Preparation of Chitosan-Diatomite/Calcium Alginate Composite Hydrogel Beads for the Adsorption of Congo Red Dye

In this paper, novel eco-friendly cross-linked chitosan-diatomite/calcium alginate (CS-DE@CA) composite hydrogel beads were successfully prepared for water purification. The obtained sorbents were characterized and studied by using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), which confirmed the successful modification and encapsulation of diatomite into hydrogel beads. The adsorption performance of composite beads for Congo red in an aqueous solution was studied by ultraviolet-visible spectrophotometry. In particular, the CS-DE@CA exhibited higher removal efficiencies (~89.9%) than the removal efficiencies (~83.6%) of the DE@CA (in the temperature = 20 °C, 100 mL, 50 mg/L, and pH = 7). It was also found that adsorption capacity of Congo red increased from 23.28 mg/g to 38.84 mg/g when the starting concentration increased from 25 mg/L to 75 mg/L. The adsorption process was dominated by chemisorption, and its maximum adsorption capacity for Congo red was calculated to be 48.42 mg/g by Langmuir model. Additionally, the as-prepared sorbent maintained an exceptional adsorption capacity after four adsorption–desorption cycles. Overall, this study also provides new guidance and avenues for further fabrication and development of eco-friendly purifier for the removal of Congo red in contaminated water.