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Lignin is a promising precursor to produce graphene materials due to its high carbon and aromatic contents. Upgrading lignin into graphene materials has gained significant interests as it offers a cost‐effective and sustainable route to produce high‐performance carbon materials. This review provides a comprehensive overview of the state‐of‐the‐art technologies on lignin to graphene materials with a focus on thermal catalytic and photothermal upgrading. The applications of lignin‐derived graphene materials and the perspectives for mass production of such graphene materials are also discussed.

 

This study aimed to explore lignin as a naturally occurring aromatic precursor for the synthesis of LIG and further fabrication of ultrasensitive strain sensors for the detection of small deformations. One-step direct laser writing (DLW) induced high quality porous graphene, so called laser induced graphene (LIG), from kraft lignin under the conditions optimized for laser power, focus distance, and lignin loading. An electrode based on the resulting LIG was facilely fabricated by transferring LIG onto an elastomeric substrate ( i.e. , Dragon Skin™). The novel LIG transfer was facilitated by spin coating followed by water lifting, leading to the full retention of porous graphene onto the elastomeric substrate. The strain sensor was shown to be highly sensitive to small human body motions and tiny deformations caused by vibrations. It had a working range of up to 14% strain with a gauge factor of 960 and showed high stability as evidenced by repetitive signals over 10 000 cycles at 4% strain. The sensor was also successfully demonstrated for detecting human speaking, breath, seismocardiography (SCG), and movement of pulse and eye. Overall, the lignin-derived LIG can serve as excellent piezoresistive materials for wearable, stretchable, and ultrasensitive strain sensors with applications in human body motion monitoring and sound-related applications. 

Graphene with a 3D porous structure is directly laser‐induced on lignocellulosic biopaper under ambient conditions and is further explored for multifunctional biomass‐based flexible electronics. The mechanically strong, flexible, and waterproof biopaper is fabricated by surface‐functionalizing cellulose with lignin‐based epoxy acrylate (LBEA). This composite biopaper shows as high as a threefold increase in tensile strength and excellent waterproofing compared with pure cellulose one. Direct laser writing (DLW) rapidly induces porous graphene from the biopaper in a single step. The porous graphene shows an interconnected carbon network, well‐defined graphene domains, and high electrical conductivity (e.g., ≈3 Ω per square), which can be tuned by lignin precursors and loadings as well as lasing conditions. The biopaper in situ embedded with porous graphene is facilely fabricated into flexible electronics for on‐chip and paper‐based applications. The biopaper‐based electronic devices, including the all‐solid‐state planer supercapacitor, electrochemical and strain biosensors, and Joule heater, show great performances. This study demonstrates the facile, versatile, and low‐cost fabrication of multifunctional graphene‐based electronics from lignocellulose‐based biopaper.