Styrene Detection in Water By Polythiophene Nanoparticles Suspension
Authors: Kaluza Dawid , Magna Gabriele , Kisiel Anna , Maksymiuk Krzysztof , Michalska Agata , Paolesse Roberto , Di Natale Corrado 
Published: May 2020

Introduction

The versatility of fluorescent reporters makes them adaptable to the detection of different chemicals. [1] Most fluorescent systems work in quenching mode, namely the sensor signal consists in a reduction of the emission; less frequent is the case of sensing molecules where the fluorescence is activated by the interaction. Recently, this behavior has been demonstrated in optical fluorescent reporters made of Poly(3-octylthiophene) nanoparticles have been recently reported. [2] In this work we utilized a similar approach to detect styrene in water. Styrene is an aromatic hydrocarbon, used for the preparation of polystyrene, one of the most popular polymers, widely used in many industrial processes. Here we investigated the feasibility of Poly[3-(Ethyl-6-hexanoate)thiophene-2,5-diyl], hereinafter referred to as either polythiophene or PT, nanoparticles stabilized in aqueous medium by the presence of poly-vinyl alcohol (PVA). Actually, these nanoparticles are able to sense the presence of styrene by increasing the fluorescence emission. The sensor is enough sensitive to detect the styrene dissolved in water solution from the gaseous phase. Thus, this system can be used to measure not only styrene contamination in water, but also styrene contamination in air. This latter event threats the health of workers in several industrial processes.
Saturated styrene vapors were mixed with nitrogen by mass flow controllers and then fluxed over the water solutions, obtaining different concentrations of styrene in the liquid phase (following the Henry’s law). This latter case enables to reach low concentrations in water. Results shows a high sensitivity to styrene. The selectivity has been tested comparing the response to an alcohol (ethanol) and a chlorinated solvent (chloroform).

Experimental

Synthesis of nanoparticles was performed using typical procedure for polythiophene nanosystems [2]; 100 mL of PT solution in THF (10 mg/ mL) was added to 1 mL 1 % w/w PVA on a stirrer. The THF evaporation within 5 min was resulting in nanoparticle formation. TEM images of PT nanoparticles are reported in Figure 1.
Figure 2 shows the characterization setup. Styrene saturated vapors were diluted with nitrogen gas to achieve a desired concentration and fluxed in the headspace of PT suspended in water. Saturated vapor pressures were calculated by Antoine equation, whereas air-water coefficient partition was used to calculated the concentration in water due to the solubilization. Fluorescence changes were recorded by Shimadzu RF-1501 fluorimeter.

Results

Figure 3 shows the emission spectra of PT nanoparticles in water excited at 490 nm. Styrene in water elicits the increase of emission. A peak at 585 nm in the emission spectra is observed under styrene exposure. At concentrations in air above 40 ppm, a second peak at 620 nm is observed. The intensity at 585 nm is barely linear with the concentration in air (Figure 4). Due to the emergence of the additional peak at 620 nm, the peak at 585 becomes broader, and this behavior affects the linearity of the sensor response. A proper multicomponent analysis of spectral data provides a better estimation of the styrene concentration. The linear fit of Figure 4 returns a sensitivity of about 3 ppm-1 respect to styrene in air. The sensitivity has also been measured respect to an alcohol (ethanol) and a chlorinated solvent (chloroform). Figure 5 shows that sensitivity to styrene is about an order of magnitude larger respect to chloroform and three orders of magnitude respect to ethanol.

Acknowledgements.

“Financial support from Italy-Poland Canaletto program, project PO19MO08 is gratefully acknowledged.”

References

1. R. Paolesse, D. Monti, F. Dini, C. Di Natale, Fluorescence based sensor arrays, Topics in Current Chemistry, 300, 139-174 (2010), doi: 10.1007/128_2010_97
2. E. Woźnica, K. Maksymiuk, A. Michalska, Polyacrylate microspheres for tunable fluorimetric zinc ions sensor, Analytical chemistry 86(1), 411-418 (2013), doi: 10.1021/ac4033142

Figure 1