Visualizing Hydrogen Peroxide Diffusion in Soils with Precipitation-Based Fluorescent Probe

Hydrogen peroxide (H₂O₂)-based advanced oxidation technology has emerged as a cost-effective and green solution for tackling soil pollution. Given the highly heterogeneous nature of soil, the effectiveness of H₂O₂ remediation is significantly influenced by its diffusion distance in soils. However, the dynamics of H₂O₂ diffusion and its effective range remain largely unexplored, primarily due to the lack of analytical methods for mapping H₂O₂ in soils. This study introduces a precipitation-based fluorescent probe (PFP) method for in situ, high-resolution (micrometer scale) mapping of H₂O₂ diffusion in soils. Using the PFP method, we visualized real-time H₂O₂ diffusion in various types of soils, revealing distinct diffusion patterns with rates ranging from 0.011 to >0.56 mm min^-1. The observed differences in diffusion rates are associated with soil permeability. Additionally, soils exhibited a wide range of diffusion distances, from 0.22 to >11 mm in 20 min. Soil's reactivity for H₂O₂ decomposition, a previously overlooked factor, is critical in determining the diffusion distance of H₂O₂. We further demonstrate that the efficacy of H₂O₂ diffusion in soils is a pivotal factor in controlling pollutant degradation and soil remediation efficiency. These findings enhance our understanding of reagent diffusion processes in soil remediation, informing the optimization of more efficient soil remediation strategies.