Green synthesis and mechanistic insights into carbon-rich materials in deep eutectic systems and their application for adsorption

This study overcomes the limitations of traditional biomass carbonization, which typically requires high temperature, high pressure, or toxic solvents, by introducing a green strategy for synthesizing carbon-rich materials (deep eutectic system-derived biochar, DESysChar). In this approach, monosaccharides were used as carbon sources and converted into DESysChar within a deep eutectic system (DESys) under optimized mild conditions (HBA:HBD = 1:2, 150 °C, 3 h, solid-to-liquid ratio of 1:5). This work not only pioneers the exploration of the carbonization mechanism of monosaccharides in DESys but also highlights the efficient application of DESysChar in organic dye adsorption, with yield and adsorption capacity serving as key evaluation criteria. Comprehensive characterization of the DESysChars was performed using various analytical techniques, and the carbonization mechanism was elucidated through Fourier-transform infrared spectroscopy (FTIR), zeta potential measurement, X-ray photoelectron spectroscopy (XPS), and theoretical calculations. Kinetic and isotherm studies showed that the adsorption data conformed well to pseudo-second-order kinetics and the Langmuir isotherm model. The resulting DESysChar exhibited a high content of oxygen-containing functional groups, demonstrating a strong affinity for methylene blue (MB) with a maximum adsorption capacity of 259.98 ± 0.74 mg/g. Additionally, the material showed good selectivity for cationic dyes and excellent reusability. These results provide valuable insights into the green synthesis of carbon-rich materials and the underlying mechanisms of carbonization in DESys.