Nanoporous Silica-Dye Microspheres for Enhanced Colorimetric Detection of Cyclohexanone

Zheng Li

doi:10.3390/chemosensors6030034

Abstract

Forensic detection of non-volatile nitro explosives poses a difficult analytical challenge. A colorimetric sensor comprising of ultrasonically prepared silica-dye microspheres was developed for the sensitive gas detection of cyclohexanone, a volatile marker of explosives 1,3,5-trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). The silica-dye composites were synthesized from the hydrolysis of ultrasonically sprayed organosiloxanes under mild heating conditions (150 °C), which yielded microspherical, nanoporous structures with high surface area (~300 m2/g) for gas exposure. The sensor inks were deposited on cellulose paper and given sensitive colorimetric responses to trace the amount of cyclohexanone vapors even at sub-ppm levels, with a detection limit down to ~150 ppb. The sensor showed high chemical specificity towards cyclohexanone against humidity and other classes of common solvents, including ethanol, acetonitrile, ether, ethyl acetate, and ammonia. Paper-based colorimetric sensors with hierarchical nanostructures could represent an alternative sensing material for practical applications in the detection of explosives.

Highlights

Today, there still remains a difficult scientific challenge in the accurate detection and identification of explosives and chemical or biological agents at trace amounts [1]
The resulting aerosol was carried by an N2 gas through a tube furnace at a mild heating temperature of 150–300 ◦ C to ensure the optimal porosity of the microspheres; the N2 gas flow was set at 1.0 SLPM
A new method that encapsulates a chemo-responsive dye in highly porous organosilica matrices was reported for sensitive colorimetric detection of trace amounts of cyclohexanone, a volatile explosive indicator from nitro-compounds, such as RDX and HMX

Summary

Introduction

There still remains a difficult scientific challenge in the accurate detection and identification of explosives and chemical or biological agents at trace amounts [1]. It is rather difficult to detect either RDX or HMX in the gas phase due to its extremely low volatility, with a saturated vapor pressure of only 10 ppt at ambient conditions. An alternative approach for the indirect identification of nitro explosives is to target more volatile, but non-energetic, species, introduced during their manufacturing, e.g., cyclohexanone, a common solvent used for the recrystallization of RDX or HMX [5,6]. Cyclohexanone has a significantly high vapor pressure of ~6500 ppm at 20 ◦ C, it is well-suited to act as a vapor signature for explosive sensing

Methods

Results

Conclusion