Mechanochemical activation of orange peel waste: enhanced surface reactivity and efficient cationic dye removal from...

Dye-contaminated wastewater poses a serious environmental challenge because synthetic dyes are toxic and resistant to biodegradation. Even at minimal concentrations, these pollutants can threaten ecosystems, underscoring the urgent need for efficient adsorbents. In this study, ball-milled orange peel powder (BM-OP) was explored as a sustainable adsorbent for cationic dye removal from aqueous solutions. Ball milling significantly enhanced the physicochemical properties of orange peel, increasing the surface area from 3.5 to 8.5 m² g^-1 and expanding the pore diameter from 6.3 to 13.1 nm, thereby facilitating active sites and dye diffusion. Adsorption analysis showed that the equilibrium data were reasonably defined by the Langmuir isotherm model. The fitted Langmuir capacities were 485.05 mg g^-1 for methylene blue (MB) and 583.60 mg g^-1 for methyl violet (MV). Adsorption kinetics were found to be well aligned with pseudo-second-order model (R ² = 0.99), suggesting enhanced accessibility of adsorption sites following the modification process. The results demonstrated that BM-OP could be effectively regenerated using KH₂PO₄, with desorption efficiencies of 92.4% for MB and 94.5% for MV. In addition, the adsorbent showed good reusability over eight successive adsorption-desorption cycles. These results show that BM-OP is an efficient and cost-effective adsorbent for cationic dye removal from wastewater.