Assembly of PDMS/SiO2-PTFE and activated carbon fibre as a liquid water-resistant gas sorbent structure

- Superhydrophobic gas permeable membrane and activated carbon fibre (ACF) sorbent was combined.
- DMMP irreversibly sorbed in ACF under dry conditions, and reversibly under humid conditions.
- Gas permeable membrane enhanced sorption capacity of ACF for DMMP under humid conditions.

Polytetrafluoroethylene (PTFE) membrane was dip-coated with a hexane-based solution containing polydimethylsiloxane (PDMS)-coated SiO2 nanoparticles, fluidic PDMS, and curing agent as a binder for imparting superhydrophobicity to the PTFE, with water contact angle above 160°. The dip-coated PTFE membrane showed very high gas (dimethyl methylphosphonate (DMMP) and water vapours) permeability under humidity conditions of 0-32% of relative humidity and DMMP concentrations of about 1-2 ppms with a total gas flow of 15 sccm, yet completely repelled liquid water. We used the dip-coated PTFE membrane as a protective layer to prevent contact between the gas sorbent material (namely activated carbon fibre; ACF) and the liquid water. We studied the sorption behaviour of DMMP in an assembly of ACF and a protective layer under dry conditions and two different humidity conditions (16 and 32% RH). DMMP uptake was enhanced as relative humidity increased; however, in subsequent ex-situ FT-IR analysis, the intensity of the DMMP-related signal decreased with increasing humidity during the DMMP sorption experiments. Based on these results, we suggest that DMMP can mostly irreversibly chemisorb on ACF under dry conditions, but exhibits more dominantly reversible physisorption in the presence of water vapour. ACF can act as filter of DMMP under a wide range of humidity conditions, yet the DMMP uptake mechanism of ACF differs depending on the humidity of the environment. We demonstrate the potential application of our structure as a cartridge for respirator or protection garments.

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