A Janus bio-based interfacial solar evaporator with wettability gradient for simultaneously efficient solar water evaporation and catalytic degradation of organic pollutants in wastewater

Solar-driven interfacial water evaporation has garnered widespread attention due to its sustainability and high efficiency. The material behaviors and structural designs are critical to the interfacial evaporation rate. In this study, we demonstrate a Janus bio-based photothermal evaporator with a wettability gradient by using the discarded cigarette filters (CF) as a water transport scaffold and the kraft lignin as hydrophobic and photothermal tuners. The Janus structure, consisting of a hydrophilic water-adsorbing bottom layer (deacetylated CF, DCF) and a hydrophobic photothermal upper layer (lignin-coated DCF), can reduce the heat loss, salt blocks and evaporation enthalpy of water, thus promoting the photothermal conversion efficiency and the evaporation rate. Moreover, ZIF-67 catalysts in-situ immobilized onto the DCF channels endow simultaneous pollutants degradation during the wastewater evaporation. Results show that thanks to Janus structure with wettability gradient, the as-prepared evaporator can achieve an evaporation rate of 2.73 kg m-2h- 1 under 1 kW m- 2 irradiation, with a degradation rate exceeding 91 % for various organic pollutants. Upon an outdoor solar radiation for 8 h, it can produce 9 kg m- 2 of clean freshwater. Therefore, the Janus bio-based interfacial solar evaporator, derived from the discarded CF and lignin, displays great potentials in the valorization of waste biomass and wastewater remediation.