Interfacial Unlocking by Functionalized Artificial Humic Acid Enables Sustainable Low-Temperature Pyrolytic Remediation of Petroleum-Contaminated Soil.

Pyrolytic remediation of petroleum-contaminated soil (PCS) often requires high temperatures, which increase energy demand, limit resource recovery, and impair post-treatment soil functionality. This high-temperature dependence reflects not only the cracking resistance of heavy hydrocarbons, but also strong oil-soil interfacial locking that restricts their release and conversion. Here, we tested whether targeted interfacial regulation could lower remediation severity in PCS by using functionalized artificial humic acid (FAHA) as an interface-active mediator. Potassium citrate and lignin directed the molecular evolution of artificial humic acid, while Fe complexation introduced additional reactivity during pyrolysis. Under optimal conditions, FAHA2 at 0.5 wt % lowered the remediation threshold from 480 to 390 °C. Multiscale analyses suggested that FAHA reorganized the oil-mineral interface, weakened direct mineral-petroleum interactions, and facilitated lower-temperature release of interfacially constrained petroleum fractions. During pyrolysis, FAHA-bound Fe likely evolved from Fe-S-associated with Fe-O-rich coordination environments that could further facilitate hydrocarbon conversion. Compared with direct high-temperature pyrolysis, the FAHA-assisted pathway better preserved soil functionality and showed a lower estimated gross process-carbon burden under the defined accounting boundary. These results highlight sequential interfacial-thermochemical coupling as a design principle for more sustainable remediation of interface-dominated contaminated matrices.