Valorization of sheep wool waste into K2CO3-activated carbons for efficient MB and Cu(II) removal

Sheep wool waste, an abundant keratin-rich residue rarely used for biochar production, was pyrolyzed at 400-900 °C and activated with K 2 CO 3 via two methods to generate adsorbents for methylene blue (MB) and Cu (II) removal from water. Method 2, using BC-400 activated at 900 °C, produced AC-900M2 with exceptional N 2 -BET surface area of 2845 m 2 /g, pH pzc 8.2, 90 wt% fixed carbon and 0.8 wt% nitrogen. This material excelled in MB adsorption, achieving 99% removal and q e = 400 mg/g at 200 mg/L and pH 7, with equilibrium in 4 h well described by a pseudo-second-order (PSO) rate model (k 2 = 1.59 × 10 −4 g/mg min −1 ). Dosage studies yielded a Langmuir q max of 572 mg/g. Remarkably, performance remained pH-independent from 3 to 9, suggesting that π-π interactions and pore filling contributed importantly to MB uptake despite electrostatically unfavourable conditions, in agreement with the hybrid PSO-IPD analysis and speciation considerations. For Cu (II), AC-700M2 (SSA 1070 m 2 /g, N 6.3 wt%) showed the best performance among the tested materials, with results consistent with a contribution from N/O-containing surface sites under near-neutral pH, although precipitation effects may contribute at pH 7. Method 2 produced the most porous material among the tested samples and the highest MB performance. These findings demonstrate the feasibility of wool waste as sustainable dual-pollutant adsorbents, promoting circular economy in wastewater remediation.