Enhancing the Adsorption of Methylene Blue onto Hemp Hurd Powder by Tailoring Its Surface Properties

摘要

In this study, the agriculture waste, hemp hurd powder (HP), derived from hemp (Cannabis sativa L.) was chosen as a raw material to explore its adsorption capacity for methylene blue (MB). In order to enhance the adsorption capacity, HP was modified by simple sodium chlorite bleaching, TEMPO-mediated oxidation and nanofibrillation after TEMPO-mediated oxidation to alter its surface properties preparing B-HP, T-HP and N-T-HP, respectively. The surface chemistry, thermostability, surface morphology and adsorption performance of the resulting materials were investigated systematically. Results showed that the surfaces of modified HP were altered in terms of carboxylic group and morphology. The positive correlation was found between the experimental maximum adsorption capacity for MB and the content of carboxylic groups. The adsorption behaviors of HP and modified HP fitted well with Langmuir isotherms indicating a monolayer adsorption process, with maximum monolayer adsorption capacity of 239.81 mg/g for N-T-HP. The adsorption kinetics was found to follow the pseudo-second-order kinetic model suggesting chemisorption plays the dominant role in the adsorption process. The adsorption mechanism study indicated that film diffusion was the rate-controlling step and the hydrogen bonding and electrostatic interaction could be responsible for the chemisorption of MB onto HP-based adsorbents.