Researchers assessed various structures of clay nanotubes or halloysites, which are being studied for their potential in oil spill emulsification. They tested the nanotubes to identify which structures generated the most stable emulsions and smallest oil droplets and if catalytic reactions improved at the oil-water interface. The team found that nanotubes between .4 and 1.5 micrometers length and .05 micrometers diameter, combined with increased surface hydrophobicity through salinization, yielded the most stable oil droplets of 3 – 5 micrometers diameter. Halloysites improved interfacial catalytic reaction products in terms of yield, selectivity, and separation compared to spherical nanoparticles. Halloysite concentrations up to ~2.5 mg mL-1 did not significantly reduce the enzymatic activity or growth of alkane-degrading A. borkumensis bacteria. The researchers published their findings in Advanced Materials Interfaces: Halloysites Stabilized Emulsions for Hydroformylation of Long Chain Olefins.
Pickering emulsions take place when nano or microparticles accumulate on a droplet’s surface and stabilize it against coalescence. Previous research found that halloysite clay nanotubes loaded with surfactant present an efficient, low-cost, and environmentally friendly method for creating Pickering emulsions of oil and water. This study investigated the nanotubes’ optimal structure and interactions with bacteria, which are still under investigation.
“This tubule clay has soap-like properties and may work similar to detergent dispersant for converting large spilled oil spots into tiny droplets,” said study co-author Yuri Lvov. “We optimized the halloysite clay nanotube structures for more efficient oil dispersion in salty seawater and reached very small (10 – 20 micrometers) droplet diameters, which will be better consumed by oil-eating bacteria, which is also characterized in this paper.”
Researchers prepared halloysite nanotubes of different lengths and degrees of hydrophobia and applied varying concentrations to Louisiana sweet petroleum or pure dodecene (an alkene of 12 carbon atoms ending with a double bond, which makes it useful for various applications). Trials assessing the safety of halloysite nanotubes exposed A. borkumensis bacteria to varying amounts of nanotube concentrations and observed their resulting enzymatic and physiological activity using colorimetric assays.
The cylindrical elongated particles had five-times higher droplet surface detachment energy than the same mass of spherical particles. The halloysite tubes oriented laterally at the surface of droplets, explaining the large resistance against coalescence. The oil-in-water emulsions allowed the Rhodium-based catalyst compound to efficiently convert dodecene to tridecanal (base chemical used for polymer or solvent products). This strategy proved more efficient than trials using spherical particles (silica), and the researchers noted that filling the nanotubes with reaction-enhancing chemicals could further improve the results of interfacial reactions.
The results obtained on oil emulsification and halloysite safety suggest further technology extension for oil spill remediation. Pickering emulsification can proceed with low energies similar to ocean turbulence, stability of droplets may extend to more than a week, and the oil-water interface is roughened, which helps bacteria proliferation.
Data are publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC) at doi:10.7266/N73X8533.
The study’s authors are Regine von Klitzing, Dimitrij Stehl, Tobias Pogrzeba, Reinhard Schomacker, Renata Minullina, Abhishek Panchal, Svetlana Konnova, Rawil Fakhrullin, Joachim Koetz, Helmuth Mohwald, and Yuri Lvov.
This research was made possible in part by a grant from the Gulf of Mexico Research Initiative (GoMRI) to Louisiana Tech University’s Institute for Micromanufacturing and Department of Chemical Engineering for their project The Design of Synergistic Dispersant and Herding Systems using Tubular Clay Structures and Gel Phase Materials. Other funding sources included the Collaborative Research Center “Integrated Chemical Processes in Liquid Multiphase Systems” supported by the Deutsche Forschungsgemeinschaft (DFG-TRR 63, TP A2 and B6) and the Russian Science Foundation (Grant No. 14-14-00924).
The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. An independent and academic 20-member Research Board makes the funding and research direction decisions to ensure the intellectual quality, effectiveness and academic independence of the GoMRI research. All research data, findings and publications will be made publicly available. The program was established through a $500 million financial commitment from BP. For more information, visit http://gulfresearchinitiative.org/.
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