Sustainable valorization of yellow bluestem biomass into high-performance bioadsorbent for rhodamine B sequestration from water

The textile and allied industries produce dye-containing wastewater often at high concentrations, which also contains persistent synthetic dyes, such as rhodamine B (RB), creating a need for economical and sustainable treatment materials. Yellow bluestem (YBS) (Bothriochloa ischaemum) was pyrolyzed to produce a porous carbon-based bioadsorbent and evaluated for RB removal from aqueous solution. The prepared carbon exhibits a surface area of 512 m2 g−1, total pore volume of 0.522 cm3 g−1, and mean pore diameter of 3.65 nm. Central composite design (CCD) and response surface methodology (RSM) were employed to determine the effect of initial dye concentration, adsorbent dosage, pH, and contact time. The quadratic model was highly significant (p < 0.0001), with R2 = 99.71%, an adjusted R2 = 99.41%. Numerical optimization identified selected operating condition as 80 mg L−1 RB concentration, 1.6 g L−1 adsorbent dose, pH 4.5, and 130 min contact time, with a predictive removal of approximately 96.55%. Experimental validation under these conditions in triplicate yielded removal efficiencies of 92.97, 93.56, and 93.01%, corresponding to 93.18 ± 0.33% removal and a prediction error of 1.92%. Equilibrium data were best represented by Dubinin–Radushkevich model (R2 = 0.963), with a mean adsorption energy of 0.45 kJ mol−1, supporting predominantly physical adsorption involving heterogeneous surface interactions and pore-filling contributions. Kinetic data are best described by the pseudo-second-order model (R2 = 0.997), while, intraparticle diffusion analysis indicated a multistep adsorption process. Thermodynamic analysis indicated that adsorption was endothermic and became thermodynamically favourable at higher temperature. After five regeneration cycles, the adsorbent retained 67.4% of its initial removal performance. The findings demonstrate the potential of YBS-derived carbon as a sustainable bioadsorbant for RB removal from aqueous system.