Fluorocarbon and hydrocarbon functional group incorporation into nanoporous silica employing fluorinated and hydrocarbon surfactants as templates

Abstract

Ordered mesoporous hydrocarbon functionalized ( n-decyl) silica samples are synthesized by the ‘one-pot’ (direct) synthesis method using two cationic fluorinated surfactants, C 6F 13C 2H 2NC 5H 5Cl (HFOPC) and C 8F 17C 2H 2NC 5H 5Cl (HFDePC), and a typical hydrocarbon surfactant, C 16H 33N(CH 3) 3Br (CTAB), as templates. The properties of the materials are compared to those of silica samples functionalized with a fluorocarbon functional group, heptadecafluoro-1,1,2,2-tetrahydro-decyl, whose fluorocarbon separating ability was reported earlier [33]. The pore characteristics, organic loading, and wetting properties of the resulting materials are determined for the following combinations of surfactant/functional groups: hydrocarbon/hydrocarbon, hydrocarbon/fluorocarbon, fluorocarbon/hydrocarbon and fluorocarbon/fluorocarbon. Synthesis using the longer chain fluoro-surfactant (HFDePC) template results in the highest incorporation of both n-decyl and fluorocarbon functional groups, with a corresponding loss of long-range pore order in the fluorinated material. Materials synthesized using the HFOPC template have very low levels of functional group incorporation compared to the HFDePC-templated materials. CTAB-templated materials display greater long-range pore order than the fluorocarbon templated materials. The incorporation of the fluorocarbon functional precursor is more effective (on a % yield basis) than the hydrocarbon functional precursor for silica materials synthesized using CTAB. Similarly, the use of fluorinated surfactant templates enhances fluorocarbon incorporation relative to hydrocarbon incorporation in the mesoporous material. Solubility of the precursors ( n-decyltriethoxysilane and heptadecafluoro-1,1,2,2-tetrahydro-decyltriethoxysilane) in the synthesis medium and favorable aggregation behavior of the alkane/fluoroalkane functional groups with the surfactant micelles improves the incorporation of the functional group.