Benzene, toluene, ethylbenzene, and xylenes (BTEX) are important organic pollutants. These compounds do not undergo direct photolysis in natural waters because their absorbance spectra do not overlap with solar radiation at the Earth's surface. Recent research has suggested that benzene is able to undergo direct photolysis when present at ice surfaces. However, the photolysis of toluene, ethylbenzene, and xylenes (TEX) at ice surfaces has not been investigated. Using fluorescence spectroscopy, photolysis rate constants were measured for TEX in water, in ice cubes, and in ice granules which reflect reactivity at ice surfaces. No photolysis was observed in water or ice cubes. Photolysis was observed in ice granules; rate constants were (4.5 ± 0.5) × 10(-4) s(-1) (toluene), (5.4 ± 0.3) × 10(-4) s(-1) (ethylbenzene), and (3.8 ± 1.2) × 10(-4) s(-1) (xylenes). Photolysis of TEX molecules appears to be enabled by a red shift in the absorbance spectra at ice surfaces, although photosensitization may also occur. The results suggest that direct photolysis could be an important removal pathway for TEX in snow-covered environments.
The interaction between water and surfaces is observed in our daily lives and is used in laboratories to study materials properties, such as interfacial tension. Making the connection between fundamental scientific phenomena and everyday observations is a powerful method of highlighting the importance and relevance of science to the K−12 population. Typically, expensive equipment, such as dedicated contact angle goniometers, is used in laboratories to observe how water interacts with materials. Obtaining such laboratory-grade equipment for the K−12 classroom is not only difficult but also unnecessary. Thus, we present an affordable 3D printed setup for the reliable measurement of the contact angle of water on a variety of natural and synthetic surfaces, using smart devices (e.g., cell phone, tablet) as the imaging basis. This setup enables proper backlighting, a stable camera holder for quality images, and a flat surface with an easily adjustable platform to hold the sample. Compared to simply holding the smart device by hand, the 3D printed method provided better quality images and an improved data acquisition experience when measuring the contact angle. Use in a middle school setting has shown that this 3D printed method is successful for teaching about water/surface interactions on both hydrophilic and hydrophobic surfaces. This method can easily be adapted to suit learning objectives, allowing educators to explore a range of hydrophobic and hydrophilic surfaces of both biological and synthetic origin.
The resonant nature and geometric scalability make metamaterials an ideal platform for an enhanced light–matter interaction over a broad frequency range. The mid-infrared (IR) spectral range is of great importance for vibrational spectroscopy of molecules, while IR metamaterials created from lithography-based planar nanostructures have been used to demonstrate enhanced molecular detection. Compared with visible and near-infrared, the relative long wavelengths of IR light make it possible to achieve three-dimensional (3D) IR metamaterials via the state-of-the-art 3D fabrication techniques. Here, we design and fabricate a 3D printed plasmonic metamaterial absorber (MMA), and by performing Fourier-transform IR spectroscopy, we demonstrate that a series of molecular fingerprint vibrations of glycine can be significantly enhanced by the high absorption mode supported by the 3D meta-atoms of the MMA. The observed enhanced IR detection can also be partially attributed to the improved accessibility offered by the 3D architecture of the MMA. In particular, due to capillary forces during the drying process, the microscale 3D printed features lead to selective analyte deposition in high-field regions, which provides another degree of freedom in the design of the 3D printed structures for surface-enhanced IR detection. Our study shows the flexibility of metastructures based on advanced 3D printing technology in tailoring the interaction between IR light and materials on a subwavelength scale.
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