Single-step production of N-doped graphene powder from palm kernel shell at 500 °C

The rapid growth of the palm oil industry has led to significant waste generation, including palm kernel shells (PKS), an underutilized agricultural biomass. This study explores the sustainable conversion of PKS into graphitic and nitrogen-doped graphene through a single-step heating process at moderate temperatures. Carbonization was optimized at 450 °C and 500 °C with varying dwelling times (30, 60, and 90 min) to enhance graphitic carbon formation. Comprehensive characterization using Raman spectroscopy, thermogravimetric analysis (TGA), CHNS, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) mapping, and X-ray photoelectron spectroscopy (XPS) was conducted to evaluate structural, thermal, and compositional features. Raman deconvolution and Tuinstra-Koenig (TK) relation calculations revealed crystallinity percentages ranging from 33.72 % to 37.00 %, with the highest graphitic order observed in the sample carbonized at 450 °C for 90 min. TGA showed that the 500 °C, 60-minute condition achieved the highest thermal stability, while XRD confirmed the presence of both amorphous carbon and crystalline mineral phases such as calcium carbonate and magnetite, explaining the 17.3 % discrepancy in elemental CHNS data. Ball milling of the 500 °C, 90-minute carbonized sample produced few-layer graphene with an I_D/I_G ratio of 0.65 and I_2D/I_G of 0.33. XPS analysis verified the incorporation of nitrogen atoms, indicating passive self-doping derived from the biomass. This study demonstrates a cost-effective, scalable, and eco-friendly route to producing nitrogen-doped graphene from PKS, addressing agricultural waste valorization while enabling promising applications in energy storage, catalysis, and environmental remediation.