This work introduces an environmentally sustainable and cost-effective strategy for synthesizing graphene nanomaterials from agricultural residues—walnut shells and apricot stones. The synthesis pathway combines desilication, controlled pre-carbonization, chemical activation with KOH, and mild exfoliation to produce few-layer graphene with a high degree of structural order. The process, conducted at 523–573 K for pre-carbonization and 1123 K for activation, enables the formation of graphene sheets with a specific surface area of approximately 1300 m²/g, carbon content of 80–90%, and average pore diameter below 100 nm. The materials were comprehensively characterized using SEM, TEM, Raman spectroscopy, and BET analysis. Raman spectra revealed an I_G/I_2D ratio of ~1.5–2 a.u., confirming the presence of 4–5 graphene layers. Compared to conventional biomass-derived graphene routes, the developed approach ensures enhanced porosity, higher graphitic ordering, and improved purity, demonstrating its strong potential for energy storage, adsorptive purification, and environmentally benign nanotechnology applications.

This study presents the development of an environmentally benign and economically viable methodology for the synthesis of graphene-containing carbon materials derived from renewable agricultural residues, specifically walnut shells, rice husks, and apricot stones. The proposed synthesis route involves sequential stages of controlled pre-carbonization, desilicification, chemical activation with potassium hydroxide (KOH), and subsequent mild exfoliation, resulting in the formation of few-layer graphene with a high degree of structural ordering. Pre-carbonization carried out at 523–573 K, followed by activation at 1123 K, yields graphene sheets exhibiting a specific surface area of 1300–1800 m²/g, a carbon content of 60–90%, and an average pore diameter below 100 nm. The synthesized materials were subjected to comprehensive physicochemical characterization using BET surface area analysis, Raman spectroscopy, FTIR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic absorption flame emission spectrophotometry. Raman spectroscopic analysis revealed an I_G/I_2D intensity ratio of approximately 1.5–2.0, indicating the presence of graphene structures consisting of approximately four to five layers. To enhance adsorption performance, the graphene-containing carbon materials were further functionalized with sulfuric acid, and the successful incorporation of surface functional groups was confirmed by FTIR spectroscopy. The adsorption properties of the functionalized graphene-containing carbon materials were evaluated in aqueous solutions containing sodium, potassium, calcium, and magnesium salts, demonstrating adsorption efficiencies of up to 80%. Compared to conventional biomass-derived graphene synthesis methods, the developed approach produces materials with enhanced porosity, higher graphitic ordering, and improved chemical purity. These characteristics highlight the strong potential of the synthesized graphene-containing carbon materials for applications in energy storage systems, adsorption-based water purification technologies, and environmentally sustainable nanotechnological applications.

The rapid demand for sustainable and efficient energy storage solutions has prompted the pursuit of eco-friendly electrode materials. Biomass-derived carbons from food waste offer a promising pathway to meet this need by combining waste valorization, environmental benefits, and high electrochemical performance. This review highlights that food waste biomass is an effective and inexpensive source of precursors for producing high-performance carbon materials for supercapacitors. Food waste, which includes fruit peels and vegetable residues, cereal husks, and oilseed residues, is a good source of lignocellulosic components, heteroatoms, and structural features that determine the electrochemical characteristics of the derived carbons. These wastes produce hierarchically porous carbons with high surface areas (>1500 m² g⁻¹) on pyrolysis and activation that provide superior ion transport, wettability and pseudocapacitive behaviour. Their electrochemical performance includes capacitances up to 520 F g⁻¹ and energy densities of 35–70 Wh kg⁻¹ in optimized systems, particularly under extended voltage windows or in hybrid supercapacitor configurations, and high cycling stability is equal to or even better than traditional carbons such as activated carbon and graphene. Additionally, biomass valorization contributes to a high level of greenhouse gas capture, decreases landfill, and correlates with the idea of a circular economy. The commercialization potential of biomass-based supercapacitors is supported by recent developments in AI-based optimization, combined with scalable synthesis methods, which would support ecologically, economically, and technologically sustainable energy storage on a large scale.