Picosecond laser treated aluminium surface for photothermal seawater desalination

Interfacial solar steam generation has been proposed as an eco-friendly way for water desalination. However, the current interfacial evaporator still suffers from a complex process, high preparation cost, and poor stability. Here, by means of picosecond laser treatment of the aluminium surface, we developed a superhydrophilic, anti-gravity wicking, and efficient solar desalination evaporator. The picosecond laser treated aluminium (PLAL) surface has an open capillary structure, which contributes to the rapid transfer and evaporation of seawater. Moreover, larger size water clusters are formed on the surface, hence lowering its enthalpy of water evaporation dramatically to 541.25 ± 0.07 kJ/kg, which can effectively increase the evaporation rate to 1.24 kg·m−2·h−1 under one sun irradiation (1 Kw·m−2) even with only 67% energy efficiency, and is 0.3 kg·m−2·h−1 higher than that treated by high-cost femtosecond laser. Even under weaker natural sunlight, the evaporation rate remains 0.7–0.9 kg·m−2·h−1. Additional experiments were carried out at low laser power (30%) to evaluate the effect of PLAL surface structure on anti-gravity wicking. Additionally, during 25-day continuous desalination, the evaporation performance of PLAL surface remains stable, in contrast to that placed in ambient air, which changes to hydrophobic 20 days after laser treatment. Furthermore, low temperature annealing can restore the PLAL surface, which has been converted to hydrophobic, to superhydrophilic. The reason for transition may attribute to the increase in the carbon content of the surface causing an increase in the relative content of the CC bond of the surface. The PLAL surface fabricated here is easy to fabricate and scale-up and exhibits the potential to efficient desalinate seawater and purify wastewater, etc.