Understanding and optimizing green synthesis from cellulose to reduced graphene oxide with enhanced photothermal properties

Reduced graphene oxide (rGO) is a promising photothermal material due to its thermal stability, electrical conductivity, and strong near-infrared (NIR) laser absorption. However, conventional synthesis routes disrupt the sp² carbon framework, diminishing photothermal conversion efficiency, and involve environmental hazards. Here, we report a chemical-free reduction-then-exfoliation strategy using cellulose as a renewable precursor to produce high-quality rGO with preserved sp² domains. Cellulose is first thermally converted into graphite-like biochar with a high C/O ratio, followed by ultrasonication-assisted exfoliation guided by theoretical calculations. Compared with conventionally synthesized rGO at similar C/O ratios, the cellulose-derived rGO exhibits a 62% lower I_D/I_G ratio, indicating significantly improved preservation of sp² domains. This structural advantage leads to enhanced photothermal performance, with a 10.1–33.0% higher temperature increase under comparable near-infrared irradiation conditions. Simulation-guided optimization of surfactant addition further reduces exfoliation energy, resulting in a 40% increase in yield at the optimal ratio. Life-cycle assessment demonstrates substantial sustainability benefits, including up to 48% reduction in ecosystem impact, 42% reduction in resource depletion, and 48% lower human health damage, together with approximately 50% improvement in cost efficiency compared to conventional methods. This work provides a high-performance and eco-efficient pathway for rGO production and establishes a mechanistic framework linking precursor structure, processing strategy, and functional performance for biomass-derived carbon materials.