One-step ultrafast deflagration synthesis of N-doped WO2.9 nanorods for solar water evaporation

Highlights: • The N-doped WO_2.9 nanorods are rationally obtained via the one-step deflagration route. • The Na clusters, as the reductant capturing O from WO₃, in situ derived from deflagration can be removed easily. • The NaN₃ addition effects the concentration of surface defects and N-doped. • The introducing of surface defects and N-doped enhances the water evaporation efficiency. Up to now, the seawater desalination utilizing solar water evaporation has been considered as the most promising solution to solve water-shortage problems. Thus, preparing efficient photo-thermal conversion materials for water evaporation with an ultrafast and cheap method is a big challenge. Herein, the N-WO_2.9 photo-thermal materials with the oxygen vacancy and N co-doping are synthesized by an ultrafast one-step NaN₃ deflagration method. The deflagration produces Na clusters and N radicals, subsequently the former acts as a reductant capturing partial O from WO₃, and the latter is partly doped in crystal lattice, which causes the phase transition from WO₃ to N-WO_2.9 and leads to a narrowed band gap. The modified materials significantly increase solar absorption and photo-thermal conversion, especially in visible and near infrared light. Hence, the N-doped WO_2.9/cellulose paper photo-thermal membranes possess the superb water evaporation rate of 1.45 kg m^-2h⁻¹, stable efficiency of 83.1%, and the excellent desalination capability under 1 solar illumination. In addition, the deflagration method simultaneously achieving oxygen vacancy and high N-doping have opened up a new route for the design and synthesis of photo-thermal semiconductor materials.