High-Performance Porous Carbon Derived from Corncob Cellulose via Phosphoric Acid Activation for Efficient Methylene Blue Adsorption

The widespread industrial application of commercial activated carbon for wastewater remediation is constrained by the prohibitive operational costs. To overcome this economic barrier, this study proposes a sustainable valorization strategy for corncob, an abundant agricultural residue, by engineering a low-cost, high-performance cellulose-based adsorbent (CBA). High-purity cellulose was efficiently fractionated from corncobs (yield: 88.95%) utilizing a hydrogen peroxide-assisted formic acid organosolv process under optimized conditions (30 wt % H₂O₂, 70 °C, 4 h). The extracted cellulose was subsequently converted to porous carbon via phosphoric acid activation. Structural characterization revealed that the optimized CBA possesses a well-developed mesoporous architecture with a high specific surface area of 1079.995 m²·g^-1. The adsorption behaviors were best described by the Langmuir isotherm and pseudo-second-order kinetic models, suggesting a monolayer chemisorption mechanism driven primarily by electrostatic interactions. Remarkably, CBA exhibited an exceptional maximum adsorption capacity (<i>Q</i>_max) of 509.10 mg·g^-1 for Methylene Blue at pH 9. Furthermore, thermodynamic analysis confirmed the spontaneous nature of the process, and the adsorbent retained approximately 80% of its initial capacity after five regeneration cycles. This work provides a viable pathway for the upcycling of lignocellulosic waste into value-added functional materials for environmental applications.