Black wattle tannin nanoparticles as recyclable, efficient polyphenol-based emulsifiers for enhanced oil recovery

Chemical flooding is a widely employed enhanced oil recovery (EOR) technique, but conventional agents such as surfactants and polymers face significant limitations, including poor thermal and salinity tolerance, environmental concerns, and high costs. Herein, we report a sustainable Pickering emulsifier system based on black wattle tannin nanoparticles (BWTNPs) prepared via a simple nanoprecipitation method. These polyphenol-derived nanoparticles exhibit strong interfacial activity, significantly reducing oil-water interfacial tension and forming stable oil-in-water emulsions across a broad concentration range. The emulsions remain stable under harsh reservoir conditions (60 °C, high salinity) and exhibit reversible pH-responsive demulsification behavior, enabling efficient oil-water separation and nanoparticle recyclability. Simulated flooding experiments confirm that BWTNP-stabilized emulsions substantially enhance oil recovery efficiency compared to water flooding (77.5% vs. 50%). Leveraging renewable plant-derived materials, this work offers a green, recyclable, and effective emulsification strategy for next-generation chemical EOR technologies.