Lignin-Enhanced Biofoam for Gravity-Resistant Detoxification in Urban Environments

Conventional decontamination methods used in urban warfare or terrorist scenarios typically rely on liquid solvents because of their high decontamination efficiency. Nevertheless, gravity causes the liquids to rapidly run off vertical surfaces and ceilings, resulting in short residence times and reduced decontamination efficacy. To address this limitation, viscosity modifiers have been used to improve the retention of decontamination agents. However, highly viscous formulations typically suffer from poor sprayability and are difficult to rinse off, complicating both application and postuse cleanup. Herein, we present a gravity-resistant, fast-acting biofoam enhanced with hydroxyl-rich depolymerized lignin (HDL) derivatives, a sustainable and biodegradable material. HDL was synthesized via hydrothermal treatment, which yielded an 11-fold increase in hydroxyl group content relative to that of native lignin. This increase significantly improved water retention and foam stability. The resulting hydroxyl-rich depolymerized lignin foam (HDLF) adhered to vertical urban surfaces for over 10 min, allowing sufficient contact time for detoxification despite its low viscosity. Foam stability was further enhanced by hydrogen bonding among the hydroxyl groups in HDL. Specifically, HDLF achieved over 90% detoxification efficiency through the hydrolytic degradation of chemical warfare agents and exhibited an environmentally safe end-of-life. Furthermore, it was easily removed from the wall surface, demonstrating that it can overcome the limitations of conventional viscosity-modifier-based decontaminants. This study introduces a high-performance, ecologically compatible formulation for urban detoxification.