Martin Hollamby - New Applications in CO₂ Dispersions

PhD, October 2005 -

Martin carried out his undergraduate degree in this department, working for Paul Bartlett in his final year. His project mainly involves the synthesis of nanoparticles in condensed CO₂ and is sponsored by Kodak.

The environmental threat posed by waste industrial solvent is well documented. In 2003 it was estimated that over 350,000 tonnes of volatile organic compounds, 34% of the total amount were generated from solvent usage. This problem has motivated the scientific world to research possible alternative "greener" solvents. One alternative is supercritical CO₂ being cheap, tuneable, non-toxic, inert, non-flammable, recyclable and environmentally benign. Unfortunately CO₂ alone is a poor solvent for most chemicals; surface active species are required to boost solubility [1], thus it is not usually possible to directly substitute it for conventional solvents. Suitable industrial applications must be found.

One such application could be a catalytic system, consisting of a surfactant stabilised nanoparticle solution. The possibilities extending from such a system are wide; it would offer 100% catalyst recovery (by merely lowering CO₂ pressure), plus the solvent properties could also be tailored for higher efficiency by careful adjustment of temperature and pressure. The catalytic material employed in such a system could be synthesised in microemulsions, a technique which yields surfactant coated nanoparticles [2].

The choice of surfactant however is less obvious. Current technology presents no clear hydrocarbon surfactant candidate to stabilise the particles in CO₂, although ongoing work in the Eastoe group looks promising [3]. Thus in this project we have turned back to fluorinated surfactants, in particular fluorinated AOT analogues DiHCF4 and DiCF4, which have been found to stabilise water-in-CO₂ [3] and water-in-fluorocarbon microemulsions [4] at high pressure. We hope to find firstly a stable "fluorinated microemulsion" (water/f-surfactant/f-carbon) at ambient temperature, pressure. After this stage we will attempt to employ this microemulsion to synthesise nanoparticles and attempt to re-disperse them in CO₂.

DiHCF4	DiCF4

[1] J Eastoe, S Gold Phys. Chem. Chem. Phys. 7 (2005) 1352

[2] Review paper - Recent Advances in Nanoparticle Synthesis in Reversed Micelles - yet to be published

[3] J Eastoe et al, Phys. Chem. Chem. Phys. 2 (2000) 5235

[4] Steytler et al, Langmuir, 19 (2003) 8715