Removal Kinetics of Methylene Blue from Aquatic Medium using Hydrogel Nanocomposite Prepared by Ultrasound

Pollutants are removed from the environment in a short time when water or biological fluids contain certain substances enter the hydrogel. In this research, we synthesized four kinds of acrylic hydrogels (performance about 50%) and applied for the kinetic sorption study of methylene blue (MB) from aqueous solutions. The adsorption of MB on the developed adsorbents (containing Fe₃O₄, ZnSe, and starch) was examined in a batch system. Characterization of the prepared acrylic adsorbents was performed by UV, FT-IR, SEM and XRD analyzes. The results showed that the four hydrogels could efficiently remove MB from solutions. The residual concentration of MB was analyzed by UV–Vis spectrophotometry at 662 nm (λmax). First the calibration curve of methylene blue dyes was obtained. Then the UV spectrum was taken from the mixture of gel and methylene blue at different concentrations (78,125, 13,950 and 19,531 ppm) and different time intervals (0–10 min) and the graph of the adsorption changes was obtained for each one. These graphs showed the kinetics of adsorption and showed this fact that the adsorption process has followed the Langmuir isotherm (the adsorption values q_max of 42 mg.g⁻¹), and in some cases the Freundlich model. Among the kinetic models applied, the pseudo-second-order (k about 0.3 M⁻¹.min⁻¹) kinetic model was identified with the highest regression coefficients (the first in the high concentrations and the second in the low concentrations). A proposed adsorption mechanism to acrylic hydrogel was illustrated based on the chemical structure of MB and related hydrogel. The stability and reusability of hydrogels and the recovery of absorbed pollutants are among the advantages of this method which shows its economic efficiency.