One-step fabrication of chitosan-Fe(OH)₃ beads for efficient adsorption of anionic dyes

In this study, we reported the one-step synthesis of chitosan-Fe(OH)₃ beads without the use of acid solvent, which could be used as effective adsorbents for anionic dyes removal. The preparation process was easy and green. The as-prepared beads were characterized for structural and morphological analysis in detail using several techniques, such as Scanning Electron Microscope, Fourier Transform Infrared Spectroscopy, X-Ray Diffraction, X-ray photoelectron spectroscopy and Thermogravimetric analysis. The content of Fe(OH)₃ in chitosan-Fe(OH)₃ beads was 54.64 wt%. The removal efficiencies toward anionic dyes: congo red (CR) and methyl orange (MO) by chitosan-Fe(OH)₃ beads were higher than pure chitosan beads. Moreover, the incorporation of Fe(OH)₃ into chitosan beads could overcome the obstacle that powdery Fe(OH)₃ particles are difficult to be separated from the adsorption solutions. The maximum adsorption capacities from Langmuir model for CR and MO by chitosan-Fe(OH)₃ beads were 445.32 and 314.45 mg/g, respectively. The thermodynamic data indicated that the adsorption processes were spontaneous and endothermic. In addition, chitosan-Fe(OH)₃ beads also showed good reusability and the removal efficiencies for both dyes retained above 95% after five cycles. From this work, it suggests that chitosan-Fe(OH)₃ beads have great potential as low-cost and effective adsorbents for the removal of anionic dyes.