Graphene Aerogel Derived from Luffa Sponge Biochar for Efficient Dye Removal from Wastewater

In this study, we report for the first time the synthesis of a novel three-dimensional graphene aerogel composite adsorbent (LGA) derived from luffa sponge biochar (LSBC) for the efficient removal of methylene blue (MB) from aqueous solution. The synthesis involves an effective alkali-activated pyrolysis process followed by a one-step solvothermal electrostatic coassembly. LSBC acts as a reinforcing and bridging agent, effectively preventing the aggregation of graphene nanosheets and promoting the formation of a three-dimensional hierarchical porous network. As a result, LSBC imparts several desirable properties to LGA, including superhydrophilicity, with a water contact angle of 8.0°, and abundant oxygen-containing functional groups. Microscopy and surface analyses reveal that LGA possesses a rich pore structure with a specific surface area of 237 m²/g, more than seven times greater than that of GA, significantly enhancing its dye adsorption performance. The effects of pH (4.0–8.0), initial dye concentration (25–250 mg/L), adsorbent dosage (0.1–0.6 g/L), temperature (25–45 °C), and contact time (15–420 min) on adsorption efficiency are systematically investigated. The results show that the adsorption process follows the Langmuir isotherm and pseudo-second-order kinetic models. The MB removal mechanism is primarily governed by π–π interactions, hydrogen bonding, electrostatic attraction and pore filling, with a maximum adsorption capacity of 1108.5 mg/g at pH 6.0, outperforming most reported biomass-based graphene adsorbents. Furthermore, LGA demonstrates excellent stability and reusability, retaining >90% of its initial adsorption capacity after 12 consecutive adsorption–desorption cycles. This low-cost, high-performance adsorbent offers an effective and sustainable solution for dye-contaminated wastewater treatment, while also demonstrating the high-value utilization of agricultural waste.