Weakening the hydrogen bonds with ~3 μm fluorescence for enhanced solar water evaporation

Solar-driven interfacial evaporation gradually becomes a green and potential technology to obtain fresh water from seawater or sewage. However, due to the existence of hydrogen bonds between water molecules, the water evaporation requires high energy to overcome intermolecular forces. Herein, to reduce the difficulty of water evaporation, the composite absorbers with ~3 μm fluorescence emission were fabricated by depositing β-NaYF₄: 20Yb³⁺,15Er³⁺ (mol%) phosphors on porous Sm_0.5Sr_0.5CoO_3−δ ceramic absorbers. The phosphors were prepared by hydrothermal method, and had the highest ~3 μm fluorescence intensity after treating at 500 °C. The fluorescence of 500 °C heat-treated phosphor shifted the hydrogen bond absorption peak by 3.6 nm to the low wavelength direction, which represented the weakening of hydrogen bonds. The composite absorber consisting of 500 °C heat-treated phosphor and ceramic absorber showed the excellent evaporation rate (1.59 kg m⁻² h⁻¹). By optimizing the deposition amount of phosphor, the evaporation rate was increased to 1.62 kg m⁻² h⁻¹ when the phosphor content was 2.43 g m⁻². This work provides a new idea to reduce the energy of water evaporation and improve the efficiency of interfacial evaporation system.