a Thermal images of the flat GM@Cu foil and SGM absorber under sunlight illumination in an open environment. b Temperatures of the flat GM@Cu foil (black) and SGM absorber (red) after various periods of illumination. Error bars on the Y-axis show standard deviations calculated from the measured temperatures. c Mass change of water with SGM absorber as function of time under one sun illumination. Inset: surface wetting property of SGM absorber. d, e Measured d absorbance spectra and e Raman spectra of SGM absorbers before, after 12 h, and after 24 h of heating at 100 °C in air.