This study develops an energy-efficient route for producing sustainable, high-performance activated carbons from tea twig ( Camellia sinensis ) waste for the removal of methylene blue (MB⁺) as a model cationic dye. Tea twigs were carbonized at 300, 400, and 500°C and subsequently subjected to mild KOH activation, producing activated carbons KA1-KA3 without an additional high-temperature activation step. The materials were characterized by XRD, FTIR, BET surface area analysis, SEM-EDX, Raman, and UV-Vis spectroscopy to correlate crystallinity, surface chemistry, and pore structure with adsorption behaviour. Batch adsorption experiments were conducted over a wide initial concentration range (20-2500 mg L−1) and relevant pH conditions, followed by kinetic modelling (pseudo-first-order, pseudo-second-order, and two-stage intraparticle diffusion) and equilibrium isotherm analysis (Langmuir, Freundlich, and Temkin). A fixed-bed column simulation was also performed to assess dynamic performance and scalability. Among the prepared carbons, KA1 (300°C) exhibited a predominantly amorphous structure, the highest BET surface area (685 m2 g−1), a favourable micro–mesoporous network (average pore diameter ∼2.72 nm), and abundant oxygen-containing surface groups, resulting in the best overall adsorption performance, particularly at low-to-intermediate concentrations (e.g., 96.0% removal at 20 mg L−1). At constant adsorbent dosage, removal efficiency decreased with increasing initial concentration due to progressive site limitation, while the equilibrium uptake increased and approached a practical saturation-like plateau. Within the investigated range, KA1 and KA2 reached a practical high-loading plateau uptake of ∼250 mg g−1, whereas KA3 approached ∼300 mg g−1 at high loadings. Kinetic fitting showed that the pseudo-first-order model provided the most consistent description of adsorption kinetics ( R 2 = 0.995-0.999; lowest SSE), and intraparticle diffusion plots revealed two distinct linear regions, indicating that diffusion contributes to the overall rate but is not the sole rate-limiting step. Equilibrium modelling indicated Langmuir-type behaviour for KA1 and KA2 (e.g., R 2 = 0.989 for KA1), while KA3 was better represented by the heterogeneity-sensitive Freundlich model. Mechanistically, adsorption is dominated by physisorption-driven pathways, including π–π interactions, electrostatic/polar contributions associated with oxygenated surface groups, hydrogen bonding, and pore-filling within the heterogeneous micro–mesoporous network. The pH drift test yielded pHₚzc ≈ 5.2, supporting a pH-robust adsorption response. Fixed-bed simulation using KA1 achieved 97.98% MB removal with a well-defined mass-transfer zone, while regeneration tests conducted at C 0= 240 mg L−1 showed ∼78% capacity retention after five cycles with >95% mass recovery. In summary, this work demonstrates that low-temperature KOH activation of tea twig waste can yield efficient activated carbons for cationic dye removal and provides an integrated batch–simulation assessment supporting practical applicability and energy-saving advantages over conventional high-temperature activation routes. © 2026 Elsevier B.V.