3D-printed tripodal porous wood-mimetic cellulosic composite evaporator for salt-free water desalination

Solar desalination based on interfacial evaporation has been proven promising in producing clean water. However, so far, the lack of a facile preparation strategy and effective salt rejection has profoundly limited its potential for practical applications. Herein, inspired by the unique liquid transportation of natural wood, we report on a three-dimensional (3D) printed tripodal porous wood-mimetic cellulosic composite evaporator for long-term salt rejection, starting from cost-effective materials such as cellulose and carbon black. The printed evaporator displays a broadband solar absorption (>97%) and an extremely low thermal conductivity (0.075 W m−1 K−1), indicating its high photothermal conversion efficiency and outstanding thermal management. The printed tripodal porous evaporator contains large-sized channels (∼1 mm in diameter) that function as salt regenerating pathways, micropores (∼30 μm) and submicron pores (∼1 μm) for rapid water transport and efficient supply. Fluidic simulation reveals that large channels with high water flux lead to the salt concentration gradient between large and small channels via submicropores, meanwhile, the concentrated water at the top layer transports downward by diffusion and convection, further making the spontaneous horizontal and vertical salt exchange. Such a tripodal porous structure endows the evaporator with a high efficiency of ∼75% in a highly concentrated salt solution (15 wt% NaCl) under 1 sun irradiation, as well as superior salt-rejection property (100 h continuous evaporation in 15 wt% NaCl). This strategy, starting with sustainable cellulose-based composite materials and being able to balance the evaporation performance and long-term stability, opens up new doors toward clean water production.