Efficient WaterEvaporation Using Black Silicon

The black silicon (b-Si)plasma-etched nanostructured surface of crystalline Siwas used as a light absorber due to its extremely low reflectivity (<1%) at the visible-to-near-IR spectral range. Flat Fresnel lenses of 1.47 and 0.36 m² were used to focus light onto b-Si, which was a photothermal absorber. Experiments to distill water were carried out from October 2021 to April 2022 in Obihiro (42°55′N 143°12′E), Hokkaido, Northern Japan. The same b-Si has biocidal properties (antibactericidal, antiviral, and antifungal) due to mechanical nanoscale needles, which complement the water purification when gray water sources are used in applications.