Banyan-inspired hierarchical evaporators for efficient solar photothermal conversion

Abstract

As a direct approach to utilize the abundant solar energy, solar steam generation surges in recent decade to generate fresh water from sewage and seawater, while still suffering from challenges like a limited photothermal efficiency and scale manufacturing. To enhance the solar energy utilization efficiency, inspired from banyan tree, we demonstrate a new, scalable and low-cost hierarchical evaporator, comprising an activated carbon-cotton fabric as photothermal leaves, commercial polyester pillars as prop roots, and expandable polyethylene foams, to largely utilize solar energy. The both sides of fabric and lateral area of polyester pillars collectively contribute to a rather high evaporation rate 1.95 kg m−2 h−1, with enhanced solar efficiency under 1 sun illumination. Polyester pillars as water paths can reduce the contact area between the photothermal layer and bulk water to prevent heat loss. The hierarchical evaporator is able to enhance solar energy utilization by increasing the extra evaporation area including the bottom side of fabric and lateral area of polyester pillars and thus behave most similarly to the transpiration process of banyan tree from both sides of leaves and prop roots. Moreover, the proposed hierarchical evaporator is further demonstrated to possess anti-salt-clogging performance by changing the number of polyester pillars. The banyan-inspired hierarchical evaporator is scalable, feasible, and low-cost, showing great potential for direct industrial applications of solar energy on clean water generation and sewage treatment.