Efficient water evaporation 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 visible to near-IR spectra range. Flat Fresnel lenses of 1.47 and 0.36 m2 were used to focus light onto b-Si, which served as a photo-thermal absorber. Experiments to distill water were carried out in January 2021, winter conditions, in Obihiro (42◦55’N 143◦12’E) Northern Japan. The same b-Si has the biocidal property (anti-bactericidal, anti- virus, anti-fungi) due to mechanical nanoscale needles, which complement the water purification when grey water sources are used in application.