Photothermal radiometric image identification of microplastics through near-infrared excitation

Near-infrared excitation photothermal radiometric image identification is demonstrated as a rapid analysis tool for visualizing different types of microplastics (MPs). The excitation wavelengths used for four types of plastic materials, polyethylene terephthalate, polystyrene, polyvinyl chloride, and polypropylene, were 1662 nm, 1681 nm, 1716 nm, and 1725 nm, respectively, in the near-infrared region. After irradiating for 20 s with a specified wavelength, a photothermal radiometric image was recorded with a commercially available thermal camera. Each of the four types of MPs in a 2 mm square and with a 1 mm thickness was successfully visualized. A simple thermal diffusion analysis predicts a time-dependent increase in the temperature rise of each of the plastic materials having their own specific physical properties.