Kirkendall effect enhanced sustained-release Fe-C composites for long-term reductive dechlorination of trichloroethylene: Interfacial reactions and slow-release degradation

Rebounding and lagging during the process of remediating contaminated sites are challenging problems. A potential solution is developing slow-release materials that could assist in the long-term remediation of contaminated sites. This study synthesised a slow-release Fe-C composite (CSBC-nZVI@beta-CD), which exhibits a synergistic effect of encapsulated layers and nanocracks, using a liquid-phase reduction method. Furthermore, the reduction and dechlorination mechanism of trichloroethene (TCE) was systematically investigated. The introduction of beta-cyclodextrin (beta-CD) intensified the Kirkendall effect, forming nano zero-valent iron (nZVI) with abundant radial nanocracks and a litchi-like appearance on the biochar surface. Additionally, beta-CD created an encapsulation layer measuring 5-7 nm on the surface of nZVI, improving its electron transport capacity and hydrophobic properties. The CSBC-nZVI@beta-CD nanocomposite successfully removed 99 % of TCE in solution within 2 h and accomplished a degradation efficiency of 98.9 % within 15 d. The synergistic effect of the beta-CD encapsulating layer and nanocracks facilitated the reactivity and electron-retarding capacity, resulting in a broad pH tolerance and anti-interference ability. Density-functional theory (DFT) calculations and experimental methods were used to study the mechanism of TCE reduction dechlorination; the unique structure of beta-CD tended to bind with Fe as well as adsorb TCE, thereby facilitating electron transfer and the enrichment of TCE at the reaction interface. In addition, the sustained-release Fe-C composites reduced the bonding energy required during the TCE degradation reaction and promoted the complete reaction of the product. Overall, CSBC-nZVI@beta CD exhibited significant potential for the long-term remediation of groundwater.