Environmentally sustainable renewable luffa-derived biomass graphene nanosheets for efficient Cr (VI) removal:...

In this study, an environmentally sustainable and renewable biomass-derived from luffa agricultural waste was used as a cost-effective precursor for graphene synthesis through chemical activation and graphitization processes. Luffa-based graphene nanosheets (LGN) were synthesized and characterized using FTIR, SEM, AFM, Raman, and XRD techniques. Structural and textural analyses of the synthesized LGN confirmed the formation of a three-dimensional graphene architecture with an ultrahigh specific surface area of 2,646.3 m² g⁻¹, representing a significant increase compared to raw luffa (12.056 m² g⁻¹). Consequently, LGN achieved a high maximum adsorption capacity toward Cr(VI) of 103.73 mg g⁻¹ in water, which is approximately tenfold higher than that of the raw luffa. Optimization using Box-Behnken design predicted the optimal operating conditions at pH 2.1, adsorbent dose of 0.44 g L^-1, contact time of 44 min, and initial Cr (VI) concentration of 10 mg L^-1, with a predicted removal efficiency of 97.50%. The adsorption behavior of Cr (VI) on LGN conformed to the Freundlich isotherm and pseudo-second-order kinetics, indicating heterogeneous, multilayer adsorption dominated by strong adsorbate-adsorbent interactions. Thermodynamic analysis revealed that Cr (VI) adsorption onto LGN is spontaneous, endothermic, and diffusion-driven, with enhanced molecular mobility and reduced surface affinity at elevated temperatures. LGN maintained Cr (VI) removal efficiency over four regeneration cycles, decreasing from 94.35% to only 85.71%, confirming its structural stability and economic viability for repeated use. The findings confirm the potential of green-synthesized, biomass-derived graphene nanosheets as a sustainable and efficient adsorbent for Cr (VI) removal from aqueous environments.