Stable and Responsive Fluorescent Carbon Nanotube Silica Gels
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1258-R12-07
Stable and Responsive Fluorescent Carbon Nanotube Silica Gels Gautam Gupta1,¥, Juan G. Duque2,¥, Stephen K. Doorn1, and Andrew M. Dattelbaum1 1
Center for Integrated Nanotechnologies, MS K771, Los Alamos National Laboratory, Los Alamos, NM 87545 2 ¥
Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545 Authors contributed equally to work
ABSTRACT Here we report a general route to prepare silica nanocomposite gels doped with fluorescent single walled carbon nanotubes (SWNT). We show that tetramethylorthosilicate (TMOS) vapors can be used to gel an aqueous suspension of surfactant-wrapped SWNT while maintaining fluorescence from the semiconducting nanotubes. The vapor phase silica process is performed at room temperature and is simple, reproducible, relatively quick, and requires no dilution of SWNT dispersions. However, exposure of aqueous SWNT suspensions to TMOS vapors resulted in an acidification of the suspension prior to gelation that caused a decrease in the emission signal from sodium dodecylsulfate (SDS) wrapped SWNT. We also show that although the SWNT are encapsulated in silica the emission signal from the encapsulated SWNT may be attenuated by exposing the nanocomposites to small aromatic molecules known to mitigate SWNT emission. These results demonstrate a new route for the preparation of highly luminescent SWNT/silica composite materials that are potentially useful for future sensing applications. INTRODUCTION Single walled carbon nanotubes (SWNT) possess unique mechanical, electrical and luminescence properties due to their nanoscale structure based on a cylindrical sheet of graphene. (1-3) As such, carbon nanotubes show a promising future in the fields of sensing, optics, nanotechnology, electronics, and materials science. Recently, we have been particularly focused on exploiting the near-infrared (NIR) emission signal arising from isolated semiconducting SWNT for sensing applications.(4, 5) Isolation of SWNT can be readily accomplished by suspending SWNT in aqueous solution via addition of surfactants.(6, 7) In order to fully harness the unique NIR properties of SWNT, there is a need to develop nanocomposites that readily incorporate isolated nanotubes. Silica is an ideal material for encapsulation of fluorescent SWNT, as it is generally inert, optically transparent, and permeable.(5) Here we used a vapor diffusion method to prepare silica nanocomposites containing fluorescent SDS-wrapped SWNT. The SWNT/silica nanocomposites prepared in this way retain over 50% of the initial emission signal intensity observed from SWNT prior to encapsulation. In addition, the SWNT luminescence signal was shown to be sensitive to the addition of small aromatic compounds, which demonstrates the possibility of future sensing applications with these materials.
EXPERIMENTAL SWNT were synthesized by high-pressure decomposition of carbon monoxide (HiPco).(6, 8) The SWNT dispersion (10 mg/l) was prepared at 1 wt% sodium dodecylsulfate (SDS) in D2O using standard suspension procedures.(7)
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