Chitosan hydrogel beads impregnated with hexadecylamine for improved reactive blue 4 adsorption

• Chitosan beads impregnated with hexadecylamine (HDA) were prepared.
• The impregnated chitosan beads are successfully applied to remove reactive blue 4.
• Various models and isotherms were employed to describe the adsorption process.
• The adsorption capacity of impregnated chitosan beads was 1.43 times higher.

Adsorption performance of chitosan (CS) hydrogel beads was investigated after impregnation of CS with hexadecylamine (HDA) as a cationic surfactant, for the elimination of reactive blue 4 (RB4) from wastewater. The CS/HDA beads formed with 3.8% HDA were the most effective adsorbent. The adsorption capacity was increased by 1.43 times from 317 mg/g (CS) to 454 mg/g (CS/HDA). The RB4 removal increased with decrease in the pH of dye solution from 4 to 9. The isotherm data obtained from RB4 adsorption on CS and CS/HDA are adequately described by Freundlich model (R2 = 0.946 and 0.934, χ2 = 22.414 and 64.761). The kinetic study revealed that the pseudo-second-order rate model (R2 = 0.996 and 0.997) was in better agreement with the experimental data. The negative values of ΔG° (−2.28 and −6.30 kJ/mol) and ΔH° (−172.18 and −101.62 kJ/mol) for CS beads and HDA modified CS beads, respectively; suggested a spontaneous and exothermic process for RB4 adsorption.