Synthesis and characterization of 2-hydroxy-3-methoxyphenyl imino chitosan as a novel adsorbent for effective removal of methyl orange

Organic dyes are major contributors to industrial wastewater pollution, particularly from the textile sector. Approximately 10-15% of synthetic dyes produced globally are released into wastewater, posing significant environmental risks. In this study, a novel 2-hydroxy-3-methoxyphenyl imino-chitosan (HMPI-chitosan) was chemically synthesized and evaluated as a green biosorbent for methyl orange (MO) removal from contaminated water. The formation of imine functional groups was confirmed by FT-IR spectroscopy, while SEM revealed smooth, porous, and uniform beads with an average particle size of 776.4 μm. Transmission electron microscopy (TEM) analysis further confirmed the nanoscale internal structure and uniform morphology of HMPI-chitosan beads. XRD patterns indicated the amorphous nature of the material. BET analysis showed a marked increase in surface area and porosity from 8.6 m²/g for native chitosan to 42.8 m²/g for HMPI-chitosan, confirming enhanced structural properties and greater accessibility of active sites. Adsorption performance was evaluated under varying conditions of pH (4-8), contact time (5-25 min), adsorbent dosage (20-60 mg), initial dye concentration (5-35 ppm), and temperature (25-50 °C). Rapid kinetics were observed, with a maximum adsorption capacity of 8.3 mg/g. The process followed the pseudo-second-order kinetic model (R² = 0.990), and equilibrium data were well fitted by the Langmuir isotherm (R² = 0.992), confirming monolayer adsorption onto a homogeneous surface. Thermodynamic analysis revealed negative Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°), indicating a spontaneous, exothermic process with decreased randomness at the solid-liquid interface. Under optimized conditions (pH 4, 20 min contact time, 30 mg adsorbent dosage, 35 ppm initial concentration, and 30 °C), the biosorbent achieved > 98% removal efficiency. These results highlight HMPI-chitosan as a promising, eco-friendly adsorbent for practical wastewater treatment applications.