Stoppers and Skins on Clay Nanotubes Help Stabilize Oil-in-Water Emulsions and Modulate the Release of Encapsulated Surfactants

Abstract

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.

Halloysite nanotubes filled with salicylic acid and sodium diclofenac: effects of vacuum pumping on loading and release properties

“…In general, electrostatic interactions are convenient to target the interaction/adsorption site for halloysite nanotubes [35][36][37][38]. Most interestingly, halloysite nanotubes can be loaded with negatively charged active species, such as biological molecules, anti-corrosion compounds and antioxidants that can be protected inside the inner lumen of the nanotubes [39][40][41]. This one is a very important property, which endows the preparation of new smart nanocontainers for loading, storage and sustained release of chemical agents [42][43][44][45].…”

Manipulation of the halloysite clay nanotube lumen for environmental remediation: a review

“…Vijay John's group has conducted some research on the sustained release of a dispersant by the halloysite lumen for oil spill remediation. 147,[163][164][165][166][167] In their latest research work, 147 the dispersant (i.e., surfactant Tween 80) was loaded and stored inside the halloysite lumen by vacuum impregnation, then wax formed a skin around the dispersant-loaded halloysite nanotubes, thus providing a way to effectively sequester the dispersant cargo for controlled release (Fig. 10a).…”

Integrating Halloysite Nanostraws in Porous Catalyst Supports to Enhance Molecular Transport

“… 14 , 15 The lumen can be used to load a variety of compounds including drugs and surfactants. 16 − 18 Of key importance is the lumen diameter of 15–30 nm, which is significantly higher than the 2–4 nm pore size of MCM-41. Thus, HNTs when inserted into particles of MCM-41 would allow easier access of molecules that approach the size of the pores of MCM-41.…”