Preparation of lignin-based carbon foam monoliths with high strength and developed micrometer-sized cell/nano-sized porous structures using a self-bubbling method

Abstract

Lignin is an attractive renewable feedstock used for the production of carbon materials because of its abundance and high carbon content. This work aims to explore a scalable technology to produce carbon foams from lignin. A lignin self-bubbling method has been developed in this study using zinc chloride as the catalyst for the thermal decomposition of lignin, resole as a cross-linking agent and a surfactant as the foaming assistant agent. The effects of dosage of zinc chloride and resole, type and dosage of surfactant, foaming temperature, heat treatment on the structure and properties of the materials have been investigated. The results show that the structure and properties of the resultant lignin-based carbon foams without any fractures is highly tunable depending on the amount of zinc chloride, resole and surfactants used, the foaming temperature in the self-bubbling process and post-heat treatment step. It is found that the non-ionic surfactant Tween-80 can significantly improve the mechanical strength and porosity of monolithic lignin-based carbon foams. The lignin-based carbon foams prepared using a self-bubbling method under ambient pressure not only exhibit a compressive strength of ˃4 MPa and an electric conductivity of 0.79 S cm−1, but also bear a developed structure of micrometer-sized cells with a low density of 0.3 g cm−3 and nanometer-sized pores with surface area of ˃175 m2 g−1. Furthermore, the lignin-based carbon foams have high thermal and structural stability to resist burning for various applications and exhibit excellent performance in oil/water separation, which retain 91% of the adsorption capacity toward oils even after being recycled 20 times.