Beyond electrostatic interaction: Ball milling-induced dominance of pore filling and π-π stacking for methylene blue adsorption on tobacco stem derived activated carbon

Conventional understanding of cationic dye adsorption on carbonaceous materials predominantly emphasizes electrostatic attraction. Herein, we report a ball-milled tobacco stem-derived activated carbon (BMTSAC) that exhibits superior adsorption capacity for methylene blue (MB) via a distinct and more resilient mechanism. Ball milling reduced the particle size to 440 nm and increased the specific surface area to 1171.5 m 2 /g, while concurrently modifying the surface chemistry and pore structure that fundamentally shifted the dominant adsorption pathway. The key finding is the dominance of non-electrostatic interactions, namely pore filling and π-π stacking, over electrostatic attraction. This was evidenced by the high MB uptake (520.7 mg/g) under highly acidic conditions (pH = 2.0), far below the point of zero charge (pH PZC  = 3.0), and the material's robust performance under high ionic strength. The adsorption process followed the pseudo-second-order kinetic and Langmuir isotherm models, with a maximum adsorption capacity of 776.3 mg/g. The revelation of this mechanism shift underscores the superior potential of BMTSAC for treating complex industrial wastewater where pH fluctuates and ionic strength is high. After 5 cycles, BMTSAC maintained excellent reusability with only a 10.6 % capacity loss, further supporting its strong practical application prospects.