Closed-loop photothermal extraction and catalytic degradation for remediation of phenol-contaminated soil

Solar-driven photothermal evaporation has emerged as a low-carbon, energy-efficient approach for environmental remediation, but its application to volatile organic contaminants in soils remains challenged by rapid volatilization and limited mass transfer within soil matrices. Here, we present a biochar-supported NiO/TiO₂/polyvinyl alcohol/gelatin evaporator (BNT-H) that integrates evaporation-driven extraction with interfacial catalytic degradation for in situ phenol removal from soil. Under 1 kW m⁻² irradiation, BNT-H achieved an evaporation rate of 2.45 kg m⁻² h⁻¹. By controlling light intensity in a closed system, phenol was continuously transported to the photocatalytically active interface, where it was catalytically degraded. Volatile compounds not fully degraded were condensed and returned to the soil, re-entering the evaporation-catalysis cycle. This closed-loop process of evaporation, condensation, and reprocessing effectively minimized uncontrolled VOC emissions. Outdoor experiments demonstrated that the BNT-H system removed over 99% of phenol from soil with an initial concentration of 17.0 mg kg⁻¹ within seven days. Wheat germination in the remediated soil reached 97%, indicating substantial alleviation of phenol-induced phytotoxicity. Overall, this work presents a low-carbon strategy that shows potential for scale-up in VOC-contaminated soil remediation and provides mechanistic insights into coupling photothermal evaporation with interfacial catalysis for pollutant control.