Recycling papermill waste lignin into recyclable and flowerlike composites for effective oil/water separation

A micrometer-sized porous material with superhydrophobicity surface is produced via one-step synthesis using Kraft lignin, a waste from pulp and paper industry, as the starting material. Non-fluorinated silane precursor is used for lignin modification to avoid the environmental, cost, and toxicity issues arising from fluorinated precursor. The silane-modified lignin has rather rough flower-like surface microstructures formed by closely-packed crater pores of different sizes ranging from nanometers to micrometers. The modified lignin exhibits superhydrophobic property with a water contact angle of 156°. The material can effectively separate immiscible oil/water mixtures with higher than 99% efficiency, and surfactant-stabilized oil/water emulsions with higher than 98% efficiency. The material shows good recyclability and reusability for oil/water mixture and emulsion separation. The silane modification is an attractive route to develop waste lignin into useful materials with potential applications in oil/water separation, which uses a naturally derived and renewable raw material with a single-step fabrication strategy.