The use of chemical dispersants is a well-established approach to oil spill remediation where surfactants in an appropriate solvent are contacted with the oil to reduce the oil–water interfacial tension and create small oil droplets capable of being sustained in the water column. Dispersant formulations typically include organic solvents, and to minimize environmental impacts of dispersant use and avoid surfactant wastage it is beneficial to use water-based systems and target the oil–water interface. The approach here involves the tubular clay minerals known as halloysite nanotubes (HNTs) that serve as nanosized reservoir for surfactants. Such particles generate Pickering emulsions with oil, and the release of surfactant reduces the interfacial tension to extremely low values allowing small droplets to be formed that are colloidally stable in the water column. We report new findings on engineering the surfactant-loaded halloysite nanotubes to be stimuli responsive such that the release of surfactant is triggered by contact with oil. This is achieved by forming a thin coating of wax to stopper the nanotubes to prevent the premature release of surfactant. Surfactant release only occurs when the wax dissolves upon contact with oil. The system thus represents an environmentally benign approach where the wax coated HNTs are dispersed in an aqueous solvent and delivered to an oil spill whereupon they release surfactant to the oil–water interface upon contact with oil.

This work develops the concepts of particle-stabilized emulsions using tubular natural clays known as halloysites to attach to the oil–water interface and stabilize oil-in-water emulsions. Such halloysite nanotubes (HNT) serve as reservoirs for surfactants and can deliver surfactants to the oil–water interface and thus lower the oil–water interfacial tension. This two-step concept of surfactant delivery and droplet stabilization by particles has significant implications to oil spill remediation. However, to deliver surfactant loaded HNTs in a water-based solvent slurry, it is important to stopper the nanotubes to prevent premature release of the surfactant. This work focuses on the use of an environmentally benign two-dimensional metal–organic framework formed by coordinating Fe­(III) with a polyphenolic as a stoppering agent. Such metal–phenolic networks (MPN) form a skin around the HNTs, thus providing a way to effectively sequester surfactant cargo for controlled release. Cryo-scanning electron microscopy (Cryo-SEM) shows that these HNTs and HNT bundles attach to the oil–water interface with side-on orientation. Inverted drop tensiometry was used to characterize the dynamic interfacial tension resulting from the release of a model surfactant (Tween 80) from the HNTs and indicates that the MPN stoppers are effective in sequestering the surfactant cargo for extended periods at neutral pH values. Release triggered by MPN disassembly at acidic pH values can be performed just prior to delivery to oil spills. The concepts and scalability of this process have significant implications for oil spill remediation, enhanced oil recovery, and biomedical and pharmaceutical applications.