Processing of Surfactant Templated Nano-Structured Silica Films Using Compressed Carbon Dioxide as Interpreted from In Situ Fluorescence Spectroscopy

作者：Ghosh Kaustav; Rankin Stephen E; Lehmler Hans Joachim; Knutson Barbara L^*

来源：Journal of Physical Chemistry B, 2012, 116(38): 11646-11655.

DOI：10.1021/jp305113b

The local environment and dynamics of compressed carbon dioxide (CO2) penetration in surfactant templated silica film synthesis is interpreted from the in situ fluorescence emission spectra of pyrene (Py) and a modified pyrene probe. Pyrene emission in cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB) templated silica films is monitored immediately after casting and during processing with gaseous and supercritical (sc) CO2 (17-172 bar, 45 degrees C). The solvatochromic emission spectra of pyrene in CTAB templated films suggest CO2 penetration in both the micelle interface and its interior. An anchored derivative of pyrene, 1-pyrenehexadecanoic acid (C-16-pyr), is established for probing CPB films, where the pyrene moiety is preferentially oriented toward the micelle interior, thus limiting quenching by the pyridinium headgroup of CPB. CO2 processing of CPB templated silica films results in an increase in the time scale for probe mobility, suggesting an increased time scale of silica condensation through CO, processing. The mobility of C-16-pyr increases with pressure from gaseous to sc CO2 processing and persists for over 5 h for sc CO2 processing at 172 bar and 45 degrees C compared to about 25 min for the unprocessed film. The delivery of CO2 soluble solutes to specific regions of surfactant templated mesoporous materials is examined via the nonradiative energy transfer (NRET) between pyrene and CO2-solubilized naphthalene.

• 出版日期2012-9-27