Efficient Adsorption of Methylene Blue by Polyaminocarboxylated Modified Hydrochar Derived from Sugarcane Bagasse

Sugarcane bagasse (SCB) was transformed into polyaminocarboxylated modified hydrochar (ACHC) by hydrothermal carbonization (HTC), which was then followed by activation, etherification, amination, and carboxylation successively. ACHC was systematically characterized, and batch adsorption studies were used to assess its methylene blue (MB) adsorption capacity. Adsorption was analyzed by adsorption isotherm models, the adsorption mass transfer model, and the adsorption thermodynamics model. Density functional theory (DFT) was utilized to explain adsorption mechanisms. The findings demonstrated the adsorption was one type of endothermic, spontaneous, and homogenous monolayer adsorption with intra-particle diffusion, containing both chemical and physical adsorption, involving electrostatic attraction, hydrogen bonding, and π-π interaction. At 303 and 323 K, the highest adsorption capacity was 1017.29 and 1060.45 mg·g−1, respectively. Furthermore, when the recycle time was 4, the equilibrium adsorption capacity remained at 665.43 mg·g−1, which implied fairly good regeneration performance. The modification provided a simple, environmentally friendly, and economical solution for converting sugarcane bagasse into an efficient adsorbent for MB treatment.