Enhancing O₂ resistance during storage and 2, 4-dichlorophenol degradation reaction of nano zero-valent iron by in-situ formation on the partially delignified stalk

Nano zero-valent iron (NZVI) as reductants for pollutant removal is commonly studied. Nevertheless, its poor resistance to O₂ restricts its applicability, especially for polluted surface water bodies treatment. Here we proposed a method to enhance the O₂ resistance of NZVI by in-situ synthesis on a partially delignified stalk (SS/Fe). Compared to NZVI, SS/Fe did not ignite when exposed to air pulse during preparation, possessed a 56.1 % higher remaining 2, 4-dichlorophenol degradation performance after 28-day air exposure, and degraded 2, 4-dichlorophenol in the presence of O₂ with an equal efficiency to that under N₂. The characterization and DFT results indicated that the residual lignin in the stalk played a key role in controlling the structure and O₂ resistance of NZVI. Lignin in the stalk wrapped and anchored ∼ 2 nm NZVI forming a spherical particle of size 49 ± 21 nm which further aggregated forming a tertiary structure of size 790 ± 280 nm. During air exposure, the phenolic hydroxy and methoxy groups in lignin changed the reaction equilibrium among Fe⁰, Fe²⁺, and Fe³⁺ by reducing Fe³⁺ and acting as electron donors for Fe⁰ and Fe²⁺. During 2, 4-dichlorophenol degradation, the lignin wrapping resulted in superior adsorption of 2, 4-dichlorophenol on SS/Fe and a lower electron transfer path between 2, 4-dichlorophenol and SS/Fe compared with that of interaction between O₂ and SS/Fe. This work provided a feasible method to facilitate the application of NZVI in treating polluted surface water bodies.