Microwave-assisted pyrolysis of waste hemp biomass for the synthesis of graphene oxide–like material: A feedstock-process-structure-property relationship study

The manufacturability of multifunctional graphene oxide (GO) from waste hemp biomass offers environmental, economic, and sustainability benefits. This research, for the first time, introduces hemp as a feedstock for developing GO-like material via one-step microwave-assisted pyrolysis using a 2 3 full-factorial design, with particular emphasis on feedstock particle size as a structural design variable alongside microwave power and residence time. Raman spectroscopy confirmed defect-rich sp 2 carbon structures with intensity ratios of the D-band to G-band (I D /I G ) consistently near unity (0.99–1.07) across all conditions. X-ray diffraction (XRD) revealed characteristic GO-like (001) reflections at 2θ ≈ 13.3–13.6°, corresponding to d-spacings of 0.651–0.664 nm and crystallite sizes of 1.90–2.11 nm, confirming the formation of 2–3-layer, oxygen-functionalized, putative few-layer carbon structures. Furthermore, Fourier-transform infrared (FT-IR) analysis verified the presence of O–H, C=O, C–O-C (epoxy), and C=C functional groups consistent with GO chemistry. Brunauer-Emmett-Teller (BET) physisorption showed that the highest specific surface area (423.4 m 2 g −1 ) and total pore volume (0.47 cm 3 g −1 ) were achieved under 900 W/60 min/fine particles (300–425 μm), while prolonged exposure (90 min) caused pore coalescence and structural densification. Carbon content ranged from 18.78 to 72.76 wt%, with the highest values at 900 W/60 min. Feedstock particle size played a critical role: finer particles enabled more uniform microwave heating, superior pore development, and improved carbon retention under extended residence time. These findings establish a quantitative feedstock–process–structure relationship for hemp-derived GO-like materials, providing a scalable, solvent-free synthesis route for carbon nanostructure property tailoring.