Non-fluorinated lignin-based melamine sponges with superhydrophobic and photothermal properties for multi-functional applications

Frequent oil spills and the discharge of oily wastewaters become a significant threat to the environment and ecosystem. Herein, a non-fluorinated lignin-based melamine sponge with superhydrophobic and photothermal properties (labeled as MS@COF/LPs/PDMS) has been achieved by decorating with covalent organic framework (COF), lignin particles (LPs) and PDMS. The MS@COF/LPs/PDMS shows excellent surface superhydrophobicity with a water contact angle of 152.3° and a sliding angle of 6°. The adsorption capacities of the MS@COF/LPs/PDMS range from 38.4 g/g to 100.3 g/g for various oils and organic solvents, and the separation efficiency of the MS@COF/LPs/PDMS for CCl4 reaches 99.7 %. Furthermore, the maximum surface temperature of the MS@COF/LPs/PDMS reaches 61.2 °C because of the thermal vibration of LPs and COF under solar irradiation (1.0 kW/m2). Surprisingly, the MS@COF/LPs/PDMS can rapidly adsorb a droplet of crude oils within 32 s due to the superoleophilicity and excellent photothermal effect. Besides, the melting time of the MS@COF/LPs/PDMS (400 s) reduces by 70 % for an ice droplet under solar irradiation than that of pristine melamine sponge (1330 s). Thus, this study provides new insights into the rational design of low-cost lignin-based melamine sponges for the applications of oil/water separation, crude oil recovery, and de-icing.