Synthesis of graphitic biocarbons from lignin fostered by concentrated solar energy

The approach aiming at replacing fossil-based carbons by graphitic biocarbon has gained momentum in applications from environmental remediation to battery electrodes and supercapacitors, reducing their environmental impact. To address biocarbon high production temperature and energy consumption, this work uses lignin, a renewable feedstock, and concentrated solar as a sustainable energy source. New insights into lignin's graphitization mechanism using solar energy are provided. Graphene layers stacking appears as early as 1000 °C in solar carbonization. The structuration and reduction of amorphous carbon was further highlighted at 1400 °C and 1800 °C. At 2000 °C, high graphitic (L_a(XRD) ≈ 9.1 nm, d₀₀₂ = 0.3386 nm, 110 stacked layers) and turbostratic (d₀₀₂ = 0.3593 nm, 5.5 stacked layers) phases are obtained, showing the structural heterogeneity of solar biocarbon. Contrariwise, conventional biocarbon from electrical heating was homogeneous with limited carbonization at 1800 °C (L_a(XRD) ≈ 3.8 nm, d₀₀₂ = 0.3600 nm, 4.4 stacked layers). Textural analysis of solar biocarbons showed aligned graphene layers whereas only random texture was observed on conventional samples. This work established that solar carbonization triggers and enhances graphene layers stacking and growth at lower temperatures whereas conventional carbonization allows the progressive apparition of short graphene layers before stacking and growth.