution on the surface of the photocatalyst revealed that the density of water molecules was higher in the vicinity of the In atoms. Most of these water molecules were bound water at low water content. With the increase of water content, more free water appeared near the In atoms. These findings help to deepen the understanding of the effect of photocatalysts on the distribution and transport of water molecules in hydrogels, and provide an important reference for the design of more efficient photocatalytic hydrogen-producing materials.