A loofah-based all-day-round solar evaporator with phenolic lignin as the light-absorbing material for a highly efficient photothermal conversion

Solar interfacial evaporation has received widespread attention as an emerging and sustainable approach to solve freshwater scarcity. However, traditional photothermal conversion materials, which are crucial components of solar evaporators, are mostly petroleum-based and are thus non-eco-friendly and expensive. This paper reports the application of aminated phenolated lignin as an efficient photothermal material and elucidates the photothermal conversion mechanism of lignin. By regulating the number of grafted conjugated structures in a simple process, a controllable and efficient photothermal conversion efficiency can be obtained. The biodegradable loofah is utilized as a water transmission layer, and thus an all-biomass solar evaporator was successfully obtained. Additionally, the evaporator enabled an all-day-round seawater desalination by releasing thermal energy stored in the polyethylene glycol loaded in the loofah sponge. The obtained evaporator did not only exhibit a high evaporation efficiency of up to 97.6% with an evaporation rate of 1.75 kg m−2h−1 under 1 sun, but also showed excellent cost-effectiveness (280 g h−1 $−1), which is superior to that of previously reported evaporators. Furthermore, the evaporator delivered an excellent salt-resistant performance after 25 cycles, which is conducive to long-term practical applications. The prepared evaporator with the characteristics of cost effectiveness, energy conservation, environmental friendliness, ease of preparation, stability, great evaporation efficiency has a great potential in solar evaporation applications.