Optimizing the Preparation of Meso- and Microporous Canola Stalk-Derived Hydrothermal Carbon via Response Surface Methodology for Methylene Blue Removal

In this work, design of experiments–response surface methodology (RSM) was implemented to predict the importance of hydrothermal carbonization (HTC) key parameters and their interactions in the preparation of canola-stalk-derived hydrochar via HTC technique. According to the RSM results, temperature and reaction time were found to be the most important control factors. The possible optimum conditions were found to be 207 °C and 82 min for temperature and time, respectively, in order to achieve a hydrochar with the maximum mass yield (solid yield 53.38%), carbon recovery rate (52.66), and O/C ratio (0.69). Furthermore, the optimized hydrochar was successfully activated via potassium hydroxide (KOH), under mild activation conditions. Synthesized microporous activated carbon demonstrated the highly improved Brunauer–Emmett–Teller (BET) surface area of 474.87 m2 g–1 compared to the low BET surface area of mesoporous hydrochar (SBET of 2.69 m2 g–1). Porous activated carbon was used as an adsorbent for methylene blue removal that showed a promising dye removal capacity of 93.4 mg g–1. The morphological and chemical compositions of the solid materials were analyzed by various techniques, including elemental analysis, field emission scanning electron microscopy (FESEM), BET analysis, Fourier transform infrared (FTIR) spectroscopy, and energy-dispersive X-ray spectroscopy.