Carbon Nanotube/Chitosan Hydrogel for Adsorption of Acid Red 73 in Aqueous and Soil Environments

Acid red 73 is an azo dye, and its residue can pollute the environment and seriously threaten human health and life. In this study, a composite adsorbent with a three-dimensional network structure was prepared by modifying chitosan hydrogel with multiwalled carbon nanotubes, and its ability to remove acid red 73 from aqueous and soil environments was evaluated. In the aqueous samples, 70 mg of the adsorbent realized a saturated adsorption capacity of 101.07 mg/g and a removal rate of 92.23% at pH = 5. The thermodynamics conformed with the Langmuir adsorption isotherm and pseudo second-order adsorption kinetic models. In the soil samples, 100 mg of the adsorbent realized 24.73mg/g adsorption capacity 49.45% removal rate. When the pH of the soil was between 4–7, the removal rate and adsorption capacity do not change much; hence, the pH is maintained between 5.2–6.8, which is very suitable for the growth of general plants. The experimental results demonstrated that the composite adsorbent maintained a microporous structure and good removal rate of acid red 73 over multiple adsorption cycles.