Biomass constructing double-layer 3D solar evaporator for highly-efficient seawater desalination and wastewater treatment

Inspired by plant transpiration, a high-performance double-layer 3D solar evaporator is directly constructed using all biomasses. The unique porous structures endow the evaporator with extremely high solar efficiency of 96.4 % and seawater evaporation rate of 3.31 kg m −2 h −1 under 1 Sun, as well as a strong removal ability in salt/heavy metal ions, organic dyestuffs and acid/alkali substances. • The double-layer 3D evaporator is constructed using renewable natural biomasses. • The evaporator can reache a stable evaporation rate of 3.31 kg m −2 h −1 for seawater. • Microvillus-form structures is unique for ion removal and anti-salt accumulation. • This strategy shows a sustainable and green way for preparing solar evaporators. 3D solar-driven evaporator with high efficiency and good thermal management, is a promising strategy for solving freshwater shortage. However, its practical application is vitally restricted by the utilization of non-degradable polymers and expensive photothermal materials, as well as the pollutions of waste-plastics and microplastics. Herein, inspired by plant transpiration, biomasses of starch, cuttlefish ink, sodium alginate, and bamboo are used to greenly construct a high-performance double-layer 3D evaporator. Therein, a bamboo obtained from water-assisted carbonization, with strong solar-conversion and hydrophilicity, serves as the shell to supply heat and pump water continuously. The core layer, a dual-crosslinked starch-based hydrogel, consisting of plentiful micro-nano-sized pores with rich microvilli inside, exhibits outstanding properties in hydrophilicity, photothermal conversion and purification effect. Such 3D structure significantly reduces heat loss and improves water transporting and purifying efficiency. This evaporator performs extremely high solar efficiency of 96.4 % and seawater evaporation rate of 3.31 kg m −2 h −1 under 1 Sun, and affects little by super-high salinity and long-time usage. Meanwhile, it maintains excellent removal rate to salt/heavy metal ions, organic dyestuffs and acid/alkali substances. This study provides an instructive strategy for the cost-effective and sustainable fabrication of high-efficiency 3D solar-driven evaporator using only cheap and renewable biomass resources.