Abstract
Volatile organic compounds (VOCs) are one of the most commonly detected contaminants in water. The occurrence is mainly in gasoline and other petroleum-based products, fumigants, paints and plastics. Releases into the environment and the widespread use have an impact on the ecosystem such as humans and animals due to their toxicity, mutagenicity, and carcinogenicity. VOCs may persist in groundwater and may enter drinking water supplies. In this paper, a diamond-like carbon (DLC)-coated silicon waveguide in combination with a polymer film (ethylene/propylene copolymer, E/P-co) for enrichment of analytes was investigated to determine its suitability for ATR-FTIR (attenuated total reflection Fourier transform infrared) spectroscopic detection of VOCs. The DLC film was fluorine-terminated enhancing the adhesion of the hydrophobic polymer to the waveguide surface. The analytes diffuse into the hydrophobic polymer whereas water is excluded from the emanating evanescent field. Therefore, direct detection in aqueous systems is enabled. Nine VOCs, i.e., ethylbenzene (EB), trichloroethylene (TCE), tetrachloroethylene (TeCE), the xylene isomers (p-xylene, pXYL; m-xylene, mXYL; o-xylene, oXYL), naphthalene (NAPH), toluene (TOL), and benzene (BENZ), were evaluated simultaneously qualitatively and quantitatively showing the potential of DLC coatings revealing high sensitivities in the low ppb to ppm concentration range, i.e., 50 ppb for TeCE. To the best of our knowledge, this is the first time of IR spectroscopic detection of VOCs in aqueous solutions using DLC-coated waveguides in combination with a hydrophobic polymer. By utilizing a DLC-coated waveguide, a versatile sensor for real-time monitoring in harsh environments such as effluents, leaking pipelines, and underground storage tanks is feasible due to response times within a few minutes.
Highlights
Volatile organic compounds (VOCs) are contained in gasoline, diesel fuel and various petroleum-based products and originate from industrial effluents, sewage disposal, oil storage wastes, and oil tanker accidents
The cleaned Si wafers were treated with a pulsed filtered cathodic arc deposition with a high-purity graphite cathode in a deposition chamber obtaining a diamond-like carbon (DLC) layer with a thickness of 30 nm
At the end of the DLC deposition step, SF6 was induced into the deposition chamber for surface termination of the DLC revealing a highly hydrophobic surface (F:a-C)
Summary
Volatile organic compounds (VOCs) are contained in gasoline, diesel fuel and various petroleum-based products and originate from industrial effluents, sewage disposal, oil storage wastes, and oil tanker accidents. Due to their production and widespread use, VOCs are one of the most commonly detected organic pollutants in water. Monitoring of pollutants, VOCs, in global waters including seawater, river and lake water, ground, surface and drinking water is important to maintain public health and protect the environment. The most commonly analytical techniques for detection of VOCs are chromatographic methods, i.e., gas chromatography and high-performance liquid chromatography [3,6,7,8,9]. These methods include bulky measurement equipment and are confined to laboratory use
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