Synthesis, characterization, DFT studies, and adsorption properties of sulfonated starch synthesized in deep eutectic...

Area of Science:

• Materials Science
• Green Chemistry
• Chemical Engineering

Background:

• Starch modification is crucial for developing novel functional materials.
• Deep eutectic solvents offer sustainable reaction media.
• Sulfonation enhances the properties of polysaccharides.

Purpose of the Study:

• To synthesize sulfonated starch (SS) using sulfamic acid in a deep eutectic solvent (DES).
• To optimize SS preparation conditions via orthogonal experiments.
• To investigate the adsorption performance of SS for methylene blue.

Main Methods:

• Sulfonation of starch using sulfamic acid in DES.
• Optimization using four-factor, three-level orthogonal experiments.
• Characterization by FTIR, elemental analysis, XRD, SEM, XPS, and DFT.
• Adsorption studies using methylene blue, kinetic and isotherm modeling.

Main Results:

• Optimal conditions: 1:20 starch/urea ratio, 90°C, 5h, 200 rpm.
• Sulfonation occurred on O6 atoms, slightly damaging starch granules.
• SS demonstrated a wide pH application range (5-10).
• High adsorption capacity (118.3 mg/g) and fast equilibrium (400s) for methylene blue.
• Adsorption followed pseudo-first-order kinetics and Langmuir isotherm, indicating a spontaneous, endothermic process driven by hydrogen bonding and electrostatic interactions.

Conclusions:

• Efficient synthesis of sulfonated starch achieved in DES.
• Optimized SS exhibits excellent performance for methylene blue removal.
• The study highlights SS as a promising adsorbent for wastewater treatment.